Catalytic secondary methods for the removal of tar derived from biomass gasification: use of low-cost materials and study of the effect of sulfur species on the steam reforming activity of the catalysts

Biomass gasification could potentially mitigate the actual dependency on fossil fuels. The practical application of this technology still faces many challenges to be considered a sustainable and profitable energy production source. One of the drawbacks of this technology is the production of undesirable by-products such as high molecular weight hydrocarbons collectively known as “tar” and sulfur compounds. These unwanted compounds must be removed before syngas end-use applications as they can foul pipes and reduced the performance of equipment downstream the gasifier as well as poison the catalyst used for upgrading the syngas. Catalytic steam reforming stands as an appealing tar removal technology in the small and medium sized gasification plants where heat management is crucial and recovery of the energy content within the tar compounds is desirable avoiding wastewater effluents and disposal of adsorbents. Nickel based catalysts have been the preferred choice in industrial applications for the reforming reactor. However, deactivation by carbon deposition is at present an unresolved problem which must be addressed before commercial application of biomass gasification technology. Moreover, the presence of sulfur compounds even at the low concentration found in most biomass feedstocks is deleterious for the steam reforming activity of the catalyst. This thesis comprises four experimental studies, each of them deal with a specific arguments of the hot gas cleanup technology of biomass syngas. The main focus was on the steam reforming activity of nickel-based catalyst and the effect of sulfur and the potassium-sulfur interactions on the steam reforming performance of the catalyst. The main contributions from these studies are; 1) the development of a less time and energy consuming synthesis procedure for the production of a mayenite-supported nickel catalyst using low-cost precursors. This new method involves the addition of the nickel precursor during the mayenite synthesis procedure. Compared to the “wet impregnation” technique the developed method showed slightly lower toluene steam reforming activity but greater stability, which was ascribed to a higher carbon deposition tolerance. 2) Better understanding on the sulfur poisoning of catalysts under steam reforming conditions at laboratory scale. The results evidenced that for a deeper knowledge of the sulfur poisoning, the calculation of the sulfur coverage should be more accurate and new methods for its measurement are required. 3) Comprehension of the mechanism of interaction between potassium and sulfur on a sulfur passivated commercial nickel catalyst under reforming conditions using real biomass syngas. The preferential adsorption site for sulfur and potassium was determined for the applied experimental conditions and catalyst and a mechanism involving the interaction of potassium with the sulfur chemisorbed on the active sites was propose

Use of low-cost materials for tar abatement process

In the present work char, olivine and mayenite were used as bed materials to study ability to remove tar produced in biomass thermal processing. The tar gases formed from the pyrolysis reactions of the olive pomace biomass were forced to pass through the bed material. Nitrogen was used as carrier gas. The temperature of the bed was set at 660 °C and no oxidizing agent was added during the tests. The char was produced from the pyrolysis of olive pomace biomass. Olivine was used without any pre-treatment. Mayenite was synthesized in laboratory using CaCO3 and Al2O3 as precursors. Among the tested materials, mayenite showed the best tar removal capacity and stability, with a total tar removal of about 60% after 60 min time on stream, while in the case of char and olivine the attained value was 15%. The measured average nitrogen-free gas flow value in the tests carried out with mayenite was 0.84 NL min-1, whereas in the case of char and olivine the obtained average gas flow values were 0.65 and 0.55 NL min-1, respectively. Accordingly, the higher average hydrogen amount was measured in the tests using mayenite as bed material (36%)

Pyrolysis wastewater treatment by adsorption on biochars produced by poplar biomass

yrolysis is a widely studied thermochemical process, however the disposal of the produced byproducts is an unexplored field. In particular, the acqueous phase, characterized by a high organic load (TOC), must be necessarily treated. Aims of this work is to study the potentiality of biochar as adsorbent material for the treatment of this wastewater. For this aim, pyrolysis wastewater and biochar produced in the same plant were used. Two biochars produced at different temperatures (550 and 750 °C) and an activated biochar produced by chemical activation with NaOH of the raw biomass were tested. The study shows that higher temperature in the biochar production leads to higher sorption capacity of the organic compounds due to an increase of the surface area. The activation process further increases the surface area of the biochar that becomes similar to that of a commercial activated carbon while the sorption capacity exceeds that of commercial activated carbon of 2.5 times