Remoção de CO2 do biogás por permeação em membranas

Abstract

Biogas consists of a mixture of gases, composed mainly of methane (CH4 ) and carbon dioxide (CO2 ). Among the alternatives to reuse it, purification for injection into the natural gas grid is the most interesting option from an economical point of view. Biogas purification requires the removal of CO2 and other contaminants. Taking into account the potential of membrane processes in biogas purification, this work evaluates the performance of two technologies for CO2 removal from biogas: membrane gas permeation and membrane contactors. Both technologies were compared regarding purification efficiency, energy requirements and membrane area. Gas permeation experiments were performed using two commercially available membranes, in which different CO2 concentrations and differential pressures were applied. Membrane contactor modules were also tested and some of the main operational parameters were studied, such as liquid flow rate, temperature, type of absorbent and gas composition. Based on experimental results, a simplified model was developed for gas permeation and contactors, which was used to compare the processes. Gas permeation results indicated that CO2 caused membrane plastification, which led to lower separation factors in tests with gas mixtures, in comparison to the pure gas experiments. In experiments with membrane contactors, the highest CO2 fluxes were obtained with NaOH as absorbent. The second best absorbent was diethanolamine and the worst of the three was pure water, since only physical absorption took place. Simulations indicated that, for a given CH4 purity and recovery, gas permeation required lower membrane areas and less energy than contactors.