Hydrogen production from cheese whey by catalytic steam reforming: Preliminary study using lactose as a model compound

Cheese whey is a yellowish liquid by-product of the cheese making process. Owing to its high BOD and COD values, this feedstock should not be directly discharged into the environment without appropriate treatment. Before dealing with real cheese whey, this work addresses the production of a rich hydrogen gas from lactose (the largest organic constituent of this waste) by catalytic steam reforming. This reforming process has been theoretically and experimentally studied. The theoretical study examines the effect of the temperature (300-600 °C), lactose concentration (1-10 wt.%) and N2 (0-80 cm3 STP/min) and liquid flow (0.1-0.5 mL/min) rates on the thermodynamic composition of the gas. The results show that the temperature and lactose concentration exerted the greatest influence on the thermodynamics. The experimental study, conducted in a fixed bed reactor using a Ni-based catalyst, considers the effect of the temperature (300-600 °C), lactose concentration (1-10 wt.%) and spatial time (4-16 g catalyst min/g lactose) on the global lactose conversion, product distribution on a carbon basis (gas, liquid and solid) and the compositions of the gas and liquid phases. Complete lactose conversion was achieved under all the experimental conditions. The carbon converted into gas, liquid and solid was 2-97%, 0-66% and 0-94%, respectively. The gas phase was made up of a mixture of H2 (0-70 vol.%), CO2 (20-70 vol.%), CO (2-34 vol.%) and CH4 (0-3 vol.%). The liquid phase consisted of a mixture of aldehydes, ketones, carboxylic acids, sugars, furans, alcohols and phenols. Optimal conditions for cheese whey valorisation were sought considering the energetic aspects of the process. Using a lactose concentration similar to that of cheese whey (5.5 wt.%), maxima for the CC gas (88%) and the proportion of H2 (67 vol.%) in the gas together with a carbon-free liquid stream can be achieved at 586 °C using a spatial time of 16 g catalyst min/g lactose. Theoretically, the combustion of 20% of this gas provides the energy necessary for the process enabling the transformation of 68% of the carbon present in the initial effluent into a H2 rich gas (67 vol.%) with a global H2 yield of 16 mol H2/mol lactose. In a real case it would be necessary to increase the amount of gas combusted to compensate for heat losses.