Selective conversion of sugar beet pulp into sugars and high value products by supercritical water hydrolysis

Agro-industrial biomass are considered promising resources for the production of organic carbon-based chemicals and materials. This is the case of sugar beet pulp (SBP), which is the major by-product in beet sugar industry.

SBP is produced in large amounts in both Europe and North America and it has been mainly employed as animal feed. It is composed of 20 – 25 % cellulose, 22 – 30 % hemicellulose, 24 – 32 % pectin, 10 – 15 % protein and 1 – 3% insoluble lignin on a dry basis. Its low insoluble lignin and high sugar content make SBP an interesting candidate for both biofuels and platform chemical production in biorefineries.

Figure 1. C-5 and C-6 sugars recovery after supercritical water hydrolysis of sugar beet pulp.Figure 1. C-5 and C-6 sugars recovery after supercritical water hydrolysis of sugar beet pulp.

Using the FastSugars laboratory pilot plant, SBP was hydrolyzed in supercritical water to obtain both sugars and added-value products. The experimental conditions were 390 ºC, 250 bar and reaction times between 0.11 and 0.24 seconds. As it can be seen in Figure 1, working with these very short reaction times, it was possible to selectively recover cellulose and hemicellulose as sugars (C-6 and C-5 sugars, respectively). The highest recovery for C-5 sugars (70 % w/w) was obtained at 0.15 s, while the highest recovery for C-6 sugars (74 % w/w) was obtained at 0.19 s. Increasing the reaction time, those sugars where transformed into other products such as glycoaldehyde (main retro-aldol condensation product from glucose). Then, this effluent rich in sugars and glycolaldehyde was hydrogenated over Ru/MCM-48 catalyst, obtaining in that way hexitols and ethylene glycol from SBP (full paper for effluent hydrogenation).

As it was already demonstrated for wheat bran, supercritical water also showed to be an effective method to hydrolyze sugar beet pulp into sugars and added-value products with reaction times lower than 1 second.

Celia M. Martínez

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