MARKETS PROPYLENE SUPPLY A N D
DEMAND
ESTIMATED CURRENT U S A G E OF PROPYLENE I N CHEMICALS*
(Billions of pounds per year) Primary Product
Production From refineries From ethylene plants
20.0 0 . 8 to 1 , 0 * * .2 t o 0 . 3 2 t 21 . 0 to 2 1 . 3
TOTAL
Disposition Refinery use Chemical use Refinery losses
14, 8 1 7 3, 0 19.5
to to to to
16.1 2.0Î 4.0 22.1
* * As low purity (35 to 4 5 % ) from propane cracking. t As high purity (90 plus % ) from butane and heavier. t Includes propylene recycled toe thylene plants.
Tetramer Trimer Isopropyl alcohol Propylene glycol Polypropylene glycol Ally! chloride Cumene Epichlorhydrin C4 alcohols and aldehydes Miscellaneous, including: Acrolein Allyl alcohol Chlorinated products
TOTAL
Newer uses in chemical industry require propylene of 9 9 % purity, higher than usually made Propylene — popularly eyed today as a starting point for polypropylene and Petroleum other chemicals— Chemistry is presenting some problems not experienced in its earlier uses. Valuable to the refinery, it goes into high octane gasoline at the purity at which it is produced. The same is true when it is used to make trimer, tetramer, cumene, and isopropyl alcohol. But its use in allyl chloride, acrolein, C 4 aldehydes and alcohols, and its potential widespread use to make polypropylene, demands a much higher purity. The propylene-propane separation technology and economics of high purity propylene for use in chemicals demand special attention, according to J. A. Sherred and J. R. Fair, both of Monsanto. (Gene McMullen, also of Monsanto, presented the report before the Division of Petroleum Chemistry in a Symposium on Recent Developments in Chemicals from Petroleum, in Sherred's absence.)
m
34
C&EN
APRIL
2 8,
1958
500 105 800 66 8 59 51 8 100
10 1707
* Provision not made for that consumed in Hercules's 20 million pound-per-year polypropylene plant which went into production last y e a r {C&EN, Dec. 2€ 1957, page 25).
High Purity Propylene
ACS NATIONAL MEETING
End Use
Detergents Lube-oil additives 0 x . o alcohols Detergents Acetone, solvent Resins, plastics Resins, plastics Glycerol Phenol Epoxy resins Plasticizers, solvents
Millions of Pounds Per Year
Propylene occupies a rather unique position as a chemical raw material—it is produced economically only as a b y product or a co-product. Today, it comes commercially from only t w o sources, refinery operations and ethylene plants. Refineries make the most and u s e a large part of current propylene outp-ut, estimated at 21.3 billion pounds p e r year. In general, they make a pxopane-propylene mixture containing from 40 to 60% propylene as a b y product of cracking operations. As this is a satisfactory raw material for t h e i r own use, they make no attempt to p r e pare propylene of higher purity. Ethylene plants turn out another 1.3 billion pounds. This has a p u r i t y roughly that of refinery propylene if propane pyrolysis is used to make "the ethylene, or over 907c if butane a n d heavier hydrocarbons are used. • Economics of Separation. The most practical way to purify propylene appears to be distillation, but because of propylene's high vapor pressure at atmospheric temperatures, storage is expensive (30 to 50 cents per gallon). Since raw material for high p u r i t y
ethylene is usually a C 3 fraction containing either 40 to 6 0 % propylene or over 90%, cost studies must be made separately. For the lower purity starting material, the operating pressure level significantly affects the stage requirements for separating propylene a n d propane. Sherred and Fair cost studies for pressures of 300 and 100 to 200 pounds per square inch are based on an 11.5-million-gallon-per-year plant, located in the Gulf Coast area, with a liquid feed containing a 50-50 molar mixture and with 90% recovery of propylene. These studies show that the bare conversion cost premium to be placed on high purity propylene is about 2.5 cents a gallon (ranging from 2.23 to 2.52 cents). If propylene in the feed mixture is worth 6 cents a gallon for poly-gasoline use, the bare cost of high piirity propylene is about 8.5 cents. Estimated capital cost for such a plant ranges from $520,000 to $720,0O0, not considering integration with existing process units and service facilities. Extractive distillation has been studied but is not competitive. Upgrading the 9 0 % propylene to 9Q% purity is carried out in a conventional single column distillation unit. Calculations for a plant of the same size and conditions show conversion costs to be 1.07 cents direct and 0.46 c e n t indirect. Capital cost of this p l a n t is estimated at $228,000.
