Extraction Process Analysis Essay

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2.2. Extraction process analysis
The solvent is fed from the bottom and broth from the top since the mass separation agent or solvent has a lower density than the aqueous mixture. The raffinate phase contains most of water and traces of HAc, and solvent, whereas the extract phase includes most of the solvent, HAc, and traces of water. The amount and composition of the mixed solvent significantly important for the process economy because it directly affects the composition of HAc in the extract phase. A good solvent should have a high distribution coefficient for the HAc and a high selectivity between HAc and water. Further, the solvent must be easy to separate from the HAc mixture. Since the solvent used in this work is a low boiling extraction
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Fig. 2 plots the required stage number of the extractor and the corresponding S/F for the studied solvents in order to achieve high HAc recovery of at least 99.5 wt%. This specification is strictly required in the extraction column. The feed containing 30 wt% of HAc was fed to the top of the extractor. The solvent was added to the bottom of the extractor. The extract and raffinate phases are taken from the top and bottom of the extractor, respectively. As an initial analysis, the mixed solvent containing 50 wt% of PX and 50 wt% of EA or MA. As shown in Fig. 2, the required solvent amount decreases with increasing number of stages. For the same separation task, the required amount of PX+MA is about 80% of EA with the same number of stages. For example, when the number of stages is n=15, the required solvent to feed ratio were S/F= 2.62 and 2.78 for PX+MA and PX+EA, respectively. To minimize the energy on the subsequent distillation column, the required solvent must be minimized. However, a high number of the stage of extractor column also leads to more capital cost. As described in Fig. 2, when the number of stages increases from 6 to 15, there is a significant reduce of the solvent needed. While with the stage number changing from 15 to 20, the reduce of solvent was not significant (from 2.8 to 2.62 for PX+MA and 3.02 to 2.78 for PX+EA) comparing the change from stage 6 to …show more content…
3 (a) and (b), HAc recovery mostly depends on EA or MA flow rate in the solvent stream. In addition, high PX flow rate also enhances EA or MA performance to have a high HAc flow rate in the extract stream. It was consistency with the LLE result from the previous work, the separation efficiency will be higher with the high amount of PX as the solvent. By comparing Figs. 3 (a) and (b), MA showed slightly better performance than EA on the extractor, MA produced high HAc flow rate in the extract stream with the same amount of MA and EA input on solvent stream. Especially, in the PX+MA system, while PX input on the solvent stream below around 1,000 kg/hr, only single phase take place in this system which means no separation occurs in the extraction

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