化工分離工程概述-閱讀頁(yè)
2025-01-11 01:48本頁(yè)面
【正文】 quid feed with a stripping agent ( a vapor). ? Eliminates the need to reboil the liquid at the bottom of the column. Important if the liquid is not thermally stable. ? Principle of separation: difference in volatilities ? Created or added phase: vapor ? Separating agent: stripping vapor (MSA) Refluxed Stripping ? It is employed if simple stripping is not sufficient to achieve the desired separation and contacting trays are needed above the feed tray. ? Principle of separation: difference in volatilities ? Created or added phase: vapor and liquid ? Separating agent: stripping vapor (MSA) and heat transfer (ESA) Reboiled Stripping ? If the bottoms product from a stripper is thermally stable, it may be reboiled without using an MSA ? Principle of separation: difference in volatilities ? Created or added phase: vapor ? Separating agent: heat transfer (ESA) Azeotropic Distillation ? For constant boiling mixtures, separation by distillation is not possible. An entrainer (MSA) is used which forms a heterogoneous minimum boiling azeotrope with one of the ponents in the mixture. ? Principle of separation: boiling point differences caused by formation of a heterogeneous azeotropic mixture ? Created or added phase: vapor and liquid ? Separating agent: liquid entrainer (MSA) and heat transfer (ESA) azeotrope ( MSA + i ) Liquidliquid extraction ? Used when distillation is impractical. ? The mixture to be separated is heat sensitive, ? Volatility differences are much too small ? Principle of separation: different solubilities of different species in the two liquid phases ? Created or added phase: liquid ? Separating agent: liquid solvent (MSA) Liquidliquid extraction (two solvent) Liquidliquid extraction Drying of solids ? Many chemicals are processed wet but sold in dry, solid forms. Drying is used to remove liquid from a solid by vaporizing the liquid. ? Principle of separation: evaporation of water ? Created or added phase: Vapor ? Separating agent: gas (MSA) and/or heat transfer (ESA) Crystallization ? Desired product is finely divided solid. ? Solution crystallization: The mixture is cooled and/or the solvent is evaporated to cause crystallization. ? Melt crystallization: Two or more soluble species, in the absence of a solvent, are separated by partial freezing. ? Zone melting (refining): Reverse of melt crystallization. Used for removing impurity solids in metals by moving a molten zone slowly through an ingot. ? Principle of separation: difference in freezing tendencies。這類(lèi)過(guò)程所處理的原料和產(chǎn)品通常屬于同一相，僅在組成上有差別。熱擴(kuò)散分離也屬于速率分離過(guò)程，它以溫度梯度為動(dòng)力，利用均勻的氣體或液體混合物中分子 量下的分子（或離子）向熱端漂移的現(xiàn)象所建立起來(lái)的濃度梯度，達(dá)到組分分離的目的
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