Reduction of VOC emissions by a membrane-based gas absorption process

A membrane-based gas absorption （MGA） process was evaluated for the removal of volatile organic compounds （VOCs） based on C6H6/N2 mixture. The absorption of C6H6 from a C6H6/N2 mixture was investigated using a hydrophobic polypropylene hollow fiber membrane contactor and the aqueous solution of N-formyl morpholine （NFM） as absorbent. The effects of various factors on the overall mass transfer coefficient was investigated. The experimental results showed that the removal efficiency of C6H6 could reach 99.5% in present studied system. A mathematical model based on resistance-in-series concept was presented to predict the value of overall mass transfer coefficient. The average error between the predicted and experimental values is 7.9%. In addition, conventional packed columns for VOCs removal was also evaluated for comparison.

Mathematical Model of Natural Gas Desulfurization Based on Membrane Absorption

Models of mass transfer kinetics combined with mass transfer differential equation and mass transfer resistance equation were established on the basis of double-film theory. Mass transfer process of H2 S absorption by means of polypropylene hydrophobic microporous hollow fiber membrane contactor was simulated using MDEA(N-methyldiethanolamine) as the absorption liquid and corresponding experiments of natural gas desulfurization were performed. The simulation results indicated that the removal rate of hydrogen sulfide showed positive dependence on the absorption liquid concentration and gas pressure. However, the desulfurization rate showed negative dependence on gas flow. The simulated values were in good agreement with the experimental results. The in-tube concentration of hydrogen sulfide at the same point increased with increase in the gas velocity. Axial concentration of hydrogen sulfide decreased rapidly at the beginning, and the decrease saw a slowdown during the latter half period. Hydrogen sulfide concentration dropped quickly in the radial direction, and the reduction in the radial direction was weakened with the increase of axial length due to the gradual reduction of hydrogen sulfide concentration along the tube. The desulfurization rate under given operating conditions can be predicted by this model, and the theoretical basis for membrane module design can also be provided.

Influence of osmotic distillation on membrane absorption for the treatment of high strength ammonia wastewater

Osmotic distillation(OD) was found to be a coupled process in membrane absorption(MA) for the treatment of high strength ammonia wastewater. As a result, ammonia could not be concentrated in absorption solution(AS) as expected. The inhibition of the coupled OD in MA process was investigated as well as various factors affecting the inhibition. The results indicated that the coupled OD can be effectively inhibited by heating concentrated solution and cooling dilute solution. It was also found that experimental minimum inhibition temperature difference(MITD) between concentrated and dilute solutions was different when using polyvinylidene fluoride(PVDF) and polypropylene(PP) membranes respectively, which could be ascribed to material properties, such as OD and membrane distillation(MD) coefficients of the membranes. Experimental MITDs were found to be higher than theoretical MITDs which were calculated using a simplified method.

Feasibility analysis of SO_2 absorption using a hydrophilic ceramic membrane contactor

Hydrophilic ceramic membranes would be potential candidates for membrane gas absorption if they could be applied to appropriate separation processes.This study highlights a novel concept for the practical implementation of SO_2 absorption in hydrophilic ceramic membrane that exhibits outstanding thermal and mechanical stabilities.With this aim,we investigated experimentally the performance of SO_2 absorption into aqueous sodium hydroxide (NaOH) solution in a hydrophilic alumina (Al_2O_3) membrane contactor in terms of SO_2 removal efficiency and SO_2 mass transfer flux,and compared the performance with that in a hydrophobic one.A series of experiments were performed at various conditions over a NaOH concentration range of 0–1.0 mol·L^(-1),a liquid flow rate range of 30–180 ml·min^(-1),a gas flow rate range of 120–1000 ml·min^(-1),an inlet SO_2 concentration range of 400–2000μl·L^(-1),and a temperature range of 10–35°C.It was found that the hydrophilic membrane was more competitive when using a NaOH concentration higher than 0.2 mol·L^(-1).Furthermore,it can be inferred that the hydrophilicα-Al_2O_3 membrane exhibited exceptional long-term stability under 480 h continuous operation.

Absorption of sulfur dioxide using membrane and enhancement of desorption with ultrasound

The absorption of sulfur dioxide in simulated flue gas by using liquid-containing membrane was investigated.The process of sulfur dioxide desorption from the absorbent of citrate solution was explored.The influence of the gas-phase,and the liquid-phase on absorption efficiency of sulfur dioxide and the influence of ultrasonic frequency,ultrasonic power and stirring speed on desorption efficiency of sulfur dioxide were examined.The results indicate that the absorption efficiency decreases with increasing flow velocity and sulfur dioxide content in gas-phase,and can be improved by increasing the concentration and the pH value of citrate solution.It is concluded that lower ultrasonic frequency results in a better degassing efficiency.The using of ultrasound in desorbing sulfur dioxide from citrate solution improves the desorbing efficiency in the some conditions,without changing the essence of chemical reaction.

Unexpected Selective Absorption of Lithium in Thermally Reduced Graphene Oxide Membranes

Lithium plays an increasingly important role in scientific and industrial processes, and it is extremely important to extract lithium from a high Mg^(2+)/Li^(+) mass ratio brine or to recover lithium from the leachate of spent lithiumion batteries. Conventional wisdom shows that Li^(+) with low valence states has a much weaker adsorption(and absorption energy) with graphene than multivalent ions such as Mg^(2+). Here, we show the selective adsorption of Li^(+) in thermally reduced graphene oxide(rGO) membranes over other metal ions such as Mg^(2+), Co^(2+), Mn^(2+),Ni^(2+), or Fe^(2+). Interestingly, the adsorption strength of Li^(+) reaches up to 5 times the adsorption strength of Mg^(2+),and the mass ratio of a mixed Mg^(2+)/Li^(+) solution at a very high value of 500 : 1 can be effectively reduced to 0.7 : 1 within only six experimental treatment cycles, demonstrating the excellent applicability of the rGO membranes in the Mg^(2+)/Li^(+) separation. A theoretical analysis indicates that this unexpected selectivity is attributed to the competition between cation–π interaction and steric exclusion when hydrated cations enter the confined space of the rGO membranes.

MASS TRANSFER IN MEMBRANE ABSORPTIONDESORPTION OF AMMONIA FROM AMMONIA WATER

Hydrophobic membrane can provide fast mass transfer for absorption-desorption of gasesform liquid to absorbent.The removal of ammonia from ammonia water and absorption with dilutesulphuric acid was studied in a pilot plant with polypropylene hollow fiber column,The removalrate and influences of operation temperature,flow rate and concentration on mass transferperformances were discussed mathematically.Experimental results and computer calculation show thatthe ammonia removal rate is not affected by the feed concentration for a given system.Both partialand overall mass transfer coefficients vary along the axis of the fiber,and the mass transfer for themembrane process is controlled by membrane resistance.

Absorption of Low Concentration Sulfur Dioxide Using Liquid-containing Microporous Membrane

The absorption of low concentration SO2 in flue gas by using the module of liquid-containing microporous membrane which is made up of hollow fiber and citric acid-sodium citrate buffer solution was investigated.The absorption efficiency of hydrophilic and hydrophobic membranes by using the concept of dynamic contact angle was mainly studied.The influences on absorption efficiency from absorption time,flowrate of gas phase,SO2 concentration of gas phase,air pressure,citrate concentration,pH value of solution as well as the generation of sulfate radical in absorption solution were examined.The results indicate that the hydrophobic hollow fiber membrane is better than hydrophilic membrane,the absorption efficiency decreases with increasing absorption time,gas phase flowrate,gas phase SO2 concentration and air pressure,the absorption rate and capacity of SO2 can be improved by increasing the citrate concentration,the absorption efficiency can be improved by increasing the pH value of citrate solution,the concentration of SO42-in absorption solution increases linearly with the absorption time at a rate around 0.192 g/(L-h).

Flexible regulation engineering of titanium nitride nanofibrous membranes for efficient electromagnetic microwave absorption in wide temperature spectrum

Simultaneous development of well impedance matching and strong loss capability has become a mainstream method for achieving outstanding electromagnetic microwave absorption(EMWA)performances over wide temperature range.However,it is difficult to pursue both due to the mutual restraint of relationship between impedance matching and loss capability about temperature.Here,we propose a flexible regulation engineering of titanium nitride(TiN)nanofibrous membranes(NMs,TNMs),which could be distributed uniformly in the polydimethylsiloxane(PDMS)matrix and contributed to the formation of abundant local conductive networks,generating the local conductive loss and enhancing the loss ability of EMWs.Moreover,when the TNMs are used as functional units and dispersed in the matrix,the corresponding composites exhibit an outstanding anti-reflection effect on microwaves.As hoped,under the precondition of good impedance matching,local conductive loss and polarization loss together improve the loss capacity at room temperature,and polarization loss can compensate the local conductive loss to acquire effective dielectric response at elevated temperature.Benefiting from the reasonably synergistic loss ability caused by flexible regulation engineering,the corresponding composites exhibit the perfect EMWA performances in a wide temperature range from 298 to 573 K.This work not only elaborates the ponderable insights of independent membrane in the composition-structure-function connection,but also provides a feasible tactic for resolving coexistence of well impedance matching and strong loss capability issues in wide temperature spectrum.

Enhanced H_(2) permeation and CO_(2) tolerance of self-assembled ceramic-metal-ceramic BZCYYb-Ni-CeO_(2) hybrid membrane for hydrogen separation

Perovskite-type mixed protonic-electronic conducting membranes have attracted attention because of their ability to separate and purify hydrogen from a mixture of gases generated by industrial-scale steam reforming based on an ion diffusion mechanism.Exploring cost-effective membrane materials that can achieve both high H_(2) permeability and strong CO_(2)-tolerant chemical stability has been a major challenge for industrial applications.Herein,we constructed a triple phase(ceramic-metal-ceramic)membrane composed of a perovskite ceramic phase BaZr_(0.1)Ce_(0.7)Y_(0.1)Yb_(0.1)O_(3-δ)(BZCYYb),Ni metal phase and a fluorite ceramic phase CeO_(2).Under H_(2) atmosphere,Ni metal in-situ exsolved from the oxide grains,and decorated the grain surface and boundary,thus the electronic conductivity and hydrogen separation performance can be promoted.The BZCYYbNi-CeO_(2)hybrid membrane achieved an exceptional hydrogen separation performance of 0.53 mL min^(-1)cm^(-2) at 800℃ under a 10 vol% H_(2) atmosphere,surpassing all other perovskite membranes reported to date.Furthermore,the CeO_(2) phase incorporated into the BZCYYb-Ni effectively improved the CO_(2)-tolerant chemical stability.The BZCYYbNi-CeO_(2) membrane exhibited outstanding long-term stability for at least 80 h at 700℃ under 10 vol%CO_(2)-10 vol%H_(2).The success of hybrid membrane construction creates a new direction for simultaneously improving their hydrogen separation performance and CO_(2) resistance stability.

Preparation of Calcium Carbonate Nanoparticles with a Continuous Gas-liquid Membrane Contactor： Particles Morphology and Membrane Fouling

Nanosized calcium carbonate particles were prepared with a continuous gas-liquid membrane contactor. The effects of Ca(OH)2 concentration, CO2 pressure and liquid flow velocity on the particles morphology, pressure drop and membrane fouling were studied. With rising Ca(OH)2 concentrations, the average size of the particles increased. The effects of Ca(OH)2 concentration and CO2 pressure on particles were not apparent under the experimental conditions. When the Ca(OH)2 concentration and liquid flow velocity were high, or the CO2 pressure was low, the fouling on the membrane external surface at the contactor entrance was serious due to liquid leakage, whereas the fouling was slight at exit. The fouling on the membrane inner-surface at entrance was apparent due to adsorption of raw materials. The membrane can be recovered by washing with dilute hydrochloric acid and reused for at least 6 times without performance deterioration.

Concentration of mixed acid by electrodialysis for the intensification of absorption process in acrylic acid production

The absorption process in acrylic acid production was water-intensive.The concentration of acrylic acid before distillation process was low,which induced to large amount of wastewater and enormous energy consumption.In this work,a new method was proposed to concentrate the side stream of absorption column and thus increase the concentration in bottom product by electrodialysis.The influence of operating conditions on concentration rate and specific energy consumption were investigated by a laboratory-scale device.When the voltage drop was 1 V·cP^(-1)(1 cP=10^(-3) Pa·s),flow velocity was 3 cm·s^(-1) and the temperature was 35℃,the concentration rates of acrylic acid and acetic acid could be 203.3%and 156.6%in the continual-ED process.Based on the experimental data,the absorption process combined with ED was simulated,in which the diluted solution from ED process was used as spray water and the concentrated solution was feed back to the absorption column.The results shown that the flow rate of spray water was decreased by 37.1%,and the acrylic acid concentration at the bottom of the tower was increased by 4.56%.The ions exchange membranes before and after use 1200 h were tested by membrane surface morphology(scanning electron microscope),membrane chemical groups(infrared spectra),ion exchange capacity,and membrane area resistance,which indicated the membrane were stable in the acid system.This method provides new method for energy conservation and emission reduction in the traditional chemical industry.

Simulation of CO₂and H₂S Removal Using Methanol in Hollow Fiber Membrane Gas Absorber (HFMGA)

Application of methanol solvent for physical absorption of CO2 and H2S from CO2/H2S/CH4 mixture in gas–liquid hollow fiber membrane gas absorber (HFMGA) was investigated. A computational mass transfer (CMT) model for simulation of HFMGA in the case of simultaneous separation of CO2 and H2S was developed. The membrane gas absorber model explicitly calculates for the rates of mass transfer through the membrane and components concentration profiles. Due to the lack of experimental data in the literature, the model was validated using available individual components’ water absorption data. The numerical predictions were in good agreement with the experimental data. The effects of operating conditions such as liquid velocity, gas velocity, temperature and pressure were analyzed. It is shown that methanol solvent can successfully be used for CO2 and H2S removal in membrane gas absorber. Also it is found that the concentration distribution of CO2 and H2S in the gas phase along the fiber length obeys plug flow model whereas in the methanol absorbent deeply affected by the interface concentration, absorbent velocity and diffusivity. In addition, it is shown that application of membrane gas absorber using methanol absorbents for H2S removal and at higher flow rate is more efficient. Moreover, at operating pressures above 10 atm even at low absorbent rate, H2S concentration depletion is relatively complete while at 1 atm this value is about 30%. This means that removal efficiency decreases with an increase in temperature and it is more important especially for H2S.

Permeation properties of CO2 and CH4 in asymmetric polyethersulfone/ polyesterurethane and polyethersulfone/polyetherurethane blend membranes

The transport performances of carbon dioxide and methane were studied in polyethersulfone, polyethersulfone/polyeterurethane(PES–ETPU) and polyethersulfone/polyestherurethane(PES–ESPU) blend membranes separately with different compositions. The variations in the structural characteristics of PES membrane after incorporation of ESPU and ETPU were investigated by different techniques. Additionally, the effect of pressure and composition on the permeance of CO_2, CH_4 and ideal selectivity of CO_2/CH_4 were checked on the membranes.The results revealed that the morphology of the blend membranes was affected by two opposite factors: thermodynamic enhancement and kinetic hindrance. The membranes with denser sponge layers were formed at lower ratio of PU/PES, while more porous structure with enlarged macrovoids membranes were observed at higher PU content. The results indicated that adding PU to PES membrane, caused permeance improvement of the gases with nearly no change and/or reduction in ideal selectivity of CO_2/CH_4. Moreover, PES–ETPU membranes showed higher permeability and less CO_2/CH_4 selectivity in comparison with PES–ESPU samples. For PES–ESPU membrane containing 1.5% ESPU, CO_2 permeance at 10 bar was improved up to 20% with almost no change in CO_2/CH_4 selectivity with respect to PES. Finally, response surface methodology was used to evaluate the effects of the operating parameters on the permeance and ideal selectivity.

Controlling Pore Size and its Distribution of γ-Al_2O_3 Nanofiltration Membranes

The preparation process of γ-A12O3 nanofiltration membranes were studied by N2 absorption and desorption test and retention rate vs thickness gradient curve method. It was found that template and thermal treatment were key factors for controlling pore size and its distribution. Under the optimized experimental conditions, the BJH (Barret-Joyner-Halenda) desorption average pore diameter, BJH desorption cumulative volume of pores and BET (Brunauer-Emmett-Teller) surface area of obtained membranes were about 3.9 nm, 0.33 cm3/g and 245 m2/g respectively, the pore size distribution was very narrow. Pore size decreased with the increasing of thickness and no evident change after the dense top layer was formed. The optimum thickness can be controlled by retention rate vs thickness gradient curve method.

人参皂苷Rg3对骨质疏松大鼠骨代谢及肠钙吸收功能的影响

目的:探究人参皂苷Rg3对骨质疏松(osteoporosis,OP)大鼠骨代谢及肠钙吸收功能的影响。方法:60只SPF级雌性Wistar大鼠,按照随机数字法分为空白组、模型组、阳性组、实验组,每组大鼠各15只。除空白组外,其他大鼠均采用去势(OVX法)法制备OP大鼠模型。造模成功后,空白组及模型组生理盐水灌胃[10 mL/(kg·d)],阳性组给予阿仑膦酸钠维D3灌服(每周6.25 mg/kg),实验组给予人参皂苷Rg3[80 mg/(kg·d)]灌胃治疗,连续干预治疗12周。检测各组股骨、胫骨骨密度变化,酶联免疫法检测大鼠血清中骨保护素(osteoclastogenesis inhibitory factor,OPG)、Ⅰ型前胶原氨基末端肽(procollagen typeⅠNterminal propeptide,PINP)、抗酒石酸酸性磷酸酶(tartrate resistant acid phosphatase,TRACP)、I型胶原交联C-末端肽(TypeⅠcollagen carboxy-terminal peptide,CTX-I)含量变化;原位末端标记法(TdT-mediated dUTP nick end labeling,TUNEL)法分析各组肠黏膜组织细胞凋亡情况;Masson法分析各组肠黏膜组织纤维病理改变;免疫组化法检测各组肠黏膜组织中维生素D膜相关快速反应结合蛋白(membrane-associated rapid response steroid-binding,1,25-D3-MARRS)蛋白表达;蛋白免疫印迹法及RT-PCR法检测各组Jagged1、Notch1、Hes1蛋白及mRNA表达水平。结果:大鼠造模后股骨、胫骨骨密度明显下降,血清中OPG、PINP、TRACP及CTX-I含量明显变化(P<0.05);肠黏膜组织病理发生明显改变,组织纤维化增强,细胞凋亡程度增加;肠黏膜组织1,25-D3-MARRS蛋白表达降低(P<0.05)。治疗后与模型组对比,阳性组及实验组大鼠股骨、胫骨骨密度明显升高,血清中OPG、PINP、TRACP及CTX-I含量明显改善(P<0.05);肠黏膜组织病理发生明显改善,纤维化降低,细胞凋亡程度降低;肠黏膜组织中Jagged1、Notch1、Hes1蛋白及mRNA表达明显改善(P<0.05)。结论:人参皂苷Rg3能够提高OP大鼠骨密度,减轻肠黏膜组织细胞凋亡及组织纤维化,增加肠黏膜1,25D3-MARRS蛋白表达,改善肠道钙吸收。

油田伴生气与CO_(2)驱采气CO_(2)回收技术研究进展

油田伴生气和CO_(2)驱采气的数量巨大,且其中含有较多的CO_(2),合理回收利用其中的CO_(2)是当前油田开发和气体资源利用的重要研究领域。回收其中的CO_(2)不仅响应国家环境保护政策,而且将其合理的资源化以提高经济效益。本文以油田伴生气、CO_(2)驱采气的CO_(2)回收技术为研究对象,详细介绍了当前五大类分离提纯工艺的基本原理,并对各工艺的特点以及实用性进行了综合对比与分析。另外总结分析了四类复合方法的适用性,得出变压吸附法+化学吸收法适用于较低CO_(2)浓度含量油田伴生气烃类回收和CO_(2)除杂;膜分离+变压吸附法以及膜分离+化学吸收法适用于CO_(2)浓度较高的CO_(2)驱采气的收集;化学吸收法+低温精馏法适用于制作高纯度的CO_(2)产品气。

畜禽粪污处理中氨气膜接触器回收的传质及选择性研究

对畜禽粪污好氧堆肥中产生的氨气与厌氧发酵后沼液中的氨氮进行回收,不仅可以减少污染物和温室气体的排放,达到减污降碳的目的,还能获得氮肥产品,增加粪污处理的经济性。针对现有氨气捕集过程中设备体积大和灵活性差等问题,提出了采用中空纤维膜来实现氨气捕集的目标。采用空气吹扫氨水溶液模拟了不同情形下的氨气浓度与空气流量,测试不同情形下氨气捕集的通量和回收率,分析影响氨气捕集的主要因素和传质特性。结果表明,氨气向膜内传质的阻力主要受气相传质阻力和膜的传质阻力影响,低空气流量下气相传质阻力占主导地位。提升空气流量至5 L/min时,气相传质阻力比0.5 L/min时下降53.6%,此时膜内传质阻力占主导。氨气捕集通量随进膜氨气浓度的增大而提升。在空气流量低于1 L/min下,氨氮回收率高于95%,0.5 L/min时的氨氮回收率高于99%。在氨气停留时间足够的条件下,氨氮回收率仅与酸液吸收容量相关。在温度差和浓度差的影响下,空气中的水蒸气会向膜内的吸收剂中传递。吸收剂中含质量分数26%的硫酸铵比仅含1%的硫铵溶液水回收通量高13.3倍,氨氮分离因子由41.6降低至3.06。酸液质量分数对氨气的传质无显著影响。文献对比表明典型状态下粪污处理中的氨气释放质量浓度与本研究中涉及的质量浓度区间基本一致,说明中空纤维膜捕集氨气具有较广的适用性。

Fe(Ⅱ)EDTA络合吸收耦合H_(2)-MBfR处理NO效能

构建Fe(Ⅱ)EDTA络合吸收耦合H_(2)-MBfR一体化系统,驯化具有同步反硝化及铁还原能力的混合菌种,在维持反应体系稳定反硝化性能的基础上,探究进水Fe(Ⅱ)EDTA浓度、pH值对NO去除效率的影响,分析微生物群落结构.结果表明,Fe(Ⅱ)EDTA络合吸收耦合H_(2)-MBfR还原一体化系统对NO具有稳定去除效能,最大去除效率为99.50%.提高初始Fe(Ⅱ)EDTA浓度有助于Fe(Ⅱ)EDTA-NO的生成,且体系内的NO平均去除速率随着Fe(Ⅱ)EDTA浓度的提升而提升.在Fe(Ⅱ)EDTA浓度为10mmol/L时,NO最大去除速率达到44.68mg/(m3·h).pH值升高则不利于Fe(Ⅱ)EDTA-NO的生成,控制pH值为6更适合一体化系统运行.微生物群落结构分析发现一体化阶段优势菌门Proteobacteria、Bacteroidetes和Firmicutes,在该反应器中承担着重要的功能和作用,其丰度占比分别为50.35%,16.43%,14.98%.

以富CO_(2)吸收液为汲取液的沼液中水正渗透回收特性研究

针对沼气工程存在的沼液量大难处理问题及沼气提纯的需求,提出将正渗透技术与沼气CO_(2)化学吸收分离耦合,探究了沼气CO_(2)化学吸收中的富CO_(2)吸收液作为正渗透汲取液从沼液中回收水及浓缩沼液的可行性,并以沼液浓缩过程中的水通量、沼液浓缩倍数、沼液氨氮截留率与吸收剂反向传质通量为指标,考察了汲取液种类、汲取液浓度与其他操作参数对正渗透水回收性能的影响。结果表明,富CO_(2)吸收液作为汲取液从沼液中回收水并浓缩沼液具有可行性,且随着汲取液浓度、流量和温度的增加,沼液中水向汲取液的传质通量增加,沼液浓缩倍数也相应增加,但沼液中氨氮截留率下降,同时汲取液中的吸收剂溶质向沼液的反向传质通量也增加。当采用浓度2.5mol/L、CO_(2)负荷0.5mol/mol的富CO_(2)甘氨酸钾溶液作为汲取液,汲取液温度为70℃、流速为150mL/min、沼液室温及流速为150mL/min时,采用正渗透技术从沼液中回收水的初始通量达8.05L/(m^(2)·h),经过4h运行后,沼液浓缩倍数为1.18,氨氮截留率为84.13%,反向吸收剂通量仅为2.94g/(m^(2)·h)。