Coupling the solvent-based CO2 capture processes to the metal water-splitting for hydrogen generation in a semi-continuous system

Producción CientíficaHydrogen is considered as the future energy vector. Due to scarceness in materials, obtaining hydrogen from common metals and metallic residues is gaining interest. The present work aims at coupling for the first time solvent-based CO2 capture processes with the hydrogen generation from the metal-water splitting reaction, using common elements such as Al, Zn, Mn and Fe. To do so, a novel semicontinuous facility is developed. In the process, both the CO2-Rich stream (CO2RS) and CO2 Capture-Solvent Lean stream (CO2LS) are considered. The production of H2 increased in the order Al < Mn < Fe < Zn. For pure Al, aqueous NaOH (CO2LS) showed the highest H2 yield, up to 85.5%, while Al chips (residue) showed outstanding performance. The experimental study showed that small particle sizes improve the H2 yield. This technology represents an opportunity for bringing about value-added to CO2 capture by generating at the same time green hydrogen.Ministerio de Ciencia e Innovación and Ministerio de Universidades (RTI2018-097456-B-I00)Junta de Castilla y León - FEDER (CLU-2019-04

Hydrothermal CO2 reduction using biomass derivatives as reductants

Producción CientíficaA wide range of organic substances, potentially derived from biomass, were tested as reductants for CO2 (as NaHCO3) in hydrothermal media. The reactions were carried out in batch reactors at 300 °C and 3 h. All the substances reduced CO2 to formic acid in yields up to 65%. These results agree to the mechanisms proposed in literature that suggested that reduction is carried out by primary or secondary alcohols. However, some substances without these groups gave significant yields to formic acid so new mechanisms were proposed. Out of all the compounds tested, glucose gave the highest yield to formic acid, probably due to its particular reaction pathways at the studied conditions. Effect of NaOH in the reaction using glucose was investigated to assure that formic acid is produced from bicarbonate. For ethanol and ethylenglycol, additional conditions were tested to study the dependence of the reaction with time and temperature.Ministerio de Economía, Industria y Competitividad (Project ENE2014-53459-R

Governing Chemistry of Cellulose Hydrolysis in Supercritical Water

Producción CientíficaAt 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.Ministerio de Economía, Industria y Competitividad - FEDER (Proyect CTQ2013-44143-R

Synergistic Hydrothermal Conversion of Aqueous Solutions of CO2 and Biomass Waste Liquefaction into Formate

Producción CientíficaCO2 utilization by conversion into useful chemicals can contribute to facing the problem of increasing CO2 emissions. Among other alternatives, hydrothermal transformation stands out by the high conversions achieved, just using high-temperature water as the solvent. Previous works have demonstrated that several organic compounds with hydroxyl groups derived from biomass can be used as reductants of NaHCO3 aqueous solutions as inorganic CO2 sources. Formate was obtained as the main product as it was produced by conversion both of the inorganic carbon and of the organic reductants, whose transformation into formate was promoted by the addition of NaHCO3. Based on these results, in this work, the hydrothermal conversion of NaHCO3 is performed together with the liquefaction of lignocellulosic biomass (sugarcane bagasse and pine needles) in a one-pot process. Results show that yields to formate of 10% wt/wt (with respect to the initial concentration of biomass) are achieved by hydrothermal treatment of NaHCO3 and lignocellulosic biomass at 250 °C with a residence time of 180 min. Other products, such as acetic acid and lactic acid, were also obtained. These results demonstrate the feasibility of the hydrothermal reduction of CO2 combined with the hydrothermal liquefaction of residual biomass in a simultaneous process.Junta de Castilla y Leon - EU-FEDER (program CLU-2019- 04)Ministerio de Ciencia, Innovación y Universidades (project RTI2018-097456-B-I00

Hydrolysis of cellulose in supercritical water: reagent concentration as a selectivity factor

Producción CientíficaIn this work, the influence of reagent concentration on hydrolysis reactions of cellulose in supercritical water was analyzed. The hydrolysis was carried out at 400 °C and 25 MPa with reaction times between 0.07 and 1.57 s and feeding cellulose concentrations between 5 and 20 % w/w (1.5–6 % w/w at reactor inlet). Also, a flash separator was used to separate vapor in the product stream in order to increase the final concentration. The best result for sugar production (79 % w/w) was obtained working with a cellulose concentration of 5 % w/w and 0.07-s reaction time. For glycolaldehyde production, the best result (42 % w/w) was obtained with a concentration of 20 % w/w and 1.57 s. The employment of a flash separator allowed reducing the water content by 50 %. It was also observed that by increasing the cellulose concentration in the reactor up to 4 % w/w, the hydrolysis took place with a similar kinetic as that in the heterogeneous media, thus reducing the conversion rate of cellulose in supercritical water.Ministerio de Economía, Industria y Competitividad - FEDER (Proyect CTQ2013-44143-R

Experimental determination of viscosities and densities of mixtures carbon dioxide+1-allyl-3-methylimidazolium chloride. Viscosity correlation

Producción CientíficaThe effect of viscosity reduction caused by the solubilization of CO2 is studied in order to improve the biomass processing in ionic liquids. To do so, densities and viscosities of the pure ionic liquid 1-allyl-3-methylimidazolium chloride and its mixtures with CO2 up molar fractions of 0.25 and temperatures between 333 and 372 K have been experimentally determined. Viscosities were correlated as a function of temperature and CO2 molar fractions with an average relative error of 2.5%. The viscosities of other mixtures CO2 + ionic liquids were also correlated for other ionic liquids with an average relative error between 4.4 and 13%. In general these ionic liquids present a linear decrease of viscosity with CO2 molar fractions up to around 0.5 that is more pronounced at lower temperatures and depends of each ionic liquid, and can reach between 60 and 100% viscosity reduction with respect the viscosity of the pure ionic liquid, making the CO2 a promising co-solvent for viscosity reduction in process with ionic liquids.2018-01-29Junta de Castilla y León VA295U14Marie Curie Program. Project DoHipMinisterio de Economía. Programa Ramon y Cajal, RyC RYC-2013-13976Cluster of Excellence RESOLV (EXC 1069) funded by the Deutsche Forschungsgemeinschaft

Energy recovery from effluents of supercritical water oxidation reactors

Producción CientíficaSupercritical 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 °C) 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.Ministerio de Economía, Industria y Competitividad - FEDER (Proyect CTQ2013-44143-R

Hydrothermal CO2 conversion using zinc as reductant: Batch reaction, modeling and parametric analysis of the process

Producción CientíficaHydrothermal CO2 reduction using Zn as reductant was investigated. This process has the advantage of avoiding the use of hydrogen with all its safety and environmental concerns, and allows an easy integration with CO2 capture as NaHCO3. In this work, this reaction was studied in batch reactors at temperatures from 275 to 325 °C. Conversions up to 60% were obtained with 100% selectivity towards formic acid, at reaction times between 10 and 180 min. A mathematical model correlated with data from literature was developed and is able to correctly predict both experimental and literature data with an averaged error of 3.5%. Main variables of the process were analyzed: temperature, Zn/HCO3− ratio, heating rate, Zn particle size, pressure, etc. The optimum reaction conditions found were 300 °C with a rapid heating, and particle sizes of 10 μm. Zn excess dramatically improves the yield, but a lower excess can be compensated at high pressures.Ministerio de Economía, Industria y Competitividad (Project ENE2014-53459-R

Density and viscosity measurements of (piperazine + water) and (piperazine + 2-dimethylaminoethanol + water) at high pressures

Producción CientíficaThe purpose of this paper is broadening the understanding of amine solution behaviour through the experimental measurements of density (up to 140 MPa) and viscosity (up to 100 MPa) in a temperature range from (293.15 to 393.15) K. The two selected blends are Piperazine (PZ) + Water (10% amine weight concentration) and Piperazine (PZ) + 2-Dimethylaminoethanol (DMAE) + Water (10% and 30% amine weight concentration, respectively). Densities were measured using a vibrating tube densimeter (Anton Paar DMA HPM) with an expanded uncertainty (k = 2) less than 0.7 kg·m-3. Viscosities were obtained using a falling body viscometer which was calibrated with water and dodecane. The viscosity expanded uncertainty (k = 2) ranges from 2.5% for the highest viscosity to 3.2% for the lowest one. Experimental data were fitted to modified Tamman-Tait equation for densities and modified VFT model for viscosities, obtaining good results for both equations.Junta de Castilla y León VA280P18Ministerio de Economía, Industria y Competitividad RTI2018-097456-B-I0

Determination of density, viscosity and vapor pressures of mixtures of dimethyl sulfoxide + 1-allyl-3-methylimidazolium chloride at atmospheric pressure

Producción CientíficaIn this work, densities, viscosities and vapor pressures of dimethyl sulfoxide (DMSO) + 1-allyl-3-methylimidazolium chloride (AmimCl) mixtures have been experimentally determined. Densities and viscosities were measured at temperatures T = [293.15, 373.15] K and molar fractions of dimethyl sulfoxide xDMSO = 0, 0.05, 0.1, 0.15, 0.25, 0.5, 0.75, 0.9 and 1 at atmospheric pressure with a Stabinger densimeter-viscosimeter. Viscosities and densities were found to decrease with increasing temperature and DMSO concentrations. Correlation of viscosity was made as a function of temperature and concentration with two modifications of the Seddon and Grunberg-Nissan equation, one with an average relative deviation of 6.8% and the second one of 16.3%. Vapor pressures of the mixtures were measured at T = [353.1, 433.1] K. and were correlated with Non-Random-Two-Liquid (NRTL) model, obtaining ARD% between 5 and 12%.Junta de Castilla y León, proyecto VA295U14MINECO proyecto ENE2014-53459-RMINECO Prorama Ramón y Cajal RYC-2013-1397