【作者】 陆强；

【导师】 朱锡锋；

【作者基本信息】 中国科学技术大学 ， 热能工程， 2010， 博士

【摘要】 生物质快速热解液化是一种高效的生物质转化利用技术,获得了广泛的关注,但目前还没有实现产业化应用：此外生物质热解液化技术的推广应用还面临着一大难题：常规生物油没有成熟的应用市场,作为液体燃料使用时,品质较差,作为化工原料使用时,分离提取困难。基于此背景,本文的研究内容包括以下两个方面：1.生物质选择性热解液化制备高品位液体燃料以及高附加值化学品的初步研究通过Py-GC/MS实验,研究了生物质的快速热解反应途径和机理。纤维素快速热解的反应途径主要包括：解聚形成左旋葡聚糖和脱水低聚糖等产物、解聚并脱水形成多种脱水糖衍生物、吡喃环开环而后缩醛形成呋喃类产物、吡喃环开裂形成小分子物质；木聚糖和纤维素具有较为相似的热解机理,但具体的热解反应途径则有很大的差别；生物质快速热解的产物分布受其化学组成以及灰分催化的影响。以生物质常规热解产物在线催化裂解获得高品位液体燃料为目标,通过Py-GC/MS实验考察了多种催化剂的催化效果,成功筛选出了Pd／Ce02-TiO2(金红石型)催化剂。该催化剂能够促进木质素热解低聚物的二次裂解而形成挥发性酚类产物,同时降低醛类和糖类产物,增加酮类和环戊酮类产物,但却略微增加了酸类产物,由此可知催化生物油的燃料品质(除了酸度)将会得到改善。针对生物质热解产物中最难处理的低聚物,以各种改性的介孔SBA-15为催化剂进行催化裂解研究,成功筛选出了Pd／SBA-15催化剂。该催化剂就能够极大地促进木质素热解低聚物发生裂解形成挥发性酚类产物,脱除酚类物质侧链上的羰基,并对侧链上的C=C进行加氢,同时还能大幅降低或完全脱除糖类产物、醛类产物以及含羟基的酮类产物,促进呋喃类产物的脱羰形成轻质呋喃,降低酸类产物,并增加甲醇、不含羟基的酮类物质以及烃类物质,由此可以显著提高催化生物油的燃料品质。提出了氯化锌催化热解生物质联产制备糠醛和活性炭的技术：对生物质浸渍负载ZnC12后进行快速热解时,ZnCl2的催化能够抑制木质素的热解液化以及综纤维素的开环断裂,同时促进综纤维素的解聚及脱水而主要形成糠醛和三种脱水糖衍生物(左旋葡萄糖酮、1,4：3,6-双脱水-a-D-吡喃葡萄糖和1-羟基-3,6-二氧二环[3.2.1]2-辛酮),其中脱水糖衍生物经ZnC12二次裂解后都转化为糠醛；以玉米芯为原料,在不低于15 wt%的ZnCl2负载量和340℃的热解温度下,糠醛的最高产率可达8 wt%以上；将剩余的固体产物进一步加热到500℃活化即可获得活性炭。进一步提出了生物质选择性热解液化制备其他化学品的技术：将固体超强酸和纤维素(或生物质)机械混合后进行快速热解,从而可获得高产率高纯度的左旋葡萄糖酮；在纤维素上浸渍负载KCl和CaCl2后快速热解,可以提高羟基乙醛和羟基丙酮的产率；利用固体超强酸对纤维素快速热解产物进行催化裂解,可以制备呋喃和5-甲基糠醛；等等。2.自热式生物质热解液化装置的研制以及常规生物油的分析和应用研究针对常规快速热解液化的技术要求,基于流化床式热解液化反应器,并采用两级螺旋进料系统以及喷雾与降膜复合式冷凝装置,参与研制了生物质热解液化小试装置；随后以热解副产物焦炭为热源,不可冷凝气体为流化载气,参与研制了处理量为120 kg／h的自热式热解液化中试装置；大量的热解液化试验证实了不同生物质原料热解制备生物油的产率都可达50 wt%或60 wt%以上,热值可达16～18 MJ／kg。以稻壳为原料制取的生物油,具有较高的氮和金属元素含量,并且呈现出了一些非牛顿流体特性；它的热安定性较差,这可以通过添加甲醇进行改善；腐蚀测试表明,生物油对碳钢和铝有强烈的腐蚀,对黄铜有轻微腐蚀,而对奥氏体不锈钢基本没有影响,当和柴油乳化后,乳化油的腐蚀性能大幅下降；此外,四球机摩擦磨损试验表明,生物油具有一定的润滑性能,其极压、抗磨和减摩性能都优于0#柴油。利用生物油富含羰基类、羧酸类和酚类物质的特性,将其和尿素混合后通过简单的程序加热至140℃就能够制得缓释氮肥；此外,生物油可以作为一种初级液体燃料燃烧使用,其雾化燃烧的一大技术难题是点火,通过合理的燃烧技术,能够有效地控制CO和NOx的排放。更多还原

【Abstract】 Fast pyrolysis is a promising technique to convert lignocellulosic biomass mainly into a liquid product known as bio-oil. It has received extensive attentions in recent years, but not industrially utilized at present. The commercialization of the biomass fast pyrolysis technique will encounter the poor marketability problem of bio-oils, since crude bio-oils are hard to be used as liquid fuels due to the poor fuel properties, and also difficult for chemical recovery owing to the complex chemical composition. Based on this background, the work performed in this thesis can be divided into two sections.1. Preliminary research on selective fast pyrolysis of biomass to produce high-grade liquid fuels and valued-added chemicalsAccording to the Py-GC/MS experiments, the fast pyrolytic pathways of the cellulose mainly include the depolymerization to form levoglucosan and anhydro-oligosaccharides, the depolymerization and dehydration to form various sugar derivatives, the ring-opening and acetalization to form various furan products, as well as the ring fragmentation to form various light products. Xylan has the similar reaction mechanisms as cellulose in its pyrolysis, but its detailed pyrolytic pathways differ greatly from those of cellulose. The pyrolytic product distribution of biomass materials is influenced by their component composition and the ash catalysis.On-line catalytic cracking of biomass fast pyrolysis vapors is a common upgrading way to obtain high-grade liquid fuels. Among the various catalysts tested in the Py-GC/MS. experiments, the Pd/CeO2-TiO2(Rutile) shows promising catalytic effects. The catalytic cracking by it will cause the conversion of the lignin-derived oligomers to monomeric phenolic compounds, decrease the aldehydes and sugars, increase the ketones and cyclopentanones, but also slightly increase the acids. According to these catalytic effects, the fuel properties of the catalytic bio-oil will be improved except the acidity.Various modified mesoporous SBA-15 catalysts are prepared for catalytic cracking of biomass fast pyrolysis vapors, mainly aiming at the oligomers which are difficult to upgrade. The Pd/SBA-15 catalysts show excellent catalytic capability. After catalysis, the lignin-derived oligomers will be cracked to monomeric phenols which are further decarbonylated and hydrotreated to form phenols without carbonyl group and unsaturated C-C bond on the side-chain. Moreover, the anhydrosugars are almost completely eliminated, and the furans are decarbonylated to form light ones. The linear aldehydes are significantly decreased, while the acids were slightly decreased. The linear ketones without the hydroxyl group, methanol and hydrocarbons are all increased. These catalytic effects will improve the fuel properties of the catalytic bio-oils considerably.A new technique is developed for the co-production of furfural and activated carbon from pyrolysis of biomass materials impregnated with ZnCl2. During the fast pyrolysis process, the catalysis of ZnCl2 will inhibit the devolatilization of lignin and pyrolytic ring scission of holocellulose, while promote the formation of furfural and three anhydrosugars (levoglucosenone, 1,4:3,6-dianhydro-a-D-glucopyranose). These anhydrosugars can be converted to furfural through the secondary catalysis by ZnCl2. Fast pyrolysis of the corncob impregnated with at least 15 wt% ZnCl2 at around 340℃could obtain the furfural yield over 8 wt%. The solid residues from the fast pyrolysis process can be further activated at 500℃to produce activated carbons.Several other selective fast pyrolysis techniques are developed for the production of different chemicals. Fast pyrolysis of cellulose (or biomass) mixed with solid super acids (sulfated metal oxides) allows the production of levoglucosenone with high yield and purity. Fast pyrolysis of cellulose impregnated with KCl and CaCl2 can promote the formation of hydroxyacetaldehyde and acetol. In addition, fast pyrolysis of pure cellulose followed with catalytic cracking of the vapors by using solid super acids will increase the yields of furan and 5-methyl furfural.2. Development of auto-thermal biomass fast pyrolysis sets together with analysis and application studies on the rice husk bio-oilBased on the principles of the fast pyrolysis technique, a lab-scale biomass fast pyrolysis set is firstly developed, by using fluidized bed pyrolysis reactor, two screw feeding system, as well as the combined spray and falling film condenser. Afterwards, an intermediate auto-thermal biomass fast pyrolysis set with the capacity of 120 kg/h is successfully established, by using the char product as the heat source and the non-condensable gas as the carrier gas. A large number of pyrolysis experiments indicate that the bio-oil yield from different biomass materials will be over 50 wt% or 60 wt%, and the heating value of the bio-oils is between 16 and 18 MJ/kg.Rice husk is employed to produce bio-oil on the intermediate pyrolysis set. The rice husk bio-oil contains high amounts of nitrogen and inorganic elements which are feedstock dependent, and exhibits a little non-Newtonian fluid behavior. It has poor thermal stability which can be improved by the addition of methanol. The bio-oil is very corrosive to mild steel and aluminum, slightly corrosive to brass, and non-corrosive to stainless steel. The corrosion properties will be reduced after emulsification of the bio-oil with diesel oil. Moreover, the tribological tests on a four-ball machine indicate that the bio-oil possesses some lubricity, with better extreme pressure, anti-wear and friction-reducing properties than the 0# diesel oil.The rice husk bio-oil contains abundant carbonyl, phenolic and carboxyl groups, and can react with urea to produce the slow-release organic nitrogen fertilizers very conveniently by programmed heating of the bio-oil/urea mixtures to a final temperature of 140℃. Moreover, the bio-oil can be used a low-grade liquid fuel for spray combustion, with a major problem of ignition. With the proper combustion technique, the CO and NOx emissions can be well controlled.更多还原