Produção de aerogel a partir de nanofibras de celulose obtidas de resíduos da indústria moveleira (Pinus elliottii var. elliottii) para sorção de óleos

Abstract

Petroleum is a feedstock of great economic value. Due to the aim for non-renewable feedstocks substitution, vegetable oils have been used ever more as a feedstock for fuels and polymers. Spills during oil handling are serious environmental problems. Vegetable fibers have been used for a long time now as oil sorbents during spills. Wood residues as sawdust are currently used as oil sorbents, being a cheap and available resource. However, the hydrophilic profile of vegetable fibers reduce their capacity of oil sorption. Cellulose aerogels have become a product of great interest in the oil spill remediation field due to their high porosity (95 to 99%), low specific mass (0,004 to 0,15 g.cm-3) and high surface area (>60,m².g-1), besides cellulose abundance and sustainability. The objective of this work was to develop a hydrophobic aerogel from nanocellulose nanofibers obtained from furniture industry residues (Pinus elliottii var. elliottii) processed via steam explosion acid hydrolysis for petroleum and vegetable oil sorption. In the steam explosion process the best experimental condition was observed for a volumetric acetic acid and nitric acid ratio of 15:2:1 at 120ºC and 30 minutes with a cellulose yield higher than 90% and complete removal of hemicellulose and ligning. After lyophilization an aerogel of specific mass 0,046 0,0013 g.cm-3 and porosity 97,08 0,08% was obtained. Aerogel hydrophobization yielded a contact angle of 138,78º 0,78º. The aerogel exhibited a top experimental sorption capacity (CSME) of 19,55 0,10 goil.gaerogel-1 for petroleum and 13,73 0,62 goil.gaerogel-1 for vegetable oil. Cellulose nanofibers were produced by physical means (grinding) and hydrophobization was accomplished via vapor-phase deposition of organosilane (MTMS). In wood residue hydrolysis two acids were tested (nitric acid and acetic acid) simultaneously and individually, with variations of temperature, time and reagent amount. The solid fraction rich in cellulose was grinded in a rock mill for 5 hours at 2500 rpm in a 1,5% m/m suspension in water. The obtained gel was frozen for 48 hours at -20ºC for lyophilization at -40ºC for 50 hours. The aerogels obtained by lyophilization were treated with organosilane via vapor-phase deposition for 5 hours at 70ºC. The furniture industry residue was characterized as for its amounts of cellulose, hemicellulose, lignin, ashes, extractives and humidity. The process of steam explosion was characterized through the yields of individual components (cellulose and hemicellulose). Procedures like specific mass, contact angle, porosity, morphological characterization by scanning electron microscope with field emission gun, oil absorption tests and absorption kinetic in homogeneous and heterogeneous medium of petroleum and soy oil absorption were performed to characterize the aerogel. Kinetic models of pseudo-first, pseudo-second and pseudo-nth order were fitted to experimental data in their linear and non-linear forms. The absorption in homogeneous medium of petroleum was well fitted by pseudo-first linear kinetic model. Absorption of vegetable oil was well fitted by both pseudo-first and pseudo-second models. Models in non-linear form indicated a better fit for experimental data by the pseudo-nth order model (n=0,95) for petroleum and by pseudo-first order for vegetable oil. Kinetic adjusts showed that in heterogeneous medium CSME is maintained, but sorption rate is smaller.