A new composite ZnO-coated SiC filter with photocatalytic and antibacterial properties was prepared via a simple sol–gel method. The crystallinity, grain size, and ZnO loadings played important roles in the photocatalytic and antibacterial properties of as-prepared materials. The high-efficiency photocatalytic and antibacterial properties resulted from the active oxidizing reagents and released Zn2+, respectively. The possible formation of an n–p junction between n-type ZnO and p-type SiC filter support is considered as another reason for enhanced photocatalytic performance (i.e., the effective degradation of methyl orange (MO) solution). Antibacterial activity of as-prepared samples against Escherichia coli and Staphylococcus aureus (without UV light) were also examined; after 30 min sterilization, the samples removed a maximum of 97.6 and 99.9% of these bacteria, respectively.

Organic aerosols have severe effects on human health and climate change. In this study, a pilot-scale ceramic filter was used to remove the organic aerosols from furnace flue gas produced from industrial processes. The performance of ceramic filter and long-term stability of ceramic material were investigated. It showed that gas permeation flux fluctuated at a high level, which was the result of the surface filtration and special self-regeneration of the vertical ceramic filter. Removal efficiencies of TSP, PM10, and PM 2.5 aerosols were higher than 98.5%, and the rejection mechanisms were concluded as sieving, surface adhesion, and pore channel capture. Chemical characteristics of aerosol were analyzed based on FTIR spectra. Main organic compounds in the collected aerosols were paraffin binder, carboxylic acids, and esters. Carboxylic acids and esters were the products of the chemical reactions of paraffin and oxygen at high temperatures. After a long-term operation, ceramic membranes exhibited low flexural strength loss and slight variation in pore size distribution and the microstructure remained unchanged. Therefore, porous alumina membranes have potential for applications in the of removal organic aerosol emissions from industrial processes before reaching the atmosphere.

Lactic acid, mainly produced by fermentation, has been widely used in the food, chemical, and pharmaceutical fields. Because of the high downstream processing costs in traditional technology, the cost-effective production of high-purity lactic acid has remained a challenge for decades. This study provides an integrated membrane process to recover lactic acid from sodium salt fermentation broth that consists of ceramic membrane filtration, nanofiltration (NF), and bipolar membrane electrodialysis (BMED). In the ceramic membrane process, the flux changed with the membrane pore size in the order of 50 nm > 200 nm > 500 nm > 20 nm. At an operating pressure of 0.1 MPa, the flux of the membrane with a pore size of 50 nm reached a maximum of 192 L·m–2·h–1, and the removal rate of cells was up to 99.3%. In the subsequent NF step, the flux increased linearly with the operating pressure from 0.5 to 2.0 MPa, whereas the rejection rates of Mg2+, Ca2+, and Na+ increased with increasing TMP, and a flux of 5.0 L·m–2·h–1 was obtained at the operating pressure of 2.0 MPa, with 87.7% of Ca2+, 95.0% of Mg2+, and 98.9% of protein being retained. The BMED process was developed for the conversion of 95.0% NaL into NaOH and HL, and the energy consumption was 1.05 kWh·kg–1 under a current density of 400 A·m–2. Our results indicate that the proposed integrated membrane process is technically feasible for lactic acid production from fermentation broth.

We investigated the cleaning efficiency and kinetics of multichannel ceramic membranes fouled during brine purification. The foulants were first characterized by means of SEM, EDX, and XRD analyses, and we found that mainly BaSO4 crystals were deposited on the membrane surface. A cleaning solution composed of diethylenetrinitrilopentaacetic acid (DTPA), oxalic acid, and NaOH was developed to regenerate the fouled ceramic membranes. The membranes could be completely recovered with the cleaning solution. The cleaning rate increased with the concentration of DTPA (CDTPA) and temperature (T) but was not sensitive to the crossflow velocity (CFV) or transmembrane pressure (TMP). The optimized cleaning condition was CDTPA = 1.0 × 10–3 mol/L, T = 50 °C, CFV = 3.0 m/s, and TMP = 0.10 MPa. A dissolution kinetics model associated with both the concentration factor and temperature factor was developed, which fitted well the experimental results. This model was used to determine the reaction rate constants during the cleaning process at different temperatures. Based on this model, we found that the activation energy of BaSO4 dissolution using the cleaning solution consisted of DTPA, oxalic acid, and NaOH was lower than that of using pure DTPA solution. The results support the conclusion that the compound solution provided a better cleaning performance than pure DTPA solution.

Ceramic membranes were used to separate nanosized nickel catalysts from slurry in hydrogenation of p-nitrophenol to p-aminophenol. Experimental results have revealed that the tubular ceramic membranes are capable of removing nickel catalysts with an efficiency of 100% and have no adverse impacts on the performance of catalysts. The analysis of fouling resistance in membrane filtration showed that cake layer formation on membrane surface was the main fouling mechanism. The unexpected phenomenon in cake resistance was considered to arise from the size and fractal properties of the nickel particle aggregates. A combined pore blockage and cake filtration model was utilized to describe the time-dependent flux decline. The model results agreed well with those obtained experimentally. A suitable membrane with optimized pore size which gives the highest steady flux was determined based on the model prediction. The cleaning of a fouled membrane can be achieved by use of strong acidic solutions.Research highlights▶ Ceramic membranes were used to separate nanosized nickel catalysts. ▶ Cake layer composed of nickel aggregates was the main fouling mechanism. ▶ The combined pore blockage and cake filtration model described the flux well.

A new tubular membrane reactor based on tubular metallic membrane is developed, which can solve the problem concerning in situ separation of catalyst from the reaction mixture and make the production process continuous. In this article, the feasibility of continuous ammoximation of acetone to acetone oxime over titanium silicalites-1 (TS-1) in the tubular membrane reactor was investigated. It has demonstrated that the tubular membrane reactor system can maintain a more long-term steady production of acetone oxime than that of a side-stream ceramic membrane reactor and has a higher productivity than the batch reactor. The effects of operation conditions (stirring rate, residence time, temperature, catalyst concentration, molar ratio of NH3/acetone, H2O2/acetone, and t-butanol/acetone) on the performances of the reaction system were examined via single factor experiments. Results show that the operation conditions greatly affect the conversion, selectivity of acetone ammoximation, and the filtration resistance. The acetone conversion is >94.5% and the acetone oxime selectivity remains stable at ∼98% in a 30-h continuous run.

In the desulfurization process for purification of coking gas, a huge amount of wastewater is generated. In order to recover the usable substances such as suspended sulfur (SS) and ammonium salts, e.g., (NH4)2S2O3 and NH4SCN, in the wastewater and also to avoid severe environmental problems in the case of improper disposal, an integrated membrane process mainly consisting of ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO) was proposed to treat the wastewater. In the UF process, a ceramic membrane was employed to remove SS and an efficiency of 99.9% and a steady flux of about 500 L·m−2·h−1 were achieved. In the NF step, (NH4)2S2O3 was separated from NH4SCN with a retention ratio of 95.0%, and finally 83.0% of (NH4)2S2O3 was recovered in the retentate, whereas 99.2% of NH4SCN was recovered in the permeate via dialysis with deionized water. In the RO process, NH4SCN can be recovered with an efficiency of 99.0% through a four-pass filtration process. Meanwhile, the RO permeate can be reused in the salt diafiltration process. The results show that the proposed integrated membrane process is technically feasible and economically efficient for the treatment of desulfurization wastewater generated in the coking industry.

As a reversible reaction, the hydrolysis conversion of ethyl lactate is controlled by thermodynamic equilibrium. In order to improve the yield and conversion rate of hydrolysis of ethyl lactate, ethanol in the products should be removed in time. Hydrolysis of ethyl lactate coupled by vapor permeation (VP) for removing ethanol in the products was proposed. Here, the vapor permeation was carried out with a new polydimethylsiloxane (PDMS)/ceramic composite membrane prepared by our team. The PDMS/ceramic composite membrane was first characterized by scanning electron microscopy (SEM) images, pervaporation, and vapor permeation of ethanol/water mixtures. The characterization results showed that the PDMS/ceramic composite membrane was dense and uniform and had good separation performances. The permeate flux of pervaporation of 5 wt % ethanol arrived at 2541 g·m−2·h−1, and the separation factor was 7.5 at 353 K. As for vapor permeation of 10 wt % ethanol, the permeate flux was above 400 g·m−2·h−1 and separation factor was around 11. Then, the VP aided hydrolysis of ethyl lactate was investigated with the prepared PDMS/ceramic composite membrane. By coupling with VP, the final conversion of the ethyl lactate increased from 77.1% to 98.2% with the initial molar ratio of water to ethyl lactate 10:1 at 358 K. The larger initial molar ratio of water to ethyl lactate was helpful to improve the conversion of VP aided hydrolysis of ethyl lactate. The VP aided hydrolysis of ethyl lactate with the prepared PDMS/ceramic composite membrane was significantly enhanced.

A series of two-step reactions and several special experiments were designed and carried out to discover the reaction pathway of acetone ammoximation to acetone oxime over titanium silicalites-1 (TS-1) employing 25 wt% ammonia and 30 wt% hydrogen peroxide as the ammoximation agents. The experimental results show that the acetone oxime can form even if there is no direct contact between acetone and TS-1 catalysts, indicating the hydroxylamine route may be the most important catalytic mechanism for the reaction. HPLC, GC/MS and ion chromatography characterization results show that hydrogen peroxide can oxidize acetone oxime to acetone, nitrite and nitrate in the presence of TS-1. In addition, nitrite and nitrate can form in the reaction of H2O2 and NH3 over TS-1. Based on these results, a possible overall reaction pathway of acetone ammoximation over TS-1 has been proposed.

We report the fabrication and ultrafiltration performances of an asymmetric composite membrane with a mesoporous TiO2 skin layer coated on a macroporous alumina support. Mesoporous TiO2 was first prepared and deposited on the substrate through a sol−gel process where a ethylene oxide and propylene oxide triblock polymer (PEO−PPO−PEO, P123) was used to modify the properties of the sols and also to introduce assembled pores in the skin layer. The obtained mesoporous TiO2 membrane was characterized by means of scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and nitrogen adsorption. We found that there were two types of wormlike mesopores present in the TiO2 membrane: interparticle and assembled pores. By carefully controlling the sol properties, we made the two types of pores match each other, which means the size of the interparticle pores is close or smaller than that of the assembled pores. This pore-size matching ensures a narrow pore-size distribution and, consequently, a good retention performance of the obtained TiO2 membrane. The pore size of the TiO2 membrane is ca. 6 nm, as revealed by both nitrogen adsorption and dextran separation experiments, and it has a pure water flux of 7.12 L/(m2·h·bar) and a cutoff molecular weight of 19 000 Da, which is very attractive for applications in the enrichment and separation of proteins and polypeptides.Keywords: asymmetric membrane; mesoporous titania; self-assembly; ultrafiltration

A system combining catalytic reaction with crossflow ultrafiltration (UF) was used to catalytic ammoximation of cyclohexanone to the oxime over titanium silicalite-1 (TS-1) catalysts. The effect of microsized silica particles on the performance of the catalysis/UF system was investigated in terms of catalytic activity and membrane filterability through dissolution and ultrafiltration experiments. Adding silica particles in the system inhibits the dissolution of TS-1 catalysts and increases both the reaction conversion and the selectivity significantly. Further characterizations (XRF, XRD, FTIR, etc.) indicated that the presence of silica particles remarkably limits the ammonia damage to the microstructure frame of TS-1 catalyst. In addition, silica particles play an important role in substantially removing the deposited TS-1 cake from the membrane surface, benefiting from the scouring effect. According to the results of visual observation to the tested membranes and the estimation of hydrodynamic forces acting on particles, microsized particles are hard to deposit on the membrane surface at the studied conditions and therefore a flux improvement has been achieved.

The natural mineral kaolin combined with additive Al(OH)3 and AlF3 as alumina sources was used to directly prepare macroporous mullite ceramic membrane supports through in situ reaction sintering. The effects of composition and the sintering temperature on the micro-morphology, phase development and pore structure of porous mullite support were investigated extensively. It was found that the excess SiO2 in kaolin was consumed rapidly by adding the alumina precursors with the formation of secondary mullite in the temperature range of 1300–1500 °C. During the sintering process, pore structure and stiff skeleton needle-like structure mullite formed in the support, which resulted in good pore structure and high mechanical strength. Thus, the support is suitable for the preparation of asymmetric ceramic membranes. The pore structure and the micro-morphology of the support could be controlled by adjusting raw material Al2O3 composition from 50 to 72 wt.% of Al2O3 and the sintering temperature from 1300 to 1550 °C. The porous mullite supports with the porosity of 27–55.6%, average pore size of 0.73–1.50 μm and mechanical strength of 15.5–66.7 MPa were prepared after optimization.

Membrane filtration technology combined with coagulation is widely used to purify river water. In this study, microfiltration (MF) and ultrafiltration (UF) ceramic membranes were combined with coagulation to treat local river water located at Xinghua, Jiangsu province, China. The operation parameters, fouling mechanism and pilot-scale tests were investigated. The results show that the pore size of membrane has small effect on the pseudo-steady flux for dead-end filtration, and the increase of flux in MF process is more than that in UF process for cross-flow filtration with the same increase of cross-flow velocity. The membrane pore size has little influence on the water quality. The analysis on membrane fouling mechanism shows that the cake filtration has significant influence on the pseudo-steady flux and water quality for the membrane with pore size of 50, 200 and 500 nm. For the membrane with pore size of 200 nm and backwashing employed in our pilot study, a constant flux of 150 L·m−2·h−1 was reached during stable operation, with the removal efficiency of turbidity, total organic carbon (TOC) and UV254 higher than 99%, 45% and 48%, respectively. The study demonstrates that coagulation-porous ceramic membrane hybrid process is a reliable method for river water purification.

Heterogeneous catalysts with ultrafine or nano particle size have currently attracted considerable attentions in the chemical and petrochemical production processes, but their large-scale applications remain challenging because of difficulties associated with their efficient separation from the reaction slurry. A porous ceramic membrane reactor has emerged as a promising method to solve the problem concerning catalysts separation in situ from the reaction mixture and make the production process continuous in heterogeneous catalysis. This article presents a review of the present progress on porous ceramic membrane reactors for heterogeneous catalysis, which covers classification of configurations of porous ceramic membrane reactor, major considerations and some important industrial applications. A special emphasis is paid to major considerations in term of application-oriented ceramic membrane design, optimization of ceramic membrane reactor performance and membrane fouling mechanism. Finally, brief concluding remarks on porous ceramic membrane reactors are given and possible future research interests are also outlined.

Ceramic ultrafiltration membranes were used to separate titanium silicalite-1 (TS-1) catalysts from theslurry of catalytic ammoximation of cyclohexanone to oxime. Silica was shown to have a great effect on membrane fouling in the alkaline environment of this system. In the ammoximation system, there are three main silica sources, which are residual silica on the catalyst particles surface during preparation, silica dissolved from TS-1 catalyst particles by ammonia solvent, and silica sol added into the reaction slurry to inhibit the dissolution erosion of the TS-1catalyst. The silica dissolved by ammonia has been proved to influence membrane fouling most among the three silica sources. This was because the amount of silica dissolved by ammonia was the largest, and the polymerizationof silica monomers at high concentration caused colloid particles formation, which led to a dense cake layer depositing on the membrane surface. Meanwhile, the size reduction of catalyst particles caused by alkaline dissolution also increased specific resistances of cake layers.

•Ceramic membranes are capable of removing ultrafine Mg(OH)2 precipitates.•The direct observation technique was introduced to monitor the fouling deposition and removal.•Flux decline and cake layer growth were measured to analyze the fouling mechanisms.•Fouling layer expanded and then left membrane surface in large sections during backwashing.Ceramic membranes were used to separate Mg(OH)2 precipitate from suspension in the chlor-alkali industry. Experimental results revealed that the ceramic membranes are capable of removing ultrafine Mg(OH)2 precipitates and removal rate of Mg2 + cations was higher than 99.9%. The effect of suspension concentration on the permeate flux was more prominent than the transmembrane pressure. The presence of MgCl2 was found to affect the filtration performance more significantly than NaCl. The direct observation (DO) technique was introduced to monitor the processes of fouling deposition and removal. The relationship between the visual observation and the hydraulic performance values provided better understanding instead of assumptions in fouling deposition mechanisms. During backwashing, direct observation demonstrated that fouling layer first expanded and then left the membrane surface in large sections, indicating strong cohesion between Mg(OH)2 particles in the cake layer. Using direct observation (DO) technique allows the non-invasive, in-situ visualization and quantification of fouling layer in real time compared with SEM.

Polyacrylamide has been widely used for polymer flooding in oil production. Wastewater is produced in the polymer flooding process. In this work, a ceramic membrane system was used to treat the wastewater. The effects of membrane pore size and PAM concentrations on the filtration performance were investigated. With the increase of the membrane pore size, the flux declined severely. When the PAM concentration was lower than the critical micelle concentration (CMC), the pseudo-steady flux decreased with the PAM concentration. When the PAM concentration was close to or higher than the CMC, the PAM concentration had little influence on the PSF. For the ultrafiltration membranes, the average MW of PAM in the permeate changed little with different PAM concentrations. However, for the microfiltration membranes, the average MW of PAM in the permeate decreased with the PAM concentration. The effect of NaCl concentration on the filtration of PAM solutions was studied. As the NaCl concentration increased, the change of PAM morphology caused the PSF to decrease significantly. Membrane fouling mechanisms and membrane cleaning methods were also discussed. Pore blocking and gel layer formation both contributed to the flux decline. The fouled membrane was easily cleaned by a NaOH aqueous solution with pH > 12.Highlights► Ceramic membranes with different membrane pore sizes were studied for their use in produced water treatment. ► The effects of the NaCl concentrations and the PAM concentrations on the filtration performance were investigated. ► Interactions between PAM, NaCl and membrane fouling were discussed. ► The mechanism of membrane fouling and the cleaning methods were also investigated.

A ceramic membrane reactor system was developed for the continuous ammoximation of acetone to acetone oxime over titanium silicalites-1 (TS-1) catalysts. The effects of catalyst concentration and microsized silica particles on the performances of the membrane reactor system were examined in detail. For the membrane reactor system the optimal catalyst concentration is 17.0 g L−1, obviously higher than the one obtained from the previous experiments in a batch glass reactor, because the strong adhesion of TS-1 catalyst particles on the surface of the pipeline, the tank and the membrane leads to the decrease of effective catalyst concentration. Adding the microsized silica particles can effectively inhibit the decrease of TS-1 catalysts concentration in reaction slurry and improve the operation stability of the membrane reactor system significantly, benefiting from the scouring effect and the attachment of TS-1 particles on the surfaces of larger silica particles. According to the estimation of hydrodynamic forces acting on particles, microsized silica particles are hard to deposit on the contact surfaces at the studied conditions and therefore a longer stable operation of the membrane reactor system has been achieved.

•Foundation of ceramic UF membrane in the treatment of desulfurization wastewater.•Fouling causes were sulfur and tar oil deposition on the membrane surface.•Fouling mechanism was completion of pore blocking, and then cake layer formation.•Propose an effective cleaning method with a flux recovery ratio higher than 98%.Ceramic ultrafiltration membrane was applied to treat the desulfurization wastewater to avoid environmental pollution and further reclaim sulfur. However, membrane fouling is unavoidable. The key issue to solve the fouling problem is to understand the fouling mechanism, and find an effective way to regenerate the membrane. The results showed that the dominant resistance was caused by cake formation even at a low sulfur concentration. The filtration mechanism was tested to fit the complete pore blocking model. Sulfur and tar oil deposition on the membrane surface was significant, along with salts such as thiocyanate in the wastewater. Based on these, the effectiveness of various membrane cleaning methods was evaluated. The most effective one was adding 1% (w/w) NaOH solution mixed with 0.5% (w/w) NaClO, and then cleaning for 120 min at 50 °C, eventually the flux recovery ratio was always higher than 98%. Such effectiveness has verified the compositions of the foulants vice versa. Therefore, the ceramic UF membrane can be reused as a good alternative in the wastewater treatment.