World’s First | Introduction to Yangzi Petrochemical’s Naphtha Adsorption Separation Unit (MaxEne)

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Naphtha is one of the petroleum products, also known as light oil for chemical use. It is a lightweight oil produced by processing crude oil or other raw materials and is used as a raw material in the chemical industry, primarily for reformation and other chemical processes. There are various boiling ranges depending on the application; in China, the boiling range is defined as from the initial boiling point up to around 220°C. When used as a reforming feedstock for the production of aromatics, the fraction ranging from 70°C to 145°C is referred to as light naphtha ； When the goal is to produce high-octane gasoline, fractions ranging from 70°C to 180°C are used, along with weighed naphtha ； When used as a solvent, it is called solvent naphtha ； Aromatic solvents derived from coal tar are also known as heavy naphtha or solvent naphtha. Refining and petrochemical companies have traditionally used naphtha to produce gasoline, aromatics, as well as light olefins such as ethylene and propylene. Naphtha is primarily composed of n-paraffins, isoparaffins, cycloparaffins, and aromatics, and different applications require varying compositions of hydrocarbons in naphtha. Under normal circumstances, n-alkanes are the ideal feedstocks for steam cracking to produce ethylene ； For reformation feedstocks, naphthenes and aromatics are ideal materials ； Among the components used in gasoline blending, certain isoparaffins are ideal for producing clean gasoline due to their high octane rating and low density. The requirements for the hydrocarbon composition of naphtha vary depending on its various uses, and there is a certain degree of complementarity among these needs. Therefore, how to make efficient use of the limited resources of naphtha in order to maximize its benefits in production, ensuring that it is used for aromatic compounds where appropriate and for olefins where suitable, has become an important challenge for integrated oil refining and chemical manufacturing companies. In the past, the conventional practice in refining companies was to separate naphtha into light and heavy fractions, using the light naphtha as a raw material for ethylene production or as a component in gasoline formulations, while the heavy naphtha was used as a feedstock for reforming. This approach failed to enable optimal utilization of naphtha in terms of its hydrocarbon composition. In recent years, the rapid development of naphtha separation technology has made it possible to achieve an optimized utilization of naphtha in terms of its hydrocarbon composition. Representative normal alkane separation technologies include UOP’s MaxEne and Isosiv processes in the United States, as well as Sinopec’s fixed-bed twin-tower parallel naphtha adsorption separation process. UOP’s MaxEne process uses mixed straight-run naphtha as raw material, and employs UOP’s MaxEne simulated moving bed adsorption separation technology to separate the n-paraffins from the isoparaffins in the mixed straight-run naphtha. Normal alkanes are first selectively adsorbed from naphtha, and then desorbed using an alkane-based desorbent; the desorbent is recovered by distillation and reused. This process produces two streams of products; the \"extract\" is a concentrated mixture of n-alkanes, which is fed into a naphtha cracking unit, enabling an increase in the yield of ethylene by over 30%, while the yield of propylene remains essentially unchanged ； “The residue consists of aromatic hydrocarbons, naphthenes, and isoparaffins; its octane rating increases by more than 6%, allowing it to be used directly in gasoline blending or further processed in a reforming unit. In 2013, Sinopec put into operation the MaxEne unit that utilizes UOP technology. Since its commissioning, this unit has processed over 3 million tons of naphtha in total, and all production parameters, including quality and quantity, meet the specified standards, thereby significantly increasing the overall yield of downstream petrochemical products. The adsorbent used in the MaxEne process is ADS-410 developed by UOP, while the desorbent is n-dodecane; currently, the desorbent is available in bulk supply from domestic companies. According to production data, by adopting the MaxEne process, existing naphtha cracking units can increase ethylene yield by up to 40% without affecting propylene production. At the same time, the production of reformed oil, which is used as a component in gasoline blending, can be increased by 5%, while the production of aromatics can be raised by around 10%.