The influence of nitric acid oxidation of low rank coal and its impact on coal structure☆

Álvarez, R.; Clemente, C.; Gómez-Límón, Dulce

doi:10.1016/s0016-2361(03)00176-5

Cited by 89 publications

(55 citation statements)

References 13 publications

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“…It was not selected for these reasons and also because it is recommended to avoid the presence of nitrogen in the HTL process. Alvarez et al (2003) found an increase in nitrogencontaining compounds in the demineralized coal employing nitric acid treatment that could be associated with the release of NOx during combustion. Although the citric acid demineralization pretreatment did not show the highest demineralization potential, it was selected for further HTL studies due to its low toxicity and its potential to remove inorganic components with a minimum loss of organic compounds (polysaccharides, proteins, and lipids) that are crucial for the HTL process.…”

Section: Htl Of Untreated and Demineralized Sargassum Biomassmentioning

confidence: 98%

Demineralization of Sargassum spp. Macroalgae Biomass: Selective Hydrothermal Liquefaction Process for Bio-Oil Production

et al. 2015

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Algae biomasses are considered a viable option for the production of biofuel because of their high yields of oil produced per dry weight. Brown macroalgae Sargassum spp. are one of the most abundant species of algae in the shores of Puerto Rico. Its availability in large quantity presents a great opportunity for use as a source of renewable energy. However, high ash content of macroalgae affects the conversion processes and the quality of resulting fuel products. This research studied the effect of different demineralization treatments of Sargassum spp. biomass, subsequent hydrothermal liquefaction (HTL), and bio-oil characterization. Demineralization constituted five different treatments: nanopure water, nitric acid, citric acid, sulfuric acid, and acetic acid. Performance of demineralization was evaluated by analyzing both demineralized biomass and HTL products by the following analyses: total carbohydrates, proteins, lipids, ash content, caloric content, metals analysis, Fourier transform infrared-attenuated total reflectance spectroscopy, energy dispersive spectroscopy, scanning electron microscopy, and GCMS analysis. HTL of Sargassum spp. before and after citric acid treatment was performed in a 1.8 L batch reactor system at 350°C with a holding time of 60 min and high pressures (5-21 MPa). Demineralization treatment with nitric acid was found the most effective in reducing the ash content of the macroalgae biomass from 27.46 to 0.99% followed by citric acid treatment that could reduce the ash content to 7%. Citric acid did not show significant leaching of organic components such as carbohydrates and proteins, and represented a less toxic and hazardous option for demineralization. HTL of untreated and citric acid treated Sargassum spp. resulted in bio-oil yields of 18.4 0.1 and 22.2 0.1% (ash-free dry basis), respectively. ± ±

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Section: Htl Of Untreated and Demineralized Sargassum Biomassmentioning

confidence: 98%

Demineralization of Sargassum spp. Macroalgae Biomass: Selective Hydrothermal Liquefaction Process for Bio-Oil Production

et al. 2015

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“…1,[12][13][14][15] En el caso de los ácidos húmicos obtenidos al oxidar con ácido nítrico (Figura 7) se observaron las mismas bandas registradas en los materiales obtenidos al oxidar con el peróxido de hidrogeno, con la diferencia de la presencia de bandas a 1540 y 1370 cm -1 originadas por la presencia del estiramiento simétrico N=O de los grupos nitro formados principalmente en estructuras aromáticas por la oxidación con el ácido nítrico. 16,17 Los valores del número de grupos carboxílicos (Tabla 3) en los ácidos húmicos obtenidos al oxidar con agentes químicos indican que en el caso de los tratados con peróxido de hidrogeno, las condiciones más suaves de oxidación con aire (180-200 °C) condujo a solidos con mayor número de ácidos carboxílicos. El tratamiento a temperaturas superiores especialmente con el mayor tiempo de tratamiento con la solución de peróxido de hidrogeno conducen a la formación de AH con menor número de grupos carboxílicos o a AH en los cuales el mayor tiempo de exposición al agente oxidante condujo a la descomposición de grupos oxigenados, entre ellos los carboxílicos a CO 2 .…”

Section: Resultados Y Discusiónunclassified

Aumento del contenido de ácidos húmicos en un carbón de bajo rango a través de la oxidación con aire y con peróxido de hidrogeno o ácido nítrico

Anillo-Correa¹,

Colpas-Castillo²,

Fuentes³

2013

Quím. Nova

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Recebido em 30/4/12; aceito em 18/9/12; publicado na web em 23/1/13 INCREASE OF THE CONTENT OF HUMIC ACIDS IN A LOW RANK COAL BY OXIDATION WITH AIR AND WITH HYDROGEN PEROXIDE OR NITRIC ACID. Low-rank coals are an important source of humic acids, which are important in retention processes of water and nutrients in plants. In this study coal samples of Montelibano, Colombia, were oxidized with air at different temperatures and subsequently with H 2 O 2 and HNO 3 . The materials were characterized by FTIR, proximate and elemental analysis, and quantification of humic acids. The oxidation process led to an increased content of oxygenated groups and humic acids in the carbonaceous structure. The solid oxidized with air at 200 °C for 12 h and re-oxidized with HNO 3 for 12 h showed the highest percentage of humic acids (85.3%).Keywords: coal; humic acids; oxidation. INTRODUCCIÓNLa materia orgánica natural o humus contiene una fracción soluble en soluciones alcalinas llamadas sustancias húmicas, las cuales se forman por la descomposición del material vegetal y animal que se deposita en el suelo. Durante este proceso el material orgánico es inicialmente degradado y depolimerizado para posteriormente por acción microbiológica producir nuevos componentes con un alto grado de polimerización de coloración oscura y con un carácter no biodegradable con estructuras irregulares de alto peso molecular. 1Las sustancias húmicas se clasifican dependiendo del proceso de separación utilizado; los mayores componentes del humus son los ácidos fulvicos (AF) los cuales son solubles en medio ácido y los ácidos húmicos (AH) que son insolubles en medio ácido. [2][3][4] Estudios recientes indican que los ácidos húmicos están constituidos por clusters supramoleculares formados por el ensamblaje de bio-moléculas a través de enlaces químicos; los cuales se mantienen unidos por puentes de hidrogeno y por interacciones hidrofobicas y de van der Waals.5 Los ácidos húmicos están conformados por la unión de estructuras inalteradas de segmentos poliméricos de plantas y de fragmentos orgánicos con grupos del tipo carboxílico, fenólico, aldehído, cetonico, amido y amino. Esta composición estructural le confiere a los ácidos húmicos propiedades tales como su anfifilidad y su capacidad de intercambio catiónico. 5,6 Se estima que aproximadamente un cuarto del peso molecular de las sustancias húmicas se debe a los grupos oxigenados, principalmente grupos carboxílicos que aumentan con el grado de humificación de la materia orgánica y que pueden formar carboxilatos con metales presentes en el medio, grupos fenólicos que se forman en los etapas iniciales de humificación y grupos carbonilos que por reacciones de oxidación originan grupos carboxílicos. 5,6 Las sustancias húmicas desempeñan un papel importante en la naturaleza, ya que debido a sus grupos funcionales oxigenados participan en procesos de retención de cationes que son esenciales para las plantas además de retener el calor en la superficie debido a su color oscuro. 4 Entre los usos actuales de estas ...

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“…Nitric acid treatment was associated with organic matter solubilization, which was seen as a decrease in ash content. 23 The nitric acid molecules react with inorganic matter, mostly clay and carbonate minerals leading to acid consumption. 23 An ill defined shoulder band at 1,540 cm -1 attributed to amide II was noticed to become progressively significant with increased nitric acid concentration implying more intensified attack of nitro and nitroso groups.…”

Section: Resultsmentioning

confidence: 99%

“…23 The nitric acid molecules react with inorganic matter, mostly clay and carbonate minerals leading to acid consumption. 23 An ill defined shoulder band at 1,540 cm -1 attributed to amide II was noticed to become progressively significant with increased nitric acid concentration implying more intensified attack of nitro and nitroso groups. Upon nitric acid treatment, trace nitrate compounds are expected to be present and it was shown on the FTIR spectra as a weak absorption band at 1,397 cm -1 .…”

Section: Resultsmentioning

confidence: 99%

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Reuse of nitric acid in the oxidative pretreatment step for preparation of humic acids from low rank coal of Mukah, Sarawak

Fong¹,

Lau²,

Mat³

2007

J. Braz. Chem. Soc.

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O ácido nítrico é um material eficiente na produção de ácidos húmicos. Contudo, é um item caro que torna o processo desfavorável industrialmente. Estudos indicaram que existe a possibilidade de re-utilização do ácido nítrico para oxidação; entretanto, as estruturas resultantes dos ácidos húmicos não foram estudadas. Por isso, o objetivo deste estudo foi investigar as propriedades espectroscópicas e químicas dos ácidos nitro-húmicos preparados com ácido nítrico re-utilizado. A amostra de carvão foi oxidada com ácido nítrico 5%, 10% e 15% com posterior extração dos ácidos nitro-húmicos. A concentração de ácido nítrico com melhores rendimentos foi empregada novamente em outros 2 ciclos de oxidação. As propriedades químicas e espectroscópicas dos ácidos nitro-húmicos foram avaliadas. Os resultados indicaram que o processo de oxidação geralmente melhora as propriedades funcionais ácidas dos ácidos nitro-húmicos, sendo que ácido nítrico a 10% produziu os melhores rendimentos. O ácido nítrico foi re-utilizado na extração, com bom rendimento, em torno de 78%. Estruturalmente, os ácidos nitro-húmicos produzidos com o ácido nítrico reutilizado apresentaram tamanhos moleculares maiores e menos grupos funcionais ácidos, sugerindo um menor fracionamento da estrutura.Nitric acid is an effective material for production of humic acids. Nevertheless, it is an expensive item that renders the process unfavorable industrially. Study indicated that there was a possibility to reuse the nitric acid for oxidation however the resulting structures of humic acids was not studied. Therefore, the objective of this study was to investigate the chemical and spectroscopic properties of nitrohumic acids prepared with reused nitric acid. The coal sample was oxidized with 5%, 10% and 15% of nitric acid and subjected to extraction for nitrohumic acids. Concentration of nitric acid with the most yields was reemployed for another 2 cycles of oxidation. The chemical and spectroscopic properties of nitrohumic acids were evaluated. The results indicated that oxidation process generally improved the acidic functional properties of the nitrohumic acids with 10% nitric acid producing the most promising yield. The nitric acid was reused for extraction and the percentage yield remained good at an average of 78%. Structurally, the nitrohumic acids produced with the reused nitric acid demonstrated larger molecular size and fewer acidic functional groups suggesting lesser extent of structure fractionation.

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The influence of nitric acid oxidation of low rank coal and its impact on coal structure☆

Cited by 89 publications

References 13 publications

Demineralization of Sargassum spp. Macroalgae Biomass: Selective Hydrothermal Liquefaction Process for Bio-Oil Production

Demineralization of Sargassum spp. Macroalgae Biomass: Selective Hydrothermal Liquefaction Process for Bio-Oil Production

Aumento del contenido de ácidos húmicos en un carbón de bajo rango a través de la oxidación con aire y con peróxido de hidrogeno o ácido nítrico

Reuse of nitric acid in the oxidative pretreatment step for preparation of humic acids from low rank coal of Mukah, Sarawak

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