Esther Alonso

Supercritical extraction of unsaturated products. Degradation of β-carotene in supercritical extraction processes

Abstract Supercritical carbon dioxide is a promising solvent for the extraction and crystallization processes of natural compounds, especially thermolabil compounds. It is recognized as exhibiting powerful advantages over conventional solvents. However, so far a crucial point has been ignored, the possible oxidation of unsaturated compounds due to the presence of oxygen in high purity carbon dioxide used in these processes. The highest purity grade of commercial carbon dioxide is ≈2 mg/l STP. Taking into account that the solubility of most natural compounds is ≤0.1%, this means that the oxygen/compound concentration ratio would be high. To test this drawback, the extraction of β-carotene with supercritical carbon dioxide was studied. The β-carotene solubility was found to be 3.8 mg/kg at 30 MPa and 40°C. Therefore, 263 kg of carbon dioxide would be needed to yield 1 g of β-carotene. That meant a 9 mol oxygen/mol β-carotene ratio. Results presented here suggest that β-carotene was oxidized during the extraction process.

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.

Pressurized aqueous ethanol extraction of β-glucans and phenolic compounds from waxy barley

Beta-glucans and phenolics were extracted from waxy barley using pressurized aqueous ethanol in a stirred batch reactor at 25bar and 500rpm. The effect of temperature (135-175°C), extraction time (15-55min) and ethanol content (5-20%) was evaluated. Temperature had an opposite effect on the extraction of both compounds. The higher the temperature, the lower the β-glucan extraction yield due to fragmentation, but a significant increase on the phenolic recovery was observed. Long extraction times favored the extraction of β-glucans at low temperatures and phenolics at any temperature. The ethanol content was not statistically significant on the β-glucan extraction, but helped to maintain the molecular weight of the extracted β-glucan. To obtain liquid extracts rich in high molecular weight β-glucans and phenolics, mild conditions of 151°C, 21min and 16% ethanol are needed, leading to 51% β-glucan extraction yield with a molecular weight of 500-600kDa and 5mgGAE/g barley.

Understanding bottom-up continuous hydrothermal synthesis of nanoparticles using empirical measurement and computational simulation

Continuous hydrothermal synthesis was highlighted in a recent review as an enabling technology for the production of nanoparticles. In recent years, it has been shown to be a suitable reaction medium for the synthesis of a wide range of nanomaterials. Many single and complex nanomaterials such as metals, metal oxides, doped oxides, carbonates, sulfides, hydroxides, phosphates, and metal organic frameworks can be formed using continuous hydrothermal synthesis techniques. This work presents a methodology to characterize continuous hydrothermal flow systems both experimentally and numerically, and to determine the scalability of a counter current supercritical water reactor for the large scale production (>1,000 T·year–1) of nanomaterials. Experiments were performed using a purpose-built continuous flow rig, featuring an injection loop on a metal salt feed line, which allowed the injection of a chromophoric tracer. At the system outlet, the tracer was detected using UV/Vis absorption, which could be used to measure the residence time distribution within the reactor volume. Computational fluid dynamics (CFD) calculations were also conducted using a modeled geometry to represent the experimental apparatus. The performance of the CFD model was tested against experimental data, verifying that the CFD model accurately predicted the nucleation and growth of the nanomaterials inside the reactor.

Extraction of arabinoxylans from wheat bran using hydrothermal processes assisted by heterogeneous catalysts

The extraction/hydrolysis process of arabinoxylans from destarched wheat bran was studied in this work using different mesoporous silica supports and the corresponding RuCl3-based catalysts. The effects of temperature, time, catalyst supports and ruthenium catalysts were investigated and discussed in terms of the arabinoxylans extraction yield and their polymerization degree. Relatively high temperatures (180°C), short extraction times (10min) and RuCl3 supported on Al-MCM-48 led to a high amount of extracted arabinoxylans (78%) with a low molecular weight (9kDa). Finally, a relation between the operating conditions, the arabinoxylans extraction yield and the molecular weight was stablished based on the obtained results.

Maximization of monomeric C5 sugars from wheat bran by using mesoporous ordered silica catalysts

The hydrolysis process of a real fraction of arabinoxylans derived from wheat bran was studied. The influence of catalyst type and loading, reaction time and different metal cations were discussed in terms of the hydrolysis yield of arabinose and xylose oligomers as well as the formation of furfural as degradation product. A high yield of arabinoxylans into the corresponding monomeric sugars (96 and 94% from arabino- and xylo-oligosaccharides, respectively) was obtained at relatively high temperatures (180°C) and short reaction times (15min) with a catalyst loading of 4.8g of RuCl3/Al-MCM-48 per g of initial carbon in hemicelluloses.

Dissolution of (1-3),(1-4)-β-Glucans in Pressurized Hot Water: Quantitative Assessment of the Degradation and the Effective Extraction

The purpose of this work was to study the behavior of (1-3)(1-4)-β-D-glucan in pressurized hot water. For this purpose, solid β-glucan (450 kDa) was put in water and heated at different temperatures (120, 150, and 170°C) for different times (5 to 360 minutes). At 120°C it was found that the highest soluble β-glucan concentration was measured after 60 minutes; at 150 and 170°C optimal times were 45 and 20 minutes, respectively. The maximum amount of β-glucan dissolved in each of the optimal conditions was 1.5, 2.2, and 2.0 g/L, respectively. Under those conditions an important reduction was observed in the molecular weight: at 120°C and 60 min it was 63 kDa; at 150°C and 45 min it was reduced down to 8 kDa; and at 170°C and 20 min it was only 7 kDa. Besides this reduction in the MW some hydrolysis products, such as glucose and HMF, were observed. These results revealed the convenience of using PHW to dissolve β-glucans since the operation times, compared to the conventional process (55°C, 3 h), were reduced despite the fact that the MW was significantly reduced once the β-glucan was dissolved; therefore, PHW can be used to extract β-glucans from barley under controlled conditions in order to prevent severe degradation.