Maria José Cocero - Academia.edu (original) (raw)

Papers by Maria José Cocero

Green Chemistry, 2019

Nowadays, the valorization of lignin, the major natural source of aromatics in earth, is being a ... more Nowadays, the valorization of lignin, the major natural source of aromatics in earth, is being a challenge for the scientific community. In this study, kraft lignin is effectively converted into aromatic monomers by ultrafast depolymerization in hot and pressurized water. At reaction times below 500 ms, it is possible to avoid char formation originated from undesirable condensation reactions by controlling accurately the reaction time. Under alkaline medium, the reaction reaches an optimum point at 386ºC and 300 ms with a light oil yield of 60% with a concentration in key compounds such as guaiacol, creosol, vanillin and acetovanillone of around 20 %w/w. The total aromatic monomeric yield based on lignin was 10.5 %w/w. The char formation in this point was surprisingly low (4 %w/w). Analysis and quantification of the products allows to identify the evolution of the different reaction steps and propose plausible mechanism for the depolymerization and repolymerization stages. Furthermore, it is proven that the proposed technology is equally effective to treat directly industrial black liquors with a yield higher than 50% to light oil, containing as main monomers guaiacol (2.7%), syringol (3.0%) and syringaldehyde (7.3%).

Social Science Research Network, 2022

Different lignins from different sources (hardwoods, softwoods and crop residues) and obtained as... more Different lignins from different sources (hardwoods, softwoods and crop residues) and obtained as by-products of different processes such pulping or biorefining were depolymerized in alkaline supercritical water (SCW: 386 • C and 260 bar) in an intensified continuous process to produce high value-added compounds with low-molecularweight in only 300 ms of reaction time. The products obtained were analysed to determine the yield, selectivity to monomers, chemical structure and molecular weight distribution. The char formation was low in most cases, but the proportion of heavy and light oils were variable upon the starting material used. The monoaromatics yield depends mostly on the type of lignin utilized being the nonwood biorefinery lignins less suitable for monomers production than the technical wood ones (13-8%). The monomer distribution depends on the biomass of origin and the pulping method. This technology is equally effective when directly treating a black liquor and better results are obtained if compared to the corresponding isolated lignin.

Chemical Engineering Journal, Jul 1, 2018

A techno-economic assessment of the potential for combining supercritical water oxidation with 'i... more A techno-economic assessment of the potential for combining supercritical water oxidation with 'insitu' hydrothermal synthesis of nanocatalysts using a counter current mixing reactor, Chemical Engineering

Chemical Engineering Journal, Dec 1, 2019

This work analyzes the influence of the mixer configuration on the mixing efficiency in the proce... more This work analyzes the influence of the mixer configuration on the mixing efficiency in the process of biomass ultrafast hydrolysis by supercritical water. The results of the CFD simulations of a horizontal tee, a vertical tee and a mixing cross, selected as the optimum mixing configurations, together with the experimental results obtained in our hydrolysis plant, are the base to determine the configuration which provides the best mixing performance. Although slightly higher conversions are obtained in those experiments performed with a horizontal tee, the small differences between the results demand a theoretical analysis. Therefore, according to the CFD simulation results, since the mixing cross provides the best flow distribution and temperature homogenization at the outlet of the mixers and because of the great similarity between the residence time distribution curves of the mixers, the mixing cross is selected as the optimum geometry to perform the mixing.

Journal of Supercritical Fluids, Mar 1, 2018

The supercritical water hydrolysis (SCWH) of biomass (P=250bara & T=400ºC) allows directly obtain... more The supercritical water hydrolysis (SCWH) of biomass (P=250bara & T=400ºC) allows directly obtaining sugars, which are high value products in the chemical industry, in reaction times lower than 0.2s. The process is characterized by the high selectivity values which can be obtained controlling the reaction time. Reaction kinetics show that glucose degradation is only retarded at temperatures below 250ºC. Therefore, in the traditional SCWH process, degradation control is achieved expanding the hydrolysis stream in a valve which instantaneously cools down the products. Although the selectivity values obtained are greater than 96%, the pressure is wasted on the valve expansion decreasing the global energetic efficiency of the process. In this paper a CFD simulation of a desuperheater which mixes the hydrolysis product with pressurized cooling water is presented. The temperature of the hydrolysis stream decreases below 250ºC in cooling times lower than 20ms maintaining the selectivity value over 93%. Furthermore, the pressure remains at 250bara increasing the global energetic efficiency of the process.

Industrial Crops and Products, Jul 1, 2019

In a biorefinery approach, inulin and inulin-rich biomass as Jerusalem artichoke (JA) could be tr... more In a biorefinery approach, inulin and inulin-rich biomass as Jerusalem artichoke (JA) could be transformed into platform chemicals such as fructose and/or pyruvaldehyde. To do so, the FASTSUGARS pilot plant proved to be a promising alternative for the selective conversion of biomass. In this work, inulin and JA were hydrolyzed in supercritical water (SCW) for the first time. Commercial inulin was selected as a model for fructooligosaccharides (FOS) and its reaction pathway in SCW was elucidated. It was found that fructose was the primary product from FOS hydrolysis in SCW, which was then selectively transformed into pyruvaldehyde as reaction time increased. Operating with extremely low reaction times (0.12 s) the sugars selectivity of JA was as high as 76 % w/w. Finally, comparing JA results to those from lignocellulosic biomass it was found that higher conversion was achieved in the case of JA due to its inulin-based composition.

ACS Sustainable Chemistry & Engineering, Nov 2, 2018

This paper discusses the influence of reactor design and initial consistency when partially hydro... more This paper discusses the influence of reactor design and initial consistency when partially hydrolyzing microcrystalline cellulose (MCC) in supercritical water. Experiments conducted on two pilot reactors located in Finland and in Spain showed that stopping the reaction using depressurization instead of quenching, combined with a sufficiently high MCC consistency, led to significant change in reaction kinetics. A complete particle size reduction was achieved after 50 ms only due to additional shearinduced degradation, with a low-molecular-weight product yield above 50 wt % and an average DP of 25. In addition, gradually increasing the MCC consistency triggered precipitation under higher apparent temperature, which affected both the morphology and structure of the product. A range of particles from ribbon-like cellulose II to shish-kebab structures to lamellar cellulose IV II crystals was obtained. Furthermore, heat requirements as low as 66 kJ•g −1 of product confirm the high potential and versatility of this process for refining MCC into colloidal low-molecular-weight cellulose with different particle shapes and structural properties.

Journal of Supercritical Fluids, Sep 1, 2015

Supercritical Water Oxidation (SCWO) reactors can process waste effluents achieving high conversi... more Supercritical Water Oxidation (SCWO) reactors can process waste effluents achieving high conversions, but the required extreme pressure and temperature operational conditions entail high-energy operational expenditure. SCWO has the potential to be considered a clean energy generation process, as the process effluent is a high temperature, high pressure stream with a high enthalpy content that can be converted to heat and shaft work. This ensures the self-sustained reaction and can generate excess shaft power to drive both the high-pressure pump and the air compressor. On the contrary, an efficient heat and power recovery from SCWO reactors outlet streams using conventional procedures presents several problems. First, Rankine cycles impose indirect heat transfer to the working fluid and are unable to recover the pressure energy and second, direct expansion of the effluents entails costly development of specific, efficient expansion equipment. In this work, we investigate the options for energy recovery of SCWO reactors coupled with commercial gas turbines (GT). SCWO outlet streams are mainly composed of water, nitrogen and carbon dioxide. These operating values nearly resemble the well-known and already-implemented GT steam injection procedures. The temperature of the flue gases (approx. 500 ºC) and the direct shaft work usage offers adequate energy integration possibilities for both feed preheating and compression. The wide range of commercially available GT sizes enables process scaling.

Nano Research, Aug 25, 2016

Continuous hydrothermal synthesis was highlighted in a recent review as an enabling technology fo... more 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.

Food Hydrocolloids, Oct 1, 2015

Quercetin is a strong antioxidant flavonoid with several bioactive properties such as antiinflamm... more Quercetin is a strong antioxidant flavonoid with several bioactive properties such as antiinflammatory and anticarcinogenic activities, becoming an interesting compound to be incorporated into pharmaceutical, cosmetic or food products. However, these applications are limited by the low bioavailability of this flavonoid. Quercetin is poorly soluble in aqueous media, such as gastrointestinal fluids, being also degraded by gut flora. Thus, it is necessary the development of quercetin's formulations capable of improving its water solubility resulting in increased bioavailability and thus higher biological activity of this compound. The aim of the present work was the formulation of quercetin using three distinct natural origin surfactants, namely OSA-starch, Lecithin and β-glucan, by precipitation from a pressurized ethyl acetate-in-water emulsion. Formulations of quercetin with encapsulation efficiencies up to near 76% and a micellar particle size in the range of nanometers were obtained using lecithin. An improved antioxidant activity (3-fold higher per unit mass of quercetin) was also observed in these formulations, demonstrating that lecithin is a good emulsifier for the encapsulation of quercetin. Furthermore, the addition of glycerol as co-solvent increased the colloidal stability of the suspension and the encapsulation efficiency of the flavonoid.

Journal of Supercritical Fluids, Mar 1, 2018

Biomass fractionation into its individual building blocks poses a major challenge to the biorefin... more Biomass fractionation into its individual building blocks poses a major challenge to the biorefinery concept. The recalcitrance of the lignocellulose matrix and the high crystallinity of cellulose make typical feed stocks difficult to separate into their components. Hydrothermal processing fractionates biomass by its hydrolysis. However, a deep knowledge of hydrolysis principles is required since an inappropriate selection of the operating parameters such as an excessive temperature and a long residence times causes dramatic selectivity losses. This review is divided in four main sections which present the fundamentals of lignocellulosic biomass fractionation in hemicelluloses, cellulose and lignin. As the biomass structure plays an important role, a section to study the extraction of the linked phenols that joint lignin and hemicelluloses is included.

Chemical Engineering Journal, Sep 1, 2015

In this study, the effect of temperature and pressure on cellulose and glucose hydrolysis in a hy... more In this study, the effect of temperature and pressure on cellulose and glucose hydrolysis in a hydrothermal media is analyzed. To do so, hydrolysis experiments were carried out in a continuous pilot plant capable of operating up to 400ºC, 27 MPa and residence times between 0.004 s and 40 s. This is possible using an instantaneous heating system by supercritical water injection and cooling by sudden depressurization of the hot product stream. Cellulose hydrolysis produced oligosaccharides, cellobiose, glucose and fructose. In general, concentration profiles of each component were similar for the same temperature and different pressures. Nevertheless, glucose and fructose hydrolysis reaction were strongly affected by changing the pressure, which is density. By increasing temperature and pressure, the reaction of glucose isomerization to fructose was inhibited, and the production of 5-hydroxymethylfurfural (5-HMF) through by fructose dehydration was also inhibited. On the other hand, 5-HMF production was favored by high hydroxide anion concentrations. Thus, at a constant temperature, the production of 5-HMF was increased by rising density (increasing pressure). The production of glycolaldehyde (retroaldol condensation of glucose) was increased by increasing pressure and temperature. The reaction rates of cellulose hydrolysis were fitted using the experimental data. Pressure seems to have no effect on the cellulose hydrolysis kinetic to simple sugars, and at subcritical temperatures the kinetics of glucose hydrolysis reactions did not show significant changes by increasing pressure. However, at 400ºC glucose isomerization and dehydration reactions were diminished by increasing pressure while glucose retro-aldol condensation were enhanced.

Journal of Supercritical Fluids, Nov 1, 2020

Kraft lignin was rapidly depolymerised in a continuous reactor using sub-and supercritical water.... more Kraft lignin was rapidly depolymerised in a continuous reactor using sub-and supercritical water. The reaction yielded an aromatic oil rich in high value aromatic monomers such as guaiacol, vanillin, acetovanillone and homovanillic acid. Different temperatures between 300 and 400ºC and reaction times from 60 ms were studied. An increment in reaction time at every temperature studied promoted secondary reactions of repolymerisation of the lignin products. Those undesired reactions were more relevant as List of abbreviations:

Journal of Supercritical Fluids, Dec 1, 2017

The use of natural polysaccharides is especially attractive to the pharmaceutical industry becaus... more The use of natural polysaccharides is especially attractive to the pharmaceutical industry because of their stability, availability, renewability and low toxicity. In this study, cellulose aerogels obtained from cellulose/ionic liquid solutions were prepared by supercritical drying with surface areas ranged from 154 to 434 m 2 g-1 , pore volume from 0.3 to 2.4 cm 3 g-1 and pore diameter from 7.9 to 34 nm. Drug loading capacity was 2 investigated by impregnating phytol as model compound into the aerogels, using supercritical CO2 at 100 bar, 40°C and mass ratio of phytol per gram of aerogel 10:1. The quantity of drug present is consistent in each aerogel. The aerogel prepared from 2 wt% cellulose in [Emim][DEP] solution showed the highest loading capacity. The high amount of drug loaded (approx 50% w/w) in the cellulose aerogels prepared from ionic liquid solutions shows their potential uses in the pharmaceutical or medical industry.

Chemsuschem, Feb 20, 2015

This article summarizes the recent efforts in the High Pressure Processes Group labs at UVa regar... more This article summarizes the recent efforts in the High Pressure Processes Group labs at UVa regarding the fundamentals of biomass hydrolysis in pressurized water medium. At extremely low reaction times (0.02 s), cellulose was hydrolyzed in supercritical water (400ºC and 25 MPa) obtaining a sugars yield higher than 95% w•w-1 while 5-HMF yield was lower than 0.01% w•w-1. When the reaction times was increased up to 1 s, the main product was glycolaldehyde (60% w•w-1). Independently of the reaction time, the yield of 5-HMF was always lower than 0.01% w•w-1. In order to evaluate the reaction pathway and mechanism of plant biomass 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 considered that the reactions of glucose isomerization to fructose as well as fructose dehydration to 5-HMF take place via proton or hydroxide anion association. So, their concentration was taken into account as reagent concentration in the reaction evaluations. It was found that the proton and hydroxide anion concentration in the medium due water dissociation is the determining factor in the selectivity of the process. The reaction of glucose isomerization to fructose and its further dehydration to produce 5-HMF are highly dependent on ions concentration. By increasing pOH/pH, these reactions were minimized allowing the control of 5-HMF production. At this condition, the retro-aldol condensation pathway was enhanced instead of isomerization/dehydration pathway.

SSRN Electronic Journal, 2022

Different lignins from different sources (hardwoods, softwoods and crop residues) and obtained as... more Different lignins from different sources (hardwoods, softwoods and crop residues) and obtained as by-products of different processes such pulping or biorefining were depolymerized in alkaline supercritical water (SCW: 386 • C and 260 bar) in an intensified continuous process to produce high value-added compounds with low-molecularweight in only 300 ms of reaction time. The products obtained were analysed to determine the yield, selectivity to monomers, chemical structure and molecular weight distribution. The char formation was low in most cases, but the proportion of heavy and light oils were variable upon the starting material used. The monoaromatics yield depends mostly on the type of lignin utilized being the nonwood biorefinery lignins less suitable for monomers production than the technical wood ones (13-8%). The monomer distribution depends on the biomass of origin and the pulping method. This technology is equally effective when directly treating a black liquor and better results are obtained if compared to the corresponding isolated lignin.

High pressure processes (e.g. sustainable hydrothermal manufacturing of nanomaterials [1], superc... more High pressure processes (e.g. sustainable hydrothermal manufacturing of nanomaterials [1], supercritical water oxidation (SCWO) [2] and biomass hydrolysis [3]) require high operational conditions. Water at high pressure and temperature conditions improves kinetic, selectivity and efficiency of these processes but entail high-energy operational expenditure. Use of fluids at high operational conditions makes necessary to supply heat of high quality, as well as power. Because of this, it is necessary to study reasonable solutions for energy recovery and integration in order to achieve the energy self-sufficiency of the process and, if possible, the net power production and with a viable efficiency [4]. In this work, the energy integration of supercritical water oxidation process is being studied. One solution that has been recently proposed is the integration of supercritical processes with energy production in cogeneration or Combined Heat and Power (CHP) cycles. Cogeneration is defin...

The Journal of Supercritical Fluids, 2019

The FASTSUGARS process for sugars' recovery from agricultural biomass was scaled up from laborato... more The FASTSUGARS process for sugars' recovery from agricultural biomass was scaled up from laboratory to pilot plant scale. System performance was evaluated by comparing the results obtained from sugar beet pulp and wheat bran in laboratory and pilot plants. Similar trends were found for each biomass in both plant: as reaction time increased, selectivity to sugars decreased and conversion and degradation rate increased. Then, to bring the FASTSUGARS process closer to industrial applications, the particle size of the biomass was increased in the pilot plant. It was found that the particle size acted as a mass transfer resistance, slowing down the hydrolysis of biomass, providing lower conversion and therefore reducing sugars' degradation (degradation yield was lower than 15 % in the pilot plant). In that way, higher selectivity to sugars was obtained, reaching values around 90 % for both sugar beet pulp and wheat bran in the pilot plant.

Journal of Cleaner Production, 2018

Sugar beet pulp (SBP) is the major by-product in sugar industry. To make profit out of this under... more Sugar beet pulp (SBP) is the major by-product in sugar industry. To make profit out of this undervalued residue, the FASTSUGARS process was proposed as a solution, combining the advantages of supercritical water as hydrolysis medium with very short reaction times in the so-called ultrafast reactors. Operating at 390 ºC, 25 MPa and reaction times between 0.11 and 1.15 s it was possible to convert SBP into sugars and to obtain a lignin-like solid fraction. The highest yields of C-6 and C-5 sugars (61 and 71 % w/w, respectively) were obtained at 0.11 s with the lowest yield of degradation products. The solid product obtained at 0.14 s was thoroughly analyzed by acid hydrolysis, TGA and FTIR analysis to prove its enhanced thermal properties and aromaticity. The FASTSUGARS process demonstrated being a versatile and promising technology to be integrated in the future biorefineries. Highlights • FASTSUGARS is a key step towards future sustainable biorefineries • Sugars were selectively recovered from sugar beet pulp using SCW as reaction medium • Ultrafast reactors allowed accurate control of reaction times in the range of milliseconds • The solid product after hydrolysis was mainly composed of an acid-insoluble fraction • Thorough characterization of the solid confirmed its lignin-like nature

Green Chemistry, 2019

Nowadays, the valorization of lignin, the major natural source of aromatics in earth, is being a ... more Nowadays, the valorization of lignin, the major natural source of aromatics in earth, is being a challenge for the scientific community. In this study, kraft lignin is effectively converted into aromatic monomers by ultrafast depolymerization in hot and pressurized water. At reaction times below 500 ms, it is possible to avoid char formation originated from undesirable condensation reactions by controlling accurately the reaction time. Under alkaline medium, the reaction reaches an optimum point at 386ºC and 300 ms with a light oil yield of 60% with a concentration in key compounds such as guaiacol, creosol, vanillin and acetovanillone of around 20 %w/w. The total aromatic monomeric yield based on lignin was 10.5 %w/w. The char formation in this point was surprisingly low (4 %w/w). Analysis and quantification of the products allows to identify the evolution of the different reaction steps and propose plausible mechanism for the depolymerization and repolymerization stages. Furthermore, it is proven that the proposed technology is equally effective to treat directly industrial black liquors with a yield higher than 50% to light oil, containing as main monomers guaiacol (2.7%), syringol (3.0%) and syringaldehyde (7.3%).

Social Science Research Network, 2022

Different lignins from different sources (hardwoods, softwoods and crop residues) and obtained as... more Different lignins from different sources (hardwoods, softwoods and crop residues) and obtained as by-products of different processes such pulping or biorefining were depolymerized in alkaline supercritical water (SCW: 386 • C and 260 bar) in an intensified continuous process to produce high value-added compounds with low-molecularweight in only 300 ms of reaction time. The products obtained were analysed to determine the yield, selectivity to monomers, chemical structure and molecular weight distribution. The char formation was low in most cases, but the proportion of heavy and light oils were variable upon the starting material used. The monoaromatics yield depends mostly on the type of lignin utilized being the nonwood biorefinery lignins less suitable for monomers production than the technical wood ones (13-8%). The monomer distribution depends on the biomass of origin and the pulping method. This technology is equally effective when directly treating a black liquor and better results are obtained if compared to the corresponding isolated lignin.

Chemical Engineering Journal, Jul 1, 2018

A techno-economic assessment of the potential for combining supercritical water oxidation with 'i... more A techno-economic assessment of the potential for combining supercritical water oxidation with 'insitu' hydrothermal synthesis of nanocatalysts using a counter current mixing reactor, Chemical Engineering

Chemical Engineering Journal, Dec 1, 2019

This work analyzes the influence of the mixer configuration on the mixing efficiency in the proce... more This work analyzes the influence of the mixer configuration on the mixing efficiency in the process of biomass ultrafast hydrolysis by supercritical water. The results of the CFD simulations of a horizontal tee, a vertical tee and a mixing cross, selected as the optimum mixing configurations, together with the experimental results obtained in our hydrolysis plant, are the base to determine the configuration which provides the best mixing performance. Although slightly higher conversions are obtained in those experiments performed with a horizontal tee, the small differences between the results demand a theoretical analysis. Therefore, according to the CFD simulation results, since the mixing cross provides the best flow distribution and temperature homogenization at the outlet of the mixers and because of the great similarity between the residence time distribution curves of the mixers, the mixing cross is selected as the optimum geometry to perform the mixing.

Journal of Supercritical Fluids, Mar 1, 2018

The supercritical water hydrolysis (SCWH) of biomass (P=250bara & T=400ºC) allows directly obtain... more The supercritical water hydrolysis (SCWH) of biomass (P=250bara & T=400ºC) allows directly obtaining sugars, which are high value products in the chemical industry, in reaction times lower than 0.2s. The process is characterized by the high selectivity values which can be obtained controlling the reaction time. Reaction kinetics show that glucose degradation is only retarded at temperatures below 250ºC. Therefore, in the traditional SCWH process, degradation control is achieved expanding the hydrolysis stream in a valve which instantaneously cools down the products. Although the selectivity values obtained are greater than 96%, the pressure is wasted on the valve expansion decreasing the global energetic efficiency of the process. In this paper a CFD simulation of a desuperheater which mixes the hydrolysis product with pressurized cooling water is presented. The temperature of the hydrolysis stream decreases below 250ºC in cooling times lower than 20ms maintaining the selectivity value over 93%. Furthermore, the pressure remains at 250bara increasing the global energetic efficiency of the process.

Industrial Crops and Products, Jul 1, 2019

In a biorefinery approach, inulin and inulin-rich biomass as Jerusalem artichoke (JA) could be tr... more In a biorefinery approach, inulin and inulin-rich biomass as Jerusalem artichoke (JA) could be transformed into platform chemicals such as fructose and/or pyruvaldehyde. To do so, the FASTSUGARS pilot plant proved to be a promising alternative for the selective conversion of biomass. In this work, inulin and JA were hydrolyzed in supercritical water (SCW) for the first time. Commercial inulin was selected as a model for fructooligosaccharides (FOS) and its reaction pathway in SCW was elucidated. It was found that fructose was the primary product from FOS hydrolysis in SCW, which was then selectively transformed into pyruvaldehyde as reaction time increased. Operating with extremely low reaction times (0.12 s) the sugars selectivity of JA was as high as 76 % w/w. Finally, comparing JA results to those from lignocellulosic biomass it was found that higher conversion was achieved in the case of JA due to its inulin-based composition.

ACS Sustainable Chemistry & Engineering, Nov 2, 2018

This paper discusses the influence of reactor design and initial consistency when partially hydro... more This paper discusses the influence of reactor design and initial consistency when partially hydrolyzing microcrystalline cellulose (MCC) in supercritical water. Experiments conducted on two pilot reactors located in Finland and in Spain showed that stopping the reaction using depressurization instead of quenching, combined with a sufficiently high MCC consistency, led to significant change in reaction kinetics. A complete particle size reduction was achieved after 50 ms only due to additional shearinduced degradation, with a low-molecular-weight product yield above 50 wt % and an average DP of 25. In addition, gradually increasing the MCC consistency triggered precipitation under higher apparent temperature, which affected both the morphology and structure of the product. A range of particles from ribbon-like cellulose II to shish-kebab structures to lamellar cellulose IV II crystals was obtained. Furthermore, heat requirements as low as 66 kJ•g −1 of product confirm the high potential and versatility of this process for refining MCC into colloidal low-molecular-weight cellulose with different particle shapes and structural properties.

Journal of Supercritical Fluids, Sep 1, 2015

Supercritical Water Oxidation (SCWO) reactors can process waste effluents achieving high conversi... more Supercritical Water Oxidation (SCWO) reactors can process waste effluents achieving high conversions, but the required extreme pressure and temperature operational conditions entail high-energy operational expenditure. SCWO has the potential to be considered a clean energy generation process, as the process effluent is a high temperature, high pressure stream with a high enthalpy content that can be converted to heat and shaft work. This ensures the self-sustained reaction and can generate excess shaft power to drive both the high-pressure pump and the air compressor. On the contrary, an efficient heat and power recovery from SCWO reactors outlet streams using conventional procedures presents several problems. First, Rankine cycles impose indirect heat transfer to the working fluid and are unable to recover the pressure energy and second, direct expansion of the effluents entails costly development of specific, efficient expansion equipment. In this work, we investigate the options for energy recovery of SCWO reactors coupled with commercial gas turbines (GT). SCWO outlet streams are mainly composed of water, nitrogen and carbon dioxide. These operating values nearly resemble the well-known and already-implemented GT steam injection procedures. The temperature of the flue gases (approx. 500 ºC) and the direct shaft work usage offers adequate energy integration possibilities for both feed preheating and compression. The wide range of commercially available GT sizes enables process scaling.

Nano Research, Aug 25, 2016

Continuous hydrothermal synthesis was highlighted in a recent review as an enabling technology fo... more 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.

Food Hydrocolloids, Oct 1, 2015

Quercetin is a strong antioxidant flavonoid with several bioactive properties such as antiinflamm... more Quercetin is a strong antioxidant flavonoid with several bioactive properties such as antiinflammatory and anticarcinogenic activities, becoming an interesting compound to be incorporated into pharmaceutical, cosmetic or food products. However, these applications are limited by the low bioavailability of this flavonoid. Quercetin is poorly soluble in aqueous media, such as gastrointestinal fluids, being also degraded by gut flora. Thus, it is necessary the development of quercetin's formulations capable of improving its water solubility resulting in increased bioavailability and thus higher biological activity of this compound. The aim of the present work was the formulation of quercetin using three distinct natural origin surfactants, namely OSA-starch, Lecithin and β-glucan, by precipitation from a pressurized ethyl acetate-in-water emulsion. Formulations of quercetin with encapsulation efficiencies up to near 76% and a micellar particle size in the range of nanometers were obtained using lecithin. An improved antioxidant activity (3-fold higher per unit mass of quercetin) was also observed in these formulations, demonstrating that lecithin is a good emulsifier for the encapsulation of quercetin. Furthermore, the addition of glycerol as co-solvent increased the colloidal stability of the suspension and the encapsulation efficiency of the flavonoid.

Journal of Supercritical Fluids, Mar 1, 2018

Biomass fractionation into its individual building blocks poses a major challenge to the biorefin... more Biomass fractionation into its individual building blocks poses a major challenge to the biorefinery concept. The recalcitrance of the lignocellulose matrix and the high crystallinity of cellulose make typical feed stocks difficult to separate into their components. Hydrothermal processing fractionates biomass by its hydrolysis. However, a deep knowledge of hydrolysis principles is required since an inappropriate selection of the operating parameters such as an excessive temperature and a long residence times causes dramatic selectivity losses. This review is divided in four main sections which present the fundamentals of lignocellulosic biomass fractionation in hemicelluloses, cellulose and lignin. As the biomass structure plays an important role, a section to study the extraction of the linked phenols that joint lignin and hemicelluloses is included.

Chemical Engineering Journal, Sep 1, 2015

In this study, the effect of temperature and pressure on cellulose and glucose hydrolysis in a hy... more In this study, the effect of temperature and pressure on cellulose and glucose hydrolysis in a hydrothermal media is analyzed. To do so, hydrolysis experiments were carried out in a continuous pilot plant capable of operating up to 400ºC, 27 MPa and residence times between 0.004 s and 40 s. This is possible using an instantaneous heating system by supercritical water injection and cooling by sudden depressurization of the hot product stream. Cellulose hydrolysis produced oligosaccharides, cellobiose, glucose and fructose. In general, concentration profiles of each component were similar for the same temperature and different pressures. Nevertheless, glucose and fructose hydrolysis reaction were strongly affected by changing the pressure, which is density. By increasing temperature and pressure, the reaction of glucose isomerization to fructose was inhibited, and the production of 5-hydroxymethylfurfural (5-HMF) through by fructose dehydration was also inhibited. On the other hand, 5-HMF production was favored by high hydroxide anion concentrations. Thus, at a constant temperature, the production of 5-HMF was increased by rising density (increasing pressure). The production of glycolaldehyde (retroaldol condensation of glucose) was increased by increasing pressure and temperature. The reaction rates of cellulose hydrolysis were fitted using the experimental data. Pressure seems to have no effect on the cellulose hydrolysis kinetic to simple sugars, and at subcritical temperatures the kinetics of glucose hydrolysis reactions did not show significant changes by increasing pressure. However, at 400ºC glucose isomerization and dehydration reactions were diminished by increasing pressure while glucose retro-aldol condensation were enhanced.

Journal of Supercritical Fluids, Nov 1, 2020

Kraft lignin was rapidly depolymerised in a continuous reactor using sub-and supercritical water.... more Kraft lignin was rapidly depolymerised in a continuous reactor using sub-and supercritical water. The reaction yielded an aromatic oil rich in high value aromatic monomers such as guaiacol, vanillin, acetovanillone and homovanillic acid. Different temperatures between 300 and 400ºC and reaction times from 60 ms were studied. An increment in reaction time at every temperature studied promoted secondary reactions of repolymerisation of the lignin products. Those undesired reactions were more relevant as List of abbreviations:

Journal of Supercritical Fluids, Dec 1, 2017

The use of natural polysaccharides is especially attractive to the pharmaceutical industry becaus... more The use of natural polysaccharides is especially attractive to the pharmaceutical industry because of their stability, availability, renewability and low toxicity. In this study, cellulose aerogels obtained from cellulose/ionic liquid solutions were prepared by supercritical drying with surface areas ranged from 154 to 434 m 2 g-1 , pore volume from 0.3 to 2.4 cm 3 g-1 and pore diameter from 7.9 to 34 nm. Drug loading capacity was 2 investigated by impregnating phytol as model compound into the aerogels, using supercritical CO2 at 100 bar, 40°C and mass ratio of phytol per gram of aerogel 10:1. The quantity of drug present is consistent in each aerogel. The aerogel prepared from 2 wt% cellulose in [Emim][DEP] solution showed the highest loading capacity. The high amount of drug loaded (approx 50% w/w) in the cellulose aerogels prepared from ionic liquid solutions shows their potential uses in the pharmaceutical or medical industry.

Chemsuschem, Feb 20, 2015

This article summarizes the recent efforts in the High Pressure Processes Group labs at UVa regar... more This article summarizes the recent efforts in the High Pressure Processes Group labs at UVa regarding the fundamentals of biomass hydrolysis in pressurized water medium. At extremely low reaction times (0.02 s), cellulose was hydrolyzed in supercritical water (400ºC and 25 MPa) obtaining a sugars yield higher than 95% w•w-1 while 5-HMF yield was lower than 0.01% w•w-1. When the reaction times was increased up to 1 s, the main product was glycolaldehyde (60% w•w-1). Independently of the reaction time, the yield of 5-HMF was always lower than 0.01% w•w-1. In order to evaluate the reaction pathway and mechanism of plant biomass 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 considered that the reactions of glucose isomerization to fructose as well as fructose dehydration to 5-HMF take place via proton or hydroxide anion association. So, their concentration was taken into account as reagent concentration in the reaction evaluations. It was found that the proton and hydroxide anion concentration in the medium due water dissociation is the determining factor in the selectivity of the process. The reaction of glucose isomerization to fructose and its further dehydration to produce 5-HMF are highly dependent on ions concentration. By increasing pOH/pH, these reactions were minimized allowing the control of 5-HMF production. At this condition, the retro-aldol condensation pathway was enhanced instead of isomerization/dehydration pathway.

SSRN Electronic Journal, 2022

Different lignins from different sources (hardwoods, softwoods and crop residues) and obtained as... more Different lignins from different sources (hardwoods, softwoods and crop residues) and obtained as by-products of different processes such pulping or biorefining were depolymerized in alkaline supercritical water (SCW: 386 • C and 260 bar) in an intensified continuous process to produce high value-added compounds with low-molecularweight in only 300 ms of reaction time. The products obtained were analysed to determine the yield, selectivity to monomers, chemical structure and molecular weight distribution. The char formation was low in most cases, but the proportion of heavy and light oils were variable upon the starting material used. The monoaromatics yield depends mostly on the type of lignin utilized being the nonwood biorefinery lignins less suitable for monomers production than the technical wood ones (13-8%). The monomer distribution depends on the biomass of origin and the pulping method. This technology is equally effective when directly treating a black liquor and better results are obtained if compared to the corresponding isolated lignin.

High pressure processes (e.g. sustainable hydrothermal manufacturing of nanomaterials [1], superc... more High pressure processes (e.g. sustainable hydrothermal manufacturing of nanomaterials [1], supercritical water oxidation (SCWO) [2] and biomass hydrolysis [3]) require high operational conditions. Water at high pressure and temperature conditions improves kinetic, selectivity and efficiency of these processes but entail high-energy operational expenditure. Use of fluids at high operational conditions makes necessary to supply heat of high quality, as well as power. Because of this, it is necessary to study reasonable solutions for energy recovery and integration in order to achieve the energy self-sufficiency of the process and, if possible, the net power production and with a viable efficiency [4]. In this work, the energy integration of supercritical water oxidation process is being studied. One solution that has been recently proposed is the integration of supercritical processes with energy production in cogeneration or Combined Heat and Power (CHP) cycles. Cogeneration is defin...

The Journal of Supercritical Fluids, 2019

The FASTSUGARS process for sugars' recovery from agricultural biomass was scaled up from laborato... more The FASTSUGARS process for sugars' recovery from agricultural biomass was scaled up from laboratory to pilot plant scale. System performance was evaluated by comparing the results obtained from sugar beet pulp and wheat bran in laboratory and pilot plants. Similar trends were found for each biomass in both plant: as reaction time increased, selectivity to sugars decreased and conversion and degradation rate increased. Then, to bring the FASTSUGARS process closer to industrial applications, the particle size of the biomass was increased in the pilot plant. It was found that the particle size acted as a mass transfer resistance, slowing down the hydrolysis of biomass, providing lower conversion and therefore reducing sugars' degradation (degradation yield was lower than 15 % in the pilot plant). In that way, higher selectivity to sugars was obtained, reaching values around 90 % for both sugar beet pulp and wheat bran in the pilot plant.

Journal of Cleaner Production, 2018

Sugar beet pulp (SBP) is the major by-product in sugar industry. To make profit out of this under... more Sugar beet pulp (SBP) is the major by-product in sugar industry. To make profit out of this undervalued residue, the FASTSUGARS process was proposed as a solution, combining the advantages of supercritical water as hydrolysis medium with very short reaction times in the so-called ultrafast reactors. Operating at 390 ºC, 25 MPa and reaction times between 0.11 and 1.15 s it was possible to convert SBP into sugars and to obtain a lignin-like solid fraction. The highest yields of C-6 and C-5 sugars (61 and 71 % w/w, respectively) were obtained at 0.11 s with the lowest yield of degradation products. The solid product obtained at 0.14 s was thoroughly analyzed by acid hydrolysis, TGA and FTIR analysis to prove its enhanced thermal properties and aromaticity. The FASTSUGARS process demonstrated being a versatile and promising technology to be integrated in the future biorefineries. Highlights • FASTSUGARS is a key step towards future sustainable biorefineries • Sugars were selectively recovered from sugar beet pulp using SCW as reaction medium • Ultrafast reactors allowed accurate control of reaction times in the range of milliseconds • The solid product after hydrolysis was mainly composed of an acid-insoluble fraction • Thorough characterization of the solid confirmed its lignin-like nature