Natural gas, naphtha, heavy oil, coal and its processed products (coke, coke oven gas), acetylene tail gas, etc. Can be used as a raw material for producing methanol synthesis gas. Steam reforming of natural gas and naphtha needs to be carried out in a reforming furnace with complex structure and high cost. The reformer is equipped with a radiation chamber and a convection chamber to conduct hydrocarbon steam reforming reaction at high temperature in the presence of a catalyst. Partial oxidation of heavy oil needs to be carried out in a high temperature gasifier. When solid fuel is used as raw material, water gas can be produced by intermittent gasification or continuous gasification. Intermittent gasification takes air and steam as gasification agents, and the injection and gas production stages are separated, while continuous gasification takes oxygen and steam as gasification agents, and the process is continuous.
Many catalysts used in methanol production, such as natural gas and naphtha steam reforming catalysts and methanol synthesis catalysts, are easily poisoned by sulfides and lose their activity, so sulfides must be removed. Gas desulfurization methods can be divided into two categories, one is dry desulfurization, and the other is wet desulfurization. Dry desulfurization equipment is simple, but it is relatively large because of the slow reaction speed. Wet desulfurization can be divided into physical absorption, chemical absorption and direct oxidation.
Methanol synthesis is carried out at high temperature, high pressure and in the presence of catalyst, which is a typical complex gas-solid catalytic reaction process. With the continuous development of methanol synthesis catalyst technology, the general trend is to develop from high pressure to medium and low pressure.
Crude methanol contains impurities such as water, higher alcohols, ethers and ketones, which need to be refined. The refining process includes rectification and chemical treatment. Chemical treatment mainly uses alkali to destroy impurities that are difficult to separate in the distillation process and adjust pH value. Distillation mainly removes volatile components, such as dimethyl ether, higher alcohols of ethanol, water and other non-volatile components.
The overall process of methanol production is long and complicated, which can evolve into various production processes according to different raw materials and purification methods.
Briefly describe three methods: high pressure method, medium pressure method and low pressure method and their differences.
High pressure method generally refers to the process of synthesizing methanol with zinc-chromium catalyst at 300-400℃ and 30 MPa. It has been almost 50 years since 1923 successfully synthesized methanol by this method for the first time. This method is used in methanol production all over the world, but there are some differences in design. For example, there are two heat transfer modes in methanol synthesis tower: cold tube continuous heat transfer mode and cold shock multistage heat transfer mode. The reaction gas flows along the axial direction and/or radial direction, and there is a process of by-product steam and non-by-product steam. In recent years, China has developed the technology of synthesizing methanol with copper-based catalyst under the pressure of 25-27MPa. The methanol content in the outlet gas is about 4%, and the reaction temperature is 230-290℃.
ICl low-pressure methanol process is a successful methanol production method researched by British ICl company 1966, which breaks the monopoly of high-pressure methanol synthesis method and is a major change in methanol production process. It uses 5 1- 1 copper-based catalyst, and the synthesis pressure is 5 MPa. ICL synthetic tower is a kind of multi-stage cold-shock synthetic tower with simple structure. The upper part of each catalyst layer is equipped with a rhombic cold shock gas distributor, so that the cold shock gas can enter the catalyst layer evenly to adjust the temperature in the tower. The types of low-pressure synthesis tower include tube bundle by-product steam synthesis tower of Lurge Company of the Federal Republic of Germany and three-phase methanol synthesis system of the American Institute of Electrical Research. In 1970s, Sichuan Vinylon Factory of China Ministry of Light Industry introduced a set of low-pressure methanol plant (ICI patented technology in Britain) with acetylene tail gas as raw material from Speichim Company. In the 1980s, Qilu Petrochemical Company.
The medium pressure method is further developed on the basis of the low pressure method. Due to the low operating pressure of the low-pressure method, the equipment volume is quite huge, which is not conducive to large-scale methanol production. Therefore, the medium-pressure methanol synthesis with a pressure of about 10MPa has been developed, which can more effectively reduce the cost of plant construction and methanol production. For example, ICI Company has successfully developed a 5 1-2 copper-based catalyst. Its chemical composition and activity are similar to those of low-pressure synthesis catalyst 5 1- 1, but the crystal structure of the catalyst is different, and its manufacturing cost is more expensive than that of 5 1- 1. Because this catalyst can maintain a long life under higher pressure, ICI company may increase the original synthesis pressure from 5MPa to 10 MPa, and the synthetic tower used is the same as that of the low pressure method.
3. Briefly describe the method of methanol production from natural gas:
Natural gas is the main raw material for methanol production. The main component of natural gas is methane, but it also contains a small amount of other alkanes, olefins and nitrogen. There are several methods to produce methanol from natural gas, such as steam reforming, catalytic partial oxidation, non-catalytic partial oxidation, etc. Among them, steam reforming is the most widely used method, which is carried out in a tubular furnace at atmospheric pressure or under atmospheric pressure. Because of endothermic reaction, it is necessary to supply heat from outside to maintain the required conversion temperature, which is generally achieved by burning part of fuel gas between tubes, and the steam used for conversion is directly in the device.
In the synthesis gas produced by steam reforming of natural gas, there is too much hydrogen and insufficient carbon monoxide and carbon dioxide. One of the methods to solve this problem in industry is to adopt carbon dioxide steam reforming to achieve a suitable ratio. Carbon dioxide can be supplied from outside or recovered from the flue gas of the reformer. Another method is two-stage reforming with natural gas as raw material, that is, steam reforming of natural gas in the first stage. Only about 1/4 methane reacts, and the second stage is partial oxidation with natural gas. Not only the proportion of synthesis gas obtained is appropriate, but also the amount of residual methane can be reduced because the reaction temperature in the second stage is raised above 800℃, which increases the effective gas components of methanol synthesis.
Natural gas should be purified before entering the steam reforming furnace to remove harmful impurities, and the sulfur content of purified natural gas should be less than 0. 1mL/m3. The converted gas is compressed to the synthesis section to synthesize methanol.
4. Briefly describe the method of methanol production from coal and coke.
Coal and coke are the main solid fuels for producing methanol crude feed gas. The technical routes of methanol production from coal and coke include fuel gasification, gas desulfurization, shift, decarbonization and methanol synthesis and refining.
Heat treatment of coal and coke with steam and oxygen (or air or oxygen-enriched air) is called solid fuel gasification. The combustible gas obtained by gasification is generally called coal gas, which is used as the initial raw material gas for methanol production. The main equipment of gasification is gas producer. According to the movement mode of coal in the furnace, gasification methods can be divided into fixed bed (moving bed) gasification, fluidized bed gasification and entrained flow gasification. In China, the fixed-bed intermittent gasification method is generally used to produce methanol from coal and coke.
UCJ furnace For foreign coal gasification, there are three kinds of coal gasifiers that have been industrialized at present: Corpus-Tozek, Lurgi and Winkler. There are also second and third generation coal gasifiers, mainly Texaco and Shell-Corpus.
The hydrogen-carbon ratio in the crude feed gas made of coal and coke is too low, so after gas desulfurization, it is necessary to convert excess carbon monoxide into hydrogen and carbon dioxide through shift process, and then remove excess carbon dioxide through decarbonization process.
The feed gas is compressed, synthesized and refined to produce methanol.
5. Briefly describe the method of producing methanol from oil.
There are mainly two kinds of oils used for methanol production in industry: naphtha and heavy oil.
The fraction below 220℃ obtained by crude oil rectification is called light oil, also known as naphtha. The methods of producing synthesis gas from naphtha include pressurized steam reforming, catalytic partial oxidation, pressurized non-catalytic partial oxidation, intermittent catalytic reforming and so on. At present, the main method of producing methanol feed gas from naphtha is pressurized steam reforming. Pressurized steam reforming of naphtha needs to be carried out in a reformer with complex structure. The reformer is equipped with a radiation chamber and a convection chamber. Hydrocarbon steam reforming reaction is carried out at high temperature in the presence of catalyst. After steam reforming, the composition of naphtha can meet the needs of methanol synthesis. There is no need to add carbon dioxide or set up two-stage reforming before and after reforming, and there is no need to adjust its composition through transformation and decarbonization.
Heavy oil is a product in the process of petroleum refining. According to different refining methods, it can be divided into atmospheric heavy oil, vacuum heavy oil, cracked heavy oil and their mixtures. There are two methods to produce methanol feed gas from heavy oil: partial oxidation and pyrolysis. Cracking method needs to crack heavy oil in a heat storage furnace at a high temperature above 1400℃. Although oxygen is not needed, the equipment is complicated and the operation is troublesome, resulting in a large amount of carbon black.
Partial oxidation of heavy oil refers to the combustion reaction between heavy hydrocarbons and oxygen, which releases heat, so that some hydrocarbons are thermally cracked, and the cracked products are further oxidized and reformed, and finally a synthesis gas mainly composed of H2 and CO, with a small amount of CO2 and CH4 is obtained, which is used for methanol synthesis. The synthetic gas generated by partial oxidation of heavy oil has a high hydrocarbon ratio, and the contents of carbon monoxide and carbon dioxide in the synthetic gas exceed the standard. It is necessary to convert some synthetic gas so that carbon monoxide reacts with steam to generate hydrogen and carbon dioxide.
Synthetic crude methanol needs refining to remove impurities and water, so as to obtain refined methanol.
6. Briefly describe the production method of methanol.
Co-production of methanol from synthetic ammonia is a purification process of synthetic gas, which is a new process developed to remove trace carbon oxides instead of various copper-ammonia solutions used in domestic synthetic ammonia production.
The technological conditions of combined methanol production are to add a set of methanol synthesis device between the outlet of the fifth stage compressor and the inlet of copper washing process, including methanol synthesis tower, circulator, water cooler, separator and crude methanol storage tank. The process flow is that the gas at the outlet of the fifth stage compressor is sent to the methanol synthesis tower, and most of the carbon monoxide and carbon dioxide to be removed in the copper washing process react with hydrogen in the methanol synthesis tower to generate methanol. After co-production of methanol, the content of carbon monoxide in the gas entering the copper washing process is obviously reduced, which reduces the copper washing load. At the same time, the carbon monoxide index in the shift process can be relaxed appropriately, which reduces the steam consumption of the shift. In addition, the carbon monoxide transported by the cylinders in the first parts of the compressor becomes an effective gas, which reduces the power consumption of the compressor.
After methanol co-production, the energy consumption is obviously reduced, and 50kw.h of electricity and 0.4t of steam can be saved per ton of ammonia, which is equivalent to 2 million kJ of energy consumption. The methanol co-production process must pay attention to the fine desulfurization and rectification of feed gas to ensure the service life of methanol catalyst and the quality of methanol products.