Search

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]

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]