Synthesis gas from black liquor trace components and methanol synthesis

Sammanfattning: The common European Energy and Climate policy states that in 2020 the share of biofuels for inland transports should be 10 %. Such a stipulation calls for a commercially sustainable biofuel production. A promising route for Sweden is biofuel production via gasification of black liquor, which could replace about 25 % of the current Swedish consumption of transportation fuel. The main components in the gas produced by black liquor gasification are H2, CO, CO2, N2, CH4 and H2S, which has been reported in previous work. In the present work, trace components in synthesis gas produced via black liquor gasification have been characterized, since trace components could influence the subsequent fuel synthesis. Of the trace components, the most abundant ones were benzene at an average concentration of about 60 ppm, followed by COS, with an average concentration of about 50 ppm. In addition, low amounts (i.e. a few ppm), of C2-hydrocarbons were observed in the gas. No tars were observed in the gas, but tars were observed in some deposits at pipe walls. The concentration of particles in the synthesis gas was very low; < 0.1 mg/Nm3. Submicron particles were comprised of elements such as C, O, Na, Si, S, Cl, K, and Ca, and these particles probably originated from black liquor. Larger particles were comprised mainly of Fe, S and Ni and were probably the result of corrosion of steel in the plant pipe-work. Synthesis gas was also purified by passing beds of active carbon and zinc oxide, mixed with hydrogen gas from cylinders and in the present work, for the first time, catalytically converted to methanol using bench scale equipment during 45 hours in total. The space time yield of methanol produced at a pressure of 25 bar was 0.16-0.19 g methanol/ (g catalyst h) and comparable results were obtained using synthesis gas from gas cylinders with pure gas. The spent catalyst, exposed to gas from the gasifier, was slightly enriched in Ca and Na at the inlet of the reactor and in B and Ni at the outlet of the reactor. Ca, Naand B probably stem from black liquor whereas Ni probably originates from the stainless steel in the equipment. A slight deactivation of the catalyst exposed to gas from the gasifier was identified but it was not possible to reveal the origin of the deactivation. However, the surface area and mesoporosity of the catalyst was reduced. As expected, the produced methanol also contained water and traces of hydrocarbons up to C4, ethanol and dimethyl ether. In summary, this work has shown that the synthesis gas produced by gasification of black liquor is pure and that methanol synthesis from the gas is quite feasible.