(453f) Development of Si-Based Subnanoporous Membranes and Application to Process Intensification

Amorphous SiO₂-based membranes prepared from tetraethoxysilane (TEOS) show excellent performance with high molecular sieving and permeability. To solve the most critical issues of SiO₂ membranes, that is, pore-size control and hydrothermal stability, our research group has developed metal/fluorine doped SiO₂, bridged-alkoxysilane derived organosilica (SiO_1.5), silicon oxycarbonate or preceramic polymer-based silicon carbide, and metal-coordinated aminosilica membranes. [1, 2] We have investigated various types of membrane reactors using the Si-based membranes, which include steam reforming of methane for H₂ production [3], dehydrogenation of methylcyclohexane (MCH) [4] and NH₃ [5], and decomposition of H₂SO₄ for O₂ production [6]. Our recent progresses have been extended to transesterification membrane reaction [7, 8] and NH₃-synthesis related technology [9, 10].

Transesterification reaction such as production of butyl acetate (BA) and methanol (MeOH) from methyl acetate (MA) and n-butanol (BuOH) is one of the most promising applications of membrane reactors. For realizing equilibrium shift in the transesterification for BA production, methanol-selective membranes were prepared from 1,2-bis(triethoxysilyl)acetylene (BTESA). The BTESA-derived organosilica membrane exhibited a MeOH flux exceeding 10 kg/(m² h) for MeOH/butyl acetate (BA) binary pervaporation with 10 wt% MeOH at 100 â—¦C and a MeOH separation factor exceeding 10³ because of large pore sizes tuned by triple bonds (Si-C≡C-Si). [7]

A membrane reactor (MR) using a 1,2-bis(triethoxysilyl)acetylene (BTESA)-derived organosilica membrane was applied for the transesterification reaction by extracting methanol (MeOH) in batch and flow modes. The effect of temperature on the liquid-phase batch MR (Batch-MR) performance was investigated at 60–100 ◦C. The BA yield for methyl acetate (MA)/n-butanol (BuOH) = 1 at 100 ◦C reached 84% after 10 h, which was significantly higher than that achieved at equilibrium (48%). Moreover, the performances of the Batch-MR, continuous stirred tank MR (CST-MR), and plug flow MR (PF-MR) were compared under the same reaction conditions, indicating experimental results obtained in Batch-MR and CST-MR agreed with numeric calculations without fitting parameters. [7, 8]

NH₃ has a boiling point of - 33.3 â—¦C and a saturated vapor pressure of 0.86 MPa at 20 â—¦C, which makes it simple to store and transport as energy carriers. We reported dehydrogenation membrane reactor for H₂ production from NH₃ using TEOS-derived SiO₂ membranes, and confirmed enhanced conversion of NH₃ due to selective removal of H₂ [5]. At present, production of “Green Ammonia” using renewable energy such as solar power has drawn a great deal of attention. For enabling NH₃ production at low temperature and low pressure compared with conventional Haber-Bosh process (10-30 MPa, 400-500â—¦C), we are currently working on NH₃-selective membrane reactors using two types different membranes: perfluorosulfonic acid polymer (PFSA)/ceramic composite membranes and metal-coordinated aminosilica membranes [9, 10]. Nafion and Aquivion/ ceramic membranes showed single-component NH₃ permeance that reached >9.30 × 10^-7 mol/(m² s Pa) and >1.55 × 10^-6 mol/(m² s Pa) at 50–200 â—¦C, Moreover, NH₃ permeance of >2.31 × 10^-6 mol/(m² s Pa) was obtained from Aquivion-H+ with NH₃ selectivity >90 for NH₃/H₂ and >800 for NH₃/N₂ at 50 â—¦C in a mixed system. In addition, we have found Bis[3-(trimethoxysilyl)propyl] amine (BTPA) membranes doped with different metals (Ni, Fe etc.) are also promising for NH₃-selective permeation [10].

In addition to process intensification via membrane reactor, the novel concept of steam recovery from flue gas will be introduced for simultaneous recovery of water and energy. We proposed a new system of steam and latent heat recovery from waste streams using organosilica membranes [11]. Proof-of-concept testing was conducted in a running incinerator plant. The proposed system eliminates the need for a water supply while simultaneously recovering latent heat from the waste stream. First, the long-term stability of an organosilica membrane was confirmed over the course of six months in laboratory-scale under a simulated waste stream. Second, steam recovery was demonstrated in a running waste incinerator plant, which confirmed the steady operation of this steam recovery system with a steam recovery rate.

[1] Tsuru T., Silica-Based Membranes with Molecular-Net-Sieving Properties: Development and Applications, Journal of Chemical Engineering of Japan, 51 (2018) 713-725.

[2] Tsuru T., Silicon-based subnanoporous membranes with amorphous structures, in 60 Years of the Loeb-Sourirajan Membrane: Principles, New Materials, Modelling, Characterization, and Applications, Elsevier 2022.

[3] Tsuru T., Yamaguchi K., Yoshioka T., Asaeda M., Methane steam reforming by microporous catalytic membrane reactors, AIChE J. 50 (2004) 2794.

[4] Li G., Kanezashi M., Yoshioka T., Tsuru T., Ammonia decomposition in catalytic membrane reactors: Simulation and experimental studies, AIChE J. 41 (2013) 1663

[5] Meng L., Yu X., Niimi T., Nagasawa H., Kanezashi M., Yoshioka T., Tsuru T., Methylcyclohexane dehydrogenation for hydrogen production via a bimodal catalytic membrane reactor, AIChE J. 61 (2015) 1628.

[6] Meng L., Kanezashi M., Yu X., Tsuru T., Enhanced decomposition of sulfur trioxide in the water-splitting iodine-sulfur process: Via a catalytic membrane reactor, J. Mat. Chem. A, 4 (2016) 59045

[7] Sato T., Nagasawa H., Kanezashi M., Tsuru T., Enhanced production of butyl acetate via methanol-extracting transesterification membrane reactors using organosilica membrane: Experiment and modeling, Chem. Eng. J. 429 (2022) 132188

[8] Sato T., Nagasawa H., Kanezashi M., Tsuru T., Transesterification membrane reactor with organosilica membrane in batch and continuous flow modes, Chem. Eng. J. 450 (2022) 137862

[9] Wakimoto K., Nagasawa H., Kanezashi M., Tsuru T., Ammonia permeation of fluorinated sulfonic acid polymer/ceramic composite membranes, J. Membra. Sci., 658 (2022) 120718

[10] Yang W., Nagasawa H., Kanezashi M., Tsuru T., submitted.

[11] Moriyama N., Nagasawa H., Kanezashi M., Tsuru T., Steam recovery via nanoporous and subnanoporous organosilica membranes: The effects of pore structure and operating conditions, Sep. Purif. Tech., 275 (2021) 119191.