水素分離用新型カーボン膜の開発

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🔬研究者:新規前駆体設計と炭化条件がカーボン膜の細孔構造・分離性能に与える影響を体系的に整理した材料研究の枠組みとして参照できる。

🏢実務担当者:水素精製・CO2分離プロセスの省エネ化や設備コンパクト化を検討する際の膜技術の現状と限界を把握できる。

🏛政策担当者:水素供給コスト低減に資する分離精製技術への研究開発支援の根拠として活用できる。

Our planet is increasingly signalling that human activity has disrupted its natural equilibrium. Rising sea levels, extreme weather events and ecosystems degradation underscore the urgent need for action. As the primary drivers of climate change, humans bear the responsibility to mitigate global warming and its consequences. In this context, the transition from a fossil fuel-based energy system to one that increasingly integrates renewable energy sources (RES) is a central strategy for reducing climate impacts. Hydrogen is widely regarded as a key component of the future energy landscape, particularly when produced through low-carbon pathways such as water electrolysis, photoelectrochemical water splitting, biomass gasification, and biological conversion processes. Its versatility allows for hydrogen applications in transportation, electricity generation, and heat production, although each requires specific levels of purity. Among the available techniques for hydrogen separation, such as cryogenic distillation, absorption, and adsorption, membrane technology offers distinct advantages, including higher energy efficiency and environmental compatibility, design compactness, and operational simplicity. Over the past decades, significant advances have been made in carbon membranes (CMs), improving their performance and enabling development of robust, defect-free, and tunable structures. However, despite this progress, CMs have not yet reached commercial maturity. To facilitate their transition from laboratory to industrial scale implementation, key challenges related to production process sustainability, safety and simplicity and membranes performance must be addressed. From a performance standpoint, although CMs show promising capabilities for hydrogen separation, they still lag behind Pd-based membranes, which represent the benchmark in terms of permeance and selectivity. This thesis addresses these challenges by focusing, in the first part, on improving the sustainability and safety of carbon membranes fabrication, and, in the second part, on exploring novel precursor materials and processing strategies to enhance their hydrogen separation performance and to simplify their production route. Chapter 1 provides the scientific and technological background of this work, outlining the role of hydrogen as a clean energy carrier and the challenges related to its production and purification. It reviews existing hydrogen separation technologies, emphasizing membrane processes as a sustainable alternative. Special focus is given to carbon membranes, highlighting their key advantages, current limitations, and potential for hydrogen separation. The fundamental gas transport mechanisms and governing equations are also introduced, establishing the basis for understanding the developments presented in this thesis. Chapter 2 takes a first step toward more sustainable carbon membranes fabrication by replacing the conventional solvent N-Methyl-2-pyrrolidone (NMP) with two greener alternatives, dihydrolevoglucosenone (Cyrene™) and γ-valerolactone (GVL), in the preparation of Novolac-based CMs. The influence of solvent choice on carbon structure development and membrane morphology is systematically investigated, highlighting its strong impact on gas transport properties. While CyreneTM-based membranes exhibit low selectivity values close to the Knudsen regime for H2/N2 and H2/CH4 separations, GVL-based systems show significantly improved performance. After optimization of the pyrolysis protocol, H2/N2 and H2/CH4 ideal selectivities as high as 270 and 240 are achieved at 20 °C, together with an appreciable H2 permeance of up to 7.04 · 10-8 mol m-2 s-1 Pa-1 at 200 °C. These results demonstrate the potential of GVL as a sustainable and high-performance alternative to conventional solvents. Chapter 3 introduces a systematic, phenomenological, and mechanistic methodology, referred to as SCALE, as a five-step pre-scale-up approach to identify the parameters that most strongly influence membrane performance as well as those impacting the overall safety of the production process. The use of interaction matrices enables the prioritization of key variables, highlighting solvent choice as a critical factor in both performance and safety. In this context, the thermal behaviour of the Novolac-NMP and Novolac-GVL systems introduced in Chapter 2 is investigated through cone calorimetry. The results show that replacing NMP with GVL reduces ignition propensity and the severity of combustion related phenomena. Overall, this chapter demonstrates that GVL not only provides a greener alternative to NMP but also represents a safer option from a fire-hazard perspective. Chapter 4, shifts the focus to the investigation of alternative polymeric precursors. In this chapter, a phenolic-like polymer based on 1,3,5-trimethoxybenzene-formaldehyde (TMBF) is synthesized via a polycondensation reaction. Its chemical and structural features, as well as the performance of the derived carbon membranes, are systematically studied as a function of the final carbonization temperature (500 °C - 700 °C). A clear dependence on pyrolysis conditions is observed, with increasing temperature leading to a progressive reduction in heteroatom content and modifications in the carbon structure. Membranes carbonized at 700 °C exhibit a marked improvement in separation performance, with H2/N2 and H2/CH4 ideal selectivities an order of magnitude higher than those obtained at lower temperatures, reaching values up to 157 and 131, respectively. This enhancement is attributed to the formation of micro- and ultramicroporosity within the carbon matrix. Beyond performance, which remains below state-of-the-art benchmarks, this study provides a methodological framework for the evaluation of new precursors, highlighting the critical role of carbonization temperature in determining their suitability for carbon membrane fabrication. In Chapter 5, the research moves beyond phenolic-type precursors to investigate linear polyimines characterized by a contorted molecular architecture that promotes intrinsic free volume and, upon pyrolysis, the formation of microporous carbon structures. A fluorenyl-containing polyimine (P1) is synthesized via a straightforward, catalyst-free condensation of inexpensive, commercially available monomers under mild conditions. Carbon membranes are fabricated on porous alumina supports and subjected to different carbonization temperatures (500 °C - 900 °C) and heating rates to evaluate the influence of pyrolysis on gas transport properties. Membranes carbonized at 700 °C display the most favourable balance of permeance and selectivity, exceeding the 2008 Robeson Upper Bound for H2/N2, H2/CH4, and H2/CO2 separations. The simplicity of the synthesis, combined with the reproducibility and tunability of this polymer system, underscores the potential of this precursor as a platform for high-performance hydrogen separation carbon membranes. Chapter 6 investigates an aromatic polyimine precursor (P2) incorporating kinked structural motifs designed to maximize intrinsic free volume and promote the formation of robust carbon networks upon pyrolysis. The precursor, synthesized via a simple catalyst-free route, combines high thermal stability with significant char yield, making it suitable for carbon membrane fabrication. Two distinct carbonization strategies are applied to tailor the structural evolution of the resulting membranes, revealing a strong link between processing conditions, pore architecture, and separation behaviour. In particular, controlled modulation of the micro- to ultramicropore ratio enables tuning of transport properties toward either enhanced permeance or improved selectivity. The resulting carbon membranes achieve high hydrogen permeance alongside notable selectivity, with H2/N2 and H2/CH4 values up to 214 and 759, respectively, and also show promising CO2/CH4 separation performance at room temperature. The membranes compare favourably with state-of-the-art materials, confirming their potential as high-performance candidates for hydrogen purification and carbon capture applications. Finally, Chapter 7 presents the main conclusions of the dissertation and provides an outlook with recommendations for future research. It includes a critical comparison of the performance of the developed membranes with state-of-the-art materials, encompassing both alternative membrane technologies and carbon membranes derived from different precursors, thereby highlighting the advances achieved and the remaining challenges. In the outlook, a third polyimine structure (P3) is also introduced, showing promising results for hydrogen separation applications at temperatures above 150 °C. Overall, this chapter consolidates the main findings of the thesis and defines future research directions for the further development of carbon membrane materials and processes.

• openalex https://research.tue.nl/en/publications/a241cad4-6146-4421-b6ee-1d0e3b23b39afirst seen 2026-11-10 05:05:33 · last seen 2026-11-14 05:12:57