Applied Research On The Caffeine Extraction With A Structured Packing Tower

Caffeine is a bitter, white crystalline xanthine alkaloid, and has a unique andstrong pharmacological effect. Due to its huge market demand, caffeine is mainlyprepared by chemical synthesis rather than extraction from natural plants. A largemother liquid is usually generated in the synthesis process of caffeine, while thecaffeine content in it is relatively low. The caffeine is recovered by chloroform usingdifferent extraction equipments; these devices can recover caffeine back from themother liquid, but they can’t achieve good concentration effect, so the energyconsumption of distillation in the recovery of chloroform is quite high, and the cost ofproduction correspond to increase. In order to reduce energy consumption, structuredpacking column was used in the pilot test, optimal process parameters weredetermined, and hydrodynamic performance and mass transfer performance of theextraction column were theoretical calculated and analyzed in different volumetricphase ratios according to the test data. In addition, the research refers to the specificthroughput capacity and effective height of the extraction tower under differentvolumetric phase ratios, and also provides theoretical basis and data support forcompanies to select appropriate process and equipments.The operating results showed that structured packing tower had higher capacitythan the reciprocating plate column(RPC); the most suitable volumetric phase ratio(F/S) was1.25; the maximum specific throughput capacity of this column was31.85m3/(m2·h）; the extraction of caffeine reached99.8%for5m3/h caffeine motherliquid, which was the maximum throughput of the tower in the caffeine extractionprocess; and the concentrations of caffeine and the chloroform residue in the raffinateall met the requirement of the industrial production.Because solute transfer usually affects the properties of the two phases so as toreduce hydraulic capacity, and the use of redistributors also adversely affects thehydraulic capacity of the extraction column, it is recommended that flow velocities belimited to no more than40percent of the calculated flooding values on the basis ofthe pilot test. The Becker model was not only used to correct the height of a transferunit for axial mixing, but also used to analyze the positive effects of redistributors. Inindustrial-scale structured packing column, redistributors could significantly constrain back mixing and reduce the effective height of the column. The results showed thatwhen the volumetric phase ratio (F/S) was8, the specific throughput capacity ofstructured packed tower was28.12m3/(m2·h), the holdup of dispersed phase9.45percent,the interfacial area203.8m2/m3,the number of overall mass-transfer units8.80, the height of overall mass-transfer unit1.93m and the effective height of thepacked tower17.1m.In the chemical industry the technical advantages of structured packing withhigher operational flexibility (turn down), higher allowable bed heights andmaximized throughput are taken more into consideration. This paper has a certainpractical significance for the further industrial scale of caffeine extraction and thewidespread application of the structured packing extraction column.