According to my understanding, a domestic enterprise recently announced plans to invest in the construction of propane direct oxidation acrylic acid plant, the annual production capacity of 50,000 tonnes / year, which is the second set of China’s foreign announcements of propane direct oxidation acrylic acid production unit, there are many companies have carried out the investigation of this production technology, many companies expressed a strong interest. Why are so many companies interested in propane direct oxidation acrylic acid production technology? Can the new acrylic acid production process be competitive? To this end, I did a related survey.

1、What are the acrylic acid production processes? As far as I know, there are many kinds of acrylic acid production process, respectively, there are chloroethanol method, cyanoethanol method, high-pressure Reppe (Reppe) method (high-pressure carbonyl synthesis method), alkenone method, acrylonitrile hydrolysis method, propylene direct oxidation method, and with the development of chemical technology, the last few years and derived from the new production technology, such as acetate formaldehyde method, biological method, propane one-step method and so on. Although there are many production processes, the most mature and widely used in industrialisation is only the propylene direct oxidation method. Chloroethanol method which is one of the earliest industrialised methods in the production of acrylic acid. Chloroethanol and sodium cyanide will generate cyanoethanol under the action of alkaline catalyst, after sulfuric acid reaction and dehydration treatment, acrylonitrile can be obtained, and then after hydrolysis or alcoholysis, acrylic acid can be obtained. Cyanoethanol method is a chemical reaction between raw material sodium cyanide and chloroethanol, the first step is to get the intermediate product of cyanoethanol solution, the second step is to add sulphuric acid as the catalyst for hydrolysis, and then acrylic acid can be obtained after separation and purification. High-pressure Reppe (Reppe) method for the carbonyl synthesis of acetylene and carbon monoxide, in the presence of salt in tetrahydrofuran solution for the reaction, the preparation of acrylic acid. Vinyl ketone method uses the raw material for vinyl ketone, first of all, acetic acid through the cracking reaction to obtain vinyl ketone, followed by the reaction with the formaldehyde does not contain moisture, the generation of propiolactone, as a catalyst to catalyse the reaction of isomerization of acrylic acid. Acrylonitrile hydrolysis method hydrolysis of acrylonitrile, so that it generates acrylamide and sulfate, after hydrolysis treatment, it can generate acrylic acid. Acrylic oxidation method is to mix raw material propylene with air and water vapour according to the proportion, add appropriate amount of catalyst, oxidation reaction occurs to get the intermediate product acrolein, acrolein and air, water vapour under the action of catalyst, further oxidation reaction, separation, refining to get acrylic acid. Acrylic oxidation method is the mainstream acrylic acid production process. Formaldehyde acetate method is a coal chemical synthesis route, is acetic acid and formaldehyde hydroxyl aldehyde condensation reaction synthesis of acrylic acid process. Biological method is the production of acrylic acid by glucose or other carbohydrates through biological fermentation process. Figure 1 China acrylic acid industry chain diagram

2、What are the advantages of propane one-step process? Propane direct oxidation method is the use of specific catalysts, under specific reaction conditions, so that propane and oxygen oxidation reaction to produce acrylic acid. Although the propane direct oxidation method is fundamentally different from the propylene oxidation method in terms of reaction principle, it is actually derived from the propylene oxidation method. The method takes propane and air as raw materials and obtains crude acrylic acid by oxidation, absorption, extraction and distillation. The method adopts a fixed-bed process to generate acrylic acid by direct two-step oxidation with mixed metal oxides as catalysts, which can shorten the process of dehydrogenation of propane to propylene, and can realise the recycling of raw material propane. The direct oxidation of propane to prepare acrylic acid does not pass through the acrolein process, and compared with the direct oxidation of propylene, it has the characteristics of short process and less environmental pollutants. Since it is a new technology, there is no industrial production unit at present, and the control of the reaction conditions of this process is also a key step in the acrylic acid production process of propane direct oxidation. According to the process flow, propane one-step process is significantly shorter than propylene oxidation, but due to the need for special catalyst types, so in terms of selectivity, activity and stability, the process technology puts forward a more stringent test. In addition, the raw material of propane one-step method is propane, which can be natural gas by-production of propane, or refinery by-production of propane, so it has a wide range of raw material sources than propylene direct oxidation method. From the raw material price trend, propane lower than the price of propylene, from 2009 to 2023, the price difference between the two has been maintained at about 3200 yuan / tonne, with the propane utilisation rate, and propylene supply is expected to excess, resulting in a gradual narrowing of the two price difference, to 2023, the price difference has been reduced to 1700 yuan / tonne or so. Figure 2 past year propane and propylene price trend (unit: yuan / tonne)

3, acrylic acid industry competition is intensifying? According to my understanding, the reason why everyone is actively expanding new production processes is because at present, China’s mainstream bulk chemicals have been basically in surplus and about to be in surplus, of which acrylic acid is no exception. Acrylic acid is an important monomer of acrylic ester, is the key product to achieve the expansion of industrial chain refinement, downstream can be used as the basic raw material of methyl acrylate, ethyl acrylate, butyl acrylate, isooctyl acrylate, SAP resin and acrylic acid speciality ester, and it is also due to the special supply of acrylic acid, which has led to a gradual increase in the scale of production in recent years. According to my data statistics, by the end of 2023, the scale of acrylic acid in China has exceeded 4 million tonnes/year, with an average annual growth rate of more than 4%, achieving a historical high, thus triggering further competition. The expansion of acrylic acid scale has led to the improvement of acrylic acid production. According to my statistics, by the end of 2023, China’s acrylic acid production exceeded 2.7 million tonnes/year, showing an average annual growth rate of more than 10%. China’s acrylic acid industry chain, most of the integrated mode of development, downstream more supporting acrylic esters, so the output of acrylic acid is more reflective of the growth of downstream ester production. According to the trend of the past few years, China’s acrylic acid supply to enhance, but the overall level of work rate is less than 70%. According to the industry to assess the standard of market surplus, the start rate of less than 75% is mostly in the status quo of surplus, and the acrylic acid market in the past few years, the start rate are less than 70%. It is also due to the increased competition in the acrylic acid market, resulting in a low start rate. Therefore, many proposed in the construction of enterprises are actively looking for new technologies to be from the current acrylic acid cruel market competition to find some room for survival. Throughout the other types of acrylic acid production process, most of the production process has the characteristics of unavailability of raw materials, high cost of production process and high technical barriers, so propane one-step acrylic acid has been highly concerned by the industry. Figure 3 China’s acrylic acid start rate trend (unit: 10,000 tonnes / year)

4、How much can the cost of propane one-step method be reduced? For the competition of propane one-step production process, in addition to whether this process is really mature and the possibility of industrialisation, more attention is paid to the cost of propylene direct oxidation method than how much lower? According to relevant information, propane one-step production process, propane unit consumption in 0.87-1.235, other production process accessories, extractants, blocking agents, propane oxidation catalyst, p-toluene sulfonic acid and other products, the unit cost of these basic auxiliary materials is about 440 yuan / ton. For utility works, they include fresh water, demineralised water, electricity, nitrogen, instrument air, fuel gas, circulating water and steam, etc., and these costs are around RMB 1,500/tonne. Without considering the financial costs, management fees, depreciation and other costs, the total cost of basic auxiliary materials and public works is around RMB 2,000/tonne, and this cost can also be referred to as the processing cost. From the processing cost comparison of propylene direct oxidation method, there is not much difference between the two processing costs. However, it should be noted that, due to the propane one-step production process into the maturity of the market test, some production technology, propane unit consumption can reach 0.87 or so, while some production processes can only do 1.235. Therefore, if the propane unit consumption changes, then the cost of acrylic acid also have obvious changes. According to the 0.87 propane unit consumption measurement, under the premise of the same processing cost, no matter using domestic propane or imported propane, propane one-step method has a cost advantage over propylene direct oxidation method. Judging from the theoretical changes in the past few years, the price difference between the two is around RMB 1,200/tonne. Fig. 4 Comparison of acrylic acid cost between one-step propane method (0.87 unit consumption) and propylene direct oxidation method in China (unit: yuan/tonne)

If the unit consumption of 1.235 propane is used, according to the comparison of the price trend of imported propane and domestic propane, it is calculated that the propylene direct conservation method has a certain cost advantage in the past more time, especially in the period from 2009 to 2015. However, from 2016 to 2020, the cost advantage of propylene direct oxidation method is not obvious, but the difference between the two production processes is not big. From 2021 to 2023, the cost advantage of propylene direct oxidation is more obvious. Figure 5 Comparison of acrylic acid cost between propane one-step process (1.235 unit consumption) and propylene direct oxidation process in China (unit: yuan/tonne) Source: Business News Agency That is to say, if there is a huge change in propane unit consumption, propane one-step process does not have obvious cost competitiveness, on the contrary, propylene direct oxidation process is more cost-competitive. Finally, I would like to say, propane one-step acrylic acid production process, from the point of view of the process flow has the characteristics of short process, and propane raw material is lower cost than propylene. However, due to the limitation of technical maturity, there is no actual industrial plant comparison, this comparison result is for reference only, and does not have the value of investment guidance. In my opinion, the value of propane will continue to rise in the future, driven not only by the development of the PDH industry, but also by the need to increase the utilisation of low-carbon fossil energy sources. And propylene is supplied in more ways, so the value of propylene is expected to gradually decrease. Under such a trend, it is expected that the competitiveness of propylene direct oxidation method is expected to improve more strongly. However, it should be noted that if refineries use their own by-production of propane, as well as MTO unit by-production of exhaust gas as feedstock, this competitiveness is significantly higher than propylene direct oxidation method.