Review of Olefin Isomerization - Industrial & Engineering Chemistry

March 1953

XI

W

INDUSTRIAL AND ENGINEERING CHEMISTRY

of the boiler. These data suggest that other elements may also condense out in boiler flues. The recovery of compounds from coal ash is dependent on the development of suitable methods. Although it is not the purpose of this paper to present such methods, certain directions which recovery might take have been indicated from time, to time during the course of this investigation. It would be advisable t o wash the coal to remove most of the extraneous mineral matter (shale, pyrite, and calcite for the most part) prior t o burning. The extraneous shale, however, has a composition similar t o the inherent ash. Coals which have been through a floatsink operation at 1.30 specific gravity contain only about 3% ash, practically all of which is inherent ash. This ash is fine and fluffy. If the coal is not washed prior t o burning, then most of the fine inherent ash can be floated from the heavier, coarser extraneous ash. Gravity separation of the ash effects concentation of certain compounds; for example, barium and strontium can be concentrated in this way. Germanium can be concentrated by selective mining of the bottom 3 inches and washing the coal to an equivalent specific gravity of 3.3. ,4 luxurious growth of plants over a considerable period of years is to be expected in order to produce sufficient vegetation to make a coal seam 3 feet thick. The soil in which they grow

55 1

must have had adequate mineral nutrients t o promote maximum growth. If the present inherent coal ash is representative of the original living plant ash, then these analyses indicate the optimum concentration for maximum plant growth. The enrichment of such a large number of elements by coal-forming plants suggests t h a t each element had some important function in plant nutrition. The fertilization of soils, so t h a t the equivalent of the concentrations of the elements in coal ash is available to the plants, might materially increase the production of farm crops. ACKNOWLEDGMENT

The authors gratefully acknowledge the aid of the staff of the West Virginia Geological Survey, and particularly Paul H. Price, for permission to publish this paper. LITERATURE CITED (1) Gibson, F. H., and Selvig, W. A,, U. S. Bur. Mines, Tech. Paper 669 (1944). (2) Goldschmidt, V. M., J . Chem. Soc., 1937, 656. (3) Headlee, A. J. W., and Hunter, R. G., West. Va. Geol. Survey, Morgantown, R. Va.,Repts. Invest. 8 (1951). (4) Hunter, R.G.,and Headlee,A. J. W.,AnaZ.Chem., 22,441-5(1950). (5) Slavin, Morris, IND.ENQ.CHEM., ANAL.ED., 10,407-11 (1938). R E C E I V ~for D review May 12, 1952.

ACCEPTEDOctober 30, 1952.

Review of Olefin Isomerization H. N. DUNNING‘ 331 Fir St., Park Forest, I l l .

T

4

HE subject of olefin isomerization dates back to the turn of the century and the pioneering woilc of Ipatieff (33, 36, 36). From these initial experiments, the expansion of the field has paralleled the advancement of analytical methods for hydrocarbon mixtures. In some cases the necessity for accurate analyses has been overlooked, leading to contradictory reports in the literature. Fortunately, such contradictions are few; many may be resolved in the light of later experimental evidence or of thermodynamic calculations. Twigg (80) points out that analyses of cis- and trans-2-butene mixtures are difficult because of the similarity of the physical properties of these isomers. Further, Rose (699) showed by calculation and Whitmore et al. ( 8 7 ) by experimental evidence that it is impossible to separate many of the isomeric products of n-hexene by present methods of fractional distillation. Literature reports that are based on questionable analytical methods are reviewed in this paper only in the absence of data obtained by more credible methods. The isomerization of olefins t o more highly branched forms results in marked increases in the octane ratings of olefin-containing stocks (6). The considerable olefinic content of most thermall. cracked naphthas has stimulated interest in the isomerization of these stocks. Recent developments in the petroleum industry have added impetus to isomerization studies. Gasolines prepared by the Fischer-Tropsch type synthesis are especially susceptible t o isomerization reactions because of their high olefinic content (68). Octane increases of about twice the amount of those observed with thermally cracked naphthas may be achieved. The outlook for olefin isomerization processes appears even brighter. Shale oil operations are becoming economically more attractive. Naphthas produced from shale oil are exceptionally rich in olefins, containing about 40% to 55% olefins (39). Since over 50% of the total olefins, or 75% of the aliphatic olefins, are unbranched (79), isomerization of these naphthas may be ex’ Present address, U. S. Bureau of iMines, Bartlesville, Okla.

pected to be especially profitable. Another advantage of isomerization processes is their ready adaptability for use in upgrading of gasolines in small refineries where the cost of a catalytic cracking unit necessitates dependence on thermal cracking operations. An olefin isomerization unit may be relatively small and inexpensive because of the extremely high space velocities used, low original cost of catalysts and their easy regenerability, nearly quantitative stock recovery, operation a t atmospheric pressure. THEORETICAL

The isomerization of aliphatic olefins may be classified generally as follows: Double-bond isomerization Movement of the double bond Cis-trans isomerization Chain isomerization Change in number of tertiary carbon atoms Change in position of tertiary carbon atoms in molecule Mechanisms for the double-bond isomerization of olefins on metallic catalysts have been discussed extensively by Twigg (80) and Farkas ( 1 7 ) . The “associative” mechanism of Twigg postulates that the olefin is adsorbed at both ethylenic carbons by the metal catalyst. Then one of these bonds is broken as a hydrogen atom is added t o one of the carbons. This addition correlates with the “proton affinity” calculations of Evans and Polanyi (15). Then a hydrogen atom is expelled from an adjacent carbon atom and the isomerized olefin is desorbed. The “dissociative” mechanism of Farkas ( 17 ) postulates that the C-H bond becomes loosened by catalytic artion, and the hydrogen is expelled. Then a hydrogen atom is added at the remote ethylenic carbon and the molecule is desorbed. Hay, Montgomery, and Coull (28) conclude t h a t the effective catalysts for chain isomerization of olefins are acidic in nature. An extensive survey of the literature on olefin isomerization has produced no contradictory evidence.

I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY

552

A catalyst ma,y show acidic Characteristics for several reasons: 1. The substance may be a conventional acid, according to the Bronsted theory a proton donor---e.g., sulfuric or phosphoric acid 2. The substance may be a Lewis acid or a n electron acceptor ---e.g,, boron fluoride, aluminuni chloride 3. A relatively neutral substance may adsorb hydrogcii inns or a potentially acid substance--e.g., aluminum oxide and hytlrofluoric acid, acidified Doucil 4. Two relatively neutral substances may react or u ~ i i t ~toe form a complex having acidic characteristics---e.g., silica~-aluniiuit.

’

Ttiomas (74) has offered a theory to account for the aci(lic characteristics shown by several oxide tnktures. The coninion silica-alumina crackirig catalyst is an example of this typc of c2atalyst. Neit’her silica nor alumina has decidedly acidic characteristics. However, if one iilurninuin atom shares four oxygen atoms which, in turn, arc shared by four silicoii atoms, the ,410, part of the complex has oiie n c l iiegative valence unit,. Thomas postulates that an acidic hydrogen ion is associated with thesc [our oxygen atonis surrounding tho aluniinum atom. IIencc the active part of this catalyst iiiay be w i t t e n (IlA104),L. The acidity of other catalysts oC this t,jrpe may he similarly explained. As postulated, t)hese catalysts maintain their aciditjy a t high temperatures, a highly desirable feahre. The acid-catalyzed isomerization of olefins may he consistently explained by the carbonium ion incchanism as interpreted h g several authors (48,50, 74, 86). The catalytic surfacc is coverctl to some degrec n.ith protons attached t o oxygen atoilis in tlw crystalline lattice, or to electronegative atoms chemisorbed on the catalytic surface. These protons arise as previously explained. In many essentially neutral oxides the protons arc present because of the slightly acidic nature of the hydrated oxide, for example, alumina. Under conditions prevailing on the catalytic surfacc, carbonium ions are formed by the addition of a proton to the double hond of the olefin. The action of a “Lewis acid” may bo similarly explained by the forniatiori of a heterocarbonium ion in which the electron deficient acid shares electrons originating from tho double bond of the olefin. For clarity, only the formation of a carbonium ion by the addit.ion of a proton to t,he olefin ~ v i l lbe considered in this discussion. The carbonium ion a t the iiioment of formatioii is bound to the catalytic surface by electrost’atic attraction b e t a w n the posilive carbonium ion and the electronegative donor. I n the casc of unsymmetrical olefins, the proton will generally add preferentially to one of the two ethylenic carbon atoms. From bond energies and ionization potentials, Evans and Polanyi (15) have derived values for the proton affinities of the two carbon atoms involved: Olefin H2C’=C”H, H2C ’=C”HCH3 H&’=C”( CHa)z

P’,

I>Il Kril.

175 5

152 168.5 168

Kcal. 152 189

Resultant Ions

C’

C”

Ethyl sec-Propyl tert-Butyl

Ethyl n-Propyl Isobutyl

These figures show quantitatively that see-propyl ions are favored over n-propyl ions by 7 kcal. per mole and tert-butyl ions are favored over isobutyl ions by 21 kcal. per mole, thus accounting for the changes observed in olefin isomerization reactions. At temperatures below about 250’ C., the principal reaction occurring on the surface appears to be the rearrangement of the adsorbed carbonium ion by the shift of a hydrogen atom. This moves the positive charge t o a more centrally located carbon atom, eventually resulting in thermodynamically more stable arrangements than the originally adsorbed carbonium ion. The loss of a proton from a carbon atom adjacent to the donor group a t the instant of desorption forms a molecule with the double bond closer t o the center, within thermodynamic restrictions. Alternatively, the association of the catalyst and carbonium ion may be assumed to be a loose one so that the proton expelled

Vol. 45. No. 3

may go to another olefiii molcciilc L o (orin another carboniuni ion xhich, in turn, is att,ractetl to tlic catalyst. The end product, a more stable olefin, is the sitme iii cither case. Cis-trans isomerization may be cxplained by this mechanism by a rotation of thc unsymrnctricnl groups about the “opened double bond” of the carbonium ion, prior to the expulsion of the extra proton. At higher temperatures t,he more difficult skeletal rearrangements occur to an increasing extcnt, t>houghthe proportion of branched isomers present a t equilibrium decreases as the temperature increases. This reaction is much slower than a doublebond itiovenient sirm it involves the migration of an alkyl group instead of n hydrogen atom. Thcrc are two schools of thought o n the details of this hydrogcn or alkyl-group shift. Awording to \Yhitmore (86), t,he transfer o/‘ a hydride ion and a carbanion may he visualized as t)he movcnient or an electron pair which takes with it a proton or carboliium ion. Thomas (74), among others, subscribes to this view. Greensfelder et al. ( b y ) consider tJhe shift of a proton and methyl oarbonium ion more consistent with the energetics of thc system than the shift of the hydride ion or c:arhaniori post,ulated by Whitmore. Oblad et al. (60) arc iti agrecment with thesc ~vorlccrsthat the migrating group in double-bond isomerization is a proton. T.Tlt,h this minor exception, and t,hnt of the strength of the carbonium ion-anion bond, the various workers appear to be in unusually complete accord. Berg, Sumner, and Montgorn ( 6 )point, out some theoretical liniitatinnfi to the amount of octiinc improvement that may be accomplished b y isomerization, In an isomerization process, reaction cotiditions are maintairicd which tend toward the establishment of equilibriuni. This ~quilihriurnsets a definite limit on the amount of an\- isomer t,hat m a y he formed a t any given temperature. For olefins of chain length Ce and above there are numerous isoniem -80 many that, normally no single isomer n-ill be formed in large percentage. The thennodynamic eharacteristics of the olefins through the hesenes, and of the higher I-olefins, have been calculated a n d reportcd by Kilpat,rick et al. (38). These tabulations include values of heat contents, heats of formation, heat capacities, free energies, and entropies, as well as equilibriuni constants, free energies of isomerization, and equilibrium concentrations in isomerization reactions. The octane nurnbcrs of the isomers vary considerably with structure; straightchain compounds usually exhibit lower octane numbers than highly branched forms. The shift of a double bond toward the middle of a molecule usually rcsultjsin the formation of an isomer having a higher octane number. Thermodynamic properties set a definite limit to the octane number that can be obtained by tho fullest extent of isomerization of the olefins present in the feed stock. Therefore, to obtain the maximum increase in octane ratings by an isomerization process, it is necessary t o Relect feed stocks that are high in unbranched olefin content. Thermally cracked distillates are among the best common charge stocks becausr! of their high olefinic content and low octane nnmber , C h T A LY S

Specific substances used t o catalyze olefin isomerization are recorded alphabet,ically in Table I and Table 11. Catalysts that ha,ve received wide attention have proven unusually effective, or that have given unexpected results will be discussed briefly in this section. In studying the pyrolysis o f tlic butenes, Hurd and Goldsby (SI) concluded that there was no chain branching without a catalyst. They did observe a small amount of thermally induced double-bond movement. These results are readily correlated b y the carbonium ion mechanism. Norris and Reuter (47) report that 2-pentene formed no branched pentenes when passed through a silica tube at 600” C. with a contact time of 15 seconds. This observation is in agreement with the reports of Hurd, Goodyear, and Goldsby ( 3 2 ) and Waterman et al. (84). Thcsc workers reported that thermal

March 1953


553

TABLE I. CATALYSTS FOR OLEFINISOMERIZATION Feedstock

Catalyst Acetic acid (glacial)

cis- or Imns-%Pen-

Liquid Hourly Tfmp.. Space C. Velocity, Hrs. -1 Batch

....

450-400

...

1 .9-65.0 sec,

20

tene

*

Contact Time

Alumina (Alorco)

1- or 2-Butene

Alumina

n-1- and 2-Butene

294

...

ll6sec.

Alumina

3-Methyl-I-butene

450

...

15 sec.

Alumina (activated)

2-Methyl-2-butene

263-400

137jcatalyst vol.

....

Alumina (activated)

3-Methyl-I-butene

360

137/catalyst vol.

....

Alumina (activated)

2-Pentene

266-364

137/catalyst vol.

Alumina (activated)

1-Pentene

357

Alumina.

1-Hexene

398

137/catalyst vol. 0.4

Alumina (unaqidified) Alumina (acidified)

3,3-Dimethylbutnnes n-Hexene

350 338

0.6 0.6

....

Alumina (activated)

I-Heptene

398

0.4

....

Alumina

3-Methyl-I-butene

...

16 sec.

Alumina (in copper tube)

3-Methvl-l-bi1tene

450~530

0.1-0.2

....

Alumina (from acid sol)

I-Pentene

260--371

0.5-6.0

....

acetic

Alumina on clay

.... *...

294

Batch

....

2-Methyl-2-butene

294-345

10 passes

2-Pentene

295-345

n-Butenes

+ chromium + chromium + cobalt oxide Alumina + cobalt oxide Alumina + cupric oxide Alumina + ferric oxide Alumina + ferric oxide Alumina + manganese oxide Alumina + manganese oxide Alumina + nickel oxide Alumina (Alorco) + hydrogen fluoride Alumina oxide Alumina oxide Alumina

450

..., . ...

1-Pentene

177-427

137/catalyst vol. 137/catalyst vol. 137/catalyst vol. 137/catalyst vol 137/catalyst vol. 137/catalyst vol. 137/catalyst vol. 137/catalyst vol. 137/catalyst vol. l37/aatalyst vol. 0 5-24.0

2-Pentene

260--371

1 .O-24.0

Aluminum sulfate Aluminum sulfate

1-Butene n-Butenes

270-290 294

...

...

137 sec.

Aluminum sulfate

2-Pentene

450

...

15 sec.

Aluminum sulfate

3-Methyl-1-britene

425

...

15 sec.

Aluminum sulfate (anhyd.) Aluminum sulfate (anhyd.) Aluminum sulfate (anhyd.) Ammonium thoriomol5rbdate Ammonium vanadomolybdate Bauxite

1-Hexene

335

0.6

....

3,3-Dimethylbutenes

275

0.6

....

... ...

12 sec. 12 seo.

Alumina (Aloroo) drogen fluoride

+ hy-

Z-Methyl-2-bnten~

3 11-370

2-Pentene

320-375

2-Methyl-2-butenr

358

2-Methyl-2-butene

296-347

2-Pentene

295-344

2-Methyl-2-butene

300-363

2-Pentene

305-366

2-Methyl-2-butrne

358

3,3-Dimethylbntenes 280-290 475

tene

.

I O passes 10 passes 10 passes 10 passes

Products and Comments Allnost complete cis-trans conversion; little isobutylene or side reactions Nearly equilibrium proportions of n-olefins a t contact time above about 30 scc. 0.8% Isobutene; 18% polymerization. 1- and 2-butene conversion 10% Z:Methyl-2-butene; no cracking Up t o 5.2% 3-methyl-I-butene: equilibrium proportions of 2methyl-1-butene 3.97% 3-Methyl-1-butene: 27.9% 2-methyl-1-butene; 68.2% 2methyl-2-butene Up t o 15.8% I-pentene a t 358',C.: little cracking and polymerization 78.1% 2-Pentene: little cracking and polymerization 80% 3-Hexene; methylpentenes: ethylbutene No reaction 65.4% Isomerization. 24.2% nhexenes; 9.0% i,3-dimethylbutene 70% Isomerization; 5% polymerization. considerable 3-methyl2-hexene About 10% 2-methyl-2-butene; little cracking About 60% 2-methvl-2-butene: some cracking Up t o 89.3% 2-pentene at 316O C.. 1.h.s.v. 6 ; 35.8% methylbutenes a t 371° C., 1.h.s.v 1.0: little cracking below 316O C. Some isobutylene: little cracking and polymerization 2.6-5.4% 3 Methyl 1 butene; 25.3-26.8% 2-methyl-1-butene 11.8-13.4% I-Pentene: little cracking or polymerization 1 2 4 . 3 % 3 Methyl - 1 butene; 11.3-26.0% 2-methyl-1-butene 4.6-13.6% 1-Pentene: little crackina or Dolvmerization

-

- -

-

-

10 passes I O passes

10 pawe8

....

....

....

. t . .

475

...

250-450

1.0-8.0

....

250-496

1.0-19 0

....

Bauxite

1-Butene

Benzene sulfonic acid (75%) Beryllium oxide

1-Butene

76

..*

....

1- and 2-Octene

450

0 16

....

Beryllium oxide

I-Heptene

450

About 0 1

....

Literature Reference

Ultraviolet spectra

(9)

Infrared spectra and vapor pressure Absorption in 6884% H ~ S O I Phys. and chem. properties Distn.

(41)

(64)

(47) (16)

Distn.

(16)

Distn.

(16)

Distn.

(16)

Fractiobal distn.

(94)

Fractional distn. Hydrogenation and fractionation Fractionation

(I 1) ($8)

($4)

Distn. and chem. properties Distn. and chem. properties Distn. and phys. properties

(93)

Distn.

(19)

Distn.

(16)

(33,

(60)

Distn. Distn. Distn. Distn. Distn.

10 passes 10 passes

Methods of Analysis

Distn. reaction 1.3-4.5% 3 -Methyl 1 -butene; 21.3-26.7% 2-methyl-1-butene 9.4-15.4% 1-Pentene: little cracking and polymerization L o w isomerization; excessive cracking and polymerization 18.0-78.2% 2-Pentene. u p t o 64.3% methylbutene i t 427" C., 1.h.s.v. 6.0; 25.8% cracking and 21.6% polymerization under these conditions 00-1.0% 1-Pentene. a t 371" C 1.h.s.v. 6; 86.3% Aethylbutene'd. 23.3% cracking: 19.1% poly-' merization Some 2-butene. little isobutylene 10.7% Isobutyigne;. 2% cracking: 15% polymerization No isomerization (chain) : small amount of crack'ing and polymerization

-

Distn. Distn. Distn.

(16)

Distn. and phys. properties

(60)

Distn. and phys. properties

(60)

Chem. properties Absorption in 6 8 4 4 % HzSOd Phvs. and chem. properties Phvs. and chem. properties Hydrogenation and fractionation Fractionation

Fractionation 2,3-dimethyl-i-butene 38% Toluene:, some fulvene; some Refractive index and bromine No. polymerization 3 2 % Toluene: some fulvene: some Refractive index and bromine No. polymerization 12.7-27.9% 1-Butepe; equilibrium Infrared spectra proportions of cis- and trana-2butene 15.0-29.0% 1-Butene; equilibrium Infrared spectra proportions of cis- and trans-2butene 13% 2-Butene. no cracking or Distn. and phys. polymerizatidn properties Considerable isomeric methylhep- Hydrogenation tenes; low cracking and polyand Raman merization spectra Considerable 3-methyl-2-hexene; Hydrogenation low cracking and phys. properties

(34) (89)

(8

(Continued on page 664)


554

Vol. 45, No. 3

FOR OLEFTNISOMERIZATION (Cmtinued) TABLE I. CATALYSTS

C.

Contact Time

0.5

....

358

137/catalyst vol. 0.2-1.2

10 passes

398-474

....

12.7-55.3% n-Hexenes. 3.1-12.1% 2,3-dimethylbutene, b1.9-40.7% 2-methxhentenes: 18,9-34.5% 3-methGluentenes: best isomerizational activity a t 316O C,. Little isomerization; excessive cracking and polymerization 36-90% Aromatics; 2-3070 satu-

5-Methyl-Z-hexene

424

0 2

....

50%-Aromatics; 12% saturates

50% n-Heptane, 50%

475

1-Iiexene

Calcium chloride

2-hIethyl-2-butene

Chromium oxide

1-Heptene

Chromium oxide Chromium oxide Chromium oxide

n-heptene 1-Heptene

463

0 44

Chromium oxide

2-Heptene

46.5

0 44

Chromium oxide

2-Octene

4l.X

0 44

Chromium oxide

1- a n d 2-Octene

4L;O

Low

C,hromium oxide on alumina

n-Butenes

400

0.76

Chromium oxide on alumina

Isobutene

400

0 75

Clay (activated)

n-Hexenes

260

0 2

__ I-Hexene

260-482

0 5

Doucil (acid-treated)

1-Hexene

338

0.6

Ferric oxide and ailumina Filtrol (clay)

n-Pentenes

500

3.0

Filtrol (clay)

1-Butene

400

9 0

Floridin

n-Butenes

...

. .

134 sec.

Georgia clay

1-Hexene

.33j

0 35-1.90

....

Glass tube

3-3Iethvl-1-butene

400-600

butenes

Houdry (aluminum hydrosilicate)

1-Hexene

,...

, . .

138 sec.

3s5

0 . (i

....

-~~

See alumina

~

Hydrogenation, fractionation, a n d mass spectra

(44)

Distn.

{lo.,

Sp. gr. a n d bro-

47.5

...

12 see.

260-482

0 . .5

...,

6.5% tene; ,Isobiitylene; 87, polymerization 3470 polymeri-

+

aation A t 1.h.s.v. 0.35, 23.7% n-hexenes: 6.17, 2 , 3 - dimethylbutenes: 29.5% 2-methylpentene; 23.6% 3-methylpentene; 3.27, cracking Small amount of 2-inethvl-2-butene: some cracking 7.5% Isobutylene: little cracking; 37% polymerization 35.9% 71-Hexenes; 3.5Yc dimethylbutene; 4170 2- a n d 3-methylpentenes manganese oxide-. 24% Toluene: some fulrene a n d polymerization Highest activity a t 4OO0,C.; 34.4% n-hexenes; t .O% dimethylbutenes; 31.27' 2-methylpentenes: 27.03% 3-methylpentenes; 4% .~ cracking Considerable o-xylene: catalyst deactivates rapidly Largely 2-hexene: no 2- or 3-pentene; considerable polymerization Mainly isomerization

(44)

Oxidation and esterification Distn. a n d chem. properties

(64)

?0U

li0\Y

400

Ratch

3Iolybdenum trisulfide

1-Iiexene

400

Batch

Nickel

1-Butene

76

Hatch

?To isobutenes; u p t o 92% 2-bu-

Distn. a n d ohem. properties Vapor pressure

Nickel on porcelain

cis-

...

KO isobutene; no 1-butene; a n increase of tmna from 8 t o 19%

Infrared spectra Vapor pressure

...

tene: hydrogen added

1-Butene

21

...

. .

Phosphoric acid (ortho)

1-1311tene

26-135

Ahout 0 . 1

. ..

Phosphoric acid (ortho)

cis-2-Butene

I00

Ahout 0 1

....

Phosphoric acid on carbon

n-Butenes

204

Phosphoric acid on charcoal Phosphoric acid on diatomaceous e a r t h

n-Butenes

299.1

1-Butene

100-249

Phosphoric acid on fireclay

%-Butenes

294

+

_____ See ~ alumina ~ . _nickel _

Kickel oxide alumina Perchloric acid (70yo)

122-130 sec.

Hatch 0 13

(28)

-.

1- a n d 2-Octene

.___.-.

(44)

Refractive index and broiiiiiie No. Hydrogenation fractionatioi, a n d mass spectra

I-Ilexene

+

-_

Distn. and chem. properties Absorption in 6884% HZSO4 Hydrogenation a n d fractionation

llolybdenum tiioxide

6:-124

($6)

Absorption tion in H2SO4 in 6884% HzSO4 Hydrogenation a n d fractionation

Molybdenum disulfide

and trans-2-Butene

(26)

--

mine . ..-..N.n -.

+

U 2-1 0

+

Manganese oxide alumina Molybdenum oxide on 50% n-Heptane, 60% n-heptene alumina hlolybdena-hosia-alumina 1-Ilexese


+

+

'Jq4

^.

mte9

Methods of Analysis

Sp. gr. and bromine No. 12 sec. 41 % Toluene: some fulvene; soine Refractive index a n d bromine No. polymerization 69% Aromatics; 22% naphthenes: Fractionation a n d 18-24 sec. bromine No. aboun 77, cracking 65% Aromatics; 21% naphthenes; Fractionation a n d 18-24 sec. bromine KO. about 7 % cracking 67% Aromatics; 267" paraffins: Fractionation a n d 21 sec. bromine No. 17% olefins . .. Considerabie D - X ~lene Oxidation a n d esterification .. . 0.0% Isobutene: 27% n-butenes; Distn. and absorption in HsSOa 50.4% n-butene (hydrogen added) 25.9Yc Isobutene: 0.2'35 n-butenes; Distn. a n d absorption in Hs47.4% isobutene (hydrogen added) SO4 26% 2-Methylpentenes; 23% 3- Hydrogenation a n d Rainan niethylpentenes; 2070 clacking spectra See alumina oxide See alumina cupric oxide ,.., Highest activity a t 316'C.: 20.0% Hydrogenation, n-hexenes: 9.7% 2,3-dirnethylfractionation, butenes. 38.7% 2-methylpena n d mass spectra tenes; 3i.!5" 3-methylpentenes; 4,rocracking; ZOyo polymerization .... 10.8Yo n-Hexene; 8.4% 2,3-di- Hydrogenation methylbutene; 25.2% 2-methyla n d fractionation pentene. 22.47, 3-inethylpentene; 16.6% clacking See alumina ferric oxide .... 54% RIethylbutenes: lf1.67~crack- Distn. a n d chem. ing; 11.8% polymerization properties .... 21.4r0 Isobutylene; il.iY0 2-bu- Distn. and absorp-

d b a l t oxide and alumina alumina Cupric oxide Doucil (acid-treated)

Glukov clay

Products a n d Comments

260-482

Boria-alumina

+

I

Tzinp ,

Feedstock

Catalyst

Liquid Hourly Space T-elocitf, Hrs. -

200 see.

206-244 sec. 120-525 see.

oxide 2 1 % 2-Butene: little cracking or polymerization 4-60% 2-Butene: little cracking or polymerization 6.6% 1-Butene: 87.4% 2-butene: little side reaction 17.3-34.77, Isobutylene: catalyst poorer in phosphoric acid effective: 43% cracking with active catalyst d b o u t 6OY0 isobutylene: considerable polymerization 36-10070 %Butene a t higher temwerature: small cracking. or polymerization Naximuni isobutylene; 47.2% a t contact time of 144 see.; 36% polymerization a t this contact, time

(2.9,

(42)

1-1pentene 3-Methyl-1-biitenr

2:

Low

,...

500

....

400

58 see.

n-Octeniv Diisobutylrnr

Silica PPI Silica gel

S o d i u n ~permutite

5970 n-Butenes, 16.1% isobuteiir 31.2Y0 n-Butenes, 28.87" isobutene

Sodiiini pel mutite

Z-Metliyl-~-Liitprir

Super-F'ilti 01 (clay)

Sodiiiin permutite

316 482

Contact Time

400-460

Silica-alurnina-zirconia Silica-alumina-zirconia

Siliceous earth

c.

OLEFIN ISOMERIZATION

Liquid Hourly Space Velocity. Hrs. - 1

400

...

170 see.

400

...

33 see.

1-Hexeiie

2 8 j 498

0.1 0.0

Thermal ieaction

I-Biiteiie

050-700

. .

l'lirimal reaction

2-Butene

050-700

...

12 see.

Thermal reaction

3-Jletliyl-1-hiit ?ne

400

Batcli

8-20 see. 8-20 see.

I-Pentrn~

550-600

Batch

Thrrmal ieaction

2-Pentane

650-600

Batch

Thernial ieaction

1- and 2-Octanr

3 i5-420

Batch

Tlioi iii iii dioxide

2-RZethyl-2-but crie

3.58

Ultraviolet light Cltraviolet light

trans-Z-Pe [iten? Z-Pentene

137/catalynf, 701. Batch Batch

on

(Concluded)

Products and Comments

Methods of Analysis


Most effective a t 400' C.; 22.6% Hydrogenation, fractionation, n-hexenes; 9.1% 2,a-dimethyland mass spectra butenes; 37.455 methylpentenes; 30-9% 3-methylpentenes; 5 % cracking Considerable isomerization; 41.0% Fractionation and cracking; 19.5 polymerization chem. properties Over 90% cracking; 7.1% poly- Fractionation a n d merization chem. properties Considerable isomerization; little Hydrogenation cracking or polymerization and R a m a n spectra 20% 2,4,4-Trimethyl-Z-pentene Infrared spectra (equilibrium proportion) Some 2-methyl-2-butene and Distn. and chem. cracking properties 17.17, Isobutene; 48.9% n-butene. Absorption in little cracking or polymerizatio; HzSO? 21 4 % Isobutene. 29.0% n-butene. Absorption in about 10% c;ackine or ~" aolv; HIS04 merization" 19% n-Pentenes (near equilibrium); Bbsorption in 15% cracking and polymeriza%SO4 tion Most effective a t 340' C., 1.h.s.v. Hydrogenation 0.6; 11.4% n-hexene; 9.7% 2.3and fractionation dimethylbutenes; 27.3% 2methylpentenes; 25.5% 3methylpentenes No isobutenes; 10.5-11.8% 2-bu- Distn. and chem. properties tene; 57-87% o_r?cking No isobutenes; r.o-11.7% l-bu- Distn. and chem. properties tene; 45-80y0 cracking Considerable 2-methyl-2-butene; Chein. properties little cracking Little pentenes; no branching; Distn. and chem. 10-40% cracking properties Little pentenes; no branching; Distn. and chem. properties lO-Z6% cracking Considerable isomerization; 17.8- Fractionation and bromine h-0. 56.1% polymerization Distn. Practically no reaction I

Thermal reaction

Vanadium trioxide alumina Zinc chloride

Vol. 45, No. 3

30 20

... 11 see.

8 -20 see. 1/2-12

hr.

10 Passes

GL24hr.

....

n-Heytenen

400-480

0 3

n-Ortenw

275-32;

natcii

Zinc chloside on pumice

n-Uexenes

373

0.5

....

Zino chloride on pumice

n-Hexenrs

376

Batch

1-3 hr.

Zinc cliloride on pumice

n-Octene.;

325

Batch

0.7-1.9 hr.

Zinc chloride on pumice

n-Octenes

350

0.2-0 i

....

Zinc chloride on pumice lipdrogen chloride

n-Hesrnrs

375

Rn1,:lr

2-3 hr.

Zinc chloride on pumice -t- hydrogen chloride

n-Octenrs

230

Bsicli

2-6 min.

Small amount of cis-2-pentene 30-38,% 1-Pentene; little side reaction 27-307, Isobutenes. 15% aromatics; 25% crack'ing Up t o 8.3% iso-octenes; 20% polymerization Up i o 2370 methylpentenes; moderate cracking and polymerization Considerable rnethylpentenes; moderate crackinrr and nolvmeri""+:-" Iso-octenes: 20% 20.0-4i 5.0% ._ nolymerSation

Phss. properties Chem. (bromo derivatives) R a m a n spectra Hydrogenation and SbCls, Hydrogenation and SbCla Diatn. and SbCls

""LiYll

+

Iyst formed from an acetic acid sol caused l t w thaii 1 % ' crackiiig at space velocities of 1 hour-' up t o &out 330" C. [Jnder these rondiiions, the alumina-hydrofluoi IC acid catalysts caused from 4 to 25% cracking. The alumiria-hydrofluoric acid catalyst3 also caused more polymerization and more double-bond isomerization than did the alumina catalyst (49). On the above grounds, the authors postulate that isomerization of normal olefins bv contact catalysis occurs in a manner similar t o that of alkylation, polymerization, and similar reactions, and offers a mechanisni based on the carbonium ion concept. The pure alumina gel gave the most clean-cut reaction This agrees with the o b s ~ r v x tions of Endl and Hardy (16). At lower temperatures, the 3lurniria-hydrofluoric acid catalysts pioduced a more cornplelr double-bond isomerization, but :tt about 300" C. the acidified nluminas began forming large enough amounts of branched pentenes from the I-pentene feed that the concentration of 2-pentene decreased. A L U & I I N A GEL. As observed by Ewe11 and Hardy ( 1 6 ) arid other workers, Oblad et al. (60) report that pure alumina gel was rather inactive in causing chain isomerization. Above 317" C. t hi-. mtalyst began to s h o ~chain-isomer izing activity. TToTb-

j-25.0%

Iso-oetenea:

20%

Hydrogenation and SbCls Hydrogenation and SbCls Distn. and SbCls Distn. and SbCls

6 % dimethyl-1- and 2-hexer ie under 75 atm. N1

ever the authors mention that this gel, though not treated with hydrofluoric acid or other strong acid, was nonetheless slightly acidic, owing t o its method of preparation. Further, they report that commercial alumina catalysts containing sodium were inactive. The main effect of increased space velocity was t o suppress cracking and polymerization. Above 316" C. the amounts of branched pentenes and 2-pentene in the pentene cut were relatively unaffected by varying the space velocity in the range from 1 t o 24 hours-'. This points up the fact that a t these temperatures both double-bond and chain isomerization are very fast reactions, and explains the unusually high space velocities found best for the Isoforming process (3,67), since these high space velocities suppress cracking and polymerization. These authors (60) report further that double-bond isomerization is a more rapid reaction than chain isomerization, and that the speed of chain isomerization is greatly affected by temperature and by the concentration of protons on the catalyst surface. Oblad et al. (50) report that a large proportion of 2pentene was produced a t 260' C. As the temperature was raised the ratio of 2-pentene decreased, until a t 427" C. a space velocity of 16 hours-' was required t o form equal amounts of

March 1953

i.

4

'


2-pentene and by-products. The formation of the methylbutenes in favorable amounts required a higher temperature. However, there is little difference in the ratio of methylbutenes formed at 371" C. and at 427" C. a t space velocities over 6 hours-'. Considering the production of both 2-pentene and methylbutenes, it appears that temperatures of about 370" C. and space velocities up to a t least 24 hours-' represent optimum conditions. For example, with a 1-pentene feed a t 371" C. and a space velocity of 24 hours-l, the authors report 41.7%methylbutenes, 40.9% 2-pentene, and 10.3% 1-pentene, with a loss to cracking and polymerization of only 7.1 %. ACIDIFIEDALUMINA. With an acidified alumina catalyst and 2-pentene the results of Oblad et al. (60) showed a similar trend but the difference due to space velocity was much less. At 371" C. and a space velocity of 24 hours-' they observed their largest conversion to methylbutenes (55.4%). The ratio of this product to side products was lessened, however, presumably due t o a more active catalyst since the feed (2-pentene) would not be expected to show a large difference in cracking from 1-pentene, because the equilibration of 1-pentene and 2-pentene is a faster reaction than chain isomerization. Goldwasser and Taylor (24)report extensive studies on the hexenes. Their methods of analyses are such that considerable doubt is cast on their results (69, 87). An example of their results showed that alumina a t 398" C. and a space velocity of 0.4 hour-' formed 80% hexenes consisting of 3-hexene, methylpentenes, and ethyl-1-butene. Naragon (44)and Hay et al. (18) found that alumina, unless it contains some aoid or another component (e.g., silica) to give it acidic properties, is ineffective for chain isomerization. Further, neither reports the identification of ethyl-1-butene in the products of reaction. It may be concluded from these results, and for the previously listed reasons, that alumina in a pure form does not form any large amounts of isomers due to chain branching a t temperatures up to 400" C. Hay et al. (28) demonstrated rather conclusively that it is the acidic character of isomerization catalysts that makes them effective. Alumina and Duocil (sodium permutite), which were originally alkaline, showed very little activity. When these were acidified by selective adsorption of hydrogen ions from acidic solutions, they proved to be quite active catalytically. Moreover, silica gel and activated carbon were inactive and remained inactive after acid treatment. It was shown that these catalysts do not selectively adsorb hydrogen ions from acidic solutions. Berg, Sumner, and Montgomery (6, 6) recorded an octane (CFRM) increase of 4 unitp when thermally cracked gasolines were contacted with alumina acidified with hydrochloric acid at temperatures from 190" to 230' C. SUPPORTFOR OTHER CATALYSTS.Alumina has found wide industrial use as a support for other catalytic substances. I n certain of these supported catalysts the two constituents appear to form a complex having different characteristics from either constituent. Such catalysts (of an acidic nature) have been discussed by Thomas (74). The commercial cracking catalyst, silica-alumina, which will be discussed, is a noteworthy example of this type of catalyst. I n other combinations, the alumina serves merely as an inert support of high surface area. Ewe11 and Hardy (16) studied pentene isomerization from the standpoint of approach t o equilibrium. As previously mentioned, they report that unacidified alumina caused no chain branching but did result in a shift of branches already present. Alumina precipitated with sodium hydroxide was catalytically inactive. These authors report that catalysts composed of alumina mixed with silica, cuprous oxide, and nickel oxide (NiO) produced so much cracking that they were unsatisfactory for the approach to equilibrium isomerization. Catalysts composed of alumina coprecipitated with 25% of cobaltic oxide, manganous oxide, and chromic oxide with 50% of ferric oxide were effective, producing little cracking or polymerization, These catalysts, as well as

551

alumina, produced nearly cquilibriurn proportions of the pentcne isomers a t about 358" C. with about 10 passes of the feed over the ratalyst. At about 300" C. there was considerable variation in the composition of the product. Under these conditions, alumina (activated) was the most active, the catalysts containing manganous oxide, chromic oxide, and fer1ic. oxide were about equal, being somewhat less active than alutnin~i~ while the catalyst containing manganous oxide was considerably less active. Under other conditionh, a t a high space velocily, it might be expectec! that the catalysts containing alumina plus cuprous oxide, silica, and nickel oxidr would be satisfactory since the higher space velocity would reduve the undesirable reactions of cracking and polynicrizatiori, while having relatively little effect on the isomerization. By comparing their iesults with those of Whitmore and Meunicr ( 8 8 )and Cramer and Glasebrook ( 11 ) these authors conclude: A nonterminal double bond is more stable than R ieriiiinal double bond A chain branch adjacent to it double bond is more stable Lhen a chain branch in the saturated part of the molecule

Watson (85) used a catalyst composed of molybdenum dioxide suppoi ted on alumina to treat the product of isoforming. IIe reports a hydrogen transfcr reaction to produce aromatics and isoparaffins from naphthenes and the iso-olefins formed in the isomerization reaction. Aluminum Sulfate. The catalytic effectiveness of aliiiiiiriunn sulfate has been the subject of rather contradictory 1 cpoilx Gillett ( $ 3 )reported that some 2-butene was formed by passing 1-butene over aluminum sulfate a t 270" to 290" C. Serebryakova, Rudkovski, and Frost ( 6 4 ) also found aluminum sulfate slightly active as an isomerization agent. They observed that alinniiiiim sulfate on alumina was inactive as a catalyst for chain isonieiization. Cramer and Glasebrook (11) found that anhydious aluminurn sulfate was active, since with this catalyst at 275" C. and a low space velocity, 3,3-dimethylbutene was conveitcd t o a product consisting of 89% olefin of which 33% was 2,3-dimethyl1-butene and 62% was 2J-dimethyl-2-butene. These are about equilibrium proportions. Brooks et al. ( 7 ) corrohorate this evidence in obtaining almost exactly the same pioducts under the same conditions. If it can be assumed that the aluminurn sulfate used by Hay et al (28) was catalytically similar t o that used by these workers, an interesting conclusion follows since Hay (28) reported that in the isomerization of 1-hexene aluminum sulfate, even at 335' C., showed very little activity. The conclusion is that mole highly branched olefins (for a given moleculai neight) undergo chain isomerization more readily than their less branched isomers. Though chain isomerization is involved in the conversion of 3,3-dimethyl-l-butene to 2,3-dimethyl-l-butenc and 2,3-dimethyl-2-butene, it might be contended that this should be more readily accomplished than the formation of branched-chain isomers from normal isomers, since in the former case all that is required is the shifting of a branch already formed. Though the free energy change is not so favorable in the reaction of 3,3-dimethyl-l-butene to form 2,3-dimethyl-l-butene and 2,3-dimethyl-2-butene, it is not unlikely that the activation energy here is not so large as in the reaction of 1-hexene. Considerations of the reports of several workers (7, 11, 28, 28, 43, 6 4 ) indicate that aluminum sulfate is fairly effective BS a catalyst for double-bond isomerization, and for the shifting of branches already formed, but that it is ineffective for initiating chain isomerization. Even for the more readily accomplished types of isomerization, aluminum sulfate is not a very desirable catalyst since it causes considerable side reactions ( 6 4 ) . The catalyst as commonly prepared has a very small surfave aiea compared to alumina or silica-alumina. Clays. Various types of clays have been used for the vaporphase treating of hydrocarbon streams for many years. This is due to their activity as isomerizing and desulfurizing agcrils,

558


ready availability, and relatively long life. S70ge! Good, and Greensfelder (82) found that activated Filtrol (a bentonitic clay) was efiective as a bouble-bond and chain isomerization catalyst. Serebryakova, Rudkovski, and Frost ( 6 4 ) report that a t 294" C. Floridin and Glukov clays Jyere ineffective for the isomerization of n-butenes. This temperature is somewhat lower than is commonly used in vapor-phase olefin isomerization with mild catalytic substances. Voge, Good, and Greensfelder (82) report that a t 400" C. with a Filtrol catalyst n-butene was converted t o 21.4% isobutene and 71.7% 2-butene. 500" C., with this catalyst, n-pentene formed 54% methylbutenes but gave considerable cracking and polymerization. Nilrolaeva and Frost ( 4 6 ) report that n-hexene was isomerized over activated clay a t 260" C. a t a space velocity of about 0.2 hours-' to form 35% 2-1net,hylpentene and 2370 3-methylpentene. With this catalyst, considerable cracking and polymerization were observed, as well as some saturation of olefins by hydrogen transfer. H a y et al. (28) show that with 1-hexene as a feed nearly equilibrium concentrations of the isomers are formed a t space velocities of about 0.6 to 0.6 hour-' at temperatures from 300" to 350" C. wit'h Super-Filtrol as a catalyst. Georgia clay is reported as a catalyst of low isomerizing activity (28,44). Attapulgus clay is reported by Alberding ( 1 ) t,o cause an octane (CFRM) increase of 7 units in a thermally cracked gasoline at 205' t o 425" C. Super-Filt'rol and silica-alumina are claimed as agents for the increase of octane rating in olefin-cont,aining naphthas by Schmitkons (60). Activated clay formed 58% methylbutenes from n-hexene a t 260" C. and a low space velocity. This isomerization was accompanied by 209& cracking (10). Though natural clays are fairly effective as olefin-isomerization catalysts, they have been replaced to a considerable extent by t,he "synthetic clays"-e.g., silica-alumina and silica-magnesia. Acid-treated Doucil (sodium permutite) established nearly equilibrium proportions of the isomers of 1-hexene a t temperatures from 300" t o 350' C. (28,d.i). This catalyst was about as active as Super-Filtrol or boria-alumina, and required slightly higher temperatures for the establishment, of equilibrium than did the U.O.P. phosphoric acid catalyst. Untreated Doucil was inactive as an olefin isomerization catalyst. Herington and Rideal(%9),using lOyomolybdenum dioxide on alumina and heteropoly molybdates, observed that with a feed half heptane, half heptene at. 475" C. and a space velocity of about. 0.1 hour-', a yield of about 24% aromatics was obtained. These workers noted that for aroniatization it is necessary to have a catalyst that can easily change in valence. Phosphoric Acid. Phosphoric acid in a pure form has been used as an isomerization cat,alyst. Honever, supported phosphoric acid has found much wider use. 1:nlilie alumina, phosphoric acid is inherent,ly acidic and hence does not depend on the other component for acidic propert,ies. ITmce, phosphoric acid may be supported on almost any material having a large surface area. I n isomerization studies, phosphoric acid has been supported on such varying materials as carbon, charcoal. diatomaceous earth, fire clay, fuller's earth, kieselguhr, and pumice. The first quantitative study of the contact isomerization of the normal but,enes mas that of Ipatieff, Pines, and Schaad (34). These authors found that pure orthophosphoric acid produced from 4 to 60% 2-butene from 1-butene a t a low space velocit'y as the temperature was increased from 26" to 135' C. A similar increase in isomerization wit'h an increase in temperature was observed using phosphoric acid on diat'omaceous earth. They reported that a t 249" C. and 7.8 atmospheres this catalyst converted 1-butene quantitatively into 2-butene, Jyhile a t 325" C. the isomerization was only i o to SO% complete. They attribute this apparent decrease in activity t o a partial dehydration of orthophosphoric acid t o met,aphosphoric acid. A few calculations based on the thermodynamic properties of the butenes (38) are of interest. At 227" C. the equilibrium amount of 1-butene

Vol. 45, No. 3

is 14.3%;. Therefore, the reported complete conversion of 1butene to 2-butene is in doubt. Further, a t 327" C. the equilibrium amount of 1-butene is 20.7%. The reported 70 t o 80% isomerization is, therefore, close to the equilibrium conversion. Hence, the reported inactivat'ion of the phosphoric acid catalyst seems hardly justifiable. Hov-ever, Naragon (44) and Hay et al. (88) reported a decrease in the activity of phosphoric acid on kieselguhr a t temperat'ures above about 400' C. This decrease seems reliable, even considering that the equilibrium proportion of the n-hydrocarbon increases as the temperature increases. Thus, it. seems that Ipatieff et al. ( 3 4 ) arrived a t the correct conclusion: though the accuracy of their analyses seems doubtful. Ox CLAY. Serebryakova, Rudkovski, and Frost ( 6 4 ) report that for the format'ion of isobutylene from n-butene phosphoric acid on fire clay was an effective catalyst; the most effective form was dried for only a short period prior to use. With this catalyst polymerization is an important reaction. Polymerization was reduced by diluting the feed with about 30 to 40% water vapor. Using catalysts containing a lesser amount of phosphoric acid, and drying the catalyst for a short time, these authors observed 47.2yo isobutene and 36% polymerization a t 294' C. and a contact time of 144 seconds. Serebryakova and Frost (63) extended the stjutlies of isomerization n-ith this catalyst. I n this work it was attempted t'o establish equilibrium between the branched and normal butenes. The aut'hors stated t,hat it was impossible to reach equilibrium starting with the pure isomers. However, a t 294" C. with a contact time of 144 seconds, using n-butenes as a feed, they observed t h a t the ratio of iso/normal was 0.895. This corrceponds to 47.2% of isobutene in the butene fraction. At 327' C. the equilibrium amount is 43.1 % (38). Apparently, due to poor thermodynamic data. these aut,hors were trying to reach calculated equilibrium values that were inaccurate, since this later calculated value is in good agreement with their experimental values. These workers are then in agreement with Karagon (44) to the effect that phosphoric acid on an inert support will produce equilibrium conditions of chain branching if sufficient contact. time is alloived, but that the side reaction of polymerization is a problem. Frost, Iiutikovski, and Serebryakova (f 9 ) observed that phosphoric acid on charcoal was an effective olefin isomerization catalyst, producing about 50% isobutylene from n-butene a t 294' C. with long contact times. Fujita (20) reports an early use of a catalyst now commonly used. He found that phosphoric acid on diatomaceous earth converted normal pentenes t o about 50% methylbutene a t 200" to 350" C., accompanied by some cracking and polymerizat,ion. In a study of the commercial aspects of the isomerization of n-but,enes, Oblentsev et al. (61) concur that phosphoric acid on kieselguhr is an effective catalyst. This Tvork reports that the additioii o f 207, 15 ater vapor u-ith the feed decreased polymerimtion. Ox PENICE.Korris and Reuter ( 4 7 ) found that phosphoric acid on pumice a t 525' C. caused no isomerization of 2-pentene. This could be interpreted as an unusual method of preparat,ion to give an inact,ive catalyst from a normally active substance. However, the catalyst was prepared by drying lumps of pumice that had been soaked in sirupy phosphoric acid, a common method. Using this catalyst they found that a t 500' C. 29% of 2-methyl-2-butene was produced from 3-methyl-1-butene, while no 3-methyl-1-butene was produced from 2-met'hyl-2butene under similar conditions. At this temperature the proportion of 3-methyl-1-butene in equilibrium with 2-methyl-2butene would be about 2.4% according to calculations from the data of Kilpatrick et al. (58). It appears, therefore, that the methods of analyses may not have been sensitive enough t o detect small amounts of the various Ci isomers. The fact that Hay ef nl. (28) and Saragon (44) found that phosphoric acid on

March 1953


I

Ld

559

560


Vol. 45, No. 3

March 1953

h


561

kieselguhr was an effective catalyst for establishing equilibrium among the isomeric hexenes strengthens this reasoning. Further, Petrov and Shchukin (65),using phosphoric acid on pumice, obtained 32.4% methyl pentenes from n-hexenes after 4 hours a t 325" to 350' C. ON KIESELQUHR.The U.O.P. phosphoric acid on kieselguhr catalyst is a very effective isomerization catalyst. Naragon (44) and H a y et al. (28) report that this catalyst produced equilibrium conditions a t lower temperatures than most of the other catalysts; boria-alumina, Super-Filtrol, and acid-treated Doucil were nearly as effective. However, the phosphoric acid catalyst lost much of its activity as the temperature was increased. Hay et al. (28) postulate that this loss is due to volatilization of the phosphoric acid or excessive dehydration of the catalyst in the course of reaction. Hay et al. (28) also report that Super-Filtrol was nearly as active as the phosphoric acid catalyst but retained more of its activity a t higher temperatures. COMPARATIVE ACTIVITY. Catalysts that were found to be inactive by these workers were: alumina, boron phosphatephosphoric acid, untreated Doucil, silica gel, activated carbon, sodium Zeo-Karb, acid-treated silica gel, and acid-treated carbon. Catalysts of low activity were: Georgia clay, Houdry aluminum hydrosilicate, and anhydrous aluminum sulfate. Though space velocities of 0.1 to 1.9 hour-1, were tried in theestablishment of equilibrium, the best results were obtained a t velocities from 0.5 to 0.6 hour-'. At lower space velocities isomerization was more extensive but was overcome by the accelerated reactions of cracking and polymerization. For example, a t 285" C. and a space velocity of 0.1 hour-', over U.O.P. phosphoric acid, Hay (28) observed 26.4% branched hexenes (based on feed), 22.4% cracking, and 43.1 % polymerization. On Super-Filtrol the balance was not quite so unfavorable. At higher space velocities, isomerization was somewhat less extensive. For example, a t 340' C. and a space veIocity of 1.86 hour-', over U.O.P. phosphoric acid, Hay (28) reported 61.7% branched hexenes (based on feed), 3.7% cracking, and 3.8% polymerization. Although the side reactions were decreased, the chain branching was also lowered slightly. These space velocities are very low in comparison t o the space velocities employed in industrial pilot plants. Here space velocities of 10 to 15 hour-' are common. Industrial temperatures are likewise higher, for example 510" C. Naragon (44) however, found the optimum space velocity to be about 0.5 hour-' and his highest temperature was 482' C. This disparity in space velocity may be accounted for in several nays. First, Naragon (44)and Hay et al. (38)were interested in approaching very closely t o equilibrium conditions. In industrial practice this may be economically infeasible since the initial phases of conversion may be much more easily and rapidly accomplished than the conversions as equilibrium is approached. Since the industrial aim is to strike a balance between conversion and throughput, higher space velocities than those of Naragon and Hay et al. are indicated. Further, since longer carbon chains are reputedly more easily cracked (26) and branched chains appear t o be more easily isomerized, the feed used in the industrial pilot plants is very likely to be as completely reacted as hexene, under less severe conditions-e.g., larger space velocities. The temperatures that may be used in olefin isomerization are limited by the onset of cracking. Under the relatively long contact times used, Naragon and Hay et al. found that 335' C. was close to the optimum temperature. At a much higher space velocity, a temperature somewhat higher could be used. Naragon's data (44) show that a hydrogen pressure of 200 pounds per square inch decreased the amount of isomerization. Without hydrogen, at 318' C. and a space velocity of 0.5 hour-' over a boria-alumina catalyst, he obtained 12.8 volume % of 2,3-dimethylbutene, 41.8% Zmethylpentene, and 35.4% 3methylbutene. For similar conditions under a hydrogen pressure of 200 pounds per square inch the corresponding figures were 5.975, 31.3% and 20.3%. Further, when using hydrogen the

562


liquid yield \vas reduced from 97 to 92.3%. Hydrogen pressures are detrimental to the process of olefin isomerization under usual conditions. In studying the initial phases of isomerization, Petrov and Shchukin (66) found that 1-octene and 2-octene formed largely 2-methylheptenes with phosphoric acid on pumice in large amount a t 325" to 350" C. under a pressure of 75 atmospheres of nitrogen. To explain these observations, they postulated doublebond shifts followed by chain isomerization due to movement of a methyl group. In contrast, 1-heptene under similar conditions gave initially 3-methylhexenes. They postulate that this indicates a basic difference in the initial isomerization of alkenes containing even and odd numbers of carbon atoms. Phosphoric acid has been claimed as an effective olefin isomerization agent in several patents. Forney (18) reports that with a phosphoric acid catalyst a t 190' C. the combined effects of isoforming, polymerization, and refining may be realized. The feed used was the gas and gasoline produced in clacking. Lieber (40) found that aqueous solutions of phosphoric acid a t temperatures from 95' to 300" C. produced branched olefins from n-olefins and lowered the pour point of the olefinic feed. '4rveson ( 4 ) claims that if a dehydrogenated heavy naphtha is treated with phosphoric acid on alumina a t 400" to 500" C. the octane rating is increased and there may be a production of aromatics and naphthenes. Drennan ( l a ) reports that 96% 2-butene is produced when 1-butene is treated with phosphoric acid on bauxite a t 100' C. Low pressures are preferred in this reaction. Van Peski and Lorang ( 8 1 ) found that when 12butene was treated with phosphoric acid on kieselguhr a t 250" to 275' C., from 9 to 60% isobutenes were formed. There was little acrompanying polymerization. From a correlation of the large amount of experimental data with supported phosphoric acid as a catalyst, it appears that a t temperatures of about 350" C. with a fixed space velocity the U.O.P. phosphoric acid catalyst, though less durable than the refractory catalysts such as silica-alumina, accomplishes greater conversion of olefins. Commercially the refractory catalysts have considerable advantages since the tempeiature and space velocity may both be increased to give the desired isomerization accompanied by a smaller amount of side reactions than is obtained using the phosphoric acid catalyst. Silica Compounds. Silica has proved t o be a very poor isomerization catalyst, giving a reaction differing little from the thermal reaction ( 4 7 ) . However, catalysts composed of silica and certain other oxides are among the best catalysts lrnoirn for olefin isomerization. Some of these combinations deserving mention are silica-alumina, silica-magnesia, silica-alumina-magnesia, silica-alumina-zirconia, and silica-zirconia. The acidity of such refractory mixtures has been discussed in the theoretical section according to the theory of Thomas ( 7 4 ) . Egloff, Morrell, Thomas, and Bloch carried out extensive studies with such a catalyst, an activated silica-alumina (14). In their experiments, n-butene was passed over a silica-alumina catalyst a t temperatures from 385' to 600' C. and space velocities from 0.7 to 4 hours-'. The side reactions of cracking and polymerization were objectionable, but were relatively decreased by increasing the space velocity. Cracking increased sharply with a rise in temperature, while polymerization decreased slowly above 400' C. At a space velocity of about 0.8 hour-', they report that isomerization was not sensitive to temperature changes from 400' to 600' C., but the total isobutene produced was raised by increasing the space velocity a t 600' C. since the side reactions were decreased while the isobutene content was unchanged. This amounts t o stating that a t higher temperatures, isomerization is nearly independent of changes in space velocity over a considerable range. I n view of the data of Oblad et al. (60), this conclusion is entirely valid. It might also be expected that an even more favorable balance of isobutene to side products could be attained by further increasing the space velocity. At

Vol. 45, No. 3

temperatures from 400" to 600" C. and a space velocity of 4 hours-' these workers observed 17.1 yo of isobutene, 15.7% craclring, and 12.7% polymerization, using n-butenes as a feed. These woikere ( 1 4 ) found that a silica-alumina catalyst, siinilar to commercial cracking catalybts, produced about 59y0 of 2-methylbutene from n-pcntenes a t 400" C. and a space velocity of 3.2 hours-'. There were few side reactions under these conditions. The caatalyst was also effective for the isomerizatioii of octenes (13'). Many other oxide combinations containing silica or alumina and some other oxide or oxides show a catalytic effect very similar to the commercial silica-alumina catalyst. Greensfelder and Voge ( 2 6 ) used a silica-alumina-zirconia U.O.P. cracking catalyst. Their results corroborated those of Egloff et al. (14). They observed that at a given temperature and space velocity cracking increased rapidly with molecular weight, while polymerization reached a maximum a t about a Cb chain. Saturation of the double bond also increased with molecular weight. Further, the olefin appeared to undergo the above reactions a t a faster rate than did the corresponding paraffin. OTHER FACTORS IN ISORIERIZbTIOh- REACTIONS

Branched-chain olefins proved to be much more reactive than normal olefins. This tendency is more apparent in the higher hydrocarbons. For example, 2,4,4,-trimethyI-l-penteneis more reactive than n-octene. The tiimethylpentene cracked principally to isobutene, a reaction attributed to the tertiary olefinic carbon atom. In view of the work of Twigg (80) showing the similarity of the kinetics of isomerization, hydrogenation, and hydrogen exchange (on a metal catalyst), it might be inferred that the rate of isomerization of olefins increases rapidly with molecular weight. This idea is born out by the data of Voge, Good, and Greensfelder ( 8 2 ) who fouiid that the pentenes underIT ent chain branching much more readily than the butenes. Using a Nalco silica-alumina-magnesia catalyst, these workers reported that the double-bond isomerization in butenes was very fast. At 270" C. equilibrium was established with a space velocity of 18 hours-'. At temperatures of 400' to 500' C. a considerable amount of cracking and polymerization occurred at lower space velocities. The chain branching of butenes was considerably slower than that of the pentenes. The rate of isomerization was of the same order of magnitude as the rate of catalytic cracking of gas oils a t about 500" C., but not so rapid as saturation. These workers established that the presence of molecular hydrogen acted merely as a diluent. Voge and May (83), in a study of attainment of equilibrium among the butenes, discovered that with 1-butene equilibrium was approached from the cis side. They reported further that cis-2-butene mas produced from trans-2-butene about as fast as was 1-butene. They also found that a Porocel bauxite catalyst and a silica-alumina-magnesia catalyst were effective in establishing equilibrium among the butenes a t temperatures from 200" to 630' C. Side reactions were not excessive with the first catalyst below 550' C. and with the silica-alumina-magnesia catalyst a t 200" to 210' C. Using several silica-alumina type catalysts in a temperature range of 285" to 500' C., and a t space velocities of 0.1 ' 0 1.9 hours-', Hay, Montgomery, and Coull (88) found that 1hexene isomerized to 2-hexene and 3-hexene, then to methylpentenes and finally to lesser amounts of the dimethylbutenes. Small amounts of lower and higher molecular weight products were also formed. These investigators postulate that the reaction is stepwise as follom: 1-Hexene +Methylpentenes

--+Dimethylbutenes

The evidence for this belief is that when molee of each skeletal isomer per mole of hexene converted to branched chains is plottecl against the total moles of branched hexenes produced, a Frolichtype plot (61) results. When the resulting curves are extra-

March 1953

9


polated t o 0 mole % of branched hexenes formed, it appears that initially about 55% Zmethylpentene, 45 % 3-methylpentene, and no 2,3-dimethylbutenes were formed. This would mean that the double-branched isomers arise stepwise from singly-branched isomers. Though Naragon (44)does not report such calculations, if his data are plotted in this manner, Hay’s postulate seems t o be corroborated. Egloff (14), using a silica-alumina catalyst at 375’ t o 385’ C., obtained a complex mixture of hydrocarbons in which the following were tentatively identified: the 2-, the 3-, and the 4-methylheptenes, and 2,3,4trimethylpentene. The combination of results led Petrov to postulate that the reactions that may occur fall into the sequence of double-bond shift, movement of one methyl group, movement of a second methyl group leading to double branching, and movement of a third methyl group leading t o triple branching. The data of Naragon (44) and Hay et al. (28) show that nearly equilibrium proportions of the CF,isomers are formed at space velocities of about 0.5 to 0.6 hour-’ at temperatures from 300’ to 500’ C., using silica-alumina, silica-alumina-zirconia, molybdena-boria-alumina, and boria-alumina catalysts. These catalysts require a slightly higher temperature than does the U.O.P. phosphoric acid catalyst to accomplish a given conversion, but are more durable and more readily regenerated. Therefore, the synthetic clay-e.g., silica-alumina-types of catalysts have found favor for industrial uses as in catalytic cracking. Several patents have been issued in which these catalysts are claimed as agents for olefin isomerization. Thomas and Bloch (77) used a catalyst containing alumina, silica, and thorium dioxide t o produce methylbutenes from 1pentene. The added thorium dioxide is of questionable value since the silica-alumina combination is of proved activity and since Ewe11 and Hardy (16)report that thorium dioxide caused practically no change in a 2-methyl-2-butene feed at 358’ C. with repeated contact. However, Thomas and Bloch (78) claim that silica combined with thorium dioxide effectively catalyzed the isomerization of pentene and octene. Burgin (8) claims a boric oxide on alumina catalyst for the treating of cracked gasolines. Smith and Beeck (66) claim that the formation of a lithium oxide-alumina complex on the surface of an alumina catalyst inhibits the formation of a-alumina, and thus extends the life of the catalyst. Thiele, Hull, and Schmitkons ( 7 1 ) report that the fluidized catalyst technique may be used with these catalysts in isomerization reactions. They claim an octane (CFRM) increase of about 5 units when cracked naphthas are contacted with silica alumina (72); an increase of five to 15 units with a coke-still naphtha and a catalyst composed of silica and metal oxide (70). Thiele and Schmitkons (73) claim the use of this type of catalyst in a moving bed process to increase the octane rating of thermally cracked naphthas. Thomas (76) reports that the isomerization process may be regulated to give little polymerization with n-olefins and a silicaalumina-zirconia catalyst. Thomas and Ahlberg (76)claim silicaalumina as a catalyst for the octane improvement of a thermally cracked naphtha. Gerhold (32) claims this catalyst for the production of gasoline from a gas oil of low volatility. The process offers desirable features other than octane improvement-namely, a reduction in sulfur content and improvement of color, odor, and stability in feeds originally high in sulfur or having poor color, odor, and stability. CONCLUSIONS

Olefin isomerization has been extensively studied for many years by both industrial and academic organizations. Under rather mild conditions olefins may be isomerized to form equilibrium concentrations of the various isomers. Double-bond isomerization alone is catalyzed by metallic catalysts in the pres-

563

ence of hydrogen. Both double-bond and chain isomerization are effectively catalyzed by acidic catalysts. With the latter at temperatures below 250’ C. the principal reaction is double-bond iaomerization. As the temperature is increased there is an increasing amount of chain isomerization until a t temperatures from 325’ t o 500’ C. equilibrium is closely approached at high space velocities. The various homologous olefins react sensibly alike, though ease of isomerization and cracking appears to increase with chain length. I n general, the increased thermodynamic stability resulting from moving a double bond toward the interior or from increasing the number of side chains by chain isomerization is accompanied by a considerable increase in the octane rating of the feed. The possibility of upgrading thermally cracked gasolines by isomerization of their olefinic content has been recognized for several years. The new fuels produced by the Fischer-Tropsch type synthesis and by shale oil operations may be especially susceptible t o upgrading by olefin isomerization reactions. LITERATURE CITED (1) Alberding, C. H., U. S. Patent 2,371,726 (March 20, 1945). (2) Arbuzov, Yu. A,, and Zelinskii, N. D., Compt. rend. acad. sei. U.R.S.S., 30, 717 (1941); Survey Foreign Petroleum Literature No. 310 (June 13, 1941). (3) Armistead, G., Oil Gas J . , 45, No. 22, 80 (Oct. 5, 1946). (4) Arveson, M. H., U. S. Patent 2,263,026 (Nov. 18, 1941). (5) Berg, L., Sumner, G. L., and Montgomery, C. W., IND.ENG. CHEM.,38, 734 (1946). (6) Berg, L., Sumner, G. L., and Montgomery, C. W., U. 8.Patent 2,397,639 (April 2, 1946). (7) Brooks, D. B , Howard, F. L., and Crafton, H. C., J . Research Natl. Bur. Standards, 24, 33 (1940) (8) Burgin, J., U. S. Patent 2,407,918 (Sept. 17, 1946). (9) Carr, E. P., J . Am. Chem. SOC.,51, 3041 (1929). (10) Cheltsova, M. A., and Petrov, A. D., Compt. rend. acad. ~ c i . U.R.S.S., 44, 152 (1944); Survey Foreign Petroleum Literature No. 490 (Feb. 9, 1945). (11) Cramer, P. L., and Glasebrook, A. L., J . Am. C h m . Soc., 61, 230 (1939). (12) Drennan, H. E., U. S. Patent 2,330,115 (Sept. 21, 1943). (13) Egloff, G . , Hulla, G., and Komarewsky, V. I., “Isomerization of Pure Hydrocarbons,” p. 68, New York, Reinhold Publishing Corp., 1942. (14) Egloff, G., Morrell, J. C., Thomas, C. L., and Bloch, H. S., J . Am. Chem. Soc.. 61, 3571 (1939). (15) Evans, A. G., and Polanyi, M., J . Chem. SOC.,1947, p. 252. (16) Ewelll, R. H., and Hardy, P. E., J . Am. Chem. Soc., 63, 3460 (1941). (17) Farkas, A., Trans. Faraday soc., 35, 906 (1939). (IS) Forney, W. E., U. S. Patent 2,263,266 (Nov. 18, 1941). (19) Frost, A. V., Rudkovski, D. M., and Serebryakova, E. K.. Compt. rend. acad. sci. U.R.S.S., 4, 373 (1936); Chem. Abstr., 31, 3371 (1937). (20) Fujita, J . Chem. SOC.Japan, 53, 847 (1932). (21) Gallaway, W. S., and Murray, M. J., J . Am. Chem. SOC.,70, 2584 (1948). (22) Gerhold, C. G., U. S. Patent 2,377,078 (May 29, 1945). (23) Gillett, A., Bull. 8oc. chim. Belges, 29, 192 (1920); Chem. Abstr., 16,2107 (1922). (24) Goldwasser, S., and Taylor, H. S IJ . Am. Chem. SOC.,61, 1762 (1 QRQ) \____,.

(25) Ibid., 61, 1766 (1939). (26) Greensfelder, B. S., and Voge, H. H., IND. ENG.CHEM, 3 7 , 983 (1945). (27) Greensfelder, B. S., Voge, H. H., and Good, G. M., Ibid., 41, 2573 (1949). (28) Hay, R. G., Montgomery, C. W., and Coull, J., Ibid., 37, 336 (1945). (29) Herington, E. F. G., and Rideal, E. K., Proc. Roy. SOC.London, A-184,434 (1945). (30) Hoog, H., Verheus, J., and Zuiderweg, F. J., Trans Faruday SOC.,35, 993 (1939). (31) Hurd, C. D., and Goldsby, A. R., J . Am. Chem. SOC.,56, 1812 (1934). (32) Hurd, C. D., Goodyear, G. H., and Goldsby, A. R., Ibid., 58, 236 (1936). (33) Ipatieff, V. N., Ber., 36, 2003 (1903). (34) Ipatieff, V. N., Pines, H., and Schaad, K. E., J . Am. C h m . SOC.,56, 2696 (1934).

I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY Ipatieff, V. N . , and Zdaitovetsky, B. S.,Ber., 40, 1827 (1907); Chem. Abstr., 1, 2075 (1907). Ipatieff, V. N., and Zdaitovetsky, B. F., J . Russ. Phys. Chem. Soc., 39, 897 (1907); Chem. Abstr., 2,259 (1908). Kharasch, 1LI. S., and Darkis, F. R., Chem. Revs., 5,571 (1928). Kilpatrick, J . E., Prosen, E. J., Pitzer, K. S., and Rossini, F. D., J . Research aVatZ.Bur. Standards, 36, 559 (1946). Lankford, J. D., and Ellis, C. F., IND.ENG.CHEY., 43, 31 (1951). Lieber, E., C . S.Patent 2,281,941 (May 5 , 1942). McCarthy, W. W-., and Turkevich, J., J . Chem. Phys., 12, 405 (1944). Moldavski, B. L., and Kamusher, H., Compt. rend. acad. sci. U.R.S.S., 1, 335 (1936): Chem. Abstr., 30, 6713 (1936). Mulligan, M. J., and Cramer, P. L., U. S. Patent 2,423,612 (July 8, 1947). Saragon, E. A,, IND.ENG.CHEM.,42,2490 (1950). Nemtsov, M. S., Nizovkina, T. V., and Soskina, E. A., J . Gen. Chem. U.S.S.R., 8 , 1313 (1938); Survey Foreign Petroleum Literature Index, Part 1 (1937-39). Nikolaeva, A. F., and Frost, A. V., J . Gen. Chem. U.S.S.R., 13, 733 (1943); Chem. Abstr., 39, 662 (1945). Norris, J . F., and Reuter, R., J . Am. Chem. Soc., 49, 2624 (1927). Oblad, A. G., and Gorin, &I. H., ISD. EKG.CHEX., 38, 822

Vol. 45, No. 3

(61) Schneider, V., and Frolich, P. K., IND.ENG.CHEM., 23, 1405 (1931). (62) Sehuit, G. C. A , , Hoog, H., and Verheus, J., Rec. trav. ehim., 59, 793 (1940); Chem. Abstr., 35, 4728 (1941). (63) Serebryakova, E. K., and Frost, A. V., J . Gen. Chem. U.8.S.R , 7, 122 (1937); Chem. Abstr., 31, 4570 (1937). (64) Serebryakova, E. K., Rudkovski, D. M., and Frost, A. V., Compt. rend. acad. sci. U.R.S.S., IV, 359 (1936); Survey Foreign Petroleum Literature, Special Trans. S-24 (Sept. 23, 1938). (65) Sherrili, M.L., Otto, B., and Pickett, L. W., J . Am. Chem. SOC.,51, 3023 (1929). Smith, A. E., and Beeck, 0. A, U. S. Patent 2,474,440 (June 28, 1949). Standard Oil Co. (Indiana), Petroleum Rejiner, 27, 170 (Sept. 1948, Section 2). Standard Oil Dev. Co., Brit. Patent 641,121 (Aug. 2, 1950). Thacker, C. M., Folkins, H. O., and Miller, E. L., IND.ENG. CHBM., 33, 584 (1941). Thiele, E. W.,Hull, C. &Schmitkons, ‘I., G. E., U. S. Patent 2,326,704 (.lug. 10, 1943). Ibid., 2,326,705 (Aug. 10, 1943). Ibid., 2,410,908 (Nov. 12, 1946). Thiele, E. W.,and Schmitkons, G. E., Ibid., 2,326,703 (Aug. 10, 1943). [email protected],41, 2564 (1949). Thomas, C. L., IND. Thomas, C. L., U. S. Patent 2,328,754 (Sept. 7, 1943). Thomas, C. L., and Ahlberg, J. E., Ibid., 2,371,079 (March 6, 1945). Thomas, C. L., and Bloch, H. S.,Ibid., 2,216,284 (Oct. 1, 1940). Ibid., 2,352,416 (June 27, 1944). Thorne, H. RI., Murphy, W. I. R., Ball, J. S., Stanfield, K. E., and Horne, J. W.,IND. ENG.CHEM.,43,24 (1951). Twigg, G. H., Proc. Ray. SOC.London, A-178, 106 (1941). Van Peski, A., and Lorang, H. F., U. S. Patent 2,220,693 (Nov. 5 , 1940). Voge, H. H., Good, G. M., and Greensfelder. B. S.,IND.ENG. CHEM.,38, 1033 (1946). Voge, H. H., and May, N. C., J . Am. Chem. SOC.,6 8 , 550 (1946). Waterman, H. I., Leendertse, J. J., and MoMaringal, Rec. traa. chim., 54, 79 (1935); Brit. Chem. Abstr., A, 325 (1935). Watson, C. W., U. S.Patent 2,400,795 (May 21, 1946). . 26, 668 (1948). Whitmore, F. C., Chem. E ~ QNews, Whitmore, F. C., et al., J . Am. Chem. Soc., 62, 795 (1940). Whitmore. F. C., and Meunier, P. L., J . Am. Chem. Soc., 55, 3721 (1933). Zelinskif, N. D , Arbuzov, Y . A., and Batuev, M. I., Comgt. rend. mad. Sci., U.R.S.S., 46, 150 (1945); Survey Foreign Petroleum Literature, No. 6 or 515 (June 22-29, 1945).

.----.

(1946).

Oblad, A. G., and Messenger, J. V., C. S. Patent 2,471,647 (May 31, 1949). Oblad, A. G., Messenger, J. V., and Brown, H. T., IND. ENG. CHEM.,39, 1462 (1947). Oblentsev, R., Pazhitnov, B., Rudkovski, D., and Trifel, A., Khim. Referat. Zhur., 4, No. 9, 119 (1941): Chem. Abstr., 38, 950 (1944). Petrov, A. D., and Cheltsova, M. L4., Compt. rend. acad. sci. U.R.S.S., 15, 79 (1937); Survey Foreign Petroleum Literature, No. 28 (1938). Petrov, A. D., Cheltsova, M. A., and Batuev, M. I., C ~ m p trend. . acad. sci. U.R.S.S., 56, 273 (1947); Chem. Abstr., 43, 6152 (1949). Petrov, A. D., Meshcheryakov, A. P., and Andreev, D. N., Ber. 68B,l(1935); J . Gen. Chem. U.S.S.R., 5, 972 (1935); Chem. Abstr., 29, 2145 (1935). Petrov, A. D., and Shchukin, V. I., J . Gen. Chem. U.S.S.R., 9, 506 (1939); Survey Foreign Petroleum Literature, Trans. 209 (Jan. 26, 1940). Petrov, A. D., and Shchukin, V. I., J . Gen. Chem. U.S.S.R., 11, 1092 (1941); Oil Gas J., 43, No. 37, 77 (January 20, 1945). Pines, H., J . Am. Chem. Soc., 55, 3892 (1933). Plate, A. F., and Tarasova, G. A,, J . Gen. Chem. U.S.S.R., 20, 1092 (1950); Chem. Abstr., 44,8215 (1950). Rose, A., J . A m . Ghem, Sac., 62,793 (1940). Schmitkons, G. E., U. S. Patent 2,323,570 (July 6, 1943).

RECEIVED f o r reviem May 12, 1952.

.kCCEPTED

Kovembor 24, 1952.

J

Butvlhydroxvet J

u;

J

ms

J

HOWARD C. HAAS, LEONARD 6. FARNEY, AND CLAUDE VALLE, JR. Chemical Research Laboratories, Polaroid Corp., Cambridge, Mass.

IGH polymeric materials are in general incompatible with each other. This has been demonstrated experimentally b y Dobry and Boyer-Kamenoki ( 5 ) and explained thermodynamically by Gee ( 6 ) , who has shown that the entropy gain on mixing two polymers is so small that even a slight positive heat of mixing would result in almost complete immiscibility. The difficulty of finding pairs of compatible polymers apparently accounts for the scarcity of information on systems of this type. Among the derivatives of cellulose, certain compatible pairs do exist, For example, ethylcelluloses and nitrocelluloses are miscible, probably because of specific interactions bet\\ een these two polymers which overcome differences in cohesive energy

density (11). During a study of ether derivatives of hpdroxyethylcellulose (4), the authors of this paper found that several of these seem compatible with ethylcellulose. A butyl ether of hydroxyethylcellulose containing 1.5 ethylene oxide and 2.0 t o 2.1 butyl groups per anhydroglucose unit appears compatible with ethylcellulose over the entire composition range. (The ethylcellulose was standard ethoxy Ethocel, Dow Chemical Co., Lot 14037,100 cps. viscosity, [VI = 2.18 in 80:20 toluene:ethanol, 48.5 % ethoxyl corresponding to 2.50 ethoxyl groups per anhydroglucose unit.) This compatibility probably results from similar cohesive energy densities rather than from any specific interactions between the two polymeric species.

Review of Olefin Isomerization - Industrial & Engineering Chemistry

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