BASIC INVESTIGATION OF INTEGRATING A MEMBRANE UNIT INTO HIGH-PRESSUREDECAFFEINATION PROCESSING

Within the large-scale industrial decaffeination processes using super critical CO2, caffeine is stripped from the extracting agent CO2 with water using a high-pressure washing tower. On account of the value of the product, the caffeine is recovered from the washwater with a disti llation-crystallization process. A reverse osmosis membrane process ap pears to be very suitable to replace the energy consuming distillation step to recover the caffeine and supply a cleaned water stream to be returned to the washing tower. Although this combination of a membrane process with high-pressure extraction was suggested earlier, very lit tle fundamental work and experimental data have been published so far. The presented study is concentrated on basic investigations of this p rocess. The osmotic pressure of aqueous caffeine solutions was determi ned with cryoscopy and additional membrane experiments. Membrane test cells were used to study the maximum separation of binary caffeine-wat er solutions. The influence of temperature, pressure and caffeine conc entration on membrane flow and rejection was investigated for commerci ally available RO flat sheet membranes. The results show that RO conce ntration of aqueous caffeine solutions is feasible with moderate press ures and temperatures up to 60 degrees C. Additional experiments with a non-optimized plate module supplemented the investigation of separat ion performance with approximately 50% of the test cell flux. Flux mea surements with an agitated membrane cell show that the permeation of w ater with high CO2 concentrations impairs membrane performance. A reve rse osmosis washwater recycling process should flash the washwater to atmospheric pressure before the membrane unit. (C) 1998 Elsevier Scien ce B.V. All rights reserved.