Hybrid organosilica membranes and processes: Status and outlook
Introduction
Molecular separation membranes are expected to play an important role in reaching the environmental goal to reduce CO2 emissions by approximately 50 Gt per year by 2050 [1]. Membranes can be applied as effective and energy-efficient separation systems to dehydrate wet bio-based fuels [2], [3]. Also application in the (petro)chemical industry is widely considered to significantly enhance the energy efficiency of key processes. Although exact numbers are missing, separation processes are known to be one of the more energy-intensive steps in a chemical production plant. Molecular separation membranes can play a crucial role here [4], [5], [6].
In this paper, the status and potential of hybrid organosilica membrane materials, and their use in different molecular separations are presented. An outlook is given towards further developments. Pure inorganic silica membranes have a low hydrothermal stability [7], [8], reducing the application window for dehydration of organic liquids by pervaporation to temperatures not exceeding ∼75 °C [9]. The incorporation of methyl groups [10] in the silica structure allows an increase of the application temperature to 95 °C [9]. This results in an application window with a temperature range that is similar to that of polymeric membranes like PVA [11] and polyimides [12]. Ceramic membranes will only have a value in the market when clear advantages over the commercially produced polymeric ones can be obtained. These advantages may include a higher performance, i.e. a higher selectivity and permeance, and an increased stability. As a result the application window can be broader than the more commonly used polymeric membranes. Envisaged application extensions are a higher application temperature, higher chemical stability towards strong organic solvents, acids and water, and a smaller sensitivity to swelling. The increase of operation periods under a wider range of applications will result in a positive business case for all industrial parties involved.
The focus of this review will be the preparation of membranes bridged polysilsesquioxanes precursors and their application in processes. Other types of hybrid membranes are reviewed elsewhere [13]. These current class of materials is characterized by covalent bonds between both oxygen and hydrocarbons to silicon. These materials are prepared by sol–gel processing [14] of monomers that contain an organic group that bridges typically two functional silyl groups [15]. A great variety of organic bridges can be used, including aromatic, alkyne, alkene, alkane, and functionalized moieties [16]. A general trend in mesoporous materials is that the pore diameter increases with increasing length of the bridge [16], [17], [18]. Alternatively, organic templates can be used to direct the pore formation process [19]. The positive impact of the organic bridge on the hydrothermal stability for mesoporous materials has been recognized [20]. The application of similar microporous materials in molecular separation membranes was reported as recently as 2008 [21].
This review paper is structured in a number of chapters. We start with material and preparation considerations, which include structure–property relations. With respect to preparation, our focus is on sol–gel processes, in which bridging and pendant organic groups with various structures are incorporated. This is followed by a generic overview of possible applications of these membranes. While the main focus is on pervaporation, developments in gas separation and nanofiltration are discussed as well. A pervaporation process case study is presented for the production of an acetal, which can be used as a renewable diesel additive. The topics of the last chapters are recent developments in alternative preparation methods, new support options, new processes, and an outlook towards the requirements in fundamental knowledge needed to allow further applicability.
Section snippets
Preparation of oxide membranes
Oxide microporous materials and membranes are typically prepared by conventional sol–gel approaches [14]. The mild synthesis conditions of sol–gel preparation allow the synthesis and control of nanoporous inorganic materials. Thin layers, <1 μm, can be efficiently deposited onto a support by coating with the sol before the transition to the gel phase occurs. The first membranes prepared in this way were made from tetraethylorthosilicate (TEOS) [22], [23], [24]. A microporous, pore diameter dp < 2
Pervaporation applications
The HybSi® membrane was originally developed for pervaporation applications, and not surprisingly most application-oriented papers focus on the separation of water from organic solvents. In this section, we present the technical application window with special attention to the long-term behavior.
In the publication of 2008 [21], a long term continuous pervaporation experiment at 150 °C was reported for the first time. Data for a period of over 500 days were reported, without any indication of
The production of acetal: a case study
One of the possible applications that has been suggested for pervaporation membranes is related to the dehydration of reaction mixtures [74]. Till date, membranes have found limited utilization in this field. The breakthrough in stability of the HybSi® membrane may renew the interest in this topic. The interest in acetals is increasing in recent years [75], [76], [77]. Acetals can be considered as promising bio-based diesel additives. The production of these compounds, from an alcohol and an
Origins of the high stability
The operational stability of organically bridged silica under demanding hydrothermal conditions is unique. For periodic mesoporous materials it has been established that the inclusion of organic bridges is essential for their hydrothermal stability [20]. The solubility of organosilica in water appears to be lower than that of inorganic silica [82].
The increased stability of methylated silica as compared to pure silica has been ascribed to a shielding effect rather than to stabilization of the
New manufacturing technologies
Although less extensively applied than wet chemistry processes in the field of membrane science and technology, vapor-based deposition techniques have been applied successfully. Chemical vapor deposition is a thin-film deposition process following the thermal decomposition of one or more volatile precursors at the surface of a substrate to produce the desired film. One specific example is the counter-diffusion chemical vapor deposition method [88]. The high temperature, 600 °C, and the presence
New supports
The membranes described above are often deposited in first instance on a flat ceramic discs [51]. This geometry is very suitable for fundamental research, but is unlikely to be suitable for scaling up. A tubular geometry is more appropriate in this case. A layer deposited on the outside of a ceramic tube offers mechanical resistance and easy observation [21]. One possibility to decrease costs is to increase the surface area that can be coated in one single step. This can be achieved through the
Conclusions
In this review an overview of the current status of organic–inorganic silica-based molecular membranes has been presented. It was shown that the incorporation of especially alkyl hydrocarbon bridges greatly enhances the applicability of the sol–gel membranes. Furthermore that gas phase deposition methods can be used to make functional hybrid membranes. The main advantage of this membrane system is an exceptionally high stability under especially hydrothermal conditions. Long-term data sets for
Acknowledgements
This research was supported by the Netherlands Technology Foundation STW and the EOS technology program of the Dutch Ministry of Economic Affairs, administered by Agentschap NL, and by the Institute of Sustainable Process Technology, ISPT.
References (110)
- et al.
Selective ethanol extraction from fermentation broth using a silicalite membrane
Sep. Purif. Technol.
(2002) - et al.
Process analysis and optimisation of hybrid processes for the dehydration of ethanol
Chem. Eng. Res. Des.
(2013) - et al.
Dewatering of organics by pervaporation with silica membranes
Sep. Purif. Technol.
(2001) - et al.
Hydrophobic silica membranes for gas separation
J. Membr. Sci.
(1999) - et al.
Comparision of the separation of mixtures by vapor permeation and by pervaporation using PVA composite membranes. I. Binary alcohol–water systems
J. Membr. Sci.
(1992) - et al.
High-temperature pervaporation performance of ceramic-supported polyimide membranes in the dehydration of alcohols
J. Membr. Sci.
(2008) - et al.
Hybrid organic–inorganic membranes with specific transport properties. Applications in separation and sensors technologies
Sep. Purif. Technol.
(2001) - et al.
Alkylene-bridged polysilsesquioxane aerogels: highly porous hybrid organic–inorganic materials
J. Non-Cryst. Solids
(1995) - et al.
The impact of framework organic functional groups on the hydrophobicity and overall stability of mesoporous silica materials
Mater. Chem. Phys.
(2012) - et al.
Formation and characterization of supported microporous ceramic membranes prepared by sol–gel modification techniques
J. Membr. Sci.
(1995)
Separation of inorganic/organic gas mixtures by porous silica membranes
Sep. Purif. Technol.
Sol–gel strategies for controlled porosity inorganic materials
J. Membr. Sci.
High temperature H2/CO2 separation using cobalt oxide silica membranes
Int. J. Hydrogen Energy
Hydrothermal stability of microporous silica and niobia–silica membranes
J. Membr. Sci.
Potentialities of microporous membranes for H2/CO2 separation in future fossil fuel power plants: evaluation of SiO2, ZrO2, Y2O3–ZrO2 and TiO2–ZrO2 sol–gel membranes
J. Membr. Sci.
Macroporous support coatings for molecular separation membranes having a minimum defect density
J. Membr. Sci.
Preparation of organic–inorganic hybrid silica membranes using organoalkoxysilanes: the effect of pendant groups
J. Membr. Sci.
Facile synthesis of hydrophobic microporous silica membranes and their resistance to humid atmosphere
Micropor. Mesopor. Mater.
Microporous sol–gel derived aminosilicate membrane for enhanced carbon dioxide separation
Sep. Purif. Technol.
Tubular ceramic-supported sol–gel silica-based membranes for flue gas carbon dioxide capture and sequestration
J. Membr. Sci.
Preparation of composite microporous silica membranes using TEOS and 1,2-bis(triethoxysilyl)ethane as precursors for gas separation
Chin. J. Chem. Eng.
From hydrophilic to hydrophobic HybSi® membranes: a change of affinity and applicability
J. Membr. Sci.
Effect of calcination temperature on carbon dioxide separation properties of a novel microporous hybrid silica membrane
J. Membr. Sci.
Organic “template” approach to molecular sieving silica membranes
J. Membr. Sci.
Dual-layer asymmetric microporous silica membranes
J. Membr. Sci.
Effect of calcination temperature on the PV dehydration performance of alcohol aqueous solutions through BTESE-derived silica membranes
J. Membr. Sci.
Organic–inorganic hybrid silica membranes with controlled silica network size: preparation and gas permeation characteristics
J. Membr. Sci.
Pushing membrane stability boundaries with HybSi® pervaporation membranes
J. Membr. Sci.
Acetalization reaction of ethanol with butyraldehyde coupled with pervaporation. Semi-batch pervaporation studies and resistance of HybSi® membranes to catalyst impacts
J. Membr. Sci.
Pervaporation of acetic acid aqueous solutions by organosilica membranes
J. Membr. Sci.
High-performance hybrid pervaporation membranes with superior hydrothermal and acid-stability
J. Membr. Sci.
Molecular simulation of micro-structures and gas diffusion behavior of organic–inorganic hybrid amorphous silica membranes
J. Membr. Sci.
Effect of Nb content on hydrothermal stability of a novel ethylene-bridged silsesquioxane molecular sieving membrane for H2/CO2 separation
J. Membr. Sci.
Improved performance of silica membranes for gas separation
J. Membr. Sci.
The esterification of tartaric acid with ethanol: kinetics and shifting the equilibrium by means of pervaporation
Chem. Eng. Sci.
Catalytic reactive distillation process development for 1,1 diethoxy butane production from renewable sources
Bioresour. Technol.
Preparation of a stable silica membrane by a counter diffusion chemical vapor deposition method
J. Membr. Sci.
Optimization of commercial net spacers in spiral wound membrane modules
J. Membr. Sci.
Chemical vapor deposition of coatings
Prog. Mater. Sci.
Gas diffusion and sorption properties of polysiloxane membranes prepared by PECVD
J. Membr. Sci.
Intensification of recovery of ethanol from fermentation broth using pervaporation: economical evaluation
Chem. Biochem. Eng. Q
Evolving beyond the thermal age of separation processes: membranes can lead the way
AIChE. J.
Reactive and membrane-assisted distillation: recent developments and perspective
Chem. Eng. Res. Des.
Porous silica–zirconia (50%) membranes for pervaporation of iso-propyl alcohol (IPA)/water mixtures
J. Chem. Eng. Jpn.
Long-term pervaporation performance of microporous methylated silica membranes
Chem. Commun.
Sol–gel Science – The Physics and Chemistry of Sol–gel Processing
Arylsilsesquioxane gels and related materials. New hybrids of organic and inorganic networks
J. Am. Chem. Soc.
Bridged polysilsesquioxanes. Molecular-engineered hybrid organic–inorganic materials
Chem. Mater.
Alkylene-bridged silsesquioxane sol–gel synthesis and xerogel characterization. Molecular requirements for porosity
Chem. Mater.
Cited by (74)
Effect of heat diffusivity for driving chain stitching of dual-type hybrid organosilica-derived membranes
2022, Separation and Purification TechnologyBoosting the CO<inf>2</inf> capture efficiency through aromatic bridged organosilica membranes
2022, Journal of Membrane ScienceHomogeneous sub-nanophase network tailoring of dual organosilica membrane for enhancing CO<inf>2</inf> gas separation
2022, Journal of Membrane Science