Understanding the Direct Conversion of Glycerol to Ammonia

Abstract

The production of biodiesel has increased exponentially in the past few decades. This growth has facilitated an excess creation of glycerol, which is generated as a byproduct during the formation of biodiesel. As a result, the glycerol market is oversaturated, subsequently plummeting its price to the point that it has become a waste problem for some biodiesel companies. Therefore, in order to make biodiesel production more economical, it is critical to establish glycerol as a value-added product. One option, steam reforming of glycerol to produce hydrogen is a promising idea to utilize this excess resource. In specific, this hydrogen gas can be used to produce ammonia that is consumed in the preparation of fertilizers and has several other promising future applications. Currently, ammonia is produced by using hydrogen formed from the steam reforming of methane (SRM). Theoretical studies suggest that the use of glycerol instead of methane increases the ammonia production rate while also being advantageous in both the environmental and agricultural sectors. In this study, the viability of direct catalytic conversion of glycerol to ammonia at a reduced pressure is addressed. In order to achieve this, the overall reaction was divided into three parts. The first two parts, glycerol steam reforming (GSR) and the water-gas shift (WGS) reaction were used to produce hydrogen. The third part involved the study of the ammonia synthesis reaction at a lower pressure. At first, the GSR reaction was carried out over Ni/γ-Al2O3 catalyst to produce an average hydrogen proportion of 66.12%. Likewise, the WGS reaction was conducted by implementing a Pt/HAP catalyst that was able to achieve a 100% CO conversion rate. Later, the GSR and WGS reactions were merged in a single reactor. The combined reactor increased the IV average hydrogen proportion to 69.85%. Finally, the ammonia synthesis reaction at 1 and 2.5 atm were studied by using a promoted Ru/C catalyst. Unfortunately, no traces of ammonia were found with the Ru/C catalyst that motivated the use of a naphthalene reduced Co-Mo/CeO2 catalyst. Unfortunately, the second catalyst also could not generate any ammonia. Therefore, based on the current results, the direct catalytic conversion of glycerol to ammonia is not viable at the reduced pressures investigated. As a result, future efforts at implementing other hardware to analyze the product gas while optimizing the reactor for a higher pressure are necessary.