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The process intensification in carbonylation of formaldehyde by active and passive enhancement was investigated in stirred tank reactor and membrane contactor, respectively. The increase of rotational speed and decrease of reaction solution volume was advantageous to the yield of glycolic acid in active strengthening experiments, indicating that the reaction was greatly affected by the mass transfer of CO. In passive reinforcement mode, the membrane contactor composed of PTFE hollow fibers with inner diameter of 0.85 mm or 0.42 mm was used as a novel reactor to improve the process mass transfer. The effects of reaction temperature, operation pressure, reaction time and reactant concentration were systematically studied. The results showed that membrane contactor was an effective reactor for the carbonylation of formaldehyde compared to the conventional tank reactor. This study provided a reference for the process intensification of similar gas-liquid reactions. [ABSTRACT FROM AUTHOR]

The batch and continuous synthesis of glycolic acid via carbonylation of formaldehyde using high-temperature and high-pressure poly(tetrafluoroethylene) (PTFE) membrane contactor was demonstrated in this paper. The experiments in conventional stirred tank reactor were also conducted for comparison. The results showed that the yield of glycolic acid was significantly improved in membrane contactor system compared to the stirred tank reactor. At reaction temperature of 120 °C and reaction pressure of 5.0 MPa, the yield of glycolic acid was higher than 90% when the reaction time was 1 h, while it was only about 45% in the conventional stirred tank reactor. The enhancement of yield was due to the improvement of mass transfer or dispersion of CO in membrane contactor system, which could provide larger gas-liquid contact area and shorter mass transfer distance. The stability of PTFE hollow fibre membranes was also investigated by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), liquid entry pressure (LEP), bubble point (BP) and contact angle (CA) measurements. The characterizations indicated that PTFE membranes exhibited good chemical and thermal stability in this reaction system. This study provided new idea and reference for the carbonylation of formaldehyde and similar gas-liquid reactions. • Batch and continuous synthesis of glycolic acid via carbonylation of formaldehyde in membrane contactor was demonstrated. • Mass transfer of CO is greatly enhanced in membrane contractor system compared to the conventional tank reactor. • Membrane contactor can provide larger contact area and shorter diffusion path for gas-liquid reaction. • PTFE hollow fibers exhibited good stability under high temperature and high pressure conditions. [ABSTRACT FROM AUTHOR]

Nafion-PTFE hollow fiber composite membranes were fabricated and applied in vacuum membrane distillation (VMD) process to improve the anti-fouling and anti-wetting performance in the presence of oil and surfactant. The composite membrane exhibited an underwater super-oilphobic property according to the contact angle test. The VMD performance when treating saline feed containing 3.5 wt% NaCl and 1000 ppm mineral oil for the composite membrane behaved a stable flux for 40 h. In construct, an immediate and sharply-declined flux was observed for the pristine PTFE, indicating the significant improvement in the anti-fouling property. Meanwhile, the composite membrane also alleviated the wetting phenomena caused by the surfactant comparing with the pristine PTFE membrane, and the Nafion-PTFE composite membrane behaves a stable flux and high salt rejection higher than 99.99% for 60 h treating saline feed containing O/W emulsions. The pressure depression effect of the Nafion layer on the mass transfer was analyzed. It was found that the depression could be reduced with the increasing of the feed temperature and the enhancement of the corresponding effective pore diameter of the Nafion layer, that the pressure depression factor decreased from 0.23 to 0.04 with the feed temperature increasing from 60 °C to 75 °C. Image 1 • An asymmetric composite membrane with a thin Nafion layer on the outside of a PTFE membrane was fabricated for VMD. • The application of Nafion-PTFE membrane to VMD was first studied and reported. • The Nafion-PTFE composite membrane showed good anti-fouling and anti-wetting property. [ABSTRACT FROM AUTHOR]

• Membrane contactor was used as a gas-liquid separator in pressure swing process. • The two mass transfer mechanisms were analysed through calculation of viscous flux and mass transfer coefficients. • When integrated with membrane contactor for CO 2 absorption, stable and consistent performance was observed. A new method to regenerate high pressure CO 2 absorbent is presented in this paper, where PTFE hollow fiber membrane contactor was used as a gas–liquid separator in pressure swing process. CO 2 desorption happened in the membrane contactor at the same time. The two mass transfer mechanisms were analysed through calculation of viscous flux and mass transfer coefficients. Experimental results showed that CO 2 loading in regenerated absorbent increased with absorbent flow rate. This was due to decrease in membrane area available for CO 2 desorption, as most of the membrane area was utilized for gas-liquid separation. Co-current configuration exhibited higher CO 2 desorption driving force compared to counter-current configuration, hence its CO 2 loading in regenerated absorbent was lower. When integrated with membrane contactor for CO 2 absorption, stable and consistent performance was observed. Unlike conventional flash drum, membrane contactor did not have requirement on flashed gas velocity, because the membrane itself functioned as a screen to prevent fine liquid droplets from escaping the system along with flashed gas. Results from this study show that vessel size reduction up to 2.5 times could be achieved when PTFE membrane contactor was used, with absorbent regeneration energy as low as 0.94 GJ/ton CO 2. [ABSTRACT FROM AUTHOR]

• Deep CO 2 removal using high pressure membrane contactor was proven able to reduce CO 2 content to < 0.005 mol% level, meeting requirement for atural Gas process. • Liquid phase mass transfer resistance was the highest compared to membrane phase and gas phase, showing that liquid was the bottleneck for mass transfer. • High liquid velocity was favored for better liquid phase mass transfer, resulted in high L/G ratio in deep CO 2 removal using membrane contactor. • Liquid flow rate reduction could not reduce L/G effectively as this led to more reduction in CO flux than L/G. • Membrane module length increase was able to achieve 70% reduction in L/G, with only 16% reduction in flux, offering lower energy consumption compared to conventional packed column in LNG process. Membrane contactor is a technology that intensifies conventional absorption column. However, liquid-to-gas ratios (L/G) of membrane contactor in existing reports are much higher compared to CO 2 absorption column, which results in higher solvent circulation rate and higher consumption in heating energy. This makes the technology less attractive for deep CO 2 removal. Direct reduction of liquid flow rate was not effective in lowering down L/G. Experimental results showed that 50% reduction in liquid flow rate could reduce L/G by 25%, but the reduction in CO 2 flux (33%) was higher due to decrease in liquid phase mass transfer coefficient which was dependent on liquid velocity. An alternative method to reduce L/G through membrane module length increase was proven, where L/G was reduced 70% with only 16% flux reduction. The flux reduction was only observed when L/G dropped below 0.80 L/mol and it was due to depletion of unreacted amine for CO 2 absorption. The lowest L/G value obtained in this study was 36% lower than the conventional absorption column in liquefied natural gas (LNG) process, showing that membrane contactor technology is not only energy-viable and more compact for deep CO 2 removal, but it also offers energy saving advantage. [ABSTRACT FROM AUTHOR]

• A novel aqueous-organic membrane contactor process was applied. • The novel membrane contactor process was more favorable to treat low-ammonia-content feeds. • Accompanying water transport was avoided. Nafion-PTFE hollow fiber composite membranes were applied in the ammonia removal and recovery with a novel aqueous-organic membrane contactor (AOMC) process, in which an aqueous solution and an organic solution were separated by the composite membrane. A kerosene-diluted di-(2-ethylhexyl) phosphoric acid (D2EHPA) solution was used to receive the ammonia, which could be recycled and reused after regeneration by the stripping agent (a dilute solution of H 2 SO 4 , HNO 3 , or H 3 PO 4). The new-type membrane contactor can avoid the accompanying water transport in conventional membrane contactors. The effects of experimental factors including the pH, the velocity and the initial ammonia concentration of the feed on the overall mass transfer of the ammonia were investigated. Meanwhile, how the regeneration experiment parameters influenced the stripping ratio was also studied. The results showed that the AOMC process was more favorable to treat ammonia feed with low ammonia concentrations. The ammonia removal could be over 99% under certain conditions. Additionally, the ammonia was concentrated 26.4 times after four cycles. It was found that the accompanying water transport was non-negligible in the traditional aqueous-aqueous membrane contactor (AAMC) process when treating ammonia feed of low concentrations, with the maximum water flux two orders of magnitude higher than ammonia. [ABSTRACT FROM AUTHOR]

Polytetrafluoroethylene (PTFE) is considered as a promising material for membrane contactors due to its intrinsic hydrophobicity and excellent chemical stability. In most published works concerning CO 2 absorption, PTFE hollow fiber membranes with diameter larger than 1.2 mm even 2.0 mm were applied, which lost the advantage of membrane contactor in high specific surface area and also increased the mass transfer resistance. In this study, biogas purification by membrane contactor was systematically investigated based on the smaller-diameter PTFE hollow fibers (0.9 mm) developed recently in our laboratory. CH 4 –CO 2 (40%) mixture was used as simulated biogas, and deionized water was used as absorbent for all tests. The influence of module configuration, liquid flow pattern, membrane microstructure, and gas-liquid flow velocity on CO 2 removal performance were studied in detail. Moreover, the mass transfer resistance and CH 4 recovery rate were also discussed. CO 2 content in purified biogas could be below 3% by adjusting the operating parameters. CO 2 flux and overall mass transfer coefficient (K OV) under experimental conditions ranged from 0.61 × 10−3 to 1.35 × 10−3 mol/(m2. s) and from 1.67 × 10−5 to 6.34 × 10−5 m/s, respectively. Moreover, CO 2 removal performance was stable in an operation of 36 h. PTFE hollow fibers with smaller diameter exhibited preeminent CO 2 removal efficiency, which proved great application potential in biogas upgrading by membrane contactor. [Display omitted] • PTFE hollow fiber (diameter of 0.9 mm) for biogas upgrading by membrane contactor. • Weaving configuration design of membranes significantly improved mass transfer. • Effects of fluid flow pattern and membrane microstructure were also investigated. • Smaller-diameter PTFE membrane contactor exhibited good application potential. [ABSTRACT FROM AUTHOR]