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Some very useful chemistry is dis- cussed and a good deal of reference is made to several patents assigned to the Texaco Chemical Company.

lsoplus Catalyst from Engelhard

The Engelhard Corp. have announced the development of new refinery catalysts which could lead to dramatic increases in

the yield of isobutene from refinery oper- ations. IsoPlus catalysts are aimed at help- ing to satisfy projected increases in the demand for the production of MTBE which in turn requires isobutene to be available in larger quantities than present. The use of these catalysts is seen to offer a more attractive option than, for example, invest- ment in a butane dehydrogenation plant. (Source: Chem. & Eng. News, April 20

(1992) p. 5.)

Methane Activation and Methane Coupling

The wealth of mechanistic information of relevance to catalysis that can be pro- vided by the appropriate use of isotopically

labelled molecules is well known. It is somewhat surprising that not much use is apparently being made of such tech- niques. Fortunately, some papers do ap- pear from time to time and, in a recent article, Lapszewicz and Jiang examine the CSIRO’s OXCO catalysts for methane coupling (Catal. Lett 13 (1992) p. 103). By using CH4-D2 and ‘60z-180z experi- ments, information was obtained on the

ability of the catalysis (SmzOs, MgO, y- Al2O3) to activate both methane and oxygen. The authors find no direct correla- tion between the rate of methane coupling and the rate of activation of methane and

suggest that the formulation of the methyl radical cannot be described as a simple one-step process.

Some Recent Chemical Communica- tions

Chauvin and Commerene (J. Chem. Sot., Chem. Comm., (1992) 462) describe a method for the chemical counting and characterization of the active sites present on rhenium/alumina metathesis catalysts. The results support the surface carbene hypothesis and, in addition, offer some insights on the mechanism of catalyst deactivation.

A novel Pt” ion/Pt’ catalyst system for the direct oxidation of ethane to acetic gly-

colic acids has been described by Sen and Lin (J. Chem. Sot., Chem. Comm., (1992) 508). It is proposed that initial C-H activa- tion occurs at the Pt” centre, associated with the use of &PtCl4. Ethanol and ethylene glycol are formed and these are subsequently oxidised by the correspond- ing carboxylic acids by the metallic Pt, associated with the use of Pt black. The reactions take place in aqueous media and under mild conditions.

Combined Catalytic Removal of SWNO, from Flue Gases

Haldor Topsoe A& Lyngby, Denmark, has commercialized a catalytic process for the removal of SOx and NOx from flue gases. The process, called SNOX Pro- cess, is capable of removing more than 95% of SOx and NOx. While NOx is reduced by ammonia by the usual SCR reactions, SOx is converted to 94-97% sulphuric acid that can be used for fertilizer production and other industrial purposes. The pro-

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cess has been tested to treat flue gas from a boiler at an Italian petroleum complex where it achieved 97.4% NOx reduction and over 96.5% SOx removal. In contrast, other commercial combined SOx/NOx pro- cesses achieve considerably lower remo- val efficiencies, especially for NOx. For example, the Mitsui Mining process achieves 95% SO2 removal but only 70% NOx removal. The only other commercial catalytic combined SOx/NOx removal sys-

tem, the Lurgi/Degussa/Lentjes’ DESO- NOxsystem, achieves 99% SOx removal of both SOx and NOx.

In the SNOX Process, NO, is convened to N2 with NH3 by selective catalytic reduc- tion using a Haldor Topsoe titanium-oxide monolith catalyst. The temperature is

maintained above 700°F (350°C) to avoid the problem of scaling by ammonium sul- phate formation. A particulate control de- vice is used before the process to remove the dust particles down to 0.0004 g/scf. Any remaining particulates are retained in the SO2 convener downstream, so these emissions are very minimal.

The SOx-containing flue gas is then passed through beds of Haldor Topsoe sulphuric acid catalyst. The vanadium- based catalyst oxidizes SO2 to SO3 and is

unaffected by as much as 50% watervapor

or several hundred parts per million of chlorides. The SOS in the treated gas is hydrated to sulphuric acid vapor and goes to a proprietary condenser. The sulphuric acid catalyst also oxidizes most of the CO and hydrocarbons to CO2 and H20. Also, any remaining NH3 is oxidized to NOx. This results in a slight increase in the NOx emis- sions; however, it prevents any NH3 slip. Lifetimes for both the SCR and sulphuric acid catalysts are expected in the 5-10 years range, depending on fuel charac-

teristics, according to David Collins of ABB Environmental Systems that licenses this process in North America.

A full scale SNOX plant began commer- cial operation in November 1991 to treat 106 Nm3/h of flue gas on a 305 MW coal fired power plant in Denmark. This plant has generated considerable interest with utility companies all over the world. A dem- onstration unit has been installed, and is now in startup, to treat a 35 MW equivalent slipstream from a 108 MW steam electricity generating station at the Ohio Edison Niles power plant. A recent process economic study by EPRI showed that the levelized cost of this process was about $O.Ol/kWh, making it competitive with other combined SOx/NOx process that do not achieve the same levels of removal.

SANJAY AGARWAL JERRY SPIVEY

Dehydrogenative Coupling and Homo- logation of Methane

The oxidative coupling of methane has

been a hot topic in catalysis during the last decade. In spite of the concerted efforts of

several research groups, the progress in this field has been rather limited. This

prompted Dr. Robbie Burch last year to propose a “universal law of total loo” for this reaction: thus, 99% conversion of methane with 1% selectivity to c2+ hydro- carbons, or 1% conversion with 99% selec- tivity, and all possible combinations be- tween these two extremes.

Prof. Rutger van Santen and his col- leagues (Schuit Institute of Catalysis, T.U. Eindhoven, The Netherlands) now appear to have made a breakthrough in dehy- drogenative coupling and homologation of

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