Enrico Drioli

Membrane Distillation and Related Operations—A Review

Abstract Membrane contactors represent an emerging technology in which the membrane is used as a tool for inter phase mass transfer operations: the membrane does not act as a selective barrier, but the separation is based on the phase equilibrium. In principle, all traditional stripping, scrubbing, absorption, evaporation, distillation, crystallization, emulsification, liquid‐liquid extraction, and mass transfer catalysis processes can be carried out according to this configuration. This review, specifically addressed to membrane distillation (MD), osmotic distillation (OD), and membrane crystallization (MCr), illustrates the fundamental concepts related to heat and mass transport phenomena through microporous membranes, appropriate membrane properties, and module design criteria. The most significant applications of these novel membrane operations, concerning pure/fresh water production, wastewater treatment, concentration of agro food solutions, and concentration/crystallization of organic and biological solutions, are also presented and discussed.

Biocatalytic membrane reactors: applications and perspectives.

Membranes and biotechnological tools can be used for improving traditional production systems to maintain the sustainable growth of society. Typical examples include: new and improved foodstuffs, in which the desired nutrients are not lost during thermal treatment; novel pharmaceutical products with well-defined enantiomeric compositions; and the treatment of waste-water, wherein pollution by traditional processes is a problem.

Treatment of aqueous effluents of the leather industry by membrane processes: A review

Abstract A general overview on the potentiality of membrane processes in the treatment of aqueous solutions coming from the leather industry is reported. The wet operations of the leather cycle which can be combined with or modified by membrane processes, such as microfiltration, ultrafiltration (UF), nanofiltration (NF) and reverse osmosis, have been described on the basis of consolidated applications and experimental tests on laboratory and industrial pilot scale. Some new applications are also proposed. The membranes and modules employed for the treatment of the effluents, pretreatment of fluids, cleaning procedures and fluid dynamic conditions in experimental applications are reported and discussed. An outline of direct and indirect energy analysis of tanning operations and the results of a mathematical model applied to the degreasing step are also presented. The integrated membrane processes described permit to rationalize the tanning cycle realizing the recovery and the recycle of several chemicals utilized in the tanneries. A reduction of environmental impact, a simplification of cleaning-up processes of wastewaters, an easy re-use of sludges, a decrease of disposal costs, a saving of chemicals and water and of direct and indirect energy are some advantages coming from the described membrane operations. In the future a wider application of the more consolidated membrane processes in this field is expected in the plant innovation phase of a tanning factory.

Direct contact membrane distillation: modelling and concentration experiments

Abstract Direct contact membrane distillation (DCMD) process was chosen to produce a highly concentrated apple juice using hollow fiber modules. A high 64°Brix concentration was achieved. The trans-membrane driving force decreased with increasing extra-fiber temperature but increased with higher feed and distillate flow rates in the intra- and extra-fiber volumes, respectively. Flux inversion was sensitive to small differences in temperature between the intra- and extra-fiber volumes and could be prevented by increasing the intra-fiber feed temperature by 2–4°C. Flux rates were dependent upon the temperature polarisation coefficient (TPC) and the effect of the concentration polarisation coefficient (CPC) was negligible. Trans-membrane flux was also significantly increased by thermal-osmotic distillation (TOD) using a high concentration of CaCl 2 as the permeate solution. A new model describing the fluid dynamics and membrane behaviour within the DCMD system is presented. In particular, the influence of various properties of membrane morphology, such as the distribution of pores of different diameters and elastic and other mechanical properties upon flux were taken into account in this model.

Studies on various reactor configurations for coupling photocatalysis and membrane processes in water purification

General aspects and perspectives of heterogeneous photocatalysis for the treatment of polluted aqueous effluents are presented. Some experimental results obtained by using various configurations of photocatalytic membrane reactors (PMRs) are reported. The configurations studied were: (i) irradiation of the cell containing the membrane, with three sub-cases: (i1) catalyst deposited on the membrane; (i2) catalyst in suspension, confined by means of the membrane; (i3) entrapment of the photocatalyst in a PSF membrane; (ii) irradiation of the re-circulation tank and catalyst in suspension confined by means of the membrane. In the case “(i)”, a preliminary investigation of membrane stability under UV irradiation was carried out. PMR characterization in photodegradation tests was mainly carried out in a recycle batch membrane reactor and, in some cases, in a continuous membrane reactor. The comparison between the first set of results, where the membrane was used only as a support for the photocatalyst, and the newest ones, where the adsorption of the pollutant on the membrane and membrane rejection play an important role in the global reactor performance, showed interesting perspectives and synergy for coupling photocatalysis and membranes. Furthermore, the configuration where the re-circulation tank was irradiated and the catalyst was used in suspension, appeared to be the most interesting for industrial applications. For example, in reactor optimization, high irradiation efficiency, high membrane permeate flowrate and selectivity can be obtained by sizing separately the “photocatalytic system” and the “membrane system” and taking advantage of all the best research results for each system.

Recovery and concentration of polyphenols from olive mill wastewaters by integrated membrane system.

The purpose of this work was to analyse the potentialities of an integrated membrane system for the recovery, purification and concentration of polyphenols from olive mill wastewater (OMW). The proposed system included some well-known membrane operations such as microfiltration (MF) and nanofiltration (NF), as well as others not yet investigated for this specific application, such as osmotic distillation (OD) and vacuum membrane distillation (VMD). The OMW was directly submitted to a MF operation without preliminary centrifugation. This step allowed to achieve a 91% and 26% reduction of suspended solids and total organic carbon (TOC), respectively. Moreover, 78% of the initial content of polyphenols was recovered in the permeate stream. The MF permeate was then submitted to a NF treatment. Almost all polyphenols were recovered in the produced permeate solution, while TOC was reduced from 15 g/L to 5.6 g/L. A concentrated solution enriched in polyphenols was obtained by treating the NF permeate by OD. In particular, a solution containing about 0.5 g/L of free low molecular weight polyphenols, with hydroxytyrosol representing 56% of the total, was produced by using a calcium chloride dihydrate solution as brine. The obtained solution is of interest for preparing formulations to be used in food, cosmetic and pharmaceutical industry. Besides the OD process, VMD was applied as another way for concentrating the NF permeate and the performance of both processes was compared in terms of evaporation fluxes.

Permeation through a heterogeneous membrane : the effect of the dispersed phase

By the incorporation of filler materials in a membrane one may change the permeability of the overall, dense membrane towards various gases, vapours and/or liquids. The influence of solid fillers dispersed in a polymeric matrix on permeability, diffusivity and solubility has been studied extensively in literature. In this paper the influence of the filler on overall membrane permeability resulting in an upper and a lower limit of the permeability given the filler content and the permeability of the continuous phase will be studied theoretically. From this analysis the change in membrane selectivity towards a gas mixture by incorporation of a filler, relative to the selectivity of the pure matrix membrane, can be obtained. The maximum change in membrane selectivity is a function of the filler content only, i.e. irrespective of matrix and filler permeabilities. The difficulties often encountered in estimating the filler permeability from experimental permeability data using membranes with varying amounts of the filler will be discussed, and possible solutions will be given using theoretical and experimental data.

An analysis of the performance of membrane reactors for the water–gas shift reaction using gas feed mixtures

Abstract The water–gas shift (WGS) reaction in membrane reactors has been widely studied by several authors. From these works, the increase of the CO conversion above the equilibrium values appears to be possible when hydrogen is removed through the membrane. However, to date, this feasibility has been verified mostly when feeding pure reagents to the reactor, although in an industrial context the feed normally contains several other compounds. The objective of this work has been to analyse the effect of the feed composition on the membrane reactor efficiency in order to determine the best conditions in terms of CO conversion. At this purpose, experimental tests with mixtures of different compositions have been carried out in three different systems of reaction: (1) traditional fixed-bed reactor; (2) membrane reactor with mesoporous ceramic membrane; (3) membrane reactor with palladium membrane. The experiments included permeation (for the membrane reactors) and reaction tests. The experimental results obtained with the various systems of reaction have been compared. A mathematical model has been also formulated for the different type of reactors used in order to verify the experimental results obtained. From the work carried out it can be concluded that by using the palladium membrane reactor it is possible to overcome the equilibrium conversion. Moreover, a complete conversion has been achieved for one of the mixtures fed to the reactor.

Remediation of textile effluents by membrane based treatment techniques: A state of the art review

The textile industries hold an important position in the global industrial arena because of their undeniable contributions to basic human needs satisfaction and to the world economy. These industries are however major consumers of water, dyes and other toxic chemicals. The effluents generated from each processing step comprise substantial quantities of unutilized resources. The effluents if discharged without prior treatment become potential sources of pollution due to their several deleterious effects on the environment. The treatment of heterogeneous textile effluents therefore demands the application of environmentally benign technology with appreciable quality water reclamation potential. These features can be observed in various innovative membrane based techniques. The present review paper thus elucidates the contributions of membrane technology towards textile effluent treatment and unexhausted raw materials recovery. The reuse possibilities of water recovered through membrane based techniques, such as ultrafiltration and nanofiltration in primary dye houses or auxiliary rinse vats have also been explored. Advantages and bottlenecks, such as membrane fouling associated with each of these techniques have also been highlighted. Additionally, several pragmatic models simulating transport mechanism across membranes have been documented. Finally, various accounts dealing with techno-economic evaluation of these membrane based textile wastewater treatment processes have been provided.

Effect of thermal history on water sorption, elastic properties and the glass transition of epoxy resins

Abstract The DGEBA/TETA (diglycidyl ether of bisphenol-A/triethylene tetramine) system was examined in postcuring conditions at 100°C for 3 and 6 days. Sorption kinetics and equilibria at different temperatures and mechanical tests have been performed on the two sets of samples. Thermal treatment of the epoxy resin containing sorbed water affects its subsequent water sorption characteristics, elastic modulus and glass transition temperature. Attention has also been given to the effects on solubility on thermal history in the presence of water. It was observed that the saturation values in such systems are determined once the higher temperature of the thermal cycle is defined. The differences in solubility of samples with different hygrothermal history are explained in terms of microcavities that can be formed by effect of crazing in the plasticized system exposed to high temperatures.