固定床中甲烷在不同煤焦上的裂解制氢

本文以煤焦与甲烷共转化为背景,采用小型石英管固定床反应装置,于在1123 K下对甲烷在褐煤焦、脱灰煤焦、活化煤焦以及石英砂床层上的裂解反应进行了较为详细的研究,并采用扫描电子显微镜以及比表面积测定仪对反应前后的褐煤焦、脱灰煤焦进行了表征。甲烷在脱灰煤焦和褐煤焦上的转化率相差不多,说明煤焦中的灰成分对甲烷裂解没有影响。在活化煤焦上,甲烷的转化率有了很大幅度的提高,最高可达97%左右。在脱灰煤焦活化过程中,煤焦活化程度越小越有利于甲烷的裂解,甲烷转化率最高可达97%左右,表明煤焦中的微晶对反应有影响。随着反应时间的增加,甲烷转化率以及氢气的收率逐渐降低,其主要原因是反应过程中甲烷裂解产生的积碳覆盖在煤焦表面上,使其催化活性降低。     

微波辐射下活性炭催化甲烷裂解制氢

采用石英管固定床反应器,在微波加热条件下分别研究了气氛条件、甲烷分压以及铁粉对活性炭催化裂解甲烷的影响,并与传统电加热方式下的甲烷裂解特性进行了对比研究。结果表明,活性炭在不同气氛条件下表现出不同的升温特性,活性炭在氮气和氢气中的升温效果优于甲烷气氛。铁粉的掺入有利于提高活性炭反应温度,从而促进甲烷的转化率。对反应前后的活性炭进行了扫描电镜和比表面积分析,结果表明甲烷裂解后产生的大量积炭覆盖在活性炭表面,导致比表面积和孔容减小,平均孔径增大。进而推测活性炭活性降低的主要原因是由于积炭堵塞了活性炭微孔,减少了甲烷与活性炭微孔中的活性中心位的接触。     

负载催化剂的煤焦对甲烷化反应行为的影响

研究了负载催化剂的内蒙褐煤煤焦对CO甲烷化反应的催化性能。在加压固定床反应器中比较了Ni,Co,K,Fe,Na,Ca等催化剂种类对甲烷化反应的影响,并在气化反应工艺条件范围内考察了温度、压力、CO和H_2分压、空速等条件对CO转化率和甲烷收率的影响。研究结果表明:负载催化剂煤焦对甲烷化反应具有明显的催化作用,其中金属元素K在气化甲烷化反应过程中拥有较好的双重催化作用。在反应温度600~700℃时,CO转化率和甲烷收率随着反应温度的升高而增加,表明甲烷化反应仍处于动力学控制,未达到热力学平衡。压力的增加能够显著提高CO转化率和甲烷收率,甲烷收率由0.5 MPa下的25.8%升高至3.5 MPa下的56.65%,但甲烷收率的增幅逐渐减小。CO和H_2分压的增加以及空速的降低,均能够提高反应深度,促进甲烷化反应的进行。H_2/CO摩尔比的增加,能够强化CO的转化并使甲烷收率增加。基于Langmuir-Hinshelwood模型拟合得到了负载碳酸钾催化剂煤焦的甲烷化反应动力学方程。     

褐煤焦中的矿物质对气化动力学的影响

利用热重分析仪研究了水蒸气气氛下霍林河褐煤焦和脱灰褐煤焦的气化动力学特性,并考察了脱灰前后褐煤焦孔结构的变化。结果表明:褐煤原焦气化反应速率在反应初始阶段(转化率30%)高于脱灰褐煤焦,但在反应后期低于脱灰焦,这是因为煤焦中灰分的脱除一方面去除了矿物质的催化作用,另一方面增大了煤焦的孔径,因而减小了气化剂的扩散阻力。灰层扩散控制的缩核模型可以描述褐煤焦水蒸气气化过程,而脱灰后褐煤焦水蒸气气化过程用均相模型可以很好地表示。     

微波辐射下污泥残渣催化甲烷裂解制氢

采用石英管固定床反应器,在微波加热条件下分别研究了不同功率、气氛条件、粒径以及进口甲烷浓度对污泥残渣催化甲烷裂解反应的影响。结果表明,污泥残渣对甲烷裂解反应具有良好的催化活性;增加微波功率和减小粒径均能够有效提高甲烷转化率;污泥残渣在不同气氛条件下表现出不同的温度特性,其中氮气和氢气氛围内的温度明显高于甲烷气氛中,表明甲烷裂解过程中气氛条件是影响反应进行的因素之一;进口甲烷浓度越高,甲烷的转化率越大。反应前后污泥残渣电镜扫描分析及物性参数的比较表明,甲烷裂解后产生的大量积炭覆盖在污泥残渣表面,导致比表面积降低、平均孔径增大,表明污泥残渣活性降低的原因可能与积炭覆盖表面,导致甲烷分子无法与活性中心接触所致。     

微波辐照下半焦催化甲烷裂解制氢研究

以未经任何活化的内蒙古煤热解半焦为催化剂,研究了甲烷在微波加热条件下裂解制氢的反应规律和催化剂失活机理,探讨了半焦的表面结构特征和含氧官能团,分析了反应条件对甲烷催化裂解过程的影响.研究表明,在650℃~850℃之间,内蒙古褐煤半焦是一种很好的甲烷裂解制氢催化剂,在半焦制备温度为850℃,反应温度为850℃,空速为600mL/(h·g)的条件下,半焦催化甲烷裂解的初始转化率最高达到了61.75%;升高半焦制备温度和催化反应温度以及降低空速有利于提高甲烷的转化率;半焦催化活性降低的主要原因是表面结构特性的改变和含氧官能团的减少.     

玄武岩催化甲烷裂解制 C2 烃

以天然玄武岩为甲烷裂解催化剂,通过XRF、XRD、SEM及XPS对催化剂组成、结构、表面活性物种进行了研究。利用固定床反应装置考察了不同反应温度、空速条件下玄武岩催化甲烷裂解制C_2烃的效果。结果表明,在气体空速为4 L·h-1条件下,当反应温度为1 225 K时,甲烷的转化率为7.66%,C_2烃的选择性为33.64%;当反应温度升至1 325 K时,甲烷的转化率可达17.13%,同时C_2烃的选择性为27.21%。相同温度下,气体空速越大,乙烷的选择性越高,乙炔的选择性越低。催化剂活性因表面积炭的产生而降低,积炭类型为芳烃积炭。     

煤焦加压水蒸气催化气化反应特性及甲烷释放规律研究

以内蒙褐煤焦为研究对象,K_2CO_3为催化剂,在小型加压固定床上考察了反应温度、操作压力和水碳比对煤焦水蒸气气化反应过程中碳转化率、反应速率和甲烷浓度及其累计流量的影响。结果表明,随着反应温度的增加,碳转化率和反应速率显著增加,甲烷浓度及其累计流量也增加,表明甲烷化反应在600~700℃内仍受动力学控制。操作压力的提高,碳转化率和反应速率呈先增加后减小的变化趋势,而甲烷的浓度逐渐增加,其累计流量由常压下的2.4 mL逐渐增加至3.5 MPa下的43.2 mL。随着水碳比的增加,碳转化率和反应速率大幅增加,但是甲烷的浓度逐渐降低,甲烷的累计流量受反应速率和反应平衡的共同影响,呈先增加后减小的趋势。     

煤焦加压水蒸气催化气化反应特性及甲烷释放规律研究

以内蒙褐煤焦为研究对象,K_2CO_3为催化剂,在小型加压固定床上考察了反应温度、操作压力和水碳比对煤焦水蒸气气化反应过程中碳转化率、反应速率和甲烷浓度及其累计流量的影响。结果表明,随着反应温度的增加,碳转化率和反应速率显著增加,甲烷浓度及其累计流量也增加,表明甲烷化反应在600⁷00℃内仍受动力学控制。操作压力的提高,碳转化率和反应速率呈先增加后减小的变化趋势,而甲烷的浓度逐渐增加,其累计流量由常压下的2.4 mL逐渐增加至3.5 MPa下的43.2 mL。随着水碳比的增加,碳转化率和反应速率大幅增加,但是甲烷的浓度逐渐降低,甲烷的累计流量受反应速率和反应平衡的共同影响,呈先增加后减小的趋势。     

烯烃裂解增产丙烯催化剂再生性能

由于烯烃裂解技术反应自身的特点,催化剂容易积炭失活,需要进行多次再生,因此,催化剂的再生性能对烯烃裂解技术至关重要。在实验室对中国石化中原石油化工有限责任公司烯烃裂解工业装置的ZSM-5催化剂进行了多次反应和再生试验,考察其烯烃裂解反应性能,并运用TG、XRD、NH₃-TPD、氮气物理吸附以及SEM等对再生前后的催化剂样品进行表征。结果表明,开发的烯烃裂解催化剂经过13次的反应再生过程,新鲜催化剂与再生催化剂的比表面积和孔容基本相同,烯烃转化率、丙烯及乙烯收率无明显变化,烯烃转化率仍大于73%,丙烯和乙烯收率分别大于32%和10%。且催化剂骨架结构和酸中心稳定,在多次反应与再生过程中的酸量保持不变,具有良好的再生性能。     

Hydrogen production by methane cracking over different coal chars

Hydrogen production by methane cracking over a bed of different coal chars has been studied using a fixed bed reactor system operating at atmospheric pressure and 1123 K. The chars were prepared by pyrolysing four parent coals of different ranks, namely, Jincheng anthracite, Binxian bituminous coal, Xiaolongtan lignite and Shengli lignite, in nitrogen in the same fixed bed reactor operating at different pyrolysis temperatures and times. Hydrogen was the only gas-phase product detected with a GC during methane cracking. Both methane conversion and hydrogen yield decreased with increasing time on stream and pyrolysis temperature. The lower the coal rank, the greater the catalytic effect of the char. While the Shengli lignite char achieved the highest methane conversion and hydrogen yield in methane cracking amongst all chars prepared at pyrolysis temperature of 1173 K for 30 min, a higher catalytic activity was observed for the Xiaolongtan lignite char prepared at 973 K, indicating the importance of the nature of char surfaces. The catalytic activity of the coal chars were reduced by the carbon deposition. The coal chars had legible faces and sharp apertures before being subjected to methane cracking. The surfaces and pores of coal chars were covered with carbon deposits produced by methane cracking as evident in the SEM images. The results of BET surfaces areas of the coal chars revealed that the presence of micropores in the chars was not an exclusive reason for the catalytic effect of the chars in methane cracking.     

Catalytic Performance of Coal Char for the Methane Reforming Process

A new concept of combined coal gasification and methane reforming in a single reactor was proposed as an alternative path for syngas production using coal and coalbed methane. Here, the results of this process are summarized. The experimental work was carried out in a fixed‐bed reactor. Methane cracking, CO₂/steam reforming of methane over coal char, and the effects of chars made from different types of parent coal on methane conversion were examined. The catalytic effect of coal char on methane cracking and reforming increased with decreasing coalification degree. A synergistic effect was observed in that, while the coal char catalyzed the methane reforming reactions, gasification of the coal char took place simultaneously, which counter‐balanced the deposition of carbon especially for the methane‐steam‐char system.     

固定床煤焦加氢气化制甲烷研究与开发

采用固定床反应器,在不同的反应温度(973 K~1 123 K)、压力(3 MPa~7 MPa)和制焦温度(973 K~1 073 K)下,分别研究了煤种、温度、压力和制焦温度对大同煤焦、西班牙煤焦和平顶山煤焦的加氢气化的影响;认为煤加氢气化过程分为3个反应阶段。实验结果表明,在高温、高压条件下,有利于促进甲烷的产率和提高碳转化率。     

平顶山高灰熔融性温度煤的气化反应性研究

介绍了平顶山地区有代表性的7种煤样在800℃～1 200℃下,其脱灰煤焦-CO2气化反应活性的实验,主要考察了煤种、灰含量及粒径对煤焦反应性的影响,实验结果表明:煤种对煤焦-CO2气化反应有明显影响;煤中灰分对煤焦气化反应的影响主要表现在两个方面,一是灰成分对煤焦气化反应的催化作用,二是灰熔融性影响煤焦气化排渣行为。脱灰既可以除去煤焦中具有催化作用的矿物质,又可以增大煤焦的内表面积。     

Effect of carbon deposition on porosity and reactivity of a lignite char

Carbon deposition from the cracking of methane into the pores of a lignite char occurs at a significant rate at temperatures between 815 and 855 °C. The maximum amount of carbon deposited is much less than the amount of open pore volume within the char which is potentially available to accommodate carbon. Removal of the inorganic impurities from the char by acid washing significantly reduces the extent of carbon deposition. Carbon deposition reduces surface area and open pore volume of the char and accessibility of methane into the pore structure. Deposition of carbon has a large and lasting adverse effect on the subsequent reactivity of the char to air. This has been attributed both to a decrease in active surface area, and deactivation of catalytic inorganic impurities due to coating with carbon. Deposited carbon is much less reactive to air than the lignite char. Results indicate that in order to maximize subsequent char reactivity to oxidizing gases, carbon deposition from volatiles during the conversion of coal to char should be kept to a minimum.     

秸秆灰对煤焦气化反应性的影响

钾、钙对煤焦气化反应性具有重要影响,秸秆灰中含有丰富的钾、钙。以神木煤为制焦原料,通过STA409PC同步热分析仪研究了秸秆灰对煤焦气化反应性的影响,并通过测定煤焦的碘吸附值对其比表面积及孔隙结构进行了分析。结果表明：煤与玉米秸秆共焦化所得煤焦的气化反应性明显优于单独煤焦,且与玉米秸秆的添加比例有关;采用脱灰玉米秸秆与煤共焦化所得煤焦的气化反应性与单纯煤焦相近;将与玉米秸秆等效的秸秆灰添加到煤焦中,煤焦的气化效果明显优于等效玉米秸秆与煤共焦化所得煤焦。煤焦碘吸附值测定结果表明,脱灰秸秆与煤共焦化所得煤焦的碘吸附值最大,单纯煤焦的碘吸附值最小,说明玉米秸秆及秸秆灰对煤焦的比表面积及孔隙结构具有重要的影响,与煤焦的气化反应性评价结果基本一致。     

The kinetics of coal chars hydrogasification

Hydrogasification reaction of chars produced from two rank coals was investigated in temperature up to 1173 K and pressure up to 8 MPa. The reactivity of the lignite Szczerców char has been found to be slightly higher than of the subbituminous coal Janina char produced at the same conditions. A high value of the char reactivity was observed to certain carbon conversion, above which a sharp drop takes place. It has been shown that to achieve proper carbon conversion the hydrogasification reaction must proceed at temperature above 1200 K. Based on the active centres theory the kinetic equations of the hydrogasification process were developed and the kinetic constants at the maximum reaction rate evaluated for the analyzed chars.     

Chemical reactivity of Canadian coal-derived chars

The reactivities of eight Canadian coal-derived chars of four different ranks were measured thermogra-vimetrically at 500°C. It has been found that char reactivity decreases with increase in the carbon content (or rank) of the parent coal. Chars containing more calcium and magnesium oxides have higher reactivities. The experimental results of mass conversion are well represented by the shrinking core model in which the initial stage of the reaction is kinetically controlled by chemical reaction and the later stage by gas diffusion through the ash.     

Carbon dioxide reforming of methane under periodic operation

The carbon dioxide reforming of methane under periodic operation over a commercial Ni/SiO₂·MgO catalyst was investigated at two different temperatures, 923 and 1,023 K. According to this operation, pure methane and carbon dioxide were alternately fed to the catalyst bed where methane cracking and the reverse Boudouard reaction took place, respectively. Therefore, hydrogen and carbon monoxide products appeared separately in different product streams. The performance of this operation was compared to that of the steady state operation with simultaneous feed of both carbon dioxide and methane. At 1,023 K, the methane conversion and hydrogen yield from the periodic operation initially decreased with time on stream and eventually leveled off at values about half of those obtained in the steady state operation with co-feed of both reactants. The decreased catalytic activity was due to the accumulation of carbonaceous deposit and loss of metal active sites. However, a different trend was observed at 923 K. The methane conversion and hydrogen yield were almost constant over the time on stream, although more carbonaceous deposit was progressively accumulated on the catalyst bed during the reaction course. At this temperature, the periodic operation offered the equivalent hydrogen yield to the steady state operation. The observed behavior could be due to the different mechanisms of carbon formation over the catalyst. Finally, it was found that cycle period and cycle split did not influence the reaction performance within the ranges of this study.     

碱金属Na对黑液水煤浆焦-CO2气化特性的影响

黑液中富含大量的碱金属Na及其化合物,这些碱金属将在黑液水煤浆焦气化过程中起到催化气化的作用.为了研究黑液水煤浆焦-CO2催化气化反应特性,采用XRD、SEM和热重分析技术对黑液水煤浆焦和普通水煤浆焦CO2催化气化实验进行分析,得到了焦炭表面孔隙分布情况、煤浆焦样和气化后残渣XRD分析结果,以及等温条件下气化反应时碳转化率数据.试验结果表明:黑液水煤浆焦表面密集分布很多"斑点"和微孔,说明碱金属Na盐在焦碳表面形成了活化中心点,它们在气化过程中起到催化作用;碱金属Na使焦样表面具有更强的反应位,削弱C-C键的强度,使气化反应更容易进行;同时由于碱金属催化剂在高温气化时将与煤中矿物质反应生成惰性物质,从而可能削弱催化效果.从黑液水煤浆与普通水煤浆XRD晶相分析中可以看出碱金属Na盐主要以氯化钠、硅酸钠形式存在,气化反应后生成的晶相组成主要是霞石和微斜长石.