Extraction crystallization

Type of process Operating temperature, °C Extraction Crystal conversion Acid concentration, % P3O3 Acid impurity level vs dihydrate acid P3O3 recovery, %... 

Isolate. A relatively pure chemical produced from natural raw materials by physical means, eg, distillation, extraction, crystallization, etc, and therefore natural or by chemical means, ie, via hydrolysis, bisulfite addition products, and regeneration, etc, and therefore artificial by 1993 U.S. labeling regulations. 

The USP/FCC grade of benzoic acid is usually produced by extraction and crystalliza tion, although distillation has also been used. In the extraction—crystallization process, toluene, water, and methanol have all been used and each is capable of producing a high quaUty benzoic acid product. 

The oil that remains when the solvent is removed from the extract crystallizes when cooled lo mom temperature. I his orange solid is rccrystallized from 150 ml. of hexane (Note 1) to yield... 

Dye, S.R. and Ng, K.M., 1995. Bypassing eutectics with extractive crystallization design alternatives and tradeoffs. American Institute of Chemical Engineers Journal, 41, 1456. 

In some cases we may benefit from using an external agent to carry out the desired separation through crystallization. Thus, in the case of isomeric and non-isomeric mixtures of close-boiling acidic or basic materials we may use a suitable base or acid to carry out dissociative extractive crystallization, akin to dissociative extraction referred to in Section 4.2.1. For instance, for a mixture of p- and m-cresol or p-cresol and 2,6-xylenol we may use a base like anhydrous piperazine to obtain a precipitate of relatively pure p-cresol salt of piperazine, which can then be filtered and subjected to recovery of piperazine for recycle. Similarly, we may add a substance which forms an adduct with the desired substance. 

An alternative to extraction crystallization is used to obtain a desired enantiomer after asymmetric hydrolysis by Evonik Industries. In such a way, L-amino acids for infusion solutions or as intermediates for pharmaceuticals are prepared [35,36]. For example, non-proteinogenic amino acids like L-norvaline or L-norleucine are possible products. The racemic A-acteyl-amino acid is converted by acylase 1 from Aspergillus oryzae to yield the enantiopure L-amino acid, acetic acid and the unconverted substrate (Figure 4.7). The product recovery is achieved by crystallization, benefiting from the low solubility of the product. The product mixture is filtrated by an ultrafiltration membrane and the unconverted acetyl-amino acid is reracemized in a subsequent step. The product yield is 80% and the enantiomeric excess 99.5%. 

Robustness of the process. Many transition metal-catalyzed reactions function well at the laboratory scale, but on scaling up substrate and product inhibition may be an issue, and sensitivity to impurities may also become apparent. Increasing the SCR, which is often necessary for the economics of the process, also increases the impurity catalyst ratio. It is also very important to keep the number of components to a minimum, as extraction, crystallization and distillation are the only economic means of purification. Ligands can be a nuisance in this respect, particularly if they are used in amounts over 5 mol%. Reproducibility also is a stringent requirement. Thus, possible inhibition mechanisms should be recognized in order to avoid unwanted surprises during production. 

This chapter is organized in 6 sections. Section 2 describes the geometry of (CBED). Section 3 covers the theory of electron diffraction and the principles for simulation using the Bloch wave method. Section 4 introduces the experimental aspect of quantitative CBED including diffraction intensity recording and quantification and the refinement technique for extracting crystal stmctural information. Application examples and conclusions are given in section 5 and 6. 

The insoluble calcium sulfate slurry is filtered out. Acid from this wet process is impure but can be purified by various methods. Purification steps involve precipitation, solvent extraction, crystallization, and ion exchange techniques. 

Marsh (1988), Cashman and Marsh (1988), and Cashman and Ferry (1988) investigated the application of crystal size distribution (CSD) theory (Randolph and Larson, 1971) to extract crystal growth rate and nucleation density. The following summary is based on the work of Marsh (1988). In the CSD method, the crystal population density, n(L), is defined as the number of crystals of a given size L per unit volume of rock. The cumulative distribution function N(L) is defined as... 

Thus the addition of n-pentane to mixtures of p-xylene and m-xyiene permits complete separation of the xylenes which form a binary eutectic with 11.8% para. Without the n-pentane, much para is lost in the eutectic, and none of the meta is recoverable in pure form. A detailed description of this process is given by Dale (1981), who calls it extractive crystallization. Other separation processes depend on the formation of high melting molecular compounds or clathrates with one of the constituents of the mixture. One example is carbon tetrachloride that forms a compound with p-xylene and alters the equilibrium so that its separation from m-xylene is... 

D-PL complex t [ Extraction of V (resolving agent/ J-D-PA — Lactonization Extraction Crystallization, ... 

Somewhat similar are the so-called adductive crystallization processes, often (wrongly) called extractive crystallization, where reactions of complex/ adduct formation are used to separate compounds that are otherwise difficult to separate. Examples of adductive crystallization include separation of p- and m-cresols (137), separation of o- and p - n i troch I oro ben zcn cs (138), separation of quinaldine and isoquinoline (139), separation of nonaromatic compounds from naphtha-cracking raffinate (140), and separation of p-cresol from 2,6-xylenol (141). Other examples of reactive crystallization/precipitation reported in the literature are listed in Table 5. 

Separation of Close Boiling Isomers by Adductive and Extractive Crystallization, AIChE Symp. Ser. No. 143, 1976, 72, 95. 

Lavoisier s quantitative method was crucial to the creation and to the success of the chemical revolution. Chemistry, however, is a science of qualities as well as of quantities. Chemical analysis has to be qualitative as well as quantitative. Chemists need to know what substances they are dealing with, as well as how much of each of those substances is present. Lavoisier recognized the importance of traditional operations for separating substances that were mixed rather than combined, including solvent extraction, crystallization, and fractional distillation (where substances with different boiling points are distilled at those different temperatures from a mixture). 

Perform difficult zeotropic separations later, but before azeotropic separations. Examine other options, such as extractive distillation, L-L extraction, crystallization, adsorption, or molecular sieves. 

Explain in your own words the terms separation process, distillation, absorption, scrubbing, liquid extraction, crystallization, adsorption, and leaching. (What are they and how do they work )... 

Simulate the separation processes of distillation, extraction, crystallization, and absorption. 

Many different processes are now in use in engineering practice, e.g. distillation, extraction, crystallization, freezing, etc. However, these were far less successful when applied to the disposal of wastewater or to the recirculation of the components from the wastewater stream. A real prerequisite to facilitate the introduction of no-waste technologies is the use of membrane separation. 

Purification is achieved via chemical precipitation, solvent extraction, crystallization, or ion exchange. 

Extraction-crystallization Extraction often is used in association with a crystallization operation. In the pharmaceutical and specialty chemical industries, extraction is used to recover a product compound (or remove impurities) from a crude reaction mixture, with subsequent crystallization of the product from the extract (or from the preextracted reaction mixture). In many of these applications, the product needs to be delivered as a pure crystalline solid, so crystallization is a necessary... 

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