A Study of the Physical Properties of Cellulose Derived Biofuel Components and Diesel Blends
Session chaired by Pr. Christine Rousselle
The decarbonisation of transport using alternative low carbon fuels, such as biofuels, will be a key component in achieving the reduction of greenhouse gas emissions required for Europe to become net zero in terms of CO2 emissions by 2050. Most biofuels currently used are first generation, however, the revised Renewable Energy Directive (RED) limits these to a maximum of 7% of the final energy consumption for any Member State of the European Union. Production of second generation biofuels from cellulose is an increasingly active area, with a range of conversion methods being developed, including the alcoholysis of cellulose to produce the corresponding levulinate ester and dialkyl ether from the dehydration of the alcohol. Biofuels based on mixtures of the alcohol, alkyl levulinate, and dialkyl ether have the potential to be a tailorable biofuel component mixture depending upon the final application. These second generation fuel components could play a role in increasing the biofuel content of blends using gasoline or diesel. However, the implications and effects of blending these components with gasoline or diesel are not fully understood. Compression ignition (CI) engines have an efficiency advantage over spark ignition (SI) engines, which results in lower carbon dioxide emissions per kilometre. The increased efficiency of CI engines makes them the engine of choice in the haulage industry and their use is likely to continue in the near-term future. Several alternative fuels could be used for this sector such as compressed natural gas, biodiesel, and used cooking oil. However, there is an interest in the development and utilisation of new fuel components to reduce emissions from CI engines. Reducing the emissions from CI engines is becoming a priority for the automotive industry as legislated emissions limits have been reducing with each version of the emissions standards, due to their effects on air quality as well as climate change. The use of cellulosic derived biofuel components could be one route to reduce the emissions from a CI engine. Diesel fuels sold across Europe must meet the limits for the physical properties set in the European Standard EN 590. The biofuel content of diesel fuel is limited to up to 7% biodiesel and the use of other oxygenated biofuel components results in diesel fuel blends that do not meet EN 590. Thus, amendments to EN 590 or a new standard may be required to allow for the implementation and utilisation of such diesel/biofuel blends. It is therefore important to understand the impact that blending advanced biofuel components and mixtures with diesel may have on the physical and chemical properties of the fuel. This study investigates the physical properties and blending characteristics of the biofuel components produced from alcoholysis of cellulose when blended with diesel fuels, and as a three-component biofuel blend, including their miscibility, stability, flashpoint and density. The different biofuel components considered in this study are: ethanol, diethyl ether, and ethyl levulinate along with n-butanol, di-n-butyl ether, and n-butyl levulinate. A design of experiments approach was used to generate predictive equations and response surfaces for the measurable properties for the different compositions of the ethyl and butyl based three-component biofuel blends. In these three-component blends the alkyl levulinate was at least 50 vol% of the blend which is favourable from the production point of view. Blend stability and miscibility of the components were investigated using blends of different volume fractions of diesel and the biofuel components stored at ambient temperature, typically 18 °C to 20 °C, for a duration of three months. The use of graduated test tubes enabled the quantification of any phase separation. The flash point temperature was determined using a Stanhope Seta Setaflash Series 3 plus small-scale closed cup flash point tester according to ISO 3679. Density was determined according to EN ISO 3838 at 15 °C. Both standards are fundamental for fuel safety and utilisation. Having the predictive models enables the composition of the three-component biofuel blend to be tailored for its final application. The effects of how the different ratios of the three biofuel components when blended at different volume fractions with diesel on the flash points and density of the blends were investigated. Flash points of the blends of ethyl levulinate, ethanol, diethyl ether, and diesel have been found to reduce significantly, due to the high volatility and low flash points of the diethyl ether and ethanol. For the butyl levulinate, n-butanol, di-n-butyl ether, and diesel blends the reduction in the flash points were not as significant. These changes in flash points must be taken into consideration for the storage and handling of the fuel blends and should be reflected in an appropriate standard. The effects of how the components and their blending volumes effect the flashpoints and blend density are discussed.
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