Materials selection and process

Different agricultural waste feedstocks (AS, BTB, NTB and WnS) were employed in this study. NTB and BTB were purchased from Tandojam Sindh, Jamshoro. NaOH, H₂SO₄, beakers and funnels were found in a scientific supply store near Jamshoro.

Fresh Bm samples were cleaned and baked for 10 days, to reduce their water Ct. Then, the material was cut into various sizes and taken to a grinding machine (universal UMS Dec mill). The auto balance mechanism and the operator handling the grinder ensured tiny particle components were obtained. Several particle sizes were obtained by sieving the samples. The ideal particle size was 250 nm.

Before being employed for experiments, the Bm material was dried in the oven for 24 h, at 70 °C. For the test, distilled water was used. All samples were weighed, filtered with filter paper and stored in bottles until further processing. The designed methodology in Fig. 1 proved effective to extract lignin from Bm.

Figure 1: Research methodology for extraction of lignin from Bm. 

Extraction of lignin for feedstock

In the extraction of lignin from four distinct Bm types, temperature, duration, solid-to-liquid ratio and solvent selection were relevant in ensuring high value and purity. While solid-to-liquid ratio was standardized at 1:15 in all tests, the approach employed a two-weight-percent NaOH solution. Thus, 20g NaOH were combined with 1000 mL distilled water, and oven-dried for 5 h, at 100 °C, with various changes made to the specifications.

The next step was to combine Bm samples from AS, BTB, NTB and WnS with the liquor solution at a 1:20 ratio. It involved using an oven, at 100 °C, to dry 45 g Bm and 1000 mL liquor. Following that, a sample of Bm was added to the beaker, and lignin was removed from the combined liquid with filter paper. Filtration was used to recover the pretreated Bm. All tests were consecutively performed using a hot plate stirrer and H₂SO₄, after the Bm was washed with distilled water, to remove excess alkali. It was then stored in soft bags for further testing. TGA was used to characterize extracted lignin.

Analysis of lignin extraction

In the laboratory, proximate and ultimate analyses were done to examine the feedstock. Tables 1 and 2 depict the results, which show that AS, BTB, NTB and WnS are suitable as sustainable sources for feedstock. Through proximate analysis, it was possible to determine the Ct of material that was transformed into gaseous (VM), solid (FC) and inorganic (AC) waste forms. This was accomplished by the use of standardized techniques that measured AC, FC, MC and VM. The successful implementation of Bm in energy applications requires this thorough understanding. The laboratory setting emphasizes why AS, BTB, NTB and WnS are suitable for use as Bm, given their advantageous properties (Table 1).

Table 1: Proximate analysis of the samples. 

The last evaluation comprised determining Ct from C, H, N, O and S using a specific procedure. Notably, it was discovered that NTB and BTB had higher Ct from C than WNS and AS, which produced higher heating value. S was carefully handled, since it releases SOx into the environment. Also, N can result in higher quantities of NOx. Laboratory tests were performed on AS, BTB, NTB and WnS samples, to obtain Bm, which was treated with alkali. AC, FC, MC and VM of those Bm were investigated (Table 2). These analyses provided important new information on the potential uses of these Bm in different contexts.

Table 2 Last analysis of pre-treated raw Bm materials (presented on a dry basis). 

Spectroscopic characterization of lignin

Catalysis deoxygenation is a biofuel production promotion technology that employs minerals such as Al₂O₃, CeO₂, SiO₂, TiO₂ and ZrO₂. It reduces the Ct of O, which can cause instability and corrosion. Using certain Al₂O₃-TiO₂ metal oxide catalysts is necessary to produce the required Ct of biofuel. To achieve the ideal hemicellulose levels, a two-step pretreatment procedure using alkali and acids was employed. The study’s conclusion delves into the restrictions, obstacles, commercial prospects and potential for developing cost-effective and eco-friendly ways for long-term value use of lignocellulose materials. Hydroxyl groups in phenolic and aliphatic structures cause the wide band between 3410 and 3460 cm^-1 in all lignin’s samples. Table 3 shows that a 4 h period produced 12% BTB, which is a good outcome.

Table 3: Lignin production from BTB and NTB at 100 ºC, for various time intervals. 

In Table 4, an AS yield of 13%, at 130 °C, after 4 h, was also considered a satisfactory result. With higher temperatures, yield increased.

Table 4: Lignin production of AS and WnS at 130 ºC, for various time intervals. 

Based on various Bm-to-liquor ratios, lignin extraction findings, including yields and time, are illustrated in Fig. 2(a) and (b).

Figure 2: Lignin production at (a) 100 and (b) 130 °C. 

Ct from S in lignin was determined by EDX analysis. For lignin from WnS, it was 7.46%, whereas for AS it was 2.82%. Figs. 2(a) and (b) show these changes in Ct from S. A yield analysis was performed for every experimental condition, offering a summary of the attained outcomes.

EDS

Fig. 3 shows EDS of all Bm samples. The bands at 2938 and 2842 cm^-1 were mostly due to CH stretching, which comprises methyl/methylene groups along the side chains, and fragrant methoxyl compounds. Strong bands in this location are notably visible in hemp, which is jute, and wheat lignin, with peaks at 2917 and 2847 cm^-1. These peaks were caused by CH stretching in aromatic methylene groups, which might be derived from fatty acids that are detected in lignin compositions.

Figure 3: EDX analysis for (a) AS, (b) WnS, (c) BTB and (d) NTB. 

TGA

TGA was conducted on Bm isolated from AS, BTB, NTB and WS lignin. Fig. 4 shows that, in a TGA curve plot, when the sample Ct decreased with increasing temperatures, it implied mass loss or breakdown. A negative TGA curve can represent a multitude of environmental conditions.

Figure 4: TGA of lignin Bm. 

SEM

Fig. 5 shows SEM images of lignin in several substrates. SEM uses an electron beam to create a high-resolution picture of the sample surface morphology. For acylating agents, erosion and with the side chain length contributed to the surface layer. The thickness of several components found in AS, BTB, NTB and WNS, such as cell walls, fibers and structures, were herein quantified using SEM.

Figure 5: SEM analysis of lignin from - (a) AS, (b) BTB, (c) NTB and (d) WnS. 

Challenges and perspectives

Lignin is a naturally existing chemical material that may be used to synthesize biofuels. Priorities should be given to tackling the urgent problem of shifting away from fossil fuels, towards more eco-friendly Bm options, given the growing demand for sustainable energy sources. Current renewable energy sources show significant promise for producing biofuels. Thus, it is critical to examine the characteristics of lignin Ct assessment method within the technology development framework.

With that in mind, this study explored various lignin conversion pathways, addressing important problems in the biofuel manufacturing process. Catalytic deoxygenation is a process that produces biofuel by using materials like SiO₂, ZrO₂, CeO₂, TiO₂ and Al₂O₃, and lowers Ct from O, thus minimizing instability and corrosion. Using certain Al₂O₃-TiO₂ metal oxide catalysts is necessary to produce the required Ct of biofuel. To achieve the ideal hemicellulose levels, a two-step pretreatment procedure utilizing alkali and acids was herein used.