The current status of catalyst application in the petrochemical industry

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1 Overview of the Development of the Petrochemical Industry The petrochemical industry originated in the United States. In the 1950s, countries such as Germany, Japan, the UK, and Italy successively established petrochemical enterprises, leading to rapid expansion in this sector. In 1960, the total global production of ethylene was 2.912 million tons; by 1980 it had risen to 30 million tons, representing a ten-fold increase in ethylene production over 20 years. During the same period, the growth rate of plastic production was similar to that of ethylene; synthetic fibers increased by a factor of 15; synthetic rubber increased by more than a factor of 3. Before the 1970s in our country, organic chemical raw materials were produced through coal-based chemical processes, as seen in companies such as Jihua and Taiyuan Chemical. It then began to shift toward the petrochemical route. The current level of refining technology has reached that of the early 1980s abroad, with certain processes even matching the standards of that period overseas. The overall current situation is that olefins are not fully utilized, while light aromatics have been fully utilized; the utilization of medium and heavy aromatics still needs to be developed. 　　In terms of gaseous olefins, the production of ethylene has reached over 2 million tons, while that of propylene is between 2.3 and 2.5 million tons; butadiene has not been fully utilized. Light aromatics (C6–C8) have been fully utilized, and their production volume cannot meet market demands; the effective utilization of C9 and C10 aromatics still needs to be developed, and the same is true for heavy aromatics. To ensure the supply of liquefied gas, some plants do not separate C=3 and C=4; when prices are unreasonable, they prefer to produce liquefied gas rather than C=3 and C=4. C9 aromatics are mainly used in petroleum resins, and in smaller quantities for the isomerization production of xylene, trimethylbenzene, and p-tert-butylbenzene. In the aforementioned petrochemical industry, the use of catalysts is involved in almost all process steps. It is evident that the level of catalyst utilization is one of the key technologies determining the technical level of the petrochemical industry. 2 Current Applications of Catalysts in the Petrochemical Industry 2.1 Fluidized Catalysts The particle size and distribution of such catalysts have a significant impact on the fluidization state. Leva believes that particle size is an important factor at the onset of fluidization. The work by Heerden et al. indicates that the starting velocity for fluidization varies depending on particle size; clearly, particle size is an important factor in fluidization. The optimal particle size and distribution of the catalyst are as follows: 30μm; particles larger than 80μm…10%～20%; particles smaller than 44μm…20%～40%. For fluidized catalytic cracking catalysts, natural activated clay was used initially, but later synthetic aluminum silicate and zeolite catalysts were employed. In addition, it has been suggested to use catalysts whose main component is silica, along with magnesium oxide, boron oxide, aluminum oxide, etc. The physicochemical properties of several fluidized catalytic cracking catalysts are shown in Table 1. Other products are generally similar to these catalysts. Other fluidized catalytic cracking catalysts include silica-magnesium oxide, silica-alumina-magnesium oxide, etc. Currently, such catalysts can basically meet the requirements of industrial production. However, efforts to improve the activity and stability of cracking catalysts, enhance their resistance to metal poisoning, reduce catalyst loss and consumption, and achieve good selectivity are still in progress. 2.2 Hydrogenation Catalysts The most widely used catalyst for hydrogenation refining is the aluminum-cobalt-molybdenum catalyst, which consists of alumina containing 2%–4% CoO and 9%–15% MoO3. When the catalyst contains both cobalt and molybdenum, its activity is much higher than that when it contains only cobalt or only molybdenum (Table 2). Desulfurization is carried out at 2 MPa and 380°C, with a raw material space velocity of 2.0 h-1 and a hydrogen supply amount of 600 standard m3 per m3 of raw material. 　　When the Co∶Mo ratio is changed, the activity of the catalyst also changes. The catalyst exhibits the highest activity when the atomic ratio of Co to Mo is approximately 0.2:1. The reaction of oxides with H2S and H2 causes them to change from their oxidized state to a sulfided state, with some oxides being reduced to metals. At this point, the hydrogenation activity of the catalyst **increases**. When the H2S content in the raw material is low, it is advisable to carry out sulfidation before industrial use; sulfidation involves treating the catalyst with hydrogen containing 5%–10% H2S at temperatures of 150–315°C. When some of the cobalt on the catalyst is replaced by nickel, nitrogen-containing organic compounds are hydrogenated more effectively. 　　The main types of metals used as catalysts in hydrogenation reactions include all the metals from the various groups of the periodic table, as well as copper from group B, rhenium from group B, molybdenum and tungsten from group B, and other metals as well. The results of studies by Sato et al. show that the yield of hydrogenating 1-hexene, cyclohexene, cyclododecatriene, and similar compounds into saturated substances using Ni-NaF-SiO2 is almost always 100%, and the catalyst also exhibits good stability. The Pd-Al2O3 catalyst exhibits good performance in the hydrogenation of dienes, butyraldehyde, and acetylene. Pd-CaCO3 catalysts have found industrial application in the hydrogenation of 2-butyne-1,4-diol and dehydroagarol. Alloys of skeletal nickel (Ni2Al3 and NiAl3) can be made into highly active catalysts. Alloys with a nickel content of 30% to 50% are generally used. Ni and Pb catalysts are also used in the phenol hydrogenation industry. The aforementioned metals also exhibit excellent hydrogenation effects on carbonyls, aldehydes, nitro groups, nitriles, and the like. The yields for the hydrogenation of fatty acids and lipids using RuO2 and Ru-C catalysts can reach 100%. 2.3 Petrochemical Catalysts Catalytic reforming is the main process in refineries for producing high-octane gasoline, and it is also the primary method used in petrochemical industries to produce aromatics. Due to the excellent properties of the bimetallic platinum-rhodium catalyst (Pt-Re/γ-Al2O3), platinum-rhodium catalysts have been widely adopted in refineries around the world. The bimetallic (multimetallic) reforming catalysts developed in our country include: Bimetallic 3741 (Pt-Re/η-Al2O3), 3741-2 (Pt-Re/γ-Al2O3), CB-6 (Pt-Re/γ-Al2O3), and 3861 (Pt-Sn/γ-Al2O3). Multimetallic catalysts include 3752 (Pt-Ir-Ce-Al/η-Al2O3) and CB-5 (Pt-Re-Ti/γ-Al2O3). Reforming catalysts are bifunctional catalysts; some reactions occur due to the action of acidic catalysts (such as isomerization), while other reactions take place due to the action of metal catalysts (such as dehydrogenation). The acidic function of modern reforming catalysts is provided by the support Al2O3 and the acidic component chlorine. The other metals commonly used in platinum catalysts are rhenium (Re), iridium (Ir), and tin (Sn). Its function is to prevent the growth of platinum grains and improve the carbon retention capacity of the catalyst. However, the addition of the second metal leads to a decrease in the yield of reformed oil. To address this issue, a third type of metal was introduced: titanium, lead, gold, and others. 2.4 Zeolite catalysts Zeolites are a group of crystalline silicoaluminates. These catalysts are currently widely used in the petrochemical industry; for example, catalysts prepared by loading transition metals onto zeolites via ion exchange followed by reduction with hydrogen exhibit high hydrogenation activity. Bifunctional catalysts carrying transition metals (mainly palladium and platinum) on zeolites with solid hardness have been used for a long time in industrial processes such as hydrocracking, reforming, and n-alkane isomerization. 　　Furthermore, in the field of research on new catalytic materials that are currently active internationally, the most prominent ones include molecular sieves: aluminum phosphates, aluminum silicophosphates, metal-aluminum phosphates, and metal-aluminum silicophosphate-based molecular sieves; ZSM series molecular sieves and heteroatom-doped high-silica ZSM series molecular sieves; eighteen-membered ring macroporous VPI-S and MCM-9 molecular sieves, as well as twenty-four-membered ring tetrafoil zeolites; layered clays and synthetic layered columnar molecular sieves; zeolites, L-type zeolites, etc. 2.5 Other catalysts In addition to the catalysts mentioned above, there are also catalysts such as chromium oxide-alumina, iron oxide, calcium oxide-nickel oxide, and zinc oxide in the petrochemical industry; these are widely used in the hydrogenation of hydrocarbons. Catalysts such as alloys, zinc oxide, copper oxide and reduced copper, as well as nickel frameworks, are widely used in alcohol dehydrogenation. Molybdenum oxide, vanadium oxide, tellurium oxide, and antimony oxide are widely used as oxidation catalysts. Many studies have shown that metals such as cobalt, palladium, platinum, rhodium, iridium, and ruthenium possess activity in the conversion of gaseous hydrocarbons. Although some precious metals have a higher activity per unit mass than nickel, for conversion reactions, nickel’s activity is sufficient and it is also the cheapest option. Therefore, for decades, nickel has been chosen as the best primary catalyst for the conversion of gaseous hydrocarbons. 　　In industrial processes such as ammonia and hydrogen production, the commonly used CO conversion catalysts include the Fe-Cr series (high conversion), Co-Mo-K and Co-Mo-Mg series (sulfur-resistant, low conversion), and Cu-Zn series (low conversion). Methanation catalysts use Ni as the main active component, with additives such as Ca, Mg, La, and Mo. The main component in ammonia synthesis catalysts is Fe3O4, while the additives are generally aluminum, potassium, calcium, magnesium, cobalt, etc. Cu-Zn-Al catalysts are widely used in the industrial production of methanol. Furthermore, polymerization catalysts have also seen significant development. Research and industrial application of desulfurization catalysts have also seen rapid development in recent years; in many cases, it is possible to reduce the sulfur content in the feed gas to below 0.1×10-6, and notable progress has been made particularly in the removal of COS. 3 Summary In summary, all types of catalysts are composed of special materials and structures, and they exhibit excellent activity and selectivity. Extensive research and industrial practice have shown that they are highly sensitive to toxic substances such as chlorine, arsenic, and oxygen. Therefore, it is very important to master and understand the catalysts for removing these toxins and their current status in industrial applications.