4A sleve to trap mercury from natural gas

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1/16-in Cylindrical

1/20-in Trilobe

1/20-in CDS (Computer De=lgned $ltape)

1/20-in Quadlobe

Fig. 1. Catalyst shapes. utilized at the plant. This problem was solved by utilizing a shaped extrudate, which UCI calls CDS, that was developed several years ago for use in hydrotreating catalysts. The CDS shape (Fig. 1) yields a catalyst which has an external (geometric) surface area of 1.55 and a pressure drop of 0.90 when compared to a regular 1/8inch extrudate (Table 1). The low pressure drop results from an imposed void space because the lobes cannot interlock or nestle. Most of the disadvantage of lower loading density can be overcome by utilizing the CDS in a slightly smaller size. At the time of the presentation, the catalyst had operated satisfactorily in the plant for nearly eight months. The catalyst has adequate trans-alkylation activity to handle the poly-ethylbenzene (PEB) recycle rate Table 1 Properties of Different Shapes

Shape Cylindrical CDS Trilobe Quadlobe

Rel. surf. Rel. pres. area drop 1/8 inch 1.00 1.00 1/10inch 1.55 0.90 1/10 inch 1.28 1.00 1/10 inch 1.45 1.00

Size

applied catalysis A: General

encountered (in the range of 0.004 to 0.006 PEB residue/ethylbenzene) during the operation at COSMAR.

Ag/4A Sieve to Trap Mercury from Natural Gas

What fluid, mineral or gas Can be so easily lost? Quicksilver serf, small globule, Glides and merges, glides and breaks.

This is the vaguely remembered wording in a bundle of "Poems on Chemistry", which I read several years ago. Such elusive properties of mercury make it a difficult poison in fossil fuels, especially at concentrations of parts per billion (ppb). The mercury content in natural gas is roughly 200300, 180, 50-80, 1-9, and 0.005-0.4 ppb in the gas from the gas fields of Sumatra, the Netherlands, Algeria, Middle East, and North America respectively. It is 26-40 ppb in Algerian condensate, 55 ppb in North Sea (Straffjord) crude, and 110 ppb in California (San Joaquin) crude. These hydrocarbon sources are used as feedstock in naphtha crackers, the mother plant in pe-

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trochemical complexes to produce olefins and aromatics. It is no wonder then that Hg can slip downstream and cause unexpected havoc. For instance, Hg can destroy aluminium heat exchangers and cold boxes, often used in cryogenic processes in olefin plants and also in liquefied natural gas (LNG) plants; escaping further downstream, it can also poison the supported Pd catalysts used for selective hydrogenation of acetylenes in C2, C3, and C4 olefin streams, etc. Hence Hg in natural gas, however minute and only at ppb levels it may be, has still to be removed. One method for Hg removal from natural gas is adsorption, particularly on sulphur-impregnated active carbon. Yan of Mobil has just reported [see Ind. Eng. Chem. Res., 83 (December 1994) 3010], a novel process to remove residual Hg from natural gas or light hydrocarbons. This process is based on effective trapping of Hg by amalgamation with Ag. This Ag is positioned outside the cages or pores of 4A molecular sieves which are already being used for drying such gas streams. The Ag/4A adsorbent removes both Hg and water. There is no mutual interference between the trapping and drying reactions because they occur outside and inside the 4A cages, respectively. The properties and performance of the 4A sieves for dehydration are not affected by the incorporation of Ag on the outside. The regeneration of the sieve bed has also the same schedule as before: every 2 years. The uniqueness claimed for this process is fourfold: (i) Hg removal to extremely low levels, <0.01 ppb; (ii) compatibility with the already existing process without changes in operating conditions, operation procedure, or addition of equipment; (iii) stability in long term operation; and (iv)

applied catalysis A: General

no reagent requirement and generation of no waste for disposal (eco-friendly). P.G. MENON Some Recent Publications on Catalysis from Former Soviet-Block Countries Latvias Kimijas Zurnals (the Latvian Journal of Chemistry) has been published since 1961 and appears six times a year. In a paper entitled "Oxidation of 2,6-dimethylpyridine on supported V-Mo-O catalysts. Part 2.", published in Issue No. 1, (1994, pp. 119-125), R. Abele, I. Iovel and M. Shymanska report on an investigation of the oxidation of 2,6-dimethylpyridine with oxygen from the air in the vapour phase on supported V-Mo oxide catalysts containing various promoters. The main products of the oxidation on all the catalysts under study were 2,6-pyridinedicarbaldehyde and 6-methylpyridine-2-carbaldehyde. On the catalysts promoted with Ag or Bi oxides, both aldehydes were produced in practically equal amounts. On vanadium oxide promoted with 8% of Cs or Rb, there was preferential formation of 6-methylpyridine-2-carbaldehyde. The optimum reaction conditions were nearly the same for all the catalysts studied: 380400°C, 2,6-dimethylpyridine:O2:H20 = 1:20-40:113. The selectivity towards aldehyde formation was greatly enhanced by an increased content of V4+ ions in the catalyst. An increase in the acidity of the catalyst caused the preferable formation of 6-methylpyfidine-2-carbaldehyde. Issue No. 2, 1994 (pp. 251-253) contains two notes by M.Shymanska, one on The Catalysis Club of Latvia and the other being a report on EuropaCat-I. Volume 124 No 2 -

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