Methanol-to-gasoline (MTG) technology

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This post was last edited by liaifeng on 2018-7-27 at 16:30. Methanol-to-gasoline (MTG) technology 1. Development history: In the 1970s, the American company Mobil discovered that methanol could be converted into gasoline with high selectivity using ZSM-5 molecular sieve catalysts, and it collaborated with the German company Uhde to develop the methanol-to-gasoline (MTG) process. The processes developed by foreign companies include fixed-bed and fluidized-bed processes. The fixed-bed process follows a two-step approach: methanol is first converted into dimethyl ether under the action of an alumina catalyst, and the methanol/dimethyl ether mixture is then further converted into products primarily consisting of gasoline under the action of a ZSM-5 molecular sieve catalyst. Due to the significant differences between alumina catalysts and ZSM-5 molecular sieve catalysts in terms of lifespan and process conditions, the process route becomes lengthy, involving many types of equipment and catalysts, and process control is rather complicated. Mobil/Uhde’s fixed-bed process had commercial plants built and operated successfully in New Zealand in the 1980s. Fluidized bed reactors face issues such as high catalyst loss and difficulties in scaling up for industrial use, which have prevented the development of commercial units. The technology developed by the Shanxi Coal Chemistry Institute of the Chinese Academy of Sciences involves carrying out the two reactions of dehydrating methanol to produce dimethyl ether and dehydrating methanol/dimethyl ether to produce gasoline in the same reactor using the same catalyst, thereby simplifying the process and reducing equipment investment. In terms of reaction performance, this achievement offers advantages such as mild reaction conditions, high gasoline selectivity, a long service life for the catalyst per cycle, high gasoline octane number, and low catalyst consumption per unit weight of gasoline. The \"industrial synthesis technology for small-grain ZSM-5 molecular sieves specifically for methanol\" developed by the Shanxi Coal Chemistry Institute of the Chinese Academy of Sciences passed the evaluation of its achievements organized by the Shanxi Provincial Department of Science and Technology in 2007; the expert panel unanimously agreed that this achievement \"reached the international advanced level\". ? 2 Technical Principle The main principle of the technology for converting methanol into gasoline (Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences) is that methanol undergoes dehydration in the presence of an acidic catalyst, resulting in the formation of hydrocarbons that contain no oxygen atoms at all. Under appropriate catalysts and process conditions, due to the pore structure and selective catalytic action of the molecular sieve catalyst, the carbon atom count of the hydrocarbons produced falls mainly within the range of C5–C10, which meets the basic requirements for gasoline fractions. These hydrocarbons can be used directly as gasoline product, or they can serve as high-quality feedstocks for gasoline production via petroleum-based methods, thereby improving the quality of gasoline produced through those methods. The aforementioned reaction also produces some C3–C4 hydrocarbons, which, after separation, can be used as liquefied petroleum gas (LPG). The aforementioned reaction also produces small amounts of methane and ethane; the quantity of these by-products is minimal, and they can be used as fuel in the production process. 3 Catalysts: The Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences, has developed the first generation of MTG catalysts, designated as JX6021. It currently possesses a production line with an output capacity of 150 tons per year, which is sufficient to meet the catalyst needs of industrial facilities capable of producing 400,000 tons of gasoline per year. The catalyst specifications are shown in Table 1. Table 1 Main physical property parameters of the JX6021 catalyst Parameter Value Crystal particle size, nm: 200–500 nm Unit cell parameters: a=20.061; b=19.983; c=13.418 Pore size: 4.8–5.2 Acidicity distribution: Strong acids 25–40% ； Weak acid: 60–75%; specific surface area: 400–500 m2/g. 4. Process flow and main technical parameters: The one-step methanol-to-gasoline conversion process using a fixed-bed adiabatic reactor consists of three sections: the methanol conversion section, the product separation section, and the crude gasoline processing section. The process flow for the methanol conversion section is shown in Figure 1, while the main technical parameters and indicators are listed in Table 2. Figure 1: Schematic diagram of the one-step process for converting methanol into gasoline using a fixed-bed adiabatic reactor. Table 2: Main technical parameters and specifications of the reaction process. Parameter | Specification; Reaction pressure (Mpa): 1.6; Reaction temperature (°C): 315–430; Methanol weight hourly space velocity (WHVS): 1.0–1.6; Methanol conversion rate (%): 100; Gasoline yield (% based on methanol mass): 33–36; LPG yield (% based on methanol mass): 5–8; Catalyst lifetime per cycle (in terms of methanol processing capacity, tons/ton): ≥500; Expected total lifetime (?): ≥10,000; Catalyst consumed per ton of gasoline (kg): 0.3. The raw methanol is preheated and vaporized, then mixed with recycled gas. Once it reaches the desired reaction temperature, it enters the MTG reactor equipped with JX6021 catalyst, where it is converted into a mixture of hydrocarbons mainly composed of C5–C10 compounds along with water. After cooling and separation of the material at the reactor outlet, crude gasoline, LPG, and dry gas are obtained. Dry gas mainly consists of methane and ethane, along with small amounts of hydrogen, CO?, etc. Some of this dry gas is released from the system as vent gas, while another portion is compressed and recycled to be mixed with methanol before being reintroduced into the reactor. 5 Product specifications: The gasoline produced through the methanol-to-gasoline conversion process exhibits excellent properties. Its key characteristics include a low olefin content (5–15%), a low benzene content (<0.5%), and no sulfur content; moreover, its octane rating is above 93 (RON). See Table 3 for details. Table 3? Key performance indicators of the product gasoline Item Indicator Research octane number (RON) 93 10% evaporation temperature, °C 48.7 50% evaporation temperature, °C 120.7 90% evaporation temperature, °C 171.8 Vapor pressure/Kpa 91.6 Actual gum content, mg/100mL None Induction period, min >480 Sulfur content/% (mass fraction)