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Polyaluminium chlorides (PAC) has replaced a large part of traditional aluminous coagulants for water treatment in recent years because of low dosage, high efficiency, low cost and convenient usage. This work studied the effects of salinity and temperature on the efficiency of PAC in removing oil and colloids from oily produced water (PW) and the potential of PAC for high salinity PW treatment.Minghua produced water (Di-MHPW) with salinity of 2,815 mg/L and high salinity produced water (HSPW) with salinity of 102,290 mg/L were used in this work. The efficiency of PAC and the optimal dosage were investigated by stability analyzer which allows a step-by-step vertical scanning of the dispersions. The separation time, floc volume and water quality after treatment could be obtained by stability analyzer.Transmission intensity was used to evaluate the oil-water separation in PW. High transmission intensity indicates low oil content. Without PAC, HSPW presented faster increase in transmission than low salinity PW indicating poorer stability. The zeta potential of oil drops and colloids in low salinity PW (2,815 mg/L) was −20.4mV. High salinity (102,290 mg/L) increased the zeta potential to −2.2mV, which makes the oil-in-water (O/W) emulsion unstable than low salinity PW. With the addition of PAC, HSPW results in slightly lower transmission with less floc volume. This could be explained by the floc size after the addition of PAC in two PWs. The size of formed floc in HSPW was much smaller than that in MHPW leading to slower separation of floc from aqueous phase and lower transmission intensity. Increasing the temperature enhanced the PAC efficiency in removing oil and suspended solids in both high and low salinity PWs. However, the floc volume also increased especially in Di-MHPW resulting in less water volume. In HSPW, the temperature effect on floc volume was not obvious. Though high salinity reduces the performance of PAC in water treatment, it is still an efficient flocculant for HSPW treatment with high flocculation efficiency, small floc volume and short separation time.This work provides the insight of oily produced water treatment using PAC and the effect of salinity and temperature. The results are helpful to develop novel flocculants used for high salinity produced water treatment.

To face the worldwide shortage of fresh water resources and the increase demand of oil and gas, researchers have devoted to study on application of seawater as a base fluid for hydraulic fracturing. One of the primary challenges for seawater fracturing application is the scale precipitation tendency due to the incompatibility of high sulfate concentration with high calcium, barium or strontium concentration in formation water, which will lead to overall reduction in production capacity. This work aims to develop a chemical precipitation method, which is a low cost way to remove sulfate before injection to solve the scale problem.Barium chloride dihydrate was used to precipitate sulfate from seawater for hydraulic fracturing. The chemical dosage, working temperature and precipitation time were optimized. The sulfate concentration in treated water was determined using an inductively coupled plasma mass spectrometer (ICP-MS). The sedimentation speed to separate treated water and precipitates at different precipitation time was measured using an optical particle stability analyzer. The obtained precipitates were dried at 60?C, and the morphology was observed using scanning electron microscopy (SEM) and X-ray diffraction method (XRD).Experimental results showed the barium chloride dihydrate can reduce the sulfate concentration in seawater from more than 4,000 ppm to less than 200 ppm when the dosage barium is higher than 5,500 ppm. The reaction efficiency is not altered in the temperature range from 15ºC to 45ºC. It turned out the treated seawater could meet the requirement for hydraulic fracturing application. As to the separation of water and precipitates using sedimentation method, it showed the highest speed appeared when precipitation time was 5 mins. And the addition of flocculants cannot improve the sedimentation speed. In addition, SEM results showed the size of obtained precipitates was in nanometer range. Besides, XRD confirmed the composition of precipitates were barium sulfate with purity >90%. The characterization results demonstrated the precipitates could be used as additives in drilling fluid, which will greatly reduce the operation cost.The work has revealed that barium sulfate precipitation method is promising to remove sulfate in seawater for hydraulic fracturing. Besides, the obtained barium sulfate is a commercially valuable product used in drilling fluid. Comparing to nanofiltration methods, this method is low cost and has no energy input requirement, which is suitable for a low carbon economy.

A simple synthetic route to a novel sterically hindered triptycene-based diamine, 1,3,6,8-tetramethyl-2,7-diaminotriptycene (TMDAT), and its use in the preparation of high molecular weight polyimides of intrinsic microporosity (PIM-PIs) are reported. The organosoluble TMDAT-derived polyimides displayed high Brunauer–Emmett–Teller surface areas ranging between 610 and 850 m2 g–1 and demonstrated excellent thermal stability of up to 510 °C. Introduction of the rigid three-dimensional paddlewheel triptycene framework and the tetramethyl-induced restriction of the imide bond rotation resulted in highly permeable polyimides with moderate gas-pair selectivity. The best performing polyimide made from TMDAT and a triptycene-based dianhydride showed gas transport properties located between the 2008 and 2015 polymer permeability/selectivity trade-off curves with H2 and O2 permeabilities of 2858 and 575 barrer combined with H2/N2 and O2/N2 selectivities of 24 and 4.8, respectively, after 200 days of physical aging.

This review provides a new perspective on the role of the state-of-the-art polymers of intrinsic microporosity (PIMs) in key energy-intensive membrane-based gas separations including O2/N2, H2/N2, H2/CH4, CO2/CH4, H2S/CH4, C2H4/C2H6, and C3H6/C3H8 applications. A general overview on the gas separation properties of novel PIM materials developed in the past 15 years is presented with updated performance maps on the latest pure-gas 2015 O2/N2, H2/N2, and H2/CH4 permeability/selectivity upper bounds. Specifically, functionalized ladder PIMs and polyimides of intrinsic microporosity (PIM-PIs) are discussed targeting at high-performance, plasticization-resistant membranes for demanding acid gas (CO2 and H2S) removal from CH4 in natural gas and olefin/paraffin separations. Experimental CO2/CH4 performance data of nearly 70 polymeric membrane materials available in the literature were gathered and plotted for the first time on the Robeson plot, from which a mixed-gas 2018 CO2/CH4 upper bound was proposed to provide guidance for future membrane materials development. A number of PIMs have demonstrated outstanding performances in O2/N2, H2/N2, and H2/CH4 separations, and several functionalized PIMs have shown great promises in CO2/CH4 separation under realistic mixed-gas conditions. The potential of PIMs materials and their derivatives for H2S/CH4, C2H4/C2H6, and C3H6/C3H8 separations are underexplored, and significant efforts are needed to develop stable and high-performance materials under mixed-gas conditions. Ultimately, fabricating PIMs materials into defect-free, inexpensive, thin-film composite or integrally-skinned asymmetric membranes is paramount to their successful large-scale commercialization.

A hydroxyl-functionalized triptycene-based polyimide of intrinsic microporosity (TDA1-APAF) was converted to a polybenzoxazole (PBO) by heat treatment at 460 °C under nitrogen atmosphere. TDA1-APAF treated for 15 min (TR 460) resulted in a PBO conversion of 95% based on a theoretical weight loss of 11.7 wt% of the polyimide precursor. The BET surface area of the TR 460 (680 m 2 g −1 ) was significantly higher than that of the TDA1-APAF polyimide (260 m 2 g −1 ) as determined by nitrogen adsorption at −196 °C. Heating TDA1-APAF for 30 min (TRC 460) resulted in a weight loss of 13.5 wt%, indicating full conversion to PBO and partial main-chain degradation. The TR 460 membrane displayed excellent O 2 permeability of 311 Barrer coupled with an O 2 /N 2 selectivity of 5.4 and CO 2 permeability of 1328 Barrer with a CO 2 /CH 4 selectivity of 27. Interestingly, physical aging over 150 days resulted in enhanced O 2 /N 2 selectivity of 6.3 with an O 2 permeability of 185 Barrer. The novel triptycene-based TR 460 PBO outperformed all previously reported APAF-polyimide-based PBOs with gas permeation performance close to recently reported polymers located on the 2015 O 2 /N 2 upper bound. Based on this study, thermally-rearranged membranes from hydroxyl-functionalized triptycene-based polyimides are promising candidate membrane materials for air separation, specifically in applications where space and weight of membrane systems are of utmost importance such as nitrogen production for inert atmospheres in fuel lines and tanks on aircrafts and off-shore oil- or natural gas platforms. Mixed-gas permeation experiments also demonstrated good performance of the TR 460 membrane for natural gas sweetening with a CO 2 permeability of ∼1000 Barrer and CO 2 /CH 4 selectivity of 22 at a typical CO 2 wellhead partial pressure of 10 bar.

The synthesis and gas permeation properties of a high-performance hydroxyl-functionalized PIM-polyimide (TDA1-APAF) prepared from a novel 9,10-dimethyl-2,3,6,7-triptycene tetracarboxylic dianhydride (TDA1) and a commercially available 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane (APAF) diamine monomer are reported. The microporous polymer had a BET surface area based on nitrogen adsorption of 260 m 2 g −1 . A freshly prepared sample exhibited excellent gas permeation properties: (i) CO 2 permeability of 40 Barrer coupled with a CO 2 /CH 4 selectivity of 55 and (ii) H 2 permeability of 94 Barrer with a H 2 /CH 4 selectivity of 129. Physical aging over 250 days resulted in significantly enhanced CO 2 /CH 4 and H 2 /CH 4 selectivities of 75 and 183, respectively with only ~25% loss in CO 2 and H 2 permeability. Aged TDA1-APAF exhibited 5-fold higher pure-gas CO 2 permeability (30 Barrer) and two-fold higher CO 2 /CH 4 permselectivity over conventional dense cellulose triacetate membranes at 2 bar. In addition, TDA1-APAF polyimide had a N 2 /CH 4 selectivity of 2.3, thereby making it potentially possible to bring natural gas with low, but unacceptable nitrogen content to pipeline specification. Gas mixture permeation experiments with a 1:1 CO 2 /CH 4 feed mixture demonstrated higher mixed- than pure-gas selectivity and plasticization resistance up to 30 bar. These results suggest that intrinsically microporous hydroxyl-functionalized triptycene-based polyimides are promising candidate membrane materials for removal of CO 2 from natural gas and hydrogen purification in petrochemical refinery applications.

Two intrinsically microporous polyimides were obtained by high-temperature, one-pot polycondensation reaction of novel triptycene-based dianhydrides containing dimethyl- or diisopropyl-bridgehead groups with a commercially available highly sterically hindered 3,3ʹ-dimethylnaphthidine (DMN) diamine monomer. The dimethyl bridgehead groups in the triptycene building block provided the DMN-based polyimide (TDA1-DMN) with larger surface area (760 m 2 g -1 ) than the diisopropyl-based polyimide (TDA i 3-DMN) (680 m 2 g -1 ), greater fraction of ultramicroporosity, as observed from N 2 and CO 2 NLDFT adsorption analysis, and higher gas permeability and selectivity. Wide-angle X-ray diffraction (WAXD) measurements demonstrated that TDA1-DMN and TDA i 3-DMN exhibited a bimodal pore size distribution, where TDA1-DMN showed smaller d-spacing values and broader intensity peaks. Both TDA-DMN-based polyimides showed very high gas permeabilities with moderate selectivities. For example, fresh TDA1-DMN exhibited an O 2 permeability of 783 Barrer coupled with an O 2 /N 2 selectivity of 4.3 and H 2 permeability of 3050 Barrer with H 2 /N 2 selectivity of 16.7, values that surpassed the 2008 Robeson permeability/selectivity upper bounds. Physical aging of the TDA-DMN polyimide films over a period of 250 days showed relatively small changes in permeability (∼20%) and selectivity (∼5%).

A novel polyimide of intrinsic microporosity (PIM-PI) was synthesized from a 9,10-diisopropyl-triptycene-based dianhydride (TPDA) and dihydroxyl-functionalized 4,6-diaminoresorcinol (DAR). The unfunctionalized TPDA- m -phenylenediamine ( m PDA) polyimide derivative was made as a reference material to evaluate the effect of the OH group in TPDA-DAR on its gas transport properties. Pure-gas permeability coefficients of He, H 2 , N 2 , O 2 , CH 4 , and CO 2 were measured at 35 °C and 2 atm. The BET surface area based on nitrogen adsorption of dihydroxyl-functionalized TPDA-DAR (308 m 2 g −1 ) was 45% lower than that of TPDA- m PDA (565 m 2 g −1 ). TPDA- m PDA had a pure-gas CO 2 permeability of 349 Barrer and CO 2 /CH 4 selectivity of 32. The dihydroxyl-functionalized TPDA-DAR polyimide exhibited enhanced pure-gas CO 2 /CH 4 selectivity of 46 with a moderate decrease in CO 2 permeability to 215 Barrer. The CO 2 permeability of TPDA-DAR was ∼30-fold higher than that of a commercial cellulose triacetate membrane coupled with 39% higher pure-gas CO 2 /CH 4 selectivity. The TPDA-based dihydroxyl-containing polyimide showed good plasticization resistance and maintained high mixed-gas selectivity of 38 when tested at a typical CO 2 natural gas wellhead CO 2 partial pressure of 10 atm.

The effect of hydroxyl functionalization on the m-phenylene diamine moiety of 6FDA dianhydride-based polyimides was investigated for gas separation applications. Pure-gas permeability coefficients of He, H2, N2, O2, CH4, and CO2 were measured at 35 °C and 2 atm. The introduction of hydroxyl groups in the diamine moiety of 6FDA-diaminophenol (DAP) and 6FDA-diamino resorcinol (DAR) polyimides tightened the overall polymer structure due to increased charge transfer complex formation compared to unfunctionalized 6FDA-m-phenylene diamine (mPDA). The BET surface areas based on nitrogen adsorption of 6FDA-DAP (54 m2 g−1) and of 6FDA-DAR (45 m2 g−1) were ~18% and 32% lower than that of 6FDA-mPDA (66 m2 g−1). 6FDA-mPDA had a pure-gas CO2 permeability of 14 Barrer and CO2/CH4 selectivity of 70. The hydroxyl-functionalized polyimides 6FDA-DAP and 6FDA-DAR exhibited very high pure-gas CO2/CH4 selectivities of 92 and 94 with moderate CO2 permeability of 11 and 8 Barrer, respectively. It was demonstrated that hydroxyl-containing polyimide membranes maintained very high CO2/CH4 selectivity (~75 at CO2 partial pressure of 10 atm) due to CO2 plasticization resistance when tested under high-pressure mixed-gas conditions. Functionalization with hydroxyl groups may thus be a promising strategy towards attaining highly selective polyimides for economical membrane-based natural gas sweetening.

A new solution-processable ladder polymer (PSBI-AB) of intrinsic microporosity with dibenzodioxane linkages and bis(phenazine) units was designed and synthesized by self-polymerization of an AB-type monomer containing both catechol and aromatic dichloride groups. Such polymerization is an effective way to synthesize high molecular weight polymers and has a significant advantage over AA-BB polycondensation due to the lack of the requirement for strict control over stoichiometric balance. This protocol can be used to prepare a variety of phenazine-containing ladder type PIMs from their aromatic tetramethoxy precursors. The obtained polymer had high average molecular mass, excellent thermal stability, a high BET surface area of 705 m2 g−1 and good solubility in some organic solvents such as chloroform, m-cresol and dichlorobenzene. Gas permeation measurements showed comparable results to the previously reported analogous PIM-7 for films made under the same formation protocol.

The synthesis and gas permeation properties of two 6FDA-dianhydride-based polyimides prepared from 2,6-diaminotriptycene (6FDA–DAT1) and its extended iptycene analog (6FDA–DAT2) are reported. The additional benzene ring on the extended triptycene moiety in 6FDA–DAT2 increases the free volume over 6FDA–DAT1 and reduces the chain packing efficiency. The BET surface area based on nitrogen adsorption in 6FDA–DAT2 (450 m 2 g −1 ) is ~40% greater than that of 6FDA–DAT1 (320 m 2 g −1 ). 6FDA–DAT1 shows a CO 2 permeability of 120 Barrer and CO 2 /CH 4 selectivity of 38, whereas 6FDA–DAT2 exhibits a 75% increase in CO 2 permeability to 210 Barrer coupled with a moderate decrease in selectivity (CO 2 /CH 4 =30). Interestingly, minimal physical aging was observed over 150 days for both polymers and attributed to the high internal free volume of the shape-persistent iptycene geometries. The aged polyimides maintained CO 2 /CH 4 selectivities of 25–35 along with high CO 2 permeabilities of 90–120 Barrer up to CO 2 partial pressures of 10 bar in an aggressive 50:50 CO 2 :CH 4 mixed-gas feed, suggesting potential application in membranes for natural gas sweetening.

An intrinsically microporous polyimide is synthesized in m-cresol by a one-pot high-temperature condensation reaction of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and newly designed 2,6 (7)-dihydroxy-3,7(6)-diaminotriptycene (DAT1-OH). The 6FDA-DAT1-OH polyimide is thermally stable up to 440 °C, shows excellent solubility in polar solvents, and has moderately high Brunauer-Teller-Emmett (BET) surface area of 160 m2 g−1, as determined by nitrogen adsorption at −196 °C. Hydroxyl functionalization applied to the rigid 3D triptycene-based diamine building block results in a polyimide that exhibits moderate pure-gas CO2 permeability of 70 Barrer combined with high CO2/CH4 selectivity of 50. Mixed-gas permeation studies demonstrate excellent plasticization resistance of 6FDA-DAT1-OH with impressive performance as potential membrane material for natural gas sweetening with a CO2 permeability of 50 Barrer and CO2/CH4 selectivity of 40 at a typical natural gas well partial pressure of 10 atm.