Liquid filtration fine chemicals

Safety. The MR is much safer than the MASR. (1) The reaction zone contains a much smaller amount of the reaction mixture (hazardous material), which always enhances process safety. (2) In case of pump failure, the reaction automatically stops since the liquid falls down from the reaction zone. (3) There is no need to filter the monolithic catalyst after the reaction has been completed. Filtration of the fine catalysts particles used in slurry reactors is a troublesome and time-consuming operation. Moreover, metallic catalysts used in fine chemicals manufacture are pyrophoric, which makes this operation risky. In a slurry reactor there is a risk of thermal runaways. (4) If the cooling capacity is insufficient (e.g. by a mechanical failure) a temperature increase can lead to an increase in reaction, and thus heat generation rate. 

The above conditions assume two relatively pure liquids. The presence active agent or fine dispersed solids can interfere with the coalescing process and result in a stable emulsion. Many liquid-liquid separators form a stable emulsion at the interface called a rag layer because of these agents and may require draw-off nozzles near the interfoce to prevent accumulation. The rag layer is like foam in liquid-gas systems and is typically stabilized by very fine solids. If the rag is drawn off it may be de-emulsified or broken by filtration, heating, chemical addition, or reveising the phase that is dispersed. 

Unlike the new metal alloys used as alternatives to Pd, PGMs are extensively applied in several separation processes such as miao- and ultra-filtration, gas separation, demulsification medium and membrane emulsification, gas-liquid contacting and gas dispersion. In particular, the gas dispersion process and membrane emulsification are of interest for the food, pharmaceutical, fine chemicals and cosmetic industries. 

Batch leach experiments were performed on tailings material to determine the nature of contaminants distributed on sand and silt and clay-sized fractions. For the batch leach experiments, a mixture of tailings material was prepared using a chemical dispersant (sodium hexametaphosphate (NaPO ) ). The mixture was shaken and allowed to settle in covered beakers for sufficient time such that no particles with a diameter > 50 /im remained in suspension. The fines, which remained in suspension, represented the silt and clay-sized fraction of the samples. At the end of the settling period, the liquid was decanted from the beaker. The remaining sand-sized tailings were dried and transferred to a sealed vial. The decanted solution was passed through a 0.45 /im membrane filter, previously washed with distilled water, and the filtrate was collected and placed in a sealed container. The solids were dried and transferred to a sealed vial. The samples were then analyzed by instrumental neutron activation analysis. 

Removal of solids from a solution which contains the product as a solute. The solids represent the contaminant or carry it adsorbed on the smface (e.g. heavy metals). The aim is to thicken the solids into the wash liquid, as free as possible of the solute (i.e. with a minimum loss of the product). The system overflow contains the solute at a concentration only a little lower than that in the system feed. The process essentially removes the solution from the solids in a similar way as a cake filtration process, except it can do this for fine, difficult-to-filter solids and without exposure to air or to any filter medium, in a completely enclosed pipework free of moving parts (except for the pumps). This process is gaining favour in the chemical industry and it can be driven by high pressure at the front of the washing train—see the next section. 

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