Derived Carbon Membranes Research Articles

Incorporation of composite metal-PVP derived carbon membranes for the percrystallisation of salt water

In this research using supported metal‑carbon membranes in a membrane percrystallisation application, we investigated the influence of metal ions on the formation of carbon during carbon membrane synthesis by combining polyvinylpyrrolidone (PVP) with various metal compounds, including zinc, potassium, barium, sodium, magnesium, calcium, and strontium, through calcination at 700 °C in a nitrogen atmosphere for the first time. These carbon membranes were then subjected to continuous percrystallisation experiments to produce dry salt crystals from salt solutions. The feed solution (3.5, 10, 20 wt% of salt) were used at 30, 50, and 70 °C for the performance evaluation. Intriguingly, the addition of metal elements to the PVP solution resulted in an enhancement in the total pore volume and surface area of the resulting carbon membranes. The PVP-Zn precursor exhibited the highest increase with a maximum improvement of 99 fold. Moreover, when compared to the PVP membranes alone, the composite membranes also exhibited higher fluxes. Among the tested composite carbon membranes, PVP-Ca, PVP-Zn, and PVP-Mg demonstrated the highest flux values, reaching an impressive 55 kg.m−2.h−1. Additionally, these membranes exhibited self-elimination, where salt was effectively removed from the membrane surface during percrystallisation testing. Thus, these membranes have the potential to be employed in desalination applications.

Chitosan derived carbon membranes as protective layers on zinc anodes for aqueous zinc batteries

Chitosan derived carbon membranes as protective layers on zinc anodes for aqueous zinc batteries

Catalytic arene-norbornene annulation (CANAL) ladder polymer derived carbon membranes with unparalleled hydrogen/carbon dioxide size-sieving capability

Hydrogen is an emerging energy source with a wide range of applications in transportation, electricity generation, and manufacturing of important chemicals such as ammonia and methanol. Hydrogen is commonly coproduced with CO2 using steam reforming of methane and its purification is typically achieved using energy-intensive processes such as pressure swing adsorption (PSA) and cryogenic distillation. Membrane technology with potentially lower energy consumption and lower carbon footprint could play an important role in developing a more sustainable hydrogen economy. In this study, we prepared carbon molecular sieve (CMS) membranes by the pyrolysis of a highly aromatic catalytic arene-norbornene annulation (CANAL)-Tröger's base ladder polymer of intrinsic microporosity precursor — CANAL-TB-1. CMS membranes obtained by pyrolysis between 600 and 900 °C displayed excellent gas separation performance for hydrogen/carbon dioxide separation and related applications. The CANAL-CMS-800 °C membrane showed a pure-gas hydrogen permeability of 41 Barrer with H2/CO2, H2/N2, and H2/CH4 selectivity values of 39, 1952, and >8200 at 35 °C. Increasing the pyrolysis temperature to 850 and 900 °C further boosted the selectivity. For example, the CANAL-CMS-900 °C exhibited a stable long-term mixed-gas performance over a period of 38 days with an unprecedented H2/CO2 selectivity of 174 and H2 permeability of 8.2 Barrer at 10 bar total feed pressure and 100 °C, which significantly exceeded the performance of previously reported polymers and related CMS membrane materials.

Controlled Carbonization Heating Rate for Enhancing CO2 Separation Based on Single Gas Studies

Concerns about the impact of greenhouse gas have driven the development of new separation technology to meet CO2 emission reduction targets. Membrane-based technologies using carbon membranes that are able to separate CO2 efficiently appears to be a competitive method. This research was focused on the development of carbon membranes derived from polymer blend of polyetherimide and polyethylene glycol to separate CO2 rendering it suitable to be used in many applications such as landfill gas purification, CO2 removal from natural gas or flue gas streams. Carbonization process was conducted at temperature of 923 K and 2 h of soaking time. To enhance membrane separation properties, pore structure was tailored by varying the carbonization heating rates to 1, 3, 5, and 7 K / min. The effect of carbonization heating rate on the separation performance was investigated by single gas permeabilities using CO2 , N2 , and CH4 at room temperature. Carbonization heating rate of 1 K / min produced carbon membrane with the most CO2 / N2 and CO2 / CH4 selectivity of 38 and 64, respectively, with the CO2 permeability of 211 barrer. Therefore, carbonization needs to be carried out at sufficiently slow heating rates to avoid significant loss of selectivity of the derived carbon membranes.

Vacuum-assisted tailoring of pore structures of phenolic resin derived carbon membranes

This work shows the preparation and separation performance assessment of carbon membranes derived from phenolic resin by a vacuum-assisted method and carbonisation in an inert atmosphere. The vacuum time played an important role in tailoring the structure of the membranes. For instance, pore volumes and surface areas increased from 0.81 and 834 to 2.2cm3g−1 and 1910m2g−1, respectively, as the vacuum time exposure increased from 0 to 1200s. The significant structural changes correlated very well with water permeation, as fluxes increased by 91% as the vacuum time increased from 0 to 1200s reaching up to 169Lm−2 h−1 at 5bar. Molecular weight cut-off tests showed no rejection for the smaller glucose and sucrose molecules, though this increased to ~ 80% and full rejection for 36kDa and 400kDa polyvinyl pyrrolidine. Interestingly, FTIR spectra showed that the peaks of C–H stretching vibration (2800–3200cm−1) and C–O stretching (1030cm−1) became more pronounced as a function of increasing vacuum time, strongly suggesting that the use of vacuum further assisted in the polycondensation of phenolic oligomers. Based on these outcomes, a cluster to cluster model is proposed, whereby vacuum application promoted crosslinking reactions of the phenolic resin, creating microporous regions within the clusters, and mesoporous regions between the clusters.

Carbon Membranes Prepared from a Polymer Blend of Polyethylene Glycol and Polyetherimide

AbstractThrough a dip‐coating technique, carbon membranes were produced from a polymer blend consisting of the thermally stable polymer polyetherimide (PEI) and the thermally labile polymer polyethylene glycol (PEG). The PEG/PEI carbon membranes were synthesized on an alumina support coated with an Al2O3 intermediate layer. The polymer blend ratio and carbonization temperature influenced the structure and permeation performance of the derived carbon membranes. The porosity of the PEG/PEI carbon membranes increased with higher PEG content in the blends. However, the derived carbon membranes tended to lose gas permeability with raising the carbonization temperatures. The carbon membranes were successfully optimized in order to achieve the highest CO2/CH4 and CO2/N2 selectivities.

Effects of carbonization heating rate on CO2 separation of derived carbon membranes

High performance carbon hollow fiber membranes (CHFM) for CO2 separation were prepared by manipulating of carbonization heating rates under a N2 atmosphere. During heat treatment process, carbonization of the polymeric hollow fiber membrane was conducted up to 650°C and in the range of 1–9°C/min for heating rate. The gas permeation properties were determined using a single gas permeation apparatus at room temperature. Fine-tuning of the carbonization conditions appears necessary to obtain desired permeation properties. The gas permeance for all examined gases (N2, CH4, CO2) and selectivity of CO2/CH4 and CO2/N2 was decreased and increased, respectively, for the PEI/PVP-based CHFMs prepared at low heating rate. It was found that the heating rate posses significant effect on structure and gas permeation properties of the resultant CHFMs. Experimental results indicated that, carbonization heating rate of 3°C/min is the best conditions in the preparation of CHFMs derived from polymer blends of PEI/PVP for the CO2/CH4 and CO2/N2 separation.

Effects of Curing Method on the Gas Separation Performance of Phenolic Resin/Poly(vinyl Alcohol)-Based Carbon Membrane Materials

A novel cheap blended precursor phenolic resin/poly(vinyl alcohol) (PR/PVA) was developed to prepare carbon membranes. The effect of two curing methods (i.e., crosslinker and preoxidation) on the gas separation performance of their derived carbon membranes was investigated. Thermogravimetric analysis (TGA), Differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy were used to analyze the thermal stability of precursor and the changes in functional groups on membrane surface. The gas permeation of carbon membranes was tested for H2 and N2. The results show that PR, PR/PVA, and two PR/PVA cured samples have three thermal degradation stages. The thermal stability for original PR/PVA membrane is significantly improved via the method of preoxidation or crosslinker. Similar crosslinking structure is formed by the two curing methods. However, carbon membranes from crosslinker method present two-fold higher in hydrogen permeability and four-fold higher in selectivity than that from preoxidation method.

Effects of sulfone/ketone in poly(phthalazinone ether sulfone ketone) on the gas permeation of their derived carbon membranes

A series of copolymer, poly(phthalazinone ether sulfone ketone)s (PPESKs) with the sulfone over ketone unit (S/K) ratio varying from 20/80, 50/50 to 80/20, were used as precursors to prepare carbon membranes. The effects of chemical structure as S/K ratio of PPESKs on the microstructure and gas separation performance of their derived carbon membranes were mainly investigated. The properties of PPESKs were detected in terms of density, fractional free volume, char yield, interlayer distance and glass transition temperature. During the formation process of carbon membranes (i.e., stabilization and pyrolysis), the changes in functional groups, microstructural parameters and gas permeation were monitored by FTIR, X-ray diffraction, TEM and single gas permeation techniques. The results have shown that the microstructure and gas permeation of obtained carbon membranes are significantly affected by the S/K ratio in precursor PPESKs. Carbon membranes exhibit higher selectivity and lower permeability when prepared at low pyrolytic temperature (i.e., 650 °C and 800 °C) and from PPESKs with S/K ratio equaling 50/50, followed with 20/80 and 80/20. As for carbon membranes prepared at high pyrolytic temperature (i.e., 950 °C), the selectivity order of them is well in accordance with S/K mole ratio in precursor PPESKs: 20/80 > 50/50 > 80/20, and vice versa for permeability.

Effects of precursor preoxidization on the structure and gas separation properties of polyetherimide derived carbon membranes

Polyetherimide derived carbon membranes were prepared by pretreating the precursor in air before carbonization at 700 ℃.The chemical structure,microstructure and gas separation properties of these membranes pretreated at 400,460 and 480 ℃ were characterized by FTIR,elemental analysis,XRD and gas permeation tests.The effects of preoxidization on their microstructure and gas separation properties were investigated.Results show that decomposition and oxidation-induced crosslinking reactions occur during the pretreatment.The higher the preoxidization temperature,the higher the degree of decomposition and the degree of crosslinking.After carbonization,the pretreated membranes have an amorphous structure.The differences in the crosslinked structure generated in the pretreatment leads to differences in the micropore structure of the membranes,which can be used to tune gas separation properties.The permeability of all gases investigated exhibits a maximum with a preoxidization temperature at 460 ℃,for which the O2 permeability is 8.2×10-13(m3(STP) · cm)/(m2 · s · Pa)and the O2/N2 selectivity is 14.1.

Characterization of Nanoporous Structures of Polyphenylene Oxide Derived Carbon Membranes by Means of 129Xe NMR

The 129Xe NMR spectroscopy has become a powerful technique of materials characterization because the xenon atom has a very large polarizability. It is well known that the signal of xenon sorbed in porous media is sensitively affected by the surrounding environments such as the chemistry of material surface. In this study, the pore properties of nanoporous PPO (polyphenylene oxide) derived carbon membranes were characterized by means of the variable temperature (VT)-hyperpolarized Xe NMR. The Xe NMR results showed good agreements with the adsorption results of CO2 for the PPO derived nanoporous carbon membranes. It was clearly shown that the 129Xe NMR could be used as one of the promising characterization methods of nanoporous materials with low surface area and small pore volume.

Characterization of the post-oxidized carbon membranes derived from poly(2,4-dimethyl-1,4-phenylene oxide) and their gas permeation properties

The pore dimensions and distribution of carbon membranes can be finely adjusted by various post-treatment methods to meet different separation needs and objectives. In this study, the post-oxidation effect on the gas permeation performance was investigated in the poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) derived carbon membranes with oxidation conditions (oxidation temperature and time). The post-oxidized carbon membranes were prepared by carbonization at 700 °C, followed by the air-oxidation. The permeances of gas species increased with increasing oxidation temperature and time due to increase in pore characteristic properties, such as pore volume, pore size and its distribution. The influence of the post-oxidation on the extent of the gas permeance modification was higher for gas species having a large molecular size. The carbon membranes post-oxidized at a low temperature (e.g., 200 °C) and a short time (e.g., 1 h) showed high permeation performance. The post-oxidation on the permeation results clearly showed that the gas permeation properties could be modified by appropriate oxidation conditions.

Gas permeation properties of carbon molecular sieving membranes derived from the polymer blend of polyphenylene oxide (PPO)/polyvinylpyrrolidone (PVP)

The carbon molecular sieving membranes were prepared from the polymer blend of polyphenylene oxide (PPO) and polypyrrolidone (PVP) as thermally stable and labile polymer, respectively. The permeation results for the carbon membranes derived from the polymer blends of PPO/PVP showed that the transport of gas species was affected by the molecular sieving effect and that the permeation performances had a strong dependency upon the pyrolysis temperature and PVP molecular weight. The PPO/PVP derived carbon membranes with lower PVP molecular weight than 40 K showed decreased gas permeances and increased permselectivities due to decrease in the pore structure. Meanwhile, it was observed that gas permeance for the carbon membranes of higher molecular weights than 40 K increased due to the enhanced diffusional pathways in the thermally labile polymer region. It is considered that the introduction of the thermally labile polymer leads to control the pore structure through the permeation results for the carbon membrane derived from the PPO/PVP and that the permeation performance is affected by the molecular weight and pyrolysis temperature.

Preparation of Carbon Membranes Derived from Polymer Blends in the Presence of a Thermally Labile Polymer

Carbon membranes for gas separation were prepared from the polymer blend consisting of poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) and polyvinylpyrrolidone (PVP) as the thermally stable and labile polymer, respectively. The PPO/PVP derived carbon membranes with lower PVP concentrations than 0.6 wt% showed decreased gas permeances and increased permselectivity due to decrease in the pore properties (pore volume and surface area). Meanwhile, gas permeance increased for the carbon membranes prepared with higher PVP concentrations than 0.6 wt% due to the enhanced diffusional pathways for the gas transport through carbon membranes especially in the domain of the thermally labile polymer. It is considered that the introduction of the thermally labile polymer leads to control the pore structure through the permeation results for the carbon membrane derived from the polymer blend.

Gas permeation properties for the post-oxidized polyphenylene oxide (PPO) derived carbon membranes: Effect of the oxidation temperature

Of thermosetting polymers, polyphenylene oxide (PPO) is considered as one of the alternative promising polymeric precursors for carbon-based membranes. The post-oxidized PPO derived carbon membranes were prepared by carbonization, followed by air-oxidation as post-treatment method in this study. It was observed that air-oxidation increased the pore characteristic values (pore volume, pore size and its distribution) of carbon materials. It was shown that the post-oxidation increased gas permeance due to change in the pore properties. The permeation results for the post-oxidized carbon membranes showed that the extent of the permeation modification is strongly dependent on the oxidation temperature. Also, it was observed that the post-oxidation at higher temperature changed permeation mechanism from the molecular sieving to Knudsen-like diffusion especially for larger gas species.

Influence of oxidation temperature on the gas permeation and separation properties in a microporous carbon membrane

Of thermosetting polymers, polyphenylene oxide (PPO) is considered as one of the promising alternative polymeric precursors for carbon membrane preparation. In this study, the PPO derived carbon membranes were prepared by carbonization and followed by air-oxidation as post-treatment method to modify the membrane pore structures. The characterization of the pore properties showed that air-oxidation enlarged the pore structure for the postoxidized carbon materials. The permeation results for the post-oxidized carbon membranes showed that the extent of the permeation modification was strongly dependent on the oxidation temperature. In the binary mixture gas systems, the permeation performance of the adsorbing gas species increased due to the surface diffusion mechanism. It is considered in the oxidation effect on the permeation modification that the post-oxidation of the carbon membranes increased gas permeation and separation properties.

Gas permeation properties of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) derived carbon membranes prepared on a tubular ceramic support

The carbon membranes were prepared by the pyrolyisis of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) polymer coated on the surface of the macroporous alumina tubular ceramic support. The permeation results showed that gas transport through the PPO derived carbon membranes was controlled by the molecular sieving effect. The influence of the pyrolysis temperature on the permeation performances indicates that the pore structure developed at a low temperature and then the pore characteristic values (pore volume, surface area, etc.) were increased with increasing pyrolysis temperatures, and decreased at further temperature. The correlation of the permeability versus the permselectivity for the PPO derived carbon membranes showed higher values than the upper bounds for polymeric membranes, and excellent performance comparable to polyimides derived carbon membranes.

Effects of Brominating Matrimid Polyimide on the Physical and Gas Transport Properties of Derived Carbon Membranes

Bromination modification was initially carried out on Matrimid polyimide before undergoing carbonation to produce carbon membranes. Compared with unmodified Matrimid, brominated Matrimid shows lower chain flexibility, which is demonstrated by increased glass transition temperatures and molecular simulation results. Additionally, an increase in space between polymer chains was supported by fractional free volume (FFV) and d-spacing measurements. The improvement of chain rigidity of polyimide precursors serves to strengthen the membrane morphology during the production of carbon membranes. Thermal gravimetric analysis indicates that the thermal stability of polyimide decreases after bromination. The lower thermal stability and higher FFV value of brominated Matrimid result in higher gas permeability of carbon membranes pyrolyzed at a low pyrolysis temperature, while the selectivity remained competitive to those pyrolyzed from the original Matrimid precursor under the same conditions. However, the gas permea...

Structure and Properties Relationships for Aromatic Polyimides and Their Derived Carbon Membranes: Experimental and Simulation Approaches

The main objective of this study is to investigate the factors of the chemical structure and physical properties of rigid polyimides in determining the performance of derived carbon membranes through both the experimental and simulation methods. Four polyimides made of different dianhydrides were pyrolyzed at 550 and 800 degrees C under vacuum conditions. The resultant carbon membranes exhibit excellent gas separation performances beyond the traditional upper limit line for polymer membranes. The thermal stability and the fractional free volume (FFV) of polyimides were examined by a thermogravimetric analyzer and a density meter. The chain properties of polyimide, such as flatness, chain linearity, and mobility, were simulated using the Cerius(2) software. All above characterizations of polyimides were related to the microstructure and gas transport properties of the resultant carbon membranes. It was observed that the high FFV values and low thermal stability of polyimide produce carbon membranes with bigger pore and higher gas permeability at low pyrolysis temperatures. Therefore, polyimides with big thermally labile side groups should be preferred to prepare carbon membranes at low pyrolysis temperatures for high permeability applications. On the other side, since the flatness and in-plane orientation of precursors may lead carbon membranes to ordered structure, thus obtaining high gas selectivity, linear polyimides with more coplanar aromatic rings should be first choice to prepare carbon membranes at high pyrolysis temperatures for high selectivity applications. The location of the indan group also affects chain flatness and in-plane orientation. As a result, carbon membranes derived from the BTDA-DAI precursor have superior separation performance to those derived from Matrimid.

Casting solvent effects on morphologies, gas transport properties of a novel 6FDA/PMDA–TMMDA copolyimide membrane and its derived carbon membranes

We have observed that solvents play an important role on the membrane morphology and gas separation performance of a novel 6FDA/PMDA–TMMDA copolyimide [copoly(4,4’-methylenebis(2,6-dimethyl)-2,2-bis(3,4-dicarboxylphenyl) hexafluoro propane/pyromellitic) diimide]. Copolyimide films cast from CH 2Cl 2 or NMP (1-methyl-2-pyrrolidinone) show amorphous morphology, while films cast from DMF ( N, N-dimethylformamide) have crystalline structure which has been confirmed by polarized microscope, XRD and gas sorption tests. Gas transport properties of different morphological films are significantly different. Furthermore, we also report that gas separation performance of carbon molecular sieve membranes (CMSMs) pyrolyzed from different morphological precursors is strongly dependent on pyrolysis temperatures. Results show that the permeability of CMSMs at different pyrolysis temperatures follows the order: 550 °C > 650 °C > 800 °C and the separation factor is in the order: 800 °C > 650 °C > 550 °C. The differences between CMSMs derived from different morphological precursors decrease with an increase in pyrolysis temperatures. At low pyrolysis temperature, the CMSMs’ structure and separation performance could significantly be affected by the decomposition temperature of the precursor, however, at higher pyrolysis temperatures, the dominant factor for the CMSMs’ structure and performance is the pyrolysis temperature due to the complete degradation of the polymeric precursor.