Effect of pretreatment temperature on the surface modification of diatomite with trimethylchlorosilane

Artículo científicoDiatomite samples from Costa Rica were purified using acidic treatments with hydrochloric acid, thermally treated (400–1000 C) and then silylated with trimethylchlorosilane in toluene under inert atmosphere. The purification process allows to decrease the concentration of metals presented in the crude diatomite, as is confirmed by X-ray Fluorescence (XRF) Analysis. The silylated materials were analyzed by using Hyperpolarized 129Xe Nuclear Magnetic Resonance Spectroscopy (HP 129Xe NMR), Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TGA), rehydration tests, and contact angle measurements. XRD measurements indicate that diatomite is mainly amorphous, but presents several crystalline phases (kaolinite, cristobalite, and quartz). Pretreatments at high temperatures cause changes in those crystalline phases, resulting in more amorphous materials. However, there is no difference in the overall structure of purified and thermally treated diatomite samples with respect to the silylation products. In addition, SEM measurements show no effect over the pore structure of the materials. On the other hand, TGA measurements and rehydration tests show lower losses of water for silylated materials prepared using higher pretreatment temperatures. Moreover, HP 129Xe NMR, FTIR, and contact angle measurements evidence a modification due to covalent attachment of Si(CH3)3-groups to the surface, which increases for higher pretreatment temperatures. The results provide valuable information about external factors that influence the surface modification of diatomite. This can be useful to control modifications that can be achieved in a similar way

Optimization of Lignin Extraction from Pine Wood for Fast Pyrolysis by Using γ-valerolactone-Based Binary Solvent System

Fast pyrolysis of lignin is a promising method to produce aromatic chemicals and fuels. Lignin structure and pyrolysis conditions determine the liquid yield and product selectivity. Extraction of pine wood using γ-valerolactone (GVL) mixed with water in the presence of diluted sulfuric acid obtains lignin (GVL-lignin) which shows different product yield and selectivity. The composition of the extraction medium influences the yield of GVL-lignin and affects its native structure. The GVL-to-water ratio affects the lignin yield without significantly modifying the structure of the extracted lignin, whereas the sulfuric acid concentration affects both the extraction yield and the extracted lignin structure. These structural changes influence the products distribution after fast pyrolysis, which generates phenols and alkoxy phenols as the main products in the liquid fraction. Lignin extracted with a mixture of 4/1 of GVL/H2O (w/w) with 0.075 M sulfuric acid solution produces the highest pyrolysis liquid yield. Pyrolysis of GVL-lignin at 750 °C generates the maximum liquid yield. The amount of phenols in fast pyrolysis products increases with increasing temperature and sulfuric acid concentration used in the GVL-lignin extraction. This indicates that the extraction conditions of GVL-lignin may be optimized to increase the selectivity in fast pyrolysis

Evaluación de las técnicas SEM y EDS en la investigación nanotecnológica de catalizadores para la producción de biocombustibles

Proyecto de Investigación. Instituto Tecnológico de Costa Rica. Escuela de Ciencia e Ingeniería de los Materiales. Laboratorio de Nanotecnología (ITCR); Universidad de Costa Rica, 2013Se llevó a cabo el análisis de diatomitas modificadas, propuestas como catalizadores para esterificaciones (reacciones modelo para producción de biodiesel). Los materiales estudiados fueron preparados en el Laboratorio de Investigación en Química Inorgánica (UCR) y su caracterización se desarrolló en el Laboratorio de Nanotecnología (ITCR, técnicas SEM y EDS), la Unidad de Difracción de Rayos (UCR, técnica XRD) y su laboratorio de preparación (análisis químicos). Se estudiaron modificaciones de diatomita con clorotrimetilsilano (TMCS). Se analizó cómo se afectan la morfología y composición cristalina de la diatomita debido a temperaturas de tratamiento térmico entre 400 °C y 1100 °C, así como el posterior efecto por su modificación con TMCS. Para 1100 °C se presentan cambios morfológicos hacia estructuras más lisas (demostrados con SEM). Además, por arriba de 600 °C se presentan cambio en las fases cristalinas del material (demostrado por XRD), pasando de tenerse caolinita, cristobalita, cuarzo, magnetita y óxido de sodio, aluminio y silicio, a presentarse únicamente cristobalita y cuarzo por arriba de dicha temperatura. Además, no se presentan cambios considerables entre diatomitas tratadas térmicamente y su producto de modificación con TMCS. Por otro lado, se estudió la modificación de diatomita con (3-­‐mercaptopropil)-­‐trimetoxisilano, en presencia de tetraetilortosilicado (TEOS). Los materiales muestran productos de co-­‐condensación entre el TEOS y MPTMS junto con la diatomita, que llega a formar un material compuesto por estructuras semejantes a bloques y esferas, además de estructuras típicas de diatomitas (demostrados con SEM). La presencia de MPTMS en las muestras fue corroborada por medio de determinaciones de acidez (de ácidos sulfónicos provenientes de MPTMS), además de determinaciones de % atómicos por medio de EDS. Todos estos materiales generados resultan apropiados para catalizar reacciones de esterificación

Thermogravimetric, Devolatilization Rate, and Differential Scanning Calorimetry Analyses of Biomass of Tropical Plantation Species of Costa Rica Torrefied at Different Temperatures and Times

We evaluated the thermogravimetric and devolatilization rates of hemicellulose and cellulose, and the calorimetric behavior of the torrefied biomass, of five tropical woody species (Cupressus lusitanica, Dipteryx panamensis, Gmelina arborea, Tectona grandis and Vochysia ferruginea), at three temperatures (TT) and three torrefaction times (tT) using a thermogravimetric analyzer. Through a multivariate analysis of principal components (MAPC), the most appropriate torrefaction conditions for the different types of woody biomass were identified. The thermogravimetric analysis-derivative thermogravimetry (TGA-DTG) analysis showed that a higher percentage of the hemicellulose component of the biomass degrades, followed by cellulose, so that the hemicellulose energy of activation (Ea) was less than that of cellulose. With an increase in TT and tT, the Ea for hemicellulose decreased but increased for cellulose. The calorimetric analyses showed that hemicellulose is the least stable component in the torrefied biomass under severe torrefaction conditions, and cellulose is more thermally stable in torrefied biomass. From the MAPC results, the best torrefaction conditions for calorimetric analyses were at 200 and 225 °C after 8, 10, and 12 min, for light and middle torrefaction, respectively, for the five woody species

Physical and Compression Properties of Pellets Manufactured with the Biomass of Five Woody Tropical Species of Costa Rica Torrefied at Different Temperatures and Times

The purpose of the biomass torrefaction and pelletizing processes is to increase its energy properties, be environmentally friendly, decrease shipping costs, and make handling easier. The objective of the present work is to evaluate the density, internal density variation by X-ray densitometry, moisture content, water absorption, and compression force of torrefied biomass pellets of five wood species (Cupressus lusitanica, Dipterix panamensis, Gmelina arborea, Tectona grandis, and Vochysia ferruginea) under three torrefaction temperature conditions (light, middle, and severe) and three torrefaction times (8, 10, and 12 min). The results showed that the bulk density of the pellets was 0.90–1.30 g/cm3. The density variation of the pellets was higher with torrefaction at 250 °C. The moisture content decreased with increasing torrefaction temperature from 3% to 1%. Water absorption was lower in the pellets torrefied at 250 °C. The compression force was lower in the pellets torrefied at 250 °C with approximate loads of 700 N. Based on the above results, it was concluded that pellets made with biomass torrefied at 200 °C have better energy properties and evaluated properties. According to these results, pellets fabricated with the torrefied biomass of tropical species can be used in stove, gas, and hydrogen production because the pellet presents adequate characteristics

Technology overview of fast pyrolysis of lignin: current state and potential for scale‐up

Lignin is an abundant natural polymer obtained from lignocellulosic biomass and rich in aromatic substructures. When efficiently depolymerized, it has great potential in the production of value-added chemicals. Fast pyrolysis is a promising depolymerization method, but current studies focus mainly on small quantities of lignin. To determine the potential for upscaling, we evaluated the systems used in the most relevant unit operations of fast pyrolysis of lignin. Fluidized-bed reactors have the most potential. It would be beneficial to combine them with the following: slug injectors for feeding, hot particle filters, cyclones, and fractional condensation for product separation and recovery. Moreover, upgrading lignin pyrolysis oil would allow reaching the necessary quality parameters for particular applications.ISSN:1864-564XISSN:1864-563

Production of Paper Using Biopulping of Pineapple Leaves Fibers (PALF) Followed by Chemical and Xylanase-Enzymatic Processing

Pineapple leaf fibers (PALF) were biopulped using Trametes versicolor, and the resulting biopulp was bleached with xylanase-enzymatic treatments. The biopulping was extensively described using determinations of fiber morphology, color, chemical composition, extractive content, and thermal stability using the structural characteristics determined by XRD and paper properties. The results showed that the chemical and enzymatic treatments shortened the fiber, almost to 50%, and the Kappa index decreased from 27 to 13. Cellulose and holocellulose contents increased from 65% to 74% and from 86% to 91%, respectively, but extractives, lignin (from 12% to 4%), pentosans (from 25% to 14%) and the crystallinity decreased from 58% to 67% in both chemical bleaching and further xylanase-enzymatic processing. Xylanase-enzymatic processing allowed us to obtain whiter (increased lightness color and decreased redness and yellowness tonality) and heavier paper, even though it presented decreased mechanical properties (decreased stress resistance, rupture length, tear resistance and index longitudinal tearing). The xylanase-enzymatic treatment with the best pulping and paper properties is when the biopulp is treated with a xylanase enzyme concentration of 0.04% (w/w)

Isomer-dependent catalytic pyrolysis mechanism of the lignin model compounds catechol, resorcinol and hydroquinone

The catalytic pyrolysis mechanism of the initial lignin depolymerization products will help us develop biomass valorization strategies. How does isomerism influence reactivity, product formation, selectivities, and side reactions? By using imaging photoelectron photoion coincidence (iPEPICO) spectroscopy with synchrotron radiation, we reveal initial, short-lived reactive intermediates driving benzenediol catalytic pyrolysis over H-ZSM-5 catalyst. The detailed reaction mechanism unveils new pathways leading to the most important products and intermediates. Thanks to the two vicinal hydroxyl groups, catechol (o-benzenediol) is readily dehydrated to form fulvenone, a reactive ketene intermediate, and exhibits the highest reactivity. Fulvenone is hydrogenated on the catalyst surface to phenol or is decarbonylated to produce cyclopentadiene. Hydroquinone (p-benzenediol) mostly dehydrogenates to produce p-benzoquinone. Resorcinol, m-benzenediol, is the most stable isomer, because dehydration and dehydrogenation both involve biradicals owing to the meta position of the hydroxyl groups and are unfavorable. The three isomers may also interconvert in a minor reaction channel, which yields small amounts of cyclopentadiene and phenol via dehydroxylation and decarbonylation. We propose a generalized reaction mechanism for benzenediols in lignin catalytic pyrolysis and provide detailed mechanistic insights on how isomerism influences conversion and product formation. The mechanism accounts for processes ranging from decomposition reactions to molecular growth by initial polycyclic aromatic hydrocarbon (PAH) formation steps to yield, e.g., naphthalene. The latter involves a Diels–Alder dimerization of cyclopentadiene, isomerization, and dehydrogenation.ISSN:2041-6520ISSN:2041-653

Direct Evidence on the Mechanism of Methane Conversion under Non‐oxidative Conditions over Iron‐modified Silica: The Role of Propargyl Radicals Unveiled

Radical-mediated gas-phase reactions play an important role in the conversion of methane under non-oxidative conditions into olefins and aromatics over iron-modified silica catalysts. Herein, we used operando photoelectron photoion coincidence spectroscopy to disentangle the elusive C2+ radical intermediates participating in the complex reaction network. Our experiments pinpointed different C2-C5 radical species that allow for a stepwise growth of the hydrocarbon chains. Herein, propargyl radicals (H2C-C≡C-H) are identified as essential precursors for the formation of aromatics, which contribute with the formation of heavier hydrocarbon products via hydrogen abstraction - acetylene addition routes (HACA mechanism). These results provide comprehensive mechanistic insights that are relevant for development of methane valorization processes.ISSN:1433-7851ISSN:1521-3773ISSN:0570-083