Refining purification

Solid phase peptide synthesis does not solve all purification problems however Even if every coupling step m the ribonuclease synthesis proceeded in 99% yield the product would be contaminated with many different peptides containing 123 ammo acids 122 ammo acids and so on Thus Memfield and Gutte s six weeks of synthesis was fol lowed by four months spent m purifying the final product The technique has since been refined to the point that yields at the 99% level and greater are achieved with current instrumentation and thousands of peptides and peptide analogs have been prepared by the solid phase method... 

Trona Purification Processes. Two processes, named the monohydrate and sesquicarbonate according to the crystalline intermediates, are used to produce refined soda ash from trona. Both involve the same unit operations only in different sequences. Most ash is made using the monohydrate process. Eigure 2 shows simplified flow diagrams for each. 

Refining. KroU-process hafnium sponge and electrowon hafnium do not meet the performance requirements for the two principal uses of hafnium metal. Eurther purification is accompHshed by the van Arkel-de Boer, ie, iodide bar, process (18) and by electron beam melting. 

With the improvement of refining and purification techniques, many pure olefinic monomers are available for polymerization. Under Lewis acid polymerization, such as with boron trifluoride, very light colored resins are routinely produced. These resins are based on monomers such as styrene, a-methylstryene, and vinyltoluene (mixed meta- and i ra-methylstyrene). More recently, purified i ra-methylstyrene has become commercially available and is used in resin synthesis. Low molecular weight thermoplastic resins produced from pure styrene have been available since the mid-1940s resins obtained from substituted styrenes are more recent. 

Recovery and Purification. AH processes for the recovery and refining of maleic anhydride must deal with the efficient separation of maleic anhydride from the large amount of water produced in the reaction process. Recovery systems can be separated into two general categories aqueous- and nonaqueous-based absorption systems. Solvent-based systems have a higher recovery of maleic anhydride and are more energy efficient than water-based systems. 

Electrorefining. Electrolytic refining is a purification process in which an impure metal anode is dissolved electrochemicaHy in a solution of a salt of the metal to be refined, and then recovered as a pure cathodic deposit. Electrorefining is a more efficient purification process than other chemical methods because of its selectivity. In particular, for metals such as copper, silver, gold, and lead, which exhibit Htfle irreversibHity, the operating electrode potential is close to the reversible potential, and a sharp separation can be accompHshed, both at the anode where more noble metals do not dissolve and at the cathode where more active metals do not deposit. 

Nickel. Most nickel is also refined by electrolysis. Both copper and nickel dissolve at the potential required for anodic dissolution. To prevent plating of the dissolved copper at the cathode, a diaphragm cell is used, and the anolyte is circulated through a purification circuit before entering the cathodic compartment (see Nickel and nickel alloys). 

Purification. The method used to recover the desired alkylphenol product from the reactor output is highly dependent on the downstream use of the product and the physical properties of the alkylphenol. The downstream uses vary enormously some require no refining of the alkylphenol feedstock others require very high purity materials. Physical property differences affect both the basic type of process used for recovery and the operating conditions used within that process. 

Selenium purification by zone refining is not feasible. At practical zone-refining speeds, crystallization does not occur and impurities do not segregate. However, a controlled differential thermal treatment of selenium in a long vertical glass tube has been described (45). The treatment time is several weeks to several months. 

Refining. In order to produce silicon that meets the requirements of the chemical, ie, siUcones, and primary aluminum markets, the siUcon produced in the arc furnace requires further purification. The quaUty of siUcon for the chemical siUcones industry is critical with respect to the levels of aluminum and calcium present, and the primary aluminum grade of siUcon requires low levels of calcium, iron, and phosphoms. The impurity requirements for the secondary aluminum market are not as stringent, so long as the siUcon content is >98.5%. 

In the case of low temperature tar, the aqueous Hquor that accompanies the cmde tar contains between 1 and 1.5% by weight of soluble tar acids, eg, phenol, cresols, and dihydroxybenzenes. Both for the sake of economics and effluent purification, it is necessary to recover these, usually by the Lurgi Phenosolvan process based on the selective extraction of the tar acids with butyl or isobutyl acetate. The recovered phenols are separated by fractional distillation into monohydroxybenzenes, mainly phenol and cresols, and dihydroxybenzenes, mainly (9-dihydroxybenzene (catechol), methyl (9-dihydtoxybenzene, (methyl catechol), and y -dihydroxybenzene (resorcinol). The monohydric phenol fraction is added to the cmde tar acids extracted from the tar for further refining, whereas the dihydric phenol fraction is incorporated in wood-preservation creosote or sold to adhesive manufacturers. Naphthalene Oils. Naphthalene is the principal component of coke-oven tats and the only component that can be concentrated to a reasonably high content on primary distillation. Naphthalene oils from coke-oven tars distilled in a modem pipe stiU generally contain 60—65% of naphthalene. They are further upgraded by a number of methods. 

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