Waste not, want not: sweet fuel from sugarcane debris

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  • Published: Oct 12, 2015
  • Author: Ryan De Vooght-Johnson
  • Channels: HPLC
thumbnail image: Waste not, want not: sweet fuel from sugarcane debris

Ethanol: A carbon-neutral alternative to petrol

Lignocellulose, a simple compound made up of the polymers cellulose, hemicellulose and lignin, is the material that gives plants their structure. It is also the most abundant material on Earth for making biofuel. (Image: Pixabay)

Lignocellulose, a simple compound made up of the polymers cellulose, hemicellulose and lignin, is the material that gives plants their structure. It is also the most abundant material on Earth for making biofuel. When broken down into its component parts, lignocellulose generates sugars that can be fermented to ethanol – a biofuel that can power cars. One tonne of dry plant matter can produce up to 300 litres of ethanol.

The first car to run entirely on ethanol was produced in Brazil, where researchers have now developed a way of detecting compounds that can inhibit production of the biofuel. The method, described in the Journal of Separation Science last month, was applied to sugarcane.

The fibre ‘waste’ left after the juice is extracted from sugarcane, called bagasse, can be used to manufacture an alternative to paper, building materials and – importantly – biofuel. And Brazil makes a lot of it! The 2015/2016 sugarcane harvest is estimated to generate 12.8 million tonnes of sugarcane bagasse.

However, the hydrolysis of bagasse – a critical step in bioethanol production – also leads to the production of less favourable compounds: furanic aldehydes, notably 5-hydroxymethylfurfural (HMF) and furfural. These potent inhibitory compounds are generated by the dehydration of glucose and xylose, respectively. “The detection of furanic aldehydes is very important in the bioethanol production process, because they inhibit the fermentation of sugars, consequently decreasing the production of bioethanol,” explains lead author Dr. Jose Luiz da Silva.

Various approaches have been used to identify furanic aldehydes, most based on chromatography. This study applied high-performance liquid chromatography (HPLC) alongside electrochemical detection methods. Carbon electrodes were modified with nickel nanoparticles, which provide a greater surface area, enhanced mass transport, and a higher signal-to-noise ratio than macro-electrodes. The researchers used nickel nanoparticles, as they have been used previously to detect carbohydrates by HPLC and have low detection limits, high reproducibility and are affordable.

Separating sugarcane

The researchers demonstrated their novel method for detecting furanic aldehydes using 300-mg samples of sugarcane bagasse. After the samples were hydrolysed with sulfuric acid, neutralised and filtered, they were injected into the HPLC.

The peaks in the chromatograms were identified based on the analytes’ retention times. HMF and furfural displayed peaks with retention times of 1.88 and 2.41 minutes, respectively.

To quantify the amount of the compounds in the sample, the researchers used the standard addition method. This involves adding standard to aliquots of analysed sample and is often used in complex samples, where interacting compounds can make analyte quantification difficult.

Speedy, sensitive and reliable

The electrodes detected approximately 1.54 g/kg of HMF and 11.5 g/kg of furfural in the samples. The procedure was performed using three different electrodes to confirm its reproducibility.

The researchers also assessed the accuracy of their method by measuring the recovery of the standard analytes. They injected three different concentrations of the analytes into the sample, finding that the average recovery of furfural was 96.5%, while for HMF it was 98.2%, confirming that the technique is an effective and precise means of detecting furanic aldehydes.

The analytical parameters of the method were also evaluated. Analytical curves showed limits of detection of 4.0 × 10-7 mol/l and 4.3 × 10-7 mol/l and limits of quantification of 1.3 × 10-6 and 1.4 × 10-6 mol/l for furfural and HMF, respectively.

This study shows that glassy carbon electrodes modified with nickel nanoparticles can successfully identify furanic aldehydes with HPLC. The method has a short analysis time and is selective, sensitive, reproducible and easy to perform. “The results demonstrate that the new method developed with a modified electrode has good analytical parameters and can be used to quickly detect the analytes,” adds da Silva.

This method may help scientists to find a better method of making ethanol from this waste material, and has potential in the analysis of different lignocellulose samples, such as wood and the dry matter of other plants.

Related Links

Journal of Separation Science, 2015, 38(18), 3176-3182, Determination of furanic aldehydes in sugarcane bagasse by high-performance liquid chromatography with pulsed amperometric detection using a modified electrode with nickel nanoparticles.

Nature Education, 2010, 3(9), 14, Promising Biofuel Resources: Lignocellulose and Algae.

Article by Ryan De Vooght-Johnson

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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