Danilo A. Cantero

High glucose selectivity in pressurized water hydrolysis of cellulose using ultra-fast reactors

A new reactor was developed for the selective hydrolysis of cellulose. In this study, the glucose selectivity obtained from cellulose was improved by using ultra-fast reactions in which a selective medium was combined with an effective residence time control. A selective production of glucose, fructose and cellobiose (50%) or total mono-oligo saccharides (>96%) was obtained from the cellulose in a reaction time of 0.03 s. Total cellulose conversion was achieved with a 5-hydroxymethylfural concentration lower than 5 ppm in a novel micro-reactor. Reducing the residence time from minutes to milliseconds opens the possibility of moving from the conventional m(3) to cm(3) reactor volumes.

Simultaneous and selective recovery of cellulose and hemicellulose fractions from wheat bran by supercritical water hydrolysis

Supercritical water (SCW) has been demonstrated to be an excellent solvent and reaction medium to improve the cellulose hydrolysis selectivity by controlling the reaction time. In this study the conversion of wheat bran into soluble saccharides such as glucose, xylose and arabinose was analysed at 400 °C and 25 MPa with reaction times between 0.2 and 1 s. The process yield was evaluated for two different products: C-6 (glucose derived from cellulose) and C-5 sugars (saccharide derived from hemicellulose hydrolysis). The production of glycolaldehyde, furfural and 5-hydroxymethylfural (5-HMF) was analysed as by-product formation. Operation under supercritical conditions allows a biomass liquefaction of 84% w/w at 0.3 s of residence time. The obtained solid after the hydrolysis was composed of mainly lignin (86% w/w). The highest recovery of cellulose (C-6) and hemicellulose (C-5) as soluble sugars (73% w/w) was achieved at 0.19 s of reaction time. An increase in the reaction time decreased the yield of C-6 and C-5. A total recovery of C-5 was achieved at 0.19 s. On the other hand, the highest yield (65% w/w) of C-6 was achieved at 0.22 s of reaction time. The main hydrolysis product of C-6 and C-5 was glycolaldehyde, yielding 20% w/w at 0.22 s of reaction time. Furfural and 5-HMF production was highly inhibited under the experimental conditions, obtaining yields lower than 0.5% w/w. The hydrolysis reactions were performed in a continuous pilot plant at 400 °C, 25 MPa and residence times between 0.1 s and 0.7 s.

Governing Chemistry of Cellulose Hydrolysis in Supercritical Water

At extremely low reaction times (0.02 s), cellulose was hydrolyzed in supercritical water (T=400 °C and P=25 MPa) to obtain a sugar yield higher than 95 wt%, whereas the 5-hydroxymethylfurfural (5-HMF) yield was lower than 0.01 wt %. If the reaction time was increased to 1 s, the main product was glycolaldehyde (60 wt%). Independently of the reaction time, the yield of 5-HMF was always lower than 0.01 wt%. To evaluate the reaction mechanism of biomass hydrolysis in pressurized water, several parameters (temperature, pressure, reaction time, and reaction medium) were studied for different biomasses (cellulose, glucose, fructose, and wheat bran). It was found that the H(+) and OH(-) ion concentration in the reaction medium as a result of water dissociation is the determining factor in the selectivity. The reaction of glucose isomerization to fructose and the further dehydration to 5-HMF are highly dependent on the ion concentration. By an increase in the pOH/pH value, these reactions were minimized to allow control of 5-HMF production. Under these conditions, the retroaldol condensation pathway was enhanced, instead of the isomerization/dehydration pathway.

Energetic approach of biomass hydrolysis in supercritical water.

Cellulose hydrolysis can be performed in supercritical water with a high selectivity of soluble sugars. The process produces high-pressure steam that can be integrated, from an energy point of view, with the whole biomass treating process. This work investigates the integration of biomass hydrolysis reactors with commercial combined heat and power (CHP) schemes, with special attention to reactor outlet streams. The innovation developed in this work allows adequate energy integration possibilities for heating and compression by using high temperature of the flue gases and direct shaft work from the turbine. The integration of biomass hydrolysis with a CHP process allows the selective conversion of biomass into sugars with low heat requirements. Integrating these two processes, the CHP scheme yield is enhanced around 10% by injecting water in the gas turbine. Furthermore, the hydrolysis reactor can be held at 400°C and 23 MPa using only the gas turbine outlet streams.

Supercritical water hydrolysis of cellulosic biomass as effective pretreatment to catalytic production of hexitols and ethylene glycol over Ru/MCM-48

The hydrolytic hydrogenation of cellulose was studied using mesoporous Ru/MCM-48 as a catalyst. Supercritical water (SCW) was used as a reaction medium for cellulose hydrolysis, since in this reaction medium it is possible to depolymerize cellulose with a high selectivity towards sugars (70% w/w), avoiding degradation reactions when extremely low reaction times are used. The SCW hydrolysis was carried out at 400 °C – 25 MPa and 0.20 s. The hydrogenation of the liquid product from cellulose hydrolysis in SCW was further studied by changing the temperature and reaction time to maximize the yield of hexitols. The results demonstrated the achievement of higher yields of hexitols by the subsequent hydrogenation of the liquid product from cellulose hydrolysis in SCW (49%) rather than using a one-pot catalytic hydrogenation process. Ru/MCM-48 showed better behavior than commercial Ru/C during the hydrogenation process in all cases. Ru/MCM-48 was also employed in the hydrogenation of the product from sugar beet pulp (SBP) hydrolysis in SCW. SBP was used in order to evaluate the behavior of real biomass in this process. A 15% yield of hexitols was achieved from SBP, where ethylene glycol was the main compound in the liquid product and glycerol was obtained as a byproduct too.

Hydrothermal fractionation of woody biomass: Lignin effect on sugars recovery

Subcritical water was employed to fractionate woody biomass into carbohydrates and lignin. Nine urban trees species (hardwood and softwood) from Spain were studied. The experiments were carried out in a semi-continuous reactor at 250 °C for 64 min. The hemicellulose and cellulose recovery yields were between 30%wt. and 80%wt. while the lignin content in the solid product ranged between 32%wt. and 92%wt. It was observed that an increment of solubilized lignin disfavored the hydrolysis of hemicelluloses. It was determined that the maximum extraction of hemicellulose was achieved at 20 min of solid reaction time while the extraction of celluloses not exhibited a maximum value. The hydrolysis of hemicellulose and cellulose would be governed by the hydrolysis kinetic and the polymers accessibility. In addition, the extraction of hemicellulose was negatively affected by the lignin content in the raw material while cellulose hydrolysis was not affected by this parameter.

Hydrothermal hydrolysis of grape seeds to produce bio-oil

In the present work, the hydrothermal hydrolysis of grape seeds focused on the production of bio-oil was studied. The grape seeds composition in terms of lignin, sugars, ash, extractives and bio-oil was determined. The composition of grape seeds was: 17.0 wt% of extractives; 36.8 wt% of sugars (hemicellulose and cellulose); 43.8 wt% of lignin and 2.4 wt% of ash. The grape seeds were hydrothermally treated using three different temperatures: 250 °C, 300 °C and 340 °C employing a semi-continuous reactor. The solid residue varied from 25.6–35.8 wt% depending on the hydrolysis temperature. The maximum yields of light (15.7 wt%) and heavy bio-oil (16.2 wt%) were achieved at 340 °C. The Arrhenius parameters for the kinetics of grape seeds hydrolysis in our system were k0 = 0.995 g min−1 and Ea = 13.8 kJ mol−1. The increment of the flow rate favoured the mass transfer in the system and so, the hydrolysis rate. However, the maximum hydrolysis rate was found at a water surface velocity of 2.3 cm min−1.