Aqueous processing unit operations

The separation method targets recovery of the aqueous phase from oil/water mixtures of microbial reactions by filtration through a ceramic filter module [154], The invention particularly referred to a two-phase system resulting from a process used for production of 2,6-naphthalenedicarboxylic acid using S. paucimobilis AK2M16 (PERM P-13996). The aqueous phase is said to be recovered free of microbial cells and oil. Although, it is mentioned that the reaction product can be recovered readily in high yield, the need for an additional unit operation looks obvious. 

Some of the types of equilibria involved in the unit operations separation and concentration are listed in the introduction, Section 9.17.1. Those which depend most on coordination chemistry, and for which details of metal complex formation are best understood, are associated with hydrometallurgy. Once the metal values have been transferred to an aqueous solution, the separation from other metals and concentration can be achieved by one of the following processes.3... 

The previous chapters have demonstrated that liquid-liquid extraction is a mass transfer unit operation involving two liquid phases, the raffinate and the extract phase, which have very small mutual solubihty. Let us assume that the raffinate phase is wastewater from a coke plant polluted with phenol. To separate the phenol from the water, there must be close contact with the extract phase, toluene in this case. Water and toluene are not mutually soluble, but toluene is a better solvent for phenol and can extract it from water. Thus, toluene and phenol together are the extract phase. If the solvent reacts with the extracted substance during the extraction, the whole process is called reactive extraction. The reaction is usually used to alter the properties of inorganic cations and anions so they can be extracted from an aqueous solution into the nonpolar organic phase. The mechanisms for these reactions involve ion pah-formation, solvation of an ionic compound, or formation of covalent metal-extractant complexes (see Chapters 3 and 4). Often formation of these new species is a slow process and, in many cases, it is not possible to use columns for this type of extraction mixer-settlers are used instead (Chapter 8). 

As shown in Figure 14.3, this process involved thirteen unit operations. Apart from colloidal iodate/manganate waste, significant aqueous waste was also generated. Additionally, the usage of multiple solvents (t-butanol, dichloromethane, water, and petroleum ether) in the reaction and isolation makes the synthesis, presented in Scheme 14.11, less attractive and more eco-unfriendly. 

Conventional liquid-liquid extraction is an established unit operation for transferring one or more solutes from a solution into a second, immiscible liquid. It is widely used for separating ionic and nonionic species, for example, on the basis of their preferential partitioning between an aqueous phase and a nonaqueous phase, respectively. Industrial liquid-liquid extraction equipment generally consists of a mixer, where the feed solution and the extractant liquid are intimately mixed via agitation, and a settler where the equilibrated phases are separated for further processing. 

This production expansion was made possible in no small degree by a sharp reduction in the cost of manufacture. From an original market price of 1.45 a pound in 1926, cellulose acetate dropped steadily to. 50 a pound in 1936, and further to. 30 in 1940. In addition to a lower cost as a result of the increasing quantity of production, these reductions in price were aided greatly by reductions in the cost of raw materials. Acetic acid became much cheaper during this period, and the cost of conversion of the acid to its anhydride was aided by improved process development. Recovery of acetic acid from aqueous solution also became cheaper with the adoption of extraction and azeotropic distillation processes, replacing the original recovery by evaporation of neutralized solutions. In addition, technical developments in the acetylation process increased the economy of plant unit operations. 

Effective utilization of biomass for value-added chemical product synthesis will require development of new applications of important unit operations. Carbohydrate recovery from the biomass is the key near-term application for production of commodity chemicals. Protein recovery will continue to have an important niche market in tlie purified form as food and a larger low-value market in the crude form as animal feed. Important processing information for carbohydrate depolymerization can be found in the literature from biochemical conversion of biomass. New process applications of separation technologies are just now being developed and refined for use with biomass-derived carbohydrate and protein streams. The use of an aqueous processing environment for carbohydrates will require careful consideration of the differences that type of environment entails, such as the effect on catalyst formulations. 

Before proceeding to outline specific processes it is as well to explain some terms which commonly arise when describing ion exchange unit operations. A sound basis is afforded by the column process represented in general terms by Figure 7.1 where, by way of example, it is required to remove cations and D from an aqueous solution... 

Ligands and complex catalysts derived therefrom may catalyze reactions under circumstances which require aqueous or mild conditions, such as bioorganic substrates (bioorganometallic conversions cf. Section 3.3.10.2). However, the great advantage of water-soluble catalysts is that they overcome the basic problem of homogeneously catalyzed processes the separation of the product phase from the (molecular) catalyst itself, which is soluble in it. The unit operations necessary to achieve this usually include thermal operations such as distillation, decomposition, transformation, and rectification, process steps which normally cause thermal... 

Bearing this in mind, this chapter summarizes the unit operations employed in aqueous processing, emphasizing their underlying principles. The goal is to provide the information needed to modify these unit operations for different types of solutions, and to achieve appropriate water-quality objectives. 

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