制氢驰放气优化利用方案的研究

制氢装置PSA单元产生的驰放气中含有高浓度的甲烷、氢气、一氧化碳、二氧化碳。比较了变压吸附法、溶剂吸收法和膜分离法分离驰放气中的二氧化碳,从净化气指标、总能耗、运行费用和装置投资方面进行比较,得出变压吸附法分离优于其它两种方案。另外,变压吸附法分离没有涉及化学过程,相比操作运行更简单方便,可实现在线切换吸附器,有利于装置长周期运行。     

大豆基碱性多孔碳材料的制备与性能研究

介绍了一种简单快速,低成本的制备碱性掺氮多孔碳材料的方法。以富含蛋白质的天然大豆为碳源和氮源,经过碳化和水蒸气活化制备出了碱性多孔碳材料。采用N2物理吸附,扫描电镜,Boehm滴定,傅里叶变换红外以及CO2-TPD,元素分析等技术对所得碳材料进行了表征。结果表明,大豆中蛋白质氨基酸的氮元素在制备过程中被原位保留下来,使制得的活性炭表面具有较大量的碱性基团。并且碱性基团的含量随着活化时间的延长逐渐增加。当活化温度为800℃,活化时间为20 min时,所得活性炭的碱性基团含量达到5.496mmol/g。所得碳材料用于低浓度CO2的吸附,研究发现样品BC-sa-800-5对CO2和N2混合气体具有很好的分离效果,分离因子达到8.334。     

Adsorption mechanism-based screening of cyclodextrin polymers for adsorption and separation of pesticides from water

A rational screening of cyclodextrin-based polymer (CDP), in terms of the relationship between adsorption potential and adsorbent-adsorbate, was investigated to adsorb and separate pesticides from water. Seven spherical porous CDPs were prepared with onefold or composite cyclodextrin(s) as complex and epichlorohydrin as cross-linking reagent. The adsorption kinetics and isotherms of the polymers toward a mixture of ten distinct pesticides clearly demonstrate that the adsorbents with a homogeneous open network structure can absorb pesticides via multiple adsorption interactions such as CD inclusion, loading into swelling water and physical adsorption on network. The multivariate regression analysis distinguishes the quantitative contributions of polymer properties to its adsorption potential, among which CD content, swelling capacity and pore size appear to be major influencing factors. Consequently, a facile mixture of three CDPs (i.e., β-CDP, RM-CDP and HP-CDP) was screened to obtain above prerequisite properties. The multiplex polymer could superiorly separate the pesticides at environmentally relevant levels from water.     

Mechanism analysis of solvent selectivity and energy-saving optimization in vapor recompression-assisted extractive distillation for separation of binary azeotrope

Octane and p-xylene are common components in crude gasoline, so their separation process is very important in petroleum industry. The azeotrope and near azeotrope are often separated by extractive distillation in industry, which can realize the recovery and utilization of resources. In this work, the vapor–liquid equilibrium experiment was used to obtain the vapor–liquid equilibrium properties of the difficult separation system, and on this basis, the solvent extraction mechanism was studied. The mechanism of solvent separation plays a guiding role in selecting suitable solvents for industrial separation. The interaction energy, bond length and charge density distribution of p-xylene with solvent are calculated by quantum chemistry method. The quantum chemistry calculation results and experiment results showed that N-formylmorpholine is the best solvent among the alternative solvents in the work. This work provides an effective and complete solvent screening process from phase equilibrium experiments to quantum chemical calculation. An extractive distillation simulation process with N-formylmorpholine as solvent is designed to separate octane and p-xylene. In addition, the feasibility and effectiveness of the intensified vapor recompression assisted extraction distillation are also discussed. In the extractive distillation process, the vapor recompression-assisted extraction distillation process is globally optimal. Compared with basic process, the total annual cost can be reduced by 43.2%. This study provides theoretical guidance for extractive distillation separation technology and solvent selection.     

Design and optimization of an integrated process for the purification of propylene oxide and the separation of propylene glycol by-product

It is difficult to separate the methanol and hydrocarbons in the propylene oxide (PO) purification process due to their forming azeotrope. As for this, a novel PO separation process, in that the deionized water is employed as extractant and 1,2-propylene glycol (MPG) that is formed from the PO hydrolysis reaction is recovered, is presented in this work. The salient feature of this process is that both the non-catalyzed reactions of PO hydrolysis to form MPG and dipropylene glycol (DPG) are simultaneously considered and MPG by-product with high purity is obtained in virtue of the deionized water as reflux liquid and side take-off in MPG column. In addition, the ionic liquid (IL) extractant is screened through the conductor-like screening model for segment activity coefficient (COSMO-SAC) and the comparisons of separation efficiency between the IL and normal octane (nC₈) extractant for the separation of PO and 2-methylpentane are made. With the non-random two-liquid (NRTL) thermodynamic model, the simulation and optimization design for the full flow sheet are performed and the effects of the key operation parameters such as solvent ratio, theoretical stages, feeding stage etc. on separation efficiency are detailedly discussed. The results show that the mass purity and the mass yield of PO can be up to 99.99% and 99.0%, and the condenser duty, reboiler duty and PO loss in the process with IL extractant can be decreased by 69.66%, 30.21% and 78.86% compared to ones with nC₈. The total annual cost (TAC) calculation also suggests that the TAC would be significantly reduced if using IL in replace of nC₈ for the investigated process. The presented results would provide a useful guide for improving the quality of PO product and the economic efficiency of industrial plant.     

Two-dimensional graphitic carbon nitride for membrane separation

Recent years, membrane separation technology has attracted significant research attention because of the efficient and environmentally friendly operation. The selection of suitable materials to improve the membrane selectivity, permeability and other properties has become a topic of vital research relevance. Two-dimensional (2D) materials, a novel family of multifunctional materials, are widely used in membrane separation due to their unique structure and properties. In this respect, as a novel 2D material, graphitic carbon nitride (g-C₃N₄) have found specific attention in membrane separation. This study reviews the application of carbon nitride in gas separation membranes, pervaporation membranes, nanofiltration membranes, reverse osmosis membranes, ion exchange membranes and catalytic membranes, along with describing the separation mechanisms.     

Fabrication of nickel oxide functionalized zeolite USY composite as a promising adsorbent for CO2 capture

Adsorption process is considered to be the most promising alternative for the CO₂ capture to the traditional energy-intensive amine absorption process, and the development of feasible and efficient CO₂ adsorbents is still a challenge. In this work, the NiO@USY (ultrastable Y) composites with different NiO loadings were prepared for the CO₂ adsorption using Ni(NO₃)₂ as the precursor. The composites were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, nitrogen adsorption–desorption test, scanning electron microscopy analysis, and thermogravimetric analysis, and were evaluated for the CO₂ adsorption capacity, CO₂/N₂ adsorption selectivity and CO₂ cycle adsorption capacity. The characterization results show that after the activation at 423 K, the Ni(NO₃)₂ species were well dispersed into the surface of zeolite USY, and after the further activation at 823 K, Ni(NO₃)₂ could be converted into highly dispersed NiO. The adsorption results show that the presence of the active component NiO plays an important role in improving the CO₂ adsorption performance, and the NiO@USY composite with a NiO loading of 1.5 mmol·g^-1 USY support displays a high adsorption capacity and adsorption selectivity for CO₂, and shows a good cycle stability. In addition, the Clausius–Clapeyron equation was used to evaluate the isosteric heat of adsorption of CO₂ on the NiO(1.5)@USY composite, and the heat of adsorption was 17.39–38.34 kJ·mol^-1.     

Designed synthesis of porous carbons for the separation of light hydrocarbons

The separation of light hydrocarbon mixtures (C₁-C₃) generated from petrochemical industry is vital and challenging process for obtaining valuable pure chemical feedstocks. In comparison to the energy intensive conventional separation technologies (cryogenic distillation, absorption and hydrogenation), the adsorptive separation is considered as a low energy cost and high efficiency process. Porous carbons have been demonstrated as excellent adsorbents for the separation of light hydrocarbons, owing to their designable structure and tailorable properties. This review summarizes the recent advances of using porous carbons as adsorbents for the separation of light hydrocarbons, including methane/nitrogen, methane/alkane, methane/carbon dioxide, ethylene/ethane and propylene/propane. We discuss the separation mechanisms and highlight the material features including pore structure, surface chemistry and target molecular properties that determine the separation performance. Furthermore, the challenges and development direction associated with carbonaceous adsorbents for light hydrocarbon separation are discussed, meanwhile the guidelines for the design of porous carbons are proposed.     

Electrodeposited iodide ions imprinted polypyrrole@bismuth oxyiodide film for an electrochemically switched renewable extractor towards iodide ions

Effective extraction and regeneration of radioactive iodide is one of urgent concerns for the safe utilization of nuclear energy. As a novel environmentally benign ion separation technique, electrochemically switched ion extraction (ESIE) process can be applied for effective capture and recovery of iodide ions (I^-). Herein, a novel kelp seaweed-like core/shell I^- imprinted polypyrrole@bismuth oxyiodide (PPy/I^-@BiOI) composite film is successfully prepared for the selective I^- capture in the ESIE system. It is found that the I^- can be easily trapped in the PPy/I^-@BiOI film after I^- is in situ desorbed from the film by an electrochemical reduction process since it offers particular electroactive binding sites for I^- extraction. The I^- imprinted PPy/I^-@BiOI film displays an extraction capacity as high as 325.2 mg·g^-1 for I^- with favorable stability. In particular, the extraction and desorption of I^- is achieved by adjusting the redox potential and the pristine PPy/I^-@BiOI film can be regenerated and reused for multiple times without decrease in extraction capacity. It is expected that such a PPy/I^-@BiOI film would be useful as an electrochemically switched renewable extractor that could capture and regenerate I^- from radioactive water.     

Recent advances in nanofiltration,reverse osmosis membranes and their applications in biomedical separation field

In the face of human society's great requirements for health industry, and the much stricter safety and quality standards in the biomedical industry, the demand for advanced membrane separation technologies continues to rapidly grow in the world. Nanofiltration (NF) and reverse osmosis (RO) as the high-efficient, low energy consumption, and environmental friendly membrane separation techniques, show great promise in the application of biomedical separation field. The chemical compositions, microstructures and surface properties of NF/RO membranes determine the separation accuracy, efficiency and operation cost in their applications. Accordingly, recent studies have focused on tuning the structures and tailoring the performance of NF/RO membranes via the design and synthesis of various advanced membrane materials, and exploring universal and convenient membrane preparation strategies, with the objective of promoting the better and faster development of NF/RO membrane separation technology in the biomedical separation field. This paper reviews the recent studies on the NF/RO membranes constructed with various materials, including the polymeric materials, different dimensional inorganic/organic nanomaterials, porous polymeric materials and metal coordination polymers, etc. Moreover, the influence of membrane chemical compositions, interior microstructures, and surface characteristics on the separation performance of NF/RO membranes, are comprehensively discussed. Subsequently, the applications of NF/RO membranes in biomedical separation field are systematically reported. Finally, the perspective for future challenges of NF/RO membrane separation techniques in this field is discussed.