TECHNOLOGY
Hoechst Reveals Wacker Process Details Process to convert ethylene to acetaldehyde exhibits expected cost advantages, works with different raw materials Now that Farbwerke Hoechst's two German plants to make acetaldehyde from ethylene (C&EN, Aug. 24, 1959, page 39 ) have been on stream for over a year, the company has lifted the lid on some of the process details. Operating experience has shown, Hoechst says, that the Wacker process gives high yields of acetaldehyde with a quality comparable to that from the conventional acetylene hydration process, that it will work on raw materials from a variety of sources, and that the cost advantages foreseen for it have been realized. Germany's organic chemical industry started and developed strongly on coal-based raw materials. Most of the acetaldehyde, for example, has been
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made from carbide acetylene since WTorld War I (although some in Europe is made from ethanol). From the acetaldehyde have come acetate esters, acetone, and other derivatives. But during the past few years, the German organics industry has been turning to petroleum to supply the growing quantities of raw materials it needs. With the doubling of German oil refining capacity since 1957, chemical companies are assured of constant supplies of oil fractions to feed their organic complexes. Further, petroleum ethylene is cheaper than acetylene, and handling is easier and safer. Two factors—ethylene is cheaper than acetylene, and oil supplies from which to make the ethylene are as-
sured—have been decisive in Hoechst's plans to go ahead with its Wacker process plants. In development since 1956, the process was ready for scaleup at about the time that ethylene expansions were coming on stream. Two Variants. The Wacker process for direct oxidation of ethylene to acetaldehyde was developed by Aldehyd G.m.b.H. of Munich (jointly owned by Wacker Chemie of Munich and Hoechst). It has two variants—singlestage oxidation with oxygen, and twostage oxidation with air. In both variants, ethylene is oxidized in an aqueous solution of cupric chloride and palladium chloride. The cupric chloride is reduced to cuprous chloride during the oxidation. The
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WACKER PROCESS CONSUMES PER H O U R . . . Single-Stage Variant Ethylene (at 88 p.s.i.a.) Oxygen Cooling Water Steam (at 190 p.s.i.a.) Steam (at 51 p.s.i.a.) Electricity
142,000 Cu. Ft. 77,000 Cu. Ft. 608,000 Gal. 10.8 Tons 2.5 Tons 1600 Kwh.
Two-Stage Variant Ethylene (at 176 p.s.i.a.) Cooling Water Steam (at 190 p.s.i.a.) Steam (at 51 p.s.i.a.) Electricity
142,000 Cu. Ft. 396,000 Gal. 2.5 Tons 7.5 Tons 2800 Kwh.
Based on 66,000 ton-per-year capacity, working for 8000 hr. per year.
Maybe Eastman has a better method Got a production problem? Does it involve the manu facture of a compound that's not generally avail able in the quantity or pu rity you require? Then con sider this. We are equipped for and experienced in synthesis on a custom basis for quantities in the largerthan-laboratory-but-lessthan-tankcar range. For in formation about this serv ice, or a quotation, write Distillation Products Indus tries, Eastman Organic Chemicals Department, Rochester 3, Ν. Υ.
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cuprous chloride is then oxidized back to the cupric form by oxygen or air, thus keeping the process continuous. Using oxygen, the process goes like this: Ethylene is fed into a vertical reactor filled with catalyst solution. Oxygen and recycle gas are also fed into the bottom of the reactor. The reaction takes place at the boiling point of water-slightly higher than 100° C , since the reactor carries a "slight over pressure." Heat of reaction is ab sorbed by evaporation of some of the water; the evaporated water is made up to keep catalyst solution constant. The gaseous reaction mixture (steam, unreacted ethylene, and reac tion products) goes to a separate wash ing tower, where the acetaldehyde is washed out with water. The alde hyde-free gas is recycled back to the reactor, with a side stream bled off to keep the inert content constant. The side stream is also oxidized to convert the last bit of ethylene. To oxidize with air, Hoechst has a modified process design. Ethylene flows through the catalyst solution in a single-pass reactor at higher pres sures and temperatures than in the single-stage process. The mixed reac tion products and catalysts are sepa rated by distillation in a separate unit, using the heat of reaction to supply the heat. The catalyst solution flows from the still to a regeneration unit, where the cuprous chloride is reoxidized to cupric chloride with air and
returns to the first reactor for its next cycle. Crude acetaldehyde is purified in both processes by a final distillation to separate it from water and higher-boil ing components. Its quality after re covery is comparable to that from other processes, according to Hoechst. Two-Stage Process Is Flexible. Ad vantage of the two-stage process, Hoechst points out, is that it can han dle either a pure ethylene feed or an ethylene-rich gas, since there is no re cycle gas stream. The waste air, with so much of its oxygen removed, can be used as a blanketing gas. The process will also work with oxygen in the catalyst regeneration. Both variants give about 959^ yield with alrflost no by-products, operate at low working pressures and tempera tures, consume little energy, and re quire relatively low capital investment, Hoechst adds. A 66,000 ton-per-year, single-stage plant in Germany will cost abo^t $2.9 million, a two-stage plant of about the same capacity will be sc*nie $3.7 million, but with no investnient in auxiliary oxygen facilities. \ Besides the two plants it is building fcf»r itself, Hoechst has licensed the Wacker process to Celanese, which is • now building it into its new acetyls plant at Bay City, Tex. (C&EN, Feb. 6, page 3 7 ) . Hoechst admits that sev eral other companies around the world are negotiating for licenses, although it will not name them.
Abbott Pushes Ruthenium Catalyst Work Ruthenium catalyst process for hydrogenating pyridine to piperidine to move into pilot plant Abbott Laboratories is planning to move its ruthenium catalyst process for hydrogenating pyridine to piperidine into the pilot plant stage, the company said last week. If the catalyst works as well in a continuous process as it does in lab studies, the company expects to be able to produce piperidine under much milder conditions than those required by current higher pressure catalysts. Another big advantage is that the process works with pyridine as the sole liquid phase. The current market for piperidine is about 300,000 lb. a year, Abbott's chemical market research department estimates. The reactive, secondary amine is an intermediate in synthesizing dyes, polymers, pharmaceuticals, and oil and fuel additives. Lab tests have shown several advantages for the ruthenium catalyst
HYDROGENATION BOMB. Morris Freifelder of Abbott Laboratories loads a hydrogénation bomb. Mr. Freifelder has been able to hydrogenate pyridine to piperidine under relatively moderate conditions using a ruthenium catalyst
in hydrogenating pyridine and a number of its derivatives, Abbott's Morris Freifelder says (C&EN, April 3, page 57). As the dioxide, or distributed on a carrier, ruthenium will reduce pyridine without solvent, at moderate temperature and pressures, and in quantitative yield, Mr. Freifelder says. Infrared analysis of undistilled product filtered from the catalyst shows complete conversion to piperidine, he notes. This takes place with less than 2% weight ratio of R u 0 2 to pyridine, is complete in half an hour, and goes at 95° C. and 70 atm., he says. Another factor that makes the process commercially attractive is that the raw material need not be the purest grade. Unlike other hydrogénation catalysts, ruthenium—as the dioxide or on a carrier—doesn't appear to be affected by nitrogen base poisons, Mr. Freifelder points out. Platinum oxide, for example, will reduce pyridine in a reasonable time. But an equivalent of organic or mineral acid has to be present or pyridine will poison the catalyst. Also, it's difficult to separate the piperidine economically. Raney nickel and other commercially available nickel catalysts require more drastic conditions. Reports of reductions with this catalyst generally quote pressures of 150 to 300 atm., temperatures above 150° C , and far longer reaction times, Mr. Freifelder points out. Rhodium also has been mentioned as a possible catalyst. But Abbott finds it undergoes nitrogen base poisoning too. In hydrogenating some 20 other derivatives, Mr. Freifelder found only one that was difficult. This was 2, 4, 6-trimethylpyridine. It required higher temperatures and longer reaction times, probably due to steric effects, he says. Most of the reductions could be carried out in alcohol solvents, from which separation is relatively simple, he found. Carboxyl groups aren't affected, except for nicotinic acid, which was decarboxylated. This he prevented by carrying out the reduction in aqueous sodium bicarbonate solution. Also, alcohol substituents aren't hydrogenolyzed, Mr. Freifelder notes.
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