Phase change materials for thermal energy storage

Review on phase change materials (PCMs) for cold thermal energy storage applications

The CO2 electroreduction reaction (CO2RR) to fuels and feedstocks is an attractive route to close the anthropogenic carbon cycle and store renewable energy. The generation of more reduced chemicals, especially multicarbon oxygenate and hydrocarbon products (C2+) with higher energy densities, is highly desirable for industrial applications. However, selective conversion of CO2 to C2+ suffers from a high overpotential, a low reaction rate and low selectivity, and the process is extremely sensitive to the catalyst structure and electrolyte. Here we discuss strategies to achieve high C2+ selectivity through rational design of the catalyst and electrolyte. Current state-of-the-art catalysts, including Cu and Cu–bimetallic catalysts, as well as some alternative materials, are considered. The importance of taking into consideration the dynamic evolution of the catalyst structure and composition are highlighted, focusing on findings extracted from in situ and operando characterizations. Additional theoretical insight into the reaction mechanisms underlying the improved C2+ selectivity of specific catalyst geometries and compositions in synergy with a well-chosen electrolyte are also provided. The electrochemical reduction of carbon dioxide to fuels and feedstocks has received increased attention over the past few years. In this Review, Roldan Cuenya and co-workers discuss strategies to achieve high selectivity towards multicarbon products via rational catalyst and electrolyte design.

Rational catalyst and electrolyte design for CO2 electroreduction towards multicarbon products

Natural polyphenols are valuable compounds possessing scavenging properties towards radical oxygen species, and complexing properties towards proteins. These abilities make polyphenols interesting for the treatment of various diseases like inflammation or cancer, but also for anti-ageing purposes in cosmetic formulations, or for nutraceutical applications. Unfortunately, these properties are also responsible for a lack in long-term stability, making these natural compounds very sensitive to light and heat. Moreover, polyphenols often present a poor biodisponibility mainly due to low water solubility. Lastly, many of these molecules possess a very astringent and bitter taste, which limits their use in food or in oral medications. To circumvent these drawbacks, delivery systems have been developed, and among them, encapsulation would appear to be a promising approach. Many encapsulation methods are described in the literature, among which some have been successfully applied to plant polyphenols. In this review, after a general presentation of the large chemical family of plant polyphenols and of their main chemical and biological properties, encapsulation processes applied to polyphenols are classified into physical, physico-chemical, chemical methods, and other connected stabilization methods. After a brief description of each encapsulation process, their applications to polyphenol encapsulation for pharmaceutical, food or cosmetological purposes are presented.

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Encapsulation of Natural Polyphenolic Compounds; a Review

https://pure.rug.nl/ws/files/6693298/2006ProgPolymSciNalawade.pdf

Supercritical carbon dioxide as a green solvent for processing polymer melts: Processing aspects and applications

Evaluation of paraffin/water emulsion as a phase change slurry for cooling applications

Natural extracts are widely used in groceries, in pharmaceutics and nutraceuticals. For foods these extracts are mainly used for flavoring or coloring the products. For pharmaceuticals and nutraceuticals active ingredients like antioxidants are of special interest. Traditionally these extracts are obtained by water or organic solvent extraction. Afterwards the liquid extracts are dried with classical spray drying techniques or freeze drying. In this work a new process for the gentle drying of natural extracts is presented. The process is based on a high-pressure spray technique called particles from gas saturated solutions (PGSS). The solution to be dried is dosed with a high-pressure pump to a static mixer, where compressed and preheated carbon dioxide is added. Afterwards this mixture is rapidly depressurized from high pressure via a nozzle into a spray tower, operated at ambient pressure—fine droplets are formed. By adjusting the pre-expansion conditions it is possible to evaporate the solvent in spray tower. The solvent can be withdrawn with the expanded carbon dioxide and finally a dry powder of the extract is obtained. Like the most supercritical fluid processes the drying is carried out at low temperature (30–60 °C) and in an inert, oxygen-free atmosphere. This makes the process very promising for sensitive substances. First investigations with this technique were made with green tea extracts, which contain antioxidants polyphenols. Dry and free flowing powders were obtained by the spray process without degradation of the active ingredients.

Drying of aqueous green tea extracts using a supercritical fluid spray process

An experimental study on rheological behaviors of paraffin/water phase change emulsion

A series of spraying processes designed to generate powders and composites using supercritical fluids have been proposed in the past 15 years. In this review, thermo- and fluid-dynamic aspects and engineering principles are discussed and advantages of such technologies are demonstrated. These new techniques display convincing advantages, producing competitive high-quality products with tailor-made properties. Initial industrial applications have been achieved in the production of food products and fine-chemicals.

Marcus Petermann

Papers

Evaluation of paraffin/water emulsion as a phase change slurry for cooling applications

Drying of aqueous green tea extracts using a supercritical fluid spray process

An experimental study on rheological behaviors of paraffin/water phase change emulsion

Multifunctional composites by high-pressure spray processes

Experimental study on heat capacity of paraffin/water phase change emulsion