With an exponentially growing population the need of energy is increasing likewise. Presently most of the energy needs are being fulfilled by non-renewable sources which are declining promptly which is why the think-tanks of the world are looking forward to adapting reliance on renewable energy sources. According to a study 90% of the world’s total population is going to occupy the current developing countries by 2050. Pakistan being one of them needs to reconsider its energy resources as the gas and oil reservoirs currently present in the country that are responsible for electricity generation, are expected to fulfill our energy needs for twenty-one and thirteen years respectively.
While in case of motor fuels we are switching to Compressed Natural Gas (CNG) being ignorant of its depletion and geothermal consequences. Bioenergy is considered a sustainable energy source as the organic matter yielded by complex carbohydrates produces biofuels (solid, liquid, gas) and the energy obtained by these fuels is known as Bioenergy.
First one is the biofuel obtained by oil, sugar and starch present in food crops.
Second generation refers to the fuel obtained by nonfood crops and nonfood portion of the food crops.
Third generation of biofuels is where algae are used to convert cellulosic and lignocellulosic material from the food crops into fuel. It produces multifold times higher fuel by its own weight
Pakistan being an agricultural country has all the advantages to produce biofuel from agricultural solid waste. Also we are the 5th largest sugarcane producer in the world and 9th in sugar.
It is the 2nd largest agro based industry in Pakistan therefore producing 1st generation biofuel would interrupt with value addition of agricultural sector also the 2nd and 3rd generations of biofuel could be produced from byproduct of sugar industry.
Processing 100 tons of sugarcane produces 9-10 tons of sugar while co-products include 30-32 tons of bagasse, 4-4.5tons of molasses. Both molasses and bagasse produce bioethanol but molasses has other uses too (e.g. cattle feed) besides its handy anaerobic conversion to electricity. Cogeneration from by-products of sugar industry is being done already to power that industry and it is very efficient, 3 kg of bagasse is required for generating 1 kWh of electricity through conventional technology but cogeneration through molasses is preferred due to its ease of processing while bagasse is considered for burning or providing steam only.
Co-generation has been successfully in use already but energy needs don’t end there. In the past 15 years there has been a 268% increase in the total number of registered motor vehicles in the country which ultimately hints towards a certain increase in motor fuel demand. The lignocellulosic biomass yields clean burning fuels known as biofuel i.e. with minimum Carbon dioxide emission. Basically the lignocelluloses present in bagasse could be fermented to bioethanol which is a gasoline (petrol) additive. It has been reported that cellulosic ethanol and ethanol produced from other biomass resources have the potential to cut greenhouse gas emissions by 86%. ?
Ethanol is referred to simply as bioethanol, when used as an alternative fuel. Bioethanol is an alcohol produced from organic biomass such as sugarcane bagasse, wheat or maize. Simple ethanol is used as a solvent i.e. resins, pharmaceuticals, industrial solvent, household cleaning products. It is also used as chemical intermediate i.e. petroleum derived chemicals, butadiene production and as a fuel. Ethanol is used as a disinfectant in many medicines and drugs. It is used as a fluid in many alcohol thermometers.
Bioethanol is used in a wide range of industrial applications, in the pharmaceutical sector, the chemical industry and as a fuel. Bioethanol is by far the most commonly used biofuel world-wide. 99.2% bioethanol is used as a biofuel. Primarily biofuels are used to power vehicles, but can also be used to fuel engines or fuel cells for generation of electricity. Bioethanol is used as fuel for power generation by thermal combustion and in cogeneration systems. It is also used as fuel to burn wood in fireplaces because it does not require a chimney due to the fact it does not generate dark smoke and is “flue less”. It is also used as a feedstock in the chemicals industry. Bioethanol can be blended with petroleum to produce a much more efficient fuel. It can be mixed with gasoline to any percentage and is an alternative to gasoline for flexi fuel vehicles. Most existing car engines are presumably able to function using ethanol-petrol blends of up to 15 % bioethanol with petroleum/gasoline. Bioethanol can also be used as the basis for the production of ETBE (ethyl-tertiary-butyl-ether) which is an octane booster and used in many types of petrol. Bioethanol is used as an alternative energy source in top sugarcane-producing countries such as Brazil, China, USA etc.
Agriculture in the 21st century faces two major challenges: meeting the rising food and livestock feed demand from a growing and wealthier world population and helping to meet the rising demand for biofuels and transportation.
The second and “newer” challenge is driven by high oil prices, government policies, and increased societal concerns about the role of fossil fuels in global warming. Until a decade ago, agriculture had met such challenges by increasing the amount of land area under cultivation globally and increasing crop and livestock yields through the development and application of new farming practices and technologies.
We find that private-sector investment in biofuel research was about $1.47 billion worldwide in 2009. In comparison, the major private oil companies in high-income countries and Brazil spent at least $6 billion on R&D on fossil fuels. The biofuel research investment is a relatively small amount compared with the $10.4 billion spent by the private sector on agricultural input research in 2009 and $11.5 billion spent on food industry research in 2007.
Among all countries, the United States and Brazil have dominated ethanol production, and Germany and the United States have led in biodiesel production (table 1). These countries which have the largest domestic market demand, have been in the forefront of biofuel production.
Countries that produced the most biofuel in 2008:
Country Share of global biofuel production Main feedstock
The government of Pakistan (GOP) is also looking at ways to contain rising costs of oil imports by promoting the use of biofuels. Some policies have been proposed to incentivize the growth of biofuels use and production in the country.
While the government has put more emphasis on policies focused on promoting biodiesel production, yet bioethanol has shown more promises as cheap and viable alternative fuel in the country. Pakistan is one of a few countries that can produced bioethanol without subsidy, it is economic viable, and the nation should support bioethanol development at the level that domestic feedstock (sugarcane) can support.
Pakistan is the world’s seventh largest producer of sugarcane. The sugar industry is Pakistan’s second largest industry after textiles, contributing 2 percent to GDP and 13 percent to the manufacturing sector. There are 84 sugar mills in the country, with a crushing capacity of 465,000 tons of cane per day. Cane molasses is one of the main by-products; its quantity varies depending upon the size of sugarcane crop. It has been estimated that around 80 percent of the world’s molasses is used for alcohol production. Molasses is converted into ethanol through biochemical processes based on fermentation.
Lignocellulosic material that is derived from earth or agricultural wastes is known as biomass. It is made of carbohydrate polymers i.e. cellulose and hemicellulose and an aromatic polymer i.e. lignin. This biomass is used to produce biofuel by fermentation process. Before fermentation we first hydrolyze the biomass to produce sugar and this sugar is then converted into ethanol through fermentation process.?
There are various routes of synthesizing ethanol from biomass. The main steps involve in the production process are:
Many physicochemical structural and compositional factors hinder the hydrolysis of cellulose present in biomass so it is pretreated. The purpose of pretreatment is to make the cellulose accessible to hydrolysis so that we can convert it into fuels. There are various pretreatment techniques, these are:
To reduce the cellulose crystallinity of biomass we first do comminution process in which biomass is first pass through chipping to reduce its size to 10-30mm and then grinding and/or milling that reduce it to 0.2-2mm. For this we can use different types of ball mills, Vibratory ball mill is more effective. From final particle size and biomass characteristics we can estimate the power required for mechanical comminution.
This technique is also use to reduce the crystallinity of biomass cellulose, but it is very expensive.
Lignocellulosic material can also be pretreated by pyrolysis. In this technique in the presence of oxygen and at high temperature (at 300°C) cellulose rapidly decomposes to gaseous products and residual char.
At 97°C the mild acid hydrolysis by 1 N sulphuric acid for 2.5 hr of the products that came from pyrolysis pretreatment resulted in 80-85% conversion of cellulose to reducing sugars with more than 50% glucose.
Biomass is heated at 200 to 400 °C in the absence of oxygen under atmospheric pressure as a result hemicellulose and lignin are partly decompose and water and volatile compounds are released. Main product is the solid, torrefied biomass. Combustible gas is released during the process is utilized to give process heat. Hence,it is an auto thermal process and better than pyrolysis. (Biomass technology group company).?
Lignocellulosic materials is treated with high-pressure saturated steam at 160-260 °C and pressure 0.69-4.83 MPa, initially. It is hydrolyzed with acetic acid or other acid for few minutes during steam explosion-pretreatment and then the pressure is suddenly reduced, which makes the materials undergo an explosive decompression. During process hemicellulose degrade and lignin transformed due to high temperature and increases the potential of cellulose hydrolysis.
90% efficiency of enzymatic hydrolysis was achieved in 24 h for poplar chips pretreated by steam explosion, compared to only 15% hydrolysis of untreated chips.
This process requires considerable expensive thermal energy in the form of steam. By high temperature sugar will decompose and thus reduce the available carbon source for fermentation.
This is similar to steam explosion process. In this process typically biomass is exposed to liquid ammonia (1-2 kg of ammonia/kg of dry biomass) at 90 °C) and high pressure for 30 minutes and then pressure is suddenly reduced as a result structure of material is changed by degrading hemicellulose to oligomeric sugars and deacetylate, simultaneously reduces lignin content while decrystallizing cellulose. Only small amount of material is solubilized.
By this process water holding capacity increases and higher digestibility of biomass. AFEX process was not very effective for biomass with higher lignin content.
As compare to steam explosion this process utilized low temperature to avoid sugar decomposition. In addition, ammonia is corrosive and toxic so it can damage the process equipments and it is also expensive. It is difficult to recycle all the feed in this process.
In ARP, aqueous ammonia (10-15 wt %) passes through biomass at high temperature (150-170 °C) with a fluid velocity of 1 cm/min and for 14 minutes as a result lignin is depolymerized, after which ammonia is separated, recovered and recycled.
Also known as supercritical carbon dioxide explosion process. In this process a supercritical fluid is utilized (a gaseous fluid which is compressed at temperature above its critical point to convert it into liquid form). In a reactor a supercritical or high pressure carbon dioxide is exposed to lignocellulosic material for certain time period and at 35 °C temperature to enhance the reactivity of its cellulose by explosive release of carbon dioxide pressure that degrades the cellulosic structure.
To avoid sugar decomposition by utilizing low temperature (as compared to steam explosion process) and to reduce the expenses of process (as compared to ammonia explosion process) this technique is developed.?
In this process biomass is treated with ozone at normal pressure and at room temperature, as a result lignin content of lignocellulosic material reduced and hemicellulose is slightly affected and cellulose is not affected. In vitro digestibility of treated material increases by this process.
For this process no temperature and pressure is required and ozone can be easily decomposed by using a catalytic bed or increasing the temperature means that processes can be designed to minimize environmental pollution. Disadvantage of this process is that excess quantity of ozone is required.
Acids are powerful agent for cellulose hydrolysis so they are used to hydrolyze lignocellulosic material. Usually, hydrochloric acid and sulphuric acids are used. This technique will give improved result of enzymatic hydrolysis of lignocellulosic biomass to release fermentable sugars.
Concentrated acids are toxic, corrosive and hazardous in nature so we require corrosion resistant reactor for this process this will increased cost of process. We can recover the acid to reduce cost.
For economically feasible process we used dilute hydrolysis.
In this process some bases are used for the pretreatment of lignocellulosic biomass at ambient conditions. Sodium, potassium, calcium, and ammonium hydroxides are suitable alkaline pretreatment agents. Sodium hydroxide is mostly used. This pretreatment depends on the lignin content of biomass.
In this process lignin is biodegraded by using peroxidase enzyme in the presence of hydrogen peroxide.
Organosolv process involves simultaneous pre-hydrolysis and delignification of lignocellulosic biomass supported by organic solvents and, usually, dilute aqueous acid solutions. In this process organic or aqueous organic solvent mixture with inorganic acid catalysts (HCl or H2SO4) is used to break the internal lignin and hemicellulose bonds. The solvents commonly used in the process are methanol, ethanol, acetone, ethylene glycol, tri-ethylene glycol, and tetrahydrofurfuryl alcohol. Organic acids such as oxalic, acetylsalicylic, and salicylic acids can also be used as catalysts in the organosolvation process.
In this pretreatment process we do not require high energy for the removal of lignin and degradation of hemicellulose. It is an eco-friendly process. In this process we use various types of microorganisms such as brown-, white-, and soft-rot fungi for the degradation of lignin and hemicellulose in biomass.?
In this pretreatment electric pulses are given to biomass.
In order to break down cellulose structure i.e. the long chain of glucose molecules we do hydrolysis after pretreatment process. There are two types of hydrolysis that are used for biomass, these are:
· Acid hydrolysis (involve chemical reaction)
· Enzymatic hydrolysis (involve enzymatic reaction)
In acid hydrolysis dilute acid or mineral acids are used to produce mixture of sugar and xylose as a major component and other by-products will also form that are acetic acid, furfural, phenolic compounds, or lignin degradation products. These are potential inhibitors of a microbiological utilization of this hydrolysate. Process occur in two stages. In first stage at moderate temperature xylose from hemicellulose and ate second stage at more extreme conditions cellulose is converted into glucose.
Enzymatic hydrolysis is more efficient because it utilizes cellulase enzymes, reaction is carried out at mild conditions and it do not have corrosion problem in equipment. Enzymes that are used for the hydrolysis of lignocellulosic material are produce from bacteria and fungi. These microorganisms can be aerobic or anaerobic, mesophilic or thermophilic. Cellulases are usually a mixture of several enzymes that is use to degrade cellulose into sugar.
Fermentation is a process in which microorganisms either bacteria, fungi or yeast are used to convert sugar or carbohydrates into alcohol or ethanol in the absence of air or oxygen. There are various methods of fermentation used in industry.
Simultaneous saccharification and fermentation (SSF):
Simultaneous saccharification and fermentation (SSF) is another process for production of ethanol from lignocellulosic biomass. Here, in this process enzymatic hydrolysis is performed together with the fermentation, by this we can reduce investment cost.
For cost effective process and increased rate of hydrolysis and removal of lignin we use chemical pretreatment of bagasse followed by SSF. Yield of sugar and ethanol will be high by this treatment.
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