Processes

Chromium-based technique has been used over the decades and, up to now, is the most extended technology to produce leather around the world. However, the environmental problems related to its production, with special regard to the extremely high amounts of residual chromium in the soil and in the water, are reducing the use of leather, and it is becoming replaced with the use of synthetic materials. Consequently, the current leather production is becoming unsustainable due to the higher cost of treating the effluents derived from it. To eliminate the high consumption of this mineral, a Caesalpinia spinosa (Tara) tanning technique was developed and optimized on a semi-industrial scale. The reported results indicated that, being highly superior to the traditional methods, this was possible after an extensive Tara characterization, which reported, for example, (a) IRR reported strong vibration peaks in different positions, which suggested the presence of polyphenols as a principal component of the Tara powder. This assumption was confirmed by the tannic acid content, which reported values equal to 52.25 ± 1.74 mg/g of Tara powder. These results suggested that the Tara serves as a good tannin agent. This was proven by the mechanical characteristics of the leather produced by using Tara. For example, when 10% of Tara powder was applied to the formulation, the best results were obtained in all the mechanical characteristics of the leather. Thus, for the tensile strength, the average value was equal to 340.77 ± 4.78 N/mm². Moreover, the sustainability of the process was demonstrated by the good wastewater quality, which showed a null concentration of chromium hexavalent and total chromium. As expected, the biochemical oxygen demand (BOD) and the chemical oxygen demand (COD) increased considerably, reaching values of 1461.00 mgO₂/L and 3150.30 mgO₂/L, respectively. Finally, the economic feasibility of the project was obtained through the cost/benefit and Internal Return Rate (IRR) analysis. The results reported a cost/benefit ratio equal to USD 1.03 and an IRR equal to 31%, thus the investment can be recovered after 5 years of execution of the project. This novel zero-chrome tanning process solves the long-standing environmental problems that have been linked to making leather and meets all the needs of today’s sustainable leather industry.

Tight oil reservoirs are currently a hot topic in petroleum exploration and development. However, due to the low porosity and low permeability of reservoirs and the lack of external energy supplementation, there is a significant mismatch between resources and production in tight oil. Mining and experimental studies have shown that CO₂ and gaseous hydrocarbons have a high injectivity and effective oil displacement effect in tight oil reservoirs. Currently, research is mostly focused on a single energy supplement medium, and whether CO₂ hydrocarbon mixtures can more effectively improve oil recovery needs to be further studied. The features of crude oil expansion capacity and interaction energy changes following various fluid interactions were investigated via molecular dynamics simulation techniques in response to the ambitious comprehension of the mechanistic changes underlying the CO₂–CH₄ synergistic effect during the development of tight oil reservoirs. The research results indicate that the expansion and diffusion abilities of crude oil are improved after being treated with pure CO₂, CO₂-CH₄ (9:1), CO₂-CH₄ (7:3), and CO₂-CH₄ (1:1), and enhanced with increasing CO₂ content in the injected fluid.

Air-shielding radial ultrasonic rolling electrochemical micromachining (AS-RUREMM) is proposed to fabricate high-quality micro-dimple textures on cylindrical SS304 surfaces while suppressing stray corrosion. In AS-RUREMM, an annular air sheath coaxially envelopes the electrolyte jet to confine the wetting footprint, and radial ultrasonic vibration is superimposed on a rolling cathode with micro-protrusions to intensify local mass transport and stabilize the interelectrode environment. A conductivity-centered theoretical framework is established to link air-sheathing-induced gas–liquid distribution, ultrasonic gap modulation, and the resulting current-density localization. Multiphysics simulations in COMSOL 5.3 clarify that moderate air pressure forms a stable confined gas–liquid structure that narrows the effective conductive pathway, whereas excessive air pressure increases intermittency and weakens effective gap conductivity. Experiments on SS304 tubes validate the confinement mechanism: compared with RUREMM, AS-RUREMM produces smaller pit width and depth but a higher depth-to-width ratio, indicating enhanced localization and reduced peripheral over-etching. The simulated cross-sectional profiles agree with measurements, with an overall deviation within 6%. Parameter studies identify an optimal operating window, and the combination of 0.18 MPa air pressure and 12 V pulse voltage provides the highest aspect ratio while maintaining stable machining. SEM/EDX analyses further support the improved process controllability under air shielding through reduced stray corrosion and composition changes consistent with a more regulated electrochemical dissolution environment.