Techno-economic assessment of the one-step CO₂conversion to dimethyl ether in a membrane-assisted process

This study investigates the impact of the membrane reactor (MR) technology with in-situ removal of water to boost the performance of the one-step DME synthesis via CO2 hydrogenation at process scale. Given the higher efficiency in converting the feedstock, the membrane reactor allows for a remarkable decrease in the main cost drivers of the process, i.e., the catalyst mass and the H2 feed flow, by ca. 39% and 64%, respectively. Furthermore, the MR-assisted process requires 46% less utilities than the conventional process, especially in terms of cooling water and refrigerant, with a corresponding decrease in environmental impact (i.e., 25% less CO2 emissions). Both the conventional and MR-assisted plants were found effective for the mitigation of the CO2 emissions, avoiding ca. 1.4-1.6 tonCO2/tonDME. However, given the higher reactor and process efficiency, the membrane technology contributes to a significant reduction (i.e., 25%) in the operating costs, which is a remarkable improvement in this OPEX intensive process. Nevertheless, the calculated minimum DME selling price (i.e., 1739 €/ton and 1960 €/ton for the MR-assisted and the conventional process, respectively) is over 3 times greater than the current DME market price. Yet, with the predicted decrease of renewable H2 price and a zero-to-negative cost for the CO2 feedstock, the MR-assisted system could become competitive with the benchmark between 2025 and 2050.</p

Vapor/gas separation through carbon molecular sieve membranes: Experimental and theoretical investigation

The separation of H2O vapor from (hydrogen-rich) gaseous streams is a topic of increasing interest in the context of CO2 valorisation, where the in situ water removal increases product yield and catalyst stability. In this work, composite alumina carbon molecular sieve membranes (Al-CMSM) were prepared from phenolic resin solutions loaded with hydrophilic boehmite (γ-AlO(OH)) nanosheets (0.4–1.4 wt. % in solution) which partially transform to γ-Al2O3 nanosheets upon thermal decomposition of the resin, improving the hydrophilicity and thus the adsorption-diffusion contribution of the H2O permeation. The γ-Al2O3 nanosheets showed no influence on the pore size distribution of the membranes in the range of micropores, but they increased the membrane hydrophilicity. In addition, the use of boehmite in the resin solution causes an increase in the viscosity and thus an increase in the carbon layers thickness deposited on the porous α-Al2O3 support (from 1 to 3.3 μm). Furthermore, the alumina sheets introduce defects in the carbon matrix, increasing the tortuosity of the active layer, as concluded via phenomenological modelling and parametric fitting of the experimental results. As a consequence, the water permeability exhibits a maximum (1.3ꞏ10−6 molꞏs−1 Pa−1 m−1 at 150 °C) with boehmite/alumina content of ca. 0.8 wt. %, as the combined effects of increasing hydrophilicity (which favour H2O permeability) and increasing thickness and tortuosity (which hamper permeability) upon increasing boehmite loading. Similarly, the H2O/gas perm-selectivity is optimum at 1.2 wt. % boehmite loading. We further investigated the H2O permeation mechanism by modelling the mono- and multi-layer adsorption and capillary condensation of water in microporous media, which result as the main transport mechanisms in the explored conditions.This project has received funding from the European Union’s Horizon 2020 research and innovation programme undergrant agreement No 838014 (C2Fuelproject)

Carbon molecular sieve membranes for water separation in CO₂ hydrogenation reactions:Effect of the carbonization temperature

Carbon membranes are a potentially attractive candidate for the in-situ removal of water vapor in CO2 hydrogenation reactions. Their hydrophilicity and pore structure can be tuned by properly adjusting the synthesis procedure. Herein, we assess the effect of the carbonization temperature (450–750 °C) on the performance of supported CMSM in terms of vapor/gas separation, in correlation with changes in their surface functionality and porous structure. FTIR spectra showed that the nature of the functional groups changes with the evolution of the carbonization step, leading to a gradual loss in hydrophilicity (i.e., OH stretching disappears at Tcarb ≥ 600 °C). The extent of water adsorption displays an optimum at Tcarb of 500 °C, with the membrane carbonized at 650 °C being the least hydrophilic. We found that the pore size distribution strongly influences the water permeance. At all Tcarb, adsorption-diffusion (AD) is the dominant transport mechanisms. However, as soon as ultra-micropores appear (Tcarb: 600–700 °C) molecular sieving (MS) contributes to an increase in the water permeance, despites a loss in hydrophilicity. At Tcarb ≥ 750 °C, MS pores disappear, causing a drop in the water permeance. Finally, the permeance of different gases (N2, H2, CO, CO2) is mostly affected by the pore size distribution, with MS being the dominant mechanism over the AD, except for CO2. However, the extent and mechanism of gas permeation drastically change as a function of the water content in the feed, indicating that gas/vapor molecules need to compete to access the pores of the membranes.</p

Phosphorylation of SRSF1 is modulated by replicational stress

DNA ligase I-deficient 46BR.1G1 cells show a delay in the maturation of replicative intermediates resulting in the accumulation of single- and double-stranded DNA breaks. As a consequence the ataxia telangiectasia mutated protein kinase (ATM) is constitutively phosphorylated at a basal level. Here, we use 46BR.1G1 cells as a model system to study the cell response to chronic replication-dependent DNA damage. Starting from a proteomic approach, we demonstrate that the phosphorylation level of factors controlling constitutive and alternative splicing is affected by the damage elicited by DNA ligase I deficiency. In particular, we show that SRSF1 is hyperphosphorylated in 46BR.1G1 cells compared to control fibroblasts. This hyperphosphorylation can be partially prevented by inhibiting ATM activity with caffeine. Notably, hyperphosphorylation of SRSF1 affects the subnuclear distribution of the protein and the alternative splicing pattern of target genes. We also unveil a modulation of SRSF1 phosphorylation after exposure of MRC-5V1 control fibroblasts to different exogenous sources of DNA damage. Altogether, our observations indicate that a relevant aspect of the cell response to DNA damage involves the post-translational regulation of splicing factor SRSF1 which is associated with a shift in the alternative splicing program of target genes to control cell survival or cell death

Direct conversion of CO2 to dimethyl ether in a fixed bed membrane reactor: Influence of membrane properties and process conditions: Influence of membrane properties and process conditions

The direct hydrogenation of CO2 to dimethyl ether (DME) is a promising technology for CO2 valorisation. In this work, a 1D phenomenological reactor model is developed to evaluate and optimize the performance of a membrane reactor for this conversion, otherwise limited by thermodynamic equilibrium and temperature gradients. The co-current circulation of a sweep gas stream through the permeation zone promotes both water and heat removal from the reaction zone, thus increasing overall DME yield (from 44% to 64%). The membrane properties in terms of water permeability (i.e., 4·10−7 mol·Pa−1m−2s−1) and selectivity (i.e., 50 towards H2, 30 towards CO2 and CO, 10 towards methanol), for optimal reactor performance have been determined considering, for the first time, non-ideal separation and non-isothermal operation. Thus, this work sheds light into suitable membrane materials for this applications. Then, the non-isothermal performance of the membrane reactor was analysed as a function of the process parameters (i.e., the sweep gas to feed flow ratio, the gradient of total pressure across the membrane, the inlet temperature to the reaction and permeation zone and the feed composition). Owing to its ability to remove 96% of the water produced in this reaction, the proposed membrane reactor outperforms a conventional packed bed for the same application (i.e., with 36% and 46% improvement in CO2 conversion and DME yield, respectively). The results of this work demonstrate the potential of the membrane reactor to make the CO2 conversion to DME a feasible process

Mechanics and transport phenomena in agarose-based hydrogels studied by compression-relaxation tests

Hydrogels are widespread materials, used in several frontier fields, due to their peculiar behavior: they couple solvent mass transport to system mechanics, exhibiting viscoelastic and poroelastic characteristics. The full understanding of this behavior is crucial to correctly design such complex systems. In this study agarose gels has been investigated through experimental stress-relaxation tests and with the aid of a 3D poroviscoelastic model. At the investigated experimental conditions, the agarose gels samples show a prevalent viscoelastic behavior, revealing limited water transport and an increase of the stiffness as well as of the relaxation time along with the polymer concentration. The model parameters, derived from the fitting of some experimental data, have been generalized and used to purely predict the behavior of another set of gels. The stress-relaxation tests coupled with mathematical modeling demonstrated to be a powerful tool to study hydrogels’ behavior