Carbon Membranes For Gas Separation Research Articles

Study on pervaporation performance of hydrophobically modified carbon-based membrane materials

Abstract Based on the appropriate pore size, the surface of the carbon membrane was hydrophobically modified to preferentially adsorb alcohols, so as to achieve the purpose of enriching alcohols in the penetrant. This operation is significant for expanding the application of carbon membranes for gas separation. In this work, a hydrophobic silica sol was synthesized using tetraethyl orthosilicate (TEOS) and methyltriethoxysilane (MTES) as mixed silicon sources, and it was impregnated and coated on a rolled carbon membrane. The material was then dried and thermally treated to obtain the hydrophobic carbon membrane. The preparation procedure of silica sol was also investigated, and the surface chemical structure and morphology of the hydrophobic carbon membrane were characterized by contact angle (CA), Fourier Transform infrared spectroscopy (FTIR), and scanning electron microscope (SEM). The pervaporation performance of the hydrophobic carbon membrane was inspected with both ethanol/water and isopropanol/water mixed solution. The results showed that the hydrophobic carbon membrane has favorable pervaporation performance. With the elevation of temperature, the total flux significantly increased while the selectivity slightly decreased. The increase of alcohol (ethanol and isopropanol) content also enhanced total flux, but the selectivity reduced prominently. The phenomena indicated that a relatively ideal effect had been achieved.

Gas permeation through carbon membranes: Model development and experimental validation

With a growing interest in carbon membranes for gas separation, understanding their performance and behaviour is essential for proper design of the membrane separation. Currently not many models exist that correctly describe transport through carbon membranes due to its complex nature. This work attempts to implement a general modelling approach which describes several key transport phenomena inside carbon membranes. The approach assumes a membrane wall to be a bundle of pores with parallel transport mechanisms using the pore size distribution as a weight factor to sum the different transport phenomena. This work adapts this approach specifically for carbon membranes, additionally accounting for molecular sieving and pore blocking effects. Imposing realistic boundary conditions, the model is solved using global optimization algorithms. For testing, four different CMSMs have been produced with hydroquinone and novolac precursors. Pure- and mixed gas permeation tests are done for these CMSMs with H2, N2, and CO2 and the model is fit to this permeation data. Fitting results with pure gas measurements show the model is able to predict the contributions of different mass transport mechanism for the different membranes. This is validated by comparing these results to gas-pair permselectivity data. The model is furthermore fit to mixed gas data. Existence of multi-component effects shows that the model could be further improved. Overall, the model presented in this work is shown to be able to describe complex mass transport behaviour for various different carbon membranes.

The Development of Carbon Membrane for Gas Separation: A Review

The applications of carbon membranes are becoming more important than ever due to their resilient mechanical strength, stability, and separation performance. The production of carbon membranes involves a suitable precursor that is being subjective to a pyrolysis process under controlled operating conditions that will result a porous structure to be utilized in many different separation applications. Thus, by understanding the preparation aspects of this fabrication process, the product can be manipulated, to optimize the best preparation procedure for obtaining the desired properties of a given type of membrane. This paper reviews the preparation aspects of carbon membranes, that can be manipulated to enhance the overall separation performance.

Development of a P84/ZCC Composite Carbon Membrane for Gas Separation of H2/CO2 and H2/CH4.

Hydrogen (H2) has become one of the promising alternative clean energy resources. Membrane technology is a potential method for hydrogen separation or production. This study aims to develop a new carbon membrane for hydrogen separation or production. Moreover, the permeation behavior of H2, CO2, and CH4 through a hollow fiber composite carbon membrane derived from P84 co-polyimide and with incorporation of zeolite composite carbon (ZCC) was also examined. ZCC was synthesized via the impregnation method of sucrose into zeolite-Y pores, followed by carbonization at 800 °C. Thus, this filler has a high surface area, high microporosity, ordered pore structure, and low hydrophilicity. The presence of zeolites in ZCC is predicted to increase certain gases’ affinity for the membrane. Various heating rates (1–5 °C/min) were applied during pyrolysis to understand the effect of the heating rate on the pore structure and H2/CO2 and H2/CH4 gas separation performance. Moreover, gas permeation was evaluated at various temperatures (298–373 K) to study the thermodynamic aspect of the process. A characteristic graphite peak was detected at 2θ ∼ 44° in all carbon samples. Scanning electron microscopy (SEM) observations revealed the void-free surface and the asymmetric structure of the carbon membranes. During the permeation test, it was found that gas permeation through the membrane was significantly affected by the temperature of the separation process. The highest permeability of H2, CO2, and CH4 was detected on the composite carbon membrane at a 3 °C/min heating rate with a permeation temperature of 373 K. The thermodynamic study shows that CO2 and H2 have lower activation energies compared to CH4. The transport mechanism of the membrane involved adsorption and activated surface diffusion. The permeation temperature has a large impact on the transport of small penetrants in the carbon matrix.

Carbon membrane for gas separation: A short review

For the past 30 years, membrane technology has been prominently used for various gas purification to obtain a high purity gas. Membrane acts as semipermeable wall, which the separation occurs by controlling the rate of movement of various molecules between two liquid phases or two gas phases or a liquid and a gas phase that passing through the membranes. Then, the advantages offered by membrane process such as simple operation with low energy consumption, low operating and capital cost, continuous process and unnecessary regeneration process compared to absorption and adsorption processes has attracted considerable attentions by researchers. Besides, traditional methods such as pressure swing adsorption, cryogenic distillation and amine absorption which experienced with high energy consumption, expensive and lead to adverse impact on the environment has even made membrane process as preferable method for gas separation. Polymeric materials were used to develop a membrane that can attain high selectivity and permeability with high chemical and thermal resistance.

Effects of Oxidation Condition on the Permeation Performances of Phenol-Formaldehyde Based Carbon Membranes for Gas Separation

Phenol-formaldehyde based carbon membranes in this study were prepared by (a) coating the macroporous tube phenol-formaldehyde microfiltration membranes, (b) carbonization at 800°C and (c) CO2 oxidation as an additional step. Oxidation conditions were changed in order to investigate the oxidation effect on the pore structure and permeation performances. The results showed that enlargement of the membrane pore occurred through oxidation. The permeation properties can be increased by different oxidation conditions

Preparation and characterization of supported ordered nanoporous carbon membranes for gas separation

ABSTRACTSupported ordered nanoporous carbon membranes (ONCM) were prepared by coating a membrane‐forming solution of resorcinol‐formaldehyde (RF) resin on plate support through solvent evaporation and pyrolysis. The membrane solution was formed by the organic‐organic assembly of RF resin with Pluronic F127 in the presence of triethyl orthoacetate and catalyst hydrochloric acid. The thermal stability of precursor, the microstructure, functional groups, and morphology and porous structure of resultant support and ONCM were investigated by the techniques of thermogravimetry, X‐ray diffraction, Fourier transformed infrared spectroscopy, scanning electron microscopy/transmission electron microscopy and nitrogen adsorption‐desorption, respectively. Results have shown that the as‐obtained ONCM has well‐developed porous regularity with bi‐modal narrow pore size distribution. ONCM is tightly adhered to the adopted phenolic resin‐based carbon support. Gases permeating through the ONCM are dominated by molecular sieving mechanism. The ideal gas separation factor of the supported ONCM can be reached to 46.4, 4.7 and 3.3 for H2/N2, CO2/N2 and O2/N2, respectively. The supported ONCM obtained in this work exhibits most promising application for permanent gas separation. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39925.

Towards Fabrication of Low-Cost Carbon/Ceramics Membranes: Substrate Modification

This paper presents a novel method for fabrication of carbon membranes for gas separation by mean of surface modification with a conventional 2B pencil on the low-cost macroporous Al2O3 substrate. The resulting membrane was characterized by SEM, which shows that the modified membrane is continuous and uniform without defects. Gas permeation experiments were conducted by single gas measurements (test gas: H2, CO2, O2 and N2) at 20–80 °C under 100–400 kPa. The results show that the pencil lead layer can effectively prevent deep infiltration of precursor solution into the pores of substrate, and that gas transport through carbon membrane follows the molecular sieving mechanism. Based on the modified substrate, the carbon membrane exhibits good permeability (up to the order magnitude of 10-9 mol/m2 s Pa) and separation capability such as H2/N2 of 37.3, CO2/N2 of 11.2, and O2/N2 of 8.3.

Precursor Selection and Process Conditions in the Preparation of Carbon Membrane for Gas Separation: A Review

Carbon membranes prepared by pyrolysis/carbonization of polymeric precursors have been studied in the last few years as a promising candidate for gas separation process. As the aim of this paper, a review on polymer precursor selection and effect of pyrolysis conditions on carbon membrane characteristics and performances were discussed in detail. A number of different polymer precursors have been surveyed for their utility as materials in carbon membrane fabrication. The gas transport properties of various types of carbon membrane that produced by different researchers was summarized. Furthermore, the potential applications and future directions of carbon membrane in gas separation processes were also briefly identified.

Optimizing the synthesis of composite polyvinylidene dichloride-based selective surface flow carbon membranes for gas separation

Selective surface flow (SSF) carbon membranes were fabricated by pyrolysis of polyvinylidene dichloride (PVDC) layer deposited on macroporous ceramic supports. The pore properties of PVDC carbons were examined by physical adsorption of nitrogen and subsequent micropore analysis. The measured average pore sizes range from 1.23 to 1.42 nm for PVDC carbons with the pyrolysis temperature range of 873–1273 K respectively. The advantage of PVDC-based SSF carbon membranes is their low transport resistance with typical gas permeances of 10 −6–10 −7 mol/m 2 s Pa, 2–4 orders of magnitude higher than those of carbon molecular sieve membranes. They are suitable for separation of feed streams containing strongly adsorbing species such as hydrocarbons from non/weakly adsorbing components. In this study, gas molecules of similar kinetic diameter but disparate adsorption ability like ethane and nitrogen were chosen to evaluate the membrane separation performance and the reverse-selectivity characteristic of SSF carbon membranes. Commercial PVDC solutions were used and the preparation factors like concentration of polymer precursor, carbonization temperature and coating conditions were taken into account to optimize the SSF carbon membranes performance for hydrocarbons–nitrogen separations.

Physical Design, Preparation and Functionalization of Carbon Membranes for Gas Separation

Two challenges faced by carbon membrane for application on commercial scale are its low permeability and poor mechanical strength. And it is attributed to the vermiform pore structures and special characteristics of carbon membranes. In order to solve these problems, methods such as choosing the precursors with suitable chemical structure and space mould, incorporating nano-size functional groups into precursors are employed to effectively change and improve the vermiform pore structures of carbon membranes and enhance the gas permeabilities of carbon membranes. The results indicate that the gas permeabilities of hybridized function carbon membranes are increased by 2 orders in magnitude without reducing the gas selectivity obviously. Besides, some functional carbon membranes have also revealed higher gas selectivity for some gases such as CO(2). The coal-based composite carbon membranes with high gas permselectivity are developed by dip-coating the precursors on the cheap coal-based supports invented by ourselves to improve the mechanical strength of carbon membranes.

Polymide/Fe<SUB>3</SUB>O<SUB>4</SUB>-carbonized Membranes for Gas Separation

Novel functional carbon membranes for gas separation were designed and prepared by incorporating Fe3O4 nanoparticles into carbon membranes precursor polyimide. The as-synthesized membranes were characterized by TEM, XRD and VSM. The effects of Fe3O4 addition and the final pyrolysis temperature on the gas permeability were investigated. The results show that Fe3O4 nanoparticles transformed into other phase morphologies are helpful to form the graphite-like layers during the pyrolysis process, which make the membrane with two types of carbon structure : amorphous carbon and graphite-like layers. All the functional carbon membranes exhibit magnetism. Single gas permeation test results show that the as-synthesized membranes exhibit an outstanding molecular sieving capability together with high gas permeability. The gas permeability of H-2 is 61 times higher than the pure carbon membrane and the H-2/CO2 selectivity is also improved. Fe3O4 addition and the final pyrolysis temperature siginificantly impair the gas permeability. When the Fe3O4 content is 20wt%, the permeabilities of pure gas H-2, CO2, O-2, N-2, CH4 in the functional carbon membrane are 15476, 4385, 1565, 193 and 114 Barrers (1Barrer = 1 x 10(-10) cm(3) (STP) . cm/(cm(2) . s . cmHg)), respecticvely. The final pyrolysis temperature also has a remarkable effect on the gas separation performance.

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.

Preparation of Ni-P Alloy Composite Tube-Form Carbon Membrane for Gas Separation

A novel tube-form asymmetrical carbon membrane based on phenol-formaldehyde resin (PFR) is proposed in this paper. The membrane is composed of Ni-P alloy on exterior surface of carbon support membrane by electroless plating method after adding ferrous powders (<20&m) as active particles inside the membrane procurer. The results show that the H2, N2 and CO2 permeation rate through the composite Ni-P carbon membrane decrease and gas separation factors increase with increase of Fe content, and H2, N2 and CO2 permeation rates reach 0.44, 0.10 and 0.08 m3.m-2.s-1.MPa-1, respectively; H2/N2 and H2/CO2 separation factors are 4.2 and 5.5, respectively. The morphology of the membrane is measured by Scanning Electron Microscope (SEM).

Effects of phenolic resin pyrolysis conditions on carbon membrane performance for gas separation

This work shows that the gas separation performance of phenolic resin-based carbon membranes can be adjusted by controlling the pyrolysis processing variables (heat treatment temperature, heating rate, soaking time and atmosphere). A large variety of carbon membranes for gas separation have been developed by simple carbonization of a phenolic resin film deposited on a ceramic tubular support. Thus, molecular sieve carbon membranes (MSCMs) with good capabilities towards the separation of O 2–N 2, CO 2–CH 4, CO 2–N 2 and olefin–paraffin mixtures as well as adsorption-selective carbon membranes (ASCMs) effective in the recovery of hydrocarbons from hydrocarbon–N 2 mixtures have been obtained.

Future direction of R&D in carbon membranes for gas separation

This article discusses the challenges faced by carbon membranes, and it gives an indication of the clear future potential in research and development in this field.

Preparation and Characterization of Adsorption-Selective Carbon Membranes for Gas Separation

The preparation and characterisation of adsorption-selective carbon membranes (ASCMs) is described. ASCMs can separate the components of a gas mixture depending on their adsorption strength. These membranes allow the separation of non-adsorbable or weakly adsorbable components (e.g. N2, H2, O2, etc) from the more strongly adsorbable components (e.g. hydrocarbons) in a gas mixture. They are prepared from the deposition of a thin film of a phenolic resin on the inner face of an alumina tube. Air oxidative treatment at temperatures in the range of 300–400°C, prior to carbonisation (pre-oxidation) or after carbonisation (under vacuum at 700°C) (post-oxidation) gives rise to an adsorption-selective carbon membrane. This membrane shows a high permeability and selectivity towards the separation of gas mixtures formed by hydrocarbons and N2. Taking into account the permeation and separation properties of the membranes, post-oxidation treatment is shown to be more effective than pre-oxidation. The separation characteristics of the carbon membranes are dependent on the composition of the gas mixture (i.e. proportion of more strongly adsorbable components) and temperature.

Carbon membrane for gas separation derived from coal tar pitch

Carbon membrane, with properties superior to those typically found in polymeric materials, is a new and high-performance carbonaceous material for gas separation. Carbon membrane can be produced by carbonizing various carbon-containing materials, such as thermosetting resin, pitch, coal, graphite and plants, under inert atmosphere or vacuum. Carbon membranes described in this paper are produced from the carbonization of a coal tar pitch precursor, which is heat-polymerized and preoxidized under different conditions. The results observed show that heat-polymerization temperature, preoxidative temperature and carbonization temperature have an important effect on the properties of the carbon membrane. Gas separation mechanisms on the carbon membrane involve Knudsen diffusion and viscous flow. The ideal separation factor of H 2/CO 2 on the carbon–carbon composite membrane prepared by surface coating of carbon membrane can reach 16.2, but the mechanism of the gas separation needs to be further investigated.

Carbon Membranes for Gas Separation

Two kinds of pyrolysis carbon membranes for gas separation were prepared by control of preparation conditions. One was characterized by higher selectivity and another by higher permeability. The preparation process of the carbon membranes consists of pyrolysis and activation steps. The first step was conducted under inert gas and the second step in an oxidation environment. A thermosetting phenol formaldehyde resin membrane was chosen as the precursor. Preparation conditions were important factors for the structures and properties of the resulting carbon membranes. Pore size distribution was measured and morphology was observed. Effects of membrane structure on characteristics were discussed.

Performance and pore characterization of nanoporous carbon membranes for gas separation

The performance of a novel nanoporous carbon membrane for separation of hydrogen-hydrocarbon gas mixtures is described. The membrane selectively adsorbs hydrocarbons from hydrogen at the high pressure side and the adsorbed molecules then diffuse along the pore walls to the low pressure side. Pressure levels at thigh gh and low pressure sides of the membrane and the type and flow rate of the sweep gas at the low pressure side of the membrane were varied. The effects of these variables on the hydrogen recovery and hydrocarbon rejection by the membrane were investigated. Atomic force microscopy and scanning tunnelling microscopy scans of the membrane surface suggested that the membrane pore diameters were approximately 5 Å in diameter. Comparison between pure methane diffusivity through the membrane and those through nanoporous zeolites of various pore opening alsoo suggested that the membrane pores diameters were in the range of 5–6 Å. A sensitivity analysis indicated that the membranes contained a very narrow distribution of pore sizes.