Chemical processes, factors influencing design

The rate of a chemical reaction is influenced by pressure, temperature, concentration of reactants, kinetic factors such as agitation, and the presence of a catalyst. Since the viability of a plant depends not only on reaction efficiencies but also on the capital cost factor and the cost of maintenance, it may be more economic to alter a process variable in order that a less expensive material of construction can be used. The flexibility which the process designer has in this respect depends on how sensitive the reaction efficiency is to a change in the variable of concern to the materials engineer. 

The fourth aspect is related to development of more efficient reaction media or catalysts. The dream of a chemist is to be able to induce a chemical transformation to take place quickly, efficiently, selectively, and with good specificity. Computational studies of reactions in solution allow us to understand the factors that influence reactivity and enable us to design new catalysts or solvent media with better properties. Because continuum models are fast, easy to use, and often reliable, they may be chosen for theoretical studies aimed at the development of catalysts or chemical processes. 

In chemical engineering, as well as in other scientific and technical domains, where one or more materials are physically or chemically transformed, a process is represented in its abstract form as in Fig. 1.1(a). The global process could be characterized by considering the inputs and outputs. As input variables (also called independent process variables , process command variables , process factors or simple factors ), we have deterministic and random components. From a physical viewpoint, these variables concern materials, energy and state parameters, and of these, the most commonly used are pressure and temperature. The deterministic process input variables, contain all the process variables that strongly influence the process exits and that can be measured and controlled so as to obtain a designed process output. 

A chemical process is a combination of a chemical substance transition and a technical apparatus. The main factors which are influenced by thermodynamics, kinetics and design properties of the apparatus can be combined in three characteristic numbers. These are ... 

PTC is now an established branch of catalysis, and applications for it are found in the laboratory as well as in large-scale processes. The design of PTC systems able to work in the absence of common volatile organic solvents is a promising field of research that deserves investigation in order to better understand manifold factors (solubility of the catalyst, formation of new phases, influence of the reactants on the physical state of the bulk fluid, etc.) that could influence the outcome of the reaction. However, as shown by the examples discussed here, the combined utilization of PTC and nontraditional reaction media affords new opportunities for improving numerous chemical processes while reducing emissions to the environment. 

The subjects of catalytic science include catalysis (cataljAic phenomena and principle) catalyst (composition, structure, performance and manufacturing method and principle) catalytic reaction kinetics (chemical kinetics and mechanism) as well as cataljAic reaction engineering (apparent kinetics inclucing transport process and reaction process and reactor design) etc. The main tasks of catalytic science are to elucidate the nature of catalytic active sites, the function of catalyst and reaction mechanism to explore the main factors influencing activity, selectivity and stabihty of catalyst to accumulate acknowledge for the exploitation and development of chemical catalysis and to open up its relatively new disciplines — bionic catalysis, photo catalysis, electro catalysis and photoelectric catalysis — to indicate... 

Silica compounds are generally processed in conventional internal mixers, preferably with intermeshing rotors. These mixers are designed and optimized for carbon black-fiUed compounds in which mixing is based only on physical processes. When a silica-silane reinforcing system is used, additionally a chemical reaction, the sUanization, occurs. One of the main influencing factors of the silanization reaction is the concentration of ethanol in the compound as well as in the mixer [25,26]. As the silanization finally reaches an equilibrium, low concentrations of ethanol in the compound are expected to enhance the reaction rate. 

Ultrasound can thus be used to enhance kinetics, flow, and mass and heat transfer. The overall results are that organic synthetic reactions show increased rate (sometimes even from hours to minutes, up to 25 times faster), and/or increased yield (tens of percentages, sometimes even starting from 0% yield in nonsonicated conditions). In multiphase systems, gas-liquid and solid-liquid mass transfer has been observed to increase by 5- and 20-fold, respectively [35]. Membrane fluxes have been enhanced by up to a factor of 8 [56]. Despite these results, use of acoustics, and ultrasound in particular, in chemical industry is mainly limited to the fields of cleaning and decontamination [55]. One of the main barriers to industrial application of sonochemical processes is control and scale-up of ultrasound concepts into operable processes. Therefore, a better understanding is required of the relation between a cavitation coUapse and chemical reactivity, as weU as a better understanding and reproducibility of the influence of various design and operational parameters on the cavitation process. Also, rehable mathematical models and scale-up procedures need to be developed [35, 54, 55]. 

Apart from patient-specific parameters, external factors - most importantly the concomitant uptake of certain other chemicals present in diet, environment and especially other drugs - influence drug actions. Possible effects are manifold and can affect all stages of pharmacokinetic and pharmacodynamic processes in the body. Also direct interaction and inactivation of concomitantly administered substances are possible. Drug-drug interactions via modulation of metabolism present a very hot topic in pharmaceutical research and drug design. 

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