Yields Of Desired Products Research Articles

Evaluation of batch and semi-batch reactor operation for enzymatic reactions with inhibitory kinetics

Two enzymatic reaction sequences in which one of the intermediate products is the desired one were examined under conditions of batch and semi-batch reactor operation. Semi-batch operation involves a non-instantaneous filling phase during which reaction also occurs. The kinetics were assumed to involve substrate inhibition. The effect of various operating parameters -feeding rate, reactant concentration in the feed-stream, and minimum to maximum volume of reactor contents- on the performance of semi-batch operation was examined. It was found that operating parameters can be optimally selected in order to maximize the yield of the desired product. Semi-batch operation under optimal conditions was found to be superior to batch operation on the basis of desired product yield. Implications of the results for waste minimization in pharmaceutical and specialty chemicals production are discussed.

Catalytic Cycles and Selectivity of Hydrocarbon Cracking on Y-Zeolite-Based Catalysts

Environmental concerns have created the need for selective catalysts that increase the yield of desirable products (e.g., isobutylene from hydrocarbon cracking units) or reduce the production of polluting byproducts. The development of selective catalysts may be facilitated by understanding the chemical factors controlling the rates of the various catalytic cycles available to the reactants and products. The authors have developed a kinetic model based on carbenium and carbonium ion surface chemistry for isobutane cracking and extended it to 2-methylhexane cracking over USY-based catalysts. Catalytic cycles for isobutane cracking that include initiation reactions lead to olefin production, while cycles that include hydride ion transfer reactions lead to paraffin production. The overall chemistry of the major catalytic cycles is the same for isobutane and 2-methylhexane cracking, although additional reaction pathways are available for the larger 2-methylhexane molecule. Paraffins and olefins with three or more carbon atoms can be produced from 2-methylhexane by cycles that include both initiation and hydride ion transfer reactions and the paraffin to olefin ratio cannot be greater than 1. By allowing one to build catalytic cycles, such models help identify similarities and differences in reactivity patterns for various reactants.

Direct catalytic conversion of methane

AbstractProcesses are being developed for the direct catalytic oxidative conversion of methane to higher hydrocarbons and oxygenates. The role of the catalyst in generating methyl radicals is established, and subsequent gas‐phase reactions are well understood. However, the role of several catalyst surface species remains a subject of interest. Application of present process technology using the most promising catalysts shows that direct methane conversion is not yet competitive with conventional processes. Increased yields of desirable products using new process configurations are required to obtain an economically viable process.

Pressure effects on steam pyrolysis of coal

Volatiles produced when pulverized coal is subject to very rapid temperature rise (∼ 10 5Ks −1) can be twice as great as indicated by ASTM methods. The volatiles are released in a matter of milliseconds and, if allowed to react with background steam over tens of milliseconds, they reach an equilibrium condition with the products consisting primarily of carbon monoxide, carbon dioxide, hydrogen, and water. Rapid pyrolysis reactions will likely find application in indirect processes. Such processes (e.g., the synthesis of methanol from syngas) generally operate at pressures of 30 to 35 atmospheres, and it is recognized that operation of the gasification section of the plant at elevated pressures would save downstream compression costs. High-heating-rate, high-temperature (1600–2400 K) devolatilization experiments are carried out in a 10 liter batch reactor which serves to pyrolyze a suspension of pulverized coal in a mixture of steam and nitrogen. The high heating rate of coal particles is achieved by igniting a stoichiometric mixture of hydrogen and oxygen in nitrogen diluent. A rapid quench sampling system, designed to accept gas and particle sample from the reactor interior for a short interval (∼4 ms), at a prescribed time after initiation of reaction, is used to obtain transient reaction data. At 2400 K, steam to carbon molar ratio of 2 and reaction times greater than 100 ms, an increase in pressure from 4 bar to 45 bar is found to have a small positive effect on the coal carbon conversion. The yields of carbon monoxide and hydrogen increase correspondingly. The carbon dioxide yield is independent of pressure. From economic considerations these results are of direct importance as an increase in pressure increases the yields of desirable products (carbon monoxide and hydrogen), without affecting the yield of the undesirable product (carbon dioxide).

Kinetics and mechanism of Moroccan oil shale solubilization in toluene

Unlike coal, for which solvent liquefaction dates back to the beginning of this century, treatment of oil shale using various solvents has received attention only in recent years as an alternative process to producing liquid fuels by retorting. Solvent extraction offers the promise of overcoming the relatively low yields of desirable products obtained and the high energy expenditures required in pyrolysis. The present study was undertaken to investigate the solubilization of a Moroccan oil shale at 300{degree}C and 3000 psig in toluene. In this case the extent of solubilization was measured in terms of tetrahydrofuran extractables at refluxing conditions. Analyses of the soluble material produced were obtained by gel permeation chromatography and proton NMR since these provide valuable information for mechanistic interpretations.

Kennzeichnende Verfahrens‐ und Einflußgrößen beim katalytischen Fließbett‐Cracken

AbstractCharacteristic process parameters and variables in catalytic fluidized bed cracking. Catalytic fluidized‐bed cracking occupies a distinctive position among the various conversion processes. With regard to its favorable product range, the process is characterized by low processing costs coupled with flexibility of raw materials. A number of independent process parameters are available for control of the reactions involved in catalytic cracking and for influencing the product range. The cracking reactions taking place and the interplay of the independent and dependent variables are described. Apart from the actual cracking process, particular importance attaches to the regeneration of the catalyst charged with coke since it has a decisive influence on the thermal economy of the plant. Depending upon the desired product yield or the raw materials a suitable catalyst must be chosen. Considerable progress has recently been made in catalyst development.