Energy efficient vortex-enhanced water evaporation technology for concentrated brine management: Theory and process simulation evaluation.

Desalination drinking water systems and industrial processes generating high salinity streams require practical brine management options for disposal and/or treatment. Treatment most often involves large capacity brine concentrating processes, on the order of 2000 m3/day, that rely on water evaporation, vapor compression, and condensation. A new technology adds an aerosol-generating device to the evaporation step with the goal of energy efficient operation even at smaller scales. The principles behind the tornadic flowfield that breaks up and aerosolizes water as air and water flow over the machined surface in the device are introduced. Design of a 6.8 m3/day demonstration system, based on this new technology, producing a NaCl slurry (55 wt% solids) from a 22 wt% NaCl influent is described. Simulations of the system with three influent brine concentrations and three forms of final NaCl concentrate are presented and predicted energy usage is compared to estimates for conventional systems. By varying simulation process parameters, the heat transfer performance of the evaporator/condenser is identified as having a large impact on overall efficiency. The new system is anticipated to be most competitive, on an energy usage basis, with conventional concentrator/crystallizer systems when processing higher salinity brines and producing final concentrates containing precipitated NaCl.

Effect of membrane performance variability with temperature and feed composition on pervaporation and vapor permeation system design for solvent drying.

BACKGROUND: The presence of water in organic solvents and biofuels can complicate their production and reuse because many hydrophilic solvents form difficult-to-separate mixtures with water (e.g., azeotropes). Pervaporation (PV) and vapor permeation (V⋅P) remove water from such mixtures via selective solution-diffusion transport through a membrane material. A recent article reviewed design factors that impact the effectiveness of PV/V⋅P solvent dehydration processes (J. Chem. Technol. Biotechnol 95: 495-512 (2020)). For the sake of simplicity, the earlier work assumed constant membrane permeabilities. The objective here is to explore the impact of variable permeabilities on predictions of PV/V⋅P system performance. RESULTS: A multiparameter expression relating permeability to process conditions was incorporated into the spreadsheet calculators from the previous work. Use of the expression was demonstrated with literature ethanol/water PV data for a NaA zeolite material and two poly (vinyl alcohol) (PVA) membranes. The variable permeabilities of the membranes yielded membrane area requirements that were 20-30% different from those calculated using permeances fixed at either end of the target water range. The impact of composition-dependent permeabilities was most pronounced on the fraction of ethanol transferred to the permeate for the NaA membrane. CONCLUSION: The inclusion of membrane permeabilities that vary with fluid composition and temperature noticeably altered predictions of the membrane area required to carry out water removal from ethanol by PV and of the transfer of ethanol to the permeate stream. Unless a PV/V⋅P process is expected to operate at a constant temperature and in a narrow concentration range, process performance estimates would be improved by inclusion of concentration- and temperature-dependent permeabilities or permeances.

Review of Pervaporation and Vapor Permeation Process Factors Affecting the Removal of Water from Industrial Solvents.

A recent review article (J Chem Technol Biotechnol 94: 343-365 (2019)) identified several commercially-available permselective materials for drying organic solvents with pervaporation (PV) and vapor permeation (V·P) separation processes. The membrane materials included polymeric and inorganic substances exhibiting a range in the performance characteristics: water permeance, water/solvent selectivity, and maximum use temperature. This paper provides an overview of the factors affecting the design of PV/V·P processes utilizing these membranes to remove water from common organic solvents. Properties of the specific membrane and of the solvent substantially affect the PV/V·P separation. Equally important is the impact of operating parameters on the overall separation. To study these impacts, simplified process performance equations and detailed spreadsheet calculations were developed for single-pass and recirculating batch PV systems and for single-pass V·P systems. Estimates of membrane area, permeate concentration, solvent recovery, permeate condenser temperatures, and heating requirements were calculated. Process variables included: solvent type, water permeance, water/solvent selectivity, initial and final water concentrations, operating temperature (PV) or feed pressure (V·P), temperature drop due to evaporation (PV) or feed-side pressure drop (V·P), and permeate pressure. The target solvents considered were: acetonitrile, 1-butanol, N,N-dimethyl formamide, ethanol, methanol, methyl isobutyl ketone, methyl tert-butyl ether, tetrahydrofuran, acetone, and 2-propanol.

Review: Membrane Materials for the Removal of Water from Industrial Solvents by Pervaporation and Vapor Permeation.

Organic solvents are widely used in a variety of industrial sectors. Reclaiming and reusing the solvents may be the most economically and environmentally beneficial option for managing spent solvents. Purifying the solvents to meet reuse specifications can be challenging. For hydrophilic solvents, water must be removed prior to reuse, yet many hydrophilic solvents form hard-to-separate azeotropic mixtures with water. Such mixtures make separation processes energy intensive and cause economic challenges. The membrane processes pervaporation (PV) and vapor permeation (VP) can be less energy intensive than distillation-based processes and have proven to be very effective in removing water from azeotropic mixtures. In PV/VP, separation is based on the solution-diffusion interaction between the dense permselective layer of the membrane and the solvent/water mixture. This review provides a state-of-the-science analysis of materials used as the selective layer(s) of PV/VP membranes in removing water from organic solvents. A variety of membrane materials, such as polymeric, inorganic, mixed matrix, and hybrid, have been reported in the literature. A small subset of these are commercially available and highlighted here: poly(vinyl alcohol), polyimides, amorphous perfluoro polymers, NaA zeolites, chabazite zeolites, T-type zeolites, and hybrid silicas. The typical performance characteristics and operating limits of these membranes are discussed. Solvents targeted by the U.S. Environmental Protection Agency for reclamation are emphasized and ten common solvents are chosen for analysis: acetonitrile, 1-butanol, N,N-dimethyl formamide, ethanol, methanol, methyl isobutyl ketone, methyl tert-butyl ether, tetrahydrofuran, acetone, and 2-propanol.

Review: Water recovery from brines and salt-saturated solutions: operability and thermodynamic efficiency considerations for desalination technologies.

BACKGROUND: When water is recovered from a saline source, a brine concentrate stream is produced. Management of the brine stream can be problematic, particularly in inland regions. An alternative to brine disposal is recovery of water and possibly salts from the concentrate. RESULTS: This review provides an overview of desalination technologies and discusses the thermodynamic efficiencies and operational issues associated with the various technologies particularly with regard to high salinity streams. CONCLUSION: Due to the high osmotic pressures of the brine concentrates, reverse osmosis, the most common desalination technology, is impractical. Mechanical vapor compression which, like reverse osmosis, utilizes mechanical work to operate, is reported to have the highest thermodynamic efficiency of the desalination technologies for treatment of salt-saturated brines. Thermally-driven processes, such as flash evaporation and distillation, are technically able to process saturated salt solutions, but suffer from low thermodynamic efficiencies. This inefficiency could be offset if an inexpensive source of waste or renewable heat could be used. Overarching issues posed by high salinity solutions include corrosion and the formation of scales/precipitates. These issues limit the materials, conditions, and unit operation designs that can be used.

Significance of dissolved methane in effluents of anaerobically treated low strength wastewater and potential for recovery as an energy product: A review.

The need for energy efficient Domestic Wastewater (DWW) treatment is increasing annually with population growth and expanding global energy demand. Anaerobic treatment of low strength DWW produces methane which can be used to as an energy product. Temperature sensitivity, low removal efficiencies (Chemical Oxygen Demand (COD), Suspended Solids (SS), and Nutrients), alkalinity demand, and potential greenhouse gas (GHG) emissions have limited its application to warmer climates. Although well designed anaerobic Membrane Bioreactors (AnMBRs) are able to effectively treat DWW at psychrophilic temperatures (10-30 °C), lower temperatures increase methane solubility leading to increased energy losses in the form of dissolved methane in the effluent. Estimates of dissolved methane losses are typically based on concentrations calculated using Henry's Law but advection limitations can lead to supersaturation of methane between 1.34 and 6.9 times equilibrium concentrations and 11-100% of generated methane being lost in the effluent. In well mixed systems such as AnMBRs which use biogas sparging to control membrane fouling, actual concentrations approach equilibrium values. Non-porous membranes have been used to recover up to 92.6% of dissolved methane and well suited for degassing effluents of Upflow Anaerobic Sludge Blanket (UASB) reactors which have considerable solids and organic contents and can cause pore wetting and clogging in microporous membrane modules. Microporous membranes can recover up to 98.9% of dissolved methane in AnMBR effluents which have low COD and SS concentrations. Sequential Down-flow Hanging Sponge (DHS) reactors have been used to recover between 57 and 88% of dissolved methane from Upflow Anaerobic Sludge Blanket (UASB) reactor effluent at concentrations of greater than 30% and oxidize the rest for a 99% removal of total dissolved methane. They can also remove 90% of suspended solids and COD in UASB effluents and produce a high quality effluent. In situ degassing can increase process stability, COD removal, biomass retention, and headspace methane concentrations. A model for estimating energy consumption associated with membrane-based dissolved methane recovery predicts that recovered dissolved and headspace methane may provide all the energy required for operation of an anaerobic system treating DWW at psychrophilic temperatures.

Multi-stage continuous culture fermentation of glucose-xylose mixtures to fuel ethanol using genetically engineered Saccharomyces cerevisiae 424A.

Multi-stage continuous (chemostat) culture fermentation (MCCF) with variable fermentor volumes was carried out to study the utilization of glucose and xylose for ethanol production via mixed sugar fermentation (MSF). Variable fermentor volumes were used to enable enhanced sugar utilization, accounting for differences in glucose and xylose utilization rates. Saccharomyces cerevisiae 424A-LNH-ST was used for fermentation of glucose-xylose mixtures. The dilution rates employed for continuous fermentation were based on earlier batch kinetic studies of ethanol production and sugar utilization. With a feed containing approximately 30 g L(-1) glucose and 15 g L(-1) xylose, cell washout was observed at a dilution rate of 0.8 h(-1). At dilution rates below 0.5 h(-1), complete glucose utilization was observed. Xylose consumption in the first-stage 1 L reactor was only 37% at the lowest dilution rate studied, 0.0 5h(-1). At this same flow rate, xylose consumption rose to 69% after subsequently passing through 3 and 1 L reactors in series, primarily due to the longer residence time in the 3 L reactor (0.0167 h(-1) dilution rate).

Kinetics of growth and ethanol production on different carbon substrates using genetically engineered xylose-fermenting yeast.

Saccharomyces cerevisiae 424A (LNH-ST) strain was used for fermentation of glucose and xylose. Growth kinetics and ethanol productivity were calculated for batch fermentation on media containing different combinations of glucose and xylose to give a final sugar concentration of 20+/-0.8 g/L. Growth rates obtained in pure xylose-based medium were less than those for media containing pure glucose and glucose-xylose mixtures. A maximum specific growth rate micro(max) of 0.291 h(-1) was obtained in YPD medium containing 20 g/L glucose as compared to 0.206 h(-1) in YPX medium containing 20 g/L xylose. In media containing combinations of glucose and xylose, glucose was exhausted first followed by xylose. Ethanol production on pure xylose entered log phase during the 12-24h period as compared to the 4-10h for pure glucose based medium using 2% inoculum. When glucose was added to fermentation flasks which had been initiated on a pure xylose-based medium, the rate of xylose usage was reduced indicating cosubstrate inhibition of xylose consumption by glucose.

Ethanol, acetic acid, and water adsorption from binary and ternary liquid mixtures on high-silica zeolites.

Adsorption isotherms were measured for ethanol, acetic acid, and water adsorbed on high-silica ZSM-5 zeolite powder from binary and ternary liquid mixtures at room temperature. Ethanol and water adsorption on two high-silica ZSM-5 zeolites with different aluminum contents and a high-silica beta zeolite were also compared. The amounts adsorbed were measured using a recently developed technique that accurately measures the changes in adsorbent/liquid mixture density and liquid concentration. This technique allows the adsorption of each compound in a liquid mixture to be measured. Adsorption data for binary mixtures were fit with the dual-site extended Langmuir model, and the parameters were used to predict ternary adsorption isotherms for each compound with reasonable accuracy. In ternary mixtures, acetic acid competed with ethanol and water for adsorption sites and reduced ethanol adsorption more than it reduced water adsorption.

Recent advances in VOCs removal from water by pervaporation.

Pervaporation (PV) is a separation process in which minor components of a liquid mixture are preferentially transported by partial vaporization through a non-porous permselective (selectively permeable) membrane. PV is an emerging technology in environment cleanup operations, especially in the removal of volatile organic compounds (VOCs) from industrial wastewaters or contaminated groundwaters. Current state of PV membrane development in VOC removal and improvement in process engineering, and better understanding of the interactions between VOCs and membrane materials are reviewed. Among PV process parameters documented here are process temperature, permeate pressure, feed concentration, and feed flow rate. The effects of these parameters on PV selectivity and permeation flux have been studied extensively and these studies have borne fruit in a better understanding of many aspects of PV processes. The challenge in implementing PV in practical operations lies in the further enhancement of membrane quality for specific VOCs as well as improved management and control of possible adverse hurdles coming from real systems.