Overview of the properties, applications and production processes of insoluble sulfur
1. Molecular structure and characteristics of insoluble sulfur Ordinary sulfur is a yellow solid at room temperature, and it has two allotropes. Stable below 95.6°C is orthorhombic sulfur (Ｓα), with a melting point of 112.8°C; above 95.6°C, stable is monoclinic sulfur (Ｓβ), with a melting point of 114.5°C. Both forms of sulfur exist in the form of an eight-membered ring (S8), but their crystal lattice arrangements are different.
Insoluble sulfur (InsolubleSulphur), referred to as IS, is a linear polymer generated by the ring-opening polymerization of ordinary sulfur above the critical temperature (159°C), also known as μ-shaped sulfur (Sμ). Its molecular characterization is Sn, and the number of sulfur atoms n is greater than 200, up to more than 1×108. Because its structure is similar to that of high molecular polymer, it is also called polymeric sulfur.
The commonly used insoluble sulfur product is yellow powder with a density of 1950kg/m3 and a relative molecular weight of about 30,000. Due to the difference in molecular structure, it is even insoluble in organic solvents that have strong dissolving ability for ordinary sulfur, such as carbon disulfide, toluene, etc. To obtain insoluble sulfur at room temperature, a "quenching" (i.e., rapid cooling) operation is usually used to "freeze" the chemical equilibrium existing in the high-temperature sulfur melt or steam, that is, to fix the mass ratio of insoluble sulfur to soluble sulfur at high temperature. This is the process principle for preparing insoluble sulfur at room temperature. However, insoluble sulfur products without effective chemical stabilization are still unstable and can even be reduced to soluble low-molecular rhombic sulfur within a few days [1].
2 Development overview and application prospects
2.1 Development overview of insoluble sulfur
Abroad, Dums sprayed sulfur melt into water in 1927 to obtain a Plastic sulfur is a type of polymeric sulfur. It was not until the 1930s that the American Stauffer Company first obtained a patent for the preparation of low-grade insoluble sulfur (IS mass fraction between 50 and 60), and industrialized production was achieved in the 1940s. After the 1950s, the United States, the United Kingdom, France, the former Soviet Union, Japan, and Eastern European countries such as Poland, Romania, and the Czech Republic have successively conducted research and development on insoluble sulfur. However, due to the dangers such as flammability, explosion, static electricity, corrosion, and toxicity in the production process, it was not until the late 1970s that the American Stauffer Company achieved great success. The IS quality score of its product Crystex reached 90, and it was gradually produced Oil-filled insoluble sulfur series products. Currently, this product is produced and operated by Flexsys Chemical Company (a subsidiary of the consortium of Dutch AKZO Company and American Monsanto Chemical Company), which almost monopolizes the global insoluble sulfur market.
In my country, the former Beijing Rubber Industry Research and Design Institute of the Ministry of Chemical Industry began research on insoluble sulfur preparation technology in 1974, and successively used dry methods (carbon disulfide quenching), wet methods (water medium quenching), melting methods, The gasification method produced an insoluble sulfur product with a content of 55%, and the pilot test was successful in Shanghai Nanhui tile chemical plant in 1977, which played a great role in the development of steel wire radial tires in my country. During the "Seventh Five-Year Plan" period, in order to meet the country's introduction of steel wire radial tire supporting needs, Shanghai Jinghai Chemical Co., Ltd. cooperated with the Beijing Rubber Industry Research and Design Institute to develop the "Sanqian Brand" insoluble sulfur series products, aiming at the level of Crysterex products. A new stable system was established and a production capacity of 6000t/a was formed. At the same time, the company also cooperated with the Nanhua Group Research Institute to formulate professional standards for insoluble sulfur, eliminating low-grade products with a content of 58, and developing medium and high-grade products to 16, with an IS-60 content of no less than 63, The IS-90 content is not less than 95, and some products are also exported to Germany, Brazil and the United States.
According to incomplete statistics, more than 30 research institutes, universities and chemical plants in more than 20 provinces and cities across the country are developing and researching insoluble sulfur, and have built dozens of different production units. Some enterprises Product quality has basically reached the advanced level abroad, but there are still common problems such as small scale, backward equipment in some units, and high production costs, and it does not have competitive advantages. According to statistics from the Rubber Additives Professional Committee of the China Rubber Industry Association, the domestic production capacity of insoluble sulfur in 2003 was nearly 20,000 t/a, with an output of 11,200 t and an export volume of approximately 4,000 t. However, since the thermal stability of most domestic insoluble sulfur products has not reached foreign levels, most of the high thermal stability insoluble sulfur (IS-HS) that can meet the production needs of all-steel radial tires still needs to be imported. In 2003, the import volume was about 8,000t.
In view of the huge gap and broad market prospects of domestic high thermal stability insoluble sulfur, Wuxi Qianqiao Chemical Plant built a 5000t/a production unit in Wuxi Development Zone in 2004. It is said that the thermal stability of high thermal stability insoluble sulfur is The stability index can be close to Flexsys company level. The 10,000 t/a high thermal stability insoluble sulfur project of Jiaozuo City, Henan Province Huike Chemical Co., Ltd. also started construction in December 2004. The first phase of the project is 3,000 t/a. It is planned to be completed and put into operation in August 2005.
2.2 Application prospects of insoluble sulfur
Insoluble sulfur is a rubber vulcanizing agent with excellent performance. It has the function of preventing the surface of rubber products or semi-finished products from blooming and increasing the adhesion. Conducive to improving the operating environment. At the same time, it is also a good rubber vulcanization accelerator, which can speed up the vulcanization speed and make the vulcanization uniform. At present, insoluble sulfur has been widely used in tire carcass rubber, buffer rubber, white sidewall rubber and the bonding rubber of skeleton materials, which can improve the bonding performance of rubber and copper-plated steel wire. In addition, insoluble sulfur is also suitable for rubber products such as cables, rubber rollers, oil seals, and rubber shoes. It can prevent early vulcanization, maintain good viscosity of the rubber, and have other advantages. Although the price of insoluble sulfur is 5 to 15 times that of ordinary rhombic sulfur, it is still the preferred vulcanizing agent in steel wire radial tires and other rubber composite products. At present, the amount of insoluble sulfur used in the foreign tire industry accounts for 40% of the total sulfur used, and it is still increasing.
With the development of highways, the speed of cars continues to increase, placing higher demands on tires. Ordinary bias tires can no longer meet the requirements. Because the wear resistance of radial tires is 30 to 50 times higher than that of ordinary tires, their service life is 1.5 times that of ordinary tires, they save 6 to 8 fuel, and they have the advantages of safety, comfort, and economy when driving at high speeds, they have become the key to the development of the tire industry. inevitable trend. The tire radial ratio in some developed countries has reached over 90 [2]. In recent years, due to the hot market sales and the increasingly mature technology, there has been an investment boom in the production of all-steel radial tires. In particular, the country's support policy of exempting consumption tax on the production of radial tires has also promoted the rapid development of all-steel tires. Statistics from the China Rubber Industry Association show that the national radial tire output was 19.86 million units in 1998 and reached 75 million units in 2003, with an average growth rate of 30.5%; at the same time, the tire radialization rate also increased from 22% in 1998 to 47% in 2003. . It is estimated that the national radial tire output will exceed 100 million units in 2004, and the annual demand for insoluble sulfur will reach approximately 30,000 tons.
As a major chemical industry province, Shandong Province’s rubber industry has always played an important role in the country. In recent years, with the continuous increase in investment in science and technology and the expansion of production scale, the rubber industry in Shandong Province has been developing vigorously with the help of raw material base and processing application advantages. Among them, tire production is the pillar product of Shandong Province's rubber processing industry. Its output has ranked first in the country for many years, with many well-known brands such as "Triangle", "Chengshan", "Linglong", "Huaqing" and "Huanghai". Among the top ten "Chinese famous brands" of all-steel radial tires in 2004, Shandong Province enterprises accounted for half; in the 2004 Global Tire Top 75 Ranking, Shandong Province enterprises accounted for 6 seats, which shows that Shandong Province's tire industry has a strong domestic and international reputation. important position.
It is estimated that the output of radial tires in Shandong Province will be approximately 20 million units in 2004, and the annual demand for insoluble sulfur will be approximately 6,000 tons. At the same time, since 2003, many private enterprises have also rushed to seize the radial tire market. There are more than a dozen new and expanded all-steel radial tire production lines in the province, with engineering design capabilities of more than 1.2 million units. It is expected that the output of all-steel radial tires will increase in the next two years. Maintaining ultra-high-speed growth will definitely drive the demand for insoluble sulfur.