1. In addition to the above advantages, the development of biodiesel in China has the following dual environmental protection effects.
(1) Reduce the discharge of waste oil and reduce the pressure and cost of sewage treatment. According to conservative estimates, the current amount of waste oil in Beijing has exceeded 50,000 tons/year. If it is not treated, it will cause excessive watering of the water body.
(2) Converting food waste oil to protect the health of the people. China consumes 12 million tons of vegetable oil per year, directly produces 2.5million tons of acidified oil , and the catering industry in large and medium-sized cities can produce 4 million tons of waste oil . Many unscrupulous traders extract garbage oil from sewers and swill water and sell them as edible oil. This kind of garbage oil is very unsanitary. The peroxide value, acid value, moisture and bacteria are seriously exceeded. It is a non-edible oil. Once consumed, it will destroy white blood cells and intestinal mucosa, causing poisoning and even cancer. Beijing, Tianjin, Urumqi, Hohhot, Shenyang, Zhengzhou, Xi’an, Nanning and other places have had incidents of garbage oil entering the table. The garbage oil entering the table will cause serious harm to the health of the people. In view of this, many large and medium-sized cities in China have been actively working to study the technology of using waste oil to produce biodiesel .
2.Disadvantages and limitations of biodiesel
(1) Biodiesel viscosity is large (Rapeseed oil 42; 40 soybean: 1.2 to 3.5 units petroleum diesel mm2 / s, 40 ℃), winter comes thickened thickens, the fluidity is deteriorated. In the winter, B100 pure biodiesel cannot be used at present , and only B20 biodiesel can be used .
(2) Reduced power 8%-10%. The calorific value of biodiesel is comparable to the calorific value of petrochemical diesel: 32.8 : 35.7 = 92% . At the same quality, the power is about 92 % of petrodiesel .
(3) Corrosive to engine rubber parts ( diesel before 1996 ). But B20 will not corrode rubber parts .
(4) Due to the large molecular weight of biodiesel, the viscosity is high, thus affecting the injection time course, resulting in poor jetting effect.
(5) The application range is small. At present, biodiesel is not as good as petrodiesel in the global market, and its application range is limited. In the United States, its biodiesel is only sold at certain special prices for environmental protection rules and environmental friendliness. (B20 biodiesel ) , including federal or state government fleets, urban buses, trucks, marine parks, mining areas, etc.
(6) The price of biodiesel is high. At present, the foreign biodiesel industry relies heavily on government policy support and price subsidies.
The major countries in the world have developed their own biodiesel standards. The main biodiesel standards are as follows:
DIN 51606 : The German biodiesel standard is considered to be the most stringent standard in the world and is accepted by all car manufacturers.
EN590 : 2000 began to be applied in 12 countries of the European Union , such as Iceland, Czech Republic, Norway, Switzerland, France, etc.
EN14214 : New EU standard based on DIN 51606 .
China’s first national standard for biodiesel, “Biodiesel for diesel fuel blending,” has entered the approval process. As can be seen from the above table , China’s national standard for biodiesel is a relatively high standard.
4. Current technologies used in biodiesel production
At present, biodiesel is mainly produced by chemical methods, that is, transesterification ( transesterification ) reaction of animal and vegetable oils and lower alcohols such as methanol or ethanol under acid or basic catalyst and high temperature ( 230 to 250 °C ). The corresponding fatty acid methyl ester or ethyl ester is obtained by washing and drying to obtain biodiesel. The production equipment is the same as the general oil production equipment, and about 10% of by-product glycerin can be produced in the production process .
There are currently several major processes:
• Alkaline catalysis
• acid catalysis
• lipase or bioenzymatic method
• Supercritical extraction
1.Alkali-catalyzed method: using sodium hydroxide or potassium hydroxide as a catalyst, which is the most commonly used preparation method, transesterification (lactide) reaction of vegetable oil and methanol with sodium hydroxide ( 1% by weight of fat ) or sodium methoxide (Sodium methoxide) As a catalyst, biodiesel can be obtained by mixing and stirring for about 2 hours.
2 . Acid catalysis: Because waste oil usually contains a large amount of free fatty acids, and can not be converted into biodiesel with a basic catalyst, the high free fatty acid raw materials are pretreated with concentrated sulfuric acid or phosphoric acid as an acidic catalyst. FFA isconverted to an ester. The triglyceride is then transesterified by a basic catalyst. The disadvantage of the acid catalysis process is FFAreacts with alcohol to produce water, which inhibits Esterification of FFA and transesterification of glycerol. The material may be subjected to dealcoholization and dehydration treatment after the esterification reaction.
Under the current national conditions and current oil prices in China, it is not realistic to use food-grade oils as raw materials to produce biodiesel. Food waste oil and some industrial oils are relatively low in cost. However, these waste oils usually contain relatively high free fatty acids, so these waste oils are first subjected to an acid-catalyzed method and then subjected to a transesterification reaction by a basic catalyst.
The base catalysis method and the acid catalysis method are also referred to as chemical methods.
3.Lipase or biological enzymatic method: The chemical synthesis of biodiesel has the following disadvantages: the process is complicated, the alcohol must be excessive, the subsequent process must have the corresponding alcohol recovery device, high energy consumption; deep color, due to the high temperature of unsaturated fatty acids in fat It is easy to deteriorate; the esterification product is difficult to recycle, and the cost is high; the production process has waste alkali liquor discharge.
In order to solve the above problems, people began to study the bio-enzymatic synthesis of biodiesel, that is, using animal fats and lower alcohols to carry out transesterification by lipase to prepare corresponding fatty acid methyl esters and ethyl esters. The enzymatic synthesis of biodiesel has the advantages of mild conditions, low alcohol consumption and no pollution discharge. However, the main problems at present are: low conversion rate to methanol and ethanol, generally only 40% to 60% , due to the fact that lipase is effective for esterification or transesterification of long-chain fatty alcohols, and for short-chain fatty alcohols such as methanol. Or conversion rate such as ethanol is low. Moreover, short-chain alcohols are somewhat toxic to enzymes, and the lifespan of enzymes is short. The by-product glycerin and water are difficult to recover, which not only inhibits the formation of the product, but also the toxicity of glycerol to the immobilized enzyme, so that the immobilized enzyme has a short service life. Bio-enzyme technology has not yet reached the industrial level.
4.Supercritical extraction method: Supercritical extraction method is a fat exchange reaction using a high methanol feedstock ratio ( 42 : 1 ) under supercritical conditions ( 350-400 °C and 1200 psi pressure). Its reaction time is fast and the reaction can be completed in 4 minutes.However, the operating cost is high and the energy consumption is high. The supercritical extraction method also has the advantage of not using a catalyst, eliminating the need for catalyst dissolution and separation procedures.
Another technology close to commercial production is the non-catalyst cosolvent method. The cosolvent tetrahydrofuran is used to solubilize methanol. The reaction is rapid, only 5-10 minutes, and the reaction conditions are mild. Since no catalyst is needed, it is not necessary to remove the catalyst in the finished product and by-product glycerin. But tetrahydrofuran is costly and has drugs. In order to prevent the leakage of tetrahydrofuran, the requirements for equipment are high.
It is worth mentioning that in April this year , American scientists published a new method for producing biodiesel, which is a half-credit-sized microprocessor. Methanol and feedstock enter the microprocessor through a thinner tube than the hair. The feedstock is immediately converted to biodiesel, which is 10-100 times faster than conventional production methods and does not use any chemical catalysts. The reaction conditions are mild and the energy consumption is greatly reduced. According to the scientists, it will be a revolutionary innovation and it is possible to subvert all existing production processes.
So which method has more market value?
At present, it should be the most widely used chemical method. Many countries in the world, including France, Germany, the United States and Australia, are using chemical methods to produce biodiesel on a large scale, with an annual production capacity of more than 2.5 million tons. At present, only mass chemical production can be used in mass production. Therefore, the location of the factory must be far away from the urban area – this will inevitably increase transportation costs; at the same time, you need to purchase professional production equipment.Although the use of technology is free, production equipment must be purchased from a professional manufacturer.