Biomass—thermal and catalytic processes

The biomass conversion processes are not new and they are basically composed by pyrolysis processes and heat treatments, which depend on the type of organic load, conditions of preparation, reaction, etc. 

The fermentation processes have a particular interest for ethanol production, in addition to microbiological processes however, they are not discussed in this book. In this chapter, we will discuss the thermal process and catalytic processes of second generation applied to biomass. 

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Thus, it can be seen the complexity for each mixture from biomass. Therefore, biooil obtained may undergo further steps, called second generation processes. Thermal and catalytic processes that allow the production of high value added compounds are usually used. These processes are shown in Figure 23.7. 

It has been shown that synthetic zeolites such as ZSM-5 can be used to convert oxygenated compounds derived from biomass materials into hydrocarbons which can be used as fuels or chemicals feedstocks (1,2,3,4). However, the pyrolysis oils obtained from biomass materials by different thermal and thermochemical processes (5,6) showed poor hydrocarbon yields and high tar content when contacted over ZSM-5 zeolite catalysts at high temperatures (7,8). Since the pyrolysis oils are composed of a wide variety of oxygenated compounds such as cyclopentanone, cyclopentenone, furfural, phenol, carbohydrate and carboxylic acid derivatives (9,10) it is difficult to point out exactly which family of compounds is contributing more to the observed tar and to the rapid deactivation of the catalysts. Catalytic studies on model compounds which are usually found in the biomass pyrolysis oils are therefore primordial in order to determine the best catalytic system for the up-grading of pyrolysis oils to useful hydrocarbon products. The reactions of some phenolic, carbonyl and carboxylic acid derivatives over ZSM-5 catalysts are already... 

Small reformers R D areas include compact and low cost reformers (1-5 kW) to convert fossil fuels (natural gas, gasoline) or biomass fuels (ethanol) to hydrogen via different processes (steam reforming, partial oxidation, auto-thermal, non catalytic hybrid steam reforming). Improvements in reformer efficiency, capacities and response times, and integration of purification unit are also being studied. Examples of projects include ... 

HTU [Hydro-Thermal Upgrading] A process for making liquid fuels from biomass. The biomass is made into an aqueous slurry and heated to 300°C under 200 bar. The resulting crude oil is catalytically hydrogenated to give a high-quality naphtha or diesel fuel. Developed by Royal Dutch Shell from 1982 to 1993, but not commercialized. 

Obtained data show that, the mixtures of the different types of the natural and synthetic organic polymers can be successfully converted with a high yield to light distillate fraction by pyrolysis under inert atmosphere and catalytic hydtopyrolysis in the autoclave conditions. The optimum tenqreiature of biomass / plastic mixtures conveision which coiresponds to the maximum yield of liquids is 390 - 400 C. In the CO liquefaction processes the interaction between products of natural and synthetic polymers thermal deconqwsition takes place. 

Biomass firing and probably waste firing will require tar removal. Catalytic cracking and thermal cracking, if they prove reliable, are generally regarded as the best processes as they retain much of the chemical energy of tars in the gas phase. However, experience to date on the reliability of tar... 

Carbon-based feedstocks include natural gas, light hydrocarbons, coal, and biomass. Basically, carbon-based hydrogen production technologies are thermal catalytic processes in which part of the feedstock is burned to provide the thermal energy needed for the hydrogen production. A brief review of these basic hydrogen production technologies follows. 

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