# Steam Explosion-Based Method for the Extraction of Cellulose and Lignin from Rice Straw Waste
## 3 Results and Discussion
### Comparative Analysis  
In the search for an optimised process for the extraction of cellulose from rice straw, a series of experiments were conducted to evaluate the efficacy of various treatment stages, namely alkaline pretreatment, steam explosion, oxidation, and bleaching. The primary aim was to streamline the process by assessing the impact of each stage on the cellulose yield and overall efficiency, as indicated by the thermogravimetric analysis (TGA). The yield of cellulose was calculated based on the mass yield, which involves dividing the weight of the final cellulose product by the weight of the initial raw material used. Thus, this analysis provided insights into the compositions of hemicellulose, cellulose, and lignin, and the yield of each sample [67]. The standard initial process consisted of an alkaline pretreatment followed by a 33 min steam explosion, a 5 h oxidation period, and finally, a bleaching stage [32]. From this baseline, modifications were explored, such as omitting the pretreatment, varying the steam explosion duration (33 min, 1 h, 2 h, and 4 h), implementing or excluding ScCO\({}_{2}\), and adjusting the oxidation times (3, 4, and 5 h). The bleaching stage remained constant throughout the experiments. This experimental work was guided by a thermogravimetric analysis (TGA), which measured the mass loss at varying temperatures, providing a percentage composition of hemicellulose, cellulose and lignin, and the yield, while informing on decisions regarding process adjustments. The initial comparative analysis focused on samples with and without the alkaline pretreatment stage, as shown in Figure 3. The comparison between samples revealed a negligible effect on the cellulose content, which was supported by the ANOVA analysis (\(p\)-value \(>\) 0.05). Therefore, omitting the pretreatment did not adversely affect the cellulose content, suggesting that the process could be streamlined by removing this stage, thus achieving reagent and time savings. Moreover, the yield did not show any notable decrease, indicating that the removal of the pretreatment stage could lead to savings in both reagents and time without compromising the cellulose yield. Therefore, the decision to omit the alkaline pretreatment stage was substantiated by these findings. Subsequent experiments explored the reduction in the oxidation time. Figure 4 shows the comparison between 3, 4, and 5 h oxidation periods, which, supported by the ANOVA analysis (\(p\)-value \(<\) 0.05), revealed a decrease in the cellulose percentage with the reduction of time to 3 h. This slight decrease in the cellulose content is considered acceptable when balanced against the benefits of a reduced operational time and lower costs. Furthermore, the yield remained relatively stable, supporting the decision to reduce the oxidation period to 3 h.  
In the final set of experiments, the steam explosion stage was examined under different reaction times and the presence or absence of ScCO\({}_{2}\). The results shown in Figure 5 suggest that the introduction of ScCO\({}_{2}\) did not significantly enhance the cellulose yield. This was supported by the means of the ANOVA analysis, which were \(p\)-value \(<\)0.05. Additionally, a 33 min steam explosion appeared to be as effective as longer durations, as there were no substantial gains in the cellulose concentration or yield with increased reaction times. Consequently, it was deemed reasonable to proceed without ScCO\({}_{2}\) and limit the steam explosion to 33 min. The avoidance of ScCO\({}_{2}\) not only simplifies the process but also enhances its environmental sustainability by reducing the carbon footprint associated with CO\({}_{2}\) utilisation and handling. Based on the comprehensive analysis of the cellulose percentage and yield, the process optimisations can be justified. The exclusion of the alkaline pretreatment and the reduction of the oxidation stage to 3 h streamlined the process without detriment to the final product.