Purification of Normal Paraffins C. B. KINCANNON BND EARL MANNIXG, Jr-2. Houston .~tuniifucturing-Reseur~h Luhorutory, Shell O i l Co.,Houston, Tex.
N
OIt AIAI, paraffins arc pi ewrit in pctroleum hvdi ocvtrbons but are difficult to separatc and recover in pure btate by conventionttl teehnique-. l'urihcation of normal paraffins froin h) diocarboii niixtuies 1 ) ~ tientriient with chlorosulfonic acid has lireii reportcd 1 ) ~ Hliepard, IIeniie, and Miclgley (9). Thc chlorowlfoiiic itcicl tre,ttment technique appeared to be time consuming yet quite cffective. This paper repoits a similar approach but with fortihed sulfuric acid which reacts more rapidly than chlorowlfonic acid with nonnormal paraffinic hpdrorarbons and yields normal parafins of high purity. Concentrated sulfuric acid, with or without additives (such as silver sulfate or anhydrous phosphorus pentoxide) is ucled widely for reaction9 with olefinic and aromatic hydroeai hons. The productq from these reactions are predominantly soluble in the aeid phase Thib principle i h uwd in several manufacturing proresics (2, 3, 6, 7 ) :tiid foi the analyscb of totul olefinic and ai o:n:itic hydrorarborii a s cumphfied by the method p~oposed 111 Gttwinkel (4). The 1C:Lttninltel method involves the use of hulfiiiic ncid fortified 11ith plrosphoi u q pentoxide in thc ratio of 30 giaiiiq of phoqphoius pentoxide per 100 nil. of acid. Tlie fortified acid when agitated with a hydiocarbon &le is presunied to react with all the olefinic and aromatic hydrocai \)on%, antl, i n addition, t o a limited cltent with the fiaturated hydrornrbonq. Therefore, the nietlioti usually ~ n c l i i d ea~ ctcp for dctriiiiiIiirigbo1ii~)ilityof the iatur:Lt(d h y diocarbons in the arid rnixture. The extent of solubility of the paraffinic hydrocarbons in fortified sulfuiic acid ha9 recently been found to he dependent, in part, on tht, structural type of paraffinic hydror:trhona. This is exemplified by the result< of a n exploratory study carricd out in the lahorator y aherc thr aolubilities of five purr 9:tturated hydrocartmi5 in an acid solution u ere determined. The hydrocarhorib nere met~iylryc~lohcuarlt', %niethylpentane, 2-methylbutane, 2,:~-dirnethylperitanc,arid n-octane. The acid mixture consiited of 98% sulfuric acid with 30 grams of phosphorous p e n t o d e per 100 nil of acid. Th(a reFults, which are given in Tahle I, &how that met111Iryc~lohexarie, 2-methylpentane, 2methylbutane, anti 2,3-dirnetliyl~~c1ita1ie were partially soluble i n the acid a t acid-to-oil iatio of 1:l and contact time of 5 minutes. The solubilities were increased about ninefold by the higher acid-to-oil ratio of 6: 1. n-Octane was not absorbed ti) t h r arid even a t an acid-to-oil ratio of 6: 1. Also, additional elperiniciit\ indicated that cyc1ohex:tnc reacts rapidly with thra for tificd ncid
I.:Xl'EHt W E U 1 A L
The b t oclts u#ed in tliib inveitigation were chosen as typical of those that would be used for normal paraffin production. T h e charge material consisted of narrow boiling fractions prepared by frac%ionationof West Texas 15llenberger and Michigan crudes in a coluiiin of about 60 theoretical plates. In addition, a synthetic Idend of pure hydrocarbons vats used for a study of the effect of various acid treating agcritc. The components used to prepare the various acid treating agents in this work weie concentrated sulfuric acid, caoncentrated phoqphoi ic acid, sulfur trioxide, and phoipliorua pentoxide. concentrated sulfuric acid was the m:tjoi component in each trcating agent. \ arioub concentrationq of sulfuric acid with phofiphorus pentoxide, phoshoiic acid, or 5ulfui trioxide 1% ere used in a study of the effects of operating variablrs. Finally, a mixture of sulfuric acid and sulfur trioxide (5% fuming sulfuric acid) was used to prepare quantities of pure nornial paraffins from petroleum hydrocarbon fractions. The equipment consisted of a glass container in n hich the mixture of acid and oil was contacted, a motor-driven agitator and a thermometer. The glass container u as placed inside an open top box, which served as an ice bath as a d as a safety shield and resrrvolr. The experiments Rere carried out in a ventilated hood which removed acidic gasee. In the studies of the operating variables, 100-ml. samples of hydrocarbons were treated in a 1liter flask. A stainless steel stirrer with double paddle8 was driven by a conventional laboratory scale electrical motor. For the preparation of 1 gallon quantitie8 of pure noriiial paraffins, itbout l ' / z gallons of hydrocarbon samples were treated in a 10gallon capacity borosilicate glass container. Vigorous agitation of the acid-oil mixture mas obtained nith a staiiilcss steel doublepaddled stirrer driven hy a '/io-hp. motor. J h e p t for size, the apparatus wae efisentidly the same for all experiments reported. 111
general the treating p ~ o c c d u i e~
: t ha < follom h:
The hydrocarbon sample A :is placed in the reaction vessel, :ind the acid vas added sloir IJ to prevent e\cessive temperature iiicrcases iri the reaction mi\ture. For tieatment of 11/2-gallon fractionq thc acid \$ afi siphonrd from a carboy into the reaction vessel. After the required amount of arid had been added the acid-oil mixture was stirred vigorously. In ordei to control the temperature of the reaction mixture an ice bath was used t o 1ou er the temperature when necccsary. The progress of the reaction u as rhcAcked about every hour by determining refractive iirdic-e8 on spot samples. After the treatment w m terminated thc unreacted hydrocarbon fraction URD separated from the acid phase, ivatihed v, ith alkali and water, and dried. OPERATING VARIABLES
Iiydrocarbon 1\It~thylcyclohexane 2-&I?thylpentane 2-Alethylhutane 2.S-Dimethyl~rntane n-Octane
The nioit important ope1atiiig variables in the technique (6) were strength and type of aeid, acid-to-oil ratio, and reaetion time and temperature. Tlic effects of the operating variables are strongly interrelated-e g., the efferti of strongev acid and longer reaction time are cumulative -therefore, the choice of conditions held constant in each set of (~qwrinicntsmas somewhat arbitrary. STnn\orrir 4x11T Y m 01' ACII). Separatr portions of a blend ol' purr hydrocarbons (Tnblc 11) wcre qul)jectcd to vitrious acid treatmentc with a volume ratio of ac,id-to-hydrocarbon of 10: 1. Thebe expeiinientp neie carried out at rooin temperature except that tcrnperatures were increavtl by the hcat of the reaction. The data pertaining to ti tlating condition$ antl properties of the reaction products are given in Tablc 111. The rePults were evaluated on the basis of the deniitj and refractive index of the raffiiiatc. W t h a mixtrirr of h i tlio(w1ioii~i i i ( I 1 a~ t l i ~ rithctic
Solubility, G./~IJO-E __ ____Acid, 1 vol. Arid, 6 vol. 1.0 0.5 0.6 0 . fi 0.0
9.0 4 0 B O 4.5 0.0
The preferential absorption of q-cloparaffins arid Oranrhctlchain paraffins as compard to rioriiial paraffins suggested a poe4l)le mean.; of concentrating Sind purifying normal paraffinic hydrocarbons. Some furthw cxperiments were carried out in which normal paraffins of high purity wcrc produced and a study \vas initiated to detwniiric the effects of the different varirt1)les involved in the utilization of w e h a technique.
149
INDUSTRIAL AND ENGINEERING CHEMISTRY
150
blend used in this work it is possible t o obtain numerous conhinations of three or more components that will have common properties. However, exploratory experiments have indicated the order of solubilities of t,he hydrocarbon types in the acid to be aromatics, cycloparaffins a i d isoparaffins, and lastly normal paraffins. I n this worlr a rafinat,e having the refractive index and densit,y values of a pure normal paraffin was considered t o be essentially a pure hydrocarbon, This presumption is suhstantiated by results presented later.
TABLE 11.
C031POSITIOT O F HYDROCA4RBOSBLEXDS-1'HYSICAL PROPERTIES O F ??[:RE CONI,OSEST (8) .*,p prox-
Refractire Irides, n2,O
Hydrocarbon n-Octane 2 2 4-Triniethylpentane 1'4~Dii~ethylcyclohexane (cis) 1'4-Dimethylcyclohexane (trans) 1 : 3 - ~ i m r t l ~ y 1 c y o 1 0 h e ~:cis) ane 1,3-Dirnethylcyclohexanr (trans) Toluene
1.39743 1.30145 1 ,42006 1.4~090 1.42291 1.43085 1.4!>093
iinate
Density. d;"
Vol.
74
0,70252 0.09193 0,78288
8s
o
70255) 0.7G603 / 0.78472;
~
~~CID-PCRIFICAl'IO\
-.
85 15 100
t3.40 4 1.50
67 33
10.13
Fuming HzS04 (5% 80s) 9 8 5 % IXzSO4 plus 20 g PzOa per 100 mi Fuming &SO4 (30% SOd 85% H3POa Fuming Ha804 (30% Sod
100
..
OF
C ~ R B O S BLESD
9 8 . 5 7 ~HnSOa 85% HaPo4 98.57c H ~ S O I Fuming %SO4 (307's03) 85% HaPOa 98.5% HiSOi plus 10 g. PzOa per 100 mi.
16 10
2.5
91 85
80
-0.Z6 -1.13
1G 16
82 64
-2 35
16
78
-2 65 -6 7 5
4
77 51
80
20 100
0 083
by using Pulfuric acid with either sulfur trioxide or phosphorus pentoxide in excess of the amount needed to conibine x i t h thc water in the acid. The acid niay vary considerahly in act,ual composition or method of pre2aration. For a given charge stock the most practical and efficient acid strength for a given process depends in part, on the normal paraffin content desired in the product. ACID-TO-OILRATIO. The optimum acid-to-oil ratio is dependent on the structural type and the quantity of the undesirable components present in the hydrocarbon mixture. -4 normal hexane concentrat,e was considered to be typical of those t h a t 17ould be used for normal paraffin production. The concentrate contained about 7 5 wt. yo n-hexane: 11 xt. yo isoparaffins, 10 wt. 70cycloparaffins, and 4 wt. 70aromatics. This hydrocarbon sample was h a t e d with acid (98% sulfuric acid plus 30 grams of phosphorus pentoxide per 100 ml. acid) a t different acid-to-oil rat,ios until there was no furt,her change in refractive index of the hydrocarbon layer. The results are given in Table IT.
> 100
O.SGC,94
T h e results of the first thrce experiments (Table 111)indicate t h a t acids containing free water do not yield a pure normal paraffin. On the basis of the refractive index and density of pure n-octane, the hydrocarbon products from fourth through the eighth experiment of Table 111 appear t o be essentially pure n-octane. These latter experiments were made with an acid treating agent which contained added inorganic acid anhydride in excess of the amount needed to combine with the water in the acid. T h e fourth and sixth experiments mere made with acid mixtures containing an excess of phosphorus pentoxide, and t h e fifth and eighth experiments Lwre made with acid agents containing an excess of sulfur trioxide. Since excess sulfur trioxide in t h e acid accomplished the same results as t h e acid fortified with phosphorus pentoxide, phosphorus pentoxide may act primarily as a dehydrating agent. However, the percentage of recovery appeared to be higher in experiments with the arid agents that contained phosphorus pentoxide than in experiments xvith the acid t h a t contained sulfur trioxide. T h e first two esperiments (Table 111) gave good recoveries of total hydrocarbons, b u t the recovered products contained substantial proportions of nonnormal paraffinic hydrocarbons. The third evperiment also gave good recovery, and the product appeared to contain a smaller amount of nonnormal paraffinic GTdrocarbons than it did in the first two experiments. T h e results shown in Table 111 indicate t h a t separation of normal paraffins from hydrocarbon mixtures can be accomplished
TABLE 111. EFFECTO F TIPE O b
Vol. 47, No. 1
AcidiOi,l Vol. Ratio 0.8
2.0 , ,0
7
1.3760 1.3780 I 3749
A1)proxiniate Purity, Vol. c/;.
g5 CIY 99
Reco\.rry of n-Hexane. Vol. c;
++
Refractire index (/I:?)of tlie 71-liesane concentrate was 1.3823: yiii'c hexane is 1.37486 (8).
,&-
-~ ~
*Itacid-to-oil ratio of 0.8 (Table I V ) purity was low mid recovery high, The apparent high recovery of the first experiment is, of course, due t o t h e presence of impurities in the raffinate. Treatments a t acid-to-oil ratios of 2.0 and 5.0 gave pure n-hexane; however, t h e recovery was higher for acid-to-oil ratio of 2.0 t,han for 5.0. Minimum acid consumption and maximum recovery of substantially pure normal paraffin would correspond to an acid-to-oil ratio between 0.8 and 2.0. This conclusion is based on t h e oil being subjected to only a single treatment. .4 more economical procedure may be peveral successive treatments wit,h much lower acid-to-oil ratios. I~EACTIOS TIaiE A N D TEMPER.4TURE. Reaction rate tests Wcre made to determine the effect of mixing time and maximum temperature on the purity and recovery of n-undecane. The concentra,t,e treated in these experiments contained about 70 mole Yo n-undecane. The acid was fuming sulfuric acid (5% SOa) ' and the acid-to-oil ratio v a s 2 : l . Experiments were made a t ieaction times of 1, 5, 15, and 30 minutes. KO attempt ims made to control the temperature of runs made a t 1-, 5-, and &minute intervals. T h e temperature of t h e 30-minute run was maintained around 122" F. Rith an ice bath. The n-OCrA\E F R O \ l A HYDROdata obtained from this series of experiments arc prcsentcd in Table V. I n Table V the speed of the reaction is indicated by the increases in reaction temperature of 49" F. after 1 minute, 81" F. after 5 minutes, and 128' F. after 15 minutes. T h e conditions of the ex, . 0.7045 1.3~80 periments we1 e not sufficiently seveie .. 0,7022 1.3869 t o produce pure n-undecane. Bow. 0.7041 1.3978 ever, t h e effect of time is indicated by comparison of the reqults obtained from 95 0.7027 1.3975 74 0.7029 1.3975 the 5- and 30-minute runs in whivh the average temperatures were approxi91 0 7029 1 3979 mately the qame. The data indicate t h a t longer reaction times result in lower 90 0 7028 1 3975 5Q 1 3975 normal paraffin yields with only emall gains in product purity. The effect of
INDUSTRIAL AND ENGINEERING CHEMISTRY
January 1955
plates.
151
The physical properties of the normal paraffin concen-
trates, of the products from treatment with the fortified acid, TABLE v. EFFECTO F TIME:AND TEMPERATURE-PCRIFICATIOS OF ~ - U X D E C A X E and of pure n-paraffins from the literature ( 8 ) , are given in Table Reaction time, min. 1 5 15 30 VI. ij8-117 97
68-149 126
68-196
68-126 122
These data indicate that the normal paraffins prepared by acid treatment followed by distillation are quite pure. The 83 77 80 85 % purities of normal octane, nonane, decane, and undecane were Recovery, total hydrocar83 72 80 74 bon, wt. 7% calculated from the freezing point and apparent impurities were Recovery (n-undecane), wt. found to be less than 1 mole %. The infrared spectrum of the 85 90 95 85 % normal hexane raffinate was compared with the spectrum of a a Calculated with consideration of temperature a t each 0.5-minute interval. National Bureau of Standards sample of 99.8 i 0.02 mole b Determined b y extractive crystallization with urea. purity and was found to be the same within the reproducibility of the spectrophotometer. A purity determination W&E not OF CONCESTRATES A X D PRODVCTS OF TABLEVI. PROPERTIES TREATMENT WITH SULFITtIC A C I D AGENT made of the normal dodecane raffinate; however, on the basis of refractive index and density, the Iaffinate appears to be of high Purity Calcd. purity. from Freezing Exploratory experiments indicate t h a t no final fractionation ~ ~ i Rrfractir-e l i ~ ~ Freezing Point, ~ o ~ e is required if the original concentrate contains only one normal Point, Jndex, Denslt~, Point, Paraffin O F n go d:' O F 73 paraffin. The operation merely involves distillation for preparan-Hexane tion of the concentrate, treatment with an acid agent, washing Concentrate 155 1.3823 ... ... with alkali and water, and finally drying. Product 155.7 1,3750 0.6%4 ... P u r e n-hexane The present investigation of treatment with sulfuric acid agent (8) 155.73 1.37488 0.65937 ... ... %-Octane for purification of normal paraffins was not sufficiently extensive Concentrate 259 1.4031 to permit a complete evaluation of the process. However, acid 0.7024 -70122 l0O:O Product 268.2 1.3975 Pure n-octane treatment might be attractive for certain applications, but it 18) 258.20 1.39743 0,70252 -70.23 . .. n-Nonane must compete with other processes such as extractive crystallizaConcentrate 302 1.4125 tion ( I ). Product 303.1 1.4054 o.iiis -fii:94 ir%:9 Temp. range. F. Average t e m p a , F. Purityb, (n-undecane), mole
158
.
Pure n-nonane (8) n-Decane Concentrate Product P u r e vi-decane (8) n-Undecane Concentrate Product P u r e n-undecane (8) n-Dodecane Concentrat? Product P u r e n-dodecane (8)
I
.
303.44
1 40542
0.71763
-64.33
.._
SUMMARY
346 345.6
1,4182 1.4118
0.7362
--ii:37
100'1
345.42
1.41189
0.73005
-21.39
382 383
1.4280 1,4171
0.7402
-i4:13
99.8
1.41718
0,74017
-14.07
...
Separation of normal paraffins from other hydrocarbons in a mixture can be achieved by use of strongly fortified sulfuric acid. Sulfur trioxide and phosphorus pentoxide in excess of the amount needed to combine with the water in the acid were used as fortifiers. The optimum acid-to-oil ratio for the preparation of n-hexane of 99 vol. % purity from a concentrate containing 75 vol. % was determined to be between 0.8 and 2.0. The severity of the reaction is a function of both time and temperature; however, better yields of n-undecane were obtained by increasing temperature rather than time. One gallon quantities of pure normal paraffins from six to twelve carbons were prepared by treating petroleum concentrates with fuming sulfuric acid.
384.60
...
422
1.4321 1.4215
0.7490
421.3
1.42160
0.74869
...
... I . .
...
...
temperature can be approximated by comparing t h e results obtained from the 15- and 30-minute runs, in which the average temperatures were 158' and 122" F., respectively. The data indicate that increasing the severity by higher reaction temperature rather than by longer reaction time tends to favor both recovery and purity. Thcse data are presented only as suggestive trends. Reaction temperature is one of the most important vai.iables and should be further investigated. APPLICATIONS
The technique developed for purification of normal paraffins wap used for the preparation of I-gallon quantities of normal paraffine from six to twelve carbons. The charge material consisted of narrow boiling fractions of normal paraffin concentrates. Kach fraction was treated with fuming sulfuric acid (t5% SOa) at about 5 : 1 acid-to-oil ratio, and the reaction was considered to be complete when the refractive index of a test sample was not substantially reduced by an additional treatment with fuming sulfuric acid (30% Sod. Fin:ilb the raffinate was fractionated in a Heli-Grid column equivalent to approximately 100 theoretical
LITERATURE CITED
(I) Bailey, Wm. A., Jr., Bannerot, R. -4., Fetterly, L. C., and Smith, A. G.. IND. ENG. C H E M . . 2125 ~ ~ . (1951). (2) Clark, F. hl. (to General Electric Co.), 'TJ. S. Patent 2,088,406 (July 27, 1947). (3) Ipatieff, V. (to Universal Oil Products Co.), Ibid., 2,039,799 (May 5, 1936). (4) Kattwinkel. R., Brennstof-Chene., 8, 22. 353 (1927). [ASTM, Emergency Standard (ESb45, No. 873.1 (5) Manning, E., Jr (to Shell 'Development Co.), U. S. Patent 2,508,038 (May 16, 1950). (6) RIorrell, J. C. (to Universal Oil Products Co.), Ibid., 1,853,921 (April 12, 1932). (7) Ibid., 2,029,785 (Feb. 4, 1936). (8) Rossini, F. D., and associates, "Selected Values of Properties of Hydrocarbons," Supt. Documents, U. S. Govt. Printing Office, Washington 25, D. C., 1947. (9) Shepard, A. F., Henne, A. L., and Midgley, T., J. Am. Chem. SOC., 53. 1948 (1931). I
"
.
I
ior review October 12, 19j3, ACCEPTED J u l y 10, 1954. presented at Southwest Regional R.Ieeting, ACS, Selv Olleans, La., December igp,.
