Techno-economic analysis of the trimethylbenzene production plant

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Technical and economic analysis of the trimethylbenzene production plant: In the catalytic reforming units of refineries, the para-trimethylbenzene, meta-trimethylbenzene, and ortho-trimethylbenzene derived from the reformed C9 heavy aromatics, along with their downstream products, are all important raw materials for the fine chemical industry. Therefore, the development and utilization of heavy aromatic hydrocarbon resources are in line with the development strategy of extending petrochemical products to the mid- and downstream stages, and hold great practical significance for improving economic efficiency. To leverage its advantages in the utilization of heavy aromatic hydrocarbon resources and to gradually establish a domestic base for their development and utilization, Jinzhou Petrochemical Fine Chemicals Co., Ltd. formulated a plan for the development and utilization of heavy aromatic hydrocarbons back in 1993. After more than a decade of effort, 28 million yuan was invested to develop a complete set of industrial production processes for separating high-purity products such as p-xylene and m-xylene from reformed heavy aromatic hydrocarbons; a facility for the advanced processing of reformed C9 heavy aromatic hydrocarbons was also built. In addition, in-depth research was conducted on downstream products such as o-xylene, musk, and phthalic anhydride, with certain results achieved. 1 Technical analysis of trimethylbenzene production plants 1.1 Technical analysis of p-xylene separation Technology Currently, most manufacturers of p-xylene both domestically and internationally use traditional separation processes and equipment, employing a two-column continuous distillation process to achieve a purity level of p-xylene of over 98%[2]. The American company Esso Research Engineering developed an extraction distillation method using dimethyl phthalate as a solvent to separate p-xylene. The plant of Jinzhou Petrochemical Fine Chemicals Co., Ltd. employs a three-column continuous distillation process, resulting in a purity of p-xylene above 98.5%. This setup enables the enrichment of m-xylene products and the simultaneous production of high-purity m-xylene; compared with several other plants in China, it offers certain advantages in terms of product variety and quality. However, the device consumes a large amount of energy; the maximum processing capacity of the three towers can only reach about 60% of their designed capacity, putting them at a disadvantage in terms of processing cost competition. It is planned to increase investment in technical upgrades primarily in the areas of energy conservation and consumption reduction, as well as expanding the processing capacity of the distillation towers, in order to address the current issues existing in the facility. The other several heavy aromatic hydrocarbon separation units in the country, having been built after 2002, benefit from the continuous advancement of new packing technologies and heat coupling technologies, thereby offering significant advantages in terms of distillation tower separation efficiency and energy savings. 1.2 Analysis of Production Technologies for P-Xylene Currently, the representative methods for producing p-xylene both domestically and internationally include deep cryogenic crystallization, HF-BF3 extraction/isomerization, p-xylene isomerization-distillation, extractive distillation, molecular sieve adsorption, propylene condensation to produce p-xylene, alkylation-distillation, and others. Among all the processes for producing trimethylbenzene, the industrial technologies that are relatively mature are the isomerization and alkylation of p-xylene, along with distillation. The isomerization-distillation method of p-xylene is one of the important methods for producing mesitylene. Its processes include gas-phase isomerization and liquid-phase isomerization. The catalysts used include molybdenum- and nickel-impregnated hydrogen-type mordenite, platinum-supported Al2O3, HF, and BF3. These methods typically produce by-products such as p-tert-butylbenzene, with the purity of p-trimethylbenzene reaching over 95%. Domestic Gaocheng polypropylene plants use this process. However, such methods make it difficult to obtain p-menthane with a purity of over 98%, and the cost of the product is high; as a result, they have been gradually phased out in the fierce market competition. The alkylation and distillation method uses a fraction rich in p-xylene as raw material; after an alkylation reaction, distillation is employed to separate and extract the p-xylene contained therein. The existing alkylation and distillation separation technologies are mainly divided into two types. ⑴ Using concentrated p-xylene with a boiling range of 161–168°C as the raw material, reaction additives are added to cause the o-methylphenyl, m-methylphenyl, and p-methylphenyl compounds to react, resulting in high-boiling substances; distillation is then used to obtain p-xylene with a purity of over 98%. However, the shortcomings of this method are as follows: first, the amount of additives used is too large, which increases costs and causes environmental pollution ； II. The increase in light components poses difficulties for the treatment process ； III. It has high energy consumption, and in p-xylene, the content of m-xylene is hardly ever below 1%; it is difficult for industrial plants to produce p-xylene with a content of over 98%, otherwise significant amounts of m-xylene will be lost. Langfang Tiantai Petrochemical Plant uses this type of technology. ⑵ Using enriched p-xylylene as the raw material, high-purity p-xylylene is obtained through catalytic alkylation followed by distillation. This method features simple process, no pollution, mild operating conditions, and low cost; the purity of p-tert-butylbenzene obtained can reach over 99%, with a content of o-tert-butylbenzene below 0.3%. This technology was developed by the Heilongjiang Petrochemical Research Institute, and Jinzhou Petrochemical Fine Chemicals Co., Ltd. uses it; it is currently at the leading level in China. However, this technology also has its own shortcomings that need to be improved, such as the high cost of the alkylating agent propylene, the significant consumption of propylene and energy due to secondary alkylation, and severe equipment corrosion caused by the use of AlCl3 catalysts. Jinzhou Petrochemical Fine Chemicals Co., Ltd. has conducted extensive experimental research in areas such as alternative alkylating agents, research on one-step production of p-xylene, and catalyst selection, and has achieved preliminary results that lay a foundation for reducing the production costs of p-xylene. 2 Economic Analysis of the C9 Heavy Aromatic Hydrocarbons Separation Unit 2.1 Various Economic Indicators for the C9 Heavy Aromatic Hydrocarbons Separation Unit The total cost of the heavy aromatic hydrocarbons separation unit as well as various economic indicators are shown in Table 1. (Chart omitted; please contact us if needed) 2.2 Cost analysis of the C9 heavy aromatic hydrocarbons separation unit The overall cost structure of the heavy aromatic hydrocarbons separation plant is shown in Figure 1. (The chart is omitted; please contact us if needed.) As can be seen from Figure 1, in the separation process of heavy aromatics, the cost proportion accounted for by the heavy aromatic raw materials is the highest, at 72.7%. Energy consumption accounts for a large proportion of costs, at 13.8%, while all other expenses combined account for 13.5% of the total costs. Since the heavy aromatic hydrocarbon raw material is currently priced based on related-party transactions, if the market price of 3,800 yuan per ton is used, the proportion of this raw material will be even higher, reaching 88%. Therefore, how to maintain the current prices of related-party transactions while minimizing the costs of purchased heavy aromatic hydrocarbon raw materials plays a decisive role in controlling the costs of heavy aromatic hydrocarbon separation and improving economic efficiency. Furthermore, among various costs, the reduction in energy consumption costs plays a key role in enhancing the competitiveness of products. This is because the prices of aromatic raw materials in the market are generally similar, while several newly built plants in China have certain technical advantages in terms of energy consumption. Therefore, Jinzhou Petrochemical Fine Chemicals Co., Ltd. is stepping up its efforts to save energy and reduce consumption, starting with optimizing operational procedures and process flows in order to bring the energy consumption of its facilities down to lower levels. 2.3 Analysis of economic indicators for the heavy aromatic hydrocarbons separation unit: As can be seen from Table 1, the economic benefits of the heavy aromatic hydrocarbons separation facility are quite substantial; if it can operate at full capacity based on its actual maximum processing capacity, the annual profit will amount to 24.8941 million yuan. However, since the operation of the heavy aromatic separation unit began, full-year operation at capacity has not been achieved due to constraints on the amount of raw material available. Moreover, the current profits of this facility mainly come from related-party transactions with Jinzhou Petrochemical Branch. If the price of heavy aromatic raw materials reaches 2,200 yuan per ton, the annual profit drops to 9.7875 million yuan (under full production capacity). If the price of raw materials reaches 2,718 yuan per ton at full capacity, the plant will incur losses as there will be no profit. Additionally, the 170# light solvent oil used in the products has, as part of related-party transactions, been returned to Jinzhou Petrochemical Branch for use in blending gasoline, at a relatively low settlement price. If it can be exported as a solvent oil, the price can rise from 2,600 yuan per ton to 3,400 yuan per ton, significantly improving the economic efficiency of the facility. 2.4 Break-even analysis of the heavy aromatic hydrocarbons separation unit: When the price of heavy aromatic hydrocarbon feedstock is 1,400 yuan per ton, the break-even point (BEP) for the heavy aromatic hydrocarbons separation unit, expressed as a percentage of capacity utilization, is BEP = 18.94%. The calculation results show that for this project to break even, it only needs to achieve 18.94% of its production capacity; in other words, the annual output of the main product, p-xylene, needs to reach 1,212.16 tons. When the price of heavy aromatic hydrocarbon feedstock is 2,200 yuan per ton, the break-even point (BEP) of the heavy aromatic hydrocarbon separation unit, expressed as a capacity utilization rate, is: BEP = 39.37%. The calculation results show that for this project to break even, it only needs to achieve 39.37% of its production capacity; in other words, the annual output of the main product, p-xylene, needs to reach 2,519.68 tons. 3. Economic analysis of the p-xylene production unit 3.1 Various economic indicators for the p-xylene production unit The total cost associated with p-xylene production and various economic indicators are shown in Table 2. (Chart omitted; please contact us if needed) 3.2 Analysis of the unit cost for p-xylene production The composition of the total costs associated with the p-xylene production facility is shown in Figure 2. As can be seen from Figure 2, in the production of p-xylene, the cost proportion accounted for by the p-xylene-rich feedstock is the highest, reaching 51.9%. Propylene accounts for 31.5% of the costs, and together with the costs associated with enriched trimethyl, they account for 83.4% in total. All other various expenses combined account for only 16.6% of the total cost. The price of enriched trimethylbenzene is currently based on internal company pricing; if market prices were used, the proportion of raw materials would be higher. Therefore, how to reduce the cost of raw materials and the consumption per unit of product plays a key role in controlling the production costs of p-xylene and improving economic efficiency. Furthermore, among various costs, reducing energy consumption costs also contributes to improving the competitiveness of products, while it is unlikely that other costs can be reduced. At present, although the production technologies we use hold certain advantages in the domestic market, we still need to intensify our efforts to save energy and reduce consumption, particularly by lowering the consumption of propylene, so as to significantly improve the economic efficiency of the facilities. For example: Conduct research on the production process, with the aim of replacing two alkylization steps and two distillation steps with one alkylization step and one distillation step ； Using the off-gases from MTBE production or the C4 cut oil from oil fields as substitutes for propylene as an alkylating agent, etc. 3.3 Analysis of economic indicators for the p-xylene production unit: As can be seen from Table 2, the p-xylene production facility exhibits certain economic benefits. If full production capacity is achieved, the annual profit will amount to 3.2817 million yuan. However, since the price of enriched trimethylbenzene used in production is an internal settlement price, if market raw material prices are high, the plant will incur no profit. 3.4 Break-even analysis of the p-xylene production unit: The break-even point (BEP) for the p-xylene production plant, expressed as a percentage of capacity utilization, is: BEP = 38.57%. The calculation results show that the project can break even as long as it reaches 38.57% of its production capacity, meaning an annual output of 385.7 tons of the main product, p-xylene; this indicates that the risk associated with this project is low. 4 Conclusion Through the technical and economic analysis of the heavy aromatic hydrocarbons plant, the development strategy for this plant has been determined as follows: accelerate the technological upgrades of the existing plant in order to enhance the market competitiveness of its core products. Increase efforts in new product development to gradually achieve a more standardized, refined, and high-quality product range. The heavy aromatic hydrocarbons facility should be market-oriented, accelerate the adjustment of its product structure, increase efforts in product development, and improve product quality. Only by consciously carrying out structural adjustments can one gain the upper hand in exploring and capturing markets ； Only by accelerating structural optimization and product upgrading can new drivers of economic growth and improved efficiency be established. Looking at the product structure of current heavy aromatic hydrocarbon plants, although we have key products such as p-xylene and m-xylene that give us a competitive advantage in the market, the added value of these products is low, resulting in low profitability. Guided by technology, it is necessary to strengthen market research, actively develop and produce high-value-added products, gradually build up the company’s product portfolio, and achieve seriesization, refinement, and higher quality of these products. This will inject new vitality into the development of related facilities, enhance overall market competitiveness, and improve economic efficiency. The following specific measures will be taken: 1) Accelerate the progress of technical upgrades to the facilities, achieve energy savings and reduced consumption, and enhance the market competitiveness of existing products. A series of technical upgrades will be gradually carried out on the equipment, mainly including: upgrading the heating furnace to improve thermal efficiency ； Modify the distillation tower to improve processing capacity ； Installing energy-saving devices on certain pumps to save electricity ； Modifying certain process flows to save recycled water ； Increase storage tanks to improve storage and transportation capacity ； Based on existing research, further studies will be conducted on the current production processes in order to fundamentally reduce production costs and improve product quality. 2) Increase efforts in new product development, adjust the product structure, and accelerate technological progress. Establish and improve the technological innovation system, create incentives for technological innovation, further motivate scientists and engineers to engage in such innovation, strengthen capabilities in scientific and technological development, adjust the existing product structure, and enhance competitiveness. The main tasks in new product development include: using existing equipment to process C8 resources in order to separate o-xylene, m-xylene, and p-xylene ； Accelerate the feasibility study for the phthalic anhydride project ； Accelerate scientific research on phthalic anhydride and Tibetan musk products ； Conduct research on the technical status and market conditions of downstream products in the entire heavy aromatic hydrocarbons series, and select certain products for feasibility studies ； Developing new uses for light and heavy solvent oils, etc. 3) Strengthen the management of production facilities and improve management levels. 4) Strengthen marketing efforts: Adopt modern marketing concepts, conduct market segmentation, carry out comprehensive market positioning, identify sales strategies and methods suitable for the enterprise, establish efficient and smooth distribution channels, enhance the marketing network, and use modern information technology to stay informed about market trends in order to respond quickly and effectively to market changes and seize more market opportunities. While developing the domestic market, efforts are made to expand into international markets and increase product exports.