Desenvolvimento de criogéis de celulose/biochar

Os criogéis de celulose são materiais sólidos que apresentam baixa densidade, comparável a espumas de poliuretano e poliestireno expandido, e são muito estudados nas áreas de adsorção e isolamento térmico devido sua elevada porosidade (acima de 90%) e baixa condutividade térmica (próxima a do ar – 0,03 W m-1 K-1). A utilização de estruturas de carbono, tais como o grafeno e nanotubos de carbono, em criogéis, cresce a cada ano, porém o alto custo e tecnologia na sintetização desses materiais torna-os custosos nos processos industriais. Visando a diminuição de custos, a substituição dessas estruturas pelo biochar, torna-se interessante visto que o mesmo pode ser produzido a partir de resíduos agrícolas. A utilização do biochar como reforço para criogéis de celulose trás propriedades interessantes para o mesmo, como o aumento da resistência mecânica e capacidade de adsorção (óleos, corantes,...). O presente trabalho teve como objetivo produzir criogéis de celulose/biochar e estudar estes materiais quanto a suas propriedades mecânicas, térmicas e de adsorção. Inicialmente foram comparados os criogéis de celulose/biochar com criogéis de celulose/nanoplaquetas de grafeno (GNP), para avaliar o comportamento das propriedades do biochar em relação as GNPs. Os criogéis foram produzidos a partir de uma suspensão de celulose com concentração de 1,5% (m/m) obtida em um moinho de pedras, e a esta foi adicionado o biochar em concentração de 0-100% (m/m) em relação a concentração de celulose. A suspensão de celulose/biochar foi congelada e liofilizada para a obtenção dos criogéis. Foram avaliadas as propriedades mecânicas, térmicas e de adsorção dos criogéis, sendo que no contexto geral, o biochar apresentou potencial para ser utilizado na substituição de estruturas de carbono comercialmente utilizadas, tal como as nanoplaquetas de grafeno. Na sequência do trabalho, foram avaliadas diferentes concentrações de celulose e biochar nos criogéis e avaliadas suas influências nas propriedades de condutividade térmica e capacidade de adsorção de óleos. Os criogéis de celulose/biochar, apresentaram porosidade acima de 90% e densidade aparente inferior a 0,035 g cm-3, o que demostram que são materiais extremamente leves. A adição do biochar aos criogéis de celulose proporcionam um aumento de cerca de 60% na resistência a compressão do mesmo. A condutividade térmica dos criogéis foi de 0,021 a 0,026 W m-1K-1, a adição do biochar não apresentou influência significativa nesta propriedade. Porém os criogéis de celulose/biochar possuem capacidade para serem utilizados como isolantes térmicos devido sua condutividade térmica ser muito próxima a condutividade térmica do ar e também aos materiais utilizados comercialmente. Para a capacidade de adsorção, a adição de 5% de biochar (m/m em relação a celulose) ao criogel de celulose aumentou cerca de 76% a capacidade de adsorção de petróleo. No estudo da cinética e isoterma de adsorção os modelos que mais se ajustaram ao processo foram pseudossegunda ordem e Langmuir, respectivamente. Com isso, conclui-se que o processo de adsorção de petróleo pelo criogel de celulose ocorre em monocamada. No geral, a utilização do biochar como substituto de estruturas de carbono em criogéis de celulose, apresentou propriedades semelhantes aos produtos comerciais utilizados como adsorventes e isolantes térmicos mostrando-se adequados para estas aplicações.Cellulose cryogels are solid materials that have low density, comparable to polyurethane and expanded polystyrene foams, and are widely studied in the areas of adsorption and thermal insulation due to their high porosity (above 90%) and low thermal conductivity (close to that of air – 0.03 W m-1 K-1). The use of carbon structures, such as graphene and carbon nanotubes, in cryogels, grows every year, but the high cost and technology in synthesizing these materials make them costly in industrial processes. To reduce costs, the replacement of these structures by biochar becomes interesting since it can be produced from agricultural residues. The use of biochar as a reinforcement for cellulose cryogels brings interesting properties to it, such as increased mechanical strength and adsorption capacity. The present work aimed to produce cellulose/biochar cryogels and to study these materials in terms of their mechanical, thermal, and adsorption properties. Initially, cellulose/biochar cryogels were compared with cellulose/graphene nanoplatelet (GNP) cryogels to evaluate the behavior of biochar properties to GNPs. The cryogels were produced from a cellulose suspension with a concentration of 1.5% (m/m) obtained in a stone mill, and to this was added biochar in a concentration of 0-100% (m/m) to cellulose concentration. The cellulose/biochar suspension was frozen and lyophilized to obtain cryogels. The mechanical, thermal, and adsorption properties of cryogels were evaluated, and in the general context, biochar showed potential to be used in the replacement of commercially used carbon structures, such as graphene nanoplatelets. Following this work, different concentrations of cellulose and biochar in cryogels were evaluated and their influence on the properties of thermal conductivity and oil adsorption capacity was evaluated. Cellulose/biochar cryogels showed porosity above 90% and bulk density below 0.035 g cm-3, which demonstrates that they are extremely light materials. The addition of biochar to cellulose cryogels provides an increase of about 60% in its compressive strength. The thermal conductivity of the cryogels ranged from 0.021 to 0.026 W m-1K-1, the addition of biochar had no significant influence on this property. However, cellulose/biochar cryogels are capable of being used as thermal insulators because their thermal conductivity is very close to the thermal conductivity of air and also to the materials used commercially. For the adsorption capacity, the addition of 5% biochar (w/w to cellulose) to the cellulose cryogel increased the oil adsorption capacity by about 76%. In the study of adsorption kinetics and isotherm, the models that best fit the process were pseudo second order and Langmuir, respectively. Thus, it is concluded that the process of adsorption of petroleum by the cellulose cryogel occurs in a monolayer. In general, the use of biochar as a substitute for carbon structures in cellulose cryogels presented properties similar to commercial products used as adsorbents and thermal insulators, proving to be suitable for these applications

CO2 adsorption by cryogels produced from poultry litter wastes

Poultry litter waste (PLW) is the main by-product generated by the Brazilian poultry industry. A sustainable approach for reusing this waste is the production of biochar to be further used aiming CO2 adsorption. In this work, biochars were produced by varying the N2 flow along the pyrolysis process of 150 (PLW-150) and 1000 (PLW-1000) mL min-1. PLW and biochars were characterized for their morphology, porosity, specific surface area, and CO2 adsorption capacity. From the biochars, carbon cryogels (CC) were produced aiming their use as CO2 adsorbents. The results of the cryogel adsorption test showed a CO2 adsorption capacity of 13.1±2.9 and 33.8±3.3 mg g-1 for the CC-PLW.150 and CC-PLW.1000 cryogels, respectively. Therefore, reusing this residue for cryogels production and its use in the CO2 adsorption signifies an attractive perspective to minimize the environmental damage caused by CO2 emissions

Cellulose/biochar aerogels with excellent mechanical and thermal insulation properties

Aiming at investigating the use of alternative materials for the production of thermal insulation and, mainly, to replace the carbon structures (graphene and nanotubes), extensively used in the development of aerogels, the present study had the objective to produce cellulose/biochar aerogels and to evaluate their properties. The aerogels were produced from Pinus elliottii cellulose fibers and biochar produced from these fibers. The materials were characterized in their physical, thermal and mechanical properties. They were extremely light and porous, with a density between 0.01 and 0.027 g cm−3 and porosity between 93 and 97%. Several percentages of biochars were added to the cellulose suspension (0–100% w/w). The use of 40 wt% biochar provided a 60% increase in the compressive strength of the aerogel in relation to the cellulose aerogel. Besides that, the addition of this carbonaceous structure did not influence significantly the thermal conductivity of the aerogels, which presented a thermal conductivity of 0.021–0.026 W m−1 K−1. The materials produced in the present research present a great potential to be used as insulators due to the low thermal conductivity found, which was very similar to the thermal conductivity of the air and also of commercial materials such as polyurethane foam and expanded polystyrene

Thermal degradation kinetics and lifetime prediction of cellulose biomass cryogels reinforced by its pyrolysis waste

Degradation kinetics is an important tool in order to understand and improve energy conversion and the final application of a material. Cellulose cryogels (CC) are a new class of materials that can be reinforced by several types of particle, including biochar. Apart from it, degradation kinetics and lifetime prediction of biomass cellulose cryogels reinforced by cellulose pyrolysis waste (BC) has been investigated using TG techniques and iso-conversional model free methods. Additionally, the same study was applied to cellulose cryogels reinforced by graphene nanoplatelets (NPG) to compare the behavior of a filler from waste (BC) and a noble filler (NPG). Furthermore, the influence of the addition of the fillers into the cellulose biomass were evaluated in terms of thermal stability and crystallinity. BC and GNP led to higher values of activation energies (Ea) calculated from model-free isoconversional methods and all samples degraded in two-steps. Finally, lifetime prediction was successfully applied and the CC cryogel became more stable over time, maintaining almost 80% of the mass for 1 year exposed at 180 °C. The results of this study shown that only cellulose biomass cryogels are more suitable to produce thermal insulators due to it higher thermal stability

Caracterização de aerogéis de celulose com adição de metiltrimetoxissilano (MTMS) para adsorção de petróleo

A utilização de adsorventes é uma maneira eficaz para a remoção do óleo em terra ou água. Os aerogéis são uma classe de adsorventes, que são caracterizados pela sua estrutura altamente porosa e o seu baixo teor de sólidos, o que confere ao material uma elevada capacidade de adsorção de petróleo. No presente trabalho, foi avaliada a influência da concentração de celulose e metiltrimetoxissilano (MTMS) na capacidade de adsorção de petróleo do aerogel. Os aerogéis produzidos apresentaram baixa massa específica (menor que 0,025 g cm-3) e elevada porosidade (maior que 95%). Pelas micrografias é possível visualizar alterações na superfície da fibras, com a formação de um filme, enquanto que na análise dos espectros obtidos, bandas características do silano foram identificadas nas amostras com tratamento químico. A hidrofobicidade dos aerogéis foram evidenciadas pelas medidas do ângulo de contato da superfície dos mesmos com a água, sendo obtidos valores superiores a 120°. A capacidade de adsorção dos aerogéis atingiu 78 g g-1 para o meio homogêneo e 53 g g-1 para o meio heterogêneo

Production of carbon foams from rice husk

The production of a material with rigid, multifunctional three-dimensional porous structure at a low cost is still challenging to date. In this work, a light and rigid carbon foam was prepared using rice husk as the basic element through a simple fermentation process followed by carbonization. For the fermentation process, the amount of biological yeast (7.5 g for the carbon foam CA-1P and 5 g for the carbon foam CA-2P) was used to evaluate its influence on the morphology of the foams. In order to prove that the heat treatment made in the foam alters the hydrophilic character of the rice husk foam, a chemical treatment with steam deposition was carried out. The foams were characterized by the following analyzes: apparent density, micrograph, thermogravimetry, contact angle, water sorption capacity and thermal conductivity. Visually, the CA-1P foams presented a structure with larger pores due to the greater amount of yeast used in its formulation. The heat treatment of rice potato foams proved to be as efficient as the chemical treatment for water contact angle above 90º, proving the ability of the foams to repel water/moisture. The thermal conductivity of the foams (0.029 and 0.026 W m-1 K-1 for CA-1P and CA-2P, respectively) was close to the conductivity of polyurethane foams (0.032 W m-1 K-1). Thus, the method used in the production of the carbon foams produced from the rice husk proved to be effective. In addition, the foams produced have the potential to be used for thermal insulation

Infuence of the addition of carbon structures in cellulose cryogels

The substitution of carbon structures, such as graphene and carbon nanotubes by biochar, is interesting, since the latter has considerably lower costs and similar properties to other structures. Therefore, the objective of the present paper was to evaluate the infuence of the addition of biochar (BC), produced from the pyrolysis of cellulose residues, in order to substitute graphene nanoplatelets (GNP), regarding the thermal, mechanical and adsorption aspects. The cryogels were produced from the cellulose suspension with the addition of 50 and 100 (% w/w in relation to cellulose) of BC or GNP. Extremely light cryogels (with apparent density less than 0.033 g cm−3 and porosity greater than 90%) were produced. The addition of BC and GNP showed similar values in terms of compressive strength, temperature of degradation and thermal conductivity. In the heterogeneous adsorption capacity, however, a signifcant diference was observed between the two carbon structures studied, and for this property, the GNPs showed a slight increase in the adsorption capacity in relation to BC. In the general context of the properties studied, the biochar has the potential to be used to replace commercially used carbon structures, such as graphene nanoplatelets