Selective Fast Pyrolysis Of Biomass

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.