What is the status of new, improved catalysts developed for isobutane alkylation? This has been a popular question during past National Petrochemical & Refiners Association Q&A meetings. Although respondents to the question may have changed, the answer has not.
Technologies such as alkylation will gain popularity as refiners look away from using MTBE for octane and turn towards technologies that produce highly branched paraffins. Purvin & Gertz Inc., Houston, expects demand for US alkylation capacity to rise by about 100,000 b/d should MTBE be phased out by 2005.
Refining alkylation processes traditionally use one of two liquid catalysts: sulfuric acid or hydrofluoric (HF) acid. The process combines isobutane with an olefin, usually propene or butene, to make alkylate.
Alkylate is a good gasoline blending component because it is high in octane and low in vapor pressure. It also has no olefins or aromatics.
Safety concerns surrounding traditional sulfuric and HF acids have encouraged the development of new solid and improved liquid catalysts.
Concerns
Although the traditional liquid-acid alkylation applications have proven safe and economic, there are some concerns with their use.
Both acids are toxic. Their corrosive nature requires them to be handled and operated with care. A large spill with HF acid could form a vapor cloud. Waste disposal of these acids and the rising cost of caustic regeneration for sulfuric acid are also issues.
Process licensors with a vested interest in sulfuric and HF-alkylation processes have worked hard to lower the real and perceived risks associated with existing plants.
They have developed elaborate mitigation systems that included HF detectors, isolation valves, containment systems, and water sprays. In addition, HF additives reduce the amount of aerosol formed from a leak, lowering the risk of a vapor cloud.
Players
Even with the improved reputations of sulfuric and HF acids, several companies have developed alternatives. The lead players are UOP LLC, Des Plaines, Ill., which has developed a solid catalyst, and Haldor Topsøe Inc., Houston, which has developed an improved liquid one. Institut Français du Pétrole, Rueil-Malmaison, France, also has developed a solid catalyst.
Although Neste Engineering Oy, Porvoo, Finland; Catalytica Inc., Mountainview, Calif.; and Conoco Inc. began operating a 7 b/d pilot plant at Neste's Finland technology center in 1992, they abandoned it in 1994 when the incentive to replace sulfuric acid and HF acid alkylation disappeared.
In the early 1990s, it seemed possible that HF alkylation would be banned altogether. California had proposed a ban in response to several accidents.
The incentive to continue development of alternative catalysts went away, however, says Conoco, when HF additive technology was successfully demonstrated in 1994.
Solid alternative
The industry found it difficult to develop solid-alkylation catalysts that did not deactivate too quickly. Heavy, unsaturated hydrocarbons prevented reactivation and limited catalyst life.
UOP's Alkylene process uses a solid catalyst and is one substitute for today's alkylation processes. It overcomes the problems of catalyst reactivation by contacting the catalyst with a hydrogen-saturated isobutane. The hydrogen saturates heavy hydrocarbons, which desorb from the catalyst surface.
Pilot plant tests suggest that the alkylate product from Alkylene has octane numbers and production costs comparable with traditional processes.
Liquid alternative
Haldor Topsoslash;e has an improved liquid-acid catalyst, supported on a solid medium.
While UOP's process requires a regeneration step, Haldor Topsoslash;e recovers its catalyst. The catalyst is much less toxic than sulfuric acid and HF acid. Its process is called Fixed Bed Alkylation (FBA).
Haldor Topsoslash;e has successfully tested the technology in a 0.5 b/d pilot plant for more than 4 years.
The first opportunity for Haldor Topsoslash;e's FBA in then-Amoco Corp.'s Yorktown, Va., refinery seemed like a sure thing in 1997. In late 1998, however, Amoco reversed its decision to use the technology there (OGJ, Sept. 21, 1998, p. 46).
Michael D. Grant, manager of technology sales for Haldor Topsoslash;e, said that two other companies besides Amoco have looked into licensing FBA. Changes in personnel and lack of money, however, have prevented its use.
The company is still looking for licensors to build the first unit, he said. "We're talking to a lot of other refiners, all of whom want to be second."
The next step
There has been little change in the status of new alkylation catalysts because licensors are in a lull, waiting for the first commercial opportunity.
A commercial plant would allow UOP and Haldor Topsoslash;e to further test and perfect their processes. What's likely, said Grant, is that one of these two companies will get a license in early 2001.
Once that happens, the other one will probably get one, too.
What's happening to new catalysts for alkylation? Look for a new answer in beginning of the 21st century.
