How much do you know about the styrene dehydrogenation reactor, the most complex reactor in refining and chemical processing plants? (1) Lummus process dehydrogenation reactor
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This post was last edited by HaiChuanLaoYu on 2025-10-15 at 15:43. Styrene (Styrene, C₆H₅-CH=CH₂) is an important basic organic chemical raw material; it is a colorless and transparent liquid at room temperature. Its chemical formula is C8H8, and its structure consists of a benzene ring and a vinyl group. The electrons of the vinyl group are conjugated with the benzene ring; it is insoluble in water but soluble in ethanol, ether, and most other organic solvents. In the chemical industry, styrene is an extremely important monomer, primarily used to produce polystyrene (PS), from which various plastic products are manufactured. It can also be used to produce styrene-butadiene (SBR) rubber, acrylonitrile-butadiene-styrene (ABS), and others. In 1839, German chemist Eduard Simon distilled and isolated styrene from natural resins. It was not until nearly a century later that the industrial production of styrene began to take shape. At present, the vast majority of styrene in industry is produced via the ethylbenzene route: one method involves the catalytic dehydrogenation of ethylbenzene – benzene + ethylene → ethylbenzene → (dehydrogenation) → styrene + H₂; in other words, pure benzene and ethylene are used to produce ethylbenzene, which is then dehydrogenated to yield styrene. Typically, 0.79 tons of benzene and 0.29 tons of ethylene are required per ton of styrene. ) This method accounts for over 80% of the global production volume, and the representative process technologies include UOP/Lummus, Badger/Fina, BASF, Sinopec ST, etc. Almost all of the industrial plants that have been built or put into operation in China currently also use this approach. Another method is the PO/SM co-oxidation process, in which ethylbenzene is first oxidized to ethylbenzene hydroperoxide → which is then epoxidized with propylene → thereby yielding propylene oxide (PO) + styrene (SM). As it is a combined production facility, the total construction cost is higher than that of building an ethylbenzene/styrene plant separately; both PO and SM need to have markets for their sale, and it is not suitable to construct plants of small to medium scale. Currently, only CNOOC Shell in China has such a facility. In this article, we mainly introduce the styrene dehydrogenation reactor for the catalytic dehydrogenation of ethylbenzene. In 1925, the American company Dow Chemical improved the production process for styrene by adopting an adiabatic dehydrogenation process and a single-stage adiabatic axial reactor ； Almost at the same time, Germany’s Baden Aniline Dyes Company (later BASF) began using isothermal dehydrogenation processes and isothermal tubular reactors for the production of styrene.
In 1925, the American company Dow Chemical improved the production process for styrene by adopting an adiabatic dehydrogenation process and a single-stage adiabatic axial reactor； Almost at the same time, Germany’s Baden Aniline Dyes Company (later BASF) began using isothermal dehydrogenation processes and isothermal tubular reactors for the production of styrene. The ethylbenzene dehydrogenation in an isothermal dehydrogenation reactor is an endothermic reversible reaction; the effect of temperature on kinetic and thermodynamic factors is identical, with higher temperatures having a favorable impact on both. The isothermal reactor is composed of many heat-resistant steel tubes made of nickel-chromium stainless steel or lined with copper-manganese alloys; the tube diameter is generally 100–185 mm. Catalysts are placed inside the tubes, which are heated from the outside by flue gas. Such devices have a complex structure and high manufacturing costs; therefore, for large-scale production facilities, insulated reactors are used. In Dow’s adiabatic pressure-dehydrogenation process, the recycled ethylbenzene and fresh ethylbenzene are mixed with about 10% water vapor of the total amount; they then exchange heat with the high-temperature dehydrogenation products and are heated to 520–550°C. After that, they are mixed with the remaining 90% of superheated water vapor at 720°C, and subsequently enter the dehydrogenation reactor. The temperature of the dehydrogenation products upon leaving the reactor is approximately 585°C. Adiabatic reactors have a simple structure, low manufacturing and operation costs, and high production capacity. However, the single-stage adiabatic reactor has a low one-pass conversion rate, poor selectivity, and high steam consumption. Therefore, in the 1960s and 1970s, multi-stage adiabatic reactors were developed one after another.
In the mid-1960s, the adiabatic negative-pressure dehydrogenation reactor was developed jointly by Lummus and Monsanto companies for the ethylbenzene negative-pressure dehydrogenation process. Harvesting under negative pressure can significantly promote the shift of ethylbenzene toward the styrene equilibrium, while reducing the water-to-hydrocarbon ratio and saving steam consumption. Due to the application of negative pressure, a radial reactor with low pressure drop and low resistance resulting from the catalyst bed layer becomes an inevitable choice. The Lummus two-stage adiabatic negative-pressure dehydrogenation process specifically uses a \"two-stage adiabatic intermediate-reheat radial reactor\" in the LUMMUS styrene process. The feed gas and superheated steam, after passing through a static mixer in the high-temperature section at the lower part of the first dehydrogenation reactor, flow upward along the central tube into the main body of the reactor. The interior of the reactor is equipped with three layers of internal components, arranged in a nesting style, from the inside out: a flow guide cone, an inner catalyst mesh, and an outer catalyst mesh. The flow guide cylinder is designed in a parabolic shape, with a reverse-cone structure that is thicker at the top and thinner at the bottom. It forces the mixed gas entering the reactor from below to spread outward and be compressed, thereby maintaining a uniform flow rate and distribution, and guiding it into the catalyst bed between the inner and outer screens for reaction. The partially dehydrogenated process gas accumulates at the top of the first dehydrogenation reactor and is discharged through a large pipe connecting the two reactors, entering the top of the second dehydrogenation reactor and then the tube side of the \"intermediate heat exchanger\" located above the second dehydrogenation reactor (at this point, the gas temperature is around 650°C). The shell side of the intermediate heat exchanger, on the other hand, is fed with high-temperature steam at nearly 900°C, introduced through the top nozzle of the second dehydrogenation reactor.
After being heated, the process gas enters the main body of the second dehydrogenation reactor from top to bottom. It passes through a conical parabolic guide tube that tapers from top to bottom, entering evenly into the catalyst bed between the inner and outer screens for reaction. Structural diagram of the Lummus reactor (Image source: Xu Zhigang et al., Technical Progress in Reactors for Styrene Production via Ethylbenzene Dehydrogenation). The styrene dehydrogenation reactor in the Lummus process has a very complex structure, with numerous internal components that are nested one within another; it also features built-in intermediate heat exchangers and packing boxes, etc. This imposes high requirements on the precision of reactor manufacturing, machining, and assembly. The static mixers in the internals are specified to be calculated and supplied by Sulzer, and Johnson Screens also has a strict list of suppliers (in fact, only a few manufacturers are capable of producing catalyst screens of such large sizes). At the same time, due to the high temperature in the reactors, especially at the high-temperature steam inlets of the two reactors, the design temperature exceeds 900°C. To meet these requirements, 304H is typically used as the material for the main bodies of the first and second dehydrogenation reactors, while UNS N08811 is used for the high-temperature sections. Due to the limitations in the performance of domestically produced materials, imported materials are necessary in certain situations for both types of reactors. In the intermediate heat exchanger section, a fire-resistant layer and high-temperature filler made of ceramic fiber ropes are required; special alloy surfacing is needed at the joints of the heat exchanger tube sheets, and a special deep-hole lap welding structure is also employed for the connections between the heat exchanger tubes and their tube sheets...
For the above reasons, the styrene dehydrogenation reactor in the Lummus process is considered one of the reactors with the most complex structure and greatest manufacturing difficulty among petrochemical plants. Among the many chemical machinery manufacturers in our country, only a few have experience in manufacturing such equipment. Our country began to introduce foreign styrene technologies and equipment in the 1980s. Enterprises such as Yanshan, Qilu, Maoming, and Yangzi have adopted Lummus technology, while companies like Guangzhou, Daqing, and Panjin have adopted Badger technology. As the core equipment of styrene plants, the first and second dehydrogenation reactors were all imported before the 1990s. In 2009, the third dehydrogenation reactor for Shanghai Sike’s 650,000 tons per year styrene plant built using Lummus technology was manufactured by Shanghai Petrochemical Machinery Manufacturing Co., Ltd. This marked the first time such equipment was produced domestically, and it was also the largest-department dehydrogenation reactor in operation at that time. In 2022, Sinopec Guangdong Petrochemical’s 800,000 tons per year styrene plant came online. This plant is currently the largest styrene plant using Lummus technology in the world. The first and second dehydrogenation reactors used in this plant are also among the largest of their kind – these two reactors were likewise designed and manufactured by Shanghai Petrochemical Machinery Manufacturing Co., Ltd.
How much do you know about the styrene dehydrogenation reactor, the most complex reactor in refining and chemical processing plants? (II) Badger process dehydrogenation reactor https://bbs.hcbbs.com/thread-5703092-1-1.html (Source: Haichuan Chemical Industry Forum)