![]() Prior to a new application, careful investigation in the laboratory will establish the phase equilibrium data which reveals the relationship between the number of extraction stages and the possible feed-to-solvent ratio. An optimised tray design ensures good mass transfer characteristics without leading to emulsion formation. The sieve tray facilitates controlled formation of droplets in the dispersed phase with little shear. A classical sieve tray column is well suited for such cases. ![]() If the feed and solvent have low surface tension values, the use of an ARDC column or a centrifugal extractor can result in a stable emulsion, making these options unviable. The accelerated mixing and separation result in a very small hold-up in the extractor. The mixture then enters a rotating cylinder, where it experiences high centrifugal force and quickly separates into two phases. The two phases are mixed with a high intensity in the mixing chamber of the centrifugal extractor. A centrifugal extractor with a very small hold-up and the ability to change over quickly from one batch to another addresses their concerns. The large hold-up in the ARDC column tends to deter customers in the pharmaceutical industry. The column is easy to automate and saves space. The continuous operation ensures consistent results. The desired component is transferred from one phase to another as these two phases flow counter-currently through the series of mixers and settlers. The heavy phase enters the column at the top and the light phase at the bottom. The ARDC column has a stack of mixers and settlers arranged vertically inside a long vertical column. These improvements ensured a payback of less than 12 months. The recovery rate increased from 85 to 93 % while solvent use was reduced from 10 to 7 tons. Trials were subsequently conducted on the pilot ARDC (Asymmetric Rotating Disc Contactor) column.Ī production scale extractor was designed and commissioned based on the trial results. A total of five washes achieved 85 % recovery.Įquilibrium data generated in the laboratory indicated potential for improvement by switching over to continuous and counter-current extraction. As one example, an agrochemical was previously manufactured using an established batch extraction process where 10 tons of solvent were required to process 7 tons of aqueous mass. As a result, solvent use is high and the large volume of extract leads to higher recovery costs.Ĭhanging from a batch to a continuous process can provide an attractive return on investment. Each washing cycle incrementally extracts the desired product, producing dilute extract in each subsequent cycle. When extraction is carried out conventional batch kettles, fresh solvent for extraction is added several times to the same vessel. The solvent is then recycled back to the extraction process. A small portion of the solvent from the raffinate stream is stripped out by another evaporator. The component and the solvent are separated using suitable evaporators. One flow at the outlet (the extract) is enriched with this component while another (the raffinate) is depleted of it. Part of the component is therefore transferred to it from the feed. This solvent has a certain affinity to the desired component. The feed containing a desired component is mixed intensively with an immiscible solvent. Separation by extraction is based on the different affinities of components in two immiscible liquid phases. ![]() Careful piloting is a must for successful installation with a short payback period. Operation at low temperatures is beneficial for what are in many cases heat sensitive products. The process of liquid-liquid extraction is an economical alternative for separating compounds that are difficult to purify by distillation.
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