1 . Production methods and processes
At present, there are 3 main methods of preparing biodiesel: chemical method, physical chemistry method and biological method. The commonly used chemical method is transesterification, through esterification of vegetable oil or animal oil with methanol or ethanol and other low-carbon alcohols in the presence of acidic or basic catalysts, to produce the corresponding fatty acid methyl ester or ethyl ester biodiesel. This method has the advantages of low catalyst cost, fast reaction speed, high product quality and low energy consumption, but there is a certain amount of waste liquid discharge in the production process. In order to improve the shortcomings of this method, some studies have been carried out at home and abroad, mainly focusing on the improvement of catalysts, such as the use of solid base, organic base, solid acid as catalyst, etc., but most of the environmentally friendly catalysts have problems such as slow reaction rate, high catalyst cost, catalyst poisoning and so on. The most recent breakthrough was the development of a new type of nanocatalyst by Victor Lin, a chemistry professor at Iowa State University in 2006. The catalyst is a mixture of oxide silica nanoparticles. It contains both acid and basic catalytic centers, and has the characteristics of both acid and basic catalysts: acid catalytic centers. Free fatty acids can be converted into biodiesel by esterification, and alkaline catalytic center can convert oil into biodiesel by transesterification. The catalyst has the advantages of high efficiency, simple process, easy recovery and environmental protection, and is expected to be widely used in the future. Because of the poor practicability of biological enzymatic method and supercritical method, it is difficult to be popularized and applied on a large scale. The focus of future research is still the choice of new catalysts and the optimization of esterification reaction conditions.
Petrochemical diesel oil is mainly made up of diesel distillates produced by crude oil distillation, catalytic cracking, thermal cracking, hydrocracking, petroleum coking, etc. It can also be made from shale oil processing and coal liquefaction. Compared with biodiesel and petrochemical diesel production methods and processes, although the former mainly involves esterification reaction, the latter mainly involves pyrolysis reaction, but most of the two production processes used have a high degree of similarity, such as high temperature distillation, refining and so on. Therefore, the production of biodiesel can draw lessons from and part of the use of petrochemical diesel production process and equipment, which makes the large-scale production of biodiesel has a good practical basis.
2. Engine economy and power
Because the low calorific value of biodiesel is generally smaller than that of petroleum diesel, and its density is higher than that of petroleum diesel, the fuel consumption rate of biodiesel is obviously higher than that of petroleum diesel, but the results are not very different, the overall difference is within 5% – 10%. Ge Yunshan et al. studied the effects of biodiesel and petrochemical diesel on engine economy. The results showed that the exterior characteristic fuel consumption of biodiesel was about 9% higher than that of petrochemical diesel. When the engine was not modified or adjusted, the road test of 100 km isokinetic vehicle found that the engine was fueled with 100 km isokinetic fuel of pure biodiesel. Compared with petroleum diesel, the consumption of isokinetic fuel increased by 3%-8% and 1%-4% respectively. Yuan Wenhua et al. tested the external characteristics and load characteristics of diesel engine with biodiesel and 0# diesel respectively. The results showed that when biodiesel was used, the fuel consumption rate increased to a certain extent, the lowest external characteristics fuel consumption increased by 4.3%, and the lowest load characteristics fuel consumption increased by 3.6%.
Compared with petrochemical diesel, biodiesel has low calorific value and high density. Therefore, on the premise that the volume of fuel injection remains unchanged, the fuel injected into the cylinder contains little change in energy, and the diesel engine fueled with biodiesel is not dominant in power performance. Ge Yunshan et al. through comparative studies show that for the experimental diesel engine, when no adjustment is made to the fuel injection pump, the direct combustion of biodiesel has less than 5% influence on the power performance; while the maximum fuel injection of the fuel pump remains unchanged, the direct combustion of restaurant waste oil biodiesel has less than 2.5% influence on the power performance. Grimaldi et al. conducted an experimental study on the combustion and emission characteristics of biodiesel in a common rail diesel engine. Without adjusting the injection strategy, the output power of biodiesel was reduced by about 10%. Graboski et al. found that with the increase of biodiesel blending ratio, the maximum output torque also showed a downward trend. Compared with 2# diesel, the output torque of pure biodiesel only reached 94.6%, just in line with the energy density ratio of the two fuels.
3. Emission characteristics and renewability
As biodiesel has high oxygen content, no aromatic hydrocarbons and nearly zero sulfur content, it can effectively reduce the emissions of harmful substances when used as diesel engine fuel. A large number of basic research and diesel engine tests at home and abroad have proved the superiority of biodiesel in terms of emission characteristics: fueled with biodiesel or its mixture with petrochemical diesel, smoke, CO, HC and other harmful substances emissions decreased significantly, but the NOX emissions increased slightly. Caboski et al. conducted a comparative emission test on the same Diesel Engine Fueled with petrochemical diesel and biodiesel. The results showed that the main emission PM decreased from 0.41g / (kW h) to 0.14g / (kW h) when fueled with petrochemical diesel, while the emission of NOX increased slightly, from 6.31g / (kW h) when fueled with petrochemical diesel to 7.31g /(kW h) when fueled with biodiesel. 03g/ (kW. H).
Nine et al. conducted a comparative test of petrochemical diesel and biodiesel emissions in the same natural-suction diesel engine under the conditions of “dry” and “wet” respectively. The results showed that PM emissions decreased from 1.49 g /(kW From 5.03 g /(kW Studies by Ark-oudeas, Kalligeros and others have shown that biodiesel fueled with sunflower seed oil and olive oil, respectively, significantly reduces emissions of harmful substances such as NO, CO, HC and increases combustion efficiency.
Because the production of petrochemical diesel depends on petrochemical raw materials, the regeneration cycle of petrochemical raw materials is millions of years. Therefore, from the time scale of human life, its renewability is almost zero. In terms of concept, biodiesel seems to be completely renewable. However, a certain amount of petrochemical energy is needed in the raw material production and processing of biodiesel, so biodiesel is not completely renewable. Taking biodiesel as an example, the results show that biodiesel containing 1 MJ can be produced by consuming 0.311MJ petrochemical energy (including agricultural production of soybean, soybean transportation, soybean oil production, soybean oil transportation, soybean oil conversion, biodiesel transportation and sales), and its petrochemical energy efficiency ratio is 3.215. This shows that the renewable performance of biodiesel is much better than that of petrochemical diesel, and the use of biodiesel can greatly improve the life of petrochemical energy, a limited energy source. Soybean oil conversion is the place that consumes the most petrochemical energy, which is mainly due to the production of biodiesel using ethanol and other raw materials, and we assume that ethanol production is to consume petrochemical energy such as natural gas. This also shows that we have the opportunity to use renewable resources to produce ethanol to enhance the energy efficiency ratio of petrochemical. The life cycle assessment method was applied to evaluate the project of soybean biodiesel production. The results showed that the project played a positive role in reducing greenhouse gas emissions and was more environmentally friendly than petroleum diesel.
In view of the long-term energy security of China and the world, biodiesel should be vigorously developed to delay the excessive consumption and dependence on Petrochemical energy.
4 .Main directions for future research at home and abroad
The three important factors that determine the development and utilization of biodiesel are raw materials, processing technology and combustion mechanism. Therefore, the following three aspects should be strengthened in the future.
(1) Strengthen the research on breeding, cultivation and popularization of new biodiesel raw material crops, and strive to obtain cheap raw materials for biodiesel processing. In the past, the main purpose of oil crops was to process edible oil, and the edible quality of oil was highly demanded, so many high-yielding oil crops or varieties were not paid attention to and popularized because of the quality and other reasons; however, oil crops or varieties used as biodiesel raw materials only need to consider high yield, low production costs and so on. Therefore, the potential of breeding new biodiesel oil crops or new varieties is very great, such as Jatropha curcas, rapeseed varieties with high oil yield (high erucic acid, high glucoside content) may be large-scale promotion and application. New oil crops such as Jatropha curcas, Tung oil and rape have the characteristics of wide climate adaptability, easy planting and high oil yield, which will greatly broaden the source of biodiesel raw materials, thus laying a good raw material foundation for large-scale production of biodiesel.
(2) to strengthen the research of biodiesel processing technology with high efficiency, low energy consumption and low pollution. As the esterification of biodiesel involves various complex factors such as the types of catalysts, reaction conditions, products, separation and recycling of by-products and catalysts, the new process can be innovated and improved in various aspects, and the new process can be evaluated comprehensively from the aspects of production efficiency, production cost and environmental protection characteristics. The potential of production and application of art.
(3) to strengthen the research on the combustion mechanism of biodiesel and the design and research of the new Biodiesel Engine. As a new type of renewable energy, biodiesel combustion performance will be affected by different processing technology, blending ratio and diesel engines. Therefore, a large number of systematic and in-depth studies are needed to explore the combustion mechanism of biodiesel. Although the combustion of biodiesel does not need to change the structure of the original diesel engine, the design and research of engines more suitable for biodiesel combustion will be the future direction of diesel engine development, which will further improve the combustion performance of biodiesel, engine economy and power performance.