The nine collected biomasses were dehydrated. After the collection of the raw materials, a sorting was performed. Those with a size ranging from 10 cm to 15 cm were selected. They were then dried in an oven at 105˚C for 16 h or 24 h depending on the nature of the biomass. Once the drying is completed, a part is crushed for physico-chemical characterization. The rest is carbonized directly for the manufacture of ecological coal. This technique allows reducing the humidity contained in the fuel without chemical decomposition of the biomass.

The following physico-chemical characterizations were carried out on the biomasses: acidity: the acidity was measured thanks to the pH-meter Hanna instruments PH 211/RS with the use of the standard AFNOR NF ISO 10-390 according to [5] [6]. Conductivity: It was measured with the conductivity meter model cond 3110 serial number 20,311,469 with a precision of the conductivity measurement 0.5% of the measured value ± 1 digit. Fourier Transform Infrared (FTIR) was performed using Bruker VERTEX 70 spectrometer with an absorption band range between 400 and 4000 cm⁻¹. Thermogravimetric Analysis (TGA) of the samples was performed by a TG 209 F1, ASC-Netzch apparatus in a dry environment with a heating rate of 10˚C/min at room temperature at 1000˚C.

Before the carbonization stage or the actual manufacture of the consolidated material, the dehydration process is essential. The drying of the biomass was carried out in an oven at 105˚C. The mass variation of the biomass is determined and the process is stopped when the mass becomes stable. The loss of water mass in the sample varies from 5% to 25%; % H_bs (10.37, 6.4, 5.6, 7.46, 8.56, 12.49, 20.48, 19.20, 5.6) and % H_bh (9.4, 6, 5.28, 6.94, 7.89, 11.1, 17, 16.11, 5.28) for the biomasses (Table 1).

The performance and quality of the briquettes are determined from physico-chemical parameters such as pH, density, etc. The pH of the uncharred residues is all acidic or close to neutral for some before charring as shown in Table 2. These elements all become basic but the most basic are palm kernel shells, coconut shells and corn stalks which have pH of 10.23, 10.27 and 10.06 respectively, as shown in Table 3. This increase in pH is due to the addition of the binders and the effect of carbonization performed during the briquette design process. Biomass with higher pH values performs better.

%H_bs and %H_bh = percentage in moisture content.

This technique can provide information on the nature, reactivity and arrangement of surface functional groups. Reflectance can be used to determine the chemical bonds of a sample. This method requires very little sample preparation and can be used to analyze both liquids and solids. In this technique, the wave penetrates only a few microns into the sample and it also allows to do surface characterization, as in the case of materials. The advantage of this technique in the preparation of the sample is that it allows analyses on raw samples. The Fourier transform infrared spectra of the studied samples (Figures 1-9) reveal several peaks that can be identified as follows: in all figures appear, in the interval 3327.21 - 3339 cm⁻¹, peaks that correspond to the stretching vibration of the OH and N-H groups [7]. The stretching vibrations of the aliphatic C-H alkyl groups present in the cellulose and hemicellulose of the studied biomaterials, appear in the interval 2822.31 - 2919.37 cm⁻¹. The peaks recorded in the interval 1632.76 - 1732.76 cm⁻¹ correspond to the valence vibrations of the carbonyl group C=O as in carboxylic acids. The bands recorded between 1506.68 cm⁻¹ and 1634.56 cm⁻¹ can be attributed to C-O carboxylic groups (Table 4).

To characterize the thermal behavior of the biomass, a thermal analysis was performed. A mass of 3.7729 mg of sample powder was measured under nitrogen atmosphere with a heating rate of 20˚C/min. The crucible used is made of aluminum oxide (Al₂O₃). Thermogravimetric Analysis (TGA) is a technique that

has been used extensively to study biomass pyrolysis [8] - [15]. Peanut shells, papaya stems and sawdust show two peaks. The first loss of mass which is found between 25˚C to 125˚C, denotes the first peaks corresponding to a loss of 6.49% of the total mass for peanut shells. Between 125˚C - 175˚C a loss of 7.90% is observed for the papaya stems and 7.37% for sawdust. The second loss of mass for these three samples is in the temperature range of 125˚C to 1000˚C with 79.91% for peanut shells, 80.40% for papaya stems and 82.33% for sawdust. These changes are due to a loss of free water contained in the biomass after drying the material. The second loss can be segmented into several steps and between 170˚C to 600˚C,

according to [8] it refers to the volatile organic matter. According to the theory [9] - [21], that the main constituents of the biomass, cellulose, hemicellulose and lignin, decompose thermochemically in the following temperature range: 150˚C - 350˚C, 275˚C - 350˚C, 250˚C - 500˚C, respectively. Still in the second loss, there is a loss of structural water, linked to OH hydroxyl groups, which starts from 500˚C. Palm hulls, coconut shells, corn cobs, corn straws, corn stalks, and cassava stalks show three peaks. Between 25˚C and 150˚C the first losses are respectively 5.12% to 10.47%. These losses correspond to a loss of free water or surface water contained in the biomass. The second mass loss for the biomass having three peaks is 12.82% to 57.09% spread respectively over the temperature interval from 150˚C to 300˚C with a last step which shows a mass loss is 16.09% to 80.24% between 300˚C to 1000˚C (Figures 10-18).