Sweet solution could see sugar alcohols store renewable energy forms
Sugar alcohols are usually found in a white, water-soluble solid state, and are extensively used in the food industry as thickeners and sweeteners.
Erythritol is produced from glucose by fermentation with a yeast. It can be used in chewing gum, baked goods and beverages and is naturally found in soy sauce, sake, watermelon and grapes.
Industrial production of Xylitol starts from xylan extracted from hardwoods, corncobs or the waste product of sugar cane. It is then hydrolysed into xylose and then hydrogenated into xylitol.
Sorbitol can be produced by reduction of glucose. Most sorbitol is made from corn syrup but lactose can be converted into sorbitol using whey permeate, a waste product of the dairy industry.
Sorbitol and xylitol in particular have found value as low calorie sweeteners, such as in chewing gums and mints, and applications in oral hygiene products.
Writing in the Journal of Physical Chemistry the team have devised an innovative method that uses sugar alcohols, in combination with carbon nanotubes, to store energy in heat form.
In doing so they found that heat transfer within the blend decrease as the nanotube diameter decreased. However, higher density combinations led to better heat transfer.
Insights garnered from this discovery could help with the construction of sugar alcohol-based energy storage systems that do not rely on mechanical or complex moving parts.
As by-products of the food industry, its mass production has made sugar alcohols very economically competitive.
In particular, the two alcohols used in this study — erythritol and xylitol — have appropriate melting points for domestic and industrial heating applications and have, therefore, attracted much research.
Electricity generation from renewables has grown steadily over recent years. According to the Renewable Energy Association (REA) the current proportion of electricity generated from renewables in the UK is 7.4%.
Eurostat place Germany as the largest producer of renewable energy within the EU-28 in 2014 with an 18.4 % share of the total primary energy production from all sources.
Using erythritol and xylitol as model materials, the team led by Dr Huaichen Zhang and Dr Silvia Nedea from the Eindhoven University of Technology in the Netherlands, mixed different types of sugar alcohols with carbon nanotubes of varying sizes.
They found that with one carbon nanotube (CNT) size of CNT 7,7 heat transfer within a mixture reduced as the nanotube diameter decreased.
In studying the position of the sugar alcohol molecules enclosed in the CNTs, heat transfer was influenced by both the point of interaction and the fixed size effect of SA’s confinement within the tube.
“Compact heat storage using phase change materials (PCMs) is a promising way to reduce the heating or cooling demand in the built environment. By recovering the solar heat stored in summer, the energy consumption during winter time can be greatly reduced,” the study commented.
“Sugar alcohols (SAs), have attracted much attention to function as the heat storage medium. The high supercooling effect of sugar alcohols enables the storage in liquid phase at atmospheric temperature, cutting down the insulation cost for long-term storage.”
Source: The Journal of Physical Chemistry
Published online ahead of print, DOI: 10.1021/acs.jpcc.6b05466
“Nanoscale Heat Transfer in Carbon Nanotubes - Sugar Alcohol Composite as Heat Storage Materials.”
Authors: Huaichen Zhang et al.