Pretreatment Technologies for Efficient Hydrolysis of Lignocellulosic Biomass
The technology of the production of biofuel from lignocellulosic biomass can improve world energy security and decrease its dependency on oil.
It can be obtained from both vegetables and forest resources with the chemical composition as mentioned below:
• Barley straw is with 40-44% cellulose, 28-30% hemicellulose, and 20-22% lignin
• Wood is with 44-50% cellulose, 20-26% hemicellulose, and 17-30% lignin
• Corn Stover is with 36% cellulose, 23% hemicellulose, and 17% lignin
To reduce the risk in the world energy securities, today’s world is directed to use the lignocellulose substrates to produce sustainable and inexpensive renewable biofuel.
Various factors like crystallinity degree of polymerization, particle size, and the accessible surface area of lignocellulose mass may vary during pretreatment of cellulose.
Pretreatment Methods
The main motive is to decrease the crystallinity of cellulose, increase the bio-matter surface area, break the lignin seal, and remove hemicellulose to achieve a high glucose yield. In general, this treatment method is divided into four significant groups, i.e., physical, chemical, physicochemical, and biological.
The main parameters to obtain efficient hydrolysis are cellulose’s crystallinity, surface treatment, and protection by lignin and hemicellulose.
Various effective method technologies have been identified in order to produce useful bioproducts.
One approach could not be the best selection for all types of biomass. So a basic understanding of various ways might aid us in performing good results.
Chemical Method
We can use alkali solutions and reagents like hydroxides of sodium, potassium, calcium, and ammonium in the alkali method, a widely studied chemical method.
This method is based on the susceptibility of the glucosidic bonds between hemicellulose and cellulose to acid. The concentrated acid highly accelerates the sugar conversion rate, but most of the concentrated acids are very toxic and corrosive, requiring a high operational cost.
Iconic liquids as cellulose solvent can be used in this method as most of the Iconic liquids are recoverable and reusable with non-toxicity, non-volatility, and chemical stability.
Physical Method
This is taken as a prerequisite to any other method. The process includes an increase in surface area and a decrease in the degree of polymerization and crystallinity by reducing the particle size.
This is a more eco-friendly process; however, it consumes more energy. The approaches in this method are as follows:
Milling:
We can do millings like hammer mill, disk mill, ball mill, and PFI mill. Similarly, the process like shredding, grinding, and extrusion are also applicable for this process.
Irradiation:
This process includes the application of gamma rays, electron beam, and microwave radiation.
Physicochemical Method
This is generally a combination of both physical and chemical treatment. Steam explosion is the most common and effective method in which high pressure saturated steam at a temperature of 160 – 260o C is applied to lignocellulose.
Its advantages are listed below:
- Low environmental effect
- High energy efficiency
- Limited chemical use
However, it is affected by different factors like steam temperature, residence time, and moisture content.
Biological Method
In this method, we can use bacteria and fungi to degrade hemicellulose and lignin. White-rot and brown-rot fungi are taken as the most effective in this method.
The advantages of this method are as follows:
- Cost-effective
- Yield high sugar recoveries
- No production of toxic chemicals
Summary
Thus, we have a general idea that pretreatment is essential in converting lignocellulose to important bioproducts and biofuels. The surface treatment is done through heat, chemicals, or microorganisms.
Based on each process, requirement, and technology, we can choose an economical, productive, and eco-friendly method.
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