INDUSTRIAL AND ENGINEERING CHEMISTRY
July, 1946
761
SUMMARY
dichloride, (6) benzene, (7) ethyl ether, and (8) petroleum ether. The last and least efficient solvent was approximately 75% as effective as ethanol-benzene. Ethyl ether and the low-boiling petroleum ether are laboratory wlvents and not generally applicable to commercial extraction processes; of the remaining commercially feasible solvents, the water-miscible type appears to be most effective for removal of extractives. The solvents exhibited varying selective extraction action for the various extraneous components in the wood. Th,us, the mixed solvent ethanol-benzene was the most effective solvent for removing the water- and ether-insoluble fraction. The watersoluble component was most efficiently removed with methanol. Ethanol-benzene and ethylene dichloride were about equal in their ability to remove resin acids; acetone was most efficient in extracting free fatty acids. The amounts of volatile removed by the various solvents, in the main, were comparable. Benzene extracted the largest quanti tg of esters, and the unsaponifiable fraction was most effectively removed by ethanol and by ethyl ether. The exact nature of the various components'of ponderosa pine extractives will have a bearing on their commercial valuc, and this identification is under investigation by this laboratory.
Since initial investigations by this laboratory have indicated that it is possible to remove extractives from green lumber by solvent extraction, the solvent choice would probably be governed, among other things, by its extractive action for the extraneous components in the lumber. This preliminary investigation indicated that solvents may vary materially in their ability to remove extractives from ponderosa pine sawdust. The order of extractive action of the solvents investigated thus far is: (1) ethanolbenzene, (2) ethanol, (3) methanol, (4) acetone, ( 5 ) ethylene
(1) Anderson, IsD.. FSG.CHEY..36, 662 (1944). ( 2 ) Ibid., 38, 450 (1946). (3) Dore,Ibid., 11, 556 (1919). (4) Hihbert and Phillips, Can. J . Research, 4 , 1-34 (1931). ( 5 ) Kurth, ISD. E s o . CHEM.,25, 192 (1933). ( G ) I t ~ i d . ISD. , ENG.CHEM.,AN.LL.E D . , 11, 203 (1939). (7) Kurth and Sherrard, I N D .E s c . CHEM.,23, 1156 (1931). (8) Wise, "Wood Chemistry", ACS .\lonograph 97, pp. 563-4, 4 e w York, Reinhold Pub. Corp., 1914.
rially from that in the heartwood. I n sapwood the percentage of resin acids was relatively low, 22-30%, and the fatty acid ester content was correspondingly high, 58-71%. On the other hand, in the heartwood th'e reverse was true. The resin acids predominated (64-68y0) and fatty acids, largely as esters, wwe present from 17 to 21%. The ethyl ether-solubles isolated from ponderosa pine sapwood also contain a predominance of fatty acids, mostly, however, in the form of free acids (42y0) and of esters (12%) ; the resin acid content was correspondingly lower, amounting t o about 27%. In ponderdsa pine heartwood the resin acids predominated to the extent of about 59%, free fatty acids approximately 11%, and fatty acid esters 10%. Hibbert and Phillips (4)isolated and analyzed the ethanolbenzene extract from mixed sapwood and heartwood of jack pine, and found that resin acids predominated, averaging about 13%; free fatty acids amounted to about 25%, and fatty acids as glycerides, about 6%. The ethanol-benzene extract from whole ponderosa pine wood likewise follows this same' percentage composition trend of resin acids, free fatty acids, and esters.
LITERATURE CITED
Dealkylation of' Dialkvlbenzenes J
J
USE OF SUPERATMOSPHERIC PRESSURE AND ALUMINA-SILICA CATALYST IN THE PRESENCE OF BENZENE
T
HE dealkylation of polyalkylWALTER 31. KUTZ .4KD B. B. CORSON and this method of dealkylation, benzenes has been studied for consisting in the transfer of alkyl Mellon Institute, Pittsburgh, Pa. many ycars, but practically all groups to benzene molecules, has of the work has hccn done with been utilized by numerous inaluminum chloride as catalyst (9). I n the absence of benvestigators (1, 2, 3, 4, 6, 7 , 8, 12). The dealkylation of zene the theoretical yield of monoalkylbenzene is one mole per xylene and other polyalkylbenzeIles received considerable attenmole of polyalkylbenzene, but in the presence of sufficient bention during World War I because of the unsatisfied demand for zene it is theoretically possible to obtain as many moles of monotoluene. Interest in the dealkylation of polyalkylbenzenes has alkylbenzene as there are alkyl groups in the original polyalkylagain revived because of the recent large scale production of benzene : ethylbenzene and isopropylbenzene and the desirabilitv of dealkylating by-product diethylbenzene and diisopropylbenzene. CsHa - "11, (a - 1) CsHb +nCbHjR Because of the recent Dublication of a .DaDer I bv " Hansford. Radziewanowski (10) was the first to recognize the importance Myers, and Sachanen (6) on the dealkylation of polyalkylbenof benzene as an acccptor of alkyl groups from polyalkylbcnzenes, zencs over alumina-silica catalyst a t ordinary pressure and rela-
+
Diethylbenzene was dealkylated under pressure over An alumina-silica catalyst in the presence of a large excess of benzene to produce monoethylbenzene. Operating at 400" c., 500 pounds per square inch, and 2 liquid hourly space velocity on a mixture of 1 mole of diethylbenzene and 10 moles of benzene, the yield per pass was 1 mole of monoethylbenzene, and the ultimate yield was 1.8 moles of monoethylbenzene as compared with the theoretical ultimate yield of 2 moles of monoethylbenzene. Com-
pared with diethylbenzene, xylene w a s more difficult to
dealkylate, whereas diisopropylbenzene plus 10 moles of benzene gave 1.6 moles of nionoisopropylbenzene per pass. .4 study was made of the effects of the operating variables of time, temperature, pressure, and amount of benzene. Operation at superatmospheric pressure w-as found to be preferable to operation at ordinary pressure with regard to conversion per pass, ultimate j-ield, and catalyst life.
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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. 7
per pass and also considerably lengthened the life cycle of the catalyst because of the washing effect of the dense hydrocarbon phase. Even with 36 hours of continuous operation, the average conversion per pass of diethylbenzene to monoethylbenzene was 42% of the theoretical, and the average ultimate yield over the 36-hour period was 92%; the highest yields reported by Hansford, Myers, and Sachinen (6) were 29% per pass and 63% ultimate, with a much shorter catalyst life between regenerations. A patent by Sachanen and Hansford (11) describes dealkylation under superatmospheric pressure, but the chemical composition of the feed stock was not specified (boiling range, 150-250" C.) and the conditions were so'drastic (482" C. and 40 minutes of contact time) that the product gave little information as' to the nature of the reaction. EXPERIMENTAL DETAILS
Figure 1. Dealkylation Plant
tively high temperatures, data are presented here which were obtained several years ago on the same reaction under completely different conditions. The conditions used by the previous investigators were 15 pounds per square inch, 454-538' C., and 0 to 3 moles of benzene per mole of dialkylbenzene. Under these thermally drastic conditions the ultimate yield of monoalkylbenzene was low as a result of destructive cracking, and it was impossible to employ a sufficiently long contact time to obtain a high conversion per pass. No definite information was given on the catalyst life for the dealkylation of diethylbenzene, but i t was implied that the optimum time on-stream was less than 2 hours, and that it was preferable to operate with 15-minute life cycles. The standard length of our experiments was 12 hours. Our much less drastic thermal conditions of 400" C. and a large excess of benzene (10-15 moles per mole of dialkylbenzene) repressed destructive cracking reactions and thereby favored the ultimate yield. Superatmospheric pressure made it possible to employ a sufficiently long contact time to obtain high conversion
MATERIALS.The benzene was nitration grade. The xylene contained about 65% of m-xylene and 35'% of p-xylene. The diethylbenzene and diisopropylbenzene were prepared. by the alkylation of benzene by ethylene and propylene, respectively. The amounts of the various isomers were not determined. The dialkylbenzenes were distilled through a fifteen-plate Fenske column with a reflux ratio of 10 to 1 to give products with the following constants: B.P.,
c.
(760 hIm.)
Xylene Diethjlbenrene Diisopropylbenzene
138-9 180-3 206-8
n go
1.4963 1 4938 1 4888
0 863 0.866 0 856
CATALYST.The 90% silica-107, alumina catalyst was made by dispersing freshly prepared, washed silica gel in dilute aqueous aluminum chloride and adding aqueous ammonia with stirring. The intimate mixture of silica and alumina gels was washed five times with distilled water, and the filter cake was slurried each time in the mater wash. The washed cake was dried a t 100" C., crushed, screened to 20-30 mesh, and pelleted in the form of 0.32
TABLE 1. STUDYOF l
r
~ IN THE ~ 12-HoU~ ~ ~DEALKYLATION ~ ~ ~O F DIETHYLBENZENE s E B Yield!
Charge'
Conditions
T
C. L.R.S.V.b
400 400 400
2 2 2
400 400 400 400
2 2 2 2
Product', Grams
Mole Lb./sq. in. ratio gage B / D E B B , g . D E B , & EB DEB >DEB A . Effect of Benzene Concentration 21 289 337 538 5 1562 500 14 247 137 303 10 1769 500 11 229 66 217 15 1895 500 500 500 500 500
10 10 10 10
c on
Catalyst, Gram
% of Theoretical Per
Ulti-
pass
mate
1.11 0.59 1.52
33.9 51.6 66.7
91 94 96
B . Regeneration and Catalyst Life 247 137 1769 303 265 125 305 1777 181 179 1765 303 151 187 294 1714
14 15 15 14
0.59
.... ....
1.97
51.6 55.0 37.8 32.5
94 93 92 89
Effect of Temperature 25 285 306 1779 118 212 1733 297 247 137 303 1769 265 96 1718 295
11 13 14 15
0.02 0.16 0 59 1.97
5.2 25.2 51.6 56.8
75 87 94 84
10 10 13 13
0.78 0.84 0.59 0.18 0.68 0.52 0.59 0.61
26 1 23.7 20.2 23.0 3.6 28.3 51.6 45.1
89 91 87 88 60 90 94 91
1.01 0 59 0.74
64.2 51.6 51.0
94 94 92
0 88
56 3
90
C.
2 2 2 2
300 350 400 450
500 500 500 500
10
10 10 10
D. Effect of Pressure 350 350 350 350 400 400 400 400
1 1 2 2 2 2 2 2
500 500 900 15 250 500 900
5 5 10 10 10 10 10 10
703 789 1733 1801 1750 1810 1769 1793
400 400 400
1 2 3
500 500
10 10 10
E . Effect of Space Velocity 151 48 867 149 247 137 1769 303 367 202 2637 453
2
500
2.50
500
6
14 14 14
7
14
10
F. Recycling of Recovered Diethylbensene 400 a
b
-
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
luly, 1946
10
1748
300
268
112
18
through a semimicro column (6). Very little material boiled ,between the distillation plateaus, and therefore no intermediate fractions were taken; for example, the cut point between benzene and monoethylbenzene was 107" C. and that between monoethylbenzene and diethylbenzene n-as 158" C. The distillation cuts were identified by boiling point, refractive index, and density. At the end of each experiment the catalyst was flushed (at the temperature of the experiment) with nitrogen to remove adsorbed hydrocarbon, cooled, and ground to a fine powder. The carbon on the used catalyst was determined by burning a 5-gram sample in a dry air-oxygen stream (1 volume of air, 2 volumes of oxygen) a t 650700" C., and collecting the carbon dioxide in an Ascante tube which was preceded by a drying tube. In one ex-
B beniene, EB = monoethjlbenzene, D E B = diethylbenzene. L.H.S.V (liqud hourly space velocity) 18 volume of liqrud fed per hour through an equal volume of oatalyat.
inch) pills with 4% of aluminum stearate x 0 32 cm. X ae die lubricant. The pills were heated in a stream of air a t 600' C. to remove carbon before being used as catalyst. The silica gel used was precipitated from dilute aqueous water glass by hydrochloric acid and washed six times with distilled water (filtering by suction after each wash and slurrying the filter cake in each subsequent wash) until the sodium content of the gel was lowered to 0.1%. The final silica gel cake contained about 12% of silicon dioxide. APPARATUSAND PROCEDURE.Figures 1 and 2 show the actual setup and the flow diagram of the process. The furnace consi3ted of a vertical 10 X 61 cm. (4 X 24 inch) insulated stainless steel block, electrically heated and thermostatically controlled within *3' C. of the desired temperature, and containing a longitudinal hole (2.5 cm. or 1 inch in diameter) for the catalyst tube and a parallel hole (4.8mm. or a/,a inch in diameter) for the thermocouple. The catalyst tube was of stainless steel, 2.06 cm. i.d. and 94 cm. long ( l a / l ~ and 37 inches). The 100-cc. (80gram) catalyst bed (about 30 cm. or 12 inches long) was held in place in the middle of the heated zone by plugs of steel wool, and the upper volume of the catalyst tube was packed with broken quartz for preheating. The liquid feed (benzene and dialkylbenzene) was pumped into the top of the catalyst tube by a Hills-McCanna type SA pressure pump. Nitrogen was used to maintain the pressure in the piant. The catalyzate (liquid and gas) w m taken off through a high-pressure needle valve which was followed by a water-cooled condenser. The liquid product waa stabilized, and the liberated gas was measured and analyzed. The gas was mainly nitrogen which was carried over dissolved in the liquid. The gas was analyzed by absorption and combustion, and the weight of the gas was approximated from these data. The stabilized liquid product was heated under a fifteen-plate Fenske rolumn to remove benzene, and the concentrate was distilled
periment (Table IB) where the regenerated catalyst was needed for other runs, the total catalyst (in pill form) was burned at 600' C. in air for 3 hours, and the carbon diolcide W M collected. CALCULATION O F RESULTS
yIsLD The percentage yields were calculated on the assumption that one mole of dialkylbenzene can produce t ~ o moles of monoakylbenzene~ CaHcRi
+ CsH4 +2dHsR
These yields are not to be confused with the "weight yields" reported by Hansford, Myers, and Sachanen (6) which regard, for example, a yield of 134 grams (1.264 moles) of monoethylbenzene from 134 grams (1 mole) of diethylbenaene as a 100% yield; it really corresponds to only 63.2% of the amount theoretically possible. Weight yields also vary in significance as a function of the size of the alkyl group. For example, a 100% weight yield of monoalkylbenzene corresponds to 57.6%, 63.2%, or 67.5% of the theoretical yield from xylene, diethylbenzene, or diisopropylbenzene, respectively. CONVEWIONPER PASSv3. ULTIMATEYIELD. When the conversion per pass was low, the ultimate yield waa also low. The explanation of this relationship is probably the comparatively greater loss of product by adsorption in the low-conversion experiments and the condensation reactions; the latter always take place, even when there is little dealkylation, to form high boiling, nonrecyclible hydrocarbons from the product or from the starting materials. Both of these effects would diminish the ultimate yield more for the low conversion than for the high conversion runs. DISCUSSION OF RESULTS
NEGLIGIBLE GAS AND CARBONPBODUCTION. Gas was collected and analyzed in all runs, but it was always less than 1
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 38, No. 7
from the first pa.s were the same as those of the original diethylbenzene (500 lb./sq. in., 2 l.h.s.v., mole ratio CsHs/C&& = 10; 12-hr. runs) (Table IF). The recovered diethylYield of CsHaR, bt~nzeriewas dealkylated on the second YC of Theopass to the same extent as on the first retical C on T ~ ~ Charge. ~ , ,G r a m Produrt. G r a m s Catalyst, Per Utipass; this showed that there !vas no CaH4Rz C. CsHs CaH,Rz C6HaR CsHdRz >CsH
