Performance improvement of steam gasification of pine for hydrogen-rich gas with dolomite catalyst modified by bentonite/limonite

Abstract: In this study, we adopted steam gasification of biomass, and pine fuel rods as the experimental objects. We used gas chromatography and Fourier transform infrared spectrometer to analyze components of gas and tar change during the process of gasification. We also determined catalytic performance of modified dolomite (bentonite as the carrier, dolomite as the active component and a small amount of load limonite) as temperature rose. Our experiment results showed that, high-temperature made steam gasification of biomass intensified so that steam reforming reaction intensified and thus contributing to H2 gas volume fraction in the overall upward trend in the gasification components, but hydrocarbon gas volume fraction in downward trend. Gasification gas carries gasification tar into the catalyst layer, which makes tar catalytic cracked, promotes steam reforming reaction intensified and thereby changes the composition of gasification gas. Under the condition of steam gasification with modified dolomite catalyst at 750 ℃, H2 volume fraction was 45.77%±0.23%. Compared to hydrogen-rich action of catalytic and non-catalytic conditions dolomite, gasification temperature dropped to 100oC. With the rise of temperature, modified dolomite promoted the increase of carbon oxides and hydrocarbons volume fraction, but hydrogen-rich degree weaken. The calcined dolomite contained MgO/CaO as active ingredients can cause the long carbon chain cracked in aliphatic hydrocarbons, conducive to the production of radical hydrogen ion, and be helpful to generate hydrogen. When Fe as a promoter was used, it was activated to Fe3+ by high temperature steam, and converted to Fe2+ after promoting tar cracking. Modified dolomite not only promoted the scission of carbon chain length on the hydrocarbon side chain and the formation of H2, but also promoted opening reactions of aromatic ring, decarboxylation and dehydroxylation reactions, thereby making tar after pyrolysis easily to be converted into small molecule gas carbon containing, which helped to reduce the production of tars gasified and improved the gasification efficiency. The catalyst active center Fe3+ decreased at higher temperature, which made the gaining weight of homemade catalyst after catalysis reduced to a minimum of 900 ℃, but compared to dolomite, the change of color and shape of modified dolomite between front and rear catalytic was small, which reflected the mechanical strength and surface area carbon optimized. The catalytic activity of dolomite was secondly to nickel-based catalyst, but it had potential economic value with cheaper price. In this study, we compared to steam gasification of biomass with dolomite catalyst, explored the catalytic properties of modified dolomite, which would provide useful information of dolomite modification method and studies of steam gasification of biomass. The purpose of this research was to promote the use of dolomite catalysts, and our results showed that they can be used for the treatment of tailings and to deepen the study of biomass steam gasification.