Traditional methods for solids processing involve either high temperatures, necessary for melting or viscosity reduction, or hazardous organic solvents. Owing to the negative impact of the solvents on the environment, especially on living organisms, intensive research has focused on new, sustainable methods for the processing of these substances. Applying supercritical fluids for particle formation may produce powders and composites with special characteristics. Several processes for formation and design of solid particles using dense gases have been studied intensively. The unique thermodynamic and fluid-dynamic properties of supercritical fluids can be used also for impregnation of solid particles or for the formation of solid powderous emulsions and particle coating, e.g., for formation of solids with unique properties for use in different applications. We give an overview of the application of sub- and supercritical fluids as green processing media for particle formation processes and present recent advances and trends in development.
Aerogels are outstanding materials, obtained by the sol-gel process. The production of polysaccharide aerogels is however time-consuming and their use for life-science applications is limited. To accelerate the production time, ethanol was used to induce the gelation of pectin, alginate, xanthan and guar gum. Polysaccharide aerogels were produced by dissolution in water, gelation in ethanol and supercritical drying. Only ethanol was used for the gelation without the use of any other cross-linking agent. In addition there was no solvent-exchange step prior to supercritical drying since the gelation occurred directly in ethanol. Differential scanning calorimetry was used to analyze the decompositions of the samples and also to measure their thermal conductivities. SEM and rheological analyses were performed in order to characterize the new materials.
The main aim of this study was to evaluate pressurized hot water as a green and environmentally friendly extraction medium for the isolation of phenolic compounds from larch waste wood. Such isolates could find applications in the food, feed, pharmaceutical and cosmetics industries or as natural ingredients for adhesives or biocidal coatings in the wood industry. In the first step different larch wood fractions were extracted using batch system aiming to determine the most suitable fraction for isolation. The content of extractives, total phenolic and tannin content of obtained extracts and their antioxidant activity were evaluated. Secondly, semi-continuous operation was applied, where effects of temperature, addition of ethanol and flow rate were studied. Extraction yield was monitored and extracts were again analyzed for their total phenolic content and antioxidant activity. HPLC analysis was performed, in order to study the effect of temperature and addition of ethanol on the hydrothermal degradation of phenolics during semi-continuous operation. Finally, the economics of pilot-scale and industrial-scale processes with different extractor capacities, ranging from approximately 12 to 1200 kg of woody material per day and operating at optimal conditions for isolation of larch wood extractives was evaluated, in order to determine the cost of manufacturing of such a product.
This paper provides comparisons between three different energy carriers that could be produced within areas having cheap electricity. The comparisons were made in terms of the technological efficiencies and economical viabilities for five different scenarios. Economical comparisons were based on IRR (internal rate of return) calculations and sensitivity analyses covering different independent variables such as carbon tax, electricity price and capital costs. It was discovered that SNG (synthetic natural gas) and LNG (liquid natural gas) production is economically uncompetitive compared to ammonia and methanol productions. Ammonia production would be the better choice if there were a carbon tax between 0 and 83 EUR/t of CO2. At a carbon tax higher than 83EUR/t, methanol production would be the more economical option.
This paper describes an original and innovative technical solution for exploiting low-temperature energy sources from cogeneration gas reciprocating engines installed within district heating systems. This solution is suitable for those systems in which the heat is generated by the use of reciprocating engines powered by gaseous fuel for combined heat and power production. This new technical solution utilizes low-temperature energy sources from a reciprocating gas engine which is used for a combined production of heat and power. During the operation of the cogeneration system low-temperature heat is released, which can be raised to as much as 85 °C with the use of a high-temperature heat-pump, thus enabling a high-temperature regime for heating commercial buildings, district heating or in industrial processes. In order to demonstrate the efficiency of utilizing low-temperature heat sources in the cogeneration system, an economic calculation is included which proves the effectiveness and rationality of integrating high-temperature heat-pumps into new or existing systems for combined heat and power production with reciprocating gas engines.