Biodiesel Production from Micro-algae by Heterotrophic Fermentation


      Biodiesel is a kind of clean and renewable long chain fatty acid monoester produced from oil crops (soybean, rapeseed, etc.), oil forest (Oil Palm, Pistacia chinensis, etc.), oil aquatic plants (micro-algae, etc.), animal oil, microorganism oil or waste oils and fats(WOF) through transesterifieation with short chain alcohol, also known as "green diesel". It is becoming a promising alternative to petroleum-based fuels, with its physical and chemical properties similar to that of petroleum-based fuels.

      Biodiesel has many advantages over traditional diesel:

      ⏿Environmental advantage: reducing the content of hydrocarbons, CO, particles, sulfide and nitrogenous heterocyclic compounds in air emission significantly; biodegradable; suitable to be used in cities, mines, forestry machinery or tourism vessel.

      ⏿Produced from renewable resources, meeting the needs of sustainable development.

      ⏿High kinematic viscosity, easy to form oil film in cylinder wall-layer, consequently improving lubricity of kinematic components and reducing wear of it.

      ⏿good safety performance, high flash point (200‿low volatility, more safe in the process of transportation and use.

      ⏿Good combustion performance, high Cetane Number (higher than 49), improving performance of engine, combustion residue is of subacidity, making the life of catalyst and engine oil lengthened.

      ⏿It can be used directly with no need to change diesel engine, and refueling equipment, storage equipment and special technical training is not necessary neither.

      ⏿Wide application area: It can be used alone, mixed with petroleum-based fuels or as additives to improve combustion efficiency.

      Excellent performance of biodiesel makes the air emission index meet with standards of European ῿ more rigorous than European⃿Biodiesel industry not only reduces environmental pollution caused by fossil fuel combustion, bur also eases pressure of energy shortage to a certain extent.

      The key of biodiesel process lies in raw material and production technology. According to statistics, raw material cost accounts for 75% of preparation cost. Thus, selecting cheap raw material and increasing convesion rate is the key to the practicality of biodiesel. When it comes to production technology, there are 3 main ways: ①chemical synthesis; ②biological enzyme; ③micro-algae.

      Chemical synthesis: esterification between animal or plant oil and lower alcohols such as methanol or ethanol is conducted in the condition of acid or alkaline catalyst and high temperature (230-250₿to produce fatty acid methyl ester or ethyl ester. Then, biodiesel is obtained after the process of washing and drying. Thereinto, methanol or ethanol can be recycled in the production process; production equipment is the same as ordinary equipment; about 10% by-product of glycerin is produced during production process.

      However, the method of chemical synthesis has following shortcomings: complicated process, alcohol must be excessive, follow-up process must have a corresponding Alcohol Recovery Unit; high energy consumption, deep color; esterification product is difficult to be recovered because that unsaturated fatty acid is metamorphosed easily, high cost; discharge of waste caustic liquid during production process.

      Facing above problems, people begin to turn to biological enzyme (i.e. lipase) to conduct transesterification. Free fatty acids and water mixed in reactant has no influence on enzyme’s catalytic effect. After standing, fatty acid methyl ester can be separated from glycerine and cleaner diesel is obtained.

      Currently, bottle-neck of producing biodiesel is its high cost. According to statistics, raw material cost accounts for 75% of preparation cost. Thus, selecting cheap raw material and increasing convesion rate is the key to the practicality of biodiesel. Micro-algae provides a new technical means to produce diesel.

      Producing biodiesel by the way of micro-algae has important economic and ecological significance. Its superiority to other methods lies in the following: high production capacity of micro-algae; saving agricultural resources for its using sea water as natural medium; oil yield of micro-algae is several times higher than that of terrestrial plants; biodiesel produced from micro-algae contain no sulphur; there’s no poisonous gas emission when combusted; discharges into the environment can be degraded by microorganism, with no environmental pollution.

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