**3.2 Lignocellulosic biomass**

Lignocellulose is the dry plant raw material that is abundantly available on the planet earth from which biofuels could be produced by processes like enzymatic and acid hydrolysis, pyrolysis, gasification, liquefaction and anaerobic digestion. Lignocellulose is composed of lignin—(C31H34O11)n, cellulose—C6H10O5, and hemicellulose—C5H8O4. Lignin is the second most available natural material in the world after cellulose. It is a complex aromatic polymer which could be processed to produce platform chemicals for biofuel production. Lignin has the highest specific energy content among the three and constitutes up to 15–30% by weight and contains up to 40% by energy in a lignocellulosic biomass feedstock. The cellulose component is much easier to degrade and process to several platform chemicals from which high carbon alcohols like n-pentanol, n-hexanol, cyclohexanol, and n-octanol could be derived. **Figure 3** shows the structure and composition of a typical lignocellulosic biomass feedstock.

### **3.3 Production potential**

The estimated global biomass production is 1.70 × 1011 tons per year. Global commercial lignin extraction is around 63 MMT (million metric tons) per year.

**Figure 3.** *Lignocellulosic biomass—Structure and composition.*

Lignocellulosic biomass is abundant in nature and is available at low cost and could easily form a new class of second generation biofuels. The production of high carbon alcohols using catalytic synthesis could be scaled up with much of the research required in engineering the reactor, process design and economic viability.

#### **3.4 Production pathways**

The present study utilizes biofuels that could be possibly derived from nonfood-based feedstock. Biofuels that could be derived from biomass feedstocks using microbial production include high carbon alcohols, biodiesels, jet fuels, and biogasoline [31]. As of now, mechanical microorganisms (like *Escherichia coli* and *Saccharomyces cerevisiae*) and photosynthetic life forms like cyanobacteria are built to follow up on non-sustenance-based sources and create petroleum like derivatives, called "progressed" or "drop-in" biofuels. The different pathways for the combination of biofuels derived from lignocellulosic biomass feedstock are presented in **Figure 1**. The current study utilized bioalcohols like n-octanol and cyclohexanol that could be derived from lignocellulosic biomass feedstock. n-Octanol is an aliphatic straight chain alcohol that has superior cetane number, calorific value, oxygen content, and solubility with diesel [32]. Cyclohexanol is an aromatic ring chained alcohol. Cyclohexanol has superior oxygen content but slightly lower cetane number and energy density than n-octanol. Both these bioalcohols are excellent biofuels that has huge prospects for synthesis in biorefineries. Cellulose and hemi-cellulose can be subjected to enzymatic or acid hydrolysis to be broken down to sugars. C5-C6 sugars could be dehydrated to platform chemicals like furfurals, levulinic acid. Selective microbial fermentation of C5-C6 sugars can be employed to extract high carbon alcohols using engineering micro-organisms like *E. coli*. During the past 3 years, microbial production of n-octanol has gained the interest of researchers and extended the n-butanol pathway to obtain a yield of 70 mg/L of 1-octanol using the *Clostridium* species. Several pathways were later developed with improved yield of n-octanol. Biosynthetic pathway employing multi-functional catalysts to derive linear C8 products like 1-octanol and di-octyl ether from lignocellulose. A yield of up to 93% of linear C8 alcohol products was achieved using this innovative route. Subramanian et al. proposed 1-octanol as a biofuel with diesel-like properties and engineered a biosynthetic pathway to extract it from *E. coli*. Recently, they developed an energy-efficient catalytic system that could produce a highest yield of 1-octanol (62.7%) from biomass-derived furfuralacetone and synthesized phenolic compounds like cycloalkanes, cyclohexanol and linear alkenes from a pyrolytic lignin-oil fraction using catalytic valorization through hydro-treatment [32]. Cyclohexanol can also be obtained from guaiacol which is one of the most abundant lignin de-polymerization products. They introduced an in situ catalytic hydrogenation system to convert lignin-depolymerized compounds like guaiacol and phenol to cyclohexanol using Raney nickel catalyst and devised another highly efficient hydrothermal conversion of biomass derived cyclohexanone to cyclohexanol with high yield and high selectivity using in situ hydrogenation in the presence of a copper catalyst. It achieved more than 97.74% of guaiacol conversion with 100% cyclohexanol selectivity in the presence of 20% Nickel/Magnesium-oxide catalyst. Recently, they achieved highly efficient hydrogenation of a lignin-derived monophenol (4-ethylphenol) to cyclohexanol over Pd/γ-Al2O3 (Palladium/gamma-Alumina) catalyst with selectivity up to 98.6%. Lignin can also be biodegraded to renewable biofuels using genetically modified microbes. Bacterial lignin degradation activity has been best characterized in actinobacteria. The use of microbes like *Pseudomonas stutzeri* to breakdown lignin to aromatic

monomers has been identified already. The utilization of biocatalysts could address every ones issues for high profitability and high prospects for feasible cyclohexanol process advancement.
