It is well-known that spinning of defect-free asymmetric polyimide hollow fibers is promoted by using high polymer molecular weight. On the other hand, effects of polymer molecular weight on microstructure and separation performance of dense film 6FDA-based polyimide membranes relevant to sheath layers of composite membranes are less well-explored. In this work, gas sorption, diffusion and permeation of CO2, 2 , N2 2 and CH4 4 for 6FDA-DAM dense films are considered for 45 kDa and 176 kDa weight average molecular weights. Such molecular weights are relevant for practical hollow fiber spinning of membranes. Earlier results for polystyrene samples show similar trends in dual mode sorption model results like those noted here for the 6FDA-DAM polyimide case; however, effects on permeation like those considered here were not addressed for the polystyrene case. Here we also address actual pure and mixed gas CO2 2 and CH4 4 permeation and show higher free volumes, higher gas permeability but lower 50:50 CO2/CH4 2 /CH 4 selectivity associated with the higher molecular weight sample. Analysis using the self-consistent dual-mode sorption and transport models help understand the observed trends. Our results suggest denser packing of polymer segments exists in the Henry's law environment of the low molecular weight sample. Moreover, the higher polymer segmental packing in the Henry's law environment suppresses CO2 2 plasticization with a dual-mode microstructure controlling separation performance and plasticization behavior for this important member of the 6FDA polyimide family. We show evidence of effects of charge transfer complexes as possible main features in these trends. These dense film results help guide future work on dense sheath layers on composite hollow fiber membranes.

Asymmetric carbon molecular sieve (CMS) hollow fiber membranes with tunable micro- and macro-structural morphologies for energy efficient propylene-propane separation are reported here. A sub-glass transition temperature (sub-Tg) thermal oxidative crosslinking strategy enables simultaneous optimization of the intrinsic molecular sieving properties while also reducing the thickness of the CMS "skin" derived from the 6FDA : BPDA/DAM polyimide precursors. Such synergistic tuning of CMS microstructure and macroscopic morphology of CMS hollow fibers enables significantly increased propylene permeance (reaching 186.5 GPU) while maintaining an appealing propylene/propane selectivity of 13.3 for 50/50 propylene/propane mixed gas feeds. Our findings reveal a more refined and versatile tool than available with previous O2-doping pretreatments. The advanced approach here should be broadly useful to other polyimide precursors and diverse gas pairs.

Nanoparticles can suppress asymmetric precursor support collapse during pyrolysis to create carbon molecular sieve (CMS) membranes. This advance allows elimination of standard sol-gel support stabilization steps. Here we report a simple but surprisingly important thermal soaking step at 400 °C in the pyrolysis process to obtain high performance CMS membranes. The composite CMS membranes show CO2 /CH4 (50 : 50) mixed gas feed with an attractive CO2 /CH4 selectivity of 134.2 and CO2 permeance of 71 GPU at 35 °C. Furthermore, a H2 /CH4 selectivity of 663 with H2 permeance of 240 GPU was achieved for promising green energy resource-H2 separation processes.

Polyimide-derived carbon molecular sieve (CMS) membranes mark an important step for various current, key energy-intensive separations. The excellent separation performance combined with economical scalability make CMS membranes ready to enable energy-transition-focused gas separations.

Carbon molecular sieve (CMS) membranes are attractive candidates to meet requirements for challenging gas separations. The added ability to maintain such intrinsic properties in an asymmetric morphology with a structure that we term a "Pseudo Wheel+Hub & Spoke" asymmetric form offers new opportunities. For CMS membrane, specifically, the structure provides both selective layer support and low flow resistance even for high feed pressures and fluxes in CO2 removal from natural gas. This capability is unavailable to even rigid glassy polymers due to the much higher modulus of CMS materials. Combining precursor asymmetric hollow fiber formation and optimized pyrolysis creates a defect free CMS proof-of-concept membrane for this application. Facile formation of the sheath-core spun precursor with a 6FDA-DAM sheath and Matrimid® core also avoids the need to seal defects before or after the carbonization of the precursors. The composite CMS membrane shows CO2 /CH4 (50 : 50) mixed gas feed with an attractive CO2 /CH4 selectivity of 64.3 and CO2 permeance of 232 GPU at 35 °C. A key additional benefit of the approach is reduction in use of the more costly high performance 6FDA-DAM in a composite sheath-core CMS membrane with the "Pseudo Wheel+Hub & Spoke" structure.

Increasing disposal costs and environmental concerns have encouraged desalination projects in the Permian basin to cut down produced water (PW) volumes and improve the handling. This study aims to demonstrate performance of membrane-distillation (MD) for desalinating high-salinity PW. Prior to MD, electrocoagulation (EC) and microfiltration (MF) are used as primary and secondary pretreatments, respectively. These pretreatment steps are necessary to remove constituents such as suspended solids, oil, and grease. The integrated EC-MF process was followed by vacuum MD (VMD) to recover water and concentrate the brine stream. To improve latent heat recovery, vapor compression is integrated into the vacuum membrane distillation (VMD). Our EC-MFVMD PW treatment process can treat 1000 L of PW per day, with water recoveries in the range of 30-70 %. Suspended solids and turbidity removal of 90 % and total organic carbon (TOC) removal of 60 % were achieved with EC-MF pretreatments, which effectively mitigated PW fouling potential. A custom-designed plate-and-frame VMD module was established which enabled unparalleled service flexibility to change membrane replacement and active area. Results from our systematic evaluation revealed that the flux of the commercial membranes in our VMD module varied from 5 to 66 Lm-2 h-1. The intensified VMD performance achieved by vapor compression led to remarkable improvement in energy efficiency in terms of gained output ratio (GOR = 2.7) and energy consumption per unit of water production (248 kWh m-3). This study demonstrates the capability of the MD process for PW treatment, revealing the reasonable potential for PW reuse and recycling. Although this process might be of interest for unique applications that justifies the cost, further improvements in energy consumption are required to make this technology feasible for commercialized desalination of oilfield produced waters.

Hydraulic fracturing oil- and gas-produced water is frequently highly impaired. While it is often deep well injected, there is a great deal of interest in treating and recovering this water for beneficial uses. However, multiple-unit operations are needed if these wastewaters are to be recovered. Electrocoagulation is considered a promising pretreatment technology. Herein, we have investigated the use of aluminum electrodes for electrocoagulation as a pretreatment operation. The effects of electrode arrangement, applied current, reaction time, pH and inter-electrode distance on the quality of the treated water have been investigated. The results obtained here indicate that electrocoagulation can obtain good removal of turbidity (95%), total suspended solids (TSS) (90%) and total organic carbon (TOC) (69%) by carefully choosing the reaction conditions. Sedimentation was used to separate the treated water from the sludge. The performance of the electrocoagulation process depends strongly on the quality of the feed water. The viability of a practical continuous electrocoagulation process will depend on the volume (footprint) of the reactor, which in turn will depend on operating conditions and the quality of the feed water.

A superomniphobic polyvinylidene fluoride (PVDF-F) membrane was fabricated through electronspinning to obtain an excellent antiwetting and antifouling property for the effective and efficient treatment of real produced water. Compared with pristine PVDF and hydroxyl functionalized PVDF (PVDF-O) membrane, PVDF-F mem-brane had a larger pore diameter, while its pure water flux was found to be lower than both. Neither liquids with high surface tension (water, ethanol) or low surface tension (sodium dodecyl sulfate (SDS) as surfactant, mineral oil) could wet the PVDF-F surface even up to 3 min of contact. During membrane distillation (MD) of 3.5 wt% of aquoues NaCl solution, PVDF-F could withstand 0.4 mM SDS solution without any wetting as seen from the conductivity of the permeate, which was not the case for the PVDF and PVDF-O membranes. After 18 h of MD operation using produced water, a significantly thick fouling layer was found on the PVDF and PVDF-O mem-branes containing Ca-3(PO4)(2), Sr-3(PO4)(2) and Mg-3(PO4)(2). However, PVDF-F had a very thin and reversible organic fouled layer, causing only 40% reduction in permeate flux and with a low permeate conductivity of 20 mu S cm-1. This layer was easily removed by cleaning using distilled water and 80% of the flux was recovered. On the 2nd and 3rd MD cycle, the reduction in permeate flux was within 10%. The superomniphobic PVDF-F nanofibrous membrane was run for three successful consecutive MD cycles during produced water processing without any significant fouling as well as wetting.

Hydraulic fracturing oil and gas produced water is frequently highly impaired. While it is often deep well injected, there is great interest in treating this water for beneficial uses. Given the complexity of these produced waters, multiple unit operations are necessary. Electrocoagulation has been considered as a promising pretreatment technology. Here electrocoagulation is considered as a pretreatment prior to membrane distillation. The focus of this work is on understanding the electrocoagulation process in order to design an integrated unit operation. Electrocoagulation is used to remove organic compounds that will foul the membrane leading to membrane failure during membrane distillation. Using aluminum or iron electrodes, half-cell reactions in the electrocoagulation cell and electrode potentials have been calculated. Electrocoagulation was conducted using a continuous electrocoagulation reactor with actual produced water using aluminum, iron or mixed aluminum and iron electrodes. The results obtained here indicate that electrocoagulation can obtain good removal efficiency of total organic carbon (TOC) by using different reaction conditions. Removal of organic compounds is essential to minimize fouling during membrane distillation. Further the performance of the electrocoagulation process depends strongly on the quality of the feed water. Insoluble species were more effectively coagulated than dissolved organic species. Continuous electrocoagulation shows great potential as a scalable unit operation for pretreating hydraulic fracturing produced water.

We report a novel approach to economically fabricate dual-layer composite nanoparticle-containing carbon molecular sieve (CMS) hollow fiber membranes having excellent gas separation performance. The economically favored process comprises dip coating engineered support layer fibers to form a dense skin layer in a CMSCMS precursor. The coated fibers are then pyrolyzed to form a high-performance CMS hollow fiber membrane. The nano-particle containing composite carbon molecular sieve hollow fiber membranes showed very attractive selectivities and productivities. This work shows how to produce high performance CMS hollow fiber membrane by coating, which exceeds that achieved with the standard sol-gel support stabilization technique.

Hydraulic fracturing flowback and produced water is a highly impaired wastewater containing dissolved salts polar and non-polar organic compounds, oil and surfactants. Here a combined electrocoagulation micro filtration - membrane distillation process has been used to treat this wastewater. Electrocoagulation followed by microfiltration was used to pretreat the wastewater prior membrane distillation. The initial total dissolved solids (TDS) concentration was extremely high being 245,300 mg L-1. After electrocoagulation, the total organic carbon (TOC) was reduced from 120 mg L-1 to 64 mg L-1. Tangential flow microfiltration using a 0.1 mu m pore size polyethersulfone membrane was used to separate the particulate matter after electrocoagulation and to further reduce the TOC to 44 mg L-1. Membrane distillation was used to desalinate the pretreated produced water resulting in a high quality treated water (TDS of 56 mg L-1 and TOC 1 mg L-1). Three membranes with very different surface morphology were used: commercially available polyvinylidene fluoride, electrospun poly (vinylidene fluoride-co-hexafluoropropylene) nanofibers and multiwalled carbon nanotube coated polytetrafluoroethylene. The TDS in the retentate increased to over 350,000 mg L-1. During membrane distillation, the temperature of the feed tank was maintained at 36 degrees C while the feed entered the module at 60 degrees C in order to minimize scaling on the membrane. The surface properties of an ideal membrane that is resistant to wetting and provides high flux is likely to depend on the TDS and properties of the wastewater.

Increasing world population has led to an increase in the demand for clean water. Consequently, there is an urgent need for new cost-effective technologies to recover, recycle, and reuse wastewater for beneficial uses. Membrane distillation is an emerging technology that could enable the efficient recycling of wastewater. Further membrane distillation can maximize water recovery and reuse, allowing future wastewater treatment facilities to move towards zero liquid discharge. Central to the membrane distillation process is the hydrophobic microporous membrane. The development of robust membranes that are resistant to fouling and easily regenerated is essential. Various advanced methods have been used to tailor the membrane surface structure and chemistry to suppress fouling. The cleaning protocol used will depend on the foulants present in the feed stream and the membrane surface properties. The configuration used to operate the membrane distillation process is essential to minimize operating costs and maximize water recovery. Again, the properties of the feed stream are likely to dictate the configuration used. The economic viability and sustainability of membrane distillation depend on a life cycle and techno-economic analysis for potential niche applications.

AbstractDip coating and pyrolysis processes are used to create multi‐layer asymmetric carbon molecular sieve (CMS) hollow fiber membranes with excellent gas separation properties. Coating of an economical engineered support with a high‐performance polyimide to create precursor fibers with a dense skin layer reduces material cost by 25‐fold compared to monolithic precursors or ceramic supports. CMS permeation results with CO2/CH4 (50:50) mixed gas feed show attractive CO2/CH4 selectivity of 58.8 and CO2 permeance of 310 GPU at 35 °C.

This is the first report of KCl templated carbon preparation from walnut shell. Activated carbon (AC) with high specific surface area (1958 m(2) g(-1)) was obtained by CO2 activation of KCl templated biochar at 900 degrees C. The electrochemical properties were evaluated by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. WS-90 had relatively low inner resistance of 1.7 Omega. The specific capacitance was 245.0 F g(-1) in 6 mol L-1 KOH electrolyte at a current density of 0.1 A g(-1), and it can maintain very good cyclic stability with capacitance retention ratio of 95.4% (from 245.0 to 233.7 F g(-1) at current density of 0.1 A g(-1) after 4000 cycles (0.1, 0.5, 1.0 and 5.0 A g(-1) for 1000 cycles, respectively)).

Resisting densification of hollow fiber support layers under high-temperature pyrolysis is critical to form carbon molecular sieve hollow fiber membranes with thin separation layer and attractive productivity. In this paper, a new silica particle stabilization approach is introduced to form thin-skinned composite carbon molecular sieve hollow fiber membranes with excellent resistance to support layer densification. By dispersing small-sized silica particles with low bulk density in the support layer of polymer precursor hollow fibers, composite carbon molecular sieve hollow fiber membranes were formed with highly porous supports. The composite carbon molecular sieve hollow fiber membranes showed very attractive selectivities and productivities higher than those of monolithic asymmetric carbon molecular sieve hollow fiber membranes formed by the standard sol–gel support stabilization technique.

Catalytic liquefaction can effectively convert solid biomass into liquid bio-crude that could be upgraded to advanced biofuel, but the exploration of green and efficient catalysts remain a challenge. In this study, bifunctional Zn/HZSM-5 catalysts were firstly combined with supercritical ethanol to produce bio-crude in pine sawdust catalytic liquefaction. The catalysts were characterized by BET, NH3-TPD, XRD and TEM. The effects of Zn/HZSM-5 catalysts with different Zn loading ratios on the yield and quality of bio-crude and gas were investigated. The results showed that Zn/HZSM-5 and HZSM-5 catalysts improved the yields of bio-crude compared to no catalyst treatment. The use of HZSM-5 based catalysts reduced the contents of oxygenated compounds including acids, ketones, phenols and alcohols in bio-crude products. Hydrocarbons content of the bio-crudes produced by HZSM-5 based catalysts increased compared to bio-crude produced by no catalyst treatment. Compared to HZSM-5 catalyst, Zn/HZSM-5 catalysts exhibited better catalyst performance to improve bio-crude quality due to the additional decarbonylation, decarboxylation and dehydrogenation reactions induced by Zn loading. 15%Zn/HZSM-5 catalyst resulted in the highest yields of bio-crude at 59.09 wt.%, and 10%Zn/HZSM-5 catalyst produced bio-crude with the highest hydrocarbons content at 15.03%. The four stages of mechanism for biomass liquefaction reactions on Zn/HZSM-5 catalysts in supercritical ethanol was proposed.

Hydrodeoxygenation (HDO) is an effective method for bio-oil upgrading. However, the high hydrogen consumption resulted in high bio-oil upgrading cost. In this study, an novel method of hydrogen generation from water for bio-oil HDO was reported. Zinc metal with zero valency was used to generate hydrogen through zinc hydrolysis reaction in the bio-oil HDO process. The effects of different temperatures (20 degrees C, 250 degrees C, 300 degrees C, 350 degrees C, 400 degrees C) on in situ bio-oil HDO was investigated. The results showed that high temperatures resulted in high hydrogen yield that led to promoted HDO activity over zinc metal-based materials. Although 20 degrees C bio-oil HDO process generated the highest oil phase yield at 14.07%, 400 degrees C bio-oil upgrading process produced upgraded bio-oil with highest hydrocarbons content at 68.95%. Physicochemical properties of raw bio-oil improved significantly after bio-oil HDO upgrading at higher temperatures (250 degrees C, 300 degrees C 350 degrees C and 400 degrees C). The pH of upgraded bio-oils (5.70-6.49) increased significantly compared to raw bio-oil (3.24). The higher heating value of upgraded bio-oils (28.67-33.43 MJ/kg) increased significantly compared to raw bio-oil (15.54 MJ/kg), and valuable hydrocarbons content improved significantly from 16.94% in raw bio-oil to 37.86%-68.95% in upgraded bio-oils. (C) 2017 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Lignin, an abundant biomass constituent in nature, was modified by pyrrole to produce nitrogen-doped porous carbon.

The need for renewable, sustainable sources of biofuels continues to increase as the world’s population continues to grow. Using microorganisms as biofuel producers is one area that is being researched extensively for this purpose. Anabaena sp. PCC 7120 is a filamentous strain of cyanobacteria capable of fixing atmospheric nitrogen, and has been genetically engineered to produce limonene, a cyclic hydrocarbon which has potential as a next-generation biofuel. This study analyzed the economic feasibility of a theoretical next-generation production facility that uses genetically engineered Anabaena 7120 to produce limonene. The economic feasibility of a limonene production facility was analyzed using the Farm-level Algae Risk Model (FARM). This model is an integrated systems compilation of numerous technoeconomic models that has been used previously in several algal production scenarios. FARM simulated 10 years of operation for the production facility for two scenarios. The 1st scenario used actual limonene productivity data (0.018mg/L/d) from a genetically engineered strain of filamentous cyanobacteria, while the 2nd scenario used a ‘best case’ assumption that limonene productivity can be increased 100-fold (1.8mg/L/d). It was determined that the average probability of economic success of the 1st scenario at year 5 was 0%, while the average probability of success of the 2nd scenario was 100%. Assuming no fractional reductions in OPEX and CAPEX, the average net present value (NPV) at year 5 of the 1st scenario was −$588 million, compared to $392 million for the 2nd scenario. Further analysis determined that a limonene productivity of 1.02mg/L/d is needed to yield an NPV of 0 dollars at year 5. This study shows strong evidence that a next-generation biofuel production facility utilizing genetically engineered strains of filamentous cyanobacteria could become economically feasible in the future if strains are developed with increased biofuel productivities.

Rod-shape porous carbon was prepared from aniline modified lignin via KOH activation and used as electrode materials for supercapacitors. The specific surface area, pore size and shape could be modulated by the carbonization temperature, which significantly affected the electrochemical performance. Unique rod-shape carbon with massive pores and a high BET surface area of 2265 m(2) g(-1) were obtained at 700 degrees C in contrast to irregular morphology created at other carbonization temperatures. In 6 mol L-1 KOH electrolyte, a specific capacitance of 336 F g(-1), small resistance of 0.9 Omega and stable charge/discharge at current density of 1 A g(-1) after 1, 000 cycles were achieved using rod-shape porous carbon as electrodes in an electrical double layer capacitor. (C) 2016 Elsevier B.V. All rights reserved.