【作者】 杨伏生；

【导师】 周安宁；

【作者基本信息】 西安科技大学 ， 矿物加工工程， 2019， 博士

【摘要】 共热解是实现煤与生物质高效可持续利用的重要途径。煤与生物质共热解时的相互作用,导致共热解反应过程非常复杂,长期以来,对共热解协同作用及其反应产物调控机制等理论问题的认识存在较大分歧。因此,针对上述问题,本论文以核桃壳和神府煤为研究对象,以凹凸棒土为催化剂,采用热重/微分热重分析,研究了核桃壳和神府煤的共热解和催化共热解特性与动力学；采用热重-质谱方法,并结合纤维素和木质素为模型化合物的热解研究,探讨了温度、催化剂等因素对共热解过程中挥发性产物的影响规律,揭示了核桃壳和神府煤共热解协同反应特性与反应机理。研究结果对于煤与生物质高效共热解新技术发展有一定的理论指导意义。(1)核桃壳和神府煤共热解的协同作用研究。采用热重/微分热重方法,研究了核桃壳和神府煤的共热解特性与动力学。结果表明:核桃壳与神府煤的脱挥发分温度区间部分重叠,在300-50℃范围内,核桃壳/神府煤的共热解存在协同作用,导致挥发物产量增加。核桃壳的质量份数是决定协同作用大小的重要因素,WS:SFC质量比为3:1和2:1,升温速率不低于20℃·min-1时,协同作用明显。(2)核桃壳和神府煤共热解的动力学研究。采用四种等转化率法(Friedman法、FWO法、KAS法和Starink法),计算核桃壳和神府煤共热解的表观活化能，采用Achar法和Coats-Redfern法,计算分析核桃壳和神府煤共热解机理模型。结果表明:核桃壳/神府煤(3:1)在260-360℃共热解的表观活化能均值为278.20kJ·mol-1,260-340℃时的共热解过程符合三维扩散(D3)机理。采用模型拟合法计算,得到的核桃壳/神府煤(3:1)热解表观活化能,数值上明显低于等转化率法得到的表观活化能,原因在于用模型拟合法计算活化能时,针对单一升温速率,而且预设反应机理,忽略了核桃壳和神府煤热解时的部分化学反应过程。(3)核桃壳和神府煤共热解的热重-质谱研究。采用热重-质谱联用仪,研究了核桃壳和神府煤单独热解,以及核桃壳/神府煤共热解过程中,水蒸气、二氧化碳、乙酸、呋喃、甲基呋喃和糠醛等挥发性产物生成量随温度的变化规律。结果表明:核桃壳:神府煤质量比为2:1,水蒸气、乙酸、呋喃、甲基呋喃和糠醛的生成量,与其它质量比的相比,均达到最高值;其中,乙酸的最大相对强度,是核桃壳单独热解时的3.9倍、神府煤单独热解时的7.5倍,300-500℃区间生成量为理论生成量的2.6倍,原因在于共热解协同作用促进水蒸气、乙酸、味喃、甲基味喃和糠醛的生成。(4)核桃壳和神府煤的催化共热解动力学研究。分别采用Friedman法、FWO法、KAS法和Starink法,以及Achar法和 Coats-Redfern法,研.究了凹凸棒:土对核桃壳和神府煤共热解活化能和机理模型的影响。结果表明:凹凸棒土显著催化了核桃壳/神府煤(3:1)在380℃的共热解过程;凹凸棒土以质量比1:9添加到核桃壳/神府煤(3:1)中,导致260-380℃的表观活化能均值下降22 kj·mol-1;核桃壳/神府煤(3:1)在260-340℃仍然为三维扩散(D3)机理,但380-500℃区间,催化共热解呈现二级反应(F2)机理。(5)凹凸棒土对核桃壳/神府煤共热解的催化作用机制研究。采用热重分析,对比研究了以不同质量比添加凹凸棒土时,核桃壳和神府煤催化共热解的理论失重量与实验失重量大小关系;采用热重-质谱分析,比较了以不同质量比添加凹凸棒土时,挥发性产物的生成规律。结果表明:凹凸棒土的作用受在凹凸棒土孔结构和表面结构影响,在催化剂作用下,380℃之前热解形成的乙酸、呋喃、甲基呋喃和糠醛等小分子产物数量,与无催化剂存时相比,成倍增加;380-500℃,乙酸、呋喃、糠醛的生成量减少,苯的生成量增加,其中,凹凸棒土与核桃壳/神府煤(3:1)的质量比为1:3时,苯的生成量最高。(6)核桃壳和神府煤的共热解机理研究。首先,核桃壳300℃之前热解产生的氢自由基和羟基自由基,诱导和促进神府煤的热解过程,包括:桥键和烷基侧链发生断裂、流动相脱挥发分、脂肪族基团热解,产生自由基碎片;与此同时,核桃壳300℃熔融得到的活性纤维素,断链解聚,以及木质素酚羟基分解,产生自由基碎片;最后,核桃壳和神府煤热解产生的大量自由基碎片,通过自由基稳定化,促进乙酸生成。(7)核桃壳/神府煤的催化共热解机理研究。凹凸棒土催化作用促进了共热解协同效果。首先,凹凸棒土硅轻基活性位和离子活性中心,催化核桃壳中活性纤维素断链解聚以及木质素分解,通过产生的氢自由基和羟基自由基,诱导和促进神府煤的热解过程;其次,核桃壳和神府煤热解产生的大量自由基碎片,受到凹凸棒土催化后,通过脱水、碎片化、缩合、脱羰基或脱羧基作用,形成呋喃和糠醛,部分呋喃和糠醛继续催化脱水、脱羧基和脱羰基形成轻质芳烃;最后,轻质芳烃中的甲苯和二甲苯,与乙酸、呋喃、甲基呋喃、糠醛,在凹凸棒土催化和高温作用下,发生二次反应,生成多环芳烃化合物,与煤热解产生的含芳环自由基,形成半焦。基于上述研究,建立了焦油组分分级回收的“连续式梯级热解-分步回收”催化共热解新工艺。采用梯级热解工艺,可在200-380℃阶段,回收乙酸和呋喃类化合物等可凝性小分子化学品;380-500℃阶段,回收轻质芳烃;500℃后回收重质焦油。更多还原

【Abstract】 Copyrolysis is an important way to achieve efficient and sustainable utilization of coal and biomass.The int.eraction between coal and biomass during copyrolysis,results in very complex reaction process,which leads to much controversy over theoretical issues about copyrolysis interaction and regulation mechanism of copyrolysis products for a long period.In view of the above problems,copyrolysis and catalytic copyrolysis characteristics and kinetics of the walnut shell(WS)and the Shenfu coal(SFC)with attapulgite as catalyst,were studied by thermogravimetric and differential thermogravimetric analysis.Effects of tcemperature and catalyst on volati.le products in the copyrolysis were investigated,by thermogravimetric-mass spec.trometry,combined with pyrolysis of cellulose and lignin as model compounds;reaction characteristics and synergy mechanism between the WS and the SFC was also revealed.The results have certain theoretical significance for development of new high-efficiency co-pyrolysis technology of coal and biomass.(1)Research on the synergistic effect occurred in the WS and the SFC copyrolysis.Copyrolysis characteristics and kinetics of the WS and the SFC,were studied by thermogravimetric and diff-erential therm.ogravimetric method.The results showed that devolatilization temperataure range of the walnut shell and the Shenfu coal overlapped partially.Synergistic effect could be observed in 300-500 ℃ copyrolysis of the walnut shell and the Shenfu coal,leading to increase in volatile matter production.Mass fraction of the walnut shell was an important factor determining the synergistic effect.The synergistic effect was more obvious when WS:SFC mass ratio were 3:1 and 2:1,and heating rate was not lower than20℃·min-1,(2)Kinetics of copyrolysis of the walnut shell and the Shenfu coal.Apparent activation energy of copyrolysis of the waln.ut shell and the Shenfu coal,was calculated according to four iso-conversional methods,namely Friedman method,FWO method,KAS method and Starink method.Copyrolysis mechanism model of the walnut shell and the Shenfu coal,was calculated and analyzed by Achar method and Coats-Redfern method.The results showed that apparent activation energy of the walnut shell/Shenfu coal(3:1)copyrolysis in 260-360 ℃was 278.20 kJ·mol-1,copyrolysis process during 260-340 ℃ accorded with three-dimensional diffusion(D3)mechanism.Apparent activation energy of the walnut shell/Shenfu coal(3:1)pyrolysis calculated by model-fitting method,was lower than that obtained by iso-conversional method,due to the fact that some chemical reaction processes in the walnut shell and the Shenfu coal pyrolysis was neglected,in calculation using model-fitting method,where single heating rate and preset reaction mechanism were adopted.(3)Investigation into copyrolysis of the walnut shell and the Shenfu coal by TG-MS method.TG-MS was used to investigate variation with temperature in volatile products,such as water,carbon dioxide,acetic acid,furan,methylfuran and furfural,during individual pyrolysis of the walnut shell and the Shenfu coal,together with copyrolysis of the walnut shell and the Shenfu coal.It was showed that when mass ratio of the walnut shell to the Shenfu coal was 2:1,production of water,acetic acid,furan,methylfuran and furfural,reached the highest value compared with other mass ratios,among which maximal relative strength of acetic acid was 3.9 times that for individual pyrolysis of the walnut shell,7.5 times that for the Shenfu coal pyrolysis,and acetic acid yield was 2.6 times theoretical one in 300-500 ℃,attributed to the synergistic effect which promoted formation of water,acetic acid,furan,methyl furan and furfural.(4)Study on kinetics of catalytic copyrolysis of the walnut shell and the Shenfu coal.Effects of the attapulgite on copyrolysis activation energy and mechanism model of the walnut shell and the Shenfu coal were focused,by means of Friedman,FWO,KAS and Starink methods,as well as Achar and Coats-Redfern methods,respectively.It was suggested that the attapulgite catalyzed copyrolysis of the walnut shell/Shenfu coal(3:1)at 380 ℃significantly;averaged apparent activation energy of the walnut shell/Shenfu coal(3:1)in 260-380 ℃,decreased by 22 kJ-mol-1,when attapulgite was added at mass ratio 1:9.Three-dimensional diffusion(D3)mechanism remained for the walnut shell/Shenfu coal(3:1)catalytic copyrolysis in 260-340 ℃,but second-order(F2)reaction mechanism appeared in 380-500 ℃.(5)Research on catalytic mechanism of the attapulgite on copyrolysis of the walnut shell and the Shenfu coal.Relationship between theoretical weight losses and experimental ones,for catalytic copyrolysis of the walnut shell and the Shenfu in presence of the attapulgite with different mass ratios was studied by thermogravimetric analysis;formations of volatile products were compared,before and after the attapulgite addtion at different mass ratios,by thermogravimetric-mass spectrometry.It was shown that the catalytic effect of the attapulgite was influenced by its pore structure and surface structure.In presence of the catalyst,amount of acetic acid,furan,methyl furan and furfural from copyrolysis before 380℃,multiplied compared to those formed in absence of the attapulgite;production of acetic acid,furan and furfural decreased,but benzene production increased after 380℃.When mass ratio of the attapulgite to the walnut shell/Shenfu coal(3:1)was 1:3,yield of benzene reached the highest level.(6)Research on copyrolysis of the walnut shell and the Shenfu coal.Firstly,hydrogen radicals and hydroxyl radicals,produced by pyrolysis of the walnut shell before 300 ℃induced and promoted pyrolysis of the Shenfu coal,including breakage of bridge bond and alkyl side-chains,mobile phase devolatilization,aliphatic group pyrolysis,resulting in formation of free radical fragments;meanwhile,active cellulose melted from the walnut shell at 300 ℃,underwent chain breakage and depolymerization,lignin underwent phenolic hydroxyl decomposition.Finally,great variety of free radical fragments,including methyl and carboxyl groups,produced by pyrolysis of the walnut shell and the Shenfu coal,promote formation of acetic acid through free radical stabilization.(7)Research on catalytic copyrolysis of the walnut shell/Shenfu coal.The attapulgite catalysis promoted synergistic effect during copyrolysis.Above all,silanol active sites and ionic active centers in the attapulgite,catalyzed chain breaking and depolymerization of active cellulose,along with decomposition of lignin in the walnut shell,induced and promoted pyrolysis of the Shenfu coal,with aid of generated hydrogen and hydroxyl radicals;secondly,a large quantity of free radical fragments,produced by the pyrolysis of the walnut shell and the Shenfu coal,were converted with the attapulgite catalysis into furan and furfural,through dehydration,fragmentation,condensation,decarbonylation and decarboxylation;part of furan and furfural,were catalyzed into light aromatic hydrocarbons by continued dehydration,decarboxylation and decarbonylation.Finally,toluene and xylene in light aromatic hydrocarbons,reacted with acetic acid,furan,methylfuran and furfural,in presence of the attapulgite catalysis and high temperature,forming polycyclic aromatic hydrocarbons,which condensed with free radicals containing aromatic ring from coal pyrolysis,giving semicoke.Based on the above researches,a new catalytic co-pyrolysis process,named continuous gradient pyrolysis and step-wise recovery,was established,which was expected to be used in step-wise recovery of tar components.Using this gradient pyrolysis and step-wise recovery process,condensable small molecular chemicals,such as acetic acid and furan compounds,can be recovered in 200-380 ℃;light aromatic hydrocarbons can be recovered in 380-500℃;heavy tar can be recovered after 500℃.更多还原