Methanol generation from bio-syngas: experimental analysis and modeling studies

Methanol is industrially generated from non-renewable fossil fuel sources. Owing to its widespread use in all domains, from synthesis of various chemicals to its use as an alternative fuel in the SI engines, finding a sustainable and renewable way of generating methanol would be one of the key achievements. Biomass-derived syngas for methanol generation would be one such example. However, bio-syngas has few drawbacks like (a) lower H-2 content when compared to the traditional SMR syngas, (b) the impurities present in bio-syngas are higher and need removal, (c) the biomass availability is scattered, just to name a few. In this work, we will be addressing the low H-2-containing syngas for methanol generation process. Since limited literature is available on the experimental work on methanol generation from bio-syngas (without H-2 adjustment), this work aims to bridge the research gap by presenting experimental results on direct bio-syngas to methanol generation process. This work will address the experimental comparison between two syngas compositions: one H-2 excess and the other H-2 deficient. The composition of the first syngas, namely syn1, used is like the one obtained from the SMR process. The composition of the second syngas, syn-2, is via the biomass gasification process. The H-2/(CO+CO2) values in syn-1 and syn-2 were 3.54 and 1.08, respectively. The experimental setup consisted of a high-pressure microreactor, and a Cu/ZnO/Al-2 O-3 commercial catalyst was used for the methanol generation process. The results from the experimental work were used to develop and validate the Aspen Plus (R) kinetic model. The validated model for lower H-2-containing syngas for methanol generation process would be further used for the formulation of mathematical equation for methanol yield predictions. The experiments performed indicated that the methanol yield is favored at lower temperatures and higher pressure values of 483 K and 5 MPa for both syn-1 and syn-2. The results also indicated that the high CO2/CO ratio results in increased side reactions. The observed increase in the CH4 selectivity in syn-2 when compared to syn-1 was the evidence for this increased side reactions. This is one of the key highlights as for SMR syngas-to-methanol conversion the CH4 is sometimes assumed to be inert. Finally, the developed mathematical model predicted a maximum methanol yield of 21.06% for lower H-2 syngas at a temperature of 483 K, a pressure of 5 MPa and a space velocity of 1650 ml/h(g cat). The mass balance analysis suggests using 2.27 kg of syn-1 and 5.67 kg of syn-2 for production of one kg of methanol under a similar condition of 483 K, 5 MPa and 1650 ml/h(g cat). This validated model for methanol production will find its utility for methanol yield optimization and techno-economic analysis.