Beneficiamento de biomassa residual da indústria papeleira por meio de rotas termoquímicas

Abstract

The paper and pulp industry holds great importance in the Brazilian economic landscape. This scenario drives the pursuit of renewable energies, with biomass being a viable option, albeit requiring pretreatments. The aim of this study was to evaluate the generation of value-added products through thermochemical treatments of cellulose residues from the paper industry, such as sludge and rejected cellulose fibers. Cellulosic residues collected from a paper industry in Curitiba, Paraná, described as sludge cellulose residue (SCR) and rejected fiber cellulose residue (RFC). Proximal analysis determined moisture content (RFC = 59.81% and SCR = 65.23%), volatile matter (RFC = 74.54% and SCR = 69.27%), fixed carbon (RFC = 9.76% and SCR = 2.89%), and ash content (RFC = 15.70% and SCR = 27.84%), indicating potential for energy and environmental applications. Techniques such as thermogravimetry (TGA), Fourier-transform infrared spectroscopy (FTIR), and Scanning Electron Microscopy combined with Energy Dispersive Spectroscopy (SEM-EDS) were employed to evaluate thermal degradation, chemical, and morphological properties of the materials. Additionally, mathematical modeling (MRG and MRC) of the thermochemical processes for the studied residues was performed. Thus, thermogravimetric profiles revealed typical thermal events of cellulosic biomass, both through experimental data and obtained through the proposed model adjustments, with more pronounced degradation in oxidative atmosphere. Morphological analysis showed an increase in surface degradation of RFC with increasing temperature, while SCR maintained its morphology at lower temperatures. Drying experiments were planned using Rotatable Central Composite Design (RCCD). The drying kinetics of cellulosic residues were analyzed in a module with air circulation, showing that temperature and air velocity influenced the drying time and equilibrium moisture, presenting lower values of time and equilibrium moisture for higher values of drying temperature and air velocity. Furthermore, phenomenological modeling of the drying process was conducted using the LDF model, showing that the model adequately fit the drying data of RFC but performed poorly for SCR, likely requiring the implementation of convective terms to better represent mass transfer mechanisms in residue drying. Thermochemical treatments, carbonization, and torrefaction, were planned using the Box-Behnken method, evaluating the effect of process conditions on calorific value, showing that despite lower calorific values compared to conventional biomass (RFC = 13.25 MJ kg-1 and SCR = 13.86 MJ kg-1), the RFC material stood out for considerable calorific values due to being a residual material. After thermal processes, specifically under torrefaction conditions (200°C), there was an increase in calorific value (14.32 MJ kg-1 and 15.57 MJ kg-1), reaching values comparable to traditional solid fuels (e.g., lignite).