It is a focus to reduce the energy consumption and operating cost of CO2 capture from low-pressure flue gas streams of power plants using an aqueous amine-based absorbent. In this study, CO2 capture experiments were conducted in an absorption–desorption loop system using amine-based absorbents. The gas mixture containing CO2, O2, SO2, and N2 in the composition range of flue gas from coal-fired power plant after flue gas desulfurization was selected as the feed gas. For an aqueous amine solution, the largest contribution to monoethanolamine (MEA) loss was made by evaporation during desorption, followed by the formation of sulfate and heat-stable salts. To reduce MEA loss and meanwhile decrease the energy consumption during CO2 desorption, an aqueous amine solution mixed with ionic liquid (30 wt % MEA + 40 wt % [bmim][BF4] + 30 wt % H2O) was proposed. The energy consumption of the mixed ionic liquid solution for absorbent regeneration was 37.2% lower than that of aqueous MEA solution. The MEA loss per ton of captured CO2 for the mixed solution was 1.16 kg, which is much lower than that of 3.55 kg for the aqueous amine solution. No ionic liquid loss was detected. In addition, the mixed ionic liquid solution showed a low viscosity of 3.54 mPa s at 323 K, indicating that the ionic liquid disadvantage of high viscosity can be overcome for absorbent delivery of CO2 capture.

•Pt–Al2O3 was modified to superhydrophobicity via grafting by FAS.•Hydrophobic modification greatly promoted catalytic activity and stability.•Catalytic activity heavily depended on hydrophobicity extent in humid condition.For polymer electrolyte fuel cells (PEFCs), Pt–Al2O3 catalyst coatings were developed to convert hydrogen off-gas of PEFCs to water. To ignite the hydrogen oxidation at room temperature with negligible induction period, the Pt–Al2O3 catalyst coatings on the walls were modified from hydrophilicity to superhydrophobicity via grafting by 1H,1H,2H,2H-perfluorooctyltriethoxysilane (FAS). The modified Pt–Al2O3 catalyst coatings were optimized in a channel plate reactor (CPR) that is similar to microchannel reactors in flow pattern, but is much simpler to be fabricated and can be used repeatedly. We showed that higher grafting density of FAS provided stronger repulsive force on produced water vapor (favorable effect) while more resistance for the reactants approaching to catalytic active sites (unfavorable effect). The suitable hydrophobic modification significantly promoted the catalytic activities and stabilities of the catalyst coatings under both humid and dry feed stream conditions. Under the humid feed stream condition, the most active catalyst coating of 5WM-Pt–Al2O3 showed the biggest contact angle of 150° and decreased the hydrogen concentration from 4 vol% to 632 ppm without a detectable induction period at 303 K. The microchannel reactor with superhydrophobic catalyst coatings showed great potential for conversion of hydrogen off-gas of PEFCs to water.Download high-res image (236KB)Download full-size image

•NO removal efficiency achieved 91.2% using PP membrane contactor and H2O2 saline aqueous solution.•Addition of NaCl to H2O2 solution increases solubility of NO and therefore promotes NO removal.•SO2 concentration decreased below 100 ppb which alleviated the burden of desulfuration.Development of cost-efficient denitration technologies has been a challenging task in chemical industry. Here we proposed a new denitration method by using polypropylene hollow fiber membrane contactor, through which the NO gas from a simulative flue gas was absorbed into a saline aqueous solution, and then oxidized by the added H2O2. We demonstrated that the numerous pores in the semipermeable membrane and the addition of NaCl gave rise to a high-efficient oxidation-absorption process. By combining with a theoretical study upon both classical and quantum density functional theories, we extensively examined the effects of different operation parameters including the gas and liquid flow rates, the concentrations of H2O2 and NaCl in the solution and SO2 in the mimic flue gas, the absorption temperature and the circulating time. The optimal operation parameters were identified. Finally, along with a designed industrial flow chart we evaluated the cost-efficiency of this proposed method, and found that this method could be more competitive than the current mainstream technologies for flue gas denitration.Download high-res image (131KB)Download full-size image

•Pt–Pd/Al2O3 catalyst exhibited superior resistance of water and iodine poisoning.•Reaction was ignited immediately for superhydrophobic Pt–Pd/Al2O3 catalyst at 298 K.•Hydrogen conversion kept 100% for superhydrophobic Pt–Pd/Al2O3 when T exceeded 398 K.Passive auto-catalytic recombiner (PAR) system is an important hydrogen mitigation method which has been applied in most modern light water nuclear reactors. The two challenges for the highly efficient PAR are the detrimental effect of water and poisoning by fission products. In this study, to address the two challenges, superhydrophobic Pt–Pd/Al2O3 catalyst coatings were prepared by wet impregnation method and the grafting of 1H,1H,2H,2H-perfluorooctyltriethoxysilane.The formation of a Pt–Pd intermetallic compound was confirmed by in situ diffuse reflectance infrared Fourier transform infrared spectroscopy for the Pt–Pd/Al2O3 catalyst. The Pt–Pd/Al2O3 catalyst exhibited a superior resistance of water poisoning to the monometallic catalysts. In addition, compared with the monometallic catalysts, the least influence by the iodine poisoning was observed for the Pt–Pd/Al2O3 catalyst, which is attributed to the smallest influence on the bindings of H2 and O2 on the Pt–Pd intermetallic compound by the iodine addition. For the reactor with the superhydrophobic Pt–Pd/Al2O3 catalyst coating, under the conditions simulating the nuclear accident, the reaction was ignited immediately as soon as the hydrogen was introduced at 298 K and the hydrogen conversion kept 100% when the reaction temperature exceeded 398 K. The superhydrophobic Pt–Pd/Al2O3 catalyst coating showed great potential for the mitigation of hydrogen containing various poisons during the nuclear accident.Download high-res image (173KB)Download full-size image

In this study, the preparation of MgO-Li2O catalyst for biodiesel synthesis using PDMS–PEO as a structure-directing agent has been investigated. Compared to the catalysts reported so far, LM0.12-873 (Li/Mg molar ratio=0.12, calcination temperature is 873K) exhibited an excellent performance and showed great potential in industrial application. The synergistic effect of macro- and mesopores on the templated catalysts functioned efficiently as a catalyst for transesterification. The basic strength of MgO-Li2O catalysts was enhanced due to the lattice distortion and defects created by the substitution of the Li ions in MgO lattice. The catalytic activities of MgO-Li2O depend on the amount of strong base sites with the most active catalyst of LM0.12-873 exhibiting the largest amount strong base sites.

To achieve preferential CO oxidation, a Pt–Co catalyst-coated channel plate reactor (CCPR) was produced via conventional mechanical milling and catalyst coating. The proposed reactor performed well under a wide range of operating temperatures and provided satisfactory results at low temperatures (CO concentrations of 1–10 ppm at 413–443 K and 1–50 ppm at 413–453 K). In the proposed CCPR, significant deactivation was not observed during continuous operation for 100 h. In addition, the reactor exhibited excellent tolerance to undesirable conditions, including reaction temperature runaway and feeding stream failure. Characterisation results indicated that the catalytic activity of the proposed CCPR was high due to the formation of Pt3Co intermetallic compounds and nanoscale metal particles. The capacity per channel of the proposed CCPR was approximately 50–100 times greater than those of conventional microchannel reactors; thus, problems associated with excessive reactors were significantly reduced. In general, the results indicated that CCPR has great potential in the small-scale production of hydrogen for fuel cells.Research highlights► Under a wide range of operating temperatures, a Pt–Co catalyst-coated channel plate reactor can reduce the concentration of CO from 1% to less than 10 ppm. ► The proposed reactor exhibited excellent tolerance to undesirable conditions, including reaction temperature runaway and feeding stream control failures. ► The high catalytic activity was due to the formation of Pt3Co intermetallic compounds and nanoscale metal particles.

This study investigates the use of CaO–CeO2 mixed oxides as solid base catalysts for the transesterification of Pistacia chinensis oil with methanol to produce biodiesel. These CaO–CeO2 mixed-oxide catalysts were prepared by an incipient wetness impregnation method and characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. The cerium improved the heterogeneous catalytic stability remarkably due to the defects induced by the substitution of Ca ions for Ce ions on the surface. The best catalyst was determined to be C0.15-973 (with a Ce/Ca molar ratio of 0.15 and having been calcined at 973 K), considering its catalytic and anti-leaching abilities. The effects of reaction parameters such as the methanol/oil molar ratio, the amount of catalyst amount and the reaction temperature were also investigated. For the C0.15-973 regenerated after five reuses, the biodiesel yield was 91%, which is slightly less than that of the fresh sample. The test results revealed that the CaO–CeO2 mixed oxides have good potential for use in the large-scale biodiesel production.

Membrane wetting by absorbents leads to an increase in mass transfer resistance and a deterioration in CO2 absorption performance during the membrane gas absorption process. In order to better understand the wetting mechanism of membrane pores during their prolonged contact with adsorbents, polypropylene (PP) hollow fibers were immersed in three different absorbents for up to 90 days. Monoethanolamine, methyldiethanolamine, and deionized water were applied as absorbent solutions. The characterization results of membrane samples confirm that the absorbent molecules diffuse into PP polymers during the exposure process, resulting in the swelling of the membranes. The absorption-swelling wetting mechanism is proposed to explain observations made during the wetting process. The strong reduction of contact angles indicates that the membrane surface hydrophobicity decreases remarkably during immersion due to membrane–absorbent interaction. Membrane surface morphologies and surface roughness suffer from significant and complicated changes after immersing the membrane fibers in the absorbents. Immersion in an absorbent with a high surface tension results in small changes in membrane surface morphology. As indicated by the experimental results, improving membrane surface hydrophobicity may be an effective way of overcoming wetting problems.Research highlights▶ The characterization results confirm that the absorbent molecules diffused into PP polymers during the exposure process, resulting in the swelling of the membranes. The absorption-swelling wetting mechanism is proposed to explain observations made during the wetting process. ▶ The strong reduction of contact angles indicates that membrane surface hydrophobicity decreased remarkably during immersion due to membrane–absorbent interaction. Membrane surface morphologies and surface roughness suffer from significant and complicated changes after immersing the membrane fibers in the absorbents. ▶ As indicated by the experimental results, improving membrane surface hydrophobicity may be an effective way of overcoming wetting problems.

Conventional methods for measuring diffusion coefficients (D) are complex and time consuming. This study presents a method for the continuous measurement of temperature-dependent diffusion coefficients using a confocal Raman microscope with microfluidic chips. Concentration information was collected by a Raman microscope to extract D values. An isothermal diffusion process at various temperatures was ensured by coupling the silicon-based microfluidic chip with an isothermal plate. In the simple silicon/glass chip, the heating effect induced by a Raman laser was observed to contribute to abnormally high D values. To eliminate the heating effect, a 200 nm-thick aluminum (Al) reflection film was used to coat the channel bottom. The Al film substantially reduced absorption of laser power, thus ensuring precise D values in excellent agreement with literature data. Other potential methods to eliminate the heating effect were also evaluated by computational fluid dynamics (CFD) simulations and were found impractical for implementation. Consequently, this method for the continuous measurement of temperature-dependent diffusion coefficients is proven to be accurate, efficient, and reliable.

This study presents a technology for continuous and high-efficiency alkali-catalyzed biodiesel synthesis using a metal foam reactor combined with a passive mixer. A metal foam reactor with higher pore density produces smaller droplets that result in higher efficiency of biodiesel synthesis. Compared with conventional stirred reactors, the time for high methyl ester conversion can be shortened remarkably by the use of metal foam reactors. Experimental results reveal that a metal foam reactor of 50 pores per inch exhibits an energy consumption per gram biodiesel of 1.01 J g−1, merely 1.69% and 0.77% of energy consumption of the zigzag micro-channel and conventional stirred reactors, respectively. Moreover, biodiesel yield per reactor for the metal foam reactor is approximately 60 times that of the zigzag micro-channel reactor, thus overcoming the problem of numbering up an excessive number of reactors in the application. These results indicate the great potential of metal foam reactors in small-fuel biodiesel processing plants for distributive applications.

•CFD simulation can improve the design and settings of a HTHP PRV.•Maximum flow rate of HTHP PRV occurs when curtain area is 1.18 times throat area.•Upper adjusting ring has more influence on reseating pressure than lower adjusting ring.Reliable performances of high temperature and high pressure operating steam pressure relief valves (HTHP PRVs) are extremely important for the safety of nuclear power plants. It is still a challenge to accurately describe the dynamic performance of HTHP PRVs. In this study, the accuracy of computational fluid dynamics (CFD) based modelling of the transient processes is examined. For one of the HTHP PRVs named DWPRV, the effects of different parameters on the dynamic performance were investigated by combining CFD simulation and experiments. In the simulation, the domain decomposition method (DDM) and the Grid Pre-deformation Method (GPM) were adopted to handle the moving disk geometry and the large mesh deformation. The effect of damping was also studied. It is confirmed that the use of CFD simulation can improve the design and settings of a HTHP PRV in a highly energetic service that is difficult to test due to safety reasons. For the DWPRV, it was found that the maximum flow rate occurs when the curtain area is 1.18 times the throat area. The degree of superheat ranging from 0 °C to 100 °C has a negligible effect on the performance of DWPRV regardless of the changes in the material mechanical properties with operating temperatures. The reseating pressure increases linearly with the rise in the distance between the upper adjusting ring and the sealing face. The lower adjusting ring exhibits a weak effect on the reseating pressure. For the ratios of rated lift to throat diameter equaling to 0.3 and 0.35, the DWPRV exhibits the higher blowdown for the ratio of 0.35.Download high-res image (404KB)Download full-size image

Membrane gas absorption technology is a promising alternative to conventional technologies for the mitigation of acid gases. In this study, with a polypropylene (PP) hollow fiber membrane contactor as absorber and a packed column as stripper, the influence of SO2 on the CO2 capture from coal-fired power plant flue gas was investigated in an absorption–desorption experimental set-up using aqueous monoethanolamine (MEA) as the absorbent. The experimental results showed that the MEA loss per ton captured CO2 increased with the addition of SO2, resulting in sharp decreases in CO2 removal efficiency and mass transfer rate of CO2 after initial several days of operation. This tendency is mainly attributed to the promotional effect of SO2 on the degradation of MEA by the formation of sulfate. Thus, it is necessary to regenerate MEA using a reclaimer in this case. The respective SO2 concentrations at the outlets of absorber and stripper remained constant values of 24 and 120 ppb throughout the operation although the CO2 removal efficiency decreased dramatically with time. This co-capture of CO2 and SO2 could play an important role in further desulfuration, thus alleviating the burden of desulfuration to some extent and benefiting the subsequent CO2 purification and storage. More progresses are greatly needed in high-efficiency and stable absorbents, high-efficiency reclaimer, and methods to reduce MEA loss by evaporation.Graphical abstractMEA loss and the formation of different degradation species for CO2 capture with the impurity of SO2.Download full-size imageHighlights► SO2 resulted in sharp decreases in removal efficiency and mass transfer rate of CO2. ► Sulfate showed the biggest contribution to the MEA loss followed by evaporation. ► SO2 concentrations at the outlets of absorber and stripper remained 24 and 120 ppb.

In this paper, three-dimensional finite element methods were carried out to investigate the disc flexibility effects on the PRV sealing performances. For the PRV subjected to inner pressure, the calculation results show that the location of maximum contact press on the sealing ring varies from the outer region to the inner region when the inner pressure increases from 1 to 7 MPa. The PRV with a more flexible disc exhibits a higher maximum contact press, thus resulting in a better sealing performance. For the PRV subjected to impact load in the case of re-closing process, the effects of disc flexibility on the PRV sealing performance was also studied. The finite calculation results indicate that the maximum plastic deformation is located in the outer region of the disc sealing ring and the sliding was occurred on the sealing ring, which is validated by experiments. The maximum plastic deformation and the displacement of sliding increase with a rise of disc flexibility. The plastic deformation and sliding has little effect on the sealing performance when the inner pressure close to setting pressure. As a result, the PRV with a higher disc flexibility showed a better sealing performance after re-closing impact process. The calculation results confirmed that reasonable disc flexibility is very important to guarantee a good sealing performance of PRV.