CO2 Capture by Reduced Graphene Oxide Monoliths with Incorporated CeO2 Grafted with Functionalized Polymer Brushes

The monolithic materials of reduced graphene oxide (rGO) can be used successfully in CO2 adsorption. Here, the incorporation of CeO2 particles with and without polymer brushes grafted from the particles showed that the structural properties could be changed, affecting the adsorption of CO2. Polymer brushes of (1) poly(acrylic acid) (PAA), (2) poly(vinyl caprolactam) (PVCL) and (3) poly[(2-(methacryloyloxy)ethyl) trimethylammonium chloride] (PMETAC) were grafted from CeO2 via reversible addition−fragmentation chain transfer (RAFT) polymerization. The preparation of monoliths of rGO with different modified CeO2 particles led to different thermal properties (TGA), structural changes (BET isotherms) and CO2 adsorption. The responsive character of the CeO2@polymer was proven by the DLS and UV results. The responsive character of the particles incorporated into the rGO monolith affected not only the adsorption capacity but also the microstructure and values of the surface volume of the pores of the monolith. Monoliths with porosity values for better adsorption were affected by the responsive character of the polymer.This research was funded by the Basque government, grant number GV IT999-16

Tailoring of Textural Properties of 3D Reduced Graphene Oxide Composite Monoliths by Using Highly Crosslinked Polymer Particles toward Improved CO2 Sorption

The main constraint on developing a full potential for CO2 adsorption of 3D composite monoliths made of reduced graphene oxide (rGO) and polymer materials is the lack of control of their textural properties, along with the diffusional limitation to the CO2 adsorption due to the pronounced polymers' microporosity. In this work, the textural properties of the composites were altered by employing highly crosslinked polymer particles, synthesized by emulsion polymerization in aqueous media. For that aim, waterborne methyl methacrylate (MMA) particles were prepared, in which the crosslinking was induced by using different quantities of divinyl benzene (DVB). Afterward, these particles were combined with rGO platelets and subjected to the reduction-induced self assembly process. The resulting 3D monolithic porous materials certainly presented improved textural properties, in which the porosity and BET surface area were increased up to 100% with respect to noncrosslinked composites. The crosslinked density of MMA polymer particles was a key parameter controlling the porous properties of the composites. Consequently, higher CO2 uptake than that of neat GO structures and composites made of noncrosslinked MMA polymer particles was attained. This work demonstrates that a proper control of the microstructure of the polymer particles and their facile introduction within rGO self assembly 3D structures is a powerful tool to tailor the textural properties of the composites toward improved CO2 capture performance.I.B. gratefully acknowledges the financial support of the Spanish Government (BES-2017-080221). L.S. thank s the grant P20_00328 funded by the Consejeria de Transformacion Economica, Industria, Conocimiento y Universidades of the Junta de Andalucia and by the EU FEDER funds. The authors thank the technical and human support provided by SGIker (UPV/EHU/ERDF, EU)

Efecto sinérgico entre sales inorgánicas y γ-Al2O3 para la deshidratación de xilosa a furfural

La biomasa lignocelulósica, con un alto contenido en hemicelulosa, es una de las principales fuentes de pentosas pentosas a partir de las cuales se pueden obtener biocombustibles y productos químicos de alto valor añadido, como el 2-Furfuraldehído (furfural), producido por deshidratación de xilosa mediante catálisis ácida. Se han estudiado diferentes catalizadores sólidos ácidos como alternativa a los ácidos minerales convencionales. Además, el uso de sales inorgánicas para mejorar el rendimiento a furfural, sobre todo en sistemas bifásicos, ha sido previamente recogido en la bibliografía. En este trabajo, se ha estudiado la deshidratación de xilosa a furfural empleando sistemas bifásicos agua:tolueno en presencia de γ-Al2O3 mesoporosa, y se ha evaluado el efecto de la adición de CaCl2 o MgCl2 al medio de reacción sobre el rendimiento en furfural. La γ-Al2O3 es muy activa en la deshidratación de xilosa a furfural a 175ºC, pero los rendimientos no son altos debido a reacciones secundarias (Figura 1). Sin embargo, se ha demostrado previamente que sales alcalinotérreas como el CaCl2 interaccionan con moléculas de glucosa en el medio de reacción, acelerando considerablemente su deshidratación, por lo que sería posible que también influyesen en la deshidratación de xilosa. Por ello, se ha estudiado el efecto del CaCl₂ y MgCl₂, adicionando el mismo número de moles, siendo 0.65 y 0.39 g sal·g.dis.acuosa, respectivamente. Se observa un considerable aumento, tanto de la conversión de xilosa como del rendimiento en furfural al añadir estas sales, siendo máximos (96% y 71%, respectivamente) en el caso del CaCl2, superiores a los alcanzados en presencia de γ-Al2O3.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Recovery of pentoses-containing olive stones for their conversion into furfural in the presence of solid acid catalysts

Olive stones were employed as feedstock for furfural production in two stages: 1) autohydrolysis of hemicellulosic fraction to recover their pentoses, mainly xylose, and 2) subsequent dehydration of pentoses into furfural. Autohydrolysis step was optimized by using different experimental conditions (temperature: 160-200 ºC and time: 30-75 min), giving rise to liquors with different xylose concentrations, since hydrolysis was incomplete in some cases. The combined use of a commercial γ-Al2O3 and CaCl2 led to total hydrolysis of non-hydrolyzed pentosans after autohydrolysis step, and the subsequent dehydration of pentoses into furfural. The maximum values of furfural yield and efficiency were 23 and 96%, respectively, after only 60 minutes at 150 ºC by using liquor obtained by autohydrolysis at 180 ºC and 30 min (L5.1) as source of pentoses. This liquor, L5.1, provided better catalytic results than other liquors which had shown higher xylose concentration after autohydrolysis, probably due to these latter also exhibited a higher concentration of organic acids; thus, the presence of organic acids such as acetic and lactic acid could promote side undesired reactions leading to lower furfural yields. Finally, γ-Al2O3 was more effective for furfural production under these experimental conditions than other solid acid catalysts, such as mesoporous Nb2O5, Nb-doped SBA-15 and Zr-doped HMS silicas, probably due to alumina has a higher density of acid sites.Spanish Ministry of Economy and Competitiveness (RTI2018-94918-B-C44 project), Junta de Andalucía (RNM-1565), FEDER (European Union) funds (UMA18-FEDERJA-171) and Malaga University. C.G.S. and J.A.C. thank to FEDER funds and Malaga University respectively for financial support. L.S.C. gratefully acknowledges support from Spanish MINECO via the concession of a Ramon y Cajal contract (RYC-2015-17109)

Fermentable sugars recovery from grape stalks for bioethanol production

[EN]Three different processes were investigated for the recovery of fermentable sugars from grape stalks: autohydrolysis at 121 ºC before and after a pre-washing step and acid hydrolysis (2% H2SO4 w/w) after a pre-washing step. Moreover, optimal conditions of a charcoal-based purification process were determined by experimental design. All hydrolysates, with their corresponding synthetic liquors were used as fermentation substrates for the production of metabolites by the yeast: Debaryomyces nepalensis NCYC 1026. The main fermentation product was ethanol, where a maximum production of 20.84 g/l, a conversion yield of 0.35 g ethanol/g monomeric sugars and a productivity of 0.453 g/l h were obtained from non-purified autohydrolysate liquor. In all cases, ethanol production and cell growth were better in nonpurified liquors than in synthetic liquors. These results could be influenced by the presence of other sugars in the hydrolysates, with higher concentration in non-purified ones.The authors would like to thank the Juan de la Cierva program (JCI-2011-09399) of Spanish Ministry of Science and Innovation, Department of Education, Universities and Investigation of the Basque Government (Grant of I.E., ref BFI09.164), Agrisystem Doctoral School of the Università Cattolica del Sacro Cuore, Italy– Spain Integrated Actions Program (project IT2009-0054) and Pro- getto Ager grant no 2010-2222 for supporting this wor

Valorization of olive stones to obtain furfural in the presence of gamma-Al2O3 and CaCl2

Furfural is considered as one of the 12 platform molecules derived from biomass for the synthesis of high value-added chemicals. It is mainly produced by acid-catalyzed dehydration ofpentoses, such as xylose, which can be obtained from hemicellulose, one of the main components of lignocellulosic biomass. The aim of this work was to obtain furfural from lignocellulosic wastes from the agro-food industry, such as olive stones. For this purpose, the catalytic behavior of a mesoporous g-Al2O3 as acid solid catalyst and the effect of the addition of CaCl2 in order to improve the furfural yield were evaluated. Firstly, the production of sugar-rich liquors from olive stones was optimized in a thermostated 2 L reactor under continuous stirring, by using water as solvent with a solid:liquid mass ratio of 1:10, at 160-200 °C for 30-75 minutes. The liquors H7 and H10 obtained at 180 °C and 60 minutes and 190 °C and 45 minutes, respectively, showed the highest xylose contents and they were chosen for furfural production. The catalytic dehydration of pentoses-containing liquors, mainly D-xylose, was studied in batch type glass reactors in a thermostated aluminum block under magnetic stirring, at 150 °C for 50 minutes. In a typical test, 1.5 mL of liquor, 3.5 mL of toluene, 50 mg of g-Al2O3 and 0.65 g CaCl2·g.sol -1 were added to the reaction medium. The reaction products were analyzed by HPLC. The presence of the catalyst, g- Al2O3, hardly improves the performance of furfural with respect to the non-catalytic process . However, an increase in furfural yield is observed in the presence of CaCl2, being maximum when g-Al2O3 and CaCl2 are used together (100% and 74% for H7 and H10, respectively). The lower yield attained from H10 could be due to the use of a higher temperature to obtain this liquor, since the formation of degradation products, such as formic acid, acetic acid and HMF, could promote secondary reactions of furfural, consequently decreasing the furfural yield.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Valorización de huesos de aceituna para la obtención de furfural en presencia de gamma- Al2O3 y CaCl2

En la actualidad, se considera que la biomasa lignocelulósica es una materia prima sostenible muy prometedora, ya que es la única fuente de carbono renovable que no compite con la cadena alimentaria. A partir de ella puede obtenerse energía, así como combustibles y productos químicos de alto valor añadido como el furfural, el cual ha sido identificado por el Departamento de Energía de los Estados Unidos (DOE) como una de las 12 moléculas plataforma con mayor relevancia. Así, el furfural es un precursor muy versátil para sintetizar una gran variedad de productos químicos, como el alcohol furfurílico o el ácido furoico, entre otros productos de interés. Actualmente, el furfural se produce principalmente mediante hidrólisis ácida de la hemicelulosa, uno de los principales componentes de la biomasa lignocelulósica, formada mayoritariamente por unidades de pentosas como la xilosa, cuya posterior deshidratación en presencia de un catalizador ácido conduce a furfural. En el presente trabajo se pretende la obtención de furfural a partir de licores ricos en carbohidratos procedentes de residuos lignocelulósicos, más concretamente, de huesos de aceituna. Con este fin se ha evaluado el comportamiento catalítico de una gamma-Al2O3 mesoporosa como catalizador sólido ácido, como alternativa al uso de ácidos minerales convencionales, y además, también se ha estudiado el efecto de la adición de sales inorgánicas como el CaCl2 para mejorar el rendimiento a furfural. La presencia de gamma-Al2O3 y CaCl2 permite obtener un rendimiento en furfural del 100% usando licores procedentes de los huesos de aceituna como fuente de xilosa, obtenidos tras hidrólisis a 180 ºC y 60 min.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Synergic effect between inorganic salts and gamma-Al2O3 for xylose dehydration to furfural

Lignocellulosic biomass, with a high content of hemicellulose, is the main source of pentoses, from which biofuels and value-added chemicals can be produced. Amongst the latter, 2-Furfuraldehyde (furfural, FUR) is the only unsaturated organic compound prepared from carbohydrates, obtained by acid-catalyzed dehydration of xylose (XYL). Different acid solid catalysts have been studied as alternative to conventional mineral acids, which are employed in industry. In this work, the dehydration of XYL in a biphasic water:toluene system with a mesoporous γ-Al2O3 has been studied, and the effect of the presence of CaCl2 or MgCl2 in the reaction medium on the catalytic performance was evaluated. The presence of CaCl2 and the use of γ-Al2O3 in the reaction medium for xylose dehydration to furfural were studied and compared to the non-catalytic process, at 175 °C. In all cases, high conversion values were attained with respect to the non-catalytic process. γ-Al2O3 shows a high activity, with a XYL conversion of 96%, after 90 min of reaction, but the furfural yield was lower than expected due to alumina favored secondary reactions. Thus, high furfural yields were achieved by using CaCl2 even in absence of catalyst under these experimental conditions. However, considering that side reactions are favored at high temperatures, the catalytic process was studied with CaCl2 and γ-Al2O3 at 150 °C. At this lower temperature, a synergistic effect can be inferred between γ-Al2O3 and CaCl2, reaching values of XYL conversion and FUR yield of 99% and 59%, respectively, after only 30 min of reaction. Moreover, the effect of the addition of CaCl2 and MgCl₂ was compared (Fig. 3), adding the same number of moles, corresponding to 0.65 and 0.39 gsalt·gaq.sol., respectively. Although both salts improved the catalytic performance, CaCl2 is more beneficial than MgCl2. The reaction mechanism has been studied by 1H NMR.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Resembling graphene/polymer aerogel morphology for advancing the CO2/N2 selectivity of the postcombustion CO2 capture process

The separation of CO2 from N2 remains a highly challenging task in postcombustion CO2 capture processes, primarily due to the relatively low CO2 content (3–15%) compared to that of N2 (70%). This challenge is particularly prominent for carbon-based adsorbents that exhibit relatively low selectivity. In this study, we present a successfully implemented strategy to enhance the selectivity of composite aerogels made of reduced graphene oxide (rGO) and functionalized polymer particles. Considering that the CO2/N2 selectivity of the aerogels is affected on the one hand by the surface chemistry (offering more sites for CO2 capture) and fine-tuned microporosity (offering molecular sieve effect), both of these parameters were affected in situ during the synthesis process. The resulting aerogels exhibit improved CO2 adsorption capacity and a significant reduction in N2 adsorption at a temperature of 25 °C and 1 atm, leading to a more than 10-fold increase in selectivity compared to the reference material. This achievement represents the highest selectivity reported thus far for carbon-based adsorbents. Detailed characterization of the aerogel surfaces has revealed an increase in the quantity of surface oxygen functional groups, as well as an augmentation in the fractions of micropores (<2 nm) and small mesopores (<5 nm) as a result of the modified synthesis methodology. Additionally, it was found that the surface morphology of the aerogels has undergone important changes. The reference materials feature a surface rich in curved wrinkles with an approximate diameter of 100 nm, resulting in a selectivity range of 50–100. In contrast, the novel aerogels exhibit a higher degree of oxidation, rendering them stiffer and less elastic, resembling crumpled paper morphology. This transformation, along with the improved functionalization and augmented microporosity in the altered aerogels, has rendered the aerogels almost completely N2-phobic, with selectivity values ranging from 470 to 621. This finding provides experimental evidence for the theoretically predicted relationship between the elasticity of graphene-based adsorbents and their CO2/N2 selectivity performance. It introduces a new perspective on the issue of N2-phobicity. The outstanding performance achieved, including a CO2 adsorption capacity of nearly 2 mmol/g and the highest selectivity of 620, positions these composites as highly promising materials in the field of carbon capture and sequestration (CCS) postcombustion technology.The authors acknowledge the financial support of the Basque Government and European Regional Fund (ZL-2022/00364) and (IT-1525-22). I.B. gratefully acknowledges the financial support of the Spanish Government (BES-2017-080221). L.S.-C. thanks the Grant P20_00328 funded by the Consejería de Transformación Económica, Industria, Conocimiento y Universidades of the Junta de Andalucía and by the EU FEDER funds

Bacterial nanocellulose production from carbon dioxide

Conferencia invitada presentada en: 5th International Symposium on Bacterial Cellulose. Jena Alemania, 22-23 septiembre (2022)Carbon dioxide, the primary greenhouse gas emitted by human activity, is the pollutant that most influences global warming and the consequent climate change. CO2 capture and utilization, and when possible its further valorization, is proposed as a powerful technological strategy to alleviate the problem of greenhouse gas accumulation. We have isolated a bacterial strain able to produce cellulose when growing with naphthalene as sole carbon source [1, 2]. The strain belongs to the sulphur oxidizing bacteria and can also use a number of compounds and residues as carbon source to produce cellulose. We show that the strain can grow and produce cellulose when growing with carbon dioxide as sole carbon source and reduced sulphur compounds as source of reducing power. The cellulose biofilm is produced in thin parallel layers under static conditions, and forms ball-shaped aggregates at different shaking speeds. The produced polymer has all the characteristics of bacterial nanocellulose, namely 60 nm wide - several µM long fibres, with a typical cellulose FTIR spectrum. Analysis of the strain¿s genome identified a bcs cluster for cellulose synthesis. Knock-out mutants in bcsA or bcsK genes were capable of growth with carbon dioxide, but did not produce cellulose. The genome included the gene complements for a complete Calvin-Benson-Bassham cycle for CO2 fixation and for two pathways (sor and sox) for sulphur compound oxidation. However, a cbbL mutant in the RuBisCO large subunit gene was still capable of growth with carbon dioxide, suggesting the functioning of an alternative carbon fixation pathway. A spontaneous mutant with an increased capacity of cellulose production was isolated. We identified a large chromosomal deletion in the mutant genome that included, among others, the genes for a quorum sensing regulation system. Site-directed knock-out mutants in different genes of the QS system also showed increased levels of cellulose biosynthesis. The optimum conditions for cellulose production from CO2 are being established. The bacterial nanocellulose produced can be mechanically functionalized, with the potential for CO2 capture to reach levels above those presented for other conventional and non-renewable materials.This study was supported by the European Regional Development Fund FEDER, grant PY20_00328 from the Economic Transformation, Industry, Knowledge and University Council of the Junta de Andalucía, and grant PID2020-113144RB-I00 funded by MCIN/AEI/ 10.13039/501100011033