UOP DEVELOPS NEW OXYGENATES PROCESS

UOP, Des Plaines, Ill., has developed a process it claims is "new state of the art" for making methyl or ethyl tertiary butyl ether (MTBE or ETBE) or tertiary amyl methyl ester (TAME) from olefin feedstocks.

UOP said the process, carrying the trademark Ethermax, achieves higher conversion rates than fixed bed processes: more than 99% isobutylene conversion in MTBE units and more than 91% isoamylene conversion in TAME units, compared with 96-98% and 70%, respectively, with conventional etherification technology.

UOP, Huels AG of Marl, Germany, and Koch Engineering Co. Inc., Wichita, Kan., developed the Ethermax process by combining principles of conventional fixed.bed MTBE processing with Koch's proprietary reaction with distillation (RWD) technology.

HOW IT WORKS

UOP said RWD technology is based on Koch's structured tower packing containing catalyst. Koch engineers describe it simply as a "sandwich" of conventional MTBE resin catalyst between two plates of corrugate mesh. The dual function, mass transfer/catalyst system allows effective fractionation and olefin reaction in a single zone by providing highly efficient mass and heat transfer between vapor, liquids, and solid catalyst.

Structured tower packing enables Ethermax to achieve higher ether production by overcoming equilibrium limitations of single stage, fixed bed processes, UOP said.

Most conventional fixed bed MTBE units consist of two adiabatic reactors set in series. About 90% of conversion occurs in the first reactor and about 8% in the second.

In the Ethermax process, a single adiabatic fixed bed reactor is followed by the RWD column, in which a section of trays or packing has been replaced with Koch's KataMax packing containing catalyst and where the reaction is completed at the same time products are separated. As reactor effluent enters the column, fractionation separates MTBE already formed from unreacted feed components, which then enter the catalytic section of the fractionator for more conversion.

Because of Koch's mass transfer equipment, UOP said, the Ethermax MTBE process requires less catalyst in the reactive distillation column. Unlike other reactive distillation systems, KataMax packing can be reused after the catalyst is spent.

FLOW SCHEMES

Various Ethermax flow schemes are possible.

UOP said the process can selectively, completely convert isobutylene contained in any feed stream into MTBE, regardless of concentration, including stream from dehydrogenation, steam cracking, and catalytic cracking units. A mixed feed of isobutylene and isoamylene is feasible if both MTBE and TAME are desired.

The process can be integrated with UOP'S C4 isomerization and dehydrogenation processes to create an economical, coordinated MTBE train, UOP said. Or Ethermax equipment can be retrofitted into revamps of conventional units to increase isobutylene conversion or to allow coprocessing of MTBE and TAME.

Koch tested the concept in a semicommercial plant at Wichita.

Since reaction and distillation are combined in one vessel instead of occurring in two reactors, officials said, the Ethermax process costs less to install than most fixed bed MTBE units.

A UOP spokesman estimated that, based on comparison of a 1 0,000 b/d conventional MTBE plant with the same size Ethermax plant, capital cost for the Ethermax unit would be about 15% less.

WHAT'S BEEN DONE

Huels designed and brought on stream the first high conversion MTBE unit in 1976. UOP licensed Huels' fixed bed MTBE process in 1980.

Officials said 16 UOP-Huels installations are operating worldwide. Ten of the plants are simple, single stage units producing MTBE for gasoline blending. The other six are capable of coproducing MTBE and butene-1.

Seven UOP-Huels units are in various stages of design and construction, as are numerous other plants using conventional MTBE technology from other licensors (OGJ, May 20, p. 25).

Tenneco recently broke ground for one integrated MTBE plant using conventional Huels technology at a site near Houston. A UOP official said Tenneco is evaluating a switch to the Ethermax process for the MTBE section. No contract awards have yet been made but UOP said several operators are considering new plants or retrofits of Ethermax.