Research on the Current Status of PTA Industrial Production Technology and Corresponding Strategies

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Research on the Current Status of Production Technologies in the PTA Industry and Corresponding Countermeasures Abstract: This paper provides an overview of the current production technologies in the PTA industry, identifies the main challenges faced, analyzes the gaps compared to world-class standards in terms of material and energy consumption, and offers a series of specific recommendations for the development of this industry. 1　Preface PTA, or purified terephthalic acid, is a raw material used in the production of polyester films, fibers, and packaging resins; it is also a basic chemical substance with a wide range of applications. The increasing global demand for PTA in recent years has driven continuous advancements in PTA production technologies, with the development of more cost-effective processes for producing high-purity terephthalic acid becoming a key focus of research. Every year, new PTA manufacturers emerge around the world, possessing unique patented technologies that give them a clear advantage in terms of price and quality when entering the PTA production sector. With the acceleration of global economic integration and a balanced supply and demand for PTA in the domestic market, competition in the PTA industry will become increasingly fierce. At present, some domestic enterprises still fall short of the world’s advanced standards in terms of raw material consumption, energy utilization, and operational load rate, which in turn affects the cost and market competitiveness of PTA products. Therefore, it is highly necessary to understand the main problems faced by the PTA industry in our country, to keep a comprehensive track of advanced technical information related to PTA plants, and to accelerate the localization of PTA technology. 2 Current Status of PTA Industrial Production Technology 2.1 Disparities exist in the technical and economic indicators of production facilities, resulting in high production costs for products. In recent years, PTA producers around the world have been working to develop PTA production technology in two areas: continuously expanding the production scale of these facilities, and reducing their material and energy consumption. As the production scale continues to expand, the material and energy consumption levels of a facility directly determine its competitiveness to a greater extent, becoming the most important indicator of its sophistication. However, while breakthroughs were being made in the development of PTA technology abroad, China’s PTA industry was still in the stage of digestion and absorption, with a relatively low basic level. Over the past 20 years, our country has introduced more than 10 sets of PTA production units. Through long-term production practice and technical upgrades, significant progress has been made in reducing raw material consumption, making efficient use of energy, maintaining high operating levels, and increasing the utilization rate of these units. However, there are still two issues in production at present: first, the consumption remains high; some enterprises still fail to meet the standards regarding acid consumption, oil consumption, hydrogen consumption, and energy consumption per ton of PTA produced ； Second, the equipment introduced in the early stages is severely aged and corroded, requiring renewal and renovation. In our country, the scale of PTA plants is generally small; compared to foreign plants with a capacity of 450 kt/year, they lack market competitiveness. The 250 kt/a unit introduced by Yizheng Chemical Fiber Company in 1995 is a single oxidation reactor that utilizes Amocor’s medium-temperature oxidation and hydroprocessing technologies, achieving the standards of the international industry in the 1990s. The units at Yangzi Petrochemical and Shanghai Petrochemical were introduced in the early 1980s; they utilize multiple oxidation reactors in parallel, which results in relatively outdated technology as well as high levels of material and energy consumption. Compared to the advanced PTA units available today, the PTA units introduced in our country in the early days have a significantly larger difference in terms of energy consumption; in some cases, this difference is even twice as much. For example, with today’s advanced PTA production technologies, the consumption of acetic acid is around 45 kg, and energy consumption can be less than 150 kg ； Meanwhile, Yangzi Company’s consumption of acetic acid per unit is around 55 kg, with a total energy consumption of around 300 kg. Based on the current annual production capacity of 700 kt of the Yangtze PTA plant, the plant will consume an additional 7 kt of acetic acid and 105 kt of standard oil per year [1]. 2.2 Excessive reliance on imported technologies results in high investment costs for equipment. All of the current PTA production processes in China utilize foreign patented technologies, and the production facilities established by various companies represent, to a certain extent, the world’s advanced standards at that time. However, with the development of PTA production technologies, some enterprises show certain disparities in terms of raw material consumption and energy utilization. Once domestic PTA products face competition from foreign markets, and are at a disadvantage in terms of price and quality, most companies may experience unsold inventory and declining profits, failing to meet the rapidly changing demands of the market. Furthermore, since our country does not possess the core technologies for PTA production, it faces numerous difficulties in striving to narrow the gap with foreign counterparts. At present, China is continuing to introduce and build multiple sets of PTA production facilities with a capacity of 450–500 kt. Among the costs associated with these imported facilities, the cost of process technology software accounts for a significant proportion; for example, the cost of process software packages makes up 20% of the total cost. This affects the cost of PTA products as well as their market competitiveness. Although domestic manufacturers and design departments have carried out considerable work on the technological upgrading of PTA over the years and have accumulated some experience, and relevant domestic universities have also conducted some research, the efforts remain rather scattered and the foundation is relatively weak. At present, it is still difficult to develop process software independently or complete the necessary basic design work; as a result, it is still necessary to pay high costs for software in order to acquire foreign patented technologies. At present, the limitations in China’s level of engineering design and technology development for PTA processes are largely rooted in inherent deficiencies in basic chemical engineering research [2]. For example, due to the lack of comprehensive and in-depth reaction kinetics studies, it is impossible to understand the process characteristics and the principles behind reactor design; as a result, it is difficult to determine appropriate process conditions and design parameters during the design phase ； Due to the lack of necessary cold-model studies and hot-model tests, it is difficult to determine the design and scaling of the reaction apparatus ； Due to the lack of systematic process optimization research, technical upgrades aimed at increasing production capacity, improving quality, and reducing costs fail to achieve optimal results. If we do not accelerate basic research in chemical engineering and achieve several breakthrough results now, it will remain difficult to break free from the passive situation of relying heavily on imported technologies for a considerable time to come. 3　Countermeasure Research 3.1　Adopting advanced technologies for equipment renovation The severe market conditions force PTA manufacturers to reduce product costs through either technological upgrades or process optimization; at the same time, they must strengthen management as well as their own technical development efforts. While absorbing advanced foreign technologies, independent research and development are carried out. By utilizing the technologies introduced with new devices and the achievements in localizing such technologies, it is possible to carry out partial modifications to older devices, thereby narrowing the gap between their technical and economic indicators such as material and energy consumption and those of world-leading technologies. Praxair’s new oxygen-enriched oxidation process in the United States provides a direction for the technological upgrading of existing PTA process plants. In June and December 2000, Yangzi Company successfully carried out oxygen-enriched oxidation tests on the second and first lines of the PTA unit. According to preliminary analysis, the use of oxygen-enriched oxidation technology can increase the yield of TA, help reduce the consumption of PX per unit, and enhance the capacity of each oxidation reactor by 5% to 10%; overall energy consumption can be reduced by up to about 10 kg of standard oil. The Shanghai Pharmaceutical Industry Design Institute has carried out work on energy conservation and consumption reduction for some existing facilities in China; some of these projects have been put into practice, yielding significant results ； Some have already had their plan designs completed and are waiting for the conditions to be met for implementation ； All projects show good prospects for energy savings [3]. 3.2 Building plants on an economic scale For PTA plants, achieving an economic scale is an important way to improve efficiency, and large-scale single-series plants will become the only viable option in the future. 　In the 1970s–80s, plants with a single-series capacity of less than 100 kt/a were built ； Entering the 1990s, the capacity per unit series expanded rapidly, from 225 kt/a to 250 kt/a, and even to 350 kt/a ； In the late 1990s, facilities with a capacity of 450 kt/year were already under construction ； And devices with even greater single-series capabilities may also emerge this century. Practice has shown that as the capacity of a single series increases, neither the design costs nor the management expenses rise ； Civil engineering and installation costs have increased slightly ； Only the material cost of large containers has increased, so their economies of scale are evident. According to foreign sources, when traditional technologies are used, a plant with a capacity of 450 kt/yr requires an additional investment of $23 million compared to one with a capacity of 350 kt/yr. By adopting improved technologies, a 450 kt/a plant can even have an investment level that is roughly on par with that of a 350 kt/a plant using conventional technologies. Therefore, the capacity of newly built PTA plants in our country should be no less than 350 kt/a in the future. 3.3 Accelerating the localization of PTA technology: A company can reduce costs by improving management, lowering raw material and energy consumption, and increasing productivity (the cost per ton of product can be reduced by several dozen yuan), but these measures have their limits. If investment is not significantly reduced at the fundamental level (using domestic production can reduce costs by several hundred yuan per ton of product), a newly established enterprise may turn into a loss-making unit before it even starts operating, and there are precedents for this in China. Only by relying on its own strength, drawing on foreign technologies, pursuing a path of localization, and reducing construction costs can enterprises secure a foothold in a competitive market. Once the introduced technology has been mastered through digestion and absorption, whether it is to build new facilities or upgrade existing enterprises, it is advisable to pursue a domestic production approach, and the benefits of this will be quite evident. According to statistical estimates, for the 7 PTA units that have been introduced in China, the investment required for a production capacity of 10 kt/year is between 60 million and 70 million yuan ； Once the equipment is produced domestically, it is estimated that the total investment for a 350 kt/a PTA plant will be around 1.3 billion yuan; this translates to an investment of only 37 million yuan per 10 t/a production capacity. A domestic plant was upgraded and expanded by a foreign company to an output capacity of 150–200 kt; the investment required for each 10 kt/year of production capacity is 35–40 million yuan ； Another unit in the country was modified locally; while keeping the levels of material and energy consumption roughly unchanged, its production capacity was increased by 100 kt/yr. The total investment is estimated to be around 150 million yuan, with an investment of only 15–20 million yuan required for each additional 10 kt/yr of production capacity. Of course, localization is not an easy task; it involves the localization of process technologies, engineering design, and process equipment. This requires us to digest and absorb advanced foreign technologies, and to establish a new system that integrates research, design, and production in order to achieve true localization. The more than 10 sets of PTA production units introduced in our country currently come mainly from the American company AMOCO, the British company Imperial Chemical Industries (ICI), and the Japanese company Mitsui Oil Chemicals. Their basic process flow is roughly the same, consisting of four main sections: the oxidation reaction unit, the crystallization unit, the hydrogenation refining unit, and the solvent recovery unit. The current bottlenecks and challenges in development lie in the oxidation reactor; relevant engineering research and development are required at least in four areas: liquid-phase oxidation reaction kinetics, transfer laws in oxidation reactors, mathematical models of oxidation reactors, as well as pilot and industrial tests. The liquid-phase oxidation of PX involves various physicochemical processes such as gas-liquid-solid three-phase reactions, chemical absorption, reactive crystallization, mixing, heat transfer, and mass transfer, making its mechanism highly complex. Furthermore, the research and development of units such as crystallization and purification also involves many deep-level issues in chemical engineering that require special consideration. The development of domestic palladium-on-carbon catalysts to replace imported ones primarily involves selecting coconut-shell carbon carriers with sufficient mechanical strength, while also conducting experimental studies on the deactivation mechanisms of hydrogenation catalysts in order to determine appropriate process conditions and regeneration methods. Since the key issues in the localization of PTA technology fall under the scope of research and development in chemical engineering, it is necessary to continue strengthening laboratory research, establish pilot testing facilities, and actively pursue research on process modeling and system integration. Regarding the scientific research and development for PTA production, it is necessary, on the one hand, to study the mechanism of the PX oxidation reaction, which is the core technology in PTA production, and to understand the kinetic models of this oxidation reaction. These insights can be used to expand production facilities and optimize process parameters, thereby reducing the consumption of raw materials, energy use, and operational load while ensuring product quality ； On the other hand, new catalysts, solvent systems, and process routes are being developed, such as using water as a solvent to replace acetic acid in oxidation reactions ； Methods for separating acetic acid (HAc) from water using catalytic distillation technology, etc. Seek more economical PTA production methods to reduce production costs and enhance the competitiveness of domestic products. At present, China already possesses the necessary means and capabilities for domestic development; it has a certain foundation in research as well as experience in technological upgrades. With concerted efforts, it is possible to make significant progress in three areas: reactor design, catalyst development, and system integration, thereby overcoming the technical challenges associated with domestic production and developing several innovative technologies. The R&D Institute of Yangzi Petrochemical Company is collaborating with Zhejiang University and East China University of Science and Technology to carry out experimental research on the oxidation mechanism of PX, industrial process optimization, oxygen-enriched oxidation, and TA hydrorefining. Among them, the project \"Development of a PX oxidation reactor model combining cold and hot modes\" has passed the expert evaluation organized by the Science and Technology Department of Sinopec. This project is a fundamental research initiative within the group company’s efforts to localize the PTA production process, and its completion has laid a solid foundation for the development of PTA oxidation reactors. “During this 15-year period, China is expected to achieve a series of new breakthroughs in chemical engineering research, thereby pushing process design and technology development to a new level. This will help to reverse fundamentally the country’s heavy reliance on imported technologies, leading to significant progress in the localization of PTA technology. Author profile: Li Tao, 32 years old, engineer. He graduated in 1993 from the Department of Chemical Engineering at Tianjin University, majoring in organic chemistry. He has been engaged in research and development as well as information gathering for many years, and has published over a dozen papers. References: Li Xi, Xie Gang, et al. Polyester Industry, 2002, 14(1):1. Xing Jianliang, Bai Zhengfeng, et al. Yangtze Petrochemical Industry, 2002, 17(2):9. He Qinwei, Li Zhenze, Wu Xiegong. Polyester Industry, 2002, 15(2):41. Last edited by liwening1997 on 2008-1-13 15:27.]