Supercritical fluids technology for clean biofuel production

Biofuels are liquid or gaseous fuels that are predominantly produced from biomass for transport sector applications.As biofuels are renewable,sustainable,carbon neutral and environmentally benign,they have been proposed as promising alternative fuels for gasoline and diesel engines.This paper reviews state-of-the-art application of the supercritical fluid(SCF)technique in biofuels production that includes biodiesel from vegetable oils via the transesterification process,bio-hydrogen from the gasification and bio-oil from the lique-faction of biomass,with biodiesel production as the main focus. The global biofuel situation and biofuel economics are also reviewed.The SCF has been shown to be a promising technique for future large-scale biofuel production,especially for biodiesel production from waster oil and fat.Compared with conventional biofuel production methods,the SCF technology possesses a number of advantages that includes fast inetics,high fuel production rate,ease of continuous operation and elimination of the necessity of catalysts.The harsh operation environment,i.e. the high temperature and high pressure,and its request on the materials and associated cost are the main concerns for its wide application.     

Supercritical fluids technology for clean biofuel production

Biofuels are liquid or gaseous fuels that are predominantly produced from biomass for transport sector applications. As biofuels are renewable, sustainable, carbon neutral and environmentally benign, they have been proposed as promising alternative fuels for gasoline and diesel engines. This paper reviews state-of-the-art application of the supercritical fluid (SCF) technique in biofuels production that includes biodiesel from vegetable oils via the transesterification process, bio-hydrogen from the gasification and bio-oil from the liquefaction of biomass, with biodiesel production as the main focus. The global biofuel situation and biofuel economics are also reviewed. The SCF has been shown to be a promising technique for future large-scale biofuel production, especially for biodiesel production from waster oil and fat. Compared with conventional biofuel production methods, the SCF technology possesses a number of advantages that includes fast kinetics, high fuel production rate, ease of continuous operation and elimination of the necessity of catalysts. The harsh operation environment, i.e. the high temperature and high pressure, and its request on the materials and associated cost are the main concerns for its wide application.     

Long-term decline of global atmospheric ethane concentrations and implications for methane

After methane, ethane is the most abundant hydrocarbon in the remote atmosphere. It is a precursor to tropospheric ozone and it influences the atmosphere's oxidative capacity through its reaction with the hydroxyl radical, ethane's primary atmospheric sink. Here we present the longest continuous record of global atmospheric ethane levels. We show that global ethane emission rates decreased from 14.3 to 11.3 teragrams per year, or by 21 per cent, from 1984 to 2010. We attribute this to decreasing fugitive emissions from ethane's fossil fuel source--most probably decreased venting and flaring of natural gas in oil fields--rather than a decline in its other major sources, biofuel use and biomass burning. Ethane's major emission sources are shared with methane, and recent studies have disagreed on whether reduced fossil fuel or microbial emissions have caused methane's atmospheric growth rate to slow. Our findings suggest that reduced fugitive fossil fuel emissions account for at least 10-21 teragrams per year (30-70 per cent) of the decrease in methane's global emissions, significantly contributing to methane's slowing atmospheric growth rate since the mid-1980s.     

Genomics of cellulosic biofuels

The development of alternatives to fossil fuels as an energy source is an urgent global priority. Cellulosic biomass has the potential to contribute to meeting the demand for liquid fuel, but land-use requirements and process inefficiencies represent hurdles for large-scale deployment of biomass-to-biofuel technologies. Genomic information gathered from across the biosphere, including potential energy crops and microorganisms able to break down biomass, will be vital for improving the prospects of significant cellulosic biofuel production.     

国际生物能源研究开发现状和趋势

通过对国际可再生能源研发的重点,第二、三代生物乙醇的研发动向,以及对生物天然气和生物质颗粒燃料异军突起的背景分析,反映出生物能源研发的总体状况和发展趋势。     

Identification of high-lipid producers for biodiesel production from forty-three green algal isolates in China

To identify some desirable algal strains for our future research and/or the production of algae-based biofuel, 43 green algal strains were successfully isolated from Chinese freshwaters, and then incubated in the laboratory bioreactors for the growth an doil accumulation investigations. During a 15 d incubation experiment, the accumulations of their biomass and total lipids, together with the lipid productivities for these green algal strains were systematically investigated and compared. Results indicated that the accumulations of biomass for the 43 algal strains ranged from 0.53 g/L to 6.07 g/L during the experiments, with the highest bio mass of 6.07 g/L for green algae Scenedesmus bijuga. The lipid content for the tested algal strains varied from 20% to 51% of the dry biomass at the end of cultiva tion experiments. Green algae Chlorella pyrenoidosa was one of the best oil producers based on our investigations, with the total lipid content of 51% of dry biom ass. Taking the growth rates and the accumulations of intracellu lar lipids into the consideration, 10 strains were considered to have significant potential for biofuel applications. In addition, the lipid productivities of the selected strains were further investigated.     

The impact of biofuel plantation on biodiversity: a review

Because plants convert solar energy into chemical energy stored in organisms, biomass production as an energy source can help to reduce the world＇s reliance on fossil energy and mitigate global warming. Biofuel production is a fast-growing industry that represents a new type of large-scale human disturbance on ecosystems. Thus, the benefits of biofuel production bring environmental risks that include its potential impact on biodiversity, which is still an open question. In this review, we start first with a brief overview of the evolution of biofuel concept; second, we review the state of biofuel production across the continents, with a major emphasis on the main species used and their major feedstock. For which, we found significant differences for land use and environmental cultural management of biofuel plantation between tropical and temperate regions. Third, we summarize the impacts of biofuel plantation on biodiversity at multiple scales, based on the case studied with respect to the corresponding issues. At the genetic level, introgression and contamination by aggressive genotypes are a primary risk. At the species level, habitat pollution, degradation, and disturbance caused by intensive management of biofuel plantation significantly raise the risk of habitat fragmentation, native extinction, and bio-invasion. At the ecosystem level, the large-scale homogeneous landscape of biofuel plantation results in simplified community and food web that severely damage ecosystem services, including ecosystem diversity. Finally, we compare the current and potential benefits and risks of biofuel plantations for the practical application of a biofuel industry of China. We emphasize the land use constraint from food security and biodiversity conservation, and the need for scientific research and systematic monitoring as a critical support for the sustainable development of biofuel production in China.     

Production of dimethylfuran for liquid fuels from biomass-derived carbohydrates

Diminishing fossil fuel reserves and growing concerns about global warming indicate that sustainable sources of energy are needed in the near future. For fuels to be useful in the transportation sector, they must have specific physical properties that allow for efficient distribution, storage and combustion; these properties are currently fulfilled by non-renewable petroleum-derived liquid fuels. Ethanol, the only renewable liquid fuel currently produced in large quantities, suffers from several limitations, including low energy density, high volatility, and contamination by the absorption of water from the atmosphere. Here we present a catalytic strategy for the production of 2,5-dimethylfuran from fructose (a carbohydrate obtained directly from biomass or by the isomerization of glucose) for use as a liquid transportation fuel. Compared to ethanol, 2,5-dimethylfuran has a higher energy density (by 40 per cent), a higher boiling point (by 20 K), and is not soluble in water. This catalytic strategy creates a route for transforming abundant renewable biomass resources into a liquid fuel suitable for the transportation sector, and may diminish our reliance on petroleum.     

High bacterivory by the smallest phytoplankton in the North Atlantic Ocean

Planktonic algae <5 m in size are major fixers of inorganic carbon in the ocean. They dominate phytoplankton biomass in post-bloom, stratified oceanic temperate waters. Traditionally, large and small algae are viewed as having a critical growth dependence on inorganic nutrients, which the latter can better acquire at lower ambient concentrations owing to their higher surface area to volume ratios. Nonetheless, recent phosphate tracer experiments in the oligotrophic ocean have suggested that small algae obtain inorganic phosphate indirectly, possibly through feeding on bacterioplankton. There have been numerous microscopy-based studies of algae feeding mixotrophically in the laboratory and field as well as mathematical modelling of the ecological importance of mixotrophy. However, because of methodological limitations there has not been a direct comparison of obligate heterotrophic and mixotrophic bacterivory. Here we present direct evidence that small algae carry out 40-95% of the bacterivory in the euphotic layer of the temperate North Atlantic Ocean in summer. A similar range of 37-70% was determined in the surface waters of the tropical North-East Atlantic Ocean, suggesting the global significance of mixotrophy. This finding reveals that even the smallest algae have less dependence on dissolved inorganic nutrients than previously thought, obtaining a quarter of their biomass from bacterivory. This has important implications for how we perceive nutrient acquisition and limitation of carbon-fixing protists as well as control of bacterioplankton in the ocean.     

不同紫花苜蓿栽培品种生物能源性状评价

选取了54个苜蓿品种,采用温室盆栽方法进行两次刈割,对产草量、细胞壁成分(纤维素、半纤维素和木质素)质量分数、株高、分枝数和叶茎比等生物学性状进行了方差分析和聚类分析.结果表明:苜蓿品种间产草量和细胞壁各成分质量分数存在显著差异(P＜0.01),且品种内变异大于品种间变异;产草量和细胞壁成分变异系数由大到小的顺序为:产草量(42.42％)＞木质素质量分数(17.22％)＞纤维素质量分数(12.74％)＞半纤维素质量分数(10.04％);刈割处理显著降低了半纤维素质量分数(P ＜0.01),但产草量、纤维素和木质素没有显著变化;根据产量、株高、细胞壁成分等性状将供试苜蓿品种分为五个大类,其中第Ⅱ类群和第V类群生产性能最高,且第Ⅴ类群表现出良好的再生性能;综合评价提出甘农3号、黄羊镇、和阗、WL903、三得利、大郁山、平凉和意大利作为进一步开展生物质能源性状选育的优良种质材料.     

中低温固体氧化物燃料电池电解质材料研究进展

 固体氧化物燃料电池（SOFC）是一种全固态的电化学能量转换装置,它的能量转换效率高达70%,且其尾气中的有毒成分含量极低,是未来化石燃料发电技术的理想选择之一。SOFC 具有较宽的工作温度范围,通常在450~1000℃。高温下（800~1000℃）尽管SOFC 在燃料选择方面具有更高的灵活性,但是材料性能衰减的加快、运营成本的提高,以及系统的开关速度变慢等一系列缺点也愈加明显。因而,SOFC 主要朝着低温化的趋势发展。降低SOFC 工作温度最有效的方法是提高固体电解质的电导率,以尽量减少电池的欧姆阻抗。本文综述了萤石型、钙钛矿型和复合型3 类固体电解质材料国内外的研究进展,同时展望了未来中低温SOFC 电解质材料的研究方向。钙钛矿型电解质材料在中低温下具有较高的纯离子电导率,且具备丰富的改性空间,有望成为将来中低温SOFC 电解质材料的首选。     

Hydrogen from catalytic reforming of biomass-derived hydrocarbons in liquid water

Concerns about the depletion of fossil fuel reserves and the pollution caused by continuously increasing energy demands make hydrogen an attractive alternative energy source. Hydrogen is currently derived from nonrenewable natural gas and petroleum, but could in principle be generated from renewable resources such as biomass or water. However, efficient hydrogen production from water remains difficult and technologies for generating hydrogen from biomass, such as enzymatic decomposition of sugars, steam-reforming of bio-oils and gasification, suffer from low hydrogen production rates and/or complex processing requirements. Here we demonstrate that hydrogen can be produced from sugars and alcohols at temperatures near 500 K in a single-reactor aqueous-phase reforming process using a platinum-based catalyst. We are able to convert glucose -- which makes up the major energy reserves in plants and animals -- to hydrogen and gaseous alkanes, with hydrogen constituting 50% of the products. We find that the selectivity for hydrogen production increases when we use molecules that are more reduced than sugars, with ethylene glycol and methanol being almost completely converted into hydrogen and carbon dioxide. These findings suggest that catalytic aqueous-phase reforming might prove useful for the generation of hydrogen-rich fuel gas from carbohydrates extracted from renewable biomass and biomass waste streams.     

生物质能的利用和能源植物的开发

生物质能具有资源容量大、清洁可再生特性.发展植物能源是解决矿石能源危机的可行措施,生物乙醇和生物柴油产业已在全球得到较快的发展,并受到我国政府的高度重视.为此综述了生物质能的利用方式和高产生物质植物、能源作物、类石油植物三类能源植物资源的发展情况,并结合我国的科技发展规划,对续随子、黑皂树等特色能源植物进行了介绍.     

黄花水龙克藻效应的研究及其野外应用

在接种蓝藻的富营养化水体中引种栽培了0.5、1.0、2.0、4.08、.0 kg/m35个不同初始生物量的黄花水龙(Jussiaea stipulaceaOhwi),经过草藻共培处理,结果为:在微囊藻初始密度为每毫升200万个及16 d的模拟工程实施期内,黄花水龙对水体叶绿素a及蓝藻消除率存在着正相关的量效关系,且水龙克藻作用的引种量效为1.0~4.0 kg/m3;其达到最佳克藻效果的时间与生物量成反比关系.水质监测结果显示,随着水龙初始生物量的增加,TP、TN、COD及SS等水质指标呈极显著下降.结论为黄花水龙能够通过与蓝藻竞争光照及N、P等营养元素而达到克藻效果.通过实验证实了黄花水龙可作为蓝藻水华污染环境的生态修复物种,并已在太湖入湖河道野外试验中取得良好的克藻效果,为黄花水龙的推广应用提供了必要的基础参数.     

Indirect radiative forcing of climate change through ozone effects on the land-carbon sink

The evolution of the Earth's climate over the twenty-first century depends on the rate at which anthropogenic carbon dioxide emissions are removed from the atmosphere by the ocean and land carbon cycles. Coupled climate-carbon cycle models suggest that global warming will act to limit the land-carbon sink, but these first generation models neglected the impacts of changing atmospheric chemistry. Emissions associated with fossil fuel and biomass burning have acted to approximately double the global mean tropospheric ozone concentration, and further increases are expected over the twenty-first century. Tropospheric ozone is known to damage plants, reducing plant primary productivity and crop yields, yet increasing atmospheric carbon dioxide concentrations are thought to stimulate plant primary productivity. Increased carbon dioxide and ozone levels can both lead to stomatal closure, which reduces the uptake of either gas, and in turn limits the damaging effect of ozone and the carbon dioxide fertilization of photosynthesis. Here we estimate the impact of projected changes in ozone levels on the land-carbon sink, using a global land carbon cycle model modified to include the effect of ozone deposition on photosynthesis and to account for interactions between ozone and carbon dioxide through stomatal closure. For a range of sensitivity parameters based on manipulative field experiments, we find a significant suppression of the global land-carbon sink as increases in ozone concentrations affect plant productivity. In consequence, more carbon dioxide accumulates in the atmosphere. We suggest that the resulting indirect radiative forcing by ozone effects on plants could contribute more to global warming than the direct radiative forcing due to tropospheric ozone increases.     

利用微藻热解生产生物燃料的研究进展

藻类具有生物量大、易繁殖、生长周期短、短时间内便可获得大量藻体且不占用耕地面积等许多优点。通过热解等方法,可将藻类细胞转化为非常好的可再生生物能源,这是解决能源危机的一个有效途径。     

生物质成型燃料洁净生产分析

为了定性和定量地对生物质成型燃料进行清洁生产评价,以平模和环模为成型设备的生物质一体化成型燃料生产系统为例,分析了生物质成型燃料工艺选择合理性、参数控制的有效性、生产稳定性、设备自动化程度、设备布置的合理性、公用工程节能要求等生产工艺与装备要求指标,新鲜水耗系数、能耗系数、物耗系数、清洁能源消耗系数、资源有毒有害系数等资源能源利用指标,产品合格率、产品寿命、有害产品系数等产品指标.结果表明:生物质成型燃料符合国家政策、工艺选择合理,从源头上杜绝了污染物的产生,消除了末端治理的压力;同时该系统生产稳定、自动化程度高、设备布置合理、能耗低;生产系统的新鲜水耗系数几乎为零,物耗系数小、能耗系数小、清洁能源消耗系数小、资源有毒有害系数极低;同时,生物质成型燃料是一种合格、耐烧和十分清洁的产品.     

生物质液体燃料生产系统技术经济建模及分析

利用生物质生产液体燃料是世界可再生能源发展的趋势之一。由于生物质液体燃料的原料来源及收集方式和生产工艺具有特殊性,其生产系统与现有化石液体燃料有较大区别。该文建立了包括多个通用模块的技术经济分析模型,以解决不同原料和工艺路线的生物质液体燃料生产系统的投资及成本分析和生产组织优化等问题。利用该模型对以玉米秸秆为原料的乙醇生产系统进行了案例分析。分析结果表明:目前1万t/a规模的玉米秸秆乙醇单位成本以加工费用为主,乙醇产出系数和生产操作费用系数变化对于成本影响最大。     

中国适宜发展生物液体燃料的边际土地资源分析

 在能源短缺和环境污染压力日益紧迫的背景下，生物液体燃料以其清洁、低碳、可再生性逐渐成为重要的替代能源之一。中国人多地少，在边际土地上种植非粮能源作物是发展生物液体燃料的有效途径。以中国生物液体燃料的3种主要原料作物（燃料乙醇原料甜高粱、木薯和生物柴油原料油菜）为研究对象，利用多因子综合分析法和动态阈值法评估适宜其发展的边际土地（包括宜能荒地和冬闲田）资源量并探究优化发展模式，为合理规划能源植物种植和产业布局提供数据支持。研究结果表明： 2015年，中国适宜甜高粱和木薯种植的宜能荒地面积分别为3463.67万ha和1232.82万ha，适宜油菜种植的冬闲田面积为1995.16万ha；在优化发展模式下，中国适宜生物液体燃料原料作物种植的边际土地面积可达5997.71万ha。     

生物质能转化利用技术及其研究进展

对生物质能的使用价值,国内外利用状况及生物质能转化利用的方式进行介绍。目前的生物质转化方法有直接燃烧法、生物化学法(发酵和厌氧性消化),热化学转化法(气化、热解、液化和超临界萃取)、固体成型和生物柴油制取。我国生物质能利用的重点将是生物质发电、沼气和生物质液体燃料等。