Direct catalytic cracking of crude oil to chemicals (ccCOTC) has become the development trend in the petrochemical industry. A riser is one of the key reactors in a ccCOTC process. In this work, a two-fluid model (TFM) was used to simulate a relationship between the reactor geometry and gas–solid flow in a typical riser (inside diameter of 17 mm and height of 4.5 m) established in our laboratory, with the aim of improving chemical yield and optimizing the reactor geometry in a ccCOTC process. The effects of key geometric parameters, including the angle between an oblique pipe for catalyst return and the vertical riser (α), the distance between the nozzle orifice and catalyst return oblique pipe (L), the ratio of height to diameter in the prelifting zone (H/D), and the number of catalysts returning to oblique pipes (n), on the distribution of catalyst particles and product profiles were studied. An optimized reactor geometry was proposed according to the index of gas–solid dispersion evenness. To further know the effect of the riser geometry on the product distribution, the two-fluid model (TFM) coupled with a four-lumped kinetic model was used to predict the cracking product profiles along the riser axial. It was found that the ccCOTC riser can remarkably enhance the yield of target chemicals (C2–C4 olefins, benzene, toluene, and xylene), which was approximately 3.1% higher than the result from the pilot test (using the riser before geometry optimization). This work could provide fundamental support on the design of a reactor to maximize light olefins and monocyclic aromatic hydrocarbons in the ccCOTC process.
One of the challenges to obtain high‐quality natural active substances is the selective separation of the target compound from its analogues. In this study, ionic liquids (ILs), with design flexibility, were proposed to separate artemisitene and artemisinin, typical examples of natural analogues. Based on COSMO‐RS calculation, several ILs were selected to separate artemisitene/artemisinin by experiment. It was demonstrated that the aqueous solution of N‐allyl‐N,N,N‐trimethylammonium chloride ([AA][Cl]) exhibited excellent capability for selective separation of the two compounds. Under the optimal conditions (40°C, 1 h), the separation selectivity of artemisitene/artemisinin could reach 12.23 when the initial impurity content was only 0.8 wt%. Spectroscopic analysis and molecular dynamics indicated that π–π complexation between artemisitene and [AA][Cl] plays a major role in this separation process. Moreover, the process of multistage cross‐flow extraction was compared with counter‐flow extraction, and the latter one exhibited advantages in energy consumption and product yield.
The production of light olefins by catalytic cracking is a research hotspot in the petrochemical industry. Herein, nickel was used to modify IM-5 zeolite to improve the performance in catalytic cracking. Properties of the Ni/IM-5 zeolites with different nickel loadings were characterized. It was demonstrated that nickel species were mainly located on the external surface of impregnated IM-5 zeolite, only a few Ni 2+ ions were distributed in the ion exchange site as compensation cations. Pyridine infrared results indicated that the introduction of nickel could modulate the acidity of IM-5 zeolite and increase the amount of Lewis acid sites. Compared with IM-5, Ni/IM-5 exhibited higher olefin selectivity, especially ethylene, in n-hexane cracking reactions. It was considered that nickel could provide dehydrogenation active sites and promote the formation of light olefins. Thus, the selectivity of light olefins can be improved by controlling the amount and distribution of nickel in IM-5 zeolite.
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