SCIENCE/TECHNOLOGY
New refinery process aims to reduce benzene A fluid-bed process using ZSM-5 zeolite catalyst to convert benzene to mainly C7-to-C10 alkylaromatics has been developed by engineers at Mobil Research & Development Corp. The new process employs chemistry from three other processes: benzene alkylation with light olefins, olefin equilibration and aromatization, and selective paraffin cracking-aromatic alkylation. Control of the complex mechanisms in the new process is accomplished mainly by controlling process parameters, Mobil research engineer Nicholas A. Collins explained at the recent American Chemical Society meeting in Chicago. Up to 60% benzene converDynamics simulation showing binding of huperzine A (greenish blue) to acetylcholinesterase. The enzyme's carbons (orange), oxygens (red), nitrogens (blue), sion and can be obtained, he told a Division of Petroleum Chemistry symposium on polar hydrogens (white) are shown, in addition to several water molecules. Overlapping new catalytic chemistry using molecuimages reflect dynamic motions of ligand and enzyme dunng the simulation lar sieves. Already, an Environmental Protecposter presentations. Preliminary tests been confirmed in studies on primates in tion Agency mandate requiring the peshow that huperzine A is longer lasting, the U.S. and Switzerland. less toxic, and more specific in its action Because huperzine A is produced at troleum industry to provide reformuthan these other two drugs, he says. Stud- very low levels in club moss, Kozikow- lated gasoline has caused numerous ies comparing huperzine A with velna- ski and coworkers developed a total changes in the operation of refineries. crine maleate have not been done. synthesis of the compound several More changes are anticipated. The MoPharmacological data, animal testing years ago, when he was a chemistry bil benzene reduction (MBR) process is data, and clinical data from China cur- professor at the University of Pitts- one of Mobil's responses to the manrently show that huperzine A "is the burgh [/. Am. Chem. Soc, 111, 4116 date. The process is designed to reduce best acetylcholinesterase inhibitor and (1989]. Kozikowski's group has used the benzene going into the gasoline may have the best effects in the Alzhei- this process to synthesize simplified pool by using olefins from various remer's patient," says Kozikowski. How- analogs of huperzine A [/. Org. Chem., finery sources. In the MBR process, Collins explains, ever, clinical trials that might demon- 56, 4636 (1991)]. But so far, in assays strate such advantages have not yet conducted in neuropharmacologist the light olefins are upgraded to gasoMichael McKinney's lab at Mayo Clinic line, and the gasoline octane rating inbeen conducted in the U.S. Huperzine A is the active ingredient Jacksonville, none of these analogs has creases. Conversion of olefins in the in a tea used in Chinese folk medicine. shown activity as high as that of the naphtha from fluid catalytic cracking also results in a reduction of the gaso"For several centuries, elderly people parent compound. Kozikowski and coworkers also re- line olefin content and, consequently, a in some districts of China have brewed tea from the leaves of [the club moss] cently developed a more efficient syn- lowering of Reid vapor pressure, an acHuperzia serrata . . . for improving their thetic approach to huperzine A [/. tion which is also mandated in the new memory," says medicinal chemist Xu- Chem. Soc, Chem. Commun., 1993, 860] EPA regulations. Chang He of the Shanghai Institute of and conducted supercomputer-aided The MBR process is the latest in a Materia Medica, China, coauthor of the docking studies to elucidate the way it long series of processes based on the binds to acetylcholinesterase. other huperzine A poster. effects of ZSM-5 and related zeolites. It Pharm-Eco Laboratories, Lexington, utilizes a fluid bed with continuous About 10 years ago, Chinese scientists isolated and characterized the effective Mass., is currently scaling up produc- catalyst regeneration. Both reactor and components of the tea, which included tion of huperzine A using this revised regenerator are operated with the huperzine A. Subsequent clinical trials in synthesis. And Interneuron Pharma- dense beds in turbulent mode. The China showed that huperzine A im- ceuticals, also in Lexington, Mass., has light feed permits operating with low proves memory and learning in aged in- licensed rights to develop and market recirculation rates, leaving most of the dividuals with memory impairment and the drug. The company plans to begin catalyst inventory in the reactor. also improves function in patients with preclinical toxicology studies soon and The overall process reactions are the autoimmune disease myasthenia to file an investigative new drug appli- exothermic. Since the heat of reaction is gravis—all with only minor side effects. cation with FDA by early 1994. not needed for decoking catalyst, it is The memory-facilitating effects have also Stu Borman exchanged with incoming feed. 36
SEPTEMBER 20,1993 C&EN
MBR process reduces benzene content in refinery stream
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Drug design software debuts in Chicago
Two new releases of software designed for aiding the chemist in drug discovery research were among the offerings Fluid on view at the exposition at the AmerRegenerator ZSM-5 Reformate ican Chemical Society national meeting reactor Catalyst C 5 -C 6 cut 4 splitter in Chicago. BioCAD Corp., Mountain makeup View, Calif., announced release 2.0 of _ _ * > Catalyst Debutanized withdrawal its Catalyst drug discovery software reformate Benzene-rich cut system, and Tripos Associates Inc., St. Air Louis, has added Disco pharmacoLight fluid catalytic cracker phore mapping software that feeds I Mixed olefins naphtha along with other software programs into * Heavy reformate its Molecular Spreadsheet approach to computer-aided compound design. Recycle At the basis of computer-assisted drug design is the fact that all drugs In the overall chemistry of the pro- er severity provides a combined MBR- possess chemical functionality that process, olefin-olefin reactions compete refinery gasoline with lower aromatics duces a biological effect. The software with the aromatic alkylation, and some level and increased yield of the C5 and is designed to leverage known inforselective cracking of low-octane refor- higher fraction at the same target oc- mation so that a large structure database can be searched for promising mate paraffins also occurs. The olefinic tane number. fragments produced from paraffin or Joseph Haggin leads on compounds that might exhibit olefin cracking may alkylate benzene or undergo additional olefin reactions. The ratio of aromatics to olefins in the feed is a key parameter in the performance of the MBR process. With increasing ratio, the amount of benzene conversion increases. The octane ratings of the C5 and higher fraction and MBR product also increase. At a high ratio of aromatics to olefins, the process chemistry is dominated by aromatic alkylation. Benzene conversion is accomplished through the formation of C/-to-C10 aromatics. Except for cracking of n-hexane, the other feed components pass through unchanged. At low ratios, benzene conversion may be even higher, but there are augmented reacIfyou're looking for a highly reactive source of the C-6 moiety for conden tions among the olefins and the other C5-to-C10 components. sation polymers, look no further than DBE-6 (dimethyl adipate). You'll Composition of the olefins in the enjoy low reaction temperatures. Minimal side reactions. And, because it's feed also affects MBR performance. a non-hygroscopic liquid, easy handling. What's more, DBE-6 excels in Propylene is the key component in this regard. All other things being equal, Dieckmann condensations. Anything else? That's up to you. Call with a higher propylene content, the 1-800-231-0998 for your sample. Ο MBR product stream is richer in olefinΟ II olefin reactions. CH 0-C-iCH -hC-OCH 3 2 3 Other EPA restrictions, in place or pending, limit the total aromatics content of gasoline. The MBR process converts the benzene to other aromatics. DuPont D B E Intermediates As a result, the aromatics must be examined in detail for their effects on the D 1993 DuPont Company reformulated gasoline pool. Mobil has found that adjusting (lowering) reformCIRCLE 8 ON READER SERVICE CARD Lowbenzene naphtha !-•
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