Biochemical conversion process of biomass

Biochemical conversion process of biomass

1. BIOCHEMICAL CONVERSION PROCESS OF BIOMASS S K Singh Centre for Energy Studies IIT Delhi

2. INTRODUCTION All plant materials produced through photosynthesis via carbon dioxide fixation is BIOMASS . Major source of biomass is agricultural waste, residues, fuel woods and industrial wastes. Biomass is organic matter produced plants including terrestrial plants (ones which are grown on land) and aquatic plants (ones which are grown under water). Biomass is renewable source of energy because its supplies are unlimited. We can always grow trees and crops, and waste will always exist. Biomass gets its energy from the sun. During a process called photosynthesis, sunlight gives plants the energy they need to convert water and carbon dioxide into oxygen and glucose.

3. BIOFUEL Biofuels are the fuel which are produced from biomass. Biofuels can be solid, liquid or gas fuel derived from recently dead biological materials. Some common types of biofuels are: Bioethanol, Biomethanol, Biodiesel and Biogas. Biofuels are commonly used in transportation, energy generation, cooking etc. Source: Royal Society of Chemistry

4. WHY BIOFUEL? BIOFUEL FOSSIL FUEL Biofuel is produced from present day biomass Fossil fuel is product of biomass present millions of years ago Obtained from renewable sources Obtained mainly from non-renewable sources Provides a low amount of energy per unit mass Provides a high amount of energy per unit mass Causes less pollution than fossil fuels Plays a lead role in environment pollution Emits a low amount of unfavourable gases when burnt Emits a high amount of unfavourable gases when burnt Requires more investment for their production and are costly Comparatively less investment and less cost to biofuel

5. Diagrams & Charts: Source: BioEnergy Consult Biomass Feedstock Biochemical conversion Direct combustion Thermochemical conversion Biofuels Chemical conversion

6. CONVERSION TECHNOLOGIES Direct combustion: Direct combustion of biomass in presence of oxygen/air to produce heat and by products. Some process involving are cleaning, chopping, etc. Thermochemical conversion: Thermochemical reaction can convert biomass into more valuable and convenient form of products as gaseous and liquids fuels, residue and by-products etc. Process involving are combustion, gasification, pyrolysis and liquefaction. Biochemical conversion: In biochemical processes, the bacteria and micro-organisms are used to transform the raw biomass into useful energy like methane and ethane gas. Treatments involving are pre-treatment, detoxification, hydrolysis and fermentation. Chemical conversion: In chemical processes, the chemicals are used to transform the raw biomass into useful energy like methane and ethane gas. Treatments involving are pre-treatment, detoxification, transesterification etc.

7. BIOCHEMICAL CONVERSION PROCESS Biochemical conversion is a major and an efficient pathway which involves breaking down biomass to make the carbohydrates available for processing into sugars, which can then be converted into biofuels and bioproducts through various processes. Biochemical conversion uses biocatalysts, such as enzymes, in addition to heat and other chemicals, to convert the carbohydrate portion of the biomass (hemicellulose and cellulose) into an intermediate sugar stream. These sugars are intermediate building blocks that can then be fermented or chemically catalyzed into a range of advanced biofuels and value-added chemicals. It involves treatment like pre-treatment, detoxification, hydrolysis and fermentation. It mainly involves hydrolysis of lignocellulose polysaccharides (i.e. cellulose and hemicellulose) into simple sugars and their further conversion into fuel example ethanol by fermentation organisms

8. PROCESS INVOLVED

9. FEEDSTOCK First generation feedstock: Biofuels like biodiesel and bioethanol generated are directly linked to the biomass comprising of edible stuffs like sugarcane, corn etc. However, they may come with certain restrictions such as energy consumption and utilization of arable lands, as well as the fuel versus food debate. Second generation feedstock: Biofuels formed are defined as fuels produced from a wide array of different feedstocks, especially but not limited to non-edible lignocellulosic biomass. The price for this biomass is significantly less than the price for vegetable oil, corn, and sugarcane, which is an incentive. Third generation feedstock: The most accepted definition for third-generation biofuels is fuels that would be produced from algal biomass, which has a very distinctive growth yield as compared with classical lignocellulosic biomass. Algae are known to produce biomass faster and on reduced land surface as compared with lignocellulosic biomass.

10. PRETREATMENT Due to structural characteristics of biomass, pretreatment is essential for enzyme catalyzed cellulose conversion. Without a pretreatment, enzymatic hydrolysis of cellulose is ineffective as native cellulose is well protected by hemicellulose and lignin. A pretreatment process is used to disrupt the physical and chemical barriers of lignocellulose and make the cellulose polymers more accessible for the enzymatic degradation. The factors affecting the accessibility of biomass cellulose can be divided into direct and indirect factors. Direct factors: This factor is related to accessibility to surface area. Indirect factors: This factor is related to biomass structure-relevant characteristic (pore size and volume, particle size, and specific surface area), chemical compositions (lignin, hemicelluloses, and other), and cellulose structure-relevant factors (cellulose crystallinity and degree of polymerization)

11. PRETREATMENT Pretreatment is actually the process, with an objective of removing the unwanted barriers of biomass by altering its indirect factors and improving direct factors thus enhancing the cellulose accessibility to enzymes that would degrade carbohydrate polymers into simple sugars. Feedstock pretreatment technologies are majorly classified into 4 categories: Physical & Mechanical: Treatments like chipping, milling, grinding, extrusion etc. are performed. The aim of these treatments include increasing the accessible surface area and pores size, decreasing cellulose crystallinity and densification of feedstock. Chemical and Physico-chemical: A variety of pretreatments are being developed using chemical reactions to disrupt the crystalline structure of lignocellulose and to partially or completely hydrolyze lignin and/or (hemi) celluloses. Hemicelluloses can be readily hydrolyzed e.g. under mild acidic or alkaline conditions, but cellulose is more resistant and requires a rigorous treatment. Biological: Biological pretreatment involves the use of lignocellulose degrading microorganisms, mainly white, brown and soft rot-fungi, to alter the material. These bio-catalysts are capable of degrading hemicellulose and lignin.

12. DETOXIFICATION Use of pretreatment technique that do not result in formation of by-products or use of less sever pretreatment to minimize the by-product formation is one way to avoid the inhibitory problems of lignocellulose compounds. Hence, removal of inhibitory compounds present in lignocellulose compound is an important area of research. Different techniques categorized mainly as physical, chemical, biological and in their combination were developed to lighten the toxic effect of lignocellulose compounds. Some of these includes the use of chemical additives, microbial treatments, enzymatic treatments, heating and vaporization, liquid-solid extraction. Physical detoxification: Evaporation, heating and absorptive processes are used to detoxify the compounds. However, the drawback is that this method is energy intensive and the non-volatile inhibitory compounds are unaffected – they remain in the compounds. Chemical detoxification: Chemical detoxifications have been the most popular approaches to either remove or alter the structure of lignocellulose inhibitors. Some of the popular approaches are listed:

13. DETOXIFICATION Treatment with hydrogen peroxide (H2O2) and ferrous sulphate (FeSO4) Alkaline treatments with NH 4 (OH), Ca(OH) 2 and NaOH. Treatment with reducing agents such as sodium sulphite, sodium dithionite, and sodium borohydride. Liquid-solid extraction using activated charcoal. Biological detoxification: Several biological methods including treatment with enzymes such as laccases or use of the natural or targeted genetic engineered micro-organism are proposed to overcome the inhibitory effects of pre-treated lignocellulose materials. Some methods involving biological detoxification are: Micro-organisms, such as some species of yeasts, fungi and bacteria can naturally detoxify inhibitory compounds, specifically furanaldehydes, aliphatic acids, and aromatic compounds. Enzymatic, laccases and peroxidases - particularly produced from white-rot fungi treatment is another approach to detoxify lignocellulose hydrolysates. Advantages of using these enzymes is that the detoxification can be achieved faster than what possible by microbial cultures.

14. HYDROLYSIS Hydrolysis is any chemical reaction in which a molecule of water ruptures one or more chemical bonds. Hydrolysis of lignocellulose compounds can comply with either a concentrated acid or enzyme catalysts. Hydrolysis in biochemical conversion is a process of breaking down of lignocellulose polysaccharides (i.e. cellulose and hemicellulose) into simple sugars and their further conversion into e.g. fuel ethanol by fermentation organisms. Concentrated acid: Biomass is treated with mineral acids (e.g. H2SO4, HCl) at relatively low temperatures (T<50◦C) and a high acid concentration 30–70 wt.% . Hydrolysis of (hemi) cellulose then occur, releasing the sugars into hydrolysate and leaving mostly lignin in the solid phase. Sugar yield from concentrated acid hydrolysis is usually significantly higher compare to dilute acid hydrolysis. In addition, concentrated acid hydrolysis is flexible in terms of feedstock choice which means that it can be principally applied to any kind of biomass.

15. HYDROLYSIS Some setbacks of using concentrated acid are: The released sugars would further degrade into by-products (furanaldehydes, organic acids) and lignin degradation products would also form. Concentrated acids are highly corrosive, toxic and hazardous, and require corrosion resistant equipment. Also the spent acid must be recovered in order to make the process economically viable and the hydrolysate pH neutralization requires a high amount of alkali which would results in formation of solid waste. Hence, considering environmental impacts, high investment and maintenance costs have greatly limited the commercial interests of concentrated acid hydrolysis process. Enzymatic process: Enzymatic hydrolysis is regarded as the most attractive way over concentrated acid hydrolysis. Due to the complex chemical structure of lignocellulose, multiple enzymes are often needed for the degradation of its carbohydrate polymers. For example, cellulose is hydrolyzed by a mixture of cellulase enzymes and hemicellulose is hydrolyzed by the action of different hemicellulases e.g. xylanases, mannanases , etc.

16. HYDROLYSIS Some advantages of enzymatic hydrolysis are: High sugar yield. Moderate temperatures are required for the reactions. Does not create problems related to the equipment corrosion. The formation of by-products is very low. Source: PNAS

17. FERMENTATION Fermentation is a metabolic process in which an organism converts a carbohydrate, such as starch or a sugar, into an alcohol or an acid. The sugar rich lignocellulose hydrolysates, obtained from pretreatment and enzymatic hydrolysis can be fermented to ethanol using different types of microorganisms. The yeast ( Saccharomyces cerevisiae ) is the most frequently used and commercially dominant organism employed for this purpose. The advantages of S. cerevisiae are that give high ethanol yields, exhibit relatively high ethanol and general inhibitors tolerance. Source: Bioenergy research group

18. FERMENTATION Modes of fermentation: Fermentation can be performed in three different modes namely, Batch, Fed-batch and Continuous. Batch Mode: A microorganism is inoculated to a specific volume and the fermentation is performed until the sugars are depleted. Advantages: This mode is simple, inexpensive, contain low risk of contamination and possibility to utilize the sugars efficiently. Disadvantages: However, this process is labor intensive, time consuming (cleaning, sterilization, cell lag phase, cell growth and harvesting for each batch), and the overall productivity is low. Fed-batch mode: Microorganism is continuously added to the fermentation, and substrate concentration can be kept low. Advantage:  It allows to overall achieve higher product quantities overall. Disadvantages: It allows build up of inhibitory agents and toxins. Also, maximum working volume of the fermentation vessel is not utilized all the time.

19. FERMENTATION Continuous Mode: Reactant is constantly added to the fermentation vessel and at the same rate the product (fermentation broth) is removed. Hence, fermentation volume is kept constant. Advantages: This mode allows the maximum productivity and less time for cleaning, sterilization and handling of the vessel. Disadvantages: It is difficult to keep a constant population density over prolonged periods as cells are constantly drained out from the reactor. Source: Research gate

20. CONCLUSION AND FUTURE PERSPECTIVE We have seen that biofuels are made from biomass which directly comes from plant materials making it completely renewable. They are biodegradable and produce less pollution when compared to fossil fuels. However, on the other hand large areas of land are eradicated (deforestation), high level of investment is needed, high amount of water is needed. We have also seen various methods are involved in the conversion of biomass to biofuels especially biochemical conversion methods. With the passage of time bio-based fuels are taking over the market because of their environment friendly nature and inexpensive production. Since biofuels are produced from the plant-derived polysaccharides, CO2 does not increase when biofuels are used (combusted), which refers to the concept of carbon neutrality. Biofuels can be boon for us if proper research is conducted to analyze and identify the issues and concerns related to them; and then decimate those issues. We can’t rely on the fossil fuels as they are going to be depleted eventually, and they pose a serious concern to our environment as well. Eventually we would need renewable energy sources like biofuels.

21. REFRENCES Biochemical conversion of biomass to biofuels ( VENKATA PRABHAKAR SOUDHAM) https://www.slideshare.net/GurpreetSingh1377/conversion-of-biomass Characteristics of biomass (AK Jain) Non-conventional renewable resources (GD Rai) Production of Bioethanol from Agro-industrial Residues as Feedstocks( Julián A.Quintero , Luis E.Rincón , Carlos A.Cardona ) https://www.infors-ht.com/en/blog/the-difference-between-batch-fed-batch-and-continuous-processes/