Liquefaction and transformation of coal - a brief discussion of "coal to oil" technology

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This post was last edited by jordan569 on 2013-1-6 23:24 1 The necessity of converting coal into oil So far, the fuels used by humans are mainly fossil fuels (also called fossil fuels), including oil, oil shale, coal and natural gas, and the most commonly used ones are oil and coal. Since the discovery of large-scale oil deposits in the Americas and the Middle East in the mid-19th century and early 20th century, people have widely used oil as energy. With the increase in industrialization, the amount of oil used has increased dramatically. In the 10 years from 1968 to 1978 alone, the amount of oil extracted in the world was equivalent to the amount extracted in the past 110 years. The world's discovered oil reserves are approximately 4 trillion barrels, and scientists estimate that oil and natural gas resources on the earth will be exhausted within 100 years. Coal is the most abundant fossil fuel in the earth's crust. The recoverable amount of coal in the world is estimated to be 20 to 40 times greater than that of oil, and the supply period is much longer than that of oil. However, as a fuel, coal has two major disadvantages:: First, it is not clean. The sulfur contained in coal burns to form sulfur dioxide, causing serious pollution to the atmosphere and surrounding environment. ； Second, from the perspective of atomic structure, the hydrogen-to-carbon ratio (H/C) of coal is less than half that of petroleum, which limits its comprehensive utilization. In recent years, as oil resources have been dwindling, the international oil market has become unstable, which has adversely affected the economic development of various countries. People will never forget the global economic recession caused by the two oil crises in 1973 and 1979-1980. At the same time, since petroleum is the basis of the huge petrochemical industry. In addition to being used in plastics, fibers, paints, pharmaceuticals and other industries, it is also used to produce basic foods such as edible oils, proteins, sugars and synthetic glycerin. The depletion of petroleum resources will definitely affect the petrochemical industry. Therefore, from the perspective of economic and social benefits, the reuse of coal through conversion (coal to oil) is a development direction worth advocating. 2 Possibility of coal turning into oil Petroleum is a mixture of gaseous, liquid and solid hydrocarbons. It may also be formed by ancient animals and plants that have been buried underground for a long time, and is stored in porous rocks underground. Hydrocarbons (including alkanes, alkanes, etc.) in petroleum account for more than 98%. Coal is a kind of carbonaceous rock, which was formed by ancient forests being buried underground due to changes in the earth's crust, and through biochemical and geological processes over a long period of geological time. According to the degree of coalification, it can be divided into four categories: peat, lignite, bituminous coal and anthracite. It is a mixture of a variety of high-molecular organic compounds and minerals. The organic compounds are mainly carbon, followed by hydrogen, oxygen, nitrogen, sulfur, etc. It can be seen that both coal and oil are mainly composed of carbon and hydrogen elements. The main difference is that the hydrogen-carbon atom ratio H/C is different. The H/C of coal is <0.8, while the H/C of oil is >1.8. In addition, coal is a complex with a very complex chemical structure. Its basic structure is a macromolecule with side chains and functional groups as the main body of condensed aromatics. Oil is mostly composed of aliphatic straight-chain hydrocarbons, and there are also naphthenes, which have a much simpler structure than coal. Therefore, humans came up with the idea of ​​liquefying coal into oil. Our country is a large coal-producing country, and the rational and effective development and comprehensive utilization of coal resources has been placed in front of our scientific workers. In addition from * * Starting from safety, researching and developing the comprehensive utilization of coal resources is a national policy for sustainable development, so it is increasingly important to develop coal-to-oil technology. 3 The key to turning coal into oil is coal liquefaction technology. To turn coal into oil, coal must first be liquefied and then decomposed. Therefore, the key to turning coal into oil is coal liquefaction technology. The so-called liquefaction of coal is the process of converting coal into liquid products through chemical processing. Coal liquefaction can be divided into two systems: direct liquefaction and indirect liquefaction. 3.1 Direct liquefaction of coal. Direct liquefaction of coal is to directly convert coal into liquid products. This technology was first realized in the United States, Germany, the United Kingdom and Japan in the early 20th century. After the oil crisis in the 1970s, there was once again an upsurge in research into directly converting coal into liquid fuel oil. By the 1980s, the process of direct coal liquefaction became increasingly mature, and some * * The design of the 5,000-ton old demonstration plant or the 2,300-ton/B production plant has been completed. The main direct coal liquefaction processes include: ①The EDS method (Exxon hydrogen donating solvent method) is to mix coal slurry with hydrogen in a circulating hydrogen donating solvent. The solvent first picks up hydrogen atoms through the catalytic converter, and then "donates" hydrogen through the liquefaction reactor to decompose the coal. ②The hydrogen-coal method is a process that uses an ebullating bed reactor to directly add hydrogen to convert coal into liquid fuel. ③The SRC method is a liquefaction process that converts high ash and high sulfur coal into a nearly ashless and low sulfur coal. First, the solvent and pulverized coal are made into coal slurry, and then the coal slurry is mixed with hydrogen and sent to the reactor. ④Coal-oil co-refining mixes coal and residual oil into oil-coal slurry, and then refines it into liquid fuel. Since the residual oil contains most or all of the hydrogen required for the coal conversion process, hydrogen can be reduced or eliminated, thereby reducing costs. 3.2 Indirect liquefaction Indirect liquefaction of coal is to first gasify coal to produce raw gas, and then perform a modification reaction after purification to adjust the hydrogen-to-carbon ratio. It was first proposed by a German chemist in 1923. The main method of indirect coal liquefaction is called Fischer-Tropsch (F--T) synthesis technology. In this method, properly treated coal is first sent to the reactor, and is converted into CO—H2 synthesis gas in a certain flow manner through the gasification agent (air or oxygen + steam) at a certain temperature and pressure (the ash is discharged as residue). If air is used as the gasification agent, low calorific value (4.7~5.6 MJ/m3) synthesis gas can be produced. Using oxygen as the gasification agent can produce medium calorific value (11.2-13.0 MJ/m3) synthesis gas. Synthesis gas is then used as raw material, and carbon, hydrogen, and oxygen compounds are synthesized under the action of catalysts, such as alcohols, aldehydes, homologs, esters, and hydrocarbons or liquid hydrocarbons. From World War II to 1945, Germany established 9 Fischer-Tropsch synthesis units. The catalyst was composed of carbon monoxide, thorium, and magnesium. The resulting product composition was:: Gasoline 46%, diesel 23%, lubricating oil 3% and paraffin 28%. After the war, ARCE developed a catalyst composed of iron, silicon, potassium, and copper. The resulting product composition is: Gasoline 32%, diesel 21%, paraffin 47%. In 1955, a Fischer-Tropsch synthesis device with the same process was established in SASOL, an oil-depleted South Africa, and industrialized. SASOL is the world's largest and only company that produces gasoline and various chemicals through indirect coal gasification and Fischer-Tropsch synthesis technology. It has more than 26,000 employees and annual sales of US$2.5 billion. Due to process requirements, it already has 12 sets of French Air Liquide air separation equipment with a capacity of 66,900 m3/h and an oxygen purity of 98.5%, and one set of 74,000 m3/B10 air separation equipment. The total oxygen production capacity reaches 870,000 m3/h. It is known as the largest oxygen production station in the world. The SASOL I device alone gasifies 12 million tons of coal every year, requiring 400,000 m3/hour of oxygen with a purity of 98%. Then the SASOLⅡ and SASOLⅢ systems were built successively. Now, the company is the world's largest commercial coal liquefaction plant. It has built three plants, using Lurgi gasifiers and F--T synthesis reactors, with an annual output of 4 million tons of synthetic liquid fuels and chemicals and an annual coal consumption of more than 27 million tons. It is worth mentioning that according to research by the American Union Carbide Corporation, producing 1 ton of synthetic fuel from coal requires 0.3 to 1 ton of oxygen. ； A synthetic fuel device with an output of 100,000 barrels/day requires 10 to 20 sets of 2,000-2,500 tons/day oxygen generators installed in parallel. According to another investigation conducted by Shanxi Province in 1993 at SASOL Company in South Africa, it was learned that the oxygen used in coal gasification is: 1000 m3 of crude gas requires 150 m3 of oxygen with a purity of 99%. Therefore, the large-scale air separation equipment required for coal gasification and conversion will be very marketable. 4 Coal to oil In my country, mankind has realized the dream of converting coal into oil by utilizing the abundant coal resources and using direct and indirect coal liquefaction technology. Our country also attaches great importance to the liquefaction and conversion of coal. In 1980, research on direct coal liquefaction was re-launched. The direct coal liquefaction technology and equipment imported from Japan and Germany twice in 1983 and 1990 are still in use and operating today. Research on the evaluation of liquefaction characteristics of Chinese coal types and liquefaction processes, as well as research on Fischer-Tropsch synthesis, have also been ongoing. In this regard, * * Starting from the Sixth Five-Year Plan, key research projects have been arranged. After years of hard work by scientific researchers, some results are close to the early stage of industrialization, and some research results are highly innovative and in an international leading position. At present, our country has achieved good results in producing syngas from coal and is marching towards the world's first-class technology level. In addition, significant achievements have been made in the technology and process of producing oxygenated chemicals from synthesis gas, some of which are already on an industrial scale, such as synthesis gas to dimethyl ether, synthesis gas to methanol and the development of downstream products, synthesis gas to ethanol, co-production of acetaldehyde, acetic acid, etc. In particular, the catalyst preparation process is improved to prepare catalysts with high activity, special functions and special selectivity, so that the synthesis gas produced from coal can be synthesized into chemical raw materials and chemical products with higher added value. For example, the Catalysis Research Laboratory of Beijing University of Chemical Technology is * * With the support of the company, after years of hard work, the new species Fe3C nanoparticle catalyst developed was used in the Fischer-Tropsch catalytic reaction of directional and controlled conversion of syngas into propylene, and achieved breakthrough results. Nanoparticles are a new material that came out in the 1980s. Due to their small particle size, large specific surface area, high surface atomic occupancy, and special electronic structure and bulk structure of unsaturated bonds and dangling bonds on the surface, nanoparticles have unique properties in terms of optical properties, magnetism, thermal conductivity, and chemical activity, which have attracted the attention of the contemporary scientific community. The iron carbide nanoparticle catalyst prepared by Beijing University of Chemical Technology using laser pyrolysis combined with solid-state reaction has a particle size of 2nm~3nm, a specific surface area of ​​200m2/g, a reaction temperature of 260~320°C, a pressure of 1.5MPa, and a syngas air velocity of 600h-1. Under the condition of no feed gas circulation, the catalytic properties of the catalyst were tested in a continuously pressurized slurry bed reactor. The results showed that the CO conversion rate reached more than 98%. Due to the size effect of the particles, the selectivity for propylene reaches 82%. At the same time, due to the high reducibility of the catalytic system, the generation of CO2 is completely suppressed, breaking the restrictions on the distribution of SF products in Fischer-Tropsch synthesis, maximizing the conversion of CO into high value-added propylene, and achieving full utilization of resources. Because propylene is an indispensable basic chemical raw material, it is currently mostly produced by cracking or refining petroleum raw materials. This research has opened up a process route for converting coal as a resource into propylene through syngas in one step. It can be used to replace oil with rising prices and limited resources. It has important strategic significance and is also a good example of rational utilization of earth resources. After cost accounting, the cost of propylene synthesized by this method is equivalent to or slightly lower than that of propylene produced using petroleum as raw material. It is a new production process with great application prospects. The research results are in an internationally leading position and have attracted the attention of peers at home and abroad. my country has also done a lot of work on coal-to-methanol production. Methanol is produced from feed gas containing H2 and CO and can be used as chemical raw materials, solvents and fuels. Methanol is used as automobile fuel. It can be mixed with 5%, 15%, 25% (M--5, M--15, M-25) or pure methanol (M--100) in gasoline. Methanol and isobutylene are synthesized into methyl tert-butyl ether (MTBE), which is used as an octane additive for unleaded gasoline. ； Or directly synthesize low-carbon mixed alcohol (methanol 70%, low-carbon alcohol 30%) and use it as a gasoline octane additive. Methanol can also be used to produce synthetic gasoline. At present, my country's annual methanol production capacity exceeds 600,000 tons, of which about 20% is used as fuel. The indirect liquefaction of coal to produce fuel methanol has mature technology. .Note$#, $ $