In this work, physical and chemical analyses of 28 sawdust samples (tropical woods, pine woods, and oak woods) derived from the primary process of wood transformation and 4 samples of citrus residues were performed, as an option to make densified biofuels. The study included the determination of initial moisture, particle size distribution, proximate analysis, ultimate analysis, calculation of the calorific value, and ash microanalysis. The initial moisture content of the biomass samples ranged from 6.04 to 75.21%. The biomass granulometry results indicate that the highest proportion corresponds to the 1.0-mm (33.10%) (Fraction retained in mesh 0.5 mm). Other results obtained indicate the following ranges: ash content (0.27 to 6.27%), volatile matter (78.90 to 90.50%), fixed carbon (9.10 to 20.44%), carbon (49.13 to 50.78%), oxygen (42.62 to 44.49%), and hydrogen (5.24 to 6.55%). The calculated calorific value ranged from 17.65 MJ/kg to 20.72 MJ/kg. The chemical elements with the highest concentration in the biomass samples were K and Ca, followed in some cases by Al and P. The biomass with the greatest possibilities for making densified biofuels of better quality is the group of pine woods because they have low mineral content, low nitrogen content, and high calorific value.

This research characterized briquettes made with Pinus spp. sawdust without the use of additives. For this purpose, 19 samples of sawdust from different wood industries located in five states of the Mexican Republic were used. The densification process was carried out in a vertical hydraulic piston laboratory briquette machine. The briquettes were made with 40 g of sawdust, at 50 °C, 20 kPa and pressing for 5 min. The results obtained varied as follows: moisture content (4.1% to 7.2%), density (813.9 to 1,014.4 kg/m3), volumetric expansion (7.4% to 37.3%), compressive strength (4.9 to 40.8 N/mm), impact resistance index (46.7% to 200%), ash (0.1% to 1.1%), volatile matter (82.9% to 90.7%), fixed carbon (8.9% to 16.4%), and calorific value (20.5 to 22.8 MJ/kg). The density of the briquettes was within the “acceptable” classification (800 to 1,200 kg/m3). It was observed that, the higher the density, the lower the volumetric expansion, the higher the compressive strength, and the higher the impact resistance index. According to the ash content, the briquettes could achieve international quality. Due to high volatile matter values, rapid combustion of the briquettes with little generation of toxic smoke would be expected. Fixed carbon and calorific value results were acceptable.

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The basic chemical composition and calorific value of 19 samples of pine sawdust from different forest industries located in five states of the Mexican Republic (Chihuahua, Michoacán, Durango, Oaxaca, and Nuevo León) were determined. The results obtained ranged as follows: total extractives (6.1% to 23.4%), holocellulose (60.1% to 70.4%), lignin (20.5% to 25.8%), ash (0.27% to 0.95%), pH (4.1 to 5.3), and calorific value (20.1 MJ/kg to 21.0 MJ/kg). Except for the ash content, significant statistical differences were found according to the origin of the pine sawdust samples. Based on the results obtained, the sawdust biomass has the potential to obtain densified solid biofuels.

The chemical composition of hardwoods sawdust and citrus residues from four states of the Mexican Republic (Quintana Roo, Durango, Veracruz, and Sonora) were determined. The results ranged as follows: total extractives from 8.2% (Quercus spp.) to 35.0% (lime leaves), holocellulose from 45.4% (lime leaves) to 70.6% (Lysiloma latisiliquum), lignin from 3.9% (lemon peels) at 25.4% (Caesalpinia platyloba), ash from 0.4% (orange branches) to 6.3% (lemon peels), pH from 5.1 (Swartzia cubensis) to 7.3 (orange branches), and calorific value of 19.8 MJ/kg (Lysiloma latisiliquum and Quercus spp.) to 21.7 MJ/kg (Olneya tesota). With the exception of the oak samples, in all the biomass samples the extractives content is relatively high (10.1% for Lysiloma latisiliquum to 35% for Persian lime leaves), and could represent a potential for future study and applications in the field of antioxidants. Due to the chemical properties and calorific value, the biomass samples studied present potential for local use as densified biofuels (pellets or briquettes).