Feasibility and advantages of continuous synthesis of bioinspired silica Using CO2 as an Acidifying Agent

In this work, we present a method for the continuous synthesis of bioinspired porous silica (BIS) particles using carbon dioxide (CO2) as an acidifying agent. Typical BIS synthesis uses strong mineral acids (e.g., HCl) to initiate the hydrolysis and subsequent condensation reactions. The use of strong acids leads to challenges in controlling the reaction pH. The synthesis approach proposed in this work offers for the first time CO2 as an attractive alternative for the synthesis of BIS and demonstrates the continuous process. The developed method leverages the mild acidic and the self-buffering nature of the CO2 combined with additional options for controlling mass transfer rates to facilitate enhanced control of pH, which is crucial for controlling the properties of synthesized BIS. Proof of concept experiments conducted in continuous mode demonstrated a yield of over 70% and a surface area exceeding 500 m2/g. These results indicate the successful synthesis of BIS using CO2 with properties in the desired range. The enhanced pH control offered by this CO2-based process will facilitate the implementation of a sustainable and robust continuous process for BIS synthesis

Flow characteristics of Newtonian and non-Newtonian fluids in a vessel stirred by a 60° pitched blade impeller

Mean and rms velocity characteristics of two Newtonian flows at Reynolds numbers of 12,800 (glycerin solution) and 48,000 (water) and of a non-Newtonian flow (0.2% CMC solution, at a power number similar to the Newtonian glycerin flow) in a mixing vessel stirred by a 60° pitched blade impeller have been measured by laser Doppler velocimetry (LDV). The velocity measurements, resolved over 360° and 1.08° of impeller rotation, showed that the mean flow of the two power number matched glycerin and CMC flows were similar to within 3% of the impeller tip velocity and the turbulence intensities generally lower in the CMC flow by up to 5% of the tip velocity. The calculated mean flow quantities showed similar discharge coefficient and pumping efficiency in all three flows and similar strain rate between the two power number matched glycerin and CMC flows; the strain rate of the higher Reynolds number Newtonian flow was found to be slightly higher. The energy balance around the impeller indicated that the CMC flow dissipated up to 9% more of the total input power and converted 7% less into the turbulence compared to the glycerin flow with the same power input which could lead to less effective mixing processes where the micro-mixing is important

Gas-liquid reactor/separator: dynamics and operability characteristics

A comprehensive mathematical model is developed to simulate gas¿liquid reactor in which both, reactants as well as products enter or leave the reactor in gas phase while the reactions take place in liquid phase. A case of first-order reaction (isothermal) was investigated in detail using the dynamic model and numerical bifurcation tools. Strong coupling between reaction kinetics and product removal rate was found to lead to complex dynamic (including over-flow/dry-up or oscillatory) behaviour. Key parameters controlling operability and dynamic characteristics were identified. Operability maps of the reactor/separator are presented. The model and results discussed will be useful for design and operation of industrial reactor/separators

Hydrodynamic cavitation effects on advanced oxidation processes and mass transfer: A conceptual model

Advanced oxidation process (AOPs) technologies are the subject of intense research due to the need for treating refractory wastewaters. Among them, hydrodynamic cavitation (HC) is particularly well-studied because of its potential as an AOP and as a means of intensification for other processes, including other AOPs. Understanding HC and its effects is crucial for its development and practical application. This study introduces a conceptual model that integrates the presence of supercritical water (SCW) to interpret HC results. The model was validated by selected experimental scenarios focused on exploring the impact of HC on the viscosity of a soluble polymer solution, the precipitation of an ionic salt from an unsaturated solution, and the stripping of volatile organic compounds (VOCs). The results were analyzed and interpreted using the conceptual model, remarking the scenarios that cannot be explained by the generally accepted mechanisms of radicals’ formation or pyrolysis. Furthermore, the model was then applied to analyze the trends reported in the existing literature regarding the application of HC as an AOP and as a method of intensification. The occurrence of SCW as a key driving force for HC chemical and physical effects represents a novel approach with the potential to enhance the design and operation of HC systems, particularly when tailoring operating conditions to maximize SCW occurrence