Reaction, greenness energy consumption

Keywords Green chemistry alternative feedstocks benign reagents catalytic synthetic pathways natural processes biocatalysis alternative solvents safer chemicals alternative reaction conditions minimization of energy consumption... 

Principle 9 Increase energy efficiency. Since energy consumption always has some concomitant and negative side effect for the local and/or global environment, the reduction of energy is always a desired component of a green approach to any process. Beyond that, running reactions at milder or ambient temperatures and low or lower pressure is inherently safer since the likelihood and severity of accidents and fires will be reduced. The use of catalysts (which is also favored in Principle 5) often allows reactions to be run at milder conditions. 

The development of new MCRs under solvent-free conditions has emerged as an attractive alternative to conventional syntheses in the recent years. The main advantages of solvent-free processes are cost savings, decreased energy consumption, and reduced reaction times. The E factor is a measure of the greenness of a chemical process and is defined as the ratio of the weight of waste to the weight of product. One of the best ways to reduce the E factor of the reactions and their effect on the environment is to carry out the reactions under solvent-free conditions because the best solvent is no solvent. 

Catalysts are very important in green chemistry. One reason that this is so is because catalysts enable reactions to be carried out very specifically. Also, the right catalyst can enable reactions to occur with relatively less energy consumption and at relatively lower temperatures. 

The difference in energy consumption between put-and-take distillation and the membrane setup is difficult to estimate. Both technologies result in waste streams that require further treatment. Moreover, the required pressure for the membrane setup is hard to define on the base of pilot-scale experiments. It is, however, clear that the membrane setup shows a much lower mass intensity than the distillation. Mass intensity is a commonly used concept in the context of green energy and is defined as the ratio of the total mass of the reactants and the mass of the reaction products (Curzons et al., 2001). Solvent exchange by distillation typically shows a mass intensity of 5-10 kg/kg, whereas the use of membrane technology results in a value of 2-3 kg/kg. Both values are vahd for a 95% exchange, which is often the required value in industrial apphcations. 

In many cases, from the perspective of chemistry, it is difficult to understand the results of enzymatic reactions. For example, it seems strange that only one enantiomer in a racemic compound reacts in an enzymatic reaction if we do not understand the specific interactions between the enzyme and the substrate at the molecular level. The special compositions and structures of biomacromolecules endow enzymes with special functions. A typical, well-modulated biotransformation is usually considered to be a green process. It is estimated that biocatalysis technologies will decrease consumption of raw materials, water resources, and energy, and reduce waste emissions by 30% in 2020. ... 

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