Para-xylene (PX) is one of the important aromatic hydrocarbon products. The key connection point in the chemical industry is not only the most important product among the three isomers of xylene, but also the main raw material of the polyester industry.
The current downstream products are mainly purified terephthalic acid (PTA), which is then used to produce polyethylene terephthalate (PET), and a small part is used in pharmaceutical intermediates. Dimethyl terephthalate (DMT), coatings and other fields.
Subject to many factors such as project investment, raw material security, and concerns about environmental risks, production capacity expansion has been relatively slow. In the past five years, domestic PX has been in short supply, and import dependence has increased year after year. More than 50%, seriously restricting the sustainable development of downstream industries.
1. Overview of domestic PX devices
Domestic PX production capacity in 2010 It is about 8.26 Mt/a, and the output is 6.12 Mt/a. After two concentrated production capacity launches in 2012 and 2015, the production capacity reached 13.98 Mt/a. Since then, because no new projects have been put into production, the production capacity growth has stagnated.
2019 is an important time node for the development of the PX industry, and PX production capacity is ushering in explosive growth. The PX production equipment that has been built in China is shown in Table 1.
Among them, Fuhai Chuang’s 1.60 Mt/a PX unit was successfully restarted in 2019, Sinochem Hongrun’s 0.60 Mt/a PX unit was put into operation in August 2019, and Hainan Refinery’s No. Two sets of 1.00 Mt/a PX units were put into operation at the end of September.
The PX equipment supporting large-scale private refining and chemical enterprises has become the main force for the growth of PX production capacity. The 4.50 Mt/a PX equipment supporting the Dalian Hengli Refining and Chemical Integration Project has two production lines respectively. It was put into operation in March and May 2019. The 4.00 Mt/a PX unit supporting the Zhejiang Petrochemical Refining and Chemical Integration Project (Phase I) was also fully put into operation at the end of 2019. In 2019, the new domestic PX production capacity reached 10.30 Mt/a, and the total production capacity reached 24.08 Mt/a.
Table 1 Domestic PX production equipment has been built
2. Diversification of investment entities has intensified market competition
2.1 Trend of diversification of investment entities
In 2018, state-owned enterprises accounted for 59.6% of domestic PX production enterprises. In 2019, units such as Dalian Hengli and Zhejiang Petrochemical Phase I were put into operation one after another, causing the proportion of private enterprises to increase from 33.2% in 2018 to 57.3%, and the proportion of joint ventures to 4.1%. In the future, with the development needs of PTA enterprises extending to the upstream of the industrial chain, private enterprises will become the main force in development, and investment entities will become more diversified. The domestic PX competition structure in 2018 and 2019 is shown in Figure 1.
Figure 1 Domestic PX competition structure in 2018 and 2019
2.2 The trend of large-scale equipment and overcapacity
At present, the domestic aromatics industry is in the expansion and integration stage, and some old, old and Gadgets are facing obsolescence. There are 3 domestic companies with production capacity below 0.60 Mt/a, 11 companies with production capacity between 0.60 and 1.00 Mt/a, and only 2 companies with production capacity above 1.60 Mt/a, Dalian Hengli and Zhejiang Petrochemical.
In the next few years, PX projects constructed by private enterprises will lead the import substitution of PX in China. China’s PX production expansion plan from 2020 to 2024 is shown in Table 2. Zhejiang Petrochemical Refining and Chemical Integration Project (Phase II) and Shenghong Refining and Chemical Integration Project are expected to be completed and put into operation from 2020 to 2024, becoming the main force for China’s PX production capacity growth. At the same time, Sinopec, PetroChina, CNOOC and Sinochem Group will also continue to expand PX production capacity. Multiple PX projects are also expected to be completed and put into production from 2020 to 2024, becoming an important force in the growth of China’s PX production capacity. It is expected that by 2024, China’s PX production capacity will exceed 50.00 Mt/a, which will have a huge impact on imported supply. At the same time, there will be signs of overcapacity. In the long run, market competition will become more intense.
Table 2 China’s PX production expansion plan from 2020 to 2024
3. Analysis of PX production process
3.1 Aromatic hydrocarbon combined process
The aromatic hydrocarbon combined process to produce PX uses catalytically reformed naphtha as raw material, and is extracted through aromatic hydrocarbons. It is a process of extraction, disproportionation and alkylation of toluene, isomerization of xylene, and then separation through adsorption or crystallization to obtain high-purity PX. It mainly includes 5 units: catalytic reforming, aromatic hydrocarbon extraction, toluene disproportionation and transalkylation, xylene isomerization, and PX separation. In October 2011, Yangzi Petrochemical’s industrial demonstration device using its own PX adsorption and separation technology produced qualified products, marking that China has mastered a complete set of aromatics production technologies.
3.2 Toluene disproportionation
The toluene disproportionation reaction is the action of toluene as a catalyst Next, the process of producing high-purity PX through alkylation transfer. Toluene disproportionation can be considered to be based on the co-production of aromatic hydrocarbons, changing the raw material from naphtha with a complex composition to toluene, thereby eliminating the toluene separation process and reducing the complexity of the aromatic hydrocarbon co-production device to a certain extent.
3.3 Xylene isomerization process
Xylene isomerization The chemical process is a process technology in which PX-poor C8 aromatics rebalance between four isomers under the action of a catalyst. The main function is to effectively convert the C8 aromatic isomer mixture from which PX and part of o-xylene have been separated into directThe C8 aromatic hydrocarbon mixture with a near-equilibrium concentration component re-establishes the balance between C8 aromatic hydrocarbon isomers to achieve the purpose of increasing PX production.
3.4 Toluene-methanol alkylation process
Toluene-methanol Alkylation is an emerging process route for the synthesis of PX. It uses toluene and methanol as raw materials, and under the action of a catalyst, an alkylation reaction occurs to produce PX and other by-products. Generally divided into four units: raw material pretreatment, alkylation reaction, raw material recycling and PX separation and purification, the selectivity can reach more than 90%. Although it has not yet been industrialized, it is still the main direction of future research due to its advantages such as high conversion rate, low cost, and low pollution.
4. Comparison of PX production processes
The domestic PX production processes are Catalytic reforming (integrated unit), toluene disproportionation and alkylation, xylene isomerization (non-integrated unit), toluene-methanol alkylation. At this stage, the PX production process is mainly divided into two types: catalytic reforming and xylene isomerization. Among them, the majority of them are integrated aromatic hydrocarbon complex units for catalytic reforming. Currently, the only non-integrated unit for xylene isomerization in China is Qingdao Lidong. A 0.70 Mt/a production line of Chemical Industry and Fujia Dahua, the rest of the production process is currently difficult to implement due to factors such as process difficulty and raw material costs. For example, the 0.20 Mt/a toluene-methanol alkylation test device of Yangzi Petrochemical was not put into production as scheduled.
Compared with the traditional toluene disproportionation process, the biggest advantage of toluene-methanol alkylation is that it uses toluene and low-cost methanol as raw materials to produce high-purity PX , and only a small amount of by-products and C9 aromatics. Domestic coal resources are abundant and coal-to-methanol production capacity is excessive. The development and application of toluene-methanol alkylation synthesis PX technology realizes the organic combination of coal chemical industry and petrochemical industry, which will effectively alleviate the problem of domestic methanol overcapacity. In the future, the PX integrated aromatics combined unit will have more room for development than non-integrated units, and its market share will continue to rise. “Survival of the fittest and victory with innovation” will be the eternal principle of PX production technology in the future.
5. PX downstream industry analysis
The most important downstream of PX The product is PTA, accounting for 97%, and only a small part is used in DMT and other fields. Therefore, PTA can basically be used as the single downstream product of PX. PX is also an irreplaceable direct raw material of PTA, and the two are interdependent. PTA is the most important chain in the aromatics-polyester industrial chain. 75% of the PET produced by PTA and ethylene glycol is used for chemical fiber (polyester), 20% is used for bottle-grade polyester, and 5% is used for polyester film. PTA is an end product in the petrochemical industry and a front-end product in the polyester chemical fiber industry.
The last development peak of the domestic PTA industry occurred in 2011. Driven by various factors such as capital, technology and high profits, a large number of new PTA production capacities were planned one after another, and in 2012 Concentrated investment throughout the year resulted in a serious imbalance in the supply and demand structure of PTA, and profits fell into the abyss. The PTA industry has been in a downturn for five years, with the entire industry maintaining low or even negative profits, prompting repeated delays in new planned projects, resulting in low growth in PTA production capacity from 2017 to 2018. The comparison of domestic PTA production capacity and output from 2015 to 2019 is shown in Figure 2.
Figure 2 Comparison of PTA production capacity and output from 2015 to 2019
In recent years, with the rapid development of the polyester industry, the domestic PTA industry has experienced a transformation from development to bottleneck to further development, ending a ten-year industrial structure upgrade. In 2019, Sichuan Chemical Co., Ltd.’s 1.10 Mt/a PTA and Xinfengming 2.20 Mt/a PTA projects were put into production one after another. The domestic PTA production capacity reached 54.60 Mt/a, and the output reached 41.63 Mt/a. The number of production companies increased from the original 24 to 26 homes.
Domestic PTAs are mainly concentrated in privately owned and joint ventures. Among them, Yisheng, Hengli, and Jiaxing (Tongkun) account for 43.6% of the total production capacity. Sinopec and PetroChina PTAs The total amount only accounts for about 6%.
PTA’s core competitiveness lies in equipment and technology. It is a typical late-comer advantageous industry. The later it is put into production and the larger the scale, the lower the cost. In the past decade, large-capacity technology has brought about economies of scale and improvements in process technology, and the scale of a single device has also increased from the initial 0.60 Mt/a to 2.00 Mt/a. Take Xinfengming and Hengli Phase IV, which were put into operation in the fourth quarter of 2019, as examples. Their single-line scale exceeds 2.00 Mt/a. They adopt BP’s latest technology and INVISTA P8 technology respectively, and their material and energy consumption have been reduced. In the future, it will be difficult to see a single enterprise with small capacity devices below 1.00 Mt/a.
The production capacity of domestic PTA projects planned to be expanded from 2020 to 2024 is about 32.70 Mt (see Table 3), and the production capacity will be further concentrated in Hengli, Yisheng and related enterprises, Tongkun and other enterprises .
Table 3 China’s PTA production expansion plan from 2020 to 2024
In the next few years, as the production capacity of PTA and polyester continues to expand, the demand for PX from PTA will grow steadily [8]. Looking at the entire industry chain, the benefits of industry concentration are gradually tilting towards enterprises with integrated industry chains, such as Rongsheng, Hengyi, Tongkun, Hengli, Shenghong and other enterprises. No matter which field is PX, PTA or PET, the profits are By tilting and improving, enterprises integrating the industrial chain can get the maximum benefits.
6. Conclusion
China’s PX industry shows strong development momentum. In 2019, the new production capacity was 10.30 Mt/a, with a growth rate of 73.68%. The situation of high dependence on imports has been significantly improved. It is expected that by 2020, PX’s self-sufficiency rate will increase to 65% to 70%.
In the next few years, with the continuous breakthroughs in domestic aromatic hydrocarbon co-production technology and the continuous elimination of policy bottlenecks in PX projects, private chemical fiber companies will enter the upstream refining and chemical industry into supporting PX projects. It will lead the import substitution of China’s PX and form an integrated production chain model of “raw materials-finished products-downstream”. The benefits of industry concentration are gradually tilted towards enterprises with integrated industrial chains.
It is expected that China’s PX will achieve self-sufficiency in 2023 and experience overcapacity. Corporate profit margins will continue to be squeezed, and small businesses with backward equipment and lack of geographical advantages will gradually withdraw from the stage of history. At the same time, due to the escalating competition among domestic and foreign PX companies and the continuous optimization of the industrial structure, the demand for exploring overseas markets will be significantly enhanced in the future.
t/a, the growth rate is as high as 73.68%, and the situation of high dependence on imports has been significantly improved. It is expected that by 2020, PX’s self-sufficiency rate will increase to 65% to 70%.
In the next few years, with the continuous breakthroughs in domestic aromatic hydrocarbon co-production technology and the continuous elimination of policy bottlenecks in PX projects, private chemical fiber companies will enter the upstream refining and chemical industry into supporting PX projects. It will lead the import substitution of China’s PX and form an integrated production chain model of “raw materials-finished products-downstream”. The benefits of industry concentration are gradually tilted towards enterprises with integrated industrial chains.
It is expected that China’s PX will achieve self-sufficiency in 2023 and experience overcapacity. Corporate profit margins will continue to be squeezed, and small businesses with backward equipment and lack of geographical advantages will gradually withdraw from the stage of history. At the same time, due to the escalating competition among domestic and foreign PX companies and the continuous optimization of the industrial structure, the demand for exploring overseas markets will be significantly enhanced in the future. </p
