Costs separation processes

Exposure of the reaction mixture to reduced carbon monoxide pressure in the flash-tank has implications for catalyst stability. Since the metal catalyst exists principally as iodocarbonyl complexes (e.g. [Rh(CO)2l2] and [Rh(CO)2l4]" for the Rh system), loss of CO ligands and precipitation of insoluble metal species (e.g. Rhl3) can be problematic. It is found that catalyst solubility is enhanced at high water concentrations but this results in a more costly separation process to dry the product. The presence of water also results in occurrence of the water gas shift (WGS) reaction (Eq. 6), which can be catalysed by Rh and Ir iodocarbonyls, in competition with the desired carbonylation process, resulting in a lower utilisation of CO ... 

Because commercial synthetic thermoplastic polymers are either addition polymers or condensation polymers, depolymerization occurs by different routes. Addition polymers, for which the synthesis reactions are essentially not reversible, depolymerize by pyrolysis or such severe chemical attack that few useful monomers can be practically recovered. With pyrolysis, a wide spectrum of species are created, which offers little in the way of valuable reaction products without costly separation processes. The overall yield to desired products can be unattractively low. 

The economic feasibility of a bioreaction process clearly depends on the characteristics of the associated bioseparation process, especially in the usual case when the product is present at low concentration in a complex mixture. For example, the existence of an extremely efficient and low-cost separation process for a particular compound could significantly lower the final concentration of that compound required in the bioreactor to achieve a satisfactory overall process. After noting that special approaches and processes are needed for efficient recovery of small molecules (ethanol, amino acids, antibiotics, etc.) from the dilute aqueous product streams of current bioreactors, I shall discuss further only separations of proteins. These are the primary products of the new biotechnology industry, and their purification hinges on the special properties of these biological macromolecules. 

Chromatographic separations are costly separation processes if carried out for production of a substance. Therefore, chromatography is only applied for substances of high value. 

The cost of recovery of sucdnic add will be of prime importance in determining whether a cost-effective process will allow succinate-derived chemicals to compete with petrochemicals. Most succinate fermentations need to be run at or near a neutral pH and require the addition of a salt to maintain pH. Removal of the salt to achieve the isolation of the desired add is one of the challenges of developing a low-cost separation process. Various approaches toward the recovery of organic adds have been tried, but it is beyond the scope of this chapter to review organic acid separation technology. Some work has focused specifically on succinic acid and that is what will be covered here. 

Plastic wastes are often contaminated with paper. Klason et al. present an industrial method of reprocessing paper-contaminated plastic waste which does not require a difficult and costly separation process. Instead, cellulose from paper is converted to a filler. The method and equipment suggested allow for excellent dispersion of in situ formed filler. 

This technique uses starting materials that are themselves optically active and in the same orientation as the desired product. These are often naturally occurring compounds such as carbohydrates or L-amino acids. The biochemist will choose from this chiral pool . The synthetic route is designed to keep any intermediates and the final product formed in the same enantiomeric form. As a result, there is no need to carry out the costly separation process needed when a racemic mixture is produced. 

Nearly every chemical manufacturiag operation requites the use of separation processes to recover and purify the desired product. In most circumstances, the efficiency of the separation process has a significant impact on both the quality and the cost of the product (1). Liquid-phase adsorption has long been used for the removal of contaminants present at low concentrations in process streams. In most cases, the objective is to remove a specific feed component alternatively, the contaminants are not well defined, and the objective is the improvement of feed quality defined by color, taste, odor, and storage stability (2-5) (see Wastes, industrial Water, industrial watertreati nt). 

DifficultSepa.ra.tions, Difficult separations, characterized by separation factors in the range 0.95 to 1.05, are frequentiy expensive because these involve high operating costs. Such processes can be made economically feasible by reducing the solvent recovery load (260) this approach is effective, for example, in the separation of m- and -cresol, Hnoleic and abietic components of tall oil (qv), and the production of heavy water (see Deuteriumand TRITIUM, deuterium). 

Separation Processes. Separation of the catalyst from the products is a significant expense the process flow diagram and the processing cost are often dominated by the separations. Many soluble catalysts are expensive, eg, rhodium complexes, and must be recovered and recycled with high efficiency. The most common separation devices are distiUation columns extraction is also appHed. 

Equipment Costs. Equipment costs include the purchased cost of process and materials handling equipment, storage faciUties, waste treatment equipment, stmctures, and site service faciUties. Installation costs such as insulation, piping, painting and finishing, foundations, process stmctures, instmmentation, and electrical service connections are estimated or factored separately. Actual quoted prices from suppHers are the best data, but these are not usually available when estimates are made. The quick, inexpensive cost estimates are based largely on personal cost files, internal company cost data, or pubUshed cost correlations. 

When investigating the suitability of a particular resin-bound separations process, the following factors are often important (i) resin consumption (ii) solvent usage (iii) productivity-chemical, optical and volume yields (iv) total number of separations steps and (v) capital costs. For any particular process, these factors differ in their relative importance. However, when evaluating a new separations method it is useful to examine each of these factors. The nonchromatographic separation method... 

The criteria which would be most desirable for industrial application of a separation process involving a supercritical gas may be established by comparing Figs. 3IB, 3ID, and 32. The largest cost in such a process is likely to be that of gas compression. Therefore, the maximum separation possible of the two solvents should occur for the addition of a given amount of gas, and the total pressure required to dissolve this gas should be small. This is the case if the tie lines slope toward the 1-3 binary line and if the gas is readily soluble. In terms of the Margules parameters and Henry s constant, these favorable criteria are ... 

Many of the waste streams from U.S. process industries are water containing small quantities of metal ions that the law requires be removed before the wastewater is disposed of There is an economic incentive to recoup at least some of the cost of wastewater treatment by recovering and selling the metal content instead of merely disposing of the metals as sludge. Because the waste streams are dilute in desired materials, research is needed to devise efficient extraction and separation processes. 

Likewise, fly ash from power plant combustors often contains small amounts of metals or their oxides, which require costly disposal in the ever-shrinking number of approved hazardous waste landfills. Thus, there are economic incentives to recover the metal values as well as to reduce the costs of ultimate disposal. Here, too, the metal content is low, and research is needed to develop economical separation processes. In principle, advances in this area could be translated into recovery of metal values from mine tailings. 

FIGURE 6.13 The importance of separation processes in determining the eventual cost of materials and products is illustrated in this figure. Product prices correlate with the degree of dilution of the raw material in the matrix from whieh it must be isolated. A factor of two in product price is shown in the figure. Courtesy, Norman N. Li, Allied-... 

---