TENTH UNIT Removal of Chlorine and U u m Formers from Alkylates u r ( ~ ,700' I , > :iritl :I liquitl I d i'ate (space velocity) nf ~ I ~ c w I ~ c .of' ~: d pcx1 volumr~of catalyst per hour (contact more than about 0.001 weight 7' of chlorine i n tlie form of p i , thcx chlorine content of the gasoline was organic chlorides has a detrimental effect on the tc:trmthyl15;, :i rc~mov:rl of :ihout 97 to 989; of t h e lead susceptibility of aviation gasolines. I n tlie munufactui~~ of chlorine in the dkyla tc' feed. isobutane-ethylene alkylate by an aluminum chloride type of (nataThe I r m y gum valucu for tht: t\\-o alkylates used in the, inlyst, chlorine as organic chlorides may bc present t o the exteiil :rbout 30 :ind 211 mg. pc:r 100 cc., less than 57, of 0.107, by weight of the debutanized product. One purpose of h i n g prescint :is prci'ormctl gum iis indicated by d a h on s c v e r ~ l the present investigation was to find a simple method by whicli 4milar stocky. ITol101v;iy :inti Honnoll (fQ report that the addit.hese detrimental organic chlorides might be eliminated. tion of six organi r.ic1t.s (boiling up to n-amy1 chloride) to The dehydrohalogenation of aliphatic halides by contnctiug aviation gasolints ncyligihlo cffcct On the Army gum tests with solid catalysts has been studied by other investigators. tisnt of I t w thaii 0.1OC6 chlorine. Sincait Prey (4)mentions the use of natural cartiis such as bauxite m t l tlic present tillrylates cont:iin l e v t h a n thc O . l O ~ o chloriiie :ind kaolin, metallic oxides such :is alumina, thoria, and zirconia, over half thc chlorides prcrent boil ahovc n-amyl chloride, t h e and salts such as calcium and barium chlorides in thc vaporgum must be a1 trihut et1 t o components other than low-boiling phase dehydrochlorination of alkyl chlorides. Many yitents chlorides. It is not clear ,just what, thcse g u m formers arc:; they have been issued for the reniovrrl of chlorine in hydrocarbon oils mxy be higher-boiling org I * halidrs, 01' possihly they are cerby treatmcxnt with similar material in liquid or mixed-phase 1Liiri br:inched cyclic mat n t only i n small amounts. processes-for Fxample, those t o ( ar et al. (S), l l a r k s ('?), Cliavanne aiid eo-workers (9)haw sho\r.n t h a t t h c dimethylryeloShifflcr et a / . (9). ant1 Sto1cm:in ( 1 0 ) . .Isinger ( 1 ) p:issed dodecgl chloride ovvi' activated alumina :it PRESSURE about 482" F. to YOduce various isomeric FEED dodecylencs. Somc cyclization occurred T C. when cetyl chloridc v a s similarly treated. The present invcstigation \vas liniited to a detailed study of the treatment of chlorine-containing PREHEAT :ilkglatc in the vapor a phase over the bauxit'e catalyst Porocel. By passing an alkylate containing about 0.037% chlorine over Porocel in the vapor phase at "I HTS BATH I" EH STEEL TUBE about 70 pounds per s q u a r e i n c h gage Figure 1. Dehydrochlorination Unit (HTS = heat transfer salt; IPS = iron pipe size) EH = extra heavy)
THER investigators (6) have found that tlic
0
1
x i
t2 4
tl
242
PROCESS SYMPOSIUM Robert G. Haldeman and William GULF RESEARCH
B
The papers which follow (pades 242 to 267) appeared on the program of the Division of Industrial and Engineering Chemistry, for the 7945 Meeting-inPrint o f the American Chemical Society.
A. Pardee
DEVELOPMENT COMPANY, PITTSBURGH, PA.
pentancs and dimethylcyclohexanes are attacked slowly by oxygen. There may be related compounds which are more readily attacked. It should be noted that the ordinary gum-forming materials (6)-i.e., aliphatic and cyclic diolefins, mono- and diolefins attached to benzene rings-are probably absent from the charge stocks, as indicated from their history and by tests for unsaturation. The present investigation shows that the gum-forming constituents of the alkylates studied can be removed under conditions similar t o those for chlorine removal. However, the severity of this treatment is critical since, by overtreatment, the gumforming properties of the gasoline are increased. Thus, when isotherms are plotted for gum as a function of contact time, the curves pass through minima which are a function of temperature and, possibly, of initial chlorine content and type of organic chlorides present. APPARATUS AND MATERIALS
APPARATUS. Figure 1 is.a simple flow diagram of the apparatus used. A pressure of nitrogen in excess of the reactor pressure was maintained on the charge tank and on the calibrated sight glass. The flow rate was regulated by a '/s-inch needle valve, VI, the rate being determined by closing valve V , and measuring the rate of flow from the calibrated sight glass. The preheater and reactor were maintained a t reaction temperature by a commercial heat-transfer salt in a 16-inch bath, electrically heated (3000 watts) and thermally insulated. Uniformity of temperature within the salt bath was maintained by a
stirrer, and temperatures u ere measured by thermocouples conveniently placed within the bath, preheater tube, and reactor. After passing through the reactor tube, which had a capacity of about 150 cc. of catalyst, the vapors were condensed and cooled to about room temperature by a double pipe condenser with water as coolant. Constant pressure was maintained on the reactor by continuous withdrawal of condensate through the l/s-inch needle valve, V2. The product obtained during an onstream period (following a suitable prerun time) was causticwashed to remove any dissolved hydrogen chloride before chlorine determinations and other inspections were made. Fresh catalyst was charged to runs 1, 5, 9, and 10. Results from run 9 indicate that more frequent change of catalyst via5 unnecessary. ALKYLATE FEED. Two different batches of isobutane-ethylene alkylate, debutanized and caustic-washed, were used; the first (P5-28) for runs 1 through 8, the second (P2-43C) for runs 9 through 21. Table I gives inspection data on these materials; Figure 2 shows precision distillation and refractive index curves. Table I1 lists analyses estimated from these distillations. Fractions from the distillation of alkylate P2-43C were analyzed for chlorine. The results (Table 111) show that the light and heavy fractions contain the highest concentration of chlorine, but the greatest amount of chlorine is found in the '2,3-dimethylbutane fraction and the heavy ends. CATALYST.For this series of tests -10 +20 mesh Porocel (bauxite) was obtained from Attapulgus Clay Company. An analysis of this catalyst follows (corrected to 100% basis) : ~ 1 ~ 0 8
T h e products from the reaction of isobutane and ethylene, using an aluminum chloride catalyst, contain various organic chlorides. The removal of these chlorides is necessary because of their detrimental effect on the tetraethyllead susceptibility of the gasoline into which they are blended. The Army gum value of these alkylates is excessively high and may be reduced at the same time the chlorine is removed. Porocel was used in this investigation to remove organochlorides at 500-700" F., 70 pounds per square inch, and space velocities of 1 to 21 volumes of liquid feed per volume of 'catalyst per hour. Two alkylate feed stocks were used containing 0.0374 and 0.0794% b y weight chlorine, respectively. Conditions of treating to get a minimum Army gum value were found to be critical. Apparently, secondary reactions produce gum-forming compounds. A t 700°F. the curve for alkylate of higher chlorine content passes through a sharp minimum value at a contact time of about 3-7 seconds. A t lower temperatures and for the alkylate of lower initial chlorine content the minima are less pronounced. A catalyst life run at 700" F., 70 Ib. per rq. in., and space velocity of 21 vol./(vol.)(hr.)(contact time about 1.4 sec.) indicates there is no decrease in the rate of dehydrochlorination at throughputs up to about 150 grams feed per gram catalyst. Even at this high rate, about 81 % chlorine is removed from the feed.
243
FcOs
81.4 10.2 ,
Si02 Chlorine
8.3
0.1
CHLORINE AND GUM DETERMINATIONS
The organic chloride.determination, in brief, comprised burning the sample in a stream of carbon dioxide and oxygen, absorbing the hydrogen chloride formed in a sodium carbonate solution, and subsequently titrating the solution with silver nitrate to precipitate the chlorine as silver chloride using potassium chromate as indicator. This method is based on one developed by Sehulze, Wilson, and Buell (8). The method utilized in determining the tendency for gum formation is designated as Federal Standard Stock Catalog Method 335.1. The gasoline, charged to a glass container with a piece of steel of standard dimensions, is exposed in a bomb to oxygen pressure of 95-100 pounds per square inch for 5 hours. The temperature is maintained a t about 212' F. After this treatment the sample is filtered, evaporated in a weighed glass dish
244 '
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
Vol. 38. No. 3
i
N
0 N
2 3 h
" 137
2 LO
3
z
VOLUME RRCENT DISTILLED
Figure 2.
Distillation of Feed to Dehydrochlorination Unit
on a steani bath, hcated to 230" F. for 2 hours, cooled, arid weighed. The gain in weight of the dish is expressed as milligrams per 100 cc. of sample and is referred to a$ Army gum.
E
DEHYDROCHLORINATION
.-
C
+4
1
O
8
Runs 1-8 were studies of dehydrochlorination a b a function of temperature and contact time. Two sets of four runs each, a t rontact times varying from 4 to 18 seconds, were made a t about .500° and 700" F. and a t 70 pounds per square inch gape pressurr (Table I). The chlorine data are plotted in Figure 3 as a function of both contact time and liquid spare velocity. The efficiency of the process for chlorine removal a t about 5-second contact time and 500" F. is only about 667,; under the same conditions a t 704" F about 97% of the chlorine is removed. The latter treatment decreases the chlorine content from 0.0374 to about 0.001yo. DISTILLATION OF PRODUCT. The product from run 18 was distilled in a 35-plate analytical column. The distillation and refractive index curves are plotted in Figure 4, and the analysis is given in Table 11, where i t may be comparrd with similar distillationq of the two alkylate feed storks. CATALYST LIFE
m
N
Run 9 was made to determine the effect of throughput on the efficiency of the dehydrochlorination reaction. The data for this run, which was broken into nineteen periods, are given in Table I V and plotted in Figure 5. Conditions for this run were 700' F., 70 pounds per square inch gage pressure, 1.41-second contact time, and liquid space velocity of about 21 volumes of feed per volume catalyst per hour. Alkylate P2-43C containing 0.079% chlorine was used as feed. Under these conditions an efficiency of about 81% dehydrorhlorination was effected for a throughput of about 147 volumes
TABLE11. RESULTS OF (IN
Lights
2 3-Dimethylbutane dther hexanes Heptanes Octanes+
ANdLYTICAL DISTILLATION
VOLUMEPERCENT) Feed P5-28 5.0 62.5 5.0 7.0 20.5
Feed P2-43c 5.5
61.0 5.9
5.8 21.8
Product Run 18 6.5
63.5 3.5 8.0 19.5
INDUSTRIAL AND ENGINEERING CHEMISTRY
March, 1946
245
of liquid feed per volume of catalyst with a chlorine removal of about 0.0945 gram per gram of catalyst. Not until a throughput of about 6 grams of feed per gram of catalyst was there any odor of hydrogen chloride in the product. Analysis of the spent catalyst from run 9 showed a chlorine content of about 1.4y0 as compared with about 0.1% in the fresh catalyst, equivalent to a n adsorption of about 0.013 gram of chlorine per gram of catalyst. It may be concluded that the catalyst a t first adsorbs all the hydrogen chloride; then as equilibrium is approached, hydrogen chloride begins to be evolved and finally comes off a t the rate produced. GUM FORMATION
I
L W
Data on gum formation as a function of temperature and contact time are shown for both batches of alkylate in Table I and are plotted in Figure 6. These two plots indicate that the inherent gum-forming properties of the treated alkylate are functions of reaction temperature, contact time, and possibly of chlorine content of product. Each curve shows a minimum except the two 500" F. curves, which perhaps would exhibit the same behavior if data were available for longer contact times. The higher the temperature, the higher the initial rate of removal of gum-forming materials. Likewise, the minima are reached at shorter contact times as the temperature is increased. Beyond the minima, a t longer contact times, second-
Figure 4.
I
I
Figure 3.
8
7
@
8
TABLE111. CHLORINE ANALYSIS OF FRACTIONS FROM ANALYTICAL DISTILLATIOX OF ALKYLaTE FEEDP2-13C Boiling at 760 Range Mm.,
0-35 ' 35-57.5
0.627 0.6575
0
Isobutane Isopentane 2,3-dimethylbutane 2,3-Dimethylbutane Other hexanes Heptanes Octanes
57.5-60 60-75 75-99 QQ+
Total Charge
..........
.....
0.6662 55.65 54.56 0.6681 5.84 5.74 0.6889 5.85 5.93 0.728 21.76 23.31 . . . . . .
NO.
1
2 3
4 5
"
THROVWRIT, WECHT FCED/WEIWT
..." I
^
,
+
+
..........
. . . .
7W'F 7 0 LBSJSQ. IN. 1.41 SECONDS
-
0.0794 X (by mmt)
CATALYST
Catalyst Life Ted
sp. Gr.
Principal Hydrocarbons
cut
TEMPEPATm PWSSURE CONTACT TIME INITIAL CHLORINE
Figure 5.
4
Dehydrochlorination as a Function of Contact Time, Space Velocity, and Temperature
Distillation of Dehydrochlorination Product
11
5 CI SPACE VELOCITY, HR,-'
3
2
c.
.......
dz
Vol. % Wt. %
2.13 8.77
Chlorine, Wt. % Cut Charge
p r ~ ~ $ Chlorides
1.97 0.190 0.00374 Ethyl 8.49 0.048 0.00408 tert-Butyl 0.032 0.029 0.077 0.177 . . .
. . . . . . . . .
0.01746 0.00166 0.00457 0.04126 0.073 0.079
Butyl Butyl Amyl Hexyl
+
.... ....
ary reactions seem to produce gum-forming materials that apparently are not readily removed by the catalyst. The rates of these secondary reactions also increase rapidly with temperature. No proved explanation of the indicated phenomena can be given a t present. The dehydrochlorination rate increases rapidly with the temperature (Figure 3), as does the initial rate of gum removal, and there may be a correlation between these effects. The secondary effect of production of gum-forming materials which appear to be stable a t the existing conditions (ordinarily suitable for the removal of gum-forming materials) seems to indicate that such substances are different in chemical nature from those initially present. Perhaps these are alkylated naphthenes, produced by cyclization of some of the hydrocarbons following dehydrohalogenation. The existence of minima in the gum curves makes the selection of operating conditions to produce both low gum and low chlorine content critical. Fortunately, a t 700" F. the minimum for gum seems to occur a t about the optimum conditions for chlorine removal. Thus, for alkylate P5-28 (initial chlorine, 0.03770),the chlorine could be reduced
INDUSTRIAL AND ENGINEERING CHEMISTRY
246
Vol. 38, No. 3
to about O . O O l ~ o a t 700" F. and 3.3-mwnd coutact time; these are the conditions most favorable for the production of an alkylate of minimum gum-forming propertips. Chlorine analyses were not ohtaimd OII the products of runs 10-21 (alkylate charge P2-43C, initial chlorine 0.079%), so that comparison of optimum conditions for the two alkylates is not possible. However, it should he noted that thc minims in the Army gum isothcrms a t 700" F. occur a t substantially the same contact time for the two alkylates. The fact that the minimum gum value for alkyhte P2-43C is considerably higher than thc corresponding v d u c for alkylate 1'5-28 (14 and 0.2 mg. per 100 cc., respectively) the secondary reaction rate is drperident on initial properties of tlie charge-perhaps initial chlorine content and/or initial gum potential, since both properties were eonsiticrably higher in thct former alkylate. Further clarification of ihis situstion is rlwirZlbl?.
IT,
T.4RT.E
C(HI.ORISE
IS ~ ~ A T A I ~ Y SLIFW T 'rKS.1'
;iN.4LYSES
(IlTT 9) Period
Product, Grams
Chlorine Wt, % '
Katio". Feed/CataIyst
Ratiob, Ci/Catalyst
1 2 3
1.2 163 0.015 0.0008 I67 0.017 0.0022 3.4 6 4 33 1 0 014 0.0041 11.8 329 0.017 0,0076 ? 0,014 0.0121 18 8 657 0.026 0,0182 646 6 28 2 37.4 64'7 7 0.018 0.0241 44.3 8 358 0.015 0.0287 0.0333 51.7 0 0.015 646 10 0.013 0.0392 60.8 645 io.1 0.0452 11 64 I 0.015 79.2 0.0510 12 0.013 647 88.3 0 . ole 0.0571 647 13 97.8 0,014 0.0630 644 1-1 106.9 13 0,0689 0.013 645 1 1 6 . 1 16 0 ,0748 0 . 0 1 3 645 125.3 0,0807 0.017 642 17 134.5 0,0867 646 0.020 1s 146.8 19 0,0945 1080 0,018 a Expressed as w-eight of feed/weight of catalgst; feed contained 0.0794 weight chlorine. b Expressed as weight of chiorine removed/weight catalyst, and based on average chlorine content in product of 0.015 weight 5%.
ACKNOWLEDGMENT
The authors wish to express their appreciation to nic.mt)cirs of the Testing Laboratory and other members of the (Ihrmistry Division for helpful cooperation and suggcstions. LITERATURE CITED
CONTPCT TIME, SECONDS
Figure 6.
Effect of Contact Time on Gum
(1) Asinger, F., Be,., 75B, 1247-59 (1942). (2) Chavanne, G., and eo-workers, B7dI. soc. chim.H e l g . , 36, 206-21 (1927); 40, 611-25, 626-41, 673-88 (1931); 41, 209-16 (1932); J . Am. Chem. Soc., 52, 1609-22 (1930); Am. Petroleum Inst. Bull., 10,No. 55, 3 (1929). ( 3 ) Char, C., Kiihnel, P., and Geiser, N. (to Alien Property Custodian), U. S. Patent 2,328,707 (Sept. 7 , 1943). (4) Frey, F. E. (to Phillips Petroleum Co.), Ibid., 2,314,335 (Marrh 28, 1945). ( 5 ) Gruse, W. -A, and Stevens, D. li., "Chemical Technology of Petroleum", pp. 128-30, New York, McGraw-Hill Book Co., 1942. (6) Holloway, Clark, Jr., and Bonriell. W. S.,IXD.ENG.CHEM.,37, 1089 (1945). ( 7 ) Marks, E. (to The dtlantic liefining Co.). C. S.Patent 2,164,334 (July 4 , 1939). (8) Schulae, W ,-%,, Wildon, V . IT,, and Buell, A. K,, Oil Gas J . , 37, No. 45, 76 (1939). (9) Shiffler, IT., Holm, M., and Miller, >I. ( t o Standard Oil Co. of Calif.), U. S. Patent 1,869,781 (Aug. 2, 1932). (10) Ytokman, H . (to Shell Development Co.), I b i d . , 2,199,940 (May 7 , 1940).
