28 April 2011

Chemists convert seaweed to chemicals and fuels

Facile single-step conversion of macroalgal polymeric carbohydrates into Hydroxymethylfurfural

A one-step process converts everyday seaweed into a renewable chemical resource that can be used for chemical building blocks and biofuels.

An innovative idea – if adapted to a large scale – could take advantage of an abundant but so far little-used raw material to make biofuels, according to a team of green chemists in Korea. The secret ingredient: seaweed. Many varieties of seaweeds thrive in the world’s saltwater oceans and seas. Their growth is fueled by carbon dioxide. Unlike most conventional land-based plants, it is possible to produce multiple crops in a year without requiring fertile land and fresh water.

In recent years, microalgae – which are invisible to the naked eye – have been researched and exploited for use as fuels. Mostly ignored in this boom were the macroalgae – the kind you can see with your naked eye and find at the seashore. These seaweeds usually have lower oil content and have not attracted as much attention from chemists and manufacturers.

What they lack in oil, many types of seaweeds make up for in carbohydrates. The red algae species used in the current study is almost 80 percent carbohydrates. These sugars form long chemical chains called agar. The Korean researchers found two ways to convert the agar into useful products.

In one, they found that agar reacts with an acid catalyst to produce a small molecule known as Hydroxymethylfurfural (HMF). HMF is a valuable precursor to a variety of chemicals. To draw an analogy with petroleum refining, HMF would be considered the bio-based equivalent of a petrochemical like toluene that serves as the ultimate starting material for many commercial chemicals. The yield of HMF from the red algae was higher than expected, and this was attributed to unusual simple sugars and linkage patterns in the agar structure.

By adding a different catalyst to agar and introducing a solvent for the reaction, the yield was improved and two different chemical products were formed. Both of these chemicals are well known as biofuels and could be used as building block structures for specialty chemicals as well.

The product yields might be further improved by changing the seaweed growth conditions or even the species. Since the researchers discovered that the agar structure leads to unique reactivity, future work could take advantage of ways to tweak it towards a more favorable composition. Other combinations of catalyst and solvent could be explored as well.

Source: Environmentalhealthnews.org, 2011-04-29.

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