Hydrogen/hydrogen-rich Syngas Production From Bio-oil Steam Reforming And Synthesis Of F-T Liquid Fuels

Biomass is regarded as a renewable energy source, which is photo-synthesized from water and carbon dioxide by plants. Concerns about the depletion of fossil fuel reserves and the pollution caused by continuously increasing energy demands in the world make biomass an attractive alternative energy source. In the case that biomass is utilized to as an energy resource, the emission of carbon dioxide caused by its use is absorbed by newly grown biomass and this is called as carbon-neutral. In addition, for the negligible sulfur, nitrogen, and metal contents comparing with fossil fuels, biomass is a clean energy source. There is abundance of biomass in China. The development and utilization of biomass energy is very significative to the energy security of China. The main purpose of present study is: (1) to produce syngas (i.e., the bio-oil-syngas) from the bio-oil and (2) to synthesize the F-T fuels from the bio-oil-syngas.1. Steam reforming of bio-oil to produce hydrogen/hydrogen-rich syngasThe production of hydrogen and hydrogen-rich bio-oil-syngas from the catalytic steam reforming of bio-oil, generated from fast pyrolysis of biomass, was investigated by using novel metal-doped catalysts of [Ca₂₄Al₂₈O₆₄]⁴⁺·4O^-*/M (C12A7-O^-/M, M=Mg, K, Ce). The features of the steam reforming of the bio-oil, including the effects of temperature, the metal-doped content and the S/C ratio (the ratio of mol steam to mol carbon fed) on the hydrogen yield, carbon conversion (mol carbon in production gases to mol carbon fed) and the distributions of the products were measured in the fixed-bed continuous flow reactor. It was found that the Mg content 15-18 % of C12A7/Mg catalyst gave the highest yield of hydrogen and the best carbon conversion among our tested catalysts. For the C12A7/18%Mg catalyst, a hydrogen yield as high as 80% was obtained, and the maximum carbon conversion is up to 96% under the steam reforming condition (S/C>4.0, GHSV= 10000h^-1, r=750℃). The catalyst deactivation was mainly caused by the deposition of carbon (coke-formation). Initial catalyst activity can be partly maintained through periodic regeneration via the cleaning of the catalyst and the gasification of the carbon deposits. Moreover, we have studied the effect of catalyst type (C12A7/15%Mg, 12%Ni/γ-Al₂O₃, 1%Pt/γ-Al₂O₃) on the hydrogen yield, carbon conversion and the composition of bio-oil-syngas at different reaction condition such as reforming temperature (T), the molar ratio of steam to carbon fed (S/C). It was found that H₂ and CO₂ were the major reforming products together with small amount of CO, and CH₄ in the effluent gaseous products of bio-oil steam reforming. The catalyst characteristics and the intermediate species formed in the steam reforming processes were investigated by the XRD, XPS and FT-IR measurements. The mechanism of the bio-oil steam reforming was addressed according to the above investigations.2. Liquid fuels production from bio-oi-syngas via F-T synthesisThe Fischer-Tropsch synthesis (FTS) was performed in a fixed-bed flow reactor by using the H₂/CO/CO₂/N₂ mixture as a model bio-oil-syngas. 100Fe/6Cu/16Al/6K was selected as the optimum catalyst for FTS from bio-oil-syngas. The effects of temperature (T), total pressure (P), contact time (W/F) and the CO₂/(CO+CO₂) ratio (r) on the FTS performance were investigated over the co-precipitated iron catalyst of 100Fe/6Cu/16Al/6K. To obtain higher total carbon (CO+CO2) conversion and higher C₅₊ selectivity, it was found that the optimum FTS condition over the Fe/Cu/Al/K catalyst is T = 280℃～300℃, P = 1.0 MPa～2.0 MPa, W/F> 12.5 g_cat·h·mol^-1. Total carbon (CO+CO₂) conversion about 36 % and C₅₊ selectivity about 44 % were obtained at a typical reaction condition: T = 300℃, P = 1.5 MPa, W/F= 12.5 g_cat·h·mol^-1. It was also found that the CO₂/(CO+CO₂) ratio of the syngas have remarkable effect on FTS performance and r < 0.5 is more suitable for FTS in our investigated range. The characteristics of FTS catalyst were also investigated by various characterization measurements.