Discussion on the Process Optimization of Bisphenol A by Ionic Method

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Fan Hongming (Bisphenol A Plant, Xingchen Chemicals Wuxi Resin Factory, 214011) Abstract: Drawing on the many years of production experience of the Bisphenol A facility at Wuxi Resin Factory, and through the study and understanding of the production process using the ionic method, this paper summarizes the optimal operational practices for certain key factors in this production process. The aim is to lay a foundation for further development of the ionic method for producing bisphenol A. Keywords: Bisphenol A, process optimization, catalytic cracking, selectivity, color, acid removal 1. Introduction Bisphenol A is an important organic chemical raw material, mainly used in the production of polycarbonates and epoxy resins. It is reported that in 1997, 62% of the world’s bisphenol A was used in the production of polycarbonates, and 32% was used in the production of epoxy resins. At present, the major producers of bisphenol A in Europe and the United States are facing a situation of supply exceeding demand due to the expansion of their production capacities; it is estimated that this situation will continue beyond 2003. In contrast, the Asian market is still in a phase of rapid development and has relatively limited production capacity. As a result, countries such as Europe and the United States are exporting their bisphenol A to the Asian market, leading to fierce competition there. For bisphenol A manufacturers, it is essential to pay close attention to how to secure a competitive edge in the market for high-quality products. To meet the demands of the bisphenol A market, the bisphenol A production facility at Wuxi Resin Factory is making continuous efforts in this area, striving to improve technology and enhance quality. This paper makes a preliminary exploration into how bisphenol A plants can achieve process optimization to facilitate their future survival and development. 2. Discussion on the Process Optimization of Biphenol A by the Ionic Method 2.1. Introduction to the Process Flow of Biphenol A Production by the Ionic Method Theionic method for producing biphenol A involves using cation exchange resins as catalysts; phenol and propylene are used as raw materials to synthesize biphenol A under appropriate temperatures and ratio conditions. The bisphenol A is separated and purified through processes such as crystallization, centrifugation, separation, and thin-film evaporation for phenol removal. Meanwhile, the impurities and isomers formed during the catalytic reaction are subjected to high-temperature catalytic cracking to produce light components, which are then recovered and reused. The water generated during the reaction is dehydrated, and the dehydrated phenol is returned to the reaction unit. 2.2. The impact of raw materials on the quality of bisphenol A: Phenol and propylene are the two main raw materials used in the production of bisphenol A. Ensuring various technical parameters such as the color and purity of these raw materials is one of the key factors in guaranteeing the quality of bisphenol A. Some foreign companies carry out pre-treatment of the raw material phenol to ensure that the color value of the treated phenol is below 20 APHA. Since phenol is susceptible to various factors such as metal ions, organic impurities, storage temperature, and air oxidation, which can cause its color to darken, pre-treating phenol before it enters the production facility is an important measure to ensure the quality of the raw phenol. 2, 3. Improving the selectivity of catalysts in the reaction units: To produce high-quality bisphenol A, attention should be paid to and research conducted on the selection of catalysts. After a comprehensive evaluation of various criteria such as the catalyst’s reaction capacity (conversion rate), selectivity, and cost, a specific catalyst was chosen. Ensuring high selectivity of the catalyst helps reduce the formation of by-products and isomers, thereby maintaining the color and purity of the bisphenol A product. 2, 3, 1. Appropriate reaction temperature: For a given catalyst, it is necessary to select an appropriate reaction temperature; as too high a temperature accelerates the chemical reaction, it also speeds up the formation of side reactions. It is reported that cation exchange resins used abroad for the ionic production of bisphenol A can achieve a selectivity of over 95% at an operating temperature of around 75°C. 2, 3, 2. Recycling of by-products: The by-products generated during the reaction process are sent back into the reaction unit, thereby maintaining a certain concentration of these by-products in the reaction mixture. This helps to suppress the formation of by-products during the production of bisphenol A and ensures that the reaction proceeds in a way that facilitates the formation of bisphenol A. Therefore, in the bisphenol A synthesis unit process, the raw material phenol is a mixture containing bisphenol A impurities and isomers, which has been subjected to centrifugal separation and dehydration; fresh phenol is used exclusively for washing the filter cake obtained after centrifugal separation. 2, 3, 3: The reaction mixture is circulated in large quantities and multiple times within the catalytic bed of the synthesis unit. To prevent localized high temperatures in the reaction synthesis unit, which could accelerate the formation of side reactions, an important measure is to circulate the reaction mixture in large quantities and multiple times within the catalytic reaction unit. In the production process of the bisphenol A plant, the heat generated by the reaction must be removed promptly, and the reaction temperature must be strictly controlled. At the same time, it is necessary to maintain high flow rates at the feed at the bottom of the reactor, as well as at the recirculation streams in the middle and at the top of the reactor. This ensures that the reaction mixture flows evenly within the catalytic resin layer in the reactor, allowing propylene to be distributed uniformly throughout the mixture and thereby preventing localized overheating. 2, 3, 4. Selection of co-catalysts: In the production of bisphenol A in recent years, some foreign companies have applied co-catalyst technologies in their manufacturing processes. The promoter process involves modifying the active groups of the original catalyst with those of a promoter, thereby significantly enhancing its catalytic activity and selectivity. Production practices at the Industrial Experimentation Institute of the Polish Institute of Heavy Organic Synthesis and the Brachownia Chemical Plant have shown that, with the use of a catalyst, the color intensity of the reaction mixture decreased from 80–100 APHA to 20–25 APHA. The thermal stability of the bisphenol A product improved significantly, indicating a substantial reduction in its by-products. Moreover, due to the high reactivity of the catalyst, the amount of catalyst required was also significantly reduced. However, the drawback is that the lifespan of the promoter is only 1–2 years, whereas that of the original catalyst is around 5 years. 2, 4. Increasing the propylene conversion rate in the reaction unit: To boost the propylene conversion rate in the reaction unit, it is particularly important to handle the water generated during the reaction process. Practice has shown that an increase in the water content in the reaction mixture inhibits the formation of bisphenol A. The theoretical reason for this is that the active sites of the catalyst are occupied by water molecules, which reduces the catalytic activity and thus lowers the reaction rate. Therefore, for the production facility, it is necessary to ensure the timely and thorough removal of water generated by the reaction; only by maintaining a low water content in the phenol solution that is fed back into the reaction unit can a high yield of bisphenol A be achieved. 2,5-Bisphenol A impurities and isomers: catalytic cracking and reforming of light components. During the synthesis of bisphenol A, isomers or impurities such as O-P, O-O, triphenols, linear dimer cyclomers (CD), and linear dimer copolymers (COD) are formed alongside bisphenol A itself; these affect the color and purity of bisphenol A. To prevent the accumulation of by-products and isomers due to the circulation of phenol in the process, its catalytic cracking represents an important approach. At present, some foreign companies basically possess this technology. In this process, the heavier components are catalytically cracked under conditions of high temperature and vacuum, with an alkaline catalyst added; as a result of this cracking, lighter components such as phenol and p-isopropenylphenol (PIPH) are produced. These lighter components are then fractionated, condensed, and diluted before being fed into a reforming reactor containing macroporous cation exchange resin, where they undergo rearrangement to produce bisphenol A. To ensure the quality of bisphenol A products, particularly to meet the requirements for polycarbonate (PC) grade, proper operation of this process is crucial; it is necessary to increase the treatment of impurities and isomers and reduce their accumulation within the facility. At the same time, in order to minimize raw material consumption, strict process control over catalytic cracking is necessary to ensure that phenol is completely removed from the emitted tar residues, with a BPA content of around 1%, as well as appropriate levels of O-P isomers