The recent transport electrification trend is pushing governments to limit the future use of Internal Combustion Engines (ICEs). However, the rationale for this strong limitation is frequently not sufficiently addressed or justified. The problem does not seem to lie within the engines nor with the combustion by themselves but seemingly, rather with the rise in greenhouse gases (GHG), namely CO2, rejected to the atmosphere. However, it is frequent that the distinction between fossil CO2 and renewable CO2 production is not made, or even between CO2 emissions and pollutant emissions. The present revision paper discusses and introduces different alternative fuels that can be burned in IC Engines and would eliminate, or substantially reduce the emission of fossil CO2 into the atmosphere. These may be non-carbon fuels such as hydrogen or ammonia, or biofuels such as alcohols, ethers or esters, including synthetic fuels. There are also other types of fuels that may be used, such as those base... [more]

Wheat straw without pre-treatment is only converted to methane to a low degree during anaerobic digestion for fuel production due to its low hydrolysis. Current pre-treatment technologies are challenged by high expenses to energy or chemical agents. We examined the low-tech co-ensiling pre-treatment as an alternative pre-treatment of wheat straw, and compared the results with hydrothermal, chemical and mechanical pre-treatment methods. The effects of co-ensiling duration and the mixing ratio between straw and sugar beet root on the methane yields, surface morphology and chemical composition were examined. It was found that co-ensiling could improve production of methane by 34.7%, while a combined hydrothermal and chemical pre-treatment could increase the production of methane by 25.4%. The study demonstrated that the effect of co-ensiling could overlap with hydrothermal and chemical pre-treatment by having similar effects to increase lignocellulosic hydrolysis and improve methane produ... [more]

In this work, the biomass productivity for biorefinery products and growth curves of three autochthonous microalgae collected in different reservoirs (“Scenedesmus sp.” (SSP), mixture of Scenedesmus sp., Chlorella minutissima, Chlorellas sp. and Nannochloropsis sp. named “La Orden” (LO) consortium and Chlorella minutissima named “Charca Brovales” (CB) consortium) were studied in a 5.5 L column laboratory photobioreactor. Two different culture media, Arnon culture (AM) and an agriculture fertilizer-based liquid medium (FM), have been used to evaluate the growth effect of the microalgae; it was found that the medium has a clear effect on the biomass productivity and growth rate, which ranged between 0.26−0.498 g L−1 d−1 and 0.288−0.864 d−1, respectively. In general, the elemental analysis and higher heating value of microalgae biomass for the three species were independent of the culture medium used for its growth, while their lipids and sugars content depended upon the species type... [more]

In the past decades, carbon dioxide (CO2) emissions have become an important issue for many researchers and policy makers. The focus of scientists and experts in the area is mainly on lowering the CO2 emission levels. In this article, panel data is analyzed with an econometric model, to estimate the impact of renewable energy, biofuels, bioenergy efficiency, population, and urbanization level on CO2 emissions in European Union (EU) countries. Our results underline the fact that urbanization level has a negative impact on increasing CO2 emissions, while biofuels, bioenergy production, and renewable energy consumption have positive and direct impacts on reducing CO2 emissions. Moreover, population growth and urbanization level are negatively correlated with CO2 emission levels. The authors’ findings suggest that the public policies at the national level must encourage the consumption of renewable energy and biofuels in the EU, while population and urbanization level should come along wit... [more]

With an ever-increasing release of harmful greenhouse gases into the environment, there is an ongoing search for a renewable source of energy to replace the current means of producing energy. One promising source is from methanotrophic bacteria, which uses methane as its primary carbon source to produce valuable byproducts including lipids. These lipids could be used in the production of biofuels and other important industrial chemicals including plastics and surfactants. The use of methanotrophs would lower the amount of methane in the atmosphere from two sides, in the growth and cultivation of methanotrophs and in the replacement of conventional fossil fuels. The development of such a system requires a good understanding of the bacteria responsible and the steps of growth/culturing and extraction. An integrated system that uses every product of methanotrophic growth could impact multiple markets and help make this technique economically feasible as well as provide the groundwork for... [more]

The alcohols ethanol and 1-butanol are interesting options as blending components for renewable fuels. We studied whether it is possible to mix these alcohols with a little refined material, rapeseed oil, to obtain stable fuel samples. At room temperature, the stable samples consisted of rapeseed oil blended with butanol at 5 vol-%, 10 vol-%, 20 vol-%, 30 vol-% and one sample of rapeseed oil with 5 vol-% of ethanol. The samples’ fuel properties analysed were kinematic viscosity (at 40 °C), density (at 15 °C) and surface tension. Cold filter plugging point was measured for rapeseed oil with 20 vol-% and 30 vol-% of butanol. Stability of butanol or ethanol and rapeseed oil blends can be achieved at the studied volumes. The density of neat rapeseed oil and all the alcohol−rapeseed oil blends met the requirements set for residual marine fuels. The 30 vol-% butanol−rapeseed oil blend met the requirements for distillate marine oil for density, and almost for kinematic viscosity. The blends a... [more]

Biofuels provide high oxygen content for combustion and do modify properties that influence the engine operation process such as viscosity, enthalpy of vaporization, and cetane number. Some requirements of performance, fuel consumption, efficiency, and exhaust emission are necessary for the validation of these biofuels for application in engines. This work studies the effects of the use of diethyl ether (DEE) in biodiesel-ethanol blends in a DI mechanical diesel engine. The blends used in the tests were B80E20 (biodiesel 80%-ethanol 20%) and B76E19DEE5 (biodiesel 76%-ethanol 19%-DEE 5%). Fossil diesel (D100) and biodiesel (B100) were evaluated as reference fuels. The results revealed similar engine efficiencies among tested fuels at all loads. The use of B100 increased CO and NOx and decreased THC compared to D100 at the three loads tested. B80E20 fuel showed an increase in NOx emission in comparison with all fuels tested, which was attributed to higher oxygen content and lower cetane... [more]

Unsustainable consumption of biofuels contributes to deforestation and climate change, while household air pollution from burning solid biofuels in homes results in millions of premature deaths globally every year. Honduras, like many low and medium Human Development Index countries, depends on primary solid biofuels for more than 30% of its primary energy supply (as of 2013). We conducted a societal exergy analysis and developed a forest stock model for Honduras for 1971−2013 and used the results to model an energy transition from traditional wood stoves to either improved efficiency wood cookstoves or modern fuel cookstoves (using Electricity or Liquefied petroleum gas) over the period 2013−2050. The exergy analysis and forest model enabled quantification of the environmental tradeoffs between the improved efficiency and fuel switching scenarios. We find that the continued reliance on wood within both the existing and improved wood cookstove scenarios would exhaust forest stocks by 2... [more]

The paper assesses the impact of combustion of biofuels produced based on municipal sewage sludge in stoker-fired boilers on the amount of pollutant emissions and examines the tendency of ash deposition of biofuels formed during the combustion process. The combustion tests were performed in a laboratory system enabling simulation of a combustion process present in stoker-fired boilers. The study was conducted for three types of biofuels; i.e., fuel from sewage sludge and coal slime (PBS fuel), sewage sludge and meat and bone meal (PBM fuel) and fuel based on sewage sludge and sawdust (PBT) with particle size of 35 mm and 15 mm. This paper describes and compares the combustion process of biofuels with different granulation and composition and presents the results of changes in emission values of NOx, SO2, CO, and CO2. The emission results were compared with the corresponding results obtained during combustion of hard coal. The results showed that biofuels with lower particle sizes were... [more]

With the Renewable Energy Directive 2018/2001 (RED II), adopted in December 2018, the EU is continuing the political framework for the use of renewable energy sources in the transport sector for the period from 2021 to 2030. At the same time, the German federal government has set a target of reducing greenhouse gas (GHG) emissions in the transport sector by at least 40% to 42% by 2030 compared to the 1990 GHG level. To investigate the possible effects of the European and national requirements on the German GHG quota, cost-optimal fuel mixes were modelled to achieve the GHG targets of 26 fuel options in each of the nine different scenarios. The results show clear differences between the scenarios that implement the RED II targets (including 14% renewables in transport by 2030) and those that implement the climate protection target (40−42% GHG reduction compared to 1990 by 2030). If only the minimum requirements of RED II are met, the German climate protection target is clearly missed wi... [more]

Microbial lipids have been considered as promising resources for the production of renewable biofuels and oleochemicals. Various feedstocks, including sugars, crude glycerol, and volatile fatty acids, have been used as substrates for microbial lipid production, yet amino acid (AA) wastes remain to be evaluated. Here, we describe the potential to use AA wastes for lipid production with a two-stage culture mode by an oleaginous yeast strain Rhodosporidium toruloides CGMCC 2.1389. Each of the 20 proteinogenic AAs was evaluated individually as sole carbon source, with 8 showing capability to facilitate cellular lipid contents of more than 20%. It was found that L-proline was the most favored AA, with which cells accumulated lipids to a cellular lipid content of 37.3%. When blends with AA profiles corresponding to those of meat industry by-products and sheep viscera were used, the cellular lipid contents reached 27.0% and 28.7%, respectively. The fatty acid compositional analysis of these l... [more]

The supply logistics of energy biomasses generally involves a complex system of supply chains, which aim to achieve timely and cost-efficient feedstock deliveries to biomass demand points. The performance of supply chains is often examined in case studies where spatial data about biomass sources and transportation networks are deployed in varying resolutions and to different geographical extents. In this paper, we have reviewed 94 publications, in which spatial data were used in case studies that focused on analysing and optimising energy biomass supply chains. The reviewed publications were classified into 16 categories, according to the publication year, study methods and objectives, biomass types, supply system complexity and the spatial features of each study area. This review found that the use of geographical information systems in this context has increased in popularity in recent years, and that and the multiformity of the applied methods, study objectives and data sources have... [more]

Biofuel is an attractive alternative to fossil fuels since it is renewable and biodegradable—it is mainly made from edible and non-edible sources. Globally, the usage of renewable biofuels is expected to rise quickly. The rising production and use of biofuel has prompted an examination of its environmental impact. Biodiesel is a fatty acid methyl ester generated from sustainable lipid feedstock that substitutes petroleum-based diesel fuel. Non-food oils, such as Jatropha, waste cooking oil, and by-products of vegetable oil from refineries provide inexpensive feedstock for biodiesel manufacturing. Due to its increased oil yield, adequate fatty acid content, tolerance to various agro-climatic conditions, and short gestation period, Jatropha may be one of the most promoted oilseed crops worldwide. Furthermore, Jatropha can provide several economic and agronomic advantages because it is a biodegradable, renewable plant. This study examines whether Jatropha can be considered as the most pre... [more]

Walnut tree (Carya illinoensis (Wangenh.) K. Koch) is a plant species showing ecological, social, and economic importance in México. The objective was to determine biomass productivity and to characterize the raw material and biomass briquettes obtained from walnut thinning pruning. The variables evaluated were tree total height (TH), fresh biomass (FB) and dry biomass (DB) per hectare (kg ha−1). Briquettes were made by using the biomass obtained in both orchards. Laboratory tests for original biomass included moisture content (MC), ash content (AC), volatile matter (VM) and fixed carbon (FC), as well as high heating value (HHV). Briquette studies also included diameter (D), weight (W), length (L), volume (V), density (Ds), and HHV. The data were analyzed by using descriptive statistics and analysis of variance (ANOVA) under a completely randomized design with factorial arrangement. Thinning pruning in walnut orchards provides 12 kg tree−1 (998 kg ha−1) of dry biomass, with acceptable... [more]

This paper provides a simple methodology for the design of the air reactor of a chemical looping combustor to optimize its characteristics when it is employed connected to a turbo expander to produce power. The design process, given a certain objective (e.g., electric power) defines the reactor specifics, namely height and diameter, taking into account the following aspects: solids inventory of the air reactor; gas velocity; air reactor transport disengaging height (TDH); solids concentration profile along the reactor height, dense bed height; freeboard height; pressure drop depending on air reactor injectors design and configuration. The total air reactor height was about 9.5 m, while the diameter was about 1.8 m. The total inventory was about 10,880 kg; while the circulation rate in the air reactor was about 110 kg/s. The operating pressure and temperature were, respectively, 12 bar and 1200 °C. The average velocity of the gases inside the reactor was about 4 m/s. The fluidization re... [more]

The maritime transportation sector (MTS) is undertaking a major global effort to reduce emissions of greenhouse gases (GHG), e.g., sulfur oxides, nitrogen oxides, and the concentration of particulates in suspension. Substantial investment is necessary to develop alternative sustainable fuels, engines, and fuel modifications. The alternative fuels considered in this study include liquified natural gas, nuclear energy, hydrogen, electricity, and biofuels. This paper focuses on biofuels, in particular fast pyrolysis bio-oil (FPBO), a serious partial alternative in MTS. There are some drawbacks, e.g., biofuels usually require land necessary to produce the feedstock and the chemical compatibility of the resulting biofuel with current engines in MTS. The demand for sustainable feedstock production for MTS can be overcome by using cellulose-based and agroforestry residues, which do not compete with food production and can be obtained in large quantities and at a reasonably low cost. The compa... [more]

Agave bagasse is a residual biomass in the production of the alcoholic beverage tequila, and therefore, it is a promising raw material in the development of biorefineries using hot compressed water pretreatment (hydrothermal processing). Surfactants application has been frequently reported as an alternative to enhance monomeric sugars production efficiency and as a possibility to reduce the enzyme loading required. Nevertheless, the surfactant’s action mechanisms in the enzymatic hydrolysis is still not elucidated. In this work, hot compressed water pretreatment was applied on agave bagasse for biomass fractionation at 194 °C in isothermal regime for 30 min, and the effect of non-ionic surfactants (Tween 20, Tween 80, Span 80, and Polyethylene glycol (PEG 400)) was studied as a potential enhancer of enzymatic saccharification of hydrothermally pretreated solids of agave bagasse (AGB). It was found that non-ionic surfactants show an improvement in the conversion yield of cellulose to gl... [more]

Advanced processes, which are alternatives to ordinary distillation, are essential to dehydrate azeotropic alcoholic mixtures for biofuel production. In that regard, this work focuses on the analysis of heterogeneous azeotropic distillation for the separation of a 2-propanol + water mixture in order to recover the alcohol with a sufficiently low water content. By comparing the performances of various entrainers on the basis of ternary maps, isooctane was selected for further process analysis. An advantage it poses is related to the fact that traces of it within the recovered dehydrated alcohol are highly welcome with a view to its subsequent use as a fuel. Aspen Plus® V11 software was employed for the simulation of the process, thus filling the gap existing in the literature due to the lack of studies on the process analysis of the heterogeneous azeotropic distillation of the 2-propanol + water system using isooctane as an entrainer.

The effect of foliar application of Cyanobacteria and Chlorella sp. monocultures on physiological activity, element composition, development and biomass weight of basket willow (Salix viminalis L.) and the possibility to prepare biofuel from it in the fortification process was studied. Triple foliar plant spraying with non-sonicated monocultures of Cyanobacteria (Anabaena sp. PCC 7120, Microcystis aeruginosa MKR 0105) and Chlorella sp. exhibited a considerably progressive impact on metabolic activity and development of plants. This biofertilization increased cytomembrane impermeability, the amount of chlorophyll in plants, photosynthesis productivity and transpiration, as well as degree of stomatal opening associated with a decreased concentration of intercellular CO2, in comparison to control (treatments with water, Bio-Algeen S90 or with environmental sample). The applied strains markedly increased the element content (N, P, K) in shoots and the productivity of crucial growth enzymes... [more]

The aim of this research is to examine the effect of lignocellulosic biomass detoxification on the efficiency of the methane fermentation process. Both for corn straw and rye straw, the methane yield was expressed per volume of fermentation medium and per mass of volatile solids (VS) added. Lignocellulosic biomass was subjected of thermo-chemical and enzymatic sequential pretreatments. It was found that methane yield was higher by 22% when using the detoxification process. In these variants, CH4 yield was 18.86 L/L for corn straw and 17.69 L/L for rye straw; while methane yield expressed per mass of VS added was 0.31 m3/kg VS for corn straw and 0.29 m3/kg VS for rye straw. The inclusion of a detoxification step in pretreatments of biomass lignocellulosic increases the degree of organic substance decomposition and enhances methane yield. The results show that a two-step pretreatment, alkaline/enzymatic with a detoxification process, is necessary for the effective generation of high meth... [more]

This contribution focuses on utilizing blended biofuels of rapeseed oil and methanol with diesel. Rapeseed is one of the most cultivated energy crops in Europe, and its purpose in the blends is to increase the bio-content in test fuels. The purpose of methanol in the blends is to increase bio-content and compensate for the higher viscosity of the rapeseed oil. As methanol is almost insoluble in diesel and rapeseed oil, iso-butanol is used as a co-solvent. The fuel blends were tested in volumetric concentrations of diesel/rapeseed oil/methanol/iso-butanol 60/30/5/5, 50/30/10/10, and 50/10/20/20. Diesel was used as a reference. The measurements were performed on a turbocharged diesel engine Zetor 1204, loaded using the power-takeoff shaft of the Zetor Forterra 8641 tractor. In this paper, the effect of the blended fuels on performance parameters, engine efficiency, production of soot particles, and regulated and unregulated emissions are monitored and analyzed. It was found that engine p... [more]

Energy consumption is on the rise due to rapid technological progress and a higher standard of living. The use of alternative energy resources is essential to meet the rising energy demand and mitigate the carbon emissions caused due to use of fossil-based fuels. Biodiesel produced from non-edible oils such as castor seed oil (CO) can be used in diesel engines to replace fossil diesel. However, the quality and yields for CO biodiesel is low due to the presence of ricinolic acid C18:1OH (79%). In this study, two-stage conversion techniques were used to improve the yields and properties of CO biodiesel. The catalyst CaCu(OCH3)2 was prepared from waste eggshell and synthesized with copper oxide in the presence of methanol. The castor oil was subjected to pyrolysis at 450−500 °C and then transesterified in the presence of modified catalyst. The reaction parameters such as methanol-to-oil ratio and catalyst and reaction time were investigated, and the optimum combination was used to produce... [more]

Date palm trees, being an important source of nutrition, are grown at a large scale in Saudi Arabia. The biomass waste of date palm, discarded of in a non-environmentally-friendly manner at present, can be used for biofuel generation through the fast pyrolysis technique. This technique is considered viable for thermochemical conversion of solid biomass into biofuels in terms of the initial investment, production cost, and operational cost, as well as power consumption and thermal application cost. In this study, a techno-economic analysis has been performed to assess the feasibility of converting date palm waste into bio-oil, char, and burnable gases by defining the optimum reactor design and thermal profile. Previous studies concluded that at an optimum temperature of 525 °C, the maximum bio-oil, char and gases obtained from pyrolysis of date palm waste contributed 38.8, 37.2 and 24% of the used feed stock material (on weight basis), respectively, while fluidized bed reactor exhibited... [more]

Hydrogen is an environmentally friendly biofuel which, if widely used, could reduce atmospheric carbon dioxide emissions. The main barrier to the widespread use of hydrogen for power generation is the lack of technologically feasible and—more importantly—cost-effective methods of production and storage. So far, hydrogen has been produced using thermochemical methods (such as gasification, pyrolysis or water electrolysis) and biological methods (most of which involve anaerobic digestion and photofermentation), with conventional fuels, waste or dedicated crop biomass used as a feedstock. Microalgae possess very high photosynthetic efficiency, can rapidly build biomass, and possess other beneficial properties, which is why they are considered to be one of the strongest contenders among biohydrogen production technologies. This review gives an account of present knowledge on microalgal hydrogen production and compares it with the other available biofuel production technologies.

The aviation industry contributes to more than 2% of global human-induced CO2-emissions, and it is expected to increase to 3% by 2050 as demand for aviation grows. As the industry is still dependent on conventional jet fuel, an essential component for a carbon-neutral growth is low-carbon, sustainable aviation fuels, for example alternative drop-in fuels with biobased components. An optimization model was developed for the case of Sweden to examine the impacts of carbon price, blending mandates and penalty fee (for not reaching the blending mandate) on the production of renewable jet fuel (RJF). The model included biomass gasification-based Fischer−Tropsch (FT) jet fuel, Power-to-Liquid (PTL) jet fuel through the FT route and Hydrothermal liquefaction (HTL)-based jet fuel. Thus, this study aims at answering how combining different policies for the aviation sector can support the production of RJF in Sweden while reducing greenhouse gas (GHG) emissions. The results demonstrate the impor... [more]