Ind. Eng. Chem. Prod. Res. Dev. 1982, 2 1 , 483-480
"C) with hydrogen or nitrogen as charge gas, and in the presence or absence of catalyst. An autoclave with a different mixing mechanism was also chosen, since the method of mixing might affect dissolution. The yields and solution NMR spectra of the products from these experiments have been reported elsewhere (Wilson et al., 1982). CP spectra of the residues have also been reported (Wilson et al., 1982) but fa values could not be calculated because of the highly aromatic nature of the residues. Aromaticities from CP/MASS spectra are reported in this work (Figure 4). The results show that f a values continue to increase with temperature increase above 425 "C. At 450 "C, fa of residues may reach as high as.0.89. The differences between fa's observed under nitrogen or hydrogen are probably too small to be interpreted with any confidence. Nevertheless, the trend to greater aromaticity with temperature is observed for all types of experiment, which shows that f a is dependent largely on temperature, rather than charge gas or the catalyst discussed here. Literature Cited Barron, P. F.; Stephen, J. F.; Wilson, M. A. Fuel 1981, 60, 547. Barron, P. F.; Wilson, M. A. Nature (London) 1981, 239, 275. Bartuska, V. J.; Maclel, G. E.; Shaefer, J.; Stejskal. E. 0. Fuel 1977, 56, 354. van der Hart, D. L.; Retcofsky, H. L. Fuel 1976, 55, 202. Hatcher, P. G.; Rowan, R.; Mattlngly, M. A. Org. Geochem. 198Oa, 2 , 77.
483
Hatcher, P. G.; van der Hart, D. L.; Earl, W. L. Org. Geochem. 1980b, 2 , 87. Maclel, G. E.; Bartuska, V. J.; Miknis, F. P. Fuel 1978, 57, 505. Maclel, G. E.; Bartuska, V. J.; Miknis, F. P. Fuel 1979a, 58, 155. Maciel, 0. E.; Bartuska, V. J.; Miknis, F. P. Fuel I979b, 58, 391. Miknis, F. P.; Maciei, G. E.; Bartuska, V. J. Org. Geochem. 1979, 2 , 169. Miknis, F. P.; Sullivan, M.; Bartuska, V. J.; Maclel, G. E. Org. Geochem. 1981.3, 19. Newman, R. H.; Tate, K. R.; Barron, P. F.; Wilson, M. A. J. Soil. Sci. 1980, 3 1 , 623. Resing, H. A.; Garroway, A. N.; Hazlett, R. N. Fuel 1978, 57, 450. Retcofsky, H. L.; van der Hart, D. L. Fuel 1978, 57, 421. Rottendorf. H.; Wilson, M. A. Fuel 1980, 59, 175. Vassailo, A. M.; Wilson, M. A. Fuel (to be submitted). Wilson, M. A.; Barron, P. F.; Goh, K. M. Geoderma 1981a, 26, 323. Wilson, M. A.; Pugmire, R. J.; Zilm, K. W.; Goh, K. M.; Heng, S.; Grant, D. M. Nature (London) 198lb, 294, 648. Wilson, M. A.; Rottendorf, H.; Vassaiio, A. M.; Collin, P. F.; Barron, P. F. Fuel 1982, 61, 321. Whitehurst, D. D.; Mitchell, T. 0.;Farcasiu, M. "Coal Liquefaction. The Chemistry and Technology of Thermal Processes"; Academic Press: New York, 1980; pp 166-167. Zilm, K. W.; Pugmlre, R. J.; Grant, D. M.; Wood, R. E.; Wiser, W. H. Fuel 1979, 56, 11. Zilm, K. W.; Pugmire, R. J.; Carter, S. R.; Allan, J.; Grant, D. M. Fuel 1981, 60, 717.
Received for review October 13, 1981 Revised manuscript received March 29, 1982 Accepted April 21, 1982 This work waa supported under US.Department of Energy Grant No. DE-AC02-78ER05006.MO03and from CSIRO funds.
Alkylbenzene Channel Adducts: Separation of Aromatic Isomers by Extractive Crystallization with Thiourea F. P. McCandless Department of Chemical Engineering, Montana State Universiv, Bozeman, Montana 59717
&Xylene and pseudocumene (1,2,4trimethylbenzene) have been found to form channel adducts with thiourea when they are present above a critical concentration which depends on composition. There is a synergism when both materials are present, increasing the amount of both compounds included in the adduct. The recovery of o-xylene and pseudocumene from mixtures with other C8 and Cgalkylbenzenes and their use as inductors for the separations of these mixtures was investigated. With mixtures of the CBaromatics, pseudocumene exhibits a selectivity of o-xylene >> p-xylene > m-xylene > ethylbenzene with the extent of separation varying between 0.07 and 0.38. When o-xylene Is used as the inductor for the Cg aromatics the selectivity is pseudocumene >> hemimillitene > ethyltoluenes > mesitylene with the extent of separation varying between 0.05 and 0.47.
Introduction and Background Thiourea channel adducts are a class of nonstoichiometric compounds in which guest molecules are trapped in a two-dimensional channel formed by thiourea molecules. The adduct crystals form only in the presence of suitable guest compounds. Thiourea will form stable channel adducts with highly branched paraffins as well as with cyclopentane and cyclohexane and their derivatives, with certain chloro compounds such as carbon tetrachloride, and with certain branched and cyclic aldehydes, alcohols, and ketones (Angla, 1949; Fetterly, 1964). Previous investigators have reported that benzenoid compounds normally do not form stable channel adducts with thiourea unless they have side groups with proper adducting structure (e.g., benzylcyclohexane, tert-butylbenzene, or other highly substituted structures such as 1,2,4,5-tetramethylbenzene(Fetterly, 1964; Fuller, 1972). 0196-432118211221-0483$0 1.2510
Previous work in this laboratory showed that xylenes and ethylbenzene are included in thiourea adducts provided a suitable inductor such as CCl, or cyclohexane is present and that a separation of the isomers is obtained because of a difference in the tendency for the different isomers to be included in the adduct. For CCl, and cyclohexane the tendency for adduct formation is ethylbenzene > o-xylene > p-xylene > m-xylene (McCandless et al., 1974). The use of 1,2,4-trichlorobenzene as the inductor results in a selectivity of o-xylene > p-xylene > m-xylene > ethylbenzene, while with 171,2-trichlorotrifluorethane the selectivity is o-xylene > p-xylene > ethylbenzene > m-xylene (Gorton, 1980). The trichlorobenzenes and CCl, were investigated as inductors for the separation of the C9 alkylbenzenes (McCandless, 1980). Carbon tetrachloride is selective for n-propylbenzene and indane while 1,2,4- and 172,3-trichlorobenzeneare selective for pseudocumene ( 172,4-trimethylbenzene) and hemi0 1982 American Chemical Society
484
Ind. Eng. Chem. Prod. Res. Dev., Vol. 21, No. 3, 1982
Table I. Approximate Composition and Normal Boiling Points of C, and C, Aromatics in Reformate approx compn, wt %"
normal bp,"Cb
C, aromatics
ethylbenzene p-xylene m-xylene o-xylene C, aromatics cumene (isopropylbenzene) n-propylbenzene m-ethyltoluene p-ethyltoluene mesitylene (1,3,5-trimethylbenzene) o-ethyltoluene pseudocumene (1,2,4-trimethylbenzene) hemimellitene (1,2,3-trimethylbenzene) indan
21.2 18.3 40.4 20.1
136.2 138.3 139.1 144.4
0.4 5.7 21.0 9.6 9.3
152.4 159.2 161.3 162.0 164.7
9.0 34.8
165.2 169.2
8.5
176,l
1.7
178.0
nLove and Pfennig (1951). bWeast (1976).
mellitene (1,2,3-trimethylbenzene).With these, mesitylene (1,3,5-trimethylbenzene)is virtually excluded from the adduct but the selectivity is for the 1,3,5 isomer when 1,3,5-trichlorobenzene is used although the capacity is rather low. More recently, Welling (1982) showed that pseudocumene alone forms a stable channel adduct with thiobea and investigated the crystal structure using X-ray crystallographic methods. In the work reported in this paper it is shown that both o-xylene and pseudocumene will form stable adducts with thiourea only when they are present above certain criticdl concentrations which depend on composition. As a result, in some cases they can be recovered from mixtures with other alkylbenzenes found in reformate without the use of an inductor and they will induce adduct formation with other aromatic isomers. The two compounds tend to complement one another; that is, the amount of aromatics included in the adduct is greater when both compounds are present. In certain cases spectacular separations can be obtained compared with distillation. Table I presents the approximate composition and normal boiling points of the C, and C, alkylbenzenes found in reformate to emphasize the challenging separation problem which they present. Experimental Section As in the previous studies, adducts were formed by mixing the feed solution (mixture of isomers to be separated plus o-xylene or pseudocumene) with a hot slurry of thiourea in methanol and then cooling, For these mixtures adduct formation was rather slow, requiring 2 to 3 h at -17 "C. This compares with only a few seconds or minutes required to establish equilibrium for other inductors such as CCll and cyclohexane. Inspection of the crystallized solids under a microscope to show long, needle-like crystals confirmed adduct formation. In all cases the mixture was kept at -17 OC for ht least 24 h before filtration. Below certain pseudocumene and o-xylene concentrations adducts would not form using the thiourea to methanol ratio used in this study. The adduct crystals were filtered from the methanol and non-adducted hydrocarbons (the residue) and were decomposed by steam stripping. The adducted hydrocarbons were then recovered by phase separation of the condensate. The residual hydrocarbons left in the solution were re-
covered from the filtrate in a similar manner. For all tests 12.5 g of thiourea and 24 mL of methanol were used. Typically 2.5 g of hydrocarbon mixture together with varying amounts of o-xylene or pseudocumene were used to form the adducts. Analysis was accomplished using a 7.6 m X 3.2 mm column packed with 5% diisodecylphthalate + 5% Bentone 34 on HP Chromosorb W in a thermal conductivity chromatograph at 100-120 "C. Ethylbenzene and the xylenes were obtained from Aldrieh Chemical Co. The ethyltoluenes were provided (as a mixture) from Dow Chemical Co. Results The extent of separation, [, defined by Rony (1968) is an excellent indicator of the quantitative amount of separation being obtained ih an equilibrium stage and, as in the previous studies, this index was used to characterize the separations obtained by the extractive crystallization process. For a component i in a mixture distributed between two regions j = 1, 2 as a result of a separation process, n is the number of moles of component i in region j . $he distribution ratio for component i is defined as KL = n12/nc1 (1) For the extractive crystallization process under consideration the two n,,'s refer to the hydrocarbons trapped in the channels of the adduct (region 1)and the hydrocarbons remaining in the residue (region 2). Assuming component 1is the species selectively trapped in the adduct, the extent of separation is given by
-
[=
1
1
1
[1..-GZ]
Here i = 2 refers to the rest of the hydtocarbons, excluding compound 1. Equation 1 for the extractive crystallization system becomes
Here (RIA) is the ratio of tde amount of hydrocarbons left in the residue to the amouht trapped in the adduct, and y1 and x1 are the mole fractions of the material selectively trapped in the adduct, in the adduct and residue, rkspectively. [ varies between 0 (no separation) and 1 (perfect separation). The separation factor analogous to relative volatility in distillation is given by (4)
This separation index was also used to compare the extractive crystallization process with distillation for some of the binary mixtures. Pseudocumene-C9 Alkylbenzenes. A feed with the approximate composition of the alkylbenzenes in Cg reformate was mixed with the thiourea-methanol slurry using different amounts of the Cgmixture. Adduct formed only when about 5 g or more of feed was mixed with the 12.5 g of thiourea. The results of these tests are shown in Table 11. All of the adduct compositions were essentially the same, containing about 78.5% pseudocumene, but the amount of feed recovered in the adduct varied from 4.5% (0.23 g) when 5 g of feed was used to 17.9% (1.61 g) when 9 g of feed was present. The amount of pseudocumene recovered
Ind. Eng. Chem. Prod. Res. Dev., Vol. 21, No. 3, 1982 485 Table 11. Separation of t h e C, Alkylbenzenes; 12.5 g of Thiourea, 25 mL of Methanol, Various Amounts of Feed compn, wt % residue component
feed
adducta
n-propylbenzene 4.2 0.2 m-ethyltoluene 24.3 3.7 p-ethyltoluene 12.6 3.3 10.2 trace mesitylene o-ethyltoluene 7.1 3.8 pseudocumene 33.7 78.5 hemimellitene 5.2 8.8 2.8 1.7 indan total C, recovered in adduct, % pseudocumene recovered in adduct, % SPC
gfeed 5
7.5
9
10
4.4 25.3 13.1 10.8 7.3 31.5 5.0 2.6 4.6 10.8 0.092
5.5 28.2 14.4 12.1 7.7 25.3 4.5 3.0 15.9 37.0 0.319
5.1 28.7 14.6 12.4 7.3 23.9 4.4 3.0 17.9 41.8 0.360
4.9 27.9 14.0 12.0 7 .I 25.9 4.6 3.0 14.8 34.5 0.297
aAll adduct compositions were essentially the same, b N o adduct formed using 4 g of feed or less. Table 111. Recovery of Pseudocumene from C, Alkylbenzenes; 12.5 g of Thiourea, 25 mL of Methanol. Pure Pseudocumene Added to 2.5 g of C, Mixture
pseudocumene added, g 0.5 0.75 1.0 1.5 2.5 4.0 6.0
10.0
pseudocumene recovered, residue adduct wt %
Table IV. Separation of the Trimethylbenzene Isomers; 12.5 g of Thiourea, 25 mL of Methanol, 2.5 g of Mesitylene-Hkmimellitene Mixture, 4 g of Pseudocumene wt % isomer recovcompn, wt % ered in feed residue adduct adduct
compn, wt % pseudocumene feed
44.8 no adduct formed 49.0 no adduct formed 52.7 46.7 88.9 58.6 44.7 90.0 66.9 45.4 92.5 74.5 53.6 94.8 80.4 75.1 96.6 86.7 83.3 96.9
0 0 23.9 44.7 63.0 64.6 44.3 28.3
tpc 0 0 0.207 0.397 0.57 1 0.542 0.354 0.221
in the adduct varied from 10.8 to 41.8% corresponding to an extent of separation for pseudocunhene of between 0.092 and 0.360. Adduct did not form without pseudocumene present in the Cg feed. In the previous work (McCandless, 1980), an inductor (CC14or 1,2,4-trichlorobenzene) was added to 2.5 g of the Cg alkylbenzene feed to induce adduct forlhation. To compiwe the previous work with the present study, various amounts of pure pseudocumene were added to the alkylbenzene feed. The results of these tests are shown in Table 111. Adduct did not form when less than 1.0 g of pseudocumene was added to 2.5 g of the Cg feed but above this amount recovery of the pseudocumene in the adduct ranged from 23.9 to 64.6% represfnting extents of separation from 0.207 to 0.571. However, significantly, the total amount of pseudocumene recovered in adduct was always less than the amount of pute material added to the C9alkylbenzene feed mixture. This can be attributed to a solubility effect. A similar study was made to investigatk the separation of the trimethylbenzene isomers, by adding various amopnts of pseudocumene to 2.5 g of a 30% mesitylene hemiinellitene mixture. No adduct was formed when less than 1.25 g of pseudocumene was added. Essentially no mesitylene was trapped in the aaduct, resulting in an adduct phase containing mostly pseudocumene and hemimellitene. The maximum recovery of these two isomers occurred when 4 g of pseudocumeqe was added to the mesitylenehemimellitene mixture. These data are shown in Table IV. Similarly, the separation of a mixture of ethyltoluenes and pseudocumene was investigated. Again the maximum separation was obtained when 4 g of pseudocumene was added to 2.5 g of the ethyltoluene mixture. These data
mesitylene pseudocumene hemimellitene
19.2 61.5 19.3
36.8 45.0 18.2
0.3 80.6 19.1
0.7 60.7 46.1
t 0.570 0.374 0.015
Table V. Separation of Ethyltoluene and Pseudocumene. 12.5 g of Thiourea, 25 mL of Methanol, 2.5 g of Ethyltoluene Mixture, 4 g of Pseudocumene wt % recovered in residue adduct adduct
compn, wt % feed p-ethyltoluene m-ethyltoluene o-ethyltoluene pseudocumene
11.6 24.8 2.3 61.3
17.9 42.6 3.1 36.4
3.8 3.7 1.1
91.4
15.0 6.8 22.1 67.5
5 0.343 0.514 0.231 0.575
are shown in Table V. As can be seen, only a small amount of the ethyltoluene isomers are included in the adduct, the adduct phase containing 91.4% pseudocumene. However, on a pseudocumene free basis, selectivity is o> p- > methyltoluene. Psuedocumene-Cs Alkylbenzenes. With about a 25 "C difference in boiling points between pseudocumene and the xylenes, it may be practical to use pseudocumene as an inductor to separate the xylenes and ethylbhfene. As in the previous study of the separation of the Cb aromatics, all binary combinations were investigated. A preliminary study using an equimolar mixture of m- and @-xyleneindicated that an equimolar feed composition of pseuddcumene and C i s resulted in a maximum separation. The results of this study are shown in Table VI. As can be seen, the use of pseudocumene greatly favors o-xylene addudtion with the tendency for adduct formation being o-xylene >> p-xylene > m-xylene > ethylbdnzene. The separation of a mixture with the approximate composition of the CBaromatics found in reformate was also investigated, again using an equimolar amount of pseudocumene with the C8feed. The results for 3 adduction stages are shown in Table VII. As can be seen from Table VII, 90.9% o-xylene (on a pseudocumene free basis) is obtained in three successive adductions from a feed containing 19.1% o-xylene. o -Xylene-Cg Alkylbenzenes. The separation of the Cg alkylbenzenes in the presence of o-xylene was investi-
486
Ind. Eng. Chem. Prod. Res. Dev., Vol. 21, No. 3, 1982
Table VI. Separation of Binary Mixtures of the C, Aromatics; 12.5 g of Thiourea, 25 mL of Methanol, 2.5 g of 50% C, Aromatic Mix, 2.83 g of Pseudocumene system ethylbenzene-m-xylene ethylbenzene-p-xylene p-xylene-m-xylene ethylbenzene-o-xylene m-xylene-o-xylene p-xylene-o-xylene
3.30 3.93 1.15 21.63 6.28 5.74
Table VII. Separation of C, Aromatics Found in Reformate; 12.5 g of Thiourea, 25 mL of Methanol, 2.5 g of C, Mix. 2.83 of Pseudocumene pseudocumene free compn, wt % adduct adduct 1 2
Cc,/c, ratio C,/C, in adduct
a
selectivity m-xylene p-xylene p-xylene o -xylene o-xylene o-xylene
0.067 0.088 0.015 0.431 0.379 0.352
feed
ethylbenzene p-xylene m-xylene o-xylene
19.4 20.5 40.4 19.1
4.2 15.4 28.8 51.6
0.2 7.9 14.6 77.2
trace 2.9 6.2 90.9
pseudocumene
51.9
81.0
72.7
68.9
Table VIII. Separation of the C, Alkylbenzenes in the Presence of o-Xylene; 12.5 g of Thiourea, 25 mL of Methanol, 2.5 g of C, Feed, Various Amounts of o-Xylene
compn, wt % (0-xylene free) residue
component
feed
adduct
residue
n-propylbenzene m-ethyltoluene p-ethyltoluene mesitylene o-ethyltoluene pseudocumene hemimellitene indan
4.2 24.3 12.6 10.2 7.1 33.7 5.2 2.8
0.4 5.7 3.7
5.0 29.3 15.2 12.7 7.9 22.9 4.8 2.2
amount Of o-xylene mixed with 2.5 C, feed, g
total C,
tPC/Hemi aPC/Hemi
2.7 5 3.0 4.0 5.0 6.0
15.8 19.2 18.4 18.9 19.3
38.6 47.0 44.6 45.3 45.9
14.1 19.3 20.0 20.5 21.1
1.0 1.2 1.8 2.2 2.5
40.2 59.8 47.4 59.3
0 0.249 2.78
25.1 74.9 62.3 81.3 59.4 0.370 5.46
Table X. Separation of Pseudocumene and Mesitylene in the Presence of o-Xylene; 12.5 g of Thiourea, 25 mL of Met Methanol, 2.5 g of C, Mix, 5.0 g of o-Xylene compn, wt % (0-xylene free) component
feed
adduct
pseudocumene 49.7 99.2 mesitylene 50.3 0.8 total C, recovered in adduct, % pseudocumene recovered in adduct, % 70 o-xylene in adduct phase
% recovery in adduct
ratio pseudo0C,/C, cumene xylene adduct
feed
no o-xylene 5g adduct present o-xylene
pseudocumene 52.0 65.0 hemimellitene 48.0 35.0 total C, recovered in adduct, % pseudocumene recovered in adduct, % % o-xylene in adduct phase
compn, wt %= component
8.1 7.2 4.6 2.7 2.3 2.2
Table IX. Separation of Pseudocumene and Hemimellitene in the Presence of o-Xylene; 12.5 g of Thiourea, 25 mL of Methanol, 2.5 g of C, Mix. Maximum Separation Occurred with 5 g of o-Xylene
adduct 3
component
2.5 81.4 5.6 0.7
0.527 0.481 0.472 0.426 0.400 0.905
tpc 0.343 0.419 0.394 0.399 0.401
aAdduct and residue compositions were constant on an o-xylene free basis.
gated by adding various amounts of o-xylene to 2.5 g of the Cg reformate mixture. No adduct formed when less than 2.75 g of o-xylene was used. For mixtures containing 2.75 g or more o-xylene both the residue and adduct phase composition on an o-xylene free basis were essentially the same for all tests, but the amount of o-xylene included in the adduct increased with increasing o-xylene content of the feed. These data are shown in Table VIII. As can be seen, over 45% of the pseudocumene and about 20% of the o-xylene was recovered in the adduct. The separation of binary mixtures of the trimethylbenzene isomers in the presence of o-xylene was also investigated. The extent of separation was very dependent on the amount of o-xylene present and on whether or not pseudocumene was also present. Pseudocumene-Hemimellitene. For this system adduct is formed when no o-xylene is present with only 2.5 g of feed, but the recovery and separation is greatly increased in the presence of o-xylene as shown in Table IX. The separation goes through a maximum when about 5 g of o-xylene is mixed with 2.5 g of the mixture. Again, on
tPC/Mes &PC/Mes
residue 32.4 67.6 24.0 47.6 64.4 0.472 258.6
an o-xylene free basis the composition of the adduct phase was essentially constant but the amount of Cg’sincluded in the adduct varied with the amount of o-xylene in the feed. The extent of separation for pseudocumene increased from 0.249 to 0.370 and the separation factor increased from 2.78 to 5.46 with 5 g of o-xylene present. No adduct was formed when p-xylene was added to the Cgfeed in place of o-xylene. Pseudocumene-Mesitylene. For this system the presence of o-xylene was required for adduct formation when using only 2.5 g of the C9feed. Again, on an o-xylene free basis the adduct phase composition was essentially constant when various amounts of o-xylene were added to the Cg feed, and the recovery of Cg7sincreased with the maximum occurring with 5 g of o-xylene. These data are shown in Table X. As can be seen, mesitylene is essentially excluded from the adduct. Mesitylene-Hemimellitene. For this system adduct formation required a large amount of o-xylene (7.5 g). Only 2.8% of the (2,’s were recovered in the adduct phase which was 95% o-xylene. Selectivity was for hemimellitene with 6Hemi Mes = 0.0597 “Hemi Mes = 6.47. Ethyltoluenes. Adduct was formed only when a large amount of o-xylene was present. With 7.5 g of o-xylene mixed with 2.5 g of the ethyltoluene feed, recovery of the ethyltoluenes in the adduct was only about 9%. The adduct phase contained 95.8% o-xylene, and very little separation of the three ethyltoluene isomers was obtained.
Ind. Eng. Chem. Prod. Res. Dev., Vol. 21, No.
Table XI. Recovery of o-Xylene from Mixtures with Other Xylenes and Ethylbenzene; 12.5 g of Thiourea, 25 mL of Methanol, 7.5 g of o-Xylene + 2.5 g of Mixture of Other Isomers
varied somewhat, however, depending on what other isomers were present as shown in Table XI. There was no significant separation of the other isomers. General Discussion Previous research by other investigators indicated that benzenoid compounds do not form stable channel adducts with thiourea unless they have adducting side groups. However, the present work has shown that both o-xylene and pseudocumene form adducts when present above a critical concentration that depends on composition. There is a synergism when both compounds are present, increasing the total amount of adduct that is formed and increasing the amount of both compounds present in the adduct phase. This is shown in Table XII, which shows the amount of the various compounds trapped in the adduct from 12.5 g of thiourea. Tables XIII and XIV compare specific separations using pseudocumene and o-xylene as inductors with separations obtained in previous studies using 1,2,4-trichlorobenzene and CC4. As can be seen, for some of the separations the alkylbenzene inductors are superior, especially with separations involving o-xylene and pseudocumene. Additionally, because of the large difference in boiling points between the c8 and C9alkylbenzenes the inductors could easily be separated from the adduct phase by distillation. Also, they would be preferable as inductors to the chloro compounds which are toxic and possible degradation products may be objectionable. The adducts formed using the alkylbenzenes in some cases require several hours to reach equilibrium. This compares with up to 30 min to reach equilibrium for some of the other thiourea adduct systems (Fuller, 1972). The long reaction times would require large reaction vessels if the process were to be applied continuously on a large scale. The adducts containing large amounts of o-xylene appear to be less stable than those containing mostly Cg alkylbenzenes or the trichlorobenzenes, decomposing within a matter of hours when exposed to the atmosphere. This is in contrast to the Cg adducts which slowly decompose over a period of several days. The mechanism for selectivity and the basis for adduct stability is still questionable but progress is being made in solving this problem. An X-ray crystallographic study of an adduct crystal containing pseudocumene only suggests that hydrogen bonds between the methyl groups of the guest and the sulfur and N-H groups of the host thiourea molecules may be i ApOlhIlt in adduct formation.
% o-xylene
system ethylbenzene-p-xylene m -xylene-p -xylene ethylbenzene-m-xylene
recovered in adduct 39.6 43.6 48.1
0.368 0.396 0.438
Table XII. Weight of Various Hydrocarbons in Adduct Phase Using Various Amounts of o-Xylene o r Pseudocumene Inductor; 12.5 g of Thiourea, 25 mL of Methanol, 2.5 g of Isomer Mixture wt of hydrocarbon in adduct phase, g wt of inductor, pseudo- hemimelcumene litene o-xylene inductor g ~~
o-xylene ~-
0.77 0.88 1.0
0 3 5
0 1.o 2.3
0.42 0.42 0.56
~
pseudocumene o-xylene
o-xylene
_______
0 3 5
mesitylene ~
0.44 0.60
0, 3, 5 7.5
o-xylene
no adduct 0.003 0.005
hemimel- mesitylitene lene - - - - - - - - no adduct
- - - - - - -. 0.43 1.1 o-xylene
--------
0.01
0.06
1.4 pseudocumene
o-xylene m-xylene pseudocumene
0 1.49 2.83 3.54
_______ 0.33 0.63 0.56
~
no adduct - - - - - - 0.10 0.78 0.20 2.16 0.19 2.31
3, 1982 487
-
o-Xylene plus Other C8Aromatics. Adduct was not formed when less than 5 g of o-xylene was mixed with 2.5 g of a binary mixture of the other xylenes and ethylbenzene. The adducts were unstable after filtration, decomposing over a 2-3 h period when left exposed to the atmosphere. With 7.5 g of o-xylene mixed with 2.5 g of the equimolar mixture of the other c8 aromatics, the equilibrium adduct phase composition was always about 97% o-xylene. The extent of separation for the o-xylene
Table XIII. Comparison of Pseudocumene with Other Inductors in the Separation of Xylenes and Ethylbenzene pseudocumene 1,2,4d r i ~ h l o r b e n z e n e ~ CCI, system
selectivity
ethylbenzene-m-xylene ethylbenzene-p-xylene p-xylene-m-xylene ethylbenzene-0-xylene m-xylene-o -xylene p-xylene-o-xylene
m-xylene p-xylene p-xylene o-xylene o-xylene o-xylene
g
selectivity
0.067 0.088 0.015 0.431 0.379 0.352
m-xylene p-xylene p-xylene o-xylene o-xylene o-xylene
CY
3.30 3.93 1.15 21.63 6.28 5.74
CY
4.41 3.21 1.31 13.29 4.07 5.19
t;
selectivity
0.061 0.026 0.021 0.179 0.204 0.155
ethylbenzene ethylbenzene p-xylene ethylbenzene o-xylene o-xylene
F
CY
5.63 2.84 1.70 1.18 4.50 2.40
0.094 0.084 0.024 0.014 0.087 0.060
=Gorton (1980). bMcCandless et al. (1974). Table XIV. Comparison o-Xylene and 1,2,4-’kichlorobenzene as Inductors in the Separation of the Trimethylbenzene o-xylene 1,2,4-trichl~robenzene~ system
selectivity
pseudocumene-hemimellitene mesitylene-hemimellitene pseudocumene-mesitylene
pseudocumene hemimelli tene pseudocumene
aMcCandless (1980).
CY
5.5 1.36 258.6
F 0.37 0.049 0.47
selectivity pseudocumene hemimellitene pseudocumene
CY
1.8 165.4 708.0
F 0.15 0.56 0.64
488
Ind. Eng. Chem. Prod. Res. Dev. 1982, 21, 488-495
Apparently the hydrogen bonds will only form when the methyl groups are at specific locations on the benzene ring and pseudocumene and o-xylene possess the required structure (Welling, 1982). A future publication will present and discuss the results of the X-ray study. Literature Cited Angla, B. Ann. Chim. (Paris) 1948, 4(12), 639. Fetterly, L. C. I n “Non-Stoichlometric Compounds”; L. Mandiecorn, Ed.; Academic Press: New York, 1964; Chapter 10. Fuller. E. J. US. Patent 3684701, 1972. Gorton, P. J. M.S. Thesis in Chemical Engineering, Montana State University, Bozeman, MT, 1980. Love, R. M.; Pfenning, R. F. A&. Chem. Ser. 1951, No. 5 .
McCandless, F. P.; Cline, R. E.; Cioninger. M. 0. Ind. Eng. Chem. Prod. Res. D ~ V .i m , 13, 214. McCandless, F. P. I d . Eng. Chem. Rod. Res. D e v . 1980. 19. 612. Rony, P. R. Sep. Scl. 1868. 3, 239. Weast, R. C., Ed. “Handbook of Chemistry and Physics”, 57th ed.; CRC Press: Cleveland, Ohio, 1976. Welling, R. M.S. Thesis in Chemical Engineering, Montana State University, Bozeman, MT, 1982.
Received for review October 22, 1981 Accepted April 5, 1982
This material is based upon work supported by the National Science Foundation under Grant No. ENG 78-10035.
Production of Ammonium Polyphosphate Suspension Fertilizer. Phase I Horace C. Mann,” Kenneth E. McGlll, and Thomas M. Jones Tennessee Valley Authority, National Fertilizer Development Center, Muscle Shoals, Alabama 35660
TVA is developing means for producing ammonium polyphosphate (APP) base suspensions by ammoniation of merchant-grade wet-process orthophosphoric acid. I n the process, acid derived from Florida rock is preheated and liquid ammonia is vaporized by use of process heat. The acid is then ammoniated in a pipe reactor to produce APP melt which is dissolved in water to give liquid with a pH of 6. The liquid is cooled in an evaporative-type cooler, and 2% clay is incorporated to yield a base suspension of nominal 9-32-0grade that contains about 25% of the P,05 as poiyphosphate. The product is free of crystals at 27 O C , has good physical properties, and is pourable at temperatures down to -26 OC. The process can be relrofitted with a minimum of equipment changes into existing pipe-reactor liquid fertilizer facilities that currently use superphosphoric acid.
There continues to be substantial growth in the use of fertilizers in fluid form. The latest available statistics show that in 1980,35% of all U.S. fertilizer was applied as fluids, including anhydrous ammonia and nitrogen solutions. Of these fluids, a substantial 26% consisted of two- or three-component mixtures in either solution or suspension form, while the remaining 74% were nitrogen liquids, including anhydrous ammonia. Production of solution mixes usually involves production of 10-34-0 base solution in a TVA-type pipe reactor, using low-conversion superphosphoric acid as the source of P205. Use of superphosphoric acid is required to achieve the polyphosphate level (60-75% of P206)considered necessary for high solubility and good storage properties of the product mixtures. Suspension fertilizers are made either by the same route or by use of solid diammonium phosphate (DAP), monoammonium phosphate (MAP),or ammonium polyphosphate (APP) as the source of Pz05. In attempt to lower the cost of phosphate in fluid fertilizers, TVA has continually explored methods for using relatively inexpensive merchant-grade orthophosphoric acid as the source of P205in these fluids. Considerable success has been achieved since 1976 when TVA began demonstration-scaleproduction and distribution of 13-38-0 grade orthophosphate base suspension made directly from merchant-grade acid. This material, which TVA still is producing, has good handling and shipping properties, with one exception-the solidification temperature (-9 to -7 “C) is somewhat too high to allow winter handling in northern locations. Another limitation of that product has been that the production process is not readily adaptable to use in
typical, small fluid-fertilizer plants, but rather is intended for use in larger regional plants. Now, however, TVA has developed and is ready to demonstrate a new process that utilizes merchant-grade acid without these drawbacks. In this process, a polyphosphate base suspension, instead of an orthophosphate suspension, is produced directly from low-cost merchant-grade acid. Because of the presence of the polyphosphate, which will be in the range of 25 to 35% of the PzOs, the suspension will have good low-temperature storage properties and should be usable in all sections of the United States. Additionally, the process is highly energy efficient and requires no external heat; this would be important to the small manufacturer who normally does not have a source of steam. Further, the process should be readily applicable to use in typical existing pipe-reactor fluid fertilizer plants, of which there are now an estimated 130 to 150 in the United States. Retrofitting the process into an existing plant in which 10-34-0now is made from superphosphoric acid would require some additional equipment, but it would provide a liquid manufacturer the flexibility of making in the same plant both a premium 10-34-0 liquid from superphosphoric acid and base suspension from a less expensive, readily available acid.
The Process Overall development of the process has been divided into two phases. Phase I, which is the subject of the present paper, involves, as a fiist step, the pipe-reador production of an APP solution with grade limited to about 9-32-0. This limitation in grade ensures that the freshly made solution, even when cooled, will not contain crystals;
This article not subject to U.S. Copyright. Published 1982 by the American Chemical Society
