Phase equilibria and physical properties of glycerol acetates + CO2 mixtures and conceptual design of a high pressure packed columns for biosurfactants fractionation

HEGEL, PABLO E.; PEREDA, SELVA; FORTUNATTI MONTOYA, MARIANA

Campinas

Congreso; XIII BEROAMERICAN CONFERENCE ON PHASE EQUILIBRIA AND FLUID PROPERTIES FOR PROCESS DESIGN; 2022

UNICAMP

The acetylation of glycerol can be an interesting chemical route for the glycerol valorization in actual biorefineries.A mixture of three products (triacetin, diacetin and monoacetin) is commonly obtained in the industrial process. The isolation of the three compounds obtained in the reaction of acetylation is a key step in the process to get value-added products in actual biorefineries. We show in previous works GCA-EOS model predicts accurately the phase equilibria between CO2 and glycerol acetates mixtures. Also, GCA-EOS modeling of SCCO2 extractions of a commercial glycerol acetates mixture at temperatures between 301 K and 323 K and pressure between 100 bar and 130 bar shows GCA-EOS is a useful tool to design and optimize the scale up separation process.A proof of concept carried out in a bench scale high-pressure packed column at 313 K and 95 bar using a solvent to feed ratio (S/F) of 17.5 g CO2/g feed shows is technically feasible the biosurfactants fractionation process. However, an analysis of system points out it is necessary to operates the column using higher solvent to feed ratios and loading conditions nearly the flooding point to decrease the height equivalent of theoretical stage. Moreover, simulations of the unit show it is necessary to operates the column with a reflux system because a countercurrent isothermal operation shows a low recovery of the target compounds. Thus, two design options are considered: i. a countercurrent column with internal reflux using a hot finger point, and ii. a countercurrent column design using an external reflux using a high-pressure pump.The fractionation of the ternary mixture requires two columns, or a single column operated in two separation steps. In the first part, monoacetin can be obtained in the raffinate, while triacetin and diacetin can be separated in a second step. GCA-EOS modeling shows a commercial glycerol acetates mixture (23.3% g/g triacetín, 48.7% g/g diacetín y 28.0%g/g monoacetin) can be fractionated in two steps using a single column of 11 stages,feed at stage 4. It is technically viable in the initial separation to use a hot finger in the top of the column to obtain monoacetin at 95 wt.% with a high recovery (95 wt%) but it is necessary a high solvent consumption (S/F=80) to achieve the fractionation. On the other hand, triacetin and diacetin can only be fractionated with an acceptable recovery of diacetin (83 %) using external reflux generated by a recompression of the top product coming from a separator operated at 323 K and 55 bar. More favorable operating conditions to raffinate monoacetin are 306 K and 91 bar, using a reflux ratio of 1.6 and 65 kg CO2/kg of feed, and raffinate diacetin are 310 K and 93 bar, using a reflux ratio of 8 and 45 kg CO2/kg Feed.