Wei Fei, a professor at Tsinghua University, on the technology for producing hydrocarbon products through the direct cracking of crude oil

The direct pyrolysis of crude oil to produce hydrocarbon products relies primarily on using the raw materials in their heavy state to directly manufacture chemical building block compounds. Due to the overall balance of the hydrogen-carbon ratio in both the raw materials and the products, avoiding high-temperature radical reactions and dehydrogenation reactions from a reaction mechanism perspective enables the elimination of the various inefficient and non-atom-economical cyclic processes such as repeated hydrogenation and cracking of intermediate products that are currently used in petrochemical production. This results in excellent atom economy, as well as a significant reduction in investment costs and energy consumption, leading to improved profits. The reaction conditions for the direct pyrolysis of crude oil to produce olefins and aromatics that we use are quite stringent, and the reaction mechanism is also more complex. It is a process in which, under conditions of temperatures exceeding 600 degrees Celsius, a catalyst-to-crude oil ratio of more than 15 kilograms per kilogram, and a contact reaction time between the catalyst and crude oil of less than 1 second, crude oil undergoes a series of reactions such as cracking, dehydrogenation, and aromatization in a plug-flow multiphase reactor to produce olefins, aromatics, and other chemicals; the entire process is based on a combination of reaction mechanisms involving carbocations and hydrocarbon pools. Due to the extremely short reaction and residence times, high-temperature free radical reactions as well as dehydrogenation and aromatic condensation reactions are largely avoided, thereby significantly increasing the yields of olefins and aromatics and reducing coking rates.

It has four significant advantages: First, the feedstock for cracking is crude oil rather than naphtha, light diesel, or hydrogenated tail oil, eliminating the heavy oil hydrocracking units that require large amounts of energy and hydrogen in traditional processes for producing olefins and aromatics. As a result, the energy and hydrogen consumption of the entire facility is significantly reduced. Second is the traditional catalytic cracking process for producing olefins and aromatics; the main products of this process are petroleum products, while olefins and aromatics are considered by-products with low yields. Taking heavy oil catalytic cracking as an example, only 5% propylene can be obtained. In contrast, the technology for directly cracking crude oil to produce olefins and aromatics focuses on manufacturing chemicals such as olefins and aromatics; the yield of these chemicals is around 70%–80%, while the yield of gasoline and diesel is extremely low. Thirdly, among the products obtained, the dry gas content other than ethylene is low, coking is minimal, and the amounts of diesel and oil slurry are very small ； The content of monocyclic aromatics in the resulting gasoline exceeds 45%; after direct extraction of the aromatics, it is possible to reprocess them to obtain olefins and aromatics, thereby further increasing the yield of these products. Fourthly, since the overall hydrogen-carbon ratio of the raw materials and products throughout the process is balanced, it eliminates the excessive generation of hydrogen and methane in current petrochemical production processes, as well as the inefficient and non-atom-economical cycles involving repeated hydrogenation and cracking of intermediate products. This results in excellent atom economy; consequently, investment costs and energy consumption are significantly reduced, while the return on investment for the project increases markedly.

I just want to know if it’s similar to Mobil’s process

The direct pyrolysis of crude oil to produce olefins and aromatics not only imposes certain requirements on the properties of the crude oil, but also places even higher demands on the performance of the catalysts. For crude oil, its heavy metal content is required to be low; the content of nickel plus vanadium should preferably be less than three parts per million, in order to ensure that the rates of dehydrogenation and aromatic condensation reactions are suppressed. Furthermore, the content of low-carbon alkanes should not be too high either; for example, the content of alkanes with fewer than 12 carbon atoms should not exceed 30%. This is related to the insufficient activity of the catalytic cracking catalysts for low-carbon alkanes. It is best to use heavy oil with a high hydrogen content based on paraffin as the raw material, and to avoid using catalytic or coker diesel, or hydrogenated residue oil from heavy oil as raw materials. This is because a high content of heavy metals in the raw materials or too low a hydrogen content will severely affect the olefin yield ； If catalytic or coker diesel, and heavy oil hydrogenation products are used as cracking feedstocks, the yields of olefins and aromatics will decrease. As for catalysts, not only are high activity and strong ability to crack crude oil required, but good selectivity for olefins and aromatics is also necessary. At the same time, it is required that the surface of the catalyst have a mesoporous structure with low coking.

There are mainly three challenges to the industrialization of the technology for producing olefins and aromatics through direct cracking of crude oil: First, catalytic cracking of crude oil under harsh conditions of temperatures exceeding 600 degrees Celsius, a catalyst-to-oil ratio of over 15 kilograms per kilogram, and a contact time of less than 1 second requires significant suppression of backmixing as well as reduction in the formation of coking and dry gas; this imposes strict requirements on the design of new reactor structures and process control systems. Secondly, under high oil-to-fuel ratios, the conventional catalytic cracking reaction regeneration system suffers from significant backmixing and is prone to clogging; operating in areas with unstable fluidization is very difficult, which necessitates the development of new, specialized downward-flow multi-stage countercurrent fluidized bed reactors. Third, the catalysts developed must possess good activity and stability at high temperatures, as well as high selectivity for olefins and aromatics.

Through relentless efforts and experimentation, we have successfully developed the advanced catalyst preparation technology required for the direct cracking of crude oil to produce olefins and aromatics. After the downward-bed flexible heavy oil catalytic cracking/cracking technology we developed was successfully applied in an industrial test of 150,000 tons per year at Sinopec’s Jinan Refinery in China, we also developed a key core technology with entirely independent intellectual property rights for the direct cracking of crude oil to produce olefins and aromatics – namely, the multi-stage counter-current downward reactor – and completed a full-process test at a rate of 10 kilograms per hour. Our partner, Saudi Aramco, has completed industrial tests on multi-million-ton scale using downflow bed reactors, and carried out an industrial demonstration plant with a capacity of 1.2 million tons per year in South Korea, thereby accumulating extensive experience in engineering implementation as well as process control data. Thus, we have basically resolved the three major challenges that hinder the direct cracking of crude oil to produce olefins and aromatics. At present, we are working closely with Saudi Aramco to leverage our respective strengths and accelerate the optimization and industrialization of this technology.

The domestic petrochemical industry has been exploring technologies for the direct cracking of crude oil to produce olefins and aromatics for a long time; this exploration can be traced back to the 1960s, when sand-bed reactors were introduced for the direct cracking of crude oil. However, at that time, due to the prominent problems with the sand furnace project, coupled with the fact that it was a technology based on thermal pyrolysis, the expected results were not achieved. Since traditional integrated refining-ethylene (chemicals) projects not only feature long production processes and high investment costs, but also produce mainly fuel oils such as diesel, gasoline, and kerosene, only about 20% of the by-product naphtha can be used as raw material for producing olefins and aromatics. As a result, there is a shortage in the market, and olefin and aromatic products with high added value remain in short supply for a long time. Especially in the Asia-Pacific region, where demand for chemicals is high and continues to grow, the imbalance between supply and demand for olefins and aromatics was once quite pronounced. Under these circumstances, the direct conversion of crude oil into hydrocarbon products has become a focus for the petrochemical industry.

In 2000, Sinopec Luoyang Petrochemical Engineering Co., Ltd. successfully developed the technology for producing olefins from heavy oil cracking； In March 2010, the Research Institute of Petrochemical Technology of Sinopec Corporation introduced a technology for producing olefins through catalytic thermal cracking of heavy oil. These two technologies are not only explorations and attempts at producing chemicals through the direct cracking of crude oil, but can also be regarded as prototypes for such production. However, since relevant technologies have struggled to address various engineering issues such as crude oil coking, heavy metal deposition, reaction heat transfer, and catalyst deactivation, coupled with the previous shortage of refined oil supplies in China and the substantial profits associated with it, petrochemical companies had little incentive to produce more chemicals rather than oil, which led to stagnation in the technology for directly cracking crude oil to produce chemicals.

With the development of renewable energy and electric vehicles, the overall society’s demand for gasoline and diesel is growing more slowly. The surplus supply of refined oil has begun to emerge and is worsening, which has renewed the enthusiasm of petrochemical companies to develop technologies for directly cracking crude oil into hydrocarbon products that yield more chemicals and less refined oil. At the same time, Tsinghua University has achieved success in conducting industrial trials with a capacity of 150,000 tons per year for downward-flow bed flexible heavy oil catalytic cracking/cracking at the Jinan Refinery of Sinopec. The rapid development of modern coal chemical industry in China has provided extensive engineering experience for the widespread use of downward-flow beds in coal gasification processes. Japanese companies as well as Saudi Aramco have made significant progress in terms of industrial applications of downward-flow bed technologies on a million-ton scale. These efforts by domestic and foreign companies have created conditions and provided support for the development of technologies for directly cracking crude oil to produce hydrocarbon products. In July 2015, we began collaborating with Aramco to develop a plug-flow downward-bed technology for the direct cracking of crude oil into hydrocarbon products, centered around a multi-stage counter-current downward reactor.

Faced with the challenge of declining profits in refined oil production, crude oil to chemicals (COTC) technology could become the next direction for refiners. In recent years, some companies have raised the level of integrated refining and petrochemical production to a new stage of Crude Oil to Chemicals (COTC) by integrating innovative approaches into traditional refining processes or by completely overhauling those processes. Based on the current state of technology and future trends, COTC technologies can be divided into two categories: maximizing the production of chemicals from crude oil, and producing chemicals directly from crude oil. In terms of the yield of converting crude oil into basic petrochemical feedstocks, the yields for various processes are roughly as follows: 5%–10% for traditional fuel-based refineries, 10%–20% for conventional integrated refining and chemical plants, and over 40%, or even up to 80%, for plants that produce chemicals from crude oil.