The Influence of Solvents on the Liquid-Phase Adsorption Rate of n-Hexane in 5A Molecular Sieves

The main branched hydrocarbons in naphtha are isomeric hydrocarbons, cyclo-paraffins and aromatics. The naphthenic base naphtha has a high content of cyclo-paraffins while aryl naphtha has a correspondingly high content of aromatics. The work described in this paper investigates the influence of each type of principal branched hydrocarbon in naphtha on the adsorption kinetics of n-hexane in 5A molecular sieves at 283 K, 303 K and 323 K, respectively. The results obtained indicate that the effect of the solvent on the adsorption rate decreased in the sequence toluene > methyl cyclohexane > iso-octane. The apparent diffusivity coefficients and the apparent diffusional activation energies for the adsorption of n-hexane in 5A molecular sieves in the presence of different solvents were obtained by fitting the data to the kinetic model and the Arrhenius expression. The results indicate that the paraffin base naphtha is the most suitable feed for the adsorption separation of n-paraffins from branched hydrocarbons employing 5A molecular sieves. The kinetic data could also help to predict the adsorption behaviour in the adsorption bed when different kinds of naphtha are employed as the feed

Adsorption Behaviour of Normal Paraffins in a Fixed Bed Adsorber Containing 5 Å Molecular Sieves

The adsorption process for separating normal paraffins from naphtha using 5 Å molecular sieves was studied with the purpose of optimizing the utilization of naphtha and providing a proper allocation of the feeds for the steam cracking and catalytic reforming processes. The separation efficiency of the normal paraffins was > 99.9% while their purity in the desorption oil could reach 98.2%. The effects of adsorption temperature and space velocity on the adsorption process were investigated. The adsorption capacity was large and the adsorption mass-transfer zone was short when the adsorption temperature was low in the range of 180–340°C and the feed space velocity was small in the range of 30–300 h −1 . The adsorptivity of the normal paraffins improved with increasing carbon number. Long-chain normal paraffins had a notable displacement desorption relative to short-chain normal paraffins

Preparation of High-Purity Normal Hexane from Reformate Raffinate by Adsorption and Distillation Processes

In this study, a combination process of adsorption and distillation was adopted to obtain high-purity normal hexane. In the adsorption separation process, 5A zeolite was used as the adsorbent and the Shanghai Gaoqiao Petrochemical Corporation reformate raffinate containing 24.24 wt% normal hexane was separated into adsorption raffinate oil rich in non-normal paraffins and desorption oil rich in normal paraffins. At pre-specified operation conditions, concentration of n-hexane in the desorption oil reached higher than 96%. The concentrations of 3-methyl pentane and methyl cyclopentane, which are the light- and heavy-key components in the distillation tower of normal hexane, were reduced to 0.15% and 0.07%, respectively. According to the simulation results obtained using the software Aspen Plus , when the distillation tower has 15 stages, the n-hexane concentration can reach 99.02% with a recovery rate of 72.89% at the reflux ratio of 7.5. The combination process involving both adsorption and distillation has much higher efficiency than the traditional distillation process for producing the high-purity normal hexane

CuO, CeO₂ Modified Mg–Al Spinel for Removal of SO₂ from Fluid Catalytic Cracking Flue Gas

A Mg-rich Mg–Al spinel modified with CuO and CeO₂ via a cogelling method was used to remove SO₂ from fluid catalytic cracking (FCC) flue gas. It was found that the generation of a MgO–CuO solid solution was prevented in the presence of CeO₂. So CuO had a better dispersion on the adsorbent surface and showed a better catalytic oxidation activity. At the same time, when CuO was added, oxygen defects were found increased greatly in the lattice of CeO₂ by Raman spectra and in situ FTIR spectra analyses. This improved the oxygen adsorption capacity of the catalyst. High catalytic oxidation activity and oxygen adsorption capacity of the catalyst enormously promote oxidation of SO₂ to SO₃, which is much easier to adsorbed by spinel. The SO₂ breakthrough time was doubled when the Mg–Al spinel was modified with both CuO and CeO₂

Rational Formulation Design and Commercial Application of a New Hybrid Solvent for Selectively Removing H₂S and Organosulfurs from Sour Natural Gas

Based on the investigation on nonbonded interactions between solvent and organosulfur molecules, the reaction kinetics of carbonyl sulfide (COS) with chemical solvents in aqueous solutions, and experimental validation, a hybrid solvent (named UDS-2) was designed to simultaneously remove H₂S and organosulfurs from sour natural gas at high removal efficiency. The solvent components, which could enhance physical and chemical absorption of methyl mercaptan and COS, were screened using quantum chemistry method coupled with kinetics analysis. The results show that the five-membered sulfur heterocyclic compound (SUL) exhibits significant advantage of physical solubility of methyl mercaptan and COS. Meanwhile, the cyclic amine (CA) with weak steric hindrance effect as well as moderate basicity could enhance chemical removal of COS. UDS-2 solvent was obtained by blending SUL and CA with <i>N</i>-methyldiethanolamine (MDEA) at optimal proportion, and the removal efficiencies for methyl mercaptan, COS, and total organosulfur of UDS-2 were 53.1, 23.9, and 42.4 percentage points higher than those of MDEA. UDS-2 was successfully applied in a natural gas purification plant. Under the operation conditions of absorption pressure of 5.5 MPa, gas flow rate of 8.48 × 10³ N m³/h, gas–liquid ratios of 240 in absorber-I and 471 in absorber-II, the removal efficiencies for methyl mercaptan, COS, and total organosulfur are 77.6%, 74.5% and 75.6%, respectively. The contents of H₂S, CO₂, and total sulfur in purified gas can be reduced below 0.7 mg/(N m³), 0.16 vol % and 43.5 mg/(N m³), respectively, which all met the corresponding specification for Chinese first-grade commercial natural gas. Additionally, the low hydrocarbon loss of 1.34 N m³/(N m³ solution) indicates UDS-2 solvent has good selectivity for sulfur compounds over hydrocarbons

Molecular-Level-Process Model with Feedback of the Heat Effects on a Complex Reaction Network in a Fluidized Catalytic Cracking Process

A molecular-level-process model for a fluidized catalytic cracking process was developed. The work was aimed at the coarseness of the reaction network used in traditional lumping kinetic models. A feed-component matrix containing 14692 molecules was generated using a structure-oriented-lumping (SOL) method. A total of 95 groups of reaction rules were compiled, and 702943 reactions were involved. The SOL reaction kinetic model was combined with the reactor model to calculate the temperature distribution and feedback on the complex reaction network by taking into account the reaction heats in each reaction. The model was validated by the industrial data and predicted that the gasoline yield was >51% and the olefin content in gasoline was <24% at proper operation temperatures and catalyst/oil ratios. With the aid of the molecular-level model for the maximizing-isoparaffin technology, the product distribution and corresponding product quality can be controlled rationally by manipulating the operation conditions