IN RECENT YEARS, VARIOUS THERMOCHEMICAL PROCESSES HAVE BEEN STUDIED TO OBTAIN BIOENERGY. HYDROTHERMAL CARBONIZATION (HTC) HAS PROVEN TO BE A CONVENIENT ALTERNATIVE SINCE IT ALLOWS BIOMASS WITH HIGH MOISTURE AND ASH CONTENT TO BE PROCESSED WITHOUT PRIOR DRYING PROCESSES, OBTAINING A BIOFUEL WITH UP TO 20 TO 30 % MORE CALORIFIC VALUE COMPARED TO BIOMASS. HOWEVER, THE MAIN CHALLENGE IS DETERMINING OPTIMUM POINTS OF INCREASE IN CALORIFIC POWER AND ENERGY PERFORMANCE TO TRANSFORM IT INTO ECONOMICALLY FEASIBLE. THIS STUDY PROPOSES THE STUDY AND OPTIMIZATION OF THE HTC PROCESS WITH TWO CHILEAN BIOMASSES: SAWDUST (PINUS RADIATA) AND RAPESEED (BRASSICA NAPUS). MASS YIELD (MY), HIGHER HEATING VALUE (HHV), AND ENERGY YIELD (EY) WERE ANALYZED BY APPLYING A DESIGN OF EXPERIMENTS (DOE) WITH THREE FACTORS AND TWO LEVELS (23). THE VARIABLES USED AND THEIR LEVELS WERE TEMPERATURE (T): 190 - 250 °C; TIME (T): 60-120 MIN; AND BIOMASS/WATER RATIO (B/W): 8 ? 14 % FOR RAPESEED AND 10 ? 16 % FOR SAWDUST. FOR SAWDUST, INCREASING THE TEMPERATURE FROM 190 TO 250 °C RAISED HHV BY 23 % AND LOWERED MY (BY 21 %) AND EY (BY 18 %). RAPESEED HHV SHOWED AN INCREASE OF 23 %, WHILE MY AND EY DECREASED BY 11 AND 14 %. IN THE STATISTICAL ANALYSIS, THE MOST INFLUENTIAL VARIABLES FOR BOTH BIOMASSES WERE TEMPERATURE AND THE B/W RATIO, SIMILAR TO WHAT WAS FOUND IN PREVIOUS STUDIES. NEW OPERATING POINTS WERE DETERMINED TO MAXIMIZE THE HHV OF THE HYDROCHAR USING THE RESPONSE SURFACE METHODOLOGY AND THE EQUATIONS OBTAINED FROM THE DOE (R2 ABOVE 0.98). THE RESULTS ACHIEVED WERE HIGHER THAN THE AVERAGE INDICATED IN THE LITERATURE. FOR SAWDUST, AN EY OF 77 % AND AN HHV OF 28.6 MJ/KG (+48 %) WERE OBTAINED AT 280 °C, 100 MIN, AND A B/W OF 13 %. ON THE OTHER HAND, FOR RAPESEED, EY=49.2 % AND HHV=29.1 MJ/KG (+37 %) WERE ACHIEVED AT 280 °C, 90 MIN, AND A B/W RATIO OF 10 %.

THIS STUDY EMPLOYED A HYDROGEN ATMOSPHERE IN AN ANALYTICAL REACTOR TO INVESTIGATE THE THERMOCHEMICAL TRANSFORMATION OF CHILEAN OAK (CHO) AND POLYETHYLENE. THERMOGRAVIMETRIC ASSAYS AND COMPOSITIONAL ANALYSES OF THE EVOLVED GASEOUS CHEMICALS PROVIDED VALUABLE INSIGHTS REGARDING THE SYNERGISTIC EFFECTS DURING THE CO-HYDROPYROLYSIS OF BIOMASS AND PLASTICS. A SYSTEMATIC EXPERIMENTAL DESIGN APPROACH ASSESSED THE CONTRIBUTIONS OF DIFFERENT VARIABLES, REVEALING THE SIGNIFICANT INFLUENCE OF THE BIOMASS/PLASTIC RATIO AND HYDROGEN PRESSURE. ANALYSIS OF THE GAS PHASE COMPOSITION SHOWED THAT CO-HYDROPYROLYSIS WITH LDPE RESULTED IN LOWER LEVELS OF ALCOHOLS, KETONES, PHENOLS, AND OXYGENATED COMPOUNDS. CHO EXHIBITED AN AVERAGE OXYGENATED COMPOUND CONTENT OF 70.13%, WHILE LDPE AND HDPE HAD 5.9% AND 1.4%, RESPECTIVELY. EXPERIMENTAL ASSAYS UNDER SPECIFIC CONDITIONS REDUCED KETONES AND PHENOLS TO 2?3%. INCLUDING A HYDROGEN ATMOSPHERE DURING CO-HYDROPYROLYSIS CONTRIBUTES TO ENHANCED REACTION KINETICS AND REDUCED FORMATION OF OXYGENATED COMPOUNDS, INDICATING ITS BENEFICIAL ROLE IN IMPROVING REACTIONS AND DIMINISHING THE PRODUCTION OF UNDESIRED BY-PRODUCTS. SYNERGISTIC EFFECTS WERE OBSERVED, WITH REDUCTIONS OF UP TO 350% FOR HDPE AND 200% FOR LDPE COMPARED TO THE EXPECTED VALUES, ACHIEVING HIGHER SYNERGISTIC COEFFICIENTS WITH HDPE. THE PROPOSED REACTION MECHANISM PROVIDES A COMPREHENSIVE UNDERSTANDING OF THE SIMULTANEOUS DECOMPOSITION OF BIOMASS AND POLYETHYLENE POLYMER CHAINS, FORMING VALUABLE BIO-OIL PRODUCTS AND DEMONSTRATING THE HOW THE HYDROGEN ATMOSPHERE MODULATES AND INFLUENCES THE REACTION PATHWAYS AND PRODUCT DISTRIBUTION. FOR THIS REASON, THE CO-HYDROPYROLYSIS OF BIOMASS?PLASTIC BLENDS IS A TECHNIQUE WITH GREAT POTENTIAL TO ACHIEVE LOWER LEVELS OF OXYGENATED COMPOUNDS, WHICH SHOULD BE FURTHER EXPLORED IN SUBSEQUENT STUDIES TO ADDRESS SCALABILITY AND EFFICIENCY AT PILOT AND INDUSTRIAL LEVELS.