【作者】 孙道安；

【导师】 季生福；

【作者基本信息】 北京化工大学 ， 化学工程与技术， 2010， 硕士

【摘要】 我国是农业大国,每年要产生大量的秸秆等农业废弃物。然而这些秸秆等废弃物利用率很低,大量的秸秆被焚烧或弃之乱堆。生物沼气可由秸秆等农业废弃物经厌氧发酵产生,其主要成分为体积比约2：1的CH4和CO2的混合气体。根据沼气的组成特点,向其中添加适量的氧化剂氧气和水蒸气进行联合重整可将其转化制合成气。通过这种途径对沼气加以利用,不但能带来环境和经济的双重效益,而且开辟了生物质制合成气,进而制化学品的非化石路线。本研究采用浸渍法制备了Ni含量为7.5-15(wt)%的Ni/SBA-15催化剂,以及采用碱金属(Li、Na、K)、碱土金属(Mg、Ca)和稀土金属(La、Ce)、过渡金属(Fe、Co、Cu、Mn)等不同助剂改性后的M/Ni/SBA-15催化剂,同时以FeCrAl合金薄片为基体,制备了Ni/SBA-15/Al2O3/FeCrAl和M/Ni/SBA-15/Al2O3/FeCrAl(M=La、Mg、Ce)整体式催化剂,在常压固定床反应器上考察了氧气和水蒸气的添加量、Ni含量、空速以及助剂等因素对模拟生物沼气联合重整反应性能的影响,并采用XRD、H2-TPR、BET、TEM进行了催化剂结构表征。结果表明：10wt%Ni/SBA-15催化剂的性能最好,在模拟生物沼气中添加摩尔比为0.6的氧气和摩尔比为0.6的水蒸气进行联合重整反应最适宜。在800℃、空速为24000 ml/(g·h)、进料比为CH4:CO2:O2:H2O =2:1:0.6:0.6(V/V)反应条件下,CH4和CO2转化率分别为92.2%和76.3%,H2／CO比为1.35左右。10%Ni/SBA-15催化剂连续反应100h活性无明显下降。镍负载在SBA-15上,对孔道结构造成一定的影响,但没有被明显改变,10%Ni/SBA-15催化剂上活性组分与载体作用力适中,有效地促进了反应。采用过渡金属和碱金属对10%Ni/SBA-15催化剂改性,催化活性出现了不同程度的下降,而采用3wt%Mg改性后的催化剂活性得到了明显提高,在800℃下,催化剂上的CH4和CO2转化率分别高达95.6%和79.3%,高温下连续反应130h,催化剂活性几乎不变。经过3wt%Mg改性后,助剂MgO与NiO生成固溶体,提高了活性组分的分散度,从而提高了催化剂的活性。金属基整体式催化剂中,10wt%Ni/SBA-15/Al2O3/FeCrAl催化剂的活性最好,CH4和CO2转化率分别为92.4%和76.1%,与传统颗粒催化剂活性相当。经过适量的Mg、La、Ce改性后,催化剂的活性均得到了一定程度地提高,其中经3wt%La改性后的活性最好,800℃下,CH4和CO2转化率分别为94.9%和78.4%。更多还原

【Abstract】 China, as an agricultural giant yields numerous agricultural refuse, such as straw each year. However, the utilization rate of straw is very low and most is incinerated or disregarded. Biogas which is composed of CH4/CO2 with the volume ratio of 2 could be produced by anaerobic fermentation of agriculture wastes. On the basis of the gas composition of biogas, the biogas as a raw material and an appropriate amount of oxygen and steam was added for the combined reforming for the production of synthesis gas. In this way, the biogas could be effectively used and it would not only result in considerable economic and environmental benefits, but such a non-fossil route should have attractive prospects.In this paper, a series of Ni/SBA-15 catalysts with Ni content from 7.5wt% to 15wt% and the modifications were also done with alkali metal(Li, Na, K), alkaline earth metal (Mg, Ca), rare earth metal (La, Ce) and transition metal(Fe, Co, Cu, Mn) were prepared by impregnation method. On the basis of these granular catalysts, Ni/SBA-15/Al2O3/FeCrAl catalysts and M/Ni/SBA-15/Al2O3/FeCrAl (M=Mg, La, Ce) catalysts were also prepared. Finally, their catalytic performances were investigated in a continuous flow fixed-bed micro-reactor under atmospheric pressure. The catalyst structures were also characterized by X-ray diffraction (XRD), N2-adsorption/desorption, transmission electron microscopy (TEM), and H2 temperature programmed reduction (H2-TPR) techniques.The results indicated that the 10%Ni/SBA-15 catalyst exhibited the best catalytic activities for the combined reforming of the biogas to syngas. The optimal molar ratios of oxygen and steam added were both 0.6. Under the reaction conditions that the feed gas molar ratios of CH4/CO2/O2/H2O were 2/1/0.6/0.6, GHSV was 24000 ml·gcat-1·h-1 and the reaction temperature was 800℃, the conversions of CH4 and CO2 were 92.2% and 76.3%, respectively, with 1.35 of H2/CO. The catalytic activities of the catalyst did not obviously decrease after 100 h reaction time on stream. It could be concluded that the prepared molecular sieve SBA-15 obviously showed meso-porous structure and the structure of SBA-15 modified by Ni kept in good condition. The interaction force between active component and carrier was moderate, which promoted the combined reforming.The catalytic activities of 10%Ni/SBA-15 decreased more or less when it was modified by alkali or transition metal. On the whole,3wtMg% was the best choice, the conversions of CH4 and CO2 were 95.6% and 79.3% respectively. The 3%Mg/10%Ni/SBA-15 catalyst showed highly stable activity at 800℃for 130 h. The MgO promoter and NiO could form a solid solution that improved the dispersion of NiO and enhanced the activity.For the 10wt%Ni/SBA-15/Al2O3/FeCrAl catalyst, the CH4 and CO2 conversion was 92.4% and 76.1% respectively, the catalytic activities of which were similar to granular catalyst. The catalytic performance improved in different degree when 10wt%Ni/SBA-15/Al2O3/FeCrAl catalyst was modified by proper amount Mg, La, or Ce promoter. Conclusively,3wt%La promoter was the most suitable and the conversions of CH4 and CO2 were 94.9% and 78.4% respectively at 800℃.更多还原