Hydrogen and Syngas Production from Biodiesel Derived Crude Glycerol

Abstract

In the past decade, the production of biodiesel has increased dramatically. One of the major by-products of biodiesel production is crude glycerol, which is expensive to refine. As a result, the price of crude glycerol has plummeted to the point where biodiesel companies have to pay to dispose of it. This leads to an increased cost of biodiesel production. To make biodiesel production more cost-effective, it is vital that a use for this crude glycerol is found. One possible method is using steam reforming techniques to reform crude glycerol to produce hydrogen or synthesis gas. This gas can be converted to jet or diesel fuel by using Fischer-Tropsch principles or used in traditional hydrogen applications. In this study, the viability of using steam reforming techniques to convert crude glycerol into a hydrogen rich gas is addressed. To do this, the effects of the impurities in crude glycerol on catalyst life and activity were compared to pure glycerol reforming over two different steam reforming catalysts: Ni/MgO and Ni/γ-Al2O3 catalysts. Reactions over both catalysts showed that crude glycerol reforming can produce a product gas similar to the gas produced during pure glycerol reforming. Unfortunately, the impurities found in the crude glycerol limited catalyst life over time. They increase coke and tar formation and cause the reactor to plug after several hours. To solve this problem, a simple pre-wash of crude glycerol using acetic acid was performed. The acid-wash removed many of the impurities in the glycerol. Acid-washed glycerol reforming showed dramatic improvements over crude glycerol reforming. The reactions showed increased catalytic activity and little deactivation for 12 to 14 hours. Conversion of reactants to products was ~100% and the product gas had a hydrogen purity of 68-69%. Thermodynamic equilibrium predictions matched those provided by the experimental results. The role of the different impurities found in crude glycerol was considered. Experimental and thermodynamic results show that the presence of methanol can aid in producing a product gas with a high hydrogen purity but can decrease hydrogen yield. Results indicate that the presence of potassium aids in gasification of the reactant and help prevent carbon formation on the catalyst. The soaps and unreacted triglycerides found in crude glycerol increase coke and tar formation in the reactor and will eventually cause plugging. Future work needs to be performed to fully determine the role of these impurities in crude glycerol reforming.