Effect of alkali addition is shown in Fig. 4.5. At 350°C (20 min after reaction starts), the decomposition process was detected for all sulfur compounds.

It is suggested that at this higher temperature the sulfur compounds of higher mass would be decomposed into simple sulfur compounds such as H2S, SO, or SO2. The alkaline reagent neutralizes these acidic compounds to suppress the emission to the gas phase by trapping them in the liquid and solid phases as mentioned above. This phenomenon of alkali addition at various temperatures was directly observed for the first time by online system measurement.

4.4 Conclusion

The sulfur species produced in the gas phase from the hydrothermal reaction of biomass sample were directly detected with high sensitivity by an online analysis with a reaction cell directly coupled with ion-attachment mass spectrometer. The sulfur species were found in gas phase. L-cysteine during hydrothermal reaction produces H2S as well as CO and CO2 gases. Hydrothermal reactions promote the extraction mechanism of sulfur compounds from the durian fruit at certain times: 15 min at 250 and 10 min at 300 and 350°C. Adding Ca(OH)2 to the reaction system of L-cysteine, H2S, CO, and CO2 gases were decreased. For durian, alkali addition at first gave a promoting effect to the sulfur release but later promoted the decom­position of these compounds.