Study of a Biomass Sample by TGA-GC/MS and TGA-Micro GC/MS

Figure 1. TGA analysis of the biomass sample derived from empty fruit branches of palm oil; the TGA curve is colored black, the derivative Thermogravimetric (DTG) curve in red.

Interpretation
Figure 1 shows the TGA mass loss curve in black and the DTG curve in red. The biomass sample exhibits two mass loss steps. In the first step, moisture is released (about 4.3%; Table 1) up to about 200 °C. This is followed by pyrolysis of the organic substances (approximately 67.9%; Table 1).

Evaluation

Table 1. TGA results

The TGA measurement was used to determine the temperatures at which the decomposition gases were to be analyzed in the TGA-IST-GC/MS experiment. The temperatures are shown in Table 2.

Table 2. The TGA temperatures at which gas samples were collected and stored in storage loops of the storage interface.

Figure 2. TIC chromatogram corresponding to a TGA temperature of 420 °C; some of the peaks identified are labeled.

Figure 3. The first 12 minutes of the TIC chromatogram corresponding to a TGA temperature of 420 °C; the main peaks identified peaks are labeled.
Interpretation
Figure 2 shows the TIC chromatogram of the gas sample stored at 420 °C. Each peak in the TIC corresponds to a different compound. For better visualization, the first 12 min of the same TIC are shown on an expanded time scale in Figure 3. Over 50 different compounds were identified (see Table 3), mainly ketones, aldehydes, heterocyclic organic compounds, carboxylic acids, phenol, esters and furan. The most important detected compounds for biofuel production include acetic acid, phenol, acetone, BTEX, and furfural.
Evaluation

Table 3. Main evolved compounds detected by GC/MS in a TGA-GC/MS experiment.

Figure 4. GC/MS analysis of residue (evolved products that condensed in the protective tube).

Interpretation
After the TGA-IST-GC/MS experiment, the condensed products remaining in the protective tube between the TGA and IST were collected (see Section 4.3) and dissolved in isopropanol. A small volume of this solution (1 μL) was then injected manually into the GC using the same method as for the storage loops but with a 50:1 split ratio. Figure 4 shows the evolved compounds detected by GC/MS; these are mainly fatty acids and alkanes with high boiling points.

Figure 5. TCD chromatogram of Module A at about 300 °C.

Figure 6. TIC chromatogram of Module B at about 300 °C.

Figure 7. TIC chromatogram of Module C at about 325 °C.

Interpretation
Two additional TGA-Micro GC/MS experiments were performed. In the first experiment, the MS was connected to Module B and in the second to Module C. Figure 5 displays the chromatogram obtained at about 300 °C using Module A, Figure 6, at 300 °C using Module B, and Figure 7 at 325 °C with Module C. The results confirm that the first decomposition step between 100 and 200 °C corresponds only to the loss of moisture. During the second step, H20, CO, CO2, formaldehyde, acetaldehyde, and chloromethane are detected with Modules A and B. Compounds detected with Module C consisted mainly of light ketones such as acetone, light furans, acetic acid and methyl acetate (Table 4).
Evaluation

Table 4. Main compounds detected during a TGA-Micro GC/MS experiment.

Figure 8. TGA curve and emission profiles of selected evolved compounds.

Interpretation
The Micro GC/MS emission profiles in Figure 8 indicate the release of water during the first and second decomposition steps; most other compounds, excluding BTEX, are evolved in the second step (main peak on the DTG curve). BTEX compounds (benzene, toluene, ethylbenzene and xylenes) show a maximum emission peak at about 500 °C, corresponding to the shoulder in the DTG curve. Here it can also be seen that 2,3-butanedione is released in two stages: first in the second decomposition step (larger peak) and again at 500 °C (smaller peak).