Waste-minimized reactions

Reduced Emissions and Waste Minimization. Reducing harmful emissions and minimizing wastes within a process by inclusion of additional reaction and separation steps and catalyst modification may be substantially better than end-of-pipe cleanup or even simply improving maintenance, housekeeping, and process control practices. SO2 and NO reduction to their elemental products in fluid catalytic cracking units exemplifies the use of such a strategy (11). 

Gopatakrishnan, M., Ramdoss, P., and EI-Halwagi, M. (1996). Integrated design of reaction and separation systems for waste minimization. AIChE Annu. Meet., Chicago. 

Miniaturization might also be used in the distributed production of chemicals. Two examples include the safe production of hydrogen peroxide from hydrogen and oxygen or the production of chemicals or fuels from synthesis gas. More detailed study into the potential improvements in product yields, waste minimization, and costs are required to fully understand the impact of miniaturization. At this time it offers the potential to produce hazardous materials or conduct potentially dangerous oxidation reactions on a small scale that is inherently safer. 

The environmentally benign, nontoxic, and nonflammable fluids water and carbon dioxide (C02) are the two most abundant and inexpensive solvents on Earth. Water-in-C02 (w/c) or C02-in-water (c/w) dispersions in the form of microemulsions and emulsions offer new possibilities in waste minimization for the replacement of organic solvents in separations, reactions, and materials formation processes. Whereas the solvent strength of C02 is limited, these dispersions have the ability to function as a universal solvent medium by solubilizing high concentrations of polar, ionic, and nonpolar molecules within their dispersed and continuous phases. These emulsions may be phase-separated easily for product recovery (unlike the case for conventional emulsions) simply by depressurization. 

Smith K, Fry CV, Tzimas M, The use of solid supports and supported reagents in liquid phase organic reactions, in Chem. Waste Minimization (Ed. J.H. Clark), pp. 86-115, 1995, Blackie, Glasgow, UK. 

Having addressed issues related to the overall flowsheet and the reaction system, attention is now focused on the separation systems. Separation systems offer considerable scope for waste minimization. They can be generally classified into the following categories. 

Electrolytic treatment technologies have definite advantages over these more common treatment processes. The primary benefit is that chemical change in an electrochemical process is brought about by the ability to add or remove electrons from species to be treated. This eliminates the use of redox agents to treat wastes and also removes the need to treat spent redox streams. Other, equally important, benefits of electrochemical processes include close control of reactions through control of the applied potential or current lower operating temperatures and hence lower costs increased possibility of on-site treatment, especially in small-scale use possible simultaneous use of the anode and cathode for waste minimization and the ability to... 

The reaction specificity associated with enzymes reinforces the benefit of waste minimization due to their inherent ability to produce a homoge-... 

This charge separation is of paramount importance. The key problem is maintaining the charge separation, which involves minimization of the energy-wasting back reaction. Reaction centers contain an ordered array of secondary electron acceptors (Ai, A2, A3 ) that optimize the AG° that occurs at each step ... 

Senkan, S. M., Kinetic models to predict and control minor constituents in process reactions. In Industrial Environmental Chemistry Waste Minimization in Industrial Processes and Remediation of Hazardous Waste (D. T. Sawyer and A. E. Martell, eds.), p. 45. Plenum, New York, 1992. 

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