Abstract
Glycerol conversion processes such as aqueous phase reforming and hydrogenolysis generate value-added compounds highly diluted in water. Because distillation is a high energy demand separation step, adsorption could be an attractive alternative to recover these chemicals. Adsorption isotherms of 1,2-propanediol, acetol, ethylene glycol and glycerol onto activated carbon were determined by batch adsorption experiments. These isotherms were fitted slightly better to the Freundlich equation than to the Langmuir equation. Acetol is the compound with the highest adsorption at concentrations smaller than 1 M. Properties of the adsorbate such as the −OH group number, chain length, molecular size and dipole moment, besides characteristics of the adsorbent such as the surface area, oxygen and ash content, are considered to explain the observed results. Moreover, adsorption experiments were performed with mixtures of compounds and it was determined that the molar amount adsorbed is less than predicted from the adsorption isotherms of the individual compounds treated separately. In addition, the influence of the activated carbon thermal pre-treatment temperature on the adsorption capacity has been studied, the optimum being 800 °C. An analysis of the influence of the activated carbon characteristics showed that the most important parameters are the total pore volume and the ash content.
Highlights
This study constitutes the first step in employing adsorption with activated carbon for the separation of value-added compounds from aqueous solutions of glycerol conversion processes
Adsorption isotherms for 1,2-propanediol, acetol, glycerol and ethylene glycol adsorbing onto activated carbon have been slightly better fitted to the Freundlich isotherm than to the Langmuir isotherm
Acetol is the compound with the highest adsorption capacity at a solution concentration lower than 1 M
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Glycerol is the main by-product in biodiesel manufacturing from fats and vegetable oils by transesterification. The high production of biodiesel generates enormous quantities of glycerol. Glycerol is considered as a “building block molecule” in the biorefinery strategy because of its participation in various types of chemical reactions and its conversion into a large number of value-added chemicals. This has been reported in several previous studies [1,2,3,4]
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