V O L U M E 2 7 , NO. 2, F E B R U A R Y 1 9 5 5 4CKVOK LEDGXIEhT
The authors n ish to ac-knovledge the contribution of Louip Mikkelsen and Dorothy Richardson in supplying ~. . - the infrared part of the mass spectral data reported in this paper. LITERATURE CITED
Testing Materials, Philadelphia, Comniittee D-2 on Petroleuni Products and Lubricants, “Standards 011 Petroleum Products and Lubrirants,” pp. 392-400, D 936-5lT, Sovem-
-4111. Sor.
her 1953.
Birch, S. F., and 31c;illan, D. T., J . Inst. PelroZeunL, 37, 443-56 (1951).
Coleman, H. J., hdams, S . G., Eccleston, B. H., Hopkins, R. L., .\likkelsen, L., Rall, H. T., Richardson, D., Thompson, C . J., and Smith, H. 31.,Division of Petroleum Chemistry, - 4 ~CHEM. . SOC., Preprints, General Papers. p. 93, September 1953.
Day, D. T., Industrial and Technical Petroleum Reciew, Supplement, I O (hug. 2 5 , 1900). Day, D. T., Proc. -4117. Phil.Soc., 36, 112-15 (1S9i). Dineen, C;. L-., Bailey, (1. IT.,Smith, J. R . , and Ball, J. S.,- 1 s . 4 ~ . CHEM.,19,992-8 (1947). Dineen, 0. U., Thompson, C. J., Smith, J. R., and Ball, J. S., Ibid., 22,871-6 (1950).
Haresnape, D., Fidler, F. A , , and Lowry, R. -4.. Ind. Eng. Cheni., 41,2691-7 (1949).
Hastings. S.H., .4~.41.. C H m f . , 25, 420-2 (1953). Hastings, S. H., Johnson, B. H., and Lunipkin, H. E., unpublished manuscript. Hibbard, R. R., Ind. Eng. C h e m . ,41, 197-200 (1949).
185 Hopkins, Ii. L., Ibid., 43, 145GS (1951). Hopkins, R. L., and Smith, H. 31.,-4s.4~. CHEZI., 26,206-7 (1954). Jones, .4. L., Petroleum Processing, 6,132-5 (1951). Jones, .4. L., and Foreman, R. W., Ind. Eng. Chern., 44, 2249-53 (1952).
Jones, -4.L., and JIilberger, E. C., Ihid.. 45,2689-96 (1953). Karr, C., Jr., Weatherford, \Ir. D., Jr., and Capell, R. G., Ax.4~.CHEM.,26, 252-6 (1954). Kramers, H., and Broeder, J. J., -4nal. Chiin. Acta, 2, 687-92 (1948).
Lawrence, 9. S. C . , and Barby, D.. Discussions Faraday Sac., SO. 7, 255-8 (1949).
Lipkin, 31. It., Hoffecker. W. .4.,Martin, C . C., and Ledley, It. E.. -4S.41..CHEM.,20, 1 3 0 4 (1948). Ludwig. C., Sitzber. A h d . Wiss. Wien, 20, 539 (1856). .\IcKinney, C. LI., and Hopkins, R. L., .IS.%L. CHEnf., 26, 146G5 (1954).
llair, B. J., J . Research .Yatl. Bur. Standards, 34, 435-51 (1945). JIair, B. J., and Foreiati, -2.F., Ihid., 32, 165-83 (1944). llair, B. J., Sweetman, -4.J., and Rossini, F. D., Ind. Eng. Cheiiz., 39, 1072-81 (1947).
llair, B. J., and White, J. D.. J . Research .\-&Z. Bur. Standards, 15, 51-62 (1935). Mukherjee, J. K.,and Indra. 31. K., Sature, 154, 734-5 (1944). Smit, W.M.,Discussions Faraday Soc., S o . 7,248-55 (1949). Wood. A. E., Sheely, Clyde, and Trusty, rl. W., Ind. Ene. Chzm., 18, 169-71 (1926). Youta, 31..4., and Perkins, P.P.. Ibid., 19, 1247-50 (1927). Zandona, 0. J., and Rippie, C. W.,Petroleum Processing, 6, 136-7 (1951). RECEIrEn
for review July 28, 1954.
Accepted December 27, 1954.
Application of Separation Techniques to a High- BoiIing Shale-0i I DistiIlate G. U. DINNEEN, J. R. SMITH’, R. A. VAN METER, C. S. ALLBRIGHT, and W.
R. ANTHONEY*
P e t r o k u m and O i / - S h a / e Experiment Station, Bureau o f M i n e s , Laramie, w y o .
JIodern separation techniques have been used to resohe a gas oil from Colorado shale oil into simpler fractions to facilitate studies of composition. The gas oil was a complex material containing about equal quantities of hjdrocarbon and nonhj drocarbon compounds. .Idsorption techniques w-ere the principal tools used, supplemented by vacuum distillation, thermal diffusion, and adduct formation. These techniques were selected to provide maximum resolution and recovery of material and to minimize decomposition. The gas oil was separated into nitrogen, aromatic, olefinic, and saturated concentrates. These were further separated into simpler fractions. Information presented in this paper should be applicable to composition studies in other fields.
M
O D E R S separation techniques have lieen used to resolve a gas oil from Colorado shale oil into simpler fractions to facilitate composition studies. Adsorption utilizing a variety of ndsorbents was the principal tool used, supplemented by vacuum distillation, thermal diffusion, and adduct formation. These techniques n-ere selected to give maximum resolution and recovery of material, and to minimize decomposition, eo the results could be more easily related to the original gas oil. Crude shale oil obtained by most retorting processes from Colorado shale contains only a small quantity of material boiling in the
’ Present address, Stanford Research Institute, Stanford, Callf.
Present address, Tide Water -4ssociated Oil Co.. Associated, Calif.
gasoline range. Accordingly, production of volatile fuels utilizes the higher boiling fractions as raw material, and therefore knomledge of their composition is important. The separation techniques discussed in this paper were investigated for use on a gasoil fraction having a boiling range of 625’ to llOOo F. It had been distilled from a crude shale oil produced from Colorado shale in an S-T-U retort a t Rifle, Colo. The gas oil contained about 1.8% nitrogen, 0.6% sulfur, and 1.0% oxygen. As the determination of individual compounds in such a nlixture is difficult, major emphasis was placed on the identification of types of compounds. This required separation of the material into more or less homogeneous fractions. -4sample of 16 liters of the gas oil n a s first separated, by an adsorption technique utilizing F l o r i d , into two concentrates, one containing most of the nitrogen compounds originally present in the distillate, and the other containing predominantly hydrocarbons. The hydrocarbon concentrate was then further separated into concentrates of aromatic, olefinic, and saturated compounds by a two-step process, employing silica gel as the adsorbent. The aromatics were first removed from the saturates and olefins. These latter compounds were then separated from each other, using a much higher adsorbent-sample ratio than wae used to remove the aromatics. Further separations on these primary concentrates were made by vaeuum distillation, thermal diffusion, adduct formation, or additional adsorption techniques. SEPAR4TION OF G.4S O I L
Resolution of the gas oil into reasonably simple fractions was effected by a number of consecutive separation steps. An out-
ANALYTICAL CHEMISTRY
1 86 line of the techniques employed and of the quantities of the major fractions obtained is given in Figure 1. As indicated in the figure, adsorption was the principal tool used, other techniques being applied after major separations had been accomplished. Adsorption. The gas oil was a romple.; material containing substantial quantities of both hydrocarbons and nonhydrocarbons, including several distinct classes of each of these groups. For such material it seemed desirable to make the primary separations by types of compounds rather than on molecular size or shape. Adsorption and estraction are the most promising techniques for separating classes of compounds. Adsorption was selected because it usually gives sharper separations and more nearly quantitative recoveries than extraction, although the procedure may not be so simple and rapid.
I
Figure 1.
Table I.
Conditions for Preparation of Nitrogen Concentrate
Total number of runs Adsorbent Sample
Pressure Eluant for hydrocarbons Desorbent for nitrogen concentrate
23 5 kg. of Florisil, 30-00 mesh 700 grams of gas oil dissolved in 2300 ml. of pentane 20 lb./sq. inch gage 15 liters of pentane 5 liters of acetone
of hydrocarbon concentrate. T o accomplish the separation successfully with this adsorbent-sample ratio required that the sample be dissolved in about 3 volumes of pentane before being introduced into the column. Presumably, at least this amount was necessary t o prevent solidification of some of the components cis they were separated. However, higher dilutions were avoided, as they undesirably delayed entrance of all the sample into the adsorbent. The column of adsorbent was washed with pentane to remove the saturate-olefin concentrate and then with acetone to remove the aromatic concentrate. The results obtained by the separation are shown in Table 111. Most of the sulfur and all of the nitrogen in the hydrocarbon concentrate were obtained in the
I
Outline of separation techniques used on gas oil
FLORISIL. Successful concentration of the nitrogen required the use of an adsorbent having a selective affinity for compounds containing this element. Experiments in small scale glass columns showed (8) that Florisil, a synthetic magnesium silicate manufactured by the Floridin Co., was a superior adsorbent for this purpose. Under the conditions of these esperiments the Florisil retained 0.65 gram of nitrogen per 100 grams of adsorbent, This was about 50% more than was retained by the best other adsorbents tested. An additional advantage of Florisil &-asthe rapid and more nearly quantitative recovery of the nitrogen compounds by desorption with acetone or methanol. Separation of 16 liters of gas oil on Florisil was accomplished in the equipment shown schematically in Figure 2. A summary of the operating conditions used is given in Table I. Both acetone and methanol were tried as desorbents for the nitrogen concentrate. The recoveries were equivalent, but acetone was selected because of its superior operational characteristics: more rapid passage through the column and consequent reduction in the time required for a run; less desorption of water from the Florisil, so stripping of the desorbent from the eluate was simplified; and easier removal of the last traces of desorbent from the concentrate. The data in Table I1 show the separation accomplished. The total recovery of nitrogen was 260.4 grams or about 90%, and all but 5.3 grams was in tho nitrogen concentrate. The separation had little effect on the sulfur content, as the nitrogen concentrate contained only slightly more sulfur than did the hydrocarbon concentrate. SILICAGEL. The hydrocarbon concentrate obtained by elution with pentane from Florisil was separated into an aromatic concentrate and a saturate-olefin concentrate, using silica gel ( 3 ) . The separations were made in tv-o sets of equipment similar to that shown in Figure 2, except that each column consisted of 54 feet of a/,-inch stainless steel tubing. A typical run for preparing the aromatic concentrate employed 4200 grams of 28- to 200-mesh silica gel and a 500-gram charge
3" 1.0
l-7
rw S.S. ADSORPTION
CONTROL VALVE STEAM I N L E T
-
--tcp -c-
COLD-WATER OUTLET
SOLVENT CONDENSER
UNIT
I
IIII VAPOR KNOCKDOWN
c-COLD-WATER
PRODUCT
Figure 2.
4
INLET
SOLVENT
Adsorption equipment for separation of gas-oil fraction
V O L U M E 27, NO. 2, F E B R U A R Y 1 9 5 5
187
aromatic material that accumulated on the adsorbent during the series of runs was recovered and added to the aromatic concentrate. Material Balance Nitrogen Sulfur Weight Weight Weight The recoveries and properties of the concenGrams % Grama Yo Grams trates prepared in this separation are shown in Charge 100.0 16.121 1.79 288.6 0.57 91.9 Table IV. The properties of the saturate and Nitrogen concentrate 41.8 6,732 3.79 255.1 0.68 45.8 0 . 06 5,3 0 . .51 45.3 Hydrocarbon concentrate 55,l 8,887 olefin concentrates are approximately those that Loss 3.1 502 28.2 0.8 would be expected of compounds of the types indicated by the names, an indication that the Table 111. Preparation of Aromatic Concentrate separation was reasonably effective in preparing Material Balance Sulfur Nitrogen ~the t,vpe of concentrate desired. Weight Weight Weight ALUNIXA.The aromatic concentrate contained % Grams % Grams % Grams hydrocarbons of a number of structural types as Charge 100.0 8501 0.51 43.4 0.06 5.1 Aromatic concentrate 32.5 2760 1.47 40.7 0.18 5.0 well as the sulfur and oxygen compounds in the Saturate-olefin concentrate 02.2 5288 0.03 1.6 0.00 ... hydrocarbon concentrate. It would be advantaLoss 5.3 447 1.1 0.1 geous to separate compounds containing different numbers of condensed aromatic rings. Alumina is a good adsorbent for this purpose ( 5 ) . However, the separation is improved if the charge stock has a relatively narroly range of molecular sizes; the aromatic concentrate wa8 therefore distilled a t low pressure into 10 distillate fractions arid a residue (see section on distillation). Each of the distillation fractions was developed on alumina in the 10-section column (1) shown in Figure 3. The operation is outlined in Table V. This technique gave arbitrary divisions, so fractions in adjacent sections of the column were often similar. GLASS FRIT Ultraviolet spectra on the various fractions indicated a fairly sharp separation between materials having different numbers of aroADSORBENT matic rings. 25 mm. 1.0. FLOREX. The nitrogen concentrate contained approximately BALL JOINT 3.8 weight % nitrogen, 60% of which could be titrated as basic material. Extraction with aqueous mineral acid did not give a satisfactory separation of this type of nitrogen as a yield of only about 6.5% extract was obtained. Additional adsorption techniques were investigated as a means of separating basic from nonhasic nitrogen, J Table 11.
Preparation of Hydrocarbon and Nitrogen Concentrates
~~
IT
Figure 3. Multiple-section adsorption column Table IV.
aromatic concentrate. Analytical work indicated that the saturate-olefin concentrate contained about 270 aromatics. Silica gel was used to separate the saturate-olefin concentrate into saturates and olefins. This separation could have been accomplished in the previous operation, but the use of successive steps reduced the time required by about 50%. The one-step process would require treatment of the total hydrocarbon concentrate a t an adsorbent-sample ratio somewhat greater than the 60 necessary for the saturate-olefin separation. However, by the two-step process the aromatics, amounting to about one third of the hydrocarbon concentrate, were removed at the low adsorbent-sample ratio of 8, so that only about two thirds of the concentrate needed to be processed a t a ratio of 60. Furthermore, the technique used for the saturate-olefin separation permitted several runs to be made through the same batch of adsorbent without cleaning and recharging the column. The separation of the saturates from the olefins required approximately 4200 grams of silica gel to 70 grams of sample per run. T h e diluted sample was placed on gel prewet with pentane, and eluted with approximately 8 liters of pentane to remove the saturates. The product receiver was changed, and the olefins were eluted p i t h about 10 liters of pentane. Thus, by elution with pentane all of the sample was removed from the column in two distinct fractions. The first was primarily saturated, whereas the second was largely olefinic. Several successive charges of sample were separated on the same batch of adsorbent. Because of the presence of a small amount of aromatic material in the charge, the process could not be continued indefinitely. ,Six runs were usually made on a single filling of adsorbent. The
Separation of Saturate-Olefin Concentrates Material Balance Weight % Grams
Charge Olefin concentrate Saturate concentrate Aromatics returned to aromatic concentrate Loss
100.0 43.2 53,9
4323 1910 2385
2.1 0.8
91 37
Refractive Index, n Eg
Molecular Weight
1.4378 1.4458 1.4292
357 359
Table V. Conditions for Alumina Separation of Aromatic Concentrate Adsorbent Quantity per section Sample Eluant Desorbent
H-41 alumina, 14-mesh 37 grams 15 ml. of fraction diluted to 100 ml. with pentane Pentane Acetone
I n the original preparation of the nitrogen concentrate, a Florisil-sample ratio of about 7 was used. An attempt to fractionate the nitrogen concentrate further on this adsorbent by increasing the ratio to 30 gave unsatisfactory results, as shown in Table VI. Rather prolonged elutions with pentane and benzene yielded only 15% of the nitrogen concentrate in the eluate, but 5% methanol in benzene desorbed three fourths of the sample. Consideration of these results suggested t h a t a less active adsorbent might be more suitable. Florex (an extruded fuller’s earth manufactured by the Floridin Co. For analytical use, a material prepared especially to avoid contamination with organic matter should be used.) was selected because previous experiments had shown that it would A a i n about 65% as much
ANALYTICAL CHEMISTRY
188
disadvantage of maintaining the sample a t the low boiling temperature of the solvents, particularly as fractions were to be removed at rather Eluant Yield frequent intervals. Sitrogen, Weight % Fraction Volume, Weight No. Composition ml. 70 Grams Total Basic The sample of nitrogen concentrate dissolved Charge 100 0 I; 0 3.79 2 10 in pentane was charged to the Florex-packed 1 Pentane 900 2.0 0 12 column and \vas dcveloped with pentane. IR 2 Benzene 830 13 .5 0 81 3 570 methanol general, fractions w r e cut a t intervals estimated 9570 benzene 1100 75.7 4 54 3 63 2 . 17 to yield 5 % of the vharge material per fraction. These estimates were based on measurement.s of ultraviolet absorbance at 3400 -4 made on material in the stripper flask. Changes in elution-solvent composition to nitrogen as Florisil. A Florex-sample ratio of 20 for use in sepaachieve graded increases in elution strength were dictated hy R rating 115 grams of the nitrogen concentrate was selected, based marked falling off of product yield with a particular solvent comon the results of small scale runs. position. These points usually could be judged by fading of color Fractionation of the nitrogen concentrate by gradual elution in the eluate stream. Twenty-three fractions were obtained. from Florex required a series of eluants of increasing eluting The basic and nonbasic nitrogen coiitrnts of each fraction are strengths. The pure compounds used in order of their eluting sho\vn in Figure 5 . strengths were: pentane, benzene, 1,2-dichloroethane, acetone, Although complete separation of these types of compounds and methanol. T o obtain the desired gradual elution, binary was not achieved, the early fractions were much richer in nonmixtures were also used-for example, pentane n-as followed by basic nitrogen, whereas the later fractions were rich in basic pentane-benzene mixtures, then benzene alone, and so on. Exnitrogen. This distribution of types of nitrogen is shown in periments showed that in the Florex-gas oil system this technique another wa>- in Figure 6. The recovrry of nonbasic nitrogen gave satisfactory results with mixtures of pentane and benzene was a p p r o h i a t e l y equal to the recovery of material for about and of benzene and 1,Bdichloroethane. Less satisfactory rethe first 30yo,but the recovery of basic nitrogen over this range sults were obtained with mixtures containing acetone or methanol, was verv low. Thereafter, the effect of the higher basic nitrogen as these compounds tended to desorb rather than elute the sample. content of the fractions was evident, and ultimate recovery of Several olefins were investigated for use as eluants between penthis type of nitrogen slightly exceeded that of the nonbasic. tane and benzene. Mixtures of the latter compounds were supeF h t i o n solvent compositions are also shown in Figure 5. S o rior, largely because of the much greater eaPe of removing them clear-cut correlation between solvent and fraction compositions from the eluate fractions. \vas evident. Distillation. The separations described previously could be applied satisfactorily to fractions of wide boiling range because classes of compounds having distinctly different properties were involved. The concentrates obtained were still complex, so further separations were required before the ultimate aim of determining the composition of the material could be achieved. However, differences in properties on which separations within classee must hc I)a.ed may be small and are often partially nullified by Table VI.
Fractionation of Sitrogen Concentrate by .4dsorption on Florisil
I
I
I
I
I
f l l l T E 0 CLASS P L A T 1
Figure 4.
..idsorption column w-ith solvent-recj-cle sl-stem
I n the separation of 115 grams of nitrogen concentrate, 2300 grams of 30- to 60-mesh Florex was used. The glass adsorption column was 55 mm. in internal diameter and 1.7 meters long. Elution of the individual fractions required amounts of solvent ranging from 20 to 130 liters. Owing to the large volumes of solvents, equipment shown schematically in Figure 4 was constructed to provide continuous stripping and recirculation of the solvent, through a siphon metering device in order t o measure the volume. A heated flask was selected as the stripping unit because it was thought operational advantages outweighed the
-
1 I
iwoLumLc *c*l'ml ia IWWT.UC
00 NITROGZN. WT. .4
Figure .5.
Distribution of nitrogen in fraations from nitrogen concentrate
V O L U M E 27, NO. 2, F E B R U A R Y 1 9 5 5
189 may be utilized in t\Fo ways-resolution of types of compounds or isolation of individual compounds. The wide range of reagents and conditions available makes this a versatile technique, which is applicable to various types of hydrocarbons as well as to nonhydrocarbon materials. However, in most instances the results are better if the samples are not too complex.
4
1
- 0:95 - 0.94 u' & N
Oo
10
Figure 6.
20
30
w 50 SO M A T E R I A L R E C O V E R Y . WT %
ro
no
90
>--
loa
k
- 0:93 2 0 w
Comparison of material and nitrogen recoveries
-0.92 ~nolecular \\eight effwts. For example, increased number of condensed i,ings in nromatic>a tends to inweave adsorhahilit>-. but greater niolerular ,aim tc>ndsto derrease it. Therefore, distillation to malie a molec.iiIar \\.right scparation is necessary :it some stage of the woi,l; on all of thr, coricentriitrs. In the boiling range of the gas oil w r y low pi urw are requirrd for this operation to minimize decompositioi The two distillntion techniques used :ire desri,il)rd for thr aromatic. c'oiicentrate. Fractious for the :tluniirla scparation discussed under the section on adsorption were prepared by distilling about 300 ml. of the aromatic concentrate into 10 frartions and a residue. The distillation was condurted a t a n ahsolute pressure of 0.20 Z!C 0.05 mm. of mercury. r-apor temperatures a t this pressure ranged from 130" to 205" C. Thr equipment consisted of a flask surmoriiited t>y a concentric-tube column with a Claissen-type head. Column dimensions were: length, 20 em.; outside diameter, 30 nini.; and annular spare: :3.5 mm. .%bout 85% of the charge %-a*obtained as distillatcl. The other distillation utilizrd a centrifugal molecular still having a 5-inch rotor.. IXstillation of a 500-ml. sample of the aromatic concentrate was niaclc a t 10-micron pressure. Rotor teniper.s.trires from TO" to O C. in 10" increments yielded 12 o v d i e a d cuts. On the t) of physical properties, these were rec.omt)ined into five cuts, which were refractionated in the same molecular still rising smaller rotor temperature increments to give a total of about, 83y0overhead in 30 fractions. The extent of fractionation obtained by this technique is indicated by the data shown in Figure i . Thermal Diffusion. ('ompounds that are similar except for iiiolerular configuration may often be separated by thermal diffusion. The technique has been applied so Ear only to the :tromatic and nitrogen coiiwntrates. The aromatic concentrate w:is charged to a 6-foot concentric-tube steel column having an :iIiriular space of 0.012 inch, 10 withdrawal ports, and a total capacity of 35 to 40 ml. ( 2 ) . Average operating temperatures were -17" C. on t,he hot w:ill and 25' C. on the cold wall. The run was continued for 100 hours. The refractive inder of the charge was 1.529 and of the top and bottom frartions W ; I ~ 1.510 and 1.540, respectively, indicating some separation of this wide hoiling range material. A similar separation of the nitrogen cuncentrate gave top and bottom fractions whose mass spectra showed large difl'erencex The mass spectrum of the top fraction was simpler than that of the hottom fraction and had as its predominant feature :I wries of groups of four peaks. I n each group a peak differed from the corresponding peak in the preceding group by a mass of 14, suggesting the presence of only a few homologous series. Complex Formation. The formation of chemical complexes
''5'[ i 1.500L
A
io
DISTILLATE, WT. %
.A
10b.90
Figure 7 . Properties of fractions from rnoleciilar distillation of aromatic concentrate
Urea forms a solid complex with compounds that contain a long unbranched hydrocarbon chain. I n general, the complex is more stable the greater the number of carbon atoms in the chain and the fewer atoms in branched or cyclic structures to which the chain is attached. The reaction has been used frpquently to estimate the extent of branching in molecules, although the results must be interpreted with caution. Each of the saturate and olefin concentrates was treated with urea ( 7 ) . The separations were not made on a scale large enough t o provide fractions for extensive evaluation but only as an estimate of chain branching. The predominantly straight-chain character of the molecules in each concentrate was indicated by the fact that approximately 85% of each formed an adduct with urea. Confirmation of the straight-chain character of the adducted compounds was obtained from infrared spectra, Fvhich showed the presence of about, two methyl groups per molecule. Several reagents, such as 2,4,i-trinitrofluorenone and picric acid, react n-ith some aromatic compounds to give solid products. Several fractions from the alumina separation and from the molecular distillation were treated with 2,4,7-trinitrofluorenone (6). The fractions selected were those that ultraviolet spectra indirated to be richest in condensed-ring aromatics. Complexes were obtained on only a few of the fractions. Spectra indicated that material regenerated from the complex was richer in condensedring components than the original fraction but still contained a number of individual compounds. This was the case even on two fractions from which complexes with sharp melting point,s were obtained. RESULTS OF SEPARATIONS
The separations discussed in this paper were made preparatorg to identifying the types of compounds in the gas oil. Although the concentrates are still complex, some information concerning the gas oil can be obtained from them. The percentage of each roncentrate in the gas oil, calculated on a no-loss basis, is shown
ANALYTICAL CHEMISTRY
190 Table VII.
Concentrates Prepared from Gas-Oil Fraction Gas Oil, Wt. %
Nitrogen concentrate Aromatic concentrate Olefin concentrate Saturate concentrate
43 21 16
20
in Table VII. As the aromatic concentrate contains some sulfur and oxygen compounds, it can be seen that nonhydrocarbon compounds make up nearly half of the gas oil. Determinations on the nitrogen concentrate yielded the following data: nitrogen, 3.7995; oxygen, 2.55%; and molecular weight, 290. Calculation from these data indicates that many of the molecules in this concentrate must contain more than one atom other than carbon and hydrogen. The three classes of hydrocarbons are present in about equal amounts. From examination of the aromatic concentrate it appears that this material contains about equal quantities of one-, two-, and three-ring aromatic compounds. The saturate and olefin concentrates are predominantly straightchain materials. SUMMARY
A series of separation techniques, outlined in Figure 1, has been applied to a gas-oil distillate from shale oil. The techniques used were adsorption employing several different absorbents, vacuum distillation, thermal diffusion, and complex formation. The gas oil was a complex mixture of saturated, olefinic, and aromatic hydrocarbons, as well as nitrogen-, oxygen-, and sulfur-containing compounds. Hydrocarbons made up approximately half of the gas oil, This material was separated into a number of fractions, each of which was less complex than the original gas oil. Concentrates obtained were those composed of nitrogen compounds
and aromatic, saturated, and olefinic hydrocarbons The roncentrates containing the saturated and olefinic materials were further subdivided into straight- and branched-chain compounds, and the aromatic concentrate was subdivided into fractions containing different numbers of condensed aromatic rings. For the nitrogen concentrate, srparation was made into fractions containing different relative percpntages of basic and nonhasic nitrogen. 4CKVOW LEDGMENT
This project was part of the SJ-nthetic Liquid Fuels Program of the Bureau of .\lines and was performed a t the Petroleum and Oil-Shale Experiment Station under the direction of H. P. Ruc, H. I f . Thorn(,, and J. S. Ball. The authors wish to thank 1finer.r.a Landers and Eli7abeth A. Pratt for analytical determinations in connection with this project. The work was done under a cooperative agreement between the University of Wyoming and the P.S. Department of the Interior, Bureau of hlines. REFERENCES
(1) Charlet, E. AI., Lanneau, K. P., and Johnson, F. B., A N . i L .
CHEM.,
26, 861 (1954). (2) Jones, A. L., and AIilberger, E. C., I n d . Eng. Chem., 45, 2689 (1953). (3) Lipkin, 11. R., Hoffecker, W. A., Martin, C. C., and Ledley, R.E., h h L . C H E X . , 20, 130 (1948). (4) Aloore, R. T., AIcCutchan, P., and Young, D. -4.,Ibid.,23, 1639 (1951). (5) O’Donnell, G., Ibid.,23,894 (1951). ( 6 ) Orchin, AI., and Woolfolk, E. 0.. J . A m . Chem. SOC.,68, 1727 (1946). (7) Schiessler, R. W., and Flitter, D., Ibid.,74, 1720 (1952). (8) Smith, J. R., Smith, C. R., Jr., and Dinneen, G. U., ANAL.CHEX, 22,867 (1950). RECEIVED for review July 26, 195%. Accepted December 20, 1954.
A Fifty-Stage Apparatus for Distillation at Very l o w Pressures BEVERIDGE J. M A I R , A R T H U R J. P I G N O C C O , snd FREDERICK D. R O S S l N l Carnegie
institute o f
Technology, Pittsburgh, Pa.
This report describes the design, assembly, operation, and testing of a 50-stage apparatus for distillation at very low pressures, in the range 0.01 to 0.1 mm. of mercury. Results are presented for two distillations, one performed on a commercial mixture of normal paraffins C18 to C22, and the other on a concentrate of normal paraffins C I toC26 ~ obtained from petroleum. Both distillations were carried out at a vapor pressure near 0.03 mm. of mercury, a throughput of 80 ml. (liquid) per hour, and a reflux ratio of 55 to 1, w-ith a total distilling time near 1900 hours. Continuous distillation for about 6 hours was required to obtain a steady state in this 50-stage apparatus.
I n the intervening years, multistage apparatus for distillation a t very low pressures have been described by Fawcett and MeCowen ( S ) , Wollner, Matchett, and Levine ( I S ) , Brewer and Madorsky ( 2 ) , Madorsky, Bradt, and Strauss (6),Madorsky ( 4 ) , Aldershoff, Booy, Langedijk, Philippi, and Waterman (I), and Melpolder, Washall, and iilexander (9). The API Research Project 6 began in 1951 active work on the development of a multistage apparatus for distillation a t very ~ Q Wpressures. This apparatus has been referred to in a preliminary way (11). The present report gives a detailed description of the design, assembly, operation, and testing of a 50-stage ap. paratus for distillation a t very low pressures. DESCRIPTION O F APPARATUS
I
S I T S work on fractionating hydrocarbons of higher molecular weight occurring in the heavy gas-oil and lubricant fractions of petroleum, the American Petroleum Institute Research Project 6 reported in 1929 and 1935 some simple apparatus for the distillation of such material a t low pressures ( 7 , I d ) . Similar apparatus was used in the distillation a t low pressures of the “water-white oil” and the “extract oil” portions of the lubricant fraction of petroleum in an investigation that was concluded in 1938 (6, 8). It was realized, however, that really effective separation by distillation a t very low pressures would require an apparatus involving many stages of separation.
Figure 1 shows the main part of the apparatus for distillation a t very low pressures, consisting of the pot, A , the two halves of the rectifying section, B, and the reflux regulator, C. The rectifying section consists of gently sloping glass tubes (at an angle of about 3.5” to the horizontal) with internal stainless steel fittings arranged in such a manner as to constitute a succession of plates. The two halves, each containing 25 plates, are connected in series to give a total rectifying section of 50 plates. Details of the pot and the lower portion of the rectifying section are shown in Figure 2.
