Dissolved methane recovery from anaerobic effluents using hollow fibre membrane contactors

Hollow fibre membrane contactor (HFMC) systems have been studied for the desorption of dissolved methane from both analogue and real anaerobic effluents to ascertain process boundary conditions for separation. When using analogue effluents to establish baseline conditions, up to 98.9% methane removal was demonstrated. Elevated organic concentrations have been previously shown to promote micropore wetting. Consequently, for anaerobic effluent from an upflow anaerobic sludge blanket reactor, which was characterised by a high organic concentration, a nonporous HFMC was selected. Interestingly, mass transfer data from real effluent exceeded that produced with the analogue effluent and was ostensibly due to methane supersaturation of the anaerobic effluent which increased the concentration gradient yielding enhanced mass transfer. However, at high liquid velocities a palpable decline in removal efficiency was noted for the nonporous HFMC which was ascribed to the low permeability of the nonporous polymer provoking membrane controlled mass transfer. For anaerobic effluent from an anaerobic membrane bioreactor (MBR), a microporous HFMC was used as the permeate comprised only a low organic solute concentration. Mass transfer data compared similarly to that of an analogue which suggests that the low organic concentration in anaerobic MBR permeate does not promote pore wetting in microporous HFMC. Importantly, scale-up modelling of the mass transfer data evidenced that whilst dissolved methane is in dilute form, the revenue generated from the recovered methane is sufficient to offset operational and investment costs of a single stage recovery process, however, the economic return is diminished if discharge is to a closed conduit as this requires a multi-stage array to achieve the required dissolved methane consent of 0.14 mg l−1.Yorkshire Water; Severn Trent Water; Anglian Water; Northumbrian Water; EPSR

Dynamic response of ultrathin highly dense ZIF-8 nanofilms

Ultrathin ZIF-8 nanofilms are prepared by facile step-by-step dip coating. A critical withdrawal speed allows for films with a very uniform minimum thickness. The high refractive index of the films denotes the absence of mesopores. The dynamic response of the films to CO2 exposure resembles behaviour observed for nonequilibrium organic polymers

Design and synthesis of ZIF-8 and zinc-imidazole nanofilms

Over the last decade significant efforts have been devoted to the synthesis of zeolitic imidazolate framework (ZIF) films. For practical purposes such as membrane separations and chemical sensing the films must be ultrathin and often continuous on a microscopic level. Several approaches have been proposed, with dip coating offering significant advantages over more complex and expensive techniques. However, studies demonstrating nanoscale control of film density, morphology and thickness are lacking. Within the scope of this thesis, the fabrication of thin ZIF-8 and zinc-imidazole (Zn(mIm)) nanofilms is investigated, aiming at a better understanding of the films formation during the facile dip coating process. Significant attention is dedicated to the identification of the optimal synthesis parameters to fabricate ultrathin nanofilms and demonstrate their potential in chemical sensing and membrane separations. The study is divided into three primary areas and include investigation of: (i) crystalline ZIF-8 thin films derived from colloidal solutions; (ii) partially-crystalline pseudopolymorphic Zn(mIm) nanofilms; and (iii) composite Zn(mIm)@polymer nanofilms. In situ spectroscopic ellipsometry is employed in the investigations of films' morphologies and their dynamic response in the vicinity of the guest gas and vapour penetrants. The results show that films' uniformity and thickness is mainly controlled by the withdrawal speed of the support from the solutions, regardless of the dip coating technique utilised. Targeting ultrathin (<200 nm) partially-crystalline nanofilms that are continuous on a microscopic level requires simultaneous change of the reactants ratio and substitution of the metal precursor. Investigation of the intrinsic properties of Zn(mIm) nanofilms reveals the ability for the material to withstand up to 55 bar pressure and prolonged exposure to CO2 plasticising penetrant, outperforming state-of-the-art industrial polymeric thin films. Zn(mIm) nanofilms also display kinetic diameter-dependent selectivity towards alcohol vapours, indicating their potential in sensing and separation of alcohol vapours. The obtained results can be used as a guide for future development and scale up of industrial nanofilms.nrpages: 250status: publishe