Suggestions for the current development of the phosphorus chemical industry

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At present, China’s annual production capacity for phosphorus chemicals is nearly 8.5 million tons, accounting for 65% of the global total. The products exported are mainly traditional, bulk primary phosphorus chemicals, which constitutes a form of \"resource export\" and results in pollution, leading to serious consequences: (1) High energy consumption per unit of product (1 ton of yellow phosphorus requires 14,000 kWh of electricity)； (2) High emission levels and severe pollution (only yellow phosphorus generates 1.2 billion cubic meters of waste gas per year); (3) Large-scale export of low-value products leads to the consumption of large amounts of non-renewable phosphorus resources, and the Ministry of Land and Resources has classified phosphorus as a scarce resource ； (4) Almost all high-purity, high-value-added phosphorus chemical products rely on imports. Although our country is a major producer of phosphorus chemicals, and the output of such products accounts for a large share of the world’s total production, the variety of phosphorus chemical products available is quite limited, and their quality is relatively low. The overall technical level of the phosphorus chemicals industry still lags far behind international standards. Especially during the transition period following China’s entry into the WTO, when the domestic phosphorus chemical industry was opened up to foreign investors, domestic phosphorus chemical companies faced unprecedented challenges due to the technical advantages of large foreign firms in this sector. Therefore, conducting technical research on the current situation and shortcomings of China’s phosphate chemical industry, accelerating the development of high-tech technologies in this field, and narrowing the gap with world-class standards are of great significance for meeting the needs of the national economy and ensuring its safe development, for establishing a complete and advanced industrial system, for promoting the development of the western regions, and for enhancing the international competitiveness of domestic industries. 1 Purification technology for wet-process phosphoric acid 1.1 The energy crisis and environmental regulations have forced the use of purified wet-process phosphoric acid as a substitute for hot-process phosphoric acid. After more than 100 years of development, the phosphate industry and the fertilizer industry have coexisted within the broader phosphate chemicals industry, this division arising from different methods used to produce phosphoric acid from phosphate rocks. The electrolysis of phosphate rocks to obtain yellow phosphorus is used to produce hot-process phosphoric acid, thereby forming the industrial chain of the phosphate industry, while the use of sulfuric acid to decompose phosphate rocks to produce wet-process phosphoric acid forms the industrial chain of the fertilizer industry. Among them, thermal phosphoric acid faces multiple pressures related to resources, energy, and the environment due to its high energy consumption and high pollution levels. On the other hand, wet-process phosphoric acid can meet the standards of thermal phosphoric acid after purification and refinement, and can thus be used to produce industrial-grade or food-grade phosphate products in place of thermal phosphoric acid. Therefore, the landscape of the global phosphorus chemical industry has undergone significant changes over the past 10 years. By purifying wet-process phosphoric acid with a high impurity content to produce refined phosphoric acid, which is then used to manufacture various phosphorus-based products instead of hot-process phosphoric acid, this approach has become the trend in the development of advanced technologies in the global phosphorus chemical industry. Using purified wet phosphoric acid as a raw material to produce industrial-grade and food-grade phosphoric acid or phosphorus products not only significantly reduces energy consumption but also increases the added value of the products, thereby enhancing the economic benefits for enterprises. At the same time, the refined phosphoric acid residue can also be used to produce fertilizers, enabling the hierarchical and comprehensive utilization of resources in an environmentally friendly manner. However, the purification technology for wet phosphoric acid is quite challenging; in China, it remains mainly at the laboratory research or small-scale pilot test stage, and abroad only a few places have achieved industrial production. In recent years, foreign wet phosphoric acid technologies have either been unwilling to be transferred or have been transferred at exorbitantly high prices, as was the case with Hongfu Company. At the same time, foreign wet-process phosphoric acid purification technologies are not entirely suitable for the characteristics of China’s phosphate ores. At present, the development of wet phosphoric acid purification technologies, as well as the technologies for their industrialization and scale-up, have become one of the key technologies restricting the structural adjustment and technological advancement of China’s phosphate chemical industry. Therefore, it is highly necessary to conduct scientific research on wet phosphoric acid purification technologies in order to develop methods that suit the characteristics of China’s phosphate rock resources. There is a wet phosphoric acid purification technology with independent intellectual property rights in our country, eliminating the reliance on foreign technologies. 1.2 Developing new processes for the production of wet phosphoric acid to create new sources of economic growth: As the largest segment of the phosphate chemicals industry, China’s high-concentration phosphate fertilizer industry truly began to develop in the early 1980s, following a path that combined the adoption of foreign technologies with independent innovation. Through more than 20 years of effort, the overall level and production scale of this industry have now reached levels comparable to those of the world’s most advanced countries. Especially with the long-term support of **key scientific research projects and other** technological programs, the \"neutralization slurry concentration method for phosphorus-ammonium fertilizer production\" independently developed by Sichuan University takes into account the characteristics of China’s phosphorus resources, enabling the large-scale and domestic production of such facilities. Not only does this approach account for half of the total capacity in the high-concentration phosphate fertilizer industry in terms of both scale and output, but it also allows for co-production with imported facilities; by modifying and optimizing these imported facilities, it gives those using traditional processes to produce phosphate fertilizers a distinct Chinese character. China’s four major phosphorus-producing provinces—Yunnan, Guizhou, Hubei, and Sichuan—have, by leveraging their advantages in phosphorus resources as well as advanced production technologies and equipment for high-concentration phosphate fertilizers, secured a significant position in the global phosphate fertilizer industry. From the perspective of resource utilization, phosphate rock, as a non-renewable resource with limited reserves, is used solely for fertilizer production in the Yunnan and Guizhou regions where China’s high-quality phosphate rock resources are concentrated; this approach does not conform to the principle of maximizing the efficiency of resource use. Therefore, the technical route for producing phosphate fertilizers from wet-process phosphoric acid relies on key technologies such as purification techniques for wet-process phosphoric acid, in order to obtain phosphoric acid raw materials of equal quality to those produced by thermal processes. This enables seamless integration into the phosphate industry chain. The existing \"mineral-fertilizer\" model is expanded to a \"mineral-fertilizer+salt\" format, with the product structure adjusted. By focusing on fertilizers, it is possible to develop high-value phosphate chemical products, achieve scientific and economical utilization of phosphorus resources, improve the economic efficiency of phosphate fertilizer manufacturers, enhance their core competitive capabilities, and enable China’s phosphate chemical industry to effectively compete in the international market while meeting the needs of national economic development. To implement the \"mineral-fertilizer+salt\" industrial chain model, the core technology lies in the refining and purification process of wet phosphoric acid and the related industrialization equipment technologies. 1.3 There is a high demand for refined phosphates and high-purity phosphoric acid, offering broad market prospects. Phosphoric acid is the most crucial intermediate in the phosphate chemicals industry, and the production process of phosphoric acid represents the core technology of this industry. Generally, the purity of phosphoric acid products increases in sequence from agricultural grade to industrial grade, feed grade, food grade, pharmaceutical grade, and electronic grade; accordingly, the difficulty of processing the products as well as their added value also increase. Among them, with the rapid development of the electronics industry, the demand for electronic-grade phosphoric acid is increasing continuously. At the same time, fine phosphide and fine phosphate products, due to their wide application in industries such as pharmaceuticals and electronics, possess a high added value. Their market demand holds great potential, and they have become new drivers of economic growth in the phosphorus chemicals industry. Therefore, developing purification technologies for wet phosphoric acid and using such purified wet phosphoric acid to replace hot-process phosphoric acid in the production of various fine phosphides and fine phosphate products can bring significant economic benefits. At the same time, it also helps to improve the product structure of phosphorus chemical products and enhance the core competitiveness of enterprises. 2. Yellow phosphorus purification technology: Various phosphide and phosphate products manufactured using yellow phosphorus and thermal phosphoric acid play an important role in various sectors of the national economy, and they are among the key products for generating foreign exchange through exports in China. Although our country is a major producer and exporter of yellow phosphorus and thermal phosphoric acid, the variety of phosphorus products is limited, and the quality of these products is quite low. Our country uses high-tonnage, low-grade phosphorus products for export to earn foreign exchange, yet it needs a large amount of foreign currency to import expensive, high-grade refined phosphorus products. Therefore, an important aspect of developing phosphorus chemical technologies is to advance the purification techniques for yellow phosphorus, as well as the manufacturing technologies for various high-value phosphorus chemical products such as phosphides, organic phosphines, organic phosphonates, pesticides, and functional materials, in order to replace imports and meet domestic demand. As for the existing bulk phosphate products manufactured using thermal phosphoric acid, their raw material sourcing methods need to be changed. Thermal phosphoric acid is a product characterized by high energy consumption, high pollution levels, high investment costs, and high production expenses – the so-called \"four highs\". With the emergence of energy crises and an increasing awareness of environmental protection, the profit margins for producing phosphate products using thermal phosphoric acid are becoming increasingly narrow. Many small phosphate factories have closed down, and there is an urgent need to utilize wet-process phosphoric acid purification technologies in order to replace thermal phosphoric acid. In the economically more developed eastern regions, the phosphorus chemical industry relies on yellow phosphorus as a raw material to produce fine phosphides and phosphate products. Although it has faced constraints related to energy and the environment in recent years, phosphate-based products with high added value, such as those used in pharmaceuticals, electronics, and various additives, represent emerging products in this industry. These products have great market potential and constitute new growth points for the phosphorus chemical sector. Therefore, it is urgent to develop phosphorus yellow purification technologies as well as manufacturing technologies for high-end phosphorus chemical products derived from them, in order to replace imports and meet domestic demand. 3. Technology for producing phosphoric acid via wet-heat cogeneration: The refined dilute phosphoric acid obtained through solvent extraction for the purification of wet phosphoric acid needs to be concentrated to a commercial grade of 85% H3PO4. The materials used in the concentration equipment must meet very strict requirements, and the concentration processes and equipment designed for fertilizer-grade phosphoric acid are not sufficient to meet these demands. At present, large phosphate fertilizer plants in China are equipped with thermal phosphoric acid production facilities. The combustion of yellow phosphorus followed by hydration to produce thermal phosphoric acid releases a large amount of heat; it is planned to utilize this heat generated during the production of thermal phosphoric acid to concentrate and refine dilute phosphoric acid. By combining these two processes, industrial-grade phosphoric acid that meets industrial standards can be produced, which not only solves the problem of concentrating dilute phosphoric acid but also makes full use of the heat generated from the combustion of yellow phosphorus. The core idea is to improve the conventional one-step process of burning yellow phosphorus and hydrating it, by using purified wet dilute phosphoric acid instead of water to absorb phosphoric anhydride; the phosphoric acid is then subjected to cyclic vacuum evaporation, cooling, so as to remove the heat generated during combustion. Based on the purification technology for wet phosphoric acid, an industrial phosphoric acid production technique that combines wet and thermal methods has been developed. This technique makes use of the large amount of heat generated during the production of thermal phosphoric acid to concentrate the purified wet phosphoric acid, thereby achieving optimal recovery of the waste heat from thermal phosphoric acid production. This approach addresses its high energy consumption issue, reduces steam usage in the concentration process of purified wet phosphoric acid as well as the costs associated with building concentration equipment, simplifies the process, and lowers costs. Building on the existing yellow phosphorus and wet-process phosphate industries, conducting in-depth development through high-tech can save substantial amounts of investment, significantly increase the output value of these industries, and drive China’s phosphate chemical sector to develop from producing ordinary mid-to-low-end products toward higher-value, sophisticated products. 4. Kiln process for phosphoric acid production: This method of producing phosphoric acid differs significantly from traditional wet or electric furnace methods; it is called the kiln process because the reaction equipment used for decomposing phosphate rock is a rotary kiln or a tunnel kiln. Compared with wet-process phosphoric acid, this method is less restricted by the grade of phosphate rock and the content of impurities, and is not constrained by sulfur resources ； Compared to the electric furnace method, it can **reduce production energy consumption and eliminates the need for expensive electricity. Therefore, this process is highly suitable for the resource characteristics of our country and has excellent prospects for development. The new process for phosphoric acid production using kiln methods was first developed by Western Research Corporation (ORC) of Western Oil Company in the United States between 1978 and 1982; this process uses a rotary kiln as the main reactor. Certain results were achieved in its research, but the studies were halted due to technical and economic reasons. In 1987, China’s Nanhua Design Institute began research on phosphoric acid production using kiln methods, and proposed the idea of using tunnel kilns as the main reactors. Breakthrough progress has been made in small-scale experiments, resolving the most critical technical challenge in kiln-process phosphoric acid production: using a coating layer to separate the oxidation and reduction zones. Subsequently, the institute collaborated with the former Fertilizer Research Institute of the Chemical Industry Department to conduct further experimental research, determining the optimal conditions for the reaction process; as a result, the phosphorus conversion rate reached over 88%, and the bricks remaining after the reaction met the standards of **100# construction bricks. In May 1988, the former Ministry of Chemical Industry organized experts to evaluate the research work. In 2006, Hubei Sannxin Company built a tunnel kiln production facility with an annual capacity of 10,000 tons, and experts gave high praise to the results of the tests. In terms of the technical principle, kiln-process phosphoric acid is exactly the same as heat-process phosphoric acid. In other words, in high-temperature conditions, carbon is used to reduce the phosphorus in phosphate rock to elemental phosphorus vapor, which then escapes; this phosphorus vapor is oxidized to P2O5, and after being absorbed by water, it becomes phosphoric acid. The characteristic of phosphoric acid produced by the kiln method is that the reduction-oxidation reactions of phosphorus are carried out simultaneously within a rotary kiln, allowing for full utilization of the heat generated by the oxidation reactions; this thereby significantly reduces energy consumption in production. The traditional electric furnace process carries out the phosphorus reduction reaction in an electric furnace located within a yellow phosphorus plant ； The oxidation of phosphorus takes place in the combustion and hydration tower of the phosphate plant; this not only fails to make full use of the heat generated by the chemical reaction, but also requires a large amount of recycled acid and recycled cooling water to remove the heat released during phosphorus combustion, thereby increasing energy consumption. Furthermore, due to the endothermic nature of the heating and reduction reactions of the charge, the electric furnace process relies on expensive electrical energy ； The kiln process for phosphoric acid production, on the other hand, uses coal, which is relatively inexpensive. Since the principle of its production process is exactly the same as that of the electric furnace method, and phosphorus ores with high impurity content can be used, the quality of the phosphate produced is also excellent. The key technology in developing the kiln-process for phosphoric acid production at present is to effectively isolate the two zones with different atmospheric requirements for phosphorus reduction and oxidation, while not hindering heat and mass transfer between them. The material surface coating technology developed and researched in our country has successfully addressed this key technical challenge; it is a proprietary technology with independent intellectual property rights and is at the international leading level. 5 Production of electronic-grade phosphoric acid: According to relevant reports and customs statistics, in 2006 China exported food-grade phosphoric acid at around $500 per ton, and yellow phosphorus at around $1,200 per ton. In contrast, the high-purity electronic-grade phosphoric acid used in microelectronics industries such as semiconductors and LCD TVs was imported at over $2,600 per ton. Based on the calculation that about 3.6 tons of thermal phosphoric acid are produced per ton of yellow phosphorus, the added value of yellow phosphorus increases by nearly 6 times, and the overall energy consumption per unit of phosphorus product decreases significantly. This product is mainly used as acidic cleaners and etchants in the production of silicon wafers and integrated circuits. However, due to the high purity requirements, the production of electronic-grade phosphoric acid in China is virtually non-existent. At present, electronic-grade phosphoric acid is produced using yellow phosphorus through a multi-stage coupling method, and it has been accepted by the international market; as a result, the demand for it is very promising. With the development of the IT industry, high-purity electronic phosphoric acid relies entirely on imports; although some domestic companies have attempted to develop it, the purity achieved is not yet sufficient. To further overcome this technical barrier, the crystallization method is theoretically the most effective way to produce high-purity substances. The advantage of the tower-type melting and crystallization unit is that it enables repeated crystallization and separation within a single device, thereby improving purity. This device integrates the processes of melting, crystallization, and separation, and it represents the most advanced crystallization equipment available both domestically and internationally. Japan was the first to develop this technology; researchers from our country also participated in its development and made improvements upon it. Based on that, a new type of device was developed in our country, using this crystallization apparatus to produce electronic-grade phosphoric acid, which holds broad application prospects. 6 High-grade phosphates (such as polyammonium polyphosphate with high polymerization degree) are flame retardants used to improve the fire resistance of materials, prevent them from catching fire, and suppress the spread of flames. They are widely employed in the flame retardation of synthetic and natural polymer materials, including wood, rubber, paper, fibers, plastics, coatings, etc. Common flame retardants can be classified into halogen-based, phosphorus-based, aluminum-magnesium-based, boron-based, and aluminum-based types, depending on the flame-retardant elements they contain. Expansive flame retardants with ammonium polyphosphate as the main component are one of the key directions for the future development of flame retardants. It contains both phosphorus and nitrogen as flame-retardant elements, and phosphorus and nitrogen have a synergistic effect that enhances the flame-retardant properties of ammonium polyphosphate. As a halogen-free flame retardant, ammonium polyphosphate will see increasingly widespread use in flame-retardant materials. Ammonium polyphosphate is a specialized nitrogen-phosphorus-based intumescent inorganic flame retardant. It features a high content of P-N flame-retardant elements and good thermal stability; it is nearly neutral in nature, can be mixed with other substances, provides long-lasting flame retardancy, and is non-toxic with smoke-suppressing properties. As global flame retardants move toward a halogen-free direction, intumescent flame retardants based on APP as the main raw material have become a focus of research and development. China began researching and developing the synthesis techniques and applications of APP in the 1980s. In recent years, with the continuous development of industries such as high-performance coatings in the country, the total production capacity has now reached around 20 kt/year. However, the scale of production is generally small; only 4 to 5 companies have an annual output of over 1,000 tons, while most companies produce between 200 and 300 tons per year. These products are mainly used in the manufacture of fire-retardant coatings, with less use in polyolefin flame retardancy. Compared with advanced foreign levels, there is a significant gap in both product quality and quantity. In particular, the synthesis technology for ammonium polyphosphate with high polymerization degree remains undeveloped in China; therefore, it is necessary to explore some new synthesis methods. Research on the synthesis of ammonium polyphosphate under external fields such as electric and microwave fields has led to the development of new, easily controllable synthesis methods. Based on the above research, various phosphorus-based chemical products such as organic acids, organic pesticides, organic phosphine catalysts, and lithium-ion battery materials like lithium iron phosphate and lithium vanadium phosphate have been developed; these are of great importance in modern chemical industry, aviation, aerospace, and defense industries. 7 Conclusion In summary, scientific research should be conducted in the several key areas of phosphorus chemical industry development, with the aim of creating process technologies and supporting equipment that are at the world’s advanced level. Establish phosphorus chemical industry bases in regions rich in phosphorus resources in our country, adjust the product structure and layout of this industry, and shift it from a resource-intensive model to a technology-intensive one. The phosphate fertilizer industry, particularly large-scale phosphate fertilizer manufacturers and large-scale yellow phosphorus producers, should move in the direction of advanced phosphate chemical manufacturing. By selecting the most suitable area for in-depth research based on each company’s specific circumstances, it is possible to address the existing problems in the phosphate chemical industry. Make full use of the advantages of our country’s phosphorus resources to strengthen and refine our nation’s phosphorus chemical industry. Implementing a strategy for refined phosphorus chemicals is of great significance for enhancing a company’s core competitive capabilities, and it is in line with the development trend toward internationalization, larger scale, and greater refinement in the phosphorus chemicals industry.