Production of gaseous and liquid chemicals by aqueous phase reforming of crude glycerol: Influence of operating conditions on the process

Abstract

The present work studies the influence of the temperature (200–240°C), pressure (38–50bar), glycerol concentration (10–50wt.%) and mass of catalyst/ glycerol mass flow rate ratio (W/mglycerol=10–40g catalyst min/g glycerol) during the aqueous phase reforming (APR) of a glycerol solution obtained from the production of biodiesel. The operating conditions exerted a statistically significant influence on the reforming results. Specifically, the global glycerol conversion and the carbon converted into gas and liquid products varied as follows: 4–100%, 1–80% and 16–93%, respectively. The gas phase was made up of H2 (8–55vol.%), CO2 (34–66vol.%), CO (0–4vol.%) and CH4 (6–45vol.%). The liquid phase consisted of a mixture of alcohols (monohydric: methanol and ethanol; and polyhydric: 1,2-propanediol, 1,2-ethanediol, 2,3-butanediol), aldehydes (acetaldehyde), ketones (C3-ketones: acetone and 2-propanone-1-hydroxy; C4-ketones: 2-butanone-3-hydroxy and 2-butanone-1-hydroxy; and cyclic ketones), carboxylic acids (acetic and propionic acids) and esters (1,2,3-propanetriol-monoacetate), together with unreacted glycerol and water. The relative amount (free of water and un-reacted glycerol) of these compounds in the liquid phase was as follows: monohydric alcohols: 4–47%, polyhydric-alcohols: 14–68%, aldehydes: 0–5%, C3-ketones: 2–33%, C4-ketones: 0–10%, ciclo-ketones: 0–6%, carboxylic acids: 2–43%, and esters: 0–46%. This process turned out to be highly customisable for the valorisation of crude glycerol for the production of either gaseous or liquid products. Gas production is favoured at a low pressure (39bar), high temperature (238°C), high W/mglycerol ratio (38g catalyst min/g glycerol) and employing a 15wt.% glycerol solution. A high pressure (45bar), medium temperature (216°C), medium W/mglycerol ratio (22g catalyst min/g glycerol) and the feeding of a 16wt.% glycerol solution favours the production of liquid products.