Precipitation post-treatment processes

In the polymer industry, post-reaction product treatment processes such as liquid-solid separation, drying, precipitation, particle size control, and polymer purification are very complex and costly. Future polymer plants should be designed such that process equipment can be easily and quickly converted to making new products at minimal cost and with... 

Microstructure evolution in solids formed from a melt is important in processes such as prilling or casting. For example, in aluminum alloy shape casting the final microstructure depends directly on the as-cast microstructure since the only post-casting process is the heat treatment. The micro-porosity formed owing to the combined effects of the volumetric shrinkage upon the solidification of the melt and the precipitation of the dissolved hydrogen affects the final properties of the aluminum alloy. 

Inorganic non-oxide materials, such as III-V and II-VI group semiconductors, carbides, nitrides, borides, phosphides and silicides, are traditionally prepared by solid state reactions or gas-phase reaction at high temperatures. Some non-oxides have been prepared via liquid-phase precipitation or pyrolysis of organometallic precursors. However, amorphous phases are sometimes formed by these methods. Post-treatment at a high temperature is needed for crystallization. The products obtained by these processes are commonly beyond the manometer scale. Exploration of low temperature technique for preparing non-oxide nanomaterials with controlled shapes and sizes is very important in materials science. 

Active aluminas (various oxides and hydrated oxides) with high specific areas, good absorption characteristics, catalytic properties and high chemical reactivity are either produced by precipitation processes from aluminum salt solutions e.g. via thermal post-treatment of aluminum hydroxide gels, or by the calcination of a-aluminum hydroxide under specific conditions (low temperatures, very rapid heating). 

To overcome this issue Kureshy et al. [55, 56] reported dimeric form of Jacobsen s catalysts 3, 4. They used the concept of solubility modification by altering the molecular weight of the catalyst so that in a post catalytic work-up procedure the catalyst is precipitated, filtered and used for subsequent catalytic runs. The complexes 3, 4 (0.2 mol % of Co(lll)-salen unit) (Figure 2) were effectively used for HKR of racemic epoxides, e.g., styrene oxide, epichlorohydrin, 1,2-epoxypropane, 1,2-epoxyhexane, 1,2-epoxyoctane, and 1,2-epoxydodecane to achieve corresponding epoxides and 1,2-diols in high optical purity and isolated yields. In this process, once the catalytic reaction is complete the product epoxides were collected by reduced pressure distillation. Addition of diethylether to the residue precipitated the catalyst which was removed by filtration. However, the recovered catalyst was required to be reactivated by its treatment with acetic acid in air. The catalysts were reused 4 times with complete retention of its performance. 

In contrast to the dry methods, there are other conventional methods related to post heat treatment from precipitates from the aqueous solutions. The ambient aqueous routes and the hydrothermal methods at elevated temperature usually lead to rare earth precipitates like hydroxides, carbonates, instead of oxides. In fact, the hydrothermal treatment of rare earth oxide powders results in a hydration process to form hydroxides. Subsequently, the precursor could be used to produce rare earth oxide nanocrystals with post annealing at varied temperatures and in appropriate atmosphere. 

Supercritical fluid anti-solvent processes have been recently proposed as alternatives to liquid anti-solvent processes commonly employed in the industry. The key advantage of the supercritical processes over liquid ones is the possibility to completely remove the anti-solvent by pressure reduction. This step of the process is problematic in case of liquid anti-solvents since it requires complex post-processing treatments for the complete elimination of liquid residues. Furthermore, the supercritical anti-solvent is characterized by diffusivity that can be up to two orders of magnitude higher than those of liquids. Therefore, its very fast diffusion into the liquid solvent produces the supersaturation of the solute and the precipitation in micronized particles with diameters that are not possible to obtain using liquid anti-solvents or other methods. 

Traditionally, extrusion texturization of soy protein has been used to create meat analogues. Addition of sodium hydroxide during extrusion does not aid in texturization, with worse product quality at high pH (Dahl and Villota, 1991). Precipitation within the extruder at the soy isoelectric point may be necessary for adequate texturization. Huang and colleagues (1995) at Iowa Sate University devised a process in which soy protein isolate could be extruded into textile fibers. Brittleness was offset by addition of glycerol during extrusion and by various chemical treatments post-extrusion. A similar process could be developed to produce superior meat-like fibers. 

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