Researches On The Synthesis Of Hydrocarbon Fuels

The demand for energy is increasingly urgent for the rapid development of social economy. However, the depletion and the excessive use of fossil fuel have caused the global energy crisis and serious environmental pollution. Therefore, the biomass energy is regarded as an attractive energy source for its clean and renewable properities.The biomass thermochemical conversion and subsequent synthesis to clean fuel is an environmentally benign process. The systematic study of hydrocarbon synthesis was carried out in this paper.The carbon number distribution of the products of conventional Fischer-Tropsch synthesis (FTS) follows the Anderson-Schulz-Flory (ASF) model. In addition, conventional FTS is likely to yield heavier hydrocarbons (C21+), which require subsequent processes for obtaining the liquid hydrocarbons. This further requirement increases the cost and complexity of fuel production. A series of study was conducted to achieve the liquid hydrocarbon fuel-oriented synthesis.A series of Ni-promoted Co/CNTs catalysts were prepared to investigate the liquid hydrocarbon(C5-C20) production from the in-situ hydrocracking of long-chain hydrocarbons on Ni. Experimental results showed that Ni promotion had a significant effect on FTS product distribution; it led to an effective decrease of the selectivity for long-chain hydrocarbons and an increase of the selectivity for short-chain hydrocarbons. In addition, there is a proper degree of Ni promotion required for maximizing the selectivity of liquid hydrocarbons. The selectivity for liquid hydrocarbon fuel (C5-C20) on0.5Ni-Co/CNT reached a highest value of61.6%at533K,2MPa, a H2/CO mole ratio of2and GHSV of1200h"1.The maximum selectivity for gasoline range hydrocarbons (GRHs) in the conventional FTS is45%and it consists of mainly liner hydrocarbons with low octane number. The longer-chain hydrocarbons generated on the FTS catalyst can be selectively cracked on the acid sites of the zeolite to produce more GRHs Simultaneously, isomerization and alkylation also occur on the zeolite to produce more branched alkanes. Therefore, Ru, Ni promoted Co/HZSM-5catalysts were prepared to investigate the catalytic performance for GRH production. The results showed that HZSM-5had a significant influence on the product distribution, and the GRH was enriched. Both Ru and Ni promoters were beneficial for CO conversion and GRH production. The addition of Ru to the Co/HZSM-5catalyst remarkably increased the reduction degree and the amount of weaker acid sites, and obtained the high GRH selectivity of61.9%.Biochar (BC) is the residual by-product from the thermochemical conversion of biomass for bio-oil production. At present, the majority of biochar is discarded or utilized as process fuel. To search the efficient way of biochar utilization, chemical activation was carried out and a series of characterization was performed. The BET surface area increased beyond1100m2/g after activation. Moreover, the activated biochar had higher graphitization degree. And the activated biochar (ABC) has great potential to be used as catalyst or support.Based on the above results, rice husk biochar was developed as a green support to prepare the Ru based catalyst for syngas methanation, compared with the activated carbon supported Ru catalyst. The Ru/ABC catalyst demonstrated excellent activity, which was comparable or superior to the Ru/AC catalyst. A high CH4selectivity of98%and a CO conversion of100%were obtained under the proper reaction conditions over the Ru/ABC catalyst. In addition, the Ru/ABC catalyst showed high stability during a period of100h on stream.After that, the methanation of H2-deficient bio-syngas was carried out over the biochar supported Ru catalyst. In addition, different amount of H2, deriving from the bio-oil reforming, was added to the original bio-syngas to investigate the effect of H2/C on the catalytic performance. It was found that adding extra H2could significantly increase the total carbon conversion. Under the conditions of693K, H2/C=4, CO conversion of97%and CO2conversion of55%, as well as the CH4selectivity of92%could be obtained over the0.5Ru/ABC catalyst.