optimum pressure level is not clear-cut. when nonmanufacturing costs are added it is apparent that vapor recompression has some advantage. Holvever. the bare cost premium to be placed on high purity propylene is on the order of 2.5 cents per gallon. Thus: if the propylene in the feed mixture is worth 8 cents per gallon (based on contained value for polygasoline manufacture plus cost of isolating the Ca fraction). the bare cost of high purity propylene \vi11 be about 10.5 cents per gallon. The usual allowances for profit, general overhead. storage,. etc.. must be added to obtain a valid sales or transfer price. Studies of high purity propylene recovery by extractive distillation have sho\vn significantly higher costs than those given in Table IV. 'l'he direct conversion cost is slightly greater, and the manufacturing capital cost about 30yc greater than for 300 13.s.i.a. oprralion by conventional distillation. In addition. the energy requirements for recovering propylene from the solvent cause a n increase of nonmanufacturing capital by about 15% over conventional operation. For these reasons. extractive distillation operation is not shoLvn as a competitive case in Table I\'. Feed Mixtures Containing 9O+yc Propylene. Upgrading 90% propylene I O 99Yc purity is a straightforward operation best carried out according to the conventional distillation method shoivn in Figure 3: but with single column. Calculations parallel to those for Table I V have been made (Table V). Again the premises of 50,000,000 pounds per year of propylene production and 905 propylene recovery have been used.
Table V. Bare Cost of Recovering 99% Propylene from 90-10 Propylene-Propane Mixture (Ba,i\.
11.500,000 gal./yr. 99% ('rHt. 90%
recovery of C3H6)
Distillation pressure, p.s.i.a. Actual trays Tray spacing, inches Column diameter, feet Process steam, M lb./hr. Eleclricity, kw. Converted cost, d 'gal. C~HI:
300 70 18 5.5 11.4 20
Direct"
1.07
0.46 Indirectb 1.53 Total Capital cost,' thousand S 288 Manufacturing Inc,Iudes no item for cost of propylene in feed. * lnc*ludeb depreciation, loml taxes. et?., a t 15% of manufacturing capital per year. Battery limits only.
Although considerably lower than for the cost of upgrading 90% propylene is significant and must be considered in the light of any premium paid for the source cracking material. O n the other hand, the Ca fraction from such cracking operations frequently
joyc propylene,
252
INDUSTRIAL AND ENGINEERING
n 4 1
FEED MIXTURE
I ARY NSE R
FRACTI
J L
COMPRESSOR
1
_PROPYLENE
--
PRODUCT
PR 0 PA N E
PRODUCT
Figure 4. Propylene and propane are conveniently separated by vapor recompression distillation at 100 to 200 p.s.i.a. contains more than 90r, prop\lene. \vith coricspondingl\ lo\rei ukigiading cost.
Conclusions Chemical use of prop!-lene is only about 107, of the available supply. over 90Yeof which is produced by refiners as a by-product of petroleum cracking operations. An adequate supply should be available as chemical rat\' material. Should major processing changes in the refineries reduce supplies from this source. changes in ethylene plant feed stocks can take care of most chemical demands; a large proportion of the prop>lene used chemically is converted to isopropyl alcohol and tlioSt of the end uses for this alcohol can he satisfied icith ethyl alcohol. In refineries. though referred to as a by-product. prop>-lene has a definite value as a ralv material for high octane gasoline manufacture. .Is long as octane numbers continue to increase. propylene \vi11 have a steadily increasing \;aluc to a refiner).. Propylene production in refineries is ver!- much less than the quantity potentially needed for gasoline manufacture. T h e newer uses call for a material of much higher purity than that currently producrd in either refineries or ethylene plants. T h e most practical method of purification appears to be by distillation. a n expensive operation because of the low relative volatility of propane and propylene. Further. because of the high vapor pressure of propylene at atmospheric temperatures. storage is expensive (35 to 50 cents per gallon), adding further to the total investment. Finally. a chemical manufacturer, considering usc of 99+% propylene
CHEMISTRY
- __ ~
as raw material. lvould be \vt.ll advised to contemplate as a minimum a raw material cost 1x1. pound approximately 0.5 cents per pound under thr cost of 955:, eth!,lene. 'l'his figure takes into account nonmanufacturing and offsite facilities Xvhich vary pcith location. If existing de-ethanization facilities arc not adequate or rigid specifications for trace impurities must be met. the pricc may be higher. depending on individual situations.
Acknowledgment Constructive criticism of the manuscript by Kathryn O'Keeffe is % r a w fully acknoxvledged.
Literature Cited (1 I Hanson, G. H., Hogan, R. .I.. Srlson, LV. T., Cines, hi. R., 1x11. E s c . C:HFX. 44, 604 (1952). (2) Reamer. H. H., Sage, B. H., (tiid.. 43, 1628 (1951). (3) Teter, J . IV.; Shand, E. LV. #,toSinclair Refining Co.), U. S. Patrnt 2,588,056 (,March 4, 1952). RECEIVED for review J u l y 10. 1958 . ~ C C E P T E D Septembrr 24. 1958 Division of Petroleum Chemistry, Symposium on Recent Developments in Chemicals from Petroleum, 133rd Aieetina. ACS. San Francisco. Calif.! April 1958.
Errata Sheets of errata for 1958. arranged so that they may be clipped out and pasted over the incorrect material. are a\railable without charge from the Reprint Department. American Chemical Society, 3155 Sixteenth S t . , h'.M'.. \\'aqhington 6. D. C.
