Different chemical modifications were performed to the natural aluminosilicate Montanit300® in order to improve its catalytic activity in PE depolymerization. Performance of such prepared catalysts was compared to established solid acid catalysts, such as HZSM-5, sulfonated and fluorinated γ-Al2O3 and amorphous silica–alumina. Pyridine TG and DRIFTS characterization revealed mild acid treatment and aluminum grafting as successful in increasing acid site density through impurity removal and specific surface area increase. Mesoporous catalyst structure that allows facile diffusion through its pore network, together with high-density Brønsted acid sites, was found to be crucial to obtain high catalytic activity. The T50 value for PE depolymerization was lowered by 162 °C with sulfonated γ-Al2O3 solid, compared to non-catalyzed reaction, whereas with aluminum-grafted Montanit300® catalyst this value was lowered by 65 °C. PE depolymerization products present in the condensed liquid phase using aluminum-grafted Montanit300® catalyst were exclusively alkanes with chain length up to 21 carbon atoms. Liquid, coke and gas yields were found to be 53, 0.4 and 46.6%, respectively, the latter consisting of linear and branched C2–C4 alkenes and alkanes.
Catalytic depolymerization of polyethylene (PE) over several aluminosilicate catalysts was studied using thermogravimetric (TG) analysis. Procedure was proposed for decoupling mass loss related directly to the catalyst and that of PE depolymerization. The benefit of this approach is twofold: (1) it enables a more realistic kinetic analysis, and (2) reduces the total number of required experiments with the pure catalyst by more than 50 %. The activation energies of PE depolymerization over different catalysts were calculated from the treated PE-TG profiles using advanced isoconversional analysis and were compared to those obtained from raw TG profiles. The presented analysis reveals that neglecting the mass loss associated with the aluminosilicate catalyst results in underestimated values of calculated activation energies at low PE conversions, while at high conversions the values of calculated activation energies were overestimated. The apparent PE depolymerization activation energy in the presence of applied catalysts increases in the following order: amorphous silica alumina ( heulandite/clinoptilolite (M300) ( alumina grafted montmorillonite within the conversion range from 0 to 95 %.
Biochar as a soil amendment and carbon sink becomes in last period one of the vast, interesting product of slow pyrolysis. Simplest and most used industrial process arrangement is a production of biochar and heat at the same time. Proposed mass and heat balance model consist of heat consumers (heat demand side) and heat generation-supply side. Direct burning of all generated uncondensed volatiles from biomass provides heat. Calculation of the mass and heat balance of both sides reveals the internal distribution of masses and energy inside process streams and units. Thermodynamic calculations verified not only the concept but also numerical range of the results. The comparisons with recent published scientific and vendors data prove its general applicability and reliability. The model opens the possibility for process efficiency innovations. Finally, the model was adapted to give more investors favorable results and support techno-economic assessments entirely.
Through isoconversional analysis of thermogravimetric data using the differential Friedman approach, it was discovered that thermogravimetric profiles predicted by various reaction models, using kinetic parameters determined by isoconversional analysis, practically overlap over the entire conversion range. The reason for this behaviour lies in the fact that the kinetic model’s contribution during the model integration is cancelled out by the pre-exponential factor value since the same concentration term appears in the numerators of the expression from which the pre-exponential factors’ values were calculated. The observed phenomenon is hereby demonstrated by the analysis of PE degradation runs carried out at different heating rates. The results show it is possible to predict the degradation of various materials simply by correlation twins, i.e. the two functional relations between activation energy, apparent pre-exponential factor and conversion.