Solvents recyclable systems

The low molecular mass alkanes are thus able to dissolve palmitic acid and its derivatives at lower pressures than CO2. This is in agreement with Miinuklii et al. [53] who compared the solubility of CO2 and in propane in a hardened rape seed oil and found that propane is able to dissolve in the oil a lot better than the CO2. While ethane and in propane are not toxic, they are highly flammable and as such care is required if they are used as alternative solvents or even in high concentrations as co-solvents. However, despite the flammability issues associated with ethane and propane, these two solvents are non-toxic and excellent alternatives to CO2. As they are both also SC solvents, the solvent residue would be similar than when using CO2 as solvent and the solvent recycle systems are of similar complexity to using CO2. 

The use of a co-solvent can therefore significantly reduce the phase transition pressure and thus increase the solubility of palmitic acid and its derivatives in a SC solvent. However, while this reduction leads to a decrease in operating pressure, it comes at the cost of a more complicated solvent recycling system, a more complicated control philosophy and increased solvent residue in the products. The choice of the use of a co-solvent thus needs to take these aspects, as well as the nature of the co-solvent itself, into account when the use of a cosolvent is evaluated. 

Sodium hydrosulfite is produced through the Formate process where sodium formate solution, sodium hydroxide, and liquid sulfur dioxide reacted in the presence of a recycled stream of methanol solvent. Other products are sodium sulfite, sodium bicarbonate, and carbon monoxide. In the reactor, sodium hydrosulfite is precipitated to form a slurry of sodium hydrosulfite in the solution of methanol, methyl formate, and other coproducts. The mixture is sent to a pressurized filter system to recover sodium hydrosulfite crystals that are dried in a steam-heated rotary drier before being packaged. Heat supply in this process is highly monitored in order not to decompose sodium hydrosulfite to sulfite. Purging is periodically carried out on the recycle stream, particularly those involving methanol, to avoid excessive buildup of impurities. Also, vaporized methanol from the drying process and liquors from the filtration process are recycled to the solvent recovery system to improve the efficiency of the plant. 

A recyclable system for the directed rhodium-catalyzed hydroacylation of olefins was reported using a homogeneous phenol and 4,4 -dipyridyl solvent system at 150 °C. High yields were obtained even after eight cycles and the ketone product was obtained after decantation (Equation (132)).115... 

In-plant management practices may often control the volume and quality of the treatment system influent. Volume reduction can be attained by process wastewater segregation from noncontact water, by recycling or reuse of noncontact water, and by the modification of plant processes. Control of spills, leakage, washdown, and storm runoff can also reduce the treatment system load. Modifications may include the use of vacuum pumps instead of steam ejectors, recycling caustic soda solution rather than discharging it to the treatment system, and incorporation of a more efficient solvent recovery system. 

The choice of an ionic liquid was shown to be critical in experiments with [NBuJBr (TBAB, m.p. 110°C) as a catalyst carrier to isolate a cyclometallated complex homogeneous catalyst, tra .s-di(ri-acetato)-bis[o-(di-o-tolylphosphino) benzyl] dipalladium (II) (Scheme 26), which was used for the Heck reaction of styrene with aryl bromides and electron-deficient aryl chlorides. The [NBu4]Br displayed excellent stability for the reaction. The recycling of 1 mol% of palladium in [NBu4]Br after the reaction of bromobenzene with styrene was achieved by distillation of the reactants and products from the solvent and catalyst in vacuo. Sodium bromide, a stoichiometric salt byproduct, was left in the solvent-catalyst system. High catalytic activity was maintained even after the formation of visible palladium black after a fourth run and after the catalyst phase had turned more viscous after the sixth run. The decomposition of the catalyst and the formation of palladium... 

The Terra-Kleen solvent extraction technology is an on-site, batch-process system that uses a proprietary solvent to remove hazardous organic constituents from soils. The treatment system uses a solvent regeneration system that concentrates the extracted contaminants and then recycles the extraction solvent. The treated soil can often be returned to the site. The concentrated contaminants are usually transported off-site for disposal. 

A process based on the use of an immobilized C. antarctica lipase (Novozym 435) has been developed in order to perform direct esterification of natural alcohols with carboxylic acids in a solvent-free system. Based on the system represented in Figure 11.2, the process had to overcome the problem of recycling the nitrogen, once the reaction was over. 

Recently, a new rhodium recycling system was described that takes advantage of amphiphilic ligands such as Ph2ArP (Ar = 3-hydroxyphenyl, 4-carboxyphenyl). The corresponding rhodium complexes are active in the hydroformylation of 1-octene and can be separated from the products by acidic or basic extraction into water. After neutralization of the aqueous phase, the rhodium species could be extracted into a new batch of octene, with toluene as a solvent. The recovered catalyst retained only up to 87% of its activity (72). 

Miyamura et al. [170] and Kanaoka et al. [171] have succeeded in stabilizing Au clusters on polymer supports for aerobic oxidation at room temperature in the mixed solvent of water-benzotrifluoride and in water, respectively. Polymer supports could also offer new functions, such as a recycling system by using a thermoresponsive polymer-supported Au catalyst [171]. 

Tripathi, S.C., Sumathi, S., Ramanujam, A. 1999. Effects of solvent recycling on radiolytic degradation of 30% tributyl phosphate- -dodecane-HN03 system. Sep. Sci. Technol. 34 (14) 2887-2903. 

In the process, the vacuum residuum is brought to the desired extraction temperature and then sent to the extractor where solvent (straight run naphtha, coker naphtha) flows upward, extracting soluble material from the down-flowing feedstock. The solvent-deasphalted phase leaves the top of the extractor and flows to the solvent recovery system where the solvent is separated from the deasphalted oil and recycled to the extractor. 

Liquid-liquid extraction, using one or two solvents respectively, is widely used when distillation is impractical, especially when the mixture to be separated is temperature-sensitive and/or more than 100 distillation stages would be required. When one solvent is used, it selectively dissolves only one or a fraction of the components in the feed mixture. In a two-solvent extraction system, each solvent has its own specific selectivity for dissolving the components of the feed mixture. Additional separation operations are generally required to recover, for recycling, solvent from streams leaving the extraction operation. 

Plutonium is subsequently stripped to an aqueous phase containing NH20H HN03 in the CC Column. In order to increase the plutonium concentration of the CC Column product, a portion of this stream (CAIS) is recycled to the CA Column after adjustment with HNO3. The remainder of the stream (CCP) is routed to the product concentrator. The resulting concentrated and purified plutonium nitrate solution is suitable feed to other processes for conversion to the desired product form (e.g., metal or plutonium dioxide). The remainder of the PRF solvent extraction system consists of a series of columns to wash the TBP-CCI4 solvent and prepare it for reuse. 

Equipment for recycle operations differs from conventional HPLC equipment. For a recycle system to be useful, the extracolumn band spreading must be small relative to the band spreading of the column. This involves the solvent delivery system, transport tubing, and detector(s). Also, because a recycle system is a closed system with a finite volume, the operator must be aware that fast-moving materials could eventually overtake slower-moving materials and remix. To prevent peak overlap, a means must be provided to allow the operator to remove a portion of the sample components before overlap can occur. 

After the peak from the carbon tetrachloride reaches baseline, wait 15 sec and turn the recycle knob to the recycle position on the instrument or solvent delivery system. 

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