Glycerine, the simplest trihydric alcohol, is a naturally occurring substance which shows wide distribution in form of different esters termed mono-, di- and triglycerides. Usually, vegetable oils are trigycerides. For decades, this versatile, clear, colourless, viscous and syrupy tasting liquid derived industrially by the conversion of propen into epichlorohydrin followed by subsequent procession into synthetic glycerol (also called glycerine). It is widely used in the cosmetic- and pharmaceutical industry as well as within foods and beverages.
However, since the global increase of biodiesel production, in which glycerol accumulates as a by product, conventional fabrication of synthetic glycerol is rendered unnecessary and inefficient. The biodiesel manufacturing process relies mostly upon the transformation of triglyceridic fatty acids into the corresponding methyl esters by a process called transesterification. As the global production of fatty acid based biodiesel rises, the available amount of glycerol increases to the same extent. Facing the fact that each ton of biodiesel leads to about 100 kg of glycerol, it becomes obvious that every year the produced quantity of this substance multiplies. As a consequence, the market for glycerol depresses. Actually, the US Department of Energy considers glycerol as one of the 12 building block chemicals derived from biomass that can subsequently be converted into a number of high value biobased chemicals. This indicates an opportunity for an exchange of fossil feedstocks with renewable resources. In recent years, a lot of research focused on the development of feasible and economical conversion into such value added compounds. Almost all of them are traditionally prepared by raw materials of fossil origin.
Epichlorohydrin, a highly reactive chemical is generally used in the production of epoxy resins, glues and elastomers. A commercially practicable route to the procession of glycerol into epichlorohydrin was presented by Dow Chemicals. This procedure is based on a solvent free conversion using hydrochloric acid.
1,2 Propanediol, which is also called propylene glycol, is a colorless, odorless, clear and viscous liquid. This flexible chemical has a variety of possible applications. It is used as a solvent in many pharmaceuticals, as emulsification agent, as moisturizer, as a coolant in liquid cooling systems, as a lubricant in air conditioning compressors,… Many patents and scientific publication describe the conversion of glycerol to propylene glycol either via a fermentative route or via chemical procession. By now, none of these methods are exploited commercially.
1,3 Propanediol is predominantly used as a building block in the fabrication of polymers and polymeric fibers. Additionally, it can be supplemented into a range of industrial products including composites, adhesives, laminates, coatings, moldings and aliphatic polyesters. Again, a wide variety of patents and publications claim feasible fabrication methods by different innovative technologies. However, there is currently no industrial production of 1,3 propanediol by any of these technologies.
From an industrial point of view, the preparation of glycerol derived syngas (hydrogen and carbon monoxide) is one of the most innovative ideas. Employing the Fischer – Tropsch process, syngas (an abbreviation for synthesis gas) enables the tailor made preparation of a huge assortment of carbohydrates for any purpose. As the reaction temperature ranges between 225° – 300° C using platinum based catalysts, some of these techniques promise to be commercially viable. Florida Syngas has developed and already patented a technology that converts waste glycerol into syngas. Currently, the company is about to use its technology for large scale production. Also Linde, the world’s largest manufacturer of hydrogen plants, pronounced to build a demonstration plant by mid 2010 at its chemical site in Leuna, Germany, which will produce syngas from glycerol.
Besides the above mentioned, there are even more glycerol derived chemicals bearing large potential. Acrolein and Lactic Acid are among the most promising chemicals within this selection. Though, a lot of further research is required to develop economically attractive strategies. But eventually, as the decrease of glycerol prices and the increase of fossil oil cost persist, substances derived by glycerol will enter the production of modern and sustainable chemical industry.
A related article on this topic, dealing with the commercial manufacturing of glycerine derived green chemicals is yet published.
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