Two types of catalysts — homogeneous and heterogeneous — are used for processes of hydrocarbon feed demercaptanization and sulfide-alkali waste waters treating.
Both of the catalysts, homogeneous and heterogeneous, contain a catalytically active component — cobalt phthalocyanine — acting as an oxygen carrier.
Homogeneous IVKAZ catalyst is the most active and stable industrial catalyst. For kerosene and diesel fuel treating IVKAZ catalyst applied on activated carbon of AG-3 or AG-5 grades is used.
Heterogeneous catalysts of KS type were developed in VNIIUS in 1983 . They are water-insoluble cobalt phthalocyanine (up to 20 % mass) in polymer mass (polyethylene or polypropylene). Catalysts of KS and KSM types are used as packing elements of Pall, Rashig rings types, etc. An advantage of the heterogeneous catalyst is ease of a plant operation because procedures of catalyst solutions preparation and their dosing into the system are excluded. However JS «VNIIUS» refused to use heterogeneous catalyst of KS and KSM types in DMD and Serox processes because of its low activity.
Catalysts of KS and KSM types are prepared by mixing cobalt phthalocyanine powder with melted polymer. Therefore, only those cobalt phthalocyanine molecules take part in catalysis which are located on the polymer surface. Base quantity of cobalt phthalocyanine is in the polymer mass (non-porous) and does not react in the catalysis. Accordingly specific catalytic activity of heterogeneous KSM catalyst is many times lower than that of homogeneous IVKAZ catalyst. Hence, a volume of a regenerator with a heterogeneous catalyst should be 1.8-2 times larger as compared to a volume of a regenerator with a homogeneous catalyst.
Because of low activity of KSM catalyst the temperature in a regenerator should be 70-80°С that requires higher heat input as compared to homogeneous IVKAZ catalyst, where the temperature is 40-48°С.
In a case when mercaptan content in the feed exceeds a design value the reactor with a heterogeneous catalyst cannot provide a required degree of alkali regeneration, and therefore a degree of feed treatment. If in a case of homogeneous catalysis this problem is solved by simple increase of catalyst concentration in the alkaline solution, then in a case of heterogeneous catalyst the regenerator should be replaced with a device of a larger volume. Besides, the slightest contamination of KSM catalyst surface results in complete loss of its activity that took place on Omsk, Yaroslavl refineries and Novokuibyshevsk PCC [2,3,4].
Homogeneous IVKAZ catalyst is a water-soluble cobalt phthalocyanine with a promoting additive. An advantage of homogeneous IVKAZ catalyst is high specific activity (consumption of the catalyst is 0.05 g per ton of the treated feed) and flexibility of its use. Use of the homogeneous catalyst allows not only to achieve deep regeneration of an alkaline solution but also to control the process by changing the catalyst dose and its concentration in the alkaline solution, depending on feed loading and mercaptan concentration in it.
Modern IVKAZ catalyst is stable in an alkaline medium up to 100°C that is proved by successful operation of industrial DMD, DMC and Serox plants all over the world. It should be noted that leading UOP and Merichem companies, which have more than 3500 commercial plants of Merox type, use only homogeneous catalysts.
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