David Alfredo Pacheco Tanaka

The use of e-fuels, such as methanol (MeOH), is considered an alternative for the reduction of carbon emissions. MeOH can be produced from captured CO₂ and green H₂, with the exothermic (equilibrium-limited) reaction favoured at low temperatures and high pressures. However, CO₂ is a very stable molecule and requires high temperature (>200 °C) to overcome the slow activation kinetics. In this study, MeOH was synthesized from CO₂ and H₂ in a packed-bed membrane reactor (PBMR) using a commercial Cu/ZnO/Al₂O₃ catalyst and a tubular-supported, water-selective composite alumina–carbon molecular sieve membrane (Al-CMSM) immersed in the catalytic bed. A mixture of H₂/CO₂ (3/1) was fed into both sides of the membrane to increase the driving force of the gases produced by the reaction. The effect of the temperature of reaction (200, 220, and 240 °C), pressure difference (0 and 3 bar), and the sweep gas/reacting gas ratio (SW = 1, 3, 5) in the CO₂ conversion and products yield was studied. For comparison, the reactions were also carried out in a packed-bed reactor (PBR) configuration where the tubular membrane was replaced by a metallic tube of the same size. CO₂ conversion and MeOH yield are much higher in PBMR than in PBR configuration, showing the benefit of using the water-selective membrane. In PBMR, MeOH yield increases with SW and slightly decreases with the temperature, overcoming the limitation imposed by the thermodynamics.

H₂ production via membrane-assisted steam methane reforming (MA-SMR) can ensure higher energy efficiency and lower emissions compared to conventional reforming processes (SMR). Ceramic-supported Pd–Ag membranes have been extensively investigated for membrane-assisted steam methane reforming applications, with outstanding performance. However, costs, sealings for integration in the reactor structure, and resistance to solicitations remain challenging issues. In this work, the surface quality of a low-cost, porous Hastelloy-X filter is improved by asymmetric filling with α-Al₂O₃ of decreasing size and deposition of γ-Al₂O₃ as an interdiffusion barrier. On the modified support, a thin Pd–Ag layer was deposited via electroless plating (ELP), resulting in a membrane with H₂/N₂ selectivity >10,000. The permeation characteristics of the membrane were studied, followed by testing for membrane-assisted methane steam reforming. The results showed the ability of the membrane reactor to overcome thermodynamic conversion of the conventional process for all explored operating conditions, as well as ensuring 99.3% H₂ purity in the permeate stream at 500 °C and 4 bar.

The use of ammonia as a hydrogen carrier requires efficient cracking technology. A promising solution is the use of a membrane reactor (MR), which enables both ammonia decomposition and hydrogen separation to take place within the same device, providing advantages in terms of efficiency and compactness compared to conventional systems. The literature reports that ceramic-supported double-skinned Pd-Ag membranes show outstanding performance for hydrogen separation as well as good stability of the separation layer during ammonia decomposition. However, their sealing in the reactor may result in leakage increase, while their mechanical stability remains an unresolved issue. To circumvent these limitations, the use of metallic supported Pd-based membranes is recommended, due to their higher mechanical stability and ease of sealing and integration in the reactor. In this work, we propose the development of robust metallic supported hydrogen-selective membranes for integration in membrane reactors for ammonia cracking. A conventional Pd-Ag membrane was prepared on a low-cost porous Hastelloy X tubular filter, modified with α-Al₂O₃/γ-Al₂O₃ to reach the desired surface quality. The membrane was then tested for ammonia decomposition in a MR configuration, showing the ability to reach >99% NH₃ conversion above 475 °C with H₂ feed recovery >60%. The results achieved pave the way towards a possible substitute for the ceramic-supported alternatives.

Textile wastewater is widely produced and its discharge without treatment contributes to environmental pollution. The adsorption process is a suitable and eco-friendly process due to its low initial cost, no formation of degradation products, operation simplicity, insensitivity to toxic compounds, and the possibility of removal from greatly diluted solutions. Orange seed (OS) powder, from which lipids were removed by hexane extraction, was evaluated as a bio-adsorbent to remove dyes from real textile wastewater. In the screening step, pH was a more significant variable (p-value < 0.05) than bio-adsorbent dosage, temperature, stirring speed, and process time. Moreover, under optimized conditions (pH = 2.6, 0.58 g/L from OS powder and 26 °C), more than 95% of the dye was removed from real textile wastewater. Additionally, the dye removal percentage was reduced by only 4% when the volume of textile wastewater was increased from 0.05 L to 10 L. Then, 96% turbidity was removed using a 3 µm tubular ceramic membrane at a pH of 11. Furthermore, the permeate flux through the membrane was kept constant for longer than was observed at low pH (<11). Therefore, the proposed process is an interesting option, due to the fact that orange seeds are currently not valorized and, combined with the membrane process, this could prove a suitable option for the treatment of real textile wastewater.