Process parameters liquid products yield

VOCs), and to a decrease in production yields. Quantitation of these phenomena and determination of material balances and conversion yields remain the bases for process analysis and optimisation. Two kinds of parameters are required. The first is of thermodynamic nature, i.e. phase equilibrium, which requires the vapour pressure of each pure compound involved in the system, and its activity. The second is mass-transfer coefficients related to exchanges between all phases (gas and liquids) existing in the reaction process. 

The first choice for a solvent during the development of a synthetic procedure is usually an organic liquid, which is selected on the basis of its protic or aprotic nature, its polarity, and the temperature range in which the reaction is expected to proceed. Once the desired transformation is achieved, yield and selectivity are further optimized in the given medium by variation of temperature, concentration, and related process parameters. At the end of the reaction, the solvent must be removed quantitatively from the product using conventional workup techniques like aqueous extraction, distillation, or chromatography. If the synthetic procedure becomes part of a large-scale application, the solvent can sometimes be recycled, but at least parts of it will ultimately end up in the waste stream of the process. 

Screening in stationary mode will only give information about the activity of a single catalyst or a catalyst mixture. When a proper catalyst for a certain reaction is found, the next important information is the reaction kinetics. To obtain this information, several methods and reactors are recommended in the literature [66-73]. Most of them apply transient reactor operations to find detailed kinetic information. Microreactors are particularly suited for such an operation since their low internal reaction volumes enable a fast response to process parameter changes, e.g., concentration or temperature changes. This feature was already applied by some authors to increase the product yield in microreactors [70, 74, 75]. De Belle-fon [76] reported a dynamic sequential method to screen liquid-liquid and liquid-... 

Microdistillation with mass spectral analysis of the distillate yielded valuable information about the SRC s studied. Although only 2-17% of the SRC s were volatile under the conditions used, the nature of the distillate defined the completeness of process solvent separation, solvent separation parameters, and degree of depolymerization of the coal. Also, the distillate contains stable reaction intermediates between liquid products and coal itself. 

Knowledge of the effects of various independent parameters such as biomass feedstock type and composition, reaction temperature and pressure, residence time, and catalysts on reaction rates, product selectivities, and product yields has led to development of advanced biomass pyrolysis processes. The accumulation of considerable experimental data on these parameters has resulted in advanced pyrolysis methods for the direct thermal conversion of biomass to liquid fuels and various chemicals in higher yields than those obtained by the traditional long-residence-time pyrolysis methods. Thermal conversion processes have also been developed for producing high yields of charcoals from biomass. 

Correct estimation of the kinetic constants is essential in optimising process parameters for maximizing liquids production. Nevertheless, kinetic data does not contribute any predictive powers aiming to optimise yields of specific chemicals or... 

Some regularities describing the influence of co-pyrolysis process operating parameters, nature of wood biomass and plastics on the yield and composition of liquid products were established and discussed. Obtained data indicate that the optimum ten erature of biomass/plastic mixtures conversion which corresponds to the maximum yield of liquids is 390-400 C. 

In wood pyrolysis, it is known that several parameters influence the yield of pyrolytic oil and its composition. Among these parameters, wood composition, heating rate, pressure, moisture content, presence of catalyst, particle size and combined effects of these variables are known to be important. The thermal degradation of wood starts with free water evaporation. This endothermic process takes place at 120 to 150 C, followed by several exothermic reactions at 200 to 250°C, 280 to 320 C, and around 400 C, corresponding to the thermal degradation of hemicelluloses, cellulose, and lignin respectively. In addition to the extractives, the biomass pyrolytic liquid product represents a proportional combination of pyrolysates from cellulose, hemicelluloses. 

For any particular coal, the distribution of carbon, hydrogen, and oxygen in the coke is decreased as the temperature of the carbonization is increased. In addition, the yield of gases increases with the carbonization temperature while the yield of the solid (char, coke) product decreases. The yields of tar and low-molecular-weight liquids are to some extent variable but are greatly dependent on the process parameters, especially temperature (Table 13.1 and Figure 13.1), as well as the type of coal employed (Cannon et al., 1944 Davis, 1945 Poutsma, 1987 Ladner, 1988 Wanzl, 1988). 

Finally, some mention should also be made here of the process parameters insofar as maximizing the yield of liquid products requires a careful balance between tanperature, pressure, heat-up time, and residence time of any particular coal particle in the reactor as well as the addition of an appropriate catalyst (Whitehurst et al., 1980). In general, a short residence in the reactor hot zone is more conducive to higher liquid yields, especially in the presence of a hydrogen-enriched solvent (Longanbach, 1981). 

The composition and relative amounts of the products formed are dependent on process parameters such as heating rate, pressure, coal type coal (and product) residence time, coal particle size, and reactor configuration. A major disadvantage of this type of process is the large yields of char (Table 18.2) that markedly reduce the yield of liquid products. 

Later, a few small plants were built, the process parameters for which were, apparently, quite different. According to [262], the process occurred without catalyst. In this case, natural gas containing 25% ethane yielded a liquid product containing 35% methanol, 20% formaldehyde, 5% acetaldehyde, and some amounts of acetone and dimethyl acetal. According to [263], 1 m of natural gas containing 60% methane (the rest, propane and butane) was... 

The basis and various parameters for the economic analysis are given in Table II. The overall column efficiency used was obtained from a plot of efficiency vs. the product of relative volatility and liquid viscosity (9), corrected to match predicted (10) data for the propane-propylene system. The value from the plot (9) was increased by a factor required to make the efficiency of the propane-propylene binary distillation equal to 100%. Costs were calculated by the Venture Analysis method (II), because this method yields the appropriate weighting factors for the fixed and operating costs in order to calculate the total costs. Results are expressed as annual costs, before taxes. The important process variables are discussed below. 

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