Separation processes environmental impact

There is a real opportunity to reduce biodiesel production costs and environmental impact by applying modem catalyst technology, which will allow increased process flexibility to incorporate the use of low-cost high-FFA feedstock, and reduce water and energy requirement. Solid catalysts such as synthetic polymeric catalysts, zeolites and superacids like sulfated zirconia and niobic acid have the strong potential to replace liquid acids, eliminating separation, corrosion and environmental problems. Lotero et al. recently published a review that elaborates the importance of solid acids for biodiesel production. ... 

Each product system consists of a variable number of processes involved in the product life cycle. However, the product under consideration is often related to other processes that may no longer be important for the LCA study. The system boundary serves to the separation of essential and non-essential processes of the product life cycle. Since the choice of system boundaries significantly affects LCA study outcomes and in addition, its intensity and complexity, system boundaries should always be well considered and clearly defined. The choice of system boundaries is carried out with regard to the studied processes, studied environmental impacts and selected complexity of the study. Not-including any life cycle stages, processes or data must be logically reasoned and clearly explained [32]. 

The catalysts that come closest to meeting these requirements are enzymes, but in general, the products of biological process are not separated from the medium in which they are formed, rather being used in situ. The demand for high selectivity and low environmental impact suggests that there will be a desire to commercialise more... 

The Vision 21 program is focused on new concepts for coal-based energy production where modular plants could be configured to produce a variety of fuels and chemicals depending on market needs with virtually no environmental impact outside the plant s footprint. Membranes would be used to separate oxygen from air for the gasification process and to separate hydrogen and carbon dioxide from coal gas. 

The esterification by-product, water, is removed via a process column in a continuous steady-state mode of operation. The bottom product of the column, being mainly EG, flows back into the esterification reactor. The condensed top product consists mainly of water with small traces of EG. In cases where a reverse-osmosis unit is connected to the distillate flow line, the residual EG can be separated very efficiently from the water [124], The combination of a process column with reverse osmosis saves energy cost and capital investment. The total organic carbon (TOC) value of the permeate is sufficiently low to allow its discharge into a river or the sea without any environmental impact. 

Recognizing the need for a more economically and environmentally friendly citric acid recovery process, an adsorptive separation process to recover citric acid from fermentation broth was developed by UOP [9-14] using resin adsorbents. No waste gypsum is generated with the adsorption technique. The citric acid product recovered from the Sorbex pilot plant either met or exceeded all specifications, including that for readily carbonizable substances. An analysis of the citric acid product generated from a commercially prepared fermentation broth is shown in Table 6.2, along with typical production specifications. The example sited here is not related to zeolite separation. It is intent to demonstrate the impact of adsorption to other separation processes. 

For a difficult binary separation when the choices of solvent and stationary phase are already optimal, as shown in Figure 12.10a, the only way to obtain a separation with a reasonable yield using a batch process is to increase the levels of both the stationary phase and eluent relative to the amount of product injected. This leads to an increase in both separation costs and environmental impact. 

However, the possibility to integrate various membrane operations in the same process or in combination with conventional separation units, allows, in many cases better performance in terms of product quality, plant compactness, environmental impact, and energy use to be obtained. 

The application of membrane-separation processes in the treatment of wastewater of the leather industry can give a reduction of the environmental impact, a simplification of deaning-up procedures of aqueous effluents, an easy re-use of sludge, a decrease of disposal costs, and a saving of chemicals, water, and energy [22],... 

In this context photocatalytic processes in membrane reactors represent a technology of great scientific interest because they allow chemical reactions and separation process to be obtained in one step, minimizing environmental and economic impacts. 

A very promising method to solve this problem is coupling the photocatalysis with membrane techniques, obtaining a very powerful process with great innovation in water treatment. In fact, membrane processes, thanks to the selective property of the membranes, have been shown to be competitive with the other separation technologies for what concerns material recovery, energy costs, reduction of the environmental impact and selective or total removal of the components [77]. 

Melt crystallization operates with heat as a separating agent, but a crystalline product is not generated in the process. Instead, crystals formed during the operation are remelted and the melt is removed as the product. Such operations are often used to perform the final purification of products after prior separation units for example, the purity of an acrylic acid feed may be increased from 99.5 to 99.9%. Melt crystallizers do not require solids handling units nor do they utilize solid-liquid separation equipment. Finally, in some instances the use of melt crystallization can eliminate the use of solvents, thereby reducing the environmental impact of the process. 

Thermodynamic cost analysis relates the thermodynamic limits of separation systems to finite rate processes, and considers the environmental impact through the depletion of natural resources within the exergy loss concept. Still, economic analysis and thermodynamic analysis approaches may not be parallel. For example, it is estimated that a diabatic column has a lower exergy loss (39%) than that of adiabatic distillation however, this may not lead to a gain in the economic sense, yet it is certainly a gain in the thermodynamic sense. The minimization of entropy production is not always an economic criterion sometimes, existing separation equipment may be modified for an even distribution of forces or an even distribution of entropy production. Thermodynamic analysis requires careful interpretation and application. 

The atom economy of a reaction or process does not take into consideration the actual amount of product obtained in a reaction thus, it does not consider the starting materials left in the reaction mixture that must be separated from the product, or the by-products generated by secondary reactions (see Example 12.1). Several metrics have been proposed to assess the economic and environmental impact of a chemical synthetic pathway (often called... 

Separation processes by and large imply one of the most cost-intensive aspects of a chemical process, and generally have a strong environmental impact due to the type and volume of the separating agents, which are usually discarded as wastes or only partially recycled. There are several solvents that involve few environmental concerns as they are biodegradable and they have little or no toxicity (e.g., water, hexane, acetone, ethyl acetate, ethanol, and methanol). 

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