Ethanol From Cell Wall Polysaccharides Biology Essay

With lifting demand for alternate fuels, ethyl alcohol is emerging as a good option for some good grounds more significantly, it can cut down pollution. The major beginning for production of ethyl alcohol is transition of biomass by agitation. Conventionally, ethyl alcohol is made from agitation of Sugarcane or maize. However they are non economical compared with costs of fossil fuels. The recent development is production of ethyl alcohol from cellulose due to copiousness of the later. However, due to legion jobs associated with separation of cellulose, and besides due to high cost involved in hydrolysis, the production is yet to be commercially employed.

The Source stuffs may include wood waste, harvest residues and even some grasses. Ethanol is made from the cell wall constituents like cellulose, hemicelluloses and lignin. Breakdown of sugar from maize is much easier than the dislocation of sugar from cellulose doing the subsequently more complex. Presently the production employes two methods ; Biochemical and Thermochemical

Biochemical involves involves Size decrease of natural stuffs, pretreatment by hydrolysis devising usage of either dilute/ concentrated acid or by doing usage of enzymes for transition of Cellulose to glucose and so agitation of glucose and pentose by barm and/or bacteriums, and so recovery of ethyl alcohol by desiccation.

Thermochemical involves heat and chemicals breakdown cellulose to syngas. The gas obtained can be converted into ethanol thourgh pyrolysis. The advantage of thermochemical procedure is over transition of lignin which makes up one tierce of cellulosic provender stock. The procedure involves drying, transition of provender stock to syngas, transition to liquid by pyrolysis, remotion of contaminations and distillment to take H2O from ethyl alcohol.

Beginnings of Cellulose

Sugar Feedstocks

The major sugar provender stock is sugarcane. The other biomass provender stocks rich in sugar includes sorghum, Beta vulgaris, and fruits. Even though it is inexpensive to do ethyl alcohol from sugar, the beginnings are within the human nutrient concatenation and may adversely impact the concatenation if extended production to come into being.

Starch Feed stocks

Another major beginning for ethyl alcohol is starch feedstock. The long concatenation of glucose molecules in amylum can be easy broken down and the amylum provender stocks includes corn, wheat, murphy and manioc. The Starchy stuffs will be hydrolyzed with H2O and heat for dislocation of amylum into fermentable sugar.

Cellulose feedstocks,

While both the above beginnings are within the human nutrient concatenation therefore going expensive, this alternate provender stock is the most abundant 1. These cellulosic provender stocks comprises of lignin, hemicelluloses, and cellulose. Lignin which provides structural support airss major job in production of ethanol fro cellulose. The lignin encloses both cellulose and hemicelluloses and extended pretreatment procedures were needed to make the cellulose and hemicelluloses. Grasss have least lignin and trees have the highest.

Compared with amylum, the cellulose has long ironss of glucose molecules with a different structural constellation. Hyrolysis is made hard by these different structural constellation along with the encapsulation of lignin.

The other constituent hemicelluloses have same long concatenation of glucose molecules but with an extra constituent pentose.

Lignin job in Ethanol production

The major job with the production of ethyl alcohol is lignin. It is I?-glucosidases that breakdowns the cellulose to saccharify. And lignin are known to suppress I?-glucosidases. Another major job is that lignin encloses the cellulose and hemicelluloses and act as a barrier forestalling the contact between enzyme and cellulose there by suppressing the transition. Enzymes will hold non polar cellulose spheres which involves in hydrolysis of cellulose. In a recent survey, it was found the lignin was able to adhere with those non polar spheres in the enzymes ( 7 ) .

Ethanol production procedure:


Pretreatment is the readying of cellulosic provender stock for hydrolysis. The chief intent of the pretreatment is to interrupt the natural bonding between cellulose, hemi-cellulose & A ; lignin, decrease crystallinity nature & A ; complex construction. In a survey by singh, Delignification procedure increases the output of cut downing sugars. So any anterior procedure done earlier hydrolysis to cut down lignin is considered to be pretreatment.

Pretreatment methods classified on physical, chemical, physicochemical and biological.

Physical pretreatment: Physical interventions include size decrease ( milling, tear uping, mulching ) and pyrolysis.

Milling: One such physical pretreatment procedure is milling i.e. , cut downing atom size. Particle size is one the cardinal factor for the sugar transition ratio. Particle size is indirectly relative to the sugar transition rate. This is due to the fact that, smaller size atoms have higher surface country that in bend helps in higher reaction rate. Singh postulated that atom size to less than 417 micrometers does non better the cellulose transition. A. E. Abasaeed & A ; Y. Y. Lee found from their research that increasing the hardwood cellulose atom size, decreases the glucose outputs and increases the reaction clip at which maximal output occurs, utilizing dilute acerb hydrolysis.

Pyrolysis: At higher temperature, Cellulose dislocations and we get gaseous and char merchandises. Under lower temperature pyrolysis, in presence of mild acid ( 1N H2SO4, 97 grade celcius and 2.5 hours ) , the pretreatment consequences in 80-85 % transition of cellulose to cut downing sugars. This procedure is enhanced in presence of limited O and Zn chloride. ( Yu and Zhang 2003 ) .

Chemical pretreatment: Chemical pretreatment includes add-on of chemicals, which reduces the screening consequence of lignin, cut downing crystallinity and increases the cellulose puffiness. Major categorization includes Ozonolysis, Oxidative delignification, organosolv procedure and there are figure of minor categorization.

Ozonolysis: The chemical compound, ozone is used to degrade lignin and hemicellulose. Degradation of lignin consequences in higher hydrolysis rate. Main advantages of ozonolysis: efficaciously removes lignin, does non necessitate elevated environmental conditions for the procedure to take topographic point and it does non bring forth toxic or repressive stuffs. However, a big measure of ozone is required, which makes the procedure expensive.

Oxidative delignification: Peroxidase enzyme nowadays in the works tissue biodegrades lignin in presence of H202. This pretreatment is found to be working good with sugarcane bagasse. Fifty per centum of lignin is solubilized by 2 % H2O2 at 30 degree Celsius and 8 hour. ( Ye Sun et Al. 2002 )

Organosolv procedure: An organic dissolver mixture with inorganic accelerators ( Hcl & A ; H2SO4 ) is used to breakdown the linkage between lignin and saccharide. Organic dissolver used are methanol, ethanol, propanone, ethene, ethanediol, etc.. At the terminal of the procedure, dissolvers need to be removed to avoid the repressive action on farther procedure.

Physico-chemical pretreatment: These are the new pretreatments found in the last two decennaries. This type uses the combination of both physical parametric quantities and chemical features.

Steam detonation: Biomass is exposed to high-pressure concentrated steam for a certain period and so its force per unit area is fleetly reduced ( 260 grade Celsius at 0.69 Mpa ) . Steam acts on complexness construction of lignocelluloses and causes hemicellulose and lignin transmutation. Surveies shows that lower temperature, long clip procedure is better when compared to the frailty versa. Residence clip, temperature and atom size are impacting factors in the procedure. Addition of H2SO4 improves the hydrolysis rate, decreases repressive merchandises and obtains complete remotion of hemicellulose.

Advantages of steam detonation: Low energy demand, no recycling and effectual on agricultural residues. The restrictions of this pretreatment are that certain repressive compounds will be produced by uncomplete lignin break. Besides big measure of H2O is needed to take repressive compounds.

Ammonia fibre detonation ( AFEX ) : Similar to steam detonation. Lignocelluloses is subjected to liquid ammonium hydroxide at decreased temperature ( 90 degree Celsius ) and force per unit area for a period of clip ( 30mins ) and so the force per unit area is fleetly reduced. Dose of liquid ammonium hydroxide is 1-2 kg ammonia/kg dry biomass. AFEX works better with low lignin content and smaller atom size biomass. The disadvantage is that Ammonia has to be recovered for economic issues

Carbondioxide detonation: The detonation of CO2 would organize carbonaceous acid and increase the hydrolysis rate. This procedure obtains 75 % of theoretical glucose, which is comparatively low when compared with other two methods.

Irradiation: . Irradiation like negatron beam, microwave, gamma irradiation, ultraviolet irradiations is used as the beginning of irradiation. Acid or Alkali, in little measures ( 1-5 % ) , is added to the substrate and so exposed to irradiation. Azyma found that irradiations help in disintegrating the complex construction of Lignocelluloses ( Azuma et al. , 1984 ) .

Biological pretreatment: Microorganisms such as Brown-rot, whit-rot and soft putrefaction Fungis are used to degrade lignin and hemicellulose. Brown-rot can degrade cellulose, where as white and red-rot degrades cellulose and lignin. Biggest advantages of this biological intervention are that it is environmental friendly and requires really less energy input. However, the rate of hydrolysis in most biological procedure is really low. ( A.I. Hatakka. 1984 )


One of the major restrictions of biomass transit is its low denseness. The denseness ranges from 60-80 kg/m3 for agricultural straws. Due to this, it occupies high volume doing the biomass hard for storage, transit, use and handling. Density increases over 10 times after compaction. Baling, pelletization, bulge and briquetting are the four chief types of compaction procedure done on agricultural straw. Baling is a field type compaction procedure, where all other compaction procedures are industrial type. Pelletizing and briquetting are normally found in biomass solid fuel industries, frequently called as ‘binderless engineerings ‘ , which uses either piston imperativeness or a screw imperativeness.


Hydrolysis is frequently defined as the chemical reaction type in which polymers of holocelluloses breakdown into monomers. Hydrolysis produces cut downing sugars from helocelluloses, which is comprised of cellulose and hemicellulose. Hydrolysis involves exposure of chemicals, enzymes for a period of clip at a specific temperature.

Hydrolysis is the chemical reaction which involves transition of complex cell wall polyoses in the feedstocks into simpler sugar for farther agitation into ethyl alcohol. Acids and enzymes were used in ethanol production to catalyse this production procedure.

Two common types of hydrolysis are Acid hydrolysis by either dilute or concentrated acid and Enzyme hydrolysis.

Acerb Hydrolysis: Sulphuric acid and Hydrochloric acid are the powerful agents for Acid Hydrolysis. In-between these two, sulfuric acid is prevailing, as it was found to be better hydrolytic agent than Hcl. ( A.Singh et al. 1984 ) . In general, acerb hydrolysis requires either dilute Acid at higher temperature & A ; force per unit area, or concentrated acid at low temperature. Concentrated acerb hydrolysis output high monomers than dilute acerb hydrolysis. Xylan to xylose transition will be done in dilute acid hydrolysis. After this type of hydrolysis, the feedstock needs to be neutralized.

Enzymatic Hydrolysis: This method of hydrolysis a a late developed method came into being by 1970 ‘s, while the former one is being used since 19th century.

Enzymatic interventions are preferred to the chemical 1s. Cellulase enzyme, synthesized from Fungi, bacteriums and workss, is the cardinal function for the reaction. Besides enzymes are of course obstructing in the palnt proteins. However, pretreatment is ver y much necessity for enzyme hydrolysis to interrupt the crystalline lignin so the enzyme can interact with cellulose and hemicelluloses. Glucose concentration is one of the hydrolysis rate-limiting factors in enzymatic hydrolysis. ( Lynd et al. 2002 ) .


Agitation the dislocation of sugar obtained from hydrolysis procedure into ethyl alcohol by action upon micro-organism.

Types of agitation

Separate hydrolysis & A ; Fermentation

Coincident Saccharification & A ; Fermentation

Direct Microbial Conversion ( Using thermophilic Bacteria )

Seperated Hydrolysis and agitation: Pretreatment and agitation are conducted individually and glucose concentration is one of the chief hurdlings for the procedure.

Coincident sacarification and agitation ( SSF ) : This procedure requires less enzyme burden and the taint is reduced. This method is relatively faster and supply higher output. Gauss et al. , ( 1976 ) says that SSF procedure is already patented and is known as the Gulf SSF procedure.

Direct Microbial transition: It combines all the three chief procedures in lignocelluloses bioconversion ( Cellulase production, cellulose hydrolysis and agitation ) . However, it has less hydrolysis rate than SSF or SHF. The being that has been most investigated for DMC method is C. thermocellum. ( Kiyoharu F. et Al. 1996 )


Removing unwanted compounds and bettering the ethanol per centum in the concluding merchandise is called purification. Distillation procedure is employed for purification. Purification is done in two stairss: Rectification, which achieves 96 % and desiccation that achieves 99.9 % .

Options – Swtich Grass

The job with the current cellulosic ethyl alcohol production is due to lignin. To get the better of the job of lignin, switch grass has been tested over recent old ages due to its low degrees of lignin and high degrees of cellulose. Panicum Virgatum ( Switch grass ) can bring forth more 700 % energy than what it is supplied with. ( 16 ) The perennial works consumes low sum of H2O and it wont compete for nutrient with other harvests. The of import advantage of switch grass is that the 10 % of the genome is dedicated to cell wall and so by familial alteration it is further possible to increase the look of saccharides and finally high ethanol output. ( 18 )


Cell wall polysaccrides forms the most effectual beginning for production ethyl alcohol and Fuel production by this method has large feasibleness due to abundance in Biomass handiness.