**2.2 Fourier transform infrared (FTIR) spectroscopy**

The IRTrace-100 FTIR spectrophotometer (Shimadzu, Kyoto, Japan) was used for the FTIR analysis. The extracted celluloses were analyzed to investigate the difference in the functional groups after extraction. The spectral results were recorded within a range of 500–4000 cm<sup>1</sup> wavelength using 4 cm<sup>1</sup> spectral resolution and 34 scans. **Figure 1** shows several major absorption bands and the difference between the samples. DPW sample before isolation showed typical lignocellulose strong band absorption bonds. For instance, the bands at 1037 cm<sup>1</sup>


### **Table 1.**

*Physicochemical analysis of biomass (dried basis).*

MJkg<sup>1</sup> more energy than lithium ion batteries (0.8 MJkg<sup>1</sup>

*Biotechnological Applications of Biomass*

suggested [10, 11].

multiple heating rates [13].

**580**

biomass is considered a potential candidate to sustainable green alternative source of energy and chemicals due to its high energy density, volatile matter content, and global widespread [3]. The release of volatile matter and other contents in biomass has been extensively studied using pyrolysis technology. Pyrolysis involves the conversion of biomass into bio-oil, gases (volatile matter) and biochar, in the absence of oxygen [4, 5]. The technique is robust and essential in providing vital knowledge of kinetics of devolatilization of any biomass prior to further processing via different conversion technologies. In addition, pyrolysis is effective in reducing the bulky biomass into uniform, energy dense, and easily transportable fuel [6]. Despite always being the first stage in most combustion or gasification process, there are no accurate and enough data on the kinetics and reaction mechanisms of different lignocellulosic biomass [7]. This is attributed to the complexity and the varying physico-chemical properties in different lignocellulosic biomass [7]. In addition, there may be many reactions occurring from the extremely complex pyrolysis process of the lignocellulose biomass [8]. Therefore, developing accurate kinetic models to account for all reactions taking place remains a challenge [6]. Isolation of the complex lignocellulosic biomass into individual fractions and characterization of the individual fractions can provide a better understanding of the combustion kinetics and reaction mechanism. Different biomass isolation/extraction techniques such as liquid-liquid, liquid-solid, acid-base, ultrasound, and microwave-assisted extractions, among others, have been reported before [9]. The choice of the method depends on the biomass type and its fraction to be isolated [9]. Hence, each procedure affects the sample's product yields and physical, chemical, kinetic, and thermodynamic properties differently. Despite the studies on the yields and operating parameters such as solvent and time [9], less or no information is available regarding the kinetic and thermodynamic parametric studies for the combustion of the isolated lignocellulose fractions to assess the difference in the extraction processes. Different general kinetic models on lignocellulose biomass have been

Date palm waste constitutes about 500,000 metric tons per year from ca. 44 million date palm trees found in the United Arab Emirates where this research was conducted. The aims of this research are to isolate cellulose from date palm lignocellulose complex using low concentration acid-base solutions and Organosolv techniques and to model nonisothermal combustion kinetics using model-free methods and finally to predict the most probable mechanistic reaction mechanism of the isolated celluloses. Using thermal-gravimetric technique at different heating rates, kinetic and thermodynamic parameters were calculated using model-free methods, namely Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (FWO), and Starink models. The FWO model-free method compensates the experimental measurement errors. However, the KAS and Starink methods depend on the choice of good constant degree of conversion from the derivative mass loss function to provide precision of the kinetic data [12]. In addition, application of different model-free methods involves wide conversion range that allows for study of change in mechanism during a reaction and reduces mass transfer limitations by using

**2. Isolation techniques and nonisothermal kinetic studies**

The rachis part of adult date palm waste (DPW) (10–15 years old) was supplied by the UAE University farm, Al foah, Al Ain. The samples were ground to 180 micron particle size to reduce the effects of heat and mass transfer limitations. All

) [3]. Lignocellulose

**Figure 1.** *FTIR spectrum of (a) lignocellulose DPW, (b) Organosolv cellulose and (c) acid-base cellulose.*

indicating CdO, C]C and CdC bond stretching, between 2840 and 2926 cm<sup>1</sup> indicating CdH stretching and 3200–3474 cm<sup>1</sup> for OdH stretching, were assigned to cellulose, hemicellulose and lignin, respectively. Similar results were reported for other biomass in the literature [15]. However, there were noticeable changes in the functional groups of celluloses from the same biomass with reduction in the peak intensity, an indication of component(s) removal (plausibly lignin and hemicellulose). For instance, the would-be lignin and hemicellulose band intensity at 1037 cm<sup>1</sup> greatly reduced an indication of component(s) removal. The CdH bond stretching in the region of 2840 assigned to lignin in DPW was absent in isolated cellulose samples. In addition, the reduced peak intensity between 845 and 1156 cm<sup>1</sup> associated with the CdOdC asymmetrical stretching and glycosidic bond, a characteristic of cellulose, was observed. Furthermore, the decrease in OH vibration strength around 3200–3474 cm<sup>1</sup> indicates a reduction in some of the OHcontaining compounds which are phenolics from lignin. It is worth to note that both extraction methods showed similar functional groups except that the Organosolv cellulose had CdH bond assigned to lignin in the region around 2326 and 2363 cm<sup>1</sup> which was absent for the acid-base cellulose samples. The FTIR results showed the effectiveness of the cellulose isolation methods from DPW biomass complex. The samples were further characterized for their morphological differences using SEM imaging technique.

and hemicellulose. Acid-base cellulose in **Figure 2(b)** showed porous surface similar to those reported for cellulose from the teak wood [16]. However,

*SEM images of the (a) original rachis, (b) acid-base cellulose and (c). Organosolv cellulose captured at*

*Investigation of Nonisothermal Combustion Kinetics of Isolated Lignocellulosic Biomass…*

*DOI: http://dx.doi.org/10.5772/intechopen.93549*

The combustion characteristics of isolated celluloses were studied using thermogravimetric analysis (TGA). The analysis was done on a TGA (Q500, TA instrument). Samples of 6 mg (1.0) were first equilibrated at 25°C for 5 min and then heated at specific heating rates of 10, 15, 20, and 25°C/min to 900°C. The process was performed under constant nitrogen environment flowing at 20 mL/min. As the thermal decomposition progressed, the change in weight was recorded continuously as a function of temperature and time. **Figure 3** shows the isoconversion versus temperature at different heating rates for the isolated celluloses from DPW. The conversion curves for acid-base (colored) and Organosolv (black) methods below 300 and 340°C, respectively, showed similar thermal decomposition patterns at all heating rates. There was a slight shift toward higher temperature side with increasing heating rates, possibly due to the increasing thermal energy in the system [17]. However, at higher temperatures, the conversion pattern changed for both methods, possibly due to the change in the degradation chemistry of components under pyrolysis. It is worth to note that Organosolv cellulose showed better thermal stability than the acid-base cellulose. **Figure 4** shows the differential thermogravimetric (DTG) results against temperature at different heating rates for the DPW and the isolated celluloses. The results showed a typical thermal degradation of lignocellulose biomass. The curves of both samples moved downward as the heating

with uneven polished surface.

**Figure 2.**

**583**

*magnification X1000.*

**2.4 Thermogravimetric analysis (TGA)**

Organosolv cellulose (**Figure 2(c)**) showed an aggregate of cellulose block structure

#### **2.3 Scanning electron microscopy (SEM)**

The structural morphologies of the isolated cellulose were analyzed using the scanning electron microscope (JEOL Neoscope JCM-5000, Tokyo Japan). The samples were Au/C coated using vacuum spatter while clamped on the sample holder. The images were captured on spot size of 40 using 10 kV. The SEM results in **Figure 2** show a difference in the structural morphologies between the cellulose samples from the two methods. **Figure 2(a)** shows the original DPW with ring-like structures (see the arrow point) plausible to be the cellulose chiral nematic ordering, surrounded by irregular shaped structures which could be assumed to be lignin *Investigation of Nonisothermal Combustion Kinetics of Isolated Lignocellulosic Biomass… DOI: http://dx.doi.org/10.5772/intechopen.93549*

**Figure 2.**

indicating CdO, C]C and CdC bond stretching, between 2840 and 2926 cm<sup>1</sup> indicating CdH stretching and 3200–3474 cm<sup>1</sup> for OdH stretching, were assigned to cellulose, hemicellulose and lignin, respectively. Similar results were reported for other biomass in the literature [15]. However, there were noticeable changes in the functional groups of celluloses from the same biomass with reduction in the peak intensity, an indication of component(s) removal (plausibly lignin and hemicellulose). For instance, the would-be lignin and hemicellulose band intensity at 1037 cm<sup>1</sup> greatly reduced an indication of component(s) removal. The CdH bond stretching in the region of 2840 assigned to lignin in DPW was absent in isolated cellulose samples. In addition, the reduced peak intensity between 845 and 1156 cm<sup>1</sup> associated with the CdOdC asymmetrical stretching and glycosidic bond, a characteristic of cellulose, was observed. Furthermore, the decrease in OH vibration strength around 3200–3474 cm<sup>1</sup> indicates a reduction in some of the OHcontaining compounds which are phenolics from lignin. It is worth to note that both extraction methods showed similar functional groups except that the Organosolv cellulose had CdH bond assigned to lignin in the region around 2326 and 2363 cm<sup>1</sup> which was absent for the acid-base cellulose samples. The FTIR results showed the effectiveness of the cellulose isolation methods from DPW biomass complex. The samples were further characterized for their morphological differences using SEM

*FTIR spectrum of (a) lignocellulose DPW, (b) Organosolv cellulose and (c) acid-base cellulose.*

The structural morphologies of the isolated cellulose were analyzed using the scanning electron microscope (JEOL Neoscope JCM-5000, Tokyo Japan). The samples were Au/C coated using vacuum spatter while clamped on the sample holder. The images were captured on spot size of 40 using 10 kV. The SEM results in **Figure 2** show a difference in the structural morphologies between the cellulose samples from the two methods. **Figure 2(a)** shows the original DPW with ring-like structures (see the arrow point) plausible to be the cellulose chiral nematic ordering, surrounded by irregular shaped structures which could be assumed to be lignin

imaging technique.

**582**

**Figure 1.**

*Biotechnological Applications of Biomass*

**2.3 Scanning electron microscopy (SEM)**

*SEM images of the (a) original rachis, (b) acid-base cellulose and (c). Organosolv cellulose captured at magnification X1000.*

and hemicellulose. Acid-base cellulose in **Figure 2(b)** showed porous surface similar to those reported for cellulose from the teak wood [16]. However, Organosolv cellulose (**Figure 2(c)**) showed an aggregate of cellulose block structure with uneven polished surface.
