Gasification reactions catalysis

Hansen, L.K., Rathmann, 0., Olsen, A. Poulsen, K. (1997). Steam gasification of wheat straw, barley straw, willow and giganteus, Risp National Laboratory, Optics and Fluid Dynamics Department, Project No. ENS-1323/95-0010. Cerfontain, M,B Meijer, R., Kapteijn, F, Moutijn, J.A.(1987). Alkali-catalyzed carbon gasification in CO/CO2 mixtures An extended model for the oxygen exchange and gasification reaction, Journal of Catalysis, vol. 107, pp, 173-180. 

At still higher temperatures (> 700 0, pyrolytic char reacts with steam to produce hydrogen, carbon monoxide and carbon dioxide. Rates of gasification of biomass-derived chars are known to be higher than coal-derived chars (2) however, much higher temperatures are required to achieve char gasification than were initially required for the pyrolysis reactions. Catalysis of char gasification has been reported (11.12) with limited success. 

Of these inorganic materials it is the salts, oxides and metals of the series of alkali metals, alkali earth metals and transition metals which are particularly effective as catalysts. The efficiency of a catalyst is dependent on the size of the catalyst particle and its mode of distribution within the carbon. To emphasize the importance of catalysis it can be said that about 100 ppm of for example a lead salt increases the rate of oxidation of carbon by molecular oxygen by a factor of about 10 when compared with a pure carbon. It is thus possible to appreciate an earlier statement that it is very difticult to study a carbon gasification reaction which is not catalyzed in some way. The preparation of pure carbons must be in conditions as strict as those of an aseptic laboratory or a radio-chemical laboratory. 

Baker, E. Mudge, L. Wilcox, W. A., Catalysis of gas phase reactions in steam gasification of biomass. In Fundamentals of Thermochemical Biomass Conversion, Overend, R. P. et al., Ed., Elsevier Applied Science, London, 1985, pp. 1194-1208. 

This section concerns catalytic processes that transform chemicals from renewables by C-C bond breaking. Among these are thermochemical processes, such as pyrolysis and also gasification, catalytic reactions, such as catalytic cracking and different reforming reactions, and decarbonylation and decarboxylation reactions. Many of these reactions occur simultaneously, particularly in the thermochemical processes. Another technically important class of C-C bond breaking reactions is the fermentation processes, however, they will not be considered in this section since they do not involve heterogeneous catalysis. 

It is interesting to note that many of the factors that were important in controlling catalysis are also important in oxidation. The concentration and nature of surface complexes is as important in oxidative gasification as in catalysis, and the presence or absence of metal or metal-salt impurities has a profound effect on the kinetics of the reaction. The kinetics of the reaction may be influenced by mass and heat transfer in the carbons and depend, among many other factors, on the nature and structure of the carbons. ... 

Reaction of steam with carbon is one of the basic processes involved in the gasification of coals or chars to produce clean fuels. The industrial importance of this reaction is considerable, particularly at this time of spiraling energy costs. In addition, the steam-carbon reaction finds other important industrial applications, such as preventing or minimizing the coking of olefin-plant cracker-tubes. Because of its commercial importance, the steam-carbon reaction has been studied extensively, and excellent reviews are available (1,2). In addition to reaction kinetics and mechanisms, the effects of carbon structure, catalysis by metals, and impurities (anions) have been investigated (3,4, .5) ... 

Recently, controlled atmosphere electron microscopy (CAEM) or in situ TEM has allowed in situ observation of gas-solid reactions at a resolution of about 25 A. The principal feature of the technique is that a relatively high gas pressure is obtained at the specimen while preserving the low pressure needed for operation of the microscope. Various types of cell and differentially pumped systems have been described (164). The applications of CAEM to catalysis have been reviewed with special emphasis on carbon deposition, carbon gasification, and sintering studies (165). 

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