Analysis of Aromatic Hydrocarbon Technology Routes (Part 1)

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Analysis of Aromatic Hydrocarbons Production Routes (Part 1) Author/Source: China Chemical Industry News Date: 2016-08-25 Clicks: 16 ——The petroleum route: PX separation technology is key. At present, aromatic hydrocarbons in China are mainly produced through the petroleum route, and research on the processes related to this route focuses primarily on the core production step of xylene (PX) separation. PX is a key product that serves as a link in the aromatic hydrocarbons industry chain. Its raw materials come primarily from naphtha fractions; mixed xylene is separated from naphtha, then isomerized and further separated and purified to produce PX. This is information obtained by a reporter from China Chemical Industry News from the 2016 China Aromatic Hydrocarbons Industry Chain Development Conference, which concluded on August 11. Adsorption separation: the mainstream process in the petroleum route. In the production of PX from naphtha, there are many technical challenges, such as the development of new disproportionation and isomerization catalysts, as well as the efficient separation and purification of PX. In the aromatic compound production process of the petrochemical route, PX separation is the most critical unit technology. Adsorption separation is commonly used for this purpose. Due to its high degree of system integration and the difficulties involved in its development, it is also the last unit technology in the aromatic compound production process to be localized domestically. 　　The Sinopec Research Institute of Petrochemical Science is responsible for tackling the technical challenges associated with this unit. Wang Dehua, a senior engineer at the institute, explained that to accomplish this task, they have developed several generations of adsorbents over time. The development of the first generation of adsorbents began in 1996. Through research on molecular sieve synthesis, adsorbent formulation and molding processes, as well as post-treatment methods, industrial application of the first-generation adsorbent RAX-2000A was achieved in 2000, resulting in significant improvements in product purity, yield, and production capacity. Thereafter, by further optimizing the process conditions for molecular sieve synthesis and alkali treatment, they developed a second-generation adsorbent, RAX-3000, which was put into industrial use in 2011. 　　In 2011, Sinopec built the first industrial demonstration plant with an annual capacity of 30,000 tons at Yangzi Petrochemical, using the RAX-3000 domestic adsorbent and related processes. This marked Sinopec’s successful overcoming of the last barrier to independent aromatic hydrocarbon production technology – adsorption separation technology – thereby gaining mastery over the entire set of technologies required for aromatic hydrocarbon production. “Before the advent of autonomous technology, the complete set of technologies for aromatics was held by only two companies in Europe and the United States, resulting in very high technical barriers; domestic production capacity relied almost entirely on the technologies provided by foreign companies. Today, the autonomous aromatic hydrocarbon technology we have developed has been applied in Hainan Refining & Chemical’s 600,000 tons per year PX project; the adsorption separation unit has been operating steadily for over 30 months now, and the purity of the product can be maintained at 99.7% or above as required. ” That’s what Wu Wei, the deputy chief engineer of the Institute of Rock Mechanics, said. 　　According to Wang Dehua, the latest generation of RAX-4000 adsorbent developed by the Institute of Stone Sciences has passed the technical evaluation; this adsorbent enables the processing capacity of the equipment to be increased by over 20%. Multiple large-scale units for Sinopec’s aromatic compounds production technology are under design, with the largest capacity reaching 1 million tons per year. Crystallization separation: the best choice for high-concentration feedstocks. In the PX separation unit, adsorption separation isn’t the only method available; crystallization separation is also a very important separation technique. Researchers around the world have conducted extensive research in this area, developing various PX crystallization separation processes with distinct characteristics. 　　Crystallization separation technology separates PX by utilizing the differences in melting points of the various C8 aromatic components through melt crystallization. The PX crystallization separation technology has advantages such as not using any \"three types of reagents\", not generating \"three types of waste\", high product purity, low requirements for raw materials, and a simple and easy-to-control process. However, it also has disadvantages including high energy consumption and high demands for the stability of equipment and the process. 　　The PX crystallization and separation technology developed by the Shanghai Research Institute of Petrochemicals is highly distinctive. Dr. Chen Liang from the institute explained that the new PX crystallization process they developed reduces the number of crystallization steps; it uses toluene’s stereoselective disproportionation products as the raw material for crystallization, resulting in stable product quality with a PX purity of over 99.8%. The installation operates stably and reliably, and starting up and shutting down is straightforward. 　　On this basis, the Shanghai Research Institute of Petrochemical Technology further developed a combined technology of shape-selective disproportionation and crystallization separation; the crystallization feedstock does not require separation using xylene towers, and the crystallization unit eliminates the energy-intensive deep-cold crystallization process, resulting in even more significant advantages. To date, the institute has completed the development of a 100,000 tons per year process package. At the same time, the institute has combined traditional adsorption concentration with crystallization separation to create a combined technology. It employs a simplified single-tower adsorption separation process as well as a simplified crystallization separation process that does not require deep cooling. The advantage of this approach is that for new plants, inexpensive specialized adsorbents, desorbents, and processes can be used; for existing plants, the existing adsorption towers, adsorbents, and desorbents can still be utilized to double PX production capacity. To date, this combined technology has enabled the development of a process package with an annual capacity of 600,000 tons. 　　In addition, the institute developed two feasibility study plans: the first plan aims at energy savings and reduced investment; with an initial PX production capacity of 100,000 tons per year using an adsorption separation process, the combined adsorption and crystallization process reduces energy consumption from 440 kilograms of standard oil per ton of PX to 166–244 kilograms of standard oil per ton of PX, while keeping the production capacity unchanged ； The second approach aims to balance energy savings with capacity expansion; prior to the renovation, the PX production capacity was 100,000 tons per year (using an adsorption separation process). After the renovation with a combined adsorption and crystallization process, the production capacity increased to 240,000 tons per year. Meanwhile, thanks to the use of low-temperature heat utilization, the energy consumption dropped from 440 kilograms of standard oil per ton of PX to 281 kilograms of standard oil per ton of PX. 　　Chen Liang believes that crystallization separation is particularly suitable for the separation of high-concentration PX feedstock. The new PX crystallization processes and equipment developed by the Shanghai Research Institute of Petrochemical Technology can reduce the energy consumption in PX production when used for the capacity expansion of existing PX adsorption production facilities, offering good economic benefits. Foreign companies: Upgrading processes to save energy and reduce consumption. As pioneers in aromatic compound processing technologies, foreign patent holders such as the American company UOP and the French company Axens have always been at the forefront of adsorption separation technologies. With continuous improvements in adsorbents, processes, specialized equipment, and control systems, they have been able to raise the product purity from 99.2% to 99.8%, and the yield per cycle from 90% to 98%. 　　A senior manager at Honeywell UOP presented their new breakthroughs in aromatic adsorption separation. Leveraging years of experience in adsorbent manufacturing and process technology, UOP developed the LD Parex desorbent-based lightweight PX adsorption separation process in 2015. This process involves slight modifications to the ADS-47 adsorbent in order to adapt it to a system using a light desorbent (toluene) ； By avoiding the use of heavy desorbents and reducing the requirements for separation precision, as well as by adopting an optimized distillation process, it is possible to reduce the number of equipment units and trays by 20%. This results in a 15%–17% reduction in capital investment, while still maintaining the low energy consumption advantages of the original UOP high-efficiency aromatic compound plant. At present, all components of LD ParexParex have been successfully industrialized and operate reliably, enabling breakthrough advancements in terms of investment and energy consumption for aromatic plants. 　　The PX crystallization and separation technology developed by the Sibie BP Technology Alliance also features advanced energy-saving properties. Wang Jianguo, a senior engineer at CB&I Lummus, explained that the PX crystallization and separation technology, provided by BP and granted an exclusive global license to CB&I, has currently been applied at Reliance Industries’ largest aromatic compounds complex in India as well as at GS Caltex’s world-scale PX plant in South Korea. In a sense, it can be said that the BP crystallization technique has the advantage of lower energy consumption and production costs compared to selective adsorption separation techniques. 　　Furthermore, at the 2016 China Aromatic Hydrocarbons Industry Chain Development Conference, AXENS also presented the latest progress made in the development and promotion of their integrated technology for aromatic hydrocarbons plants – AXENS ParamaX. This process utilizes high-intensity continuous reforming technology, xylene isomerization technology, and molecular sieve adsorption separation technology for PX. Through continuous innovation in core technologies as well as catalysts and adsorbents, it is possible to significantly reduce the investment and operating costs of aromatic compound production facilities. In recent years, as olefin plants in the Middle East have increasingly switched to locally abundant and inexpensive ethane and propane gases, more naphtha has become available for export ； Africa and Central and South America are also major regions in the world for naphtha exports, and domestic aromatic compounds manufacturers could consider importing naphtha from these regions to produce aromatic compounds. In addition, efforts can also be made to actively expand the use of other feedstocks such as condensate. In short, it is necessary to expand the sources of raw materials to ensure the production of aromatics.