生物质热解液化技术研究与发展趋势

介绍了生物质热解液化技术,总结了该项技术在原料预处理、热解工艺和生物油分离精制3个方面的最新研究成果。在原料预处理方面,介绍了微波干燥、烘焙和酸洗3种方法;在热解工艺方面,介绍了催化热解和混合热解两种新工艺;在生物油分离精制方面,介绍了催化加氢、催化裂解、催化酯化、乳化燃油和分离提纯5种新技术,并分析展望了生物质热解液化技术的产业化发展趋势。     

我国生物质热解液化技术的现状

文章主要阐述了我国生物质热解液化技术的研究现状，包括现有的热裂解液化装置、反应动力学模型、已检测出的不同原料裂解产生的生物油成分及其物理特性分析，提出了生物油精制的必要性和未来需要研究的问题。     

生物质热化学液化技术研究进展

随着化石燃料可开采量的减少和人类对全球性环境问题的关注，生物质作为一种可再生能源，由于资源丰富，分布广泛，燃烧过程对环境的低污染性，CO2的净零排放等特性日益成为国内外众多学者研究的热点课题之一。生物质转化技术可分为生物法和热化学转化法，后者主要有气化、热解、高压液化及与煤共处理等工艺。其中生物质热化学液化由于比气化能得到更有价值的液体产物，操作温度比热解低，因而作为一项资源高效利用的新工艺日益受到重视。综述了近五年来生物质热化学液化技术方面的最新进展，提出了今后的研究动态与发展方向，并针对我国现状提出应采取的对策。     

生物质液化技术面临的挑战与技术选择

生物质液化技术可将低品位的固体生物质完全转化成高品位的液体燃料或化学品,是生物质能高效利用的主要方式之一。按照机理,液化技术可以分为热化学法、生化法、酯化法和化学合成法(间接液化),热化学法液化又分为快速热解技术和高压液化(直接液化)技术。生物质热化学法液化已成为国内外生物质液化的研究开发重点和热点,快速热解液化技术和高压液化技术是最具产业化前景的生物质能技术,生化法液化技术也是生物质能的研究热点。化学合成法液化技术并不适用于生物质液化,而利用生物柴油进一步生产生物航空煤油是得不偿失的,不仅成本高、资源利用率低,而且全生命周期碳排放增加,还不符合未来生物航煤的发展趋势。生物质含水量的高低是影响生物质液化过程中能耗、效率、污染指数和经济性指标等的关键因素,应根据含水量合理选择生物质液化技术。快速热解液化技术适用于低含水农林废弃物,高压液化和生化法液化技术适用于高含水生物质,酯化法液化技术适用于不可食用油脂,而各种液化技术均不适用于城市生活垃圾的处理,建议将其用作燃气型气化原料。     

我国生物质能源现代化应用前景展望(三)——生物质能源转化技术经济评估

秸秆、动植物油脂、微藻等生物质原料可以生产液体运输燃料,生物燃料的化学成分包括醇、酯、烃三类。燃料乙醇主要替代汽油,受到各国重视,其中纤维素乙醇技术发展较快。脂肪酸甲酯是第一代生物柴油的主要成分,价格主要受油脂原料价格的影响,由于和柴油相容性差,低温流动性不好,将逐渐被加氢生产的第二代生物柴油取代。相比醇、酯等含氧燃料,烃类生物燃料在使用性能上有很多优势。有多条技术路线可以生产烃类燃料,其中油脂加氢制喷气燃料已接近商业应用,热解油加氢可将木质生物质原料中的"木质素"组分转化为生物油,大型快速热解工厂可以和热电联产装置组成联合系统,从而提高工厂综合热效率,降低生物燃料生产成本。因此,快速热解生产汽柴油将成为主要的生物燃料生产路线。生物质与煤共气化技术通过提高气化温度,不仅可以提高生物质气化效率,减少焦油的生成,还可以解决生物质供给的季节性问题,为生物质的高效利用提供了一条新的技术途径。微藻高压液化生产柴油是最具发展潜力的第三代生物燃料技术,我国需要加强微藻养殖及加工技术攻关。     

蓝藻和松木热解液化制取生物油的试验研究

以蓝藻为研究对象,并以松木为参照,在流化床反应器中进行了热解液化制取生物油的试验研究,考察了温度对两种生物质原料热解产物的影响。研究表明,随着温度的升高,蓝藻和松木的产气率逐渐增加,产炭率逐渐减小,产油率先增加后减小,当温度为500℃时,达到最大值分别为50.4%和45.2%。采用气质联用(GCMS)测定两种生物质热解生物油的化学组成。结果表明:两种生物油的化学组分及相对含量存在一定的差异,但均属于相同的化学族类,其主要组成成分为含氮化合物、烃类、酮类、醇类、酸类、苯酚类等化合物。此外,通过元素分析可知,蓝藻生物油含氧量较松木低,有利于油品质的提高,使蓝藻热解液化制取生物油具有良好的发展前景。     

基于超临界乙醇的竹子与聚乙烯共液化研究

结合生物质的可再生特性和塑料的可作为供氢体系的优点,将超临界流体(SCF)技术用于生物质热解,以得到环境友好型的生物燃油.实验研究了竹子和聚乙烯在超临界乙醇中进行共热解的工艺参数和技术条件.并应用气质联用仪(GC-MS)对生物油产物进行分析.结果表明,竹子和甥料在恰当的工艺条件下,可以获得良好的液化效果,共液化率高于竹子的单独液化率.反应温度在250～290℃间,在不加入催化剂的条件下,竹子与聚乙烯的共液化率为40.6%;在加入碳酸钾催化剂下,共液化率达62.6%.通过GC-MS分析,热解产物中主要含C12以下的醇类、酯类、酮类和醚类,适合作为点燃式内燃机的燃料.     

生物质热解液化工艺及其影响因素

介绍了生物质的特点及生物质快速热解液化技术的一般工艺流程.综述了生物质热解过程中,反应温度、滞留时间、升温速率、反应压力、灰分、组成成分、分子结构、粒径和颗粒形状等条件对生物质热解及其产物组成和特性的影响,指出了生物质热解的技术关键.     

石油炼厂加工纤维素/木质纤维素生物质原料的前景

生物质热解与生物油改质、生物质气化与合成气费-托转化工艺是正在研究开发的第二代生物燃料技术,前者利用快速热解工艺对生物质进行热解或热加氢改质生成热解油;后者用生物质直接合成或先转化为生物油后再生成合成气,合成气经改质和转化生产费-托合成烃。许多石油公司都在以纤维素/木质纤维素为原料,研究开发在石油炼厂内对生物质原料进行后续加工和应用的相关技术。在石油炼厂中引入生物质原料,其挑战是要找到源自非食用生物质或生物质废弃物的原料,而且这些原料应易于运输并易于在炼厂中进行处理,同时应尽可能使用现有的工艺和装置。虽然石油炼厂加工生物质原料尚存在一些问题,但近来开发势头十分强劲。从长远角度来看,任何能为炼厂提供原料,生命周期分析证明能减少CO2排放,并在经济上可行的技术均会在生物燃料开发竞争中成为赢家。     

生物质高压液化技术影响因素分析及展望

文章介绍了生物质高压液化技术的优势及目前开展生物质高压液化技术的必要性和紧迫性,着重介绍了反应原料、反应温度、反应时间、反应压力、反应气氛、溶剂和催化剂等因素对生物质高压液化产物分布及产物性质的影响.指出了生物质高压液化技术目前存在的问题及今后的研究方向,以期为生物质高压液化技术的工业化发展提供指导.     

Techno-economic comparisons of hydrogen and synthetic fuel production using forest residue feedstock

Mobile distributed pyrolysis facilities have been proposed for delivery of a forest residue resource to bio-fuel facilities. This study examines the costs of producing hydrogen or synthetic petrol (gasoline) and diesel from feedstock produced by mobile facilities (bio-oil, bio-slurry, torrefied wood). Results show that using these feedstock can provide fuels at costs competitive to conventional bio-fuel production methods using gasification of a woodchip feedstock. Using a bio-oil feedstock in combination with bio-oil steam reforming or bio-oil upgrading can produce hydrogen or petrol and diesel at costs of 3.25 $ kg⁻¹ or 0.86 $ litre⁻¹, respectively, for optimally sized bio-fuel facilities. When compared on an energy basis ($ GJ⁻¹), hydrogen production costs tend to be lower than those for synthetic petrol or diesel production across a variety of bio-fuel production pathways.     

生物质热加工液化技术评述

介绍了生物质热加工液化技术中的各种热裂解液化和高压液化工艺,包括流化床、涡流烧蚀反应器、真空快速裂解反应器以及高压釜、半连续固定床等装置的工作原理和生产工艺,分析它们各自的优点和存在的问题,着重讨论了各种工艺提高生物原油产率的措施以及精制生物原油可替代柴油作为车用轻质燃油的方法,指出降低生物原油的生产成本,扩大生产规模是热加工液化的发展方向。     

Utilization of lignin: A sustainable and eco-friendly approach

The use of renewable carbon sources as a substitute for fossil resources is an extensively essential and fascinating research area for addressing the current issues related to climate and future fuel requirements. The utilization of lignocellulosic biomasses as a source for renewable fuel/chemicals/mesoporous biochar derivative is gaining considerable attention due to the neutral carbon cycle. The cellulose and hemicellulose are highly utilized components of biomass, and on the other hand, lignin is a plentiful, under-utilized component of the lignocellulosic biomass in 2G ethanol and paper industry. Significant researchers have contributed towards lignin valorization, with a central goal of the production and upgradation of phenolic, unstable, acidic and oxygen-containing bio-oil to valuable chemicals or fuel grade hydrocarbons. This review is aimed to present the lignin valorization potential from pretreatment of biomass as an initial step to the final process, i.e., lignin bio-oil upgradation with mechanistic pathways. The review offers the source, structure, composition of various lignocellulosic biomasses, followed by a discussion of various pre-treatment techniques for biomass depolymerization. Different thermochemical approaches for bio-oil production from dry and wet biomasses are highlighted with emphasis on pyrolysis and liquefaction. The physical, chemical properties of lignin bio-oil and different upgradation methods for bio-oil as well as its model compounds are thoroughly discussed. It also addresses the related activity, selectivity, stability of numerous catalysts with reaction pathways and kinetics in a broad manner. The challenges and future research opportunities of lignin valorization are discussed in an attempt to place lignin as a feedstock for the generation of valuable chemical and fuel grade hydrocarbons.     

Evaluation of esterified pyrolysis bio-oil as a diesel alternative

Refined pyrolysis bio-oil was produced via the pretreatment and esterification of pyrolysis bio-oil over 732-type ion-exchange resin. The main parameters of fuel property such as components, low calorific value and viscosity of refined pyrolysis bio-oil were analyzed. Different volume fractions of refined pyrolysis bio-oil were added to neat diesel to prepare bio-fuel blends. Combustion performances and emission characteristics of engine fueled with bio-fuel blends were analyzed at various loads. The results show that after esterification, the amount of esters and ketones in the crude pyrolysis bio-oil was significantly increased while the contents of acids, phenols and ethers were reduced. Compared with crude pyrolysis bio-oil, the pH value of refined pyrolysis bio-oil was improved to 5.6, the low calorific value increased by 14.89%, and the kinematic viscosity decreased by 10.13%. At the same load, the equivalent brake specific fuel consumption (BSFC) of bio-fuel blends was increased, the maximum cylinder pressures and the brake thermal efficiency (BTE) were both decreased but the peak of instantaneous heat release was increased slightly, and the exhaust gas temperatures also rose up. With the increase of refined pyrolysis bio-oil in bio-fuel blends, the difference between bio-fuel blends and neat diesel in the above indicators was more obvious. Besides, bio-fuel blends produced more HC, CO and smoke emissions but less NO_x emissions than neat diesel.     

Hydrothermal catalytic liquefaction mechanisms of agal biomass to bio-oil

The liquefaction mechanisms of the algal biomass to bio-oil were investigated by using Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy, respectively. It was found that NaOH was a satisfactory catalyst and contributed to helping the liquefaction of algal biomass. The bio-oil from algal biomass was composed of many compounds, including carbohydrates, alcohol, hydroxybenzene, carboxylic acid, alkene, ester, and others. The mechanism of hydrothermal catalytic liquefaction was discussed. It was found that, comparing with the husk bio-fuel, the algal bio-oil as a promising alternative fuel was more close to the traditional diesel fuel in physicochemical properties. The novel research outcomes contribute to improving the yield of bio-oil from microalgae, reducing the cost of the bio-oil and accelerating the commercial application of the algal bio-oil in the near future.     

Thermochemical conversion of sewage sludge: A critical review

The increasing levels of sewage sludge production demands research and development to introduce more commercially feasible options for reducing socio-economic and environmental problems associated with its current treatment. Sewage sludge may be processed to produce useful products or as a feedstock for energy generation. Initially, the characteristics of sewage sludge are discussed in terms of composition and the current options for its treatment with the associated environmental impacts. Processes to valorize sewage sludge are discussed, including heavy metal removal from sewage sludge, production of bio-char, production and use of activated carbon and use of sewage sludge combustion ash in cement and concrete. Thermochemical processes i.e., pyrolysis, co-pyrolysis and catalytic pyrolysis, also gasification and combustion for process intensification, energy and resource recovery from sewage sludge are then critically reviewed in detail. The pyrolysis of sewage sludge to produce a bio-oil is covered in relation to product bio-oil composition, reactor type and the use of catalysts. Gasification of sewage sludge focusses on the characteristics of the different available reactor types and the influence of a range of process parameters and catalysts on gas yield and composition. The selection and design of catalysts are of vital importance to enhance the selectivity of the selected thermochemical pyrolysis or gasification process. The catalysts used for sewage sludge treatment need more research to enable selectivity towards the targeted desired end-products along with optimization of parametric conditions and development of innovative reactor technologies. The combustion of sewage sludge is reviewed in terms of reactor technologies, flue gas cleaning systems and pollutant emissions. In addition, reactor technologies in terms of technological strength and market competitiveness with the particular application to sewage sludge are compared for the first time for thermochemical conversion. A critical comparison is made of the drying techniques, co-feedstocks and catalytic processes, reaction kinetics, reactor technologies, operating conditions to be optimized, removal of impurities, fuel properties, their constraints and required improvements. The emphasis of this review is to promote environmental sustainability for process intensification, energy and resource recovery from pyrolysis, gasification and combustion involving the use of catalysts.     

Main routes for the thermo-conversion of biomass into fuels and chemicals. Part 1: Pyrolysis systems

Since the energy crises of the 1970s, many countries have become interest in biomass as a fuel source to expand the development of domestic and renewable energy sources and reduce the environmental impacts of energy production. Biomass is used to meet a variety of energy needs, including generating electricity, heating homes, fueling vehicles and providing process heat for industrial facilities. The methods available for energy production from biomass can be divided into two main categories: thermo-chemical and biological conversion routes. There are several thermo-chemical routes for biomass-based energy production, such as direct combustion, liquefaction, pyrolysis, supercritical water extraction, gasification, air–steam gasification and so on. The pyrolysis is thermal degradation of biomass by heat in the absence of oxygen, which results in the production of charcoal (solid), bio-oil (liquid), and fuel gas products. Pyrolysis liquid is referred to in the literature by terms such as pyrolysis oil, bio-oil, bio-crude oil, bio-fuel oil, wood liquid, wood oil, liquid smoke, wood distillates, pyroligneous tar, and pyroligneous acid. Bio-oil can be used as a fuel in boilers, diesel engines or gas turbines for heat and electricity generation.     

Liquefaction of palm kernel shell in sub- and supercritical water for bio-oil production

The heavy palm oil industry in Malaysia has generated various oil palm biomass residues. These residues can be converted into liquids (bio-oil) for replacing fossil-based fuels and chemicals. Studies on the conversion of these residues to bio-oil via pyrolysis technology are widely available in the literature. However, thermochemical liquefaction of oil palm biomass for bio-oil production is rarely studied and reported. In this study, palm kernel shell (PKS) was hydrothermally liquefied under subcritical and supercritical conditions to produce bio-oil. Effects of reaction temperature, pressure and biomass-to-water ratio on the characteristics of bio-oil were investigated. The bio-oils were analyzed for their chemical compositions (by GC–MS and FT-IR) and higher heating values (HHV). It was found that phenolic compounds were the main constituents of bio-oils derived from PKS for all reaction conditions investigated. Based on the chemical composition of the bio-oil, a general reaction pathway of hydrothermal liquefaction of PKS was postulated. The HHV of the bio-oils ranged from 10.5 to 16.1 MJ/kg, which were comparable to the findings reported in the literature.     

Comparison of pyrolysis and hydrothermal liquefaction of Chlamydomonas reinhardtii. Growth studies on the recovered hydrothermal aqueous phase

The production of bio-oil by pyrolysis with a high heating rate (500 K s⁻¹) and hydrothermal liquefaction (HTL) of Chlamydomonas reinhardtii was compared. HTL led to bio-oil yield decreasing from 67% mass fraction at 220 °C to 59% mass fraction at 310 °C whereas the bio-oil yield increased from 53% mass fraction at 400 °C to 60% mass fraction at 550 °C for pyrolysis. Energy ratios (energy produced in the form of bio-oil divided by the energy content of the initial microalgae) between 66% at 220 °C and 90% at 310 °C in HTL were obtained whereas it was in the range 73–83% at 400–550 °C for pyrolysis. The Higher Heating Value of the HTL bio-oil was increasing with the temperature while it was constant for pyrolysis. Microalgae cultivation in aqueous phase produced by HTL was also investigated and showed promising results.