【作者】 张峰；

【导师】 张建树；

【作者基本信息】 石河子大学 ， 化学工程与技术， 2019， 硕士

【摘要】 煤制甲烷可以弥补我国“富煤、贫油、少气”的能源结构方式。煤直接加氢气化制甲烷因为热效率高、工艺流程简单、经济等优点,被广泛的研究。催化剂的使用使煤加氢气化所需要的苛刻条件变得更加温和。本论文主要考察了复合催化剂Fe-Co-Ca、Fe的分散程度、Fe-Ca的演变过程对煤焦催化加氢气化的影响。通过XRD、拉曼、FT-IR、TEM和BET、H₂-TPR等表征方法对煤焦和催化剂的变化情况进行分析,得到了以下主要的结论:（1）Co催化剂负载到煤/焦上用于加氢气化（CCHG）被证明是非常有催化活性的,但是Co的价格昂贵。如果用Fe部分替代Co催化剂,达到和Co催化剂一样催化效果,可达到降低催化剂成本的目的。考察了不同比例Co-Fe-Ca催化剂对加氢气化过程中的CH₄收率和CH₄生成速率的影响。通过对最佳负载1.0Co-0.5Fe-1.5Ca催化剂煤焦进行分段研究,利用XRD、TEM和拉曼研究了催化剂和煤焦的性能。结果表明,用Fe部分取代Co是可行的,在1.0Co-0.5Fe-1.5Ca催化剂存在下,甲烷产率达到71.96%,和负载1.5Co-1.5Ca催化剂的煤焦甲烷产率（71.63%）相当。Co-Fe-Ca三元催化剂在加氢气化后未发现碳化物的形成,仅仅以金属还原态的形式存在,这可能是由于Co抑制Fe₃C的形成,或Co促进了碳化铁加氢的快速转化。仅负载Fe-Ca的煤焦几乎不反应,Co-Fe-Ca共存时煤焦内部形成了孔洞结构且粗糙。催化剂的加入抑制了煤焦的石墨化过程和提高了煤焦的反应性。（2）在加压固定床反应器上研究了Fe催化剂在不同比表面积煤焦中分散程度对催化加氢气化性能的影响,利用XRD、BET、H₂-TPR、FT-IR、TEM、拉曼光谱对煤焦及催化剂进行了分析表征。结果表明,煤焦的反应活性位点和石墨化程度并非影响催化加氢气化反应的唯一因素,而催化剂的分散程度对加氢气化反应影响更大。煤焦的比表面积越大,Fe催化剂在煤焦表面分散更均匀,催化剂活性组分平均晶粒尺寸越小,并可以促进煤催化加氢气化中间相产物Fe₃C的生成,甲烷收率越高。对于比表面较高的900-Char,在氢气压力为2MPa,温度为750℃,Fe负载量为5%时,催化加氢气化甲烷收率可达53%。在900-Char上考察了Fe催化剂的负载量对催化加氢气化的影响,甲烷的收率呈先增加后降低的趋势,Fe负载量存在饱和值。（3）在加压固定床反应器中研究了煤焦催化加氢气化过程中Fe和Fe-Ca催化剂的演变。考察了Fe和Fe-Ca催化剂对CH₄收率和CH₄生成速率的影响。TEM、XRD、H₂-TPR、拉曼等手段对催化剂和煤焦的变化进行了分析,探讨了CH₄生成速率与Fe₃C与Fe的峰强度比值的关系,确定了反应速率的确定步骤和可能的反应机理。结果表明,Ca在煤焦催化加氢气化中的作用不仅是铁族金属的分散和脱硫作用,而且有利于金属铁的还原和渗碳反应。对于Fe-Ca催化的情况,在加氢气化过程中发现V_CH4与Fe₃C与Fe的相对比例呈负相关。Fe₃C比例越大,甲烷生成速率越慢。结果表明,碳化铁是一种稳定的催化加氢气化中间产物。碳化铁的消耗是甲烷生成速率的控制步骤。更多还原

【Abstract】 Natural gas from coal can make up for the energy structure characteristics of"rich coal,poor oil and little gas"in China.The direct hydrogasification of coal to methane has been extensively studied because of its high thermal efficiency,simple process and economy.The use of catalysts makes the harsh conditions required for coal hydrogasification more mild.In this paper,the effect of iron-based catalysts on catalytic hydrogasification performance was studied.The effects of Fe-Co-Ca,the dispersion of Fe and the evolution of Fe-Ca on the catalytic hydrogasification of coal char were investigated.The changes of coal char and catalyst were analyzed by XRD,Raman,FT-IR,TEM and BET.The main conclusions were as follows:（1）Cobalt has been proved to be very active in coal/char catalytic hydrogasification（CCHG）,it is expensive.Partial replacement of cobalt by iron was considered in this work in order to reduce the cost of catalyst.Co-Fe-Ca ternary catalysts are studied for hydrogasification of demineralized coal char in a fixed-bed reactor.The CH₄ yield and CH₄ formation rate was studied on catalytic hydrogasification.The optimum loading of 1.0Co-0.5Fe-1.5Ca（wt%） was studied.The properties of catalyst and char were studied by XRD,TEM and Raman.The results showed that partial substitution of Co with Fe was feasible.In the presence of 1.0Co-0.5Fe-1.5Ca（wt%） catalyst,the methane yield reached 71.96%,even higher than 71.63% of 1.5Co-1.5Ca（wt%） catalyst.The formation of carbides was not found after hydrogasification of Co-Fe-Ca ternary catalyst,but only in the form of metal reduction.This may be due to the inhibition of the formation of Fe₃C by Co or the rapid conversion of Fe₃C by Co.The interior of coal char loaded with Fe-Ca is very smooth.When Co-Fe-Ca coexists,many holes are formed in coal char and the structure is rough.The addition of catalyst inhibits the graphitization process of coal char,and increases the reaction active sites and reactivity of coal char.（2）In this paper,the effect of dispersibility of Fe on coal chars with different specific surface areas on catalytic hydrogasification performance was studied in a pressurized fixed bed reactor.The chars and catalysts were characterized by XRD,BET,H₂-TPR,FTIR,TEM and Raman spectroscopy.The results show that the active site and graphitization degree of coal char are not the only factors affecting the catalytic gasification reaction,but the dispersion of catalyst has a greater impact on the reaction.The larger the specific surface area of coal char is,the more uniform the Fe catalyst disperses on the surface of coal char and the smaller the average grain size of the active component of catalyst,which can promote the formation of the catalytically hydrogenated mesophase product Fe₃C and methane yield.For 900-Char with higher specific surface area,the methane yield can reach 53% when the hydrogen pressure is 2 MPa,the temperature is 750℃ and the Fe loading is 5wt%.The effect of Fe catalyst loading on catalytic hydrogasification was investigated at 900-char.The methane yield increased first and then decreased,and the Fe loading had a saturation point.（3）The evolution of Fe and Fe-Ca catalysts during char catalytic hydrogasification was investigated in a pressurized fixed-bed reactor.The effects of Fe and Fe-Ca catalysts on CH₄ yield and CH₄ formation rate were studied.The change of the catalysts and char was also characterized by means of the transmission electron microscopy（TEM）,X-ray diffraction（XRD）,Temperature-programmed reduction（TPR）,etc.The relationship between the CH₄ formation rate and the ratio of Fe₃C to Fe was discussed to identify the rate determining step,as well as possible reaction mechanism.The results show that the role of calcium on char catalytic hydrogasification is not only dispersion of iron-group metals and desulphurization but also promotes the reduction of metal iron as well as carburization reaction.As for Fe-Ca catalyzed case,a negative correlation between V_CH4 and ratio of Fe₃C to Fe was found during hydrogasification.The larger the proportion of Fe₃C is,the slower the methane formation rate becomes.These results indicate that iron carbide is a stable intermediate product of catalytic hydrogasification.The hydrogenation of iron carbide to form methane is the rate determining step for Fe catalyzed hydrogasification.更多还原