INDUSTRIAL AND ENGINEERING CHEMISTRY
1426
A material balance is shown in Table I and the approximate costs of production in Table 11. Using the derived cost of $15 a ton and estimating that in the straight process, in which the waste water is not recovered, a pack of 1,000,000 boxes of fruit yields about 2500 tons of feed, a balance sheet such as Table I11 may be worked out. h
TABLE 11.
COST O F
DRYING CITRUS
WASTES BY STR.4IGHT
PROCnSS
Dry house operating costs Bags Royalty Maintenance Fixed charges Selling Storage Contingencies Total per ton
$5.50 3.00 0.50 0.50 2.50 1.50 0.50 1.00 15.00
-
TABLE 111. BALANCE SHEET FOR DRYING CITRUSWASTES, BASEDON 1,000,000 BOXESOF FRUIT Tons straight dried feed Gross revenue at $25/ton Total expense at $15/ton Net revenue
2,500 $62,500 37,500 25,000
Vol. 33, No. 11
When considering the cost formerly necessary for disposal (perhaps $7500), the actual gain is $32.500 per year for a citrus cannery packing 1,000,000 boxes per season. The Citrus Patents Company, holder of the patents, has b e d royalties a t the present time a t 50 and 75 cents per ton.
Uses The primary outlet for the stock feed is to the dairies in or near the larger cities of Florida. As a feed for cows, this material has only recently been proved of value. Universities in many of the southern states have used it for several years in experimental feedings of cattle. The citrus feed has a density of 0.71 pound per quart or 18 pounds per cubic foot. This bulky material will absorb about five to eight times its own weight of water and is of great value in maintaining sufficient water in bovine diet. It is competitive with beet pulp but is cheaper; it sells for $30 per ton, while beet pulp sells for $40 per ton in Florida. The guaranteed analysis of the feed is: crude protein, not less than 6 per cent; crude fat, not less than 2.5; crude fiber, not more than 20.
Literature Cited (1) Cole, G. M., and Hall, H.W., U. S. Patent 1,991,242 (Feb. 12, 1935). (2) Lewis, G. T., Ibid., 1,973,084 (Sept. 11, 1934). (3) Lissauer, A. W., Ibid., 2,187,501 (Jan. 16, 1940).
Low-Temperature Catalytic Alkylation of Isoparaffins P. D. CAESAR AND A. W. FRANCIS
A simple mechanism is proposed which accounts for substantially all the observed paraffin isomers resulting from low-temperature alkylation of isoparaffins, and no others. A methyl group of the isoparaffin splits off and adds to one end of the double bond of the olefin, while the rest of the isoparaffin molecule adds to the other end. In any group of isomeric paraffins formed by alkylation, the relative amounts agree closely with those computed by thermodynamic equilibrium (excluding those not permitted by the mechanism).
.
ONSIDERATION of the mechanism of low-temperature alkylation of isoparaffins has been confused somewhat by the failure of classical ideas to account for the observed products. The necessity for the presence of a tertiary carbon atom suggests that the activity centers around the hydrogen at,om attached to that carbon atom. Ipatieff and Grosse (7) considered that the point of addition of the olefin is a t the tertiary carbon atom and that any unpredictable product is a result of isomerization of the hydrocarbon first formed:
C
Socony-Vacuum Oil Company, Inc., Paulsboro, N. J.
C
c-
c! + c = c t!
catalyst
C
c- &-c-c I
isomerization
JC\U4! c-6-c-c-c ?
C-b-b-C
Since our own experimental work as well as the literature indicate the substantial absence of the 2,a-dimethylbutane in the products of low-temperature alkylation of isobutane with ethylene and also of 2,2,3-trimethylbutane in the propylation of isobutane, we hesitate to adopt this mechanism. Birch and Dunstan (1) improved the situation somewhat by assuming that the hydrogen contributed to the catalyst by the isoparaffin comes from one of the primary carbon atoms, and therefore that the olefin is attached to a primary rather than to the tertiary carbon. This theory fails, however, to account for half of the observed low-temperature alkylation products of isobutane with ethylene, propylene, and the butenes. They ascribe all the other hydrocarbon products t o “secondary” reactions.
INDUSTRIAL AND E N GINEERING CHEMISTRY
November, 1941
But this term is vague and should permit the formation of
all the isomers in amounts depending perhaps on their thermodynamic stability. Yet the products, and by-products too, consist of certain special isomers, all others being practically absent. Moreover, attempts to isomerize samples of the primary products suggested by Ipatieff and Grosse (7) and by Birch and Dunstan (1)under low-temperature alkylation conditions failed to produce substantial amounts of the isomers observed in alkylation but not predicted by their theories. It is true that Birch and Dunstan ( I ) observed a gradual degradation of certain isoparaffins, such as 2,2,4- and 2,3,4trimethylpentanes, when stirred with sulfuric acid at ordinary temperatures. They postulated a reversal of the alkylation reaction followed by realkylation. Ipatieff and Grosse (6) decomposed 2,2,4-trimethylpentane with aluminum chloride. But these reactions are relatively much slower than alkylation, and the products much less specific. T o test this point further, pure 2,4-dimethylpentane, an observed product of cold acid propylation of isobutane and the primary one predicted by Birch and Dunstan's mechanism, was stirred with 97 per cent sulfuric acid a t 50" C. for 2 hours (a 30" C. higher temperature and double the time required for alkylation). Not over 15 per cent of the hydrocarbon was changed to 2,3-dimethylpentane, whereas in the alkylation the latter constituted about 50 per cent of the product. Similarly a sample of pure neohexane, a primary product of ethylation of isobutane predicted by Ipatieff and Grosse's mechanism but not observed, was treated for 2.5 hours under alkylating conditions. The product contained about 20 per cent isobutane, 20 isopentane, 50 unchanged neohexane, only about 3 of other hexanes, and about 7 per cent higher boiling material.
I n view of the great difficulty in duplicating alkylation results by isomerization, and in order to avoid the necessity of accounting for all or even half the observed products by secondary reactions, we propose the following mechanism
EQUILIBRIA OF ISOMERIC PARAFFIN TABLII. THERMODYNAMIC HYDROCARBONS AT 25' c. 'Per Cent in Alkylate A F ( n 3 0) Per Cent Calod. Found 0 32 32 200 442 68 68 800
-
n-Pentane Isopentane Neopentane
0 -1097 -1720
4 25 71
n-Hexane 2-Methylpentane 3-Methylpentane 2 2-Dimethylbutane 2:3-Dimethylbutane
0 -- 558 558 -1341
11
n-Heptane One branch 3) 2.2- and 3 3-himethylpentsnes 2 3-Dimethylpentane 2'4-Dimethylpentane T'riptane
0 -1035 1817 -1543 -1543 -2426
-1185
-
0 n-Octane 577 One branch (1) 1361 Gem groups ( 9 ) 1185 2 3- and 3 4-dimethylhexanes -1185 2:Methyl-bethylpentane -1185 2 4-Dimethylhexane 1185 2'5-Dimethylhexane -2654 dooctane 1968 2 2 3-Trimethylpentane 1968 2'3'3-Trimethylpentane 1793 2'3'4-Trimethylpentane -2752 dekamethylethsne Experimental equilibrium by Montgomery
-
--
-
e
4
11 42 32
0.7 4 14.5 9 9
40
0.3 0.8
2.9
2.1
FIGURE1. ILLUSTRATIONS (CARBONATOMS FROM PARAFFINS IN CAPITAL LITTERS) 1. Isobutane f ethylene
THE
Iso-
c c I I
C
I
c-c-c-e-c
cc-e-e
+ isubutene
3*. Isobutane
c
e
I
c
I c-c--0--0-e I
c-c--0-e-c
I
C
C
+ 1-butene
4". Isobutane
c
c
c e-c 1 1
I I c-c-e-e-c-e 6*. Isobutane
c
I I
coc-c-c (not positively identified)
+ 2-butene
c e c
I l l
cc-e-c-c
6. Isopentane $. propylene C C
I
c-c-c-e-e-e 7. Isopentane C
I
CC-C-e--0-e
1
C
a
c-c-c-e-e-c I I
+ isobutene C
1
I C
(other nonanes n o t identified)
*
Proposed Mechanism
n-Butane Isobutane
1427
13 a7 0
105 900 0
0
0 10-26
74
0 75-90
26 0 0
0
0
0 50 60 0 0 0 0 0 4.7
2.1 2.1 2.1 25 66 0 8 8 6 0 30 et aE. (9).
2::I
21
0
0 0 0 50 .h5 60 =k5
0
0
0 0 0 0-10 10-15 50-60
0 25-30 0
The authors now believe that t o predict the primary ootane isomers from alkylation with butenes, their theory must be applied to the struotures rather than to the formulas of the olefins. 1-Butene, unlike struotures of 2-butene, isobutene, propylene, or ethylene, has a methyl group and a hydrogen atom in positions favorable t o isomerization of the olefin. The two isomers now predioted are isoootane and 2,3,4-trimethylpentane: 2,8,3-trimethylpentane is prohibited by steric hindrances set up in the isomerized 1-butene.
for low-temperature alkylation of isoparaffins. It applies equally to alkylation catalyzed by cold sulfuric acid and by metal halides, since the same hydrocarbons result with both types of catalyst in those cases which have been studied. Influenced in some manner by the catalyst, the olefin is able to wedge itself in between a methyl group and the rest of the isoparaffin so that the methyl group adds to one side of the double bond and the rest of the isoparaffin to the other. The methyl group farthest from the tertiary carbon is the one split off when isopentane is the isoparaffin. Ethylene may behave as ethylidene, CH8-CH
