Andrew G. Livingston

Sub–10 nm polyamide nanofilms with ultrafast solvent transport for molecular separation

Composite membranes for filtering solvents Much research has focused on finding membranes that can purify water or extract waste carbon dioxide. However, there is also a need for the removal of small molecules from organic liquids. Many existing processes are energy-intensive and can require large quantities of solvents. Karan et al. grew confined polymer layers on a patterned sacrificial support to give rippled thin films that were then placed on ceramic membranes (see the Perspective by Freger). The composite membrane showed high flux for organic solvents and good stability and was able to separate out small molecules with high efficiency. Science, this issue p. 1347; see also p. 1317 Thin, crumpled polymer films on ceramic supports are high-flux membranes for removing small molecules from organic fluids. [Also see Perspective by Freger] Membranes with unprecedented solvent permeance and high retention of dissolved solutes are needed to reduce the energy consumed by separations in organic liquids. We used controlled interfacial polymerization to form free-standing polyamide nanofilms less than 10 nanometers in thickness, and incorporated them as separating layers in composite membranes. Manipulation of nanofilm morphology by control of interfacial reaction conditions enabled the creation of smooth or crumpled textures; the nanofilms were sufficiently rigid that the crumpled textures could withstand pressurized filtration, resulting in increased permeable area. Composite membranes comprising crumpled nanofilms on alumina supports provided high retention of solutes, with acetonitrile permeances up to 112 liters per square meter per hour per bar. This is more than two orders of magnitude higher than permeances of commercially available membranes with equivalent solute retention.

High Flux Thin Film Nanocomposite Membranes Based on Metal–Organic Frameworks for Organic Solvent Nanofiltration

Thin-film nanocomposite membranes containing a range of 50-150 nm metal-organic framework (MOF) nanoparticles [ZIF-8, MIL-53(Al), NH2-MIL-53(Al) and MIL-101(Cr)] in a polyamide (PA) thin film layer were synthesized via in situ interfacial polymerization on top of cross-linked polyimide porous supports. MOF nanoparticles were homogeneously dispersed in the organic phase containing trimesoyl chloride prior to the interfacial reaction, and their subsequent presence in the PA layer formed was inferred by a combination of contact angle measurements, FT-IR spectroscopy, SEM, EDX, XPS, and TEM. Membrane performance in organic solvent nanofiltration was evaluated on the basis of methanol (MeOH) and tetrahydrofuran (THF) permeances and rejection of styrene oligomers (PS). The effect of different post-treatments and MOF loadings on the membrane performance was also investigated. MeOH and THF permeance increased when MOFs were embedded into the PA layer, whereas the rejection remained higher than 90% (molecular weight cutoff of less than 232 and 295 g·mol(-1) for MeOH and THF, respectively) in all membranes. Moreover, permeance enhancement increased with increasing pore size and porosity of the MOF used as filler. The incorporation of nanosized MIL-101(Cr), with the largest pore size of 3.4 nm, led to an exceptional increase in permeance, from 1.5 to 3.9 and from 1.7 to 11.1 L·m(-2)·h(-1)·bar(-1) for MeOH/PS and THF/PS, respectively.

CATALYTIC WET OXIDATION OF P-COUMARIC ACID: PARTIAL OXIDATION INTERMEDIATES, REACTION PATHWAYS AND CATALYST LEACHING

Abstract The catalytic oxidation of p -coumaric acid, a compound representative of the polyphenolic fraction typically found in olive processing and wine-distillery wastewaters, has been investigated using various homogeneous and heterogeneous catalysts. Experiments have been performed with homogeneous Fe 2+ , Cu 2+ , Zn 2+ and Co 2+ ions at pH = 1, and with metal oxide catalysts in suspension at pH 3.5, 7 and 12. Additional uncatalyzed experiments have been performed and the results are compared to those of the catalyzed runs. The temperature was 403 K and the oxygen partial pressure was 2.8 MPa in all runs. The distribution of the reaction intermediates was determined, using HPLC and GCMS as the main analytical techniques, and reaction pathways are speculated. It was found that the use of catalysts could increase the rate of destruction of p -coumaric acid compared to the uncatalyzed reaction, while the distribution of the intermediate compounds was strongly dependent on the pH of the solution. A CuO·ZnO Al 2 O 3 heterogeneous catalyst was found to be effective for the oxidation of p -coumaric acid although leaching of dissolved metals to the solution was found to occur. The stability of the heterogeneous catalysts was investigated by measuring the extent of metal leaching into the solution. The results are discussed with respect to the impact of various conditions (catalyst, pH) on the oxidation of p -coumaric acid and compared to those of the uncatalyzed reaction, studied in previous work.

Ethanol utilization by sulfate-reducing bacteria : An experimental and modeling study

A mixed culture of sulfate-reducing bacteria containing the species Desulfovibrio desulfuricans was used to study sulfate-reduction stoichiometry and kinetics using ethanol as the carbon source. Growth yield was lower, and kinetics were slower, for ethanol compared to lactate. Ethanol was converted into acetate and no significant carbon dioxide production was observed. A mathematical model for growth of sulfate-reducing bacteria on ethanol was developed, and simulations of the growth experiments on ethanol were carried out using the model. The pH variation due to sulfate reduction, and hydrogen sulfide production and removal by nitrogen sparging, were examined. The modeling study is distinct from earlier models for systems using sulfate-reducing bacteria in that it considers growth on ethanol, and analyzes pH variations due to the product-formation reactions.

Sustainability assessment of organic solvent nanofiltration: from fabrication to application

Can Organic Solvent Nanofiltration (OSN) be considered green? Is OSN greener than other downstream processing technologies? These are the two main questions addressed critically in the present review. Further questions dealt with in the review are as follows: What is the carbon footprint associated with the fabrication and disposal of membrane modules? How much solvent has to be processed by OSN before the environmental burden of OSN is less than the environmental burden of alternative technologies? What are the main challenges for improving the sustainability of OSN? How can the concept of Quality by Design (QbD) improve and assist the progress of the OSN field? Does the scale have an effect on the sustainability of membrane processes? The green aspects of OSN membrane fabrication, processes development and scale-up as well as the supporting concept of QbD, and solvent recovery technologies are critically assessed and future research directions are given, in this review.

Microbial sulfate reduction in a liquid-solid fluidized bed reactor.

A liquid-solid fluidized bed reactor was used to carry out sulfate reduction with a mixed culture of sulfate reducing bacteria. The bacteria were immobilized on porous glass beads. Stable fluidized bed operation with these biofilm-coated beads was possible. The low specific gravity of the hydrated beads allowed operation at low liquid recirculation rates. H(2)S level in the reactor was controlled by N(2) sparging, which also served as the location for liquid feed and removal. Ethanol was used as the electron donor/carbon source for the bacteria. Sulfate reduction rates up to 6.33 g sulfate L(-1) day(-1) were attained in the reactor at a hydraulic retention time of 5.1 h. The effect of hydraulic retention time and biomass loading on the beads, on reactor performance, and efficiency were examined. The efficiency of sulfate reduction increases considerably as the hydraulic retention increases, until the bacteria became very strongly substrate-limited at 55h HRT. The effect of bead biomass loading on bed expansion at various liquid superficial velocities was studied. A model for the reactor was developed. Simulations of the continuous flow experiments indicate that the model can describe the system well, and thus could be used in the design/scale-up of such reactors. The model suggests that a significant increase in the sulfate reduction capacity of the system is possible by increasing the volume of the bed relative to the total liquid volume of the system.

Environmentally friendly route for the preparation of solvent resistant polyimide nanofiltration membranes

Organic Solvent Nanofiltration (OSN) is an emerging membrane separation process with the potential to replace traditional separation techniques. Its advantages include lower energy consumption than alternatives such as distillation, easy up scaling and flexibility. However, manufacturing OSN membranes involves a number of stages contributing towards the discharge of hazardous chemicals as waste. Thus the environmental advantages of employing OSN are to some extent cancelled out by the waste released during OSN membrane production. This paper describes a process for the preparation of polyimide integrally skinned asymmetric OSN membranes with adjustable molecular weight cut off (MWCO). Previously reported methods for producing polyimide based OSN membranes are modified in the presented work without compromising the performance of the membranes. The toxic solvents used to form polymer dope solution, i.e.dimethylformamide (DMF)/1,4-dioxane are replaced by an environmentally friendly dimethyl sulfoxide (DMSO)/acetone solvent system. In order to further diminish the environmental impact, isopropanol was successfully replaced with water in the crosslinking step. Scanning electron microscope images revealed that membranes with spongy matrix without macrovoids were obtained regardless the DMSO/acetone ratio.

Observations on solvent flux and solute rejection across solvent resistant nanofiltration membranes

Abstract Organic solvent nanofiltration is an emerging technology made possible by the recent development of solvent resistant nanofiltration (SRNF) membranes. These membranes have many potential applications from continuous operation over many months in refinery systems [1,2] to short term operation for a few hours in batch chemical processes [3]. In this paper, solvent flux decline and membrane separation properties are investigated (including their dependence on pressure), using methanol with quaternary alkyl ammonium bromide salts with molecular weights (MW) in the range 322 to 547 Daltons as solutes. The membranes are characterised in terms of an equivalent uniform pore size using three simple pore flow models: Ferry model, Steric Hindrance Pore (SHP) model and Verniory model.

Aqueous-aqueous extraction of organic pollutants through tubular silicone rubber membranes

The extraction of organic pollutants from one dilute aqueous solution to another dilute aqueous solution through silicone rubber membranes has been investigated. Overall mass transfer coefficients have been measured using a single membrane tube held in a glass module, and have been described using a resistances in series model. This has allowed the relative contributions of the liquid film boundary layer resistances and the membrane resistance to be elucidated, and has shown that both liquid film resistances and permeation through the membrane itself can limit the overall extraction rate. Under some conditions the membrane resistance can become negligible relative to the liquid film resistances. An important parameter for determining the magnitude of the membrane resistance is the membrane/aqueous phase partition coefficient, K. This parameter can be estimated from the Hildebrand solubility parameter of an organic compound, or quickly ascertained by performing a set of simple adsorption experiments.

Environmental impact considerations in the optimal design and scheduling of batch processes

Abstract A systematic methodology for incorporating ecological considerations in the optimal design and scheduling of batch/semi-continuous processes is presented in this paper. The methodology embeds principles from Life Cycle Analysis (LCA) within a general multi-objective formulation for the design of multipurpose batch plants, with process economics and environmental impact as distinct design objectives. An expanded boundary is defined around the process of interest, for the consistent evaluation of environmental impact, which is quantified by a set of metrics (for air, water pollution, global warming etc.). Examples from the dairy industry are presented to demonstrate the potential of the methodology to assist in arriving at environmentally friendly and economically favourable batch designs and schedules. Issues regarding the use of alternative cleaning and legislation policies on batch operation and design are also discussed.