Photoreforming of model carbohydrate mixtures from pulping industry wastewaters

The photoreforming of organic molecules is a growingly interesting technology to achieve faster hydrogen production than with water splitting, while simultaneously mineralising organic pollutants in water. This paper investigates the possibility to produce hydrogen or gaseous fuel mixtures by using simulated wastewaters of the pulping industry. Glucose was first used as model molecule for carbohydrate-containing wastewaters, while tartaric acid was the model for those rich of carboxylic acids. Different titania catalysts were prepared starting form the P25 commercial material and monometallic Pt or Au, or bi-metallic AuxPty formulations were prepared in form of surface-decorated nanomaterials. The effect of pH and co-catalysts addition was explored, achieving after 5 h of irradiation the highest glucose conversion (15.2%) and H2 productivity (4.1 mol H2 kgcat−1 hirr−1) with sample 1.0 wt%Au6Pt4/P25. This result competes with the best ones reported in the literature. Testing of tartaric acid showed much faster conversion of the substrate, but limited hydrogen productivity, ethane and CO2 being the main products, anyway leading to a valorisable gaseous fuel mixture. The best performing materials were also tested for the photoreforming of simulated wastewaters representative of pulping industry effluents, according to the two pulp processing technologies, the Kraft and sulphite ones. Similar results than tartaric acid were obtained when testing the Kraft spent liquor, mainly composed of hydroxycarboxylic acids. By contrast, the Sulphite spent liquor was mainly composed of carbohydrates, acetic and gluconic acids and led to methane as main product, possibly coming from the decarboxylation of acetic acid. The results overall testify the interest of photoreforming to valorise wastewaters into gaseous fuels in a circular economy concept.