Biobutanol Can Be Produced By Acetone Biology Essay

Biobutanol can be produced by Acetone – Butanol – Ethanol agitation procedure, as shown in Figure 2.1 This procedure has been improved by utilizing assorted strains of the bacteria either Clostridium acetobutylicum or Clostridium Beijerinckii and different substrates such as maize and molasses for many old ages. However, these substrates have high cost ensuing in high monetary value of butyl alcohol. Therefore, to bring forth butyl alcohol by utilizing biomass as a feedstock is another pick to cut down butanol monetary value.

Figure 2.1 ABE agitation procedure ( Cascone, 2008 ) .Butanol is a four C intoxicant. It contains more H and C.

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Butanol has several advantages. For illustration butyl alcohol is easier to intermix with gasolene and other hydrocarbon merchandises and is safer to manage since butyl alcohol, is less volatile and explosive, has high flash point and low vapour force per unit area. It can be shipped and distributed through bing grapevines and make fulling Stationss. An 85 % butanol/gasoline blends can be used in unmodified gasoline engines and it is cleaner firing than ethyl alcohol. ( Nigam and Singh, 2011 ) .

2.2 Lignocellulosic biomass

hypertext transfer protocol: //www. % 20structure.pngFigure 2.2 Representation of lignocellulose construction demoing cellulose, hemicellulose, and lignin fractions ( Mussatto et al.

, 2010 ) .Lignocellulosic biomass such as agricultural waste and harvest residue resources are one of the major renewable resources for fuels and chemicals. Lignocellulosic biomass consist chiefly of cellulose, hemicellulose, and lignin that are closely associated in a complex crystalline construction, as shown in Figure 2.2 These constituents are complex polymers that are closely associated with each other bring forthing the cellular composite of the vegetational biomass.

Basically, cellulose signifiers a skeleton which is surrounded by hemicellulose and lignin. The complex construction consequences in enzymatic hydrolysis handiness limited. Table 2.

1 shows the composing of assorted lignocellulosic biomass.Table 2.1 Composition of representative lignocellulosic feedstocks ( Menon et al. , 2012 )


Carbohydrate composing ( % dry wt )




Bamboo49-5018-2023Banana waste131514Corncob32.3-45.639.86.7-13.

9Corn stover35.1-39.520.

7-24.611.0-19.1Cotton chaff311130Rice straw29.2-34.723-25.917-19Rice chaff28.


315.4-20Wheat straw35-3922-3012-16Grasss25-4025-5010-30Sugarcanebagasse25-4528-3215-25Nut shells25-3022-2830-402.2.1 CelluloseCellulose is the major constituent of works biomass including about 30-60 % of entire feedstock dry affair ( Balat, 2011 ) . Cellulose is a high molecular weight additive homopolymer of repeated units of cellobiose, that is two anhydrous glucose rings joined via a I?-1,4 glycosidic linkage. The long-chain cellulose polymers are linked together by H and new wave der walls bonds, which cause the cellulose to be packed into microfibrils. The microfibrils are covered by hemicelluloses and lignin. The construction of cellulose is shown in Figure 2.

3. By organizing these H bounds, the ironss tend to set up in parallel and organize a crystalline construction. Therefore, cellulose microfibrils have both extremely crystalline parts, that is about 2/3 of the entire cellulose, and less-ordered formless parts. More ordered or crystalline cellulose is less soluble and less degradable ( Taherzadeh and Karimi, 2008 ) . The grade of cellulose crystallinity is a major factor impacting enzymatic hydrolysis of the substrate. It has been reported that a lessening in cellulose crystallinity particularly influences the initial rate of cellulose hydrolysis.

Physical or chemical pretreatment to interrupt the crystalline construction of cellulose is frequently used to advance the hydrolysis of biomass.Figure 2.3 The construction of cellulose ( hypertext transfer protocol: //www.plantoils.

in/portal/ce/blog/ 2008_12_01_archive.html ) .2.2.2 HemicelluloseThe chief characteristic that differentiates hemicellulose from cellulose is that hemicellulose has subdivisions with short sidelong ironss dwelling of different sugars which are easy hydrolyzable polymers. Hemicellulose ( 20-40 % of entire feedstock dry affair ) is a extremely bifurcate polymer of five-carbon ( pentoses ) and six-carbon ( hexoses ) sugars, as shown in Figure 2.4. Particularly, hemicelluloses contains xylose, and arabinose for five-carbon sugars and brain sugar, glucose, and mannose for six-carbon sugars.

Hemicellulose is more readily hydrolyzed compared to cellulose because of its branched, formless nature ( Lee et al. , 2007 ) . The dominant sugars in hemicelluloses are mannose in deals and xylose in hardwoods and agribusiness residues ( Taherzadeh and Karimi, 2008 ) .hypertext transfer protocol: // 2.

4 Monomers of hemicelluloses ( Taherzadeh and Karimi, 2008 ) .2.2.3 LigninLignin ( 15-25 % of entire feedstock dry affair ) is an aromatic polymer.

More specifically, p-coumaryl intoxicant, coniferyl intoxicant and sinapyl intoxicant footing are the 1s most normally encountered, as shown in Figure 2.5 ( Harmsen et al. , 2010 ) .

The basic chemical phenylpropane units of lignin are bonded together by a set of linkages to organize a really complex matrix ( Demirbas, 2008 ) . This matrix comprises a assortment of functional groups, such as hydroxyl, methoxyl and carbonyl. Lignin is one of the drawbacks of utilizing lignocellulosic biomass stuffs in agitation, as it makes lignocellulose immune to chemical and biological debasement ( Taherzadeh and Karimi, 2008 ) .Description: hypertext transfer protocol: // 2.5 Phenyl propane units ( Taherzadeh and Karimi, 2008 ) .

2.3 Pretreatment of Lignocellulosic Biomass

Pretreatment is required to change the construction of lignocellulosic biomass to do cellulose more accessible to the enzymes that convert the saccharide polymers ( cellulose and hemicelluloses ) into fermentable sugars. Pretreatment has great possible for betterment of efficiency and lowering of cost through research and development ( Mosier et al. , 2003a, B ) . The intent of the pretreatment is to take lignin and hemicellulose, cut down cellulose crystallinity, and increase the porousness of the stuffs. Pretreatment must run into the undermentioned demands: ( 1 ) better the formation of sugars or the ability to later organize sugars by enzymatic hydrolysis, ( 2 ) avoid the debasement or loss of saccharide, ( 3 ) avoid the formation of by-products repressive to the subsequent hydrolysis and agitation procedures, and ( 4 ) be cost-efficient ( Kumar et al.

, 2009 ) . In general, pretreatment methods can be classified into three classs, including physical, chemical, and biological pretreatment.Figure 2.

6 Schematic of the function of pretreatment ( Kumar et al. , 2009 ) .2.3.1 Physical PretreatmentLignocellulosic biomass can be comminuted by a combination of splintering, grinding, and milling to cut down cellulose crystallinity. The size of the stuffs is normally 10-30 millimeter after come offing and 0.2-2 millimeter after milling or crunching( Kumar et al. , 2009, Sun and Cheng, 2002, Leustean, 2009 ) .

Power demands of mechanical comminution depend on the concluding atom size and the biomass features. Power demands increase quickly with diminishing atom size. These mechanical pretreatment techniques are time-consuming, energy intensive, or expensive to treat ( Balat, 2011 ) .2.3.

2 Physico-chemical Pretreatment2.3.2.1 Steam Explosion ( Autohydrolysis )In this method, chipped biomass is treated with high-pressure saturated steam and so the force per unit area is fleetly reduced, which makes the stuffs undergo an explosive decomposition. Steam detonation is the most normally used method for the pretreatment of lignocellulosic biomass. Steam detonation increases crystallinity of cellulose by advancing crystallisation of the formless parts. Furthermore, steam detonation hydrolyses hemicelluloses easy. That is grounds that steam detonation promotes delignification ( Jeoh, 1998 ) . Ammonia Fiber ExplosionAmmonia fibre detonation ( AFEX ) is one of the alkalic physico-chemical pretreatment procedures. The stuff is subjected to liquid ammonium hydroxide at high temperature and force per unit area, and a subsequent fast decompression, similar to the steam detonation, which causes a fast saccharification of lignocellulosic biomass ( Abril et al. , 2009 ) . The system does non straight let go of any sugars but allows hemicellulose and cellulose to be attacked enzymatically and reduced to sugars ( Balat, 2011 ) . Liquid Hot-water PretreatmentCooking of lignocellulosic biomass in liquid hot H2O ( LHW ) is one of the hydrothermal pretreatment methods applied for pretreatment of lignocellulosic biomass ( Taherzadeh and Karimi, 2008 ) . LHW topics biomass to hot H2O in liquid province at high force per unit area during a fixed period and it presents elevated recovery rates for pentoses and generates low sum of inhibitors ( Tomas et al.

, 2008 ) . If the pH is maintained between 4 and 7, the debasement of monosaccharide sugars can be minimized ( Hayes, 2009 ) .2.3.3 Chemical PretreatmentChemical pretreatments were originally developed and have been studied to day of the month hold had the primary end of bettering the biodegradability of cellulose by taking lignin and/or hemicellulose, and to a lesser grade diminishing the grade of polymerisation ( DP ) and crystallinity of the cellulose constituent. Chemical pretreatment is the most studied pretreatment technique among pretreatment classs. The assorted normally used chemical pretreatments includes: acid, base, organic acids, pH-controlled liquid hot-water, and ionic liquids.2.

3.3.1 Acid PretreatmentAcid pretreatment usually aim for high outputs of sugar from lignocellulosic biomass due to this method gives high reaction rate and significantly improves cellulose hydrolysis ( Karimi et al. , 2006 ) . Acid pretreatment involves the usage of concentrated and diluted acids to interrupt the stiff construction of the lignocellulosic biomass and take hemicellulose and expose cellulose for enzymatic digestion ( Silverstein et al. , 2008 ) . The most normally used acid is dilute sulfuric acid ( H2SO4 ) , which has been commercially used for a broad assortment of biomass types such as switchgrass, maize stover, spruce ( deal ) , and poplar.

Other acids have besides been studied, such as hydrochloric acid ( HCl ) , phosphorous acid ( H3PO4 ) , and azotic acid ( HNO3 ) . Acid pretreatments have been used as parts of overall procedures in fractionating the constituents of lignocellulosic biomass due to its ability to take hemicelluloses ( Zhang et al. , 2007 ) .

The acerb add-on additions hemicellulose solubilization rate in comparing with the liquid hot H2O or steam detonation methods ; hence, the enzymatic digestibleness of cellulose is enhanced. Acid pretreatment ( remotion of hemicellulose ) followed by alkali pretreatment ( remotion of lignin ) consequences in comparatively pure cellulose ( Menon et al. , 2012 ) .

The potency of dilute acerb pre-hydrolysis as a pretreatment method was studied for sugar cane bagasse, rice hulls, peanut shells, and cassava chaffs ( Martin et al. , 2007 ) . The pre-hydrolysis was performed at 122 i‚°C during 20, 40, or 60 min utilizing 2 % H2SO4 at a solid-to-liquid ratio of 1:10.

Sugar formation increased with increasing reaction clip. Xylose, glucose, arabinose, and galactose were detected in all of the pre-hydrolysates, whereas mannose was found merely in the prehydrolysates of peanut shells and cassava chaffs. The hemicelluloses of bagasse were hydrolyzed to a high-extent giving up concentrations of xylose and arabinose of 19.1 and 2.2 g/l, severally, and a xylan transition of more than 80 % .

High-glucose concentrations ( 26-33.5 g/l ) were found in the prehydrolysates of rice hulls, likely because of hydrolysis of amylum of grain remains in the hulls. Peanut shells and cassava chaffs rendered low sums of sugars on pre-hydrolysis, bespeaking that the conditions were non terrible plenty to hydrolyse the hemicelluloses in these stuffs quantitatively.Cara et al. , ( 2008 ) studied dilute acerb pretreatment of olive tree biomass. Pretreatment was performed at 0.2, 0.6, 1.

0, and 1.4 % ( w/w ) H2SO4 and temperature scope 170-210 i‚°C. It was found that 83 % of hemicellulosic sugars in the natural stuff were recovered in the prehydrolysate obtained at 170 i‚°C, 1 % H2SO4 ; nevertheless, the enzyme handiness of the corresponding pretreated solid was non really high. The maximal enzymatic hydrolysis output ( 76.5 % ) was attained from a pretreated solid at 210 i‚°C, 1.4 % acerb concentration. Furthermore, sugar recovery in the prehydrolysate was the poorest 1 among all the experiments performed. The maximal value ( 36.

3 g sugar/100 g natural stuff ) was obtained when the olive tree biomass at 180 i‚°C and 1 % H2SO4 concentration, stand foring 75 % of all sugars in the natural stuff. Alkaline PretreatmentAlkali pretreatment refers to the application of alkalic solutions to take lignin and assorted uronic acid permutations on hemicellulose that lower the handiness of enzyme to the hemicellulose and cellulose ( Han et al. , 2009 ) These procedures are operated at lower temperatures and force per unit areas compared to other pretreatment engineerings.

Alkali pretreatment may be carried out at ambient conditions, but pretreatment clip is measured in footings of hours or yearss instead than proceedingss or seconds ( Mosier et al. , 2005 ) . Sodium, K, Ca and ammonium hydrated oxide are appropriate chemicals for alkalic pretreatment. Of these four, NaOH has been studied the most ( Kumar et al.

, 2009 ) . Dilute NaOH intervention of lignocellulosic biomass causes swelling, taking to an addition in the internal surface country, a lessening in crystallinity, separation of structural linkages between lignin and saccharides, and break of the lignin construction.Wang ( 2009 ) studied NaOH pretreatment of Coastal Bermuda grass. Coastal Bermuda grass was pretreated with NaOH 0.5 % to 3 % ( w/v ) from 15 to 90 min at 121 i‚°C. Pretreatment clip of 30 min was sufficient to accomplish a important sum of entire lignin remotion every bit long as the NaOH concentration was equal or over 1 % . On the other manus, diminishing Na hydroxide concentration from 1 to 0.5 % significantly reduced entire lignin remotion, but there was no important difference in lignin remotion between 2 and 3 % NaOH.

Up to 86 % lignin remotion was observed. The optimum NaOH pretreatment conditions at 121 i‚°C for entire reduction sugars production every bit good as glucose and xylose outputs were 15 min and 0.75 % NaOH. The entire reduction sugars output was approximately 71 % of the theoretical upper limit, and the overall transition efficiencies for glucan and xylan were 90.

43 % and 65.11 % , severally.Joshua et Al. ( 2012 ) investigated the production of ABE from algae biomass. They found that the pretreatment with acid followed by alkaline produced 8.92 g/l of soluble sugars, whereas non-pretreated algae had merely 0.

73 g/l of soluble sugar. These informations demonstrate the importance of pretreating complex substrates to bring forth fermentable sugars more expeditiously. Additionally, pretreatment increases the surface country, or bio-availability, of the substrate for bacterial enzymes to hydrolyse the biomass more resourcefully ( Kumar et al. , 2009 ) .Ponthein and Cheirsilp ( 2011 ) studied the pretreatment of thenar pressed fibre by hydrothermal, acid and base to take lignin and obtain high cellulose content fibre. The consequence indicated that the pretreatment with NaOH followed by H2SO4 gave highest cellulose content and reduced the sum of hemicellulose and lignin more than pretreatment with sodium hydrated oxide or sulphuric acid entirely.

Furthermore, Zhu et Al. ( 2006 ) besides found that the pretreatment of rice straw by base and acid increased cellulose content up to 75-80 % . The sum of hemicellulose and lignin content besides significantly decreased to 3 and 3-5 % severally. While the pretreatment with alkaline or acid entirely gave similar lignin and hemicellulose content at 7-23 and 7-15 % , severally. OzonolysisOzonolysis involves utilizing ozone gas to interrupt down the lignin and hemicellulose and increase the biodegradability of the cellulose. The pretreatment is normally carried out at room temperature and is effectual at lignin remotion without the formation of toxic byproducts ( Vidal et al.

, 1988 ) . Ozonation has been widely used to cut down the lignin content of both agricultural and forestry wastes. A drawback of ozonolysis is that a big sum of ozone is required, which can do the procedure expensive ( Kumar et al. , 2009 ) .2.3.

4 Biological PretreatmentBiological pretreatment involves micro-organisms such as brown- , white- and soft-rot Fungis that are used to degrade lignin and solubilize hemicellulose. The advantages of biological pretreatment include low energy demand and mild environmental conditions. However, the rate of hydrolysis in most biological pretreatment procedure is really low and requires careful control of growing conditions ( Sun et al. , 2002 ) .2.

3.5 Microwave PretreatmentMicrowaves ( frequences of 0.3GHz to 300GHz and wavelengths of 1 m to 1 millimeters ) lie between wireless moving ridge frequences ( RF ) and infrared ( IR ) frequences in the electromagnetic ( EM ) spectrum, as shown in Figure 8.

Microwaves can be reflected, transmitted and/or absorbed. The captive microwave energy is converted into heat within the stuff, ensuing in an addition in temperature. Gass, liquids and solids can interact with microwaves and be heated.

Under certain conditions, gases can be excited by microwaves to organize plasmas that besides can be utile for processing ( Clark and Sutton, 1996 ) .hypertext transfer protocol: // 2.7 The electromagnetic spectrum with applications at assorted frequences ( hypertext transfer protocol: //mynasadata.larc. ) .Microwave pretreatment is an energy-efficient, environmentally-friendly engineering. Microwave intervention seems to be similar to steam intervention.

However, microwave may hold new maps effectual for acceleration of responsiveness of cellulosic stuffs. In the conventional steam intervention, the cellulosic stuffs incorporating H2O have been heated by an external heat beginning, such as the electrical spirals environing the sterilizer, or high force per unit area steam has been supplied to the cellulosic stuffs externally. On the other manus, in the microwave, the cellulosic stuffs are heated internally ; hence, the H2O, cellulose, hemicelluloses, and the other low molecular compounds such as the organic acid contained in the cellulosic stuffs absorb the microwave as the kinetic energies when the polar molecules and their adjacent bunchs are forced to point to the specific way. It therefore appears that the microwave gives a direct serious daze to the polar molecules composing cellulosic stuffs ( Ooshima et al. , 1984 ) .Microwave is an alternate method for conventional warming. Compared with conduction/convection warming, which is based on superficial heat transportation ; the microwave uses the ability of direct interaction between a het object and an applied electromagnetic field to make heat.

Therefore, the warming is volumetric and rapid. When microwave is used to handle lignocelluloses, it selectively heats the more polar ( lossy ) portion and creates a “ hot topographic point ” with the nonuniform stuffs. It is hypothesized that this alone warming characteristic consequences in an “ detonation ” consequence among the atoms, and improves the break of the fractious constructions of lignocellulose. In add-on, the electromagnetic field used in microwave might make non-thermal effects that besides accelerate the devastation of the crystal constructions ( Hu et al. , 2008 ) .Compared with conventional warming techniques, microwave warming has the undermentioned extra advantages ( Jones et al.

, 2002 ) .Higher warming ratesNo direct contact between the warming beginning and the heated stuffSelective warming may be achievedGreater control of the warming or drying procedureReduced equipment size and wasteHowever, the microwave engineering has been shown possibilities to be an energy efficient technique for chemical processing. The advantages and challenges of microwave processing are summarized in Table 2.2Table 2.2 Benefits and challenges of microwave processing ( Clark and Sutton, 1996 )BenefitsChallengesCost nest eggs ( clip and energy, reduced floor infinite )Rapid warming of thermic dielectrics ( most ceramics and polymers )Precise and controlled warming ( instantaneous on/off heating )Selective warmingVolumetric and unvarying warming ( due to deep energy incursion )Short processing timesImproved quality and belongingssSynthesis of new stuffsProcessing non possible with conventional agenciesDecrease of risky emanationsIncreased merchandise outputsEnvironmentally friendly ( clean and quiet )Self-limiting warming in some stuffsPower supply can be distantClean power and procedure conditionsHeating low-loss ill absorbing stuffsControling accelerated warming ( thermic blowout )Exploiting upside-down temperature profilesExtinguishing curving and commanding plasmasEfficient transportation of microwave energy to work pieceCompatibility of the microwave procedure with the remainder of the procedure lineReluctance to abandon proved engineeringsTimingEconomicssAntonio et Al.

( 2005 ) studied thermic consequence of microwave irradiation. Microwave irradiation is rapid and volumetric, with the whole stuff heated at the same time. In contrast, conventional warming was slow and introduced into the sample from the surface. The temperature profile as shown in Figure 2.8Figure 2.8 The temperature profile after 60 sec as affected by microwave radiation ( left ) compared to intervention in oil bath ( right ) .Microwave irradiation raises the temperature of the whole reaction volume at the same time, whereas in the oil heated tubing, the reaction mixture in contact with the vas wall is heated.Hu and Wen ( 2008 ) studied microwave-based warming pretreated switchgrass, which was so hydrolyzed by cellulase enzymes.

When switchgrass was soaked in H2O and treated by microwave, entire sugar ( xylose + glucose ) output from the combined intervention and hydrolysis was 34.5 g/100 g biomass, tantamount to 58.5 % of the maximal possible sugars released. This output was 53 % higher than that obtained from conventional warming of switchgrass. With alkali lading from 0.

05 to 0.3 g alkali/g biomass, microwave pretreatment resulted in a higher sugar output than from conventional warming, with the highest output ( 90 % of maximal possible sugars ) being achieved at 0.1 g/g of alkali burden.

Scaning negatron microscope ( SEM ) images revealed that the advantage of microwave over conventional warming was due to the break of fractious constructions. At optimum conditions of 190 i‚°C, 50 g/l solid content, and 30 min intervention clip, the sugar output from the combined pretreatment and hydrolysis was 58.7 g/100 g biomass, tantamount 99 % of possible maximal sugars.

The consequences demonstrate that microwave-assisted base intervention is an efficient manner to better the enzymatic digestibleness of switchgrass.Zhu et Al. ( 2005 ) investigated microwave-assisted alkali pretreatment of wheat straw and its enzymatic hydrolysis and compared with the conventional alkali pretreatment procedure. The consequences show that the higher microwave power with shorter pretreatment clip and the lower microwave power with longer pretreatment clip had the same consequence on the weight loss and composing at the same energy ingestion. It was found that the wheat straw had a weight loss of 48.

4 % and a composing of cellulose 79.6 % , lignin 5.7 % , and hemicellulose 7.8 % after 25 min microwave assisted alkali pretreatment at 700 W, compared with a weight loss of 44.7 % and a composing of cellulose 73.5 % , lignin 7.2 % , and hemicellulose 11.

2 % after 60 min conventional alkali pretreatment. The microwave assisted alkali pretreatment removed more lignin and hemicellulose from wheat straw with shorter pretreatment clip compared with the conventional base one. Finally, the enzymatic hydrolysis of pretreated wheat straw ( substrate concentration 50 g/l, enzyme lading 20 mg/g substrate ) was besides investigated and the consequences indicated that the microwave-assisted base pre-treated wheat straw had higher hydrolysis rate, cut downing sugar concentration and glucose content in the hydrolysate than the conventional base pretreated one.

Microwave-assisted alkali pretreatment is a possible option of wheat straw pre-treatment for it enzymatic hydrolysis.Zhu et Al. ( 2006 ) besides examined three microwave/chemical procedures for pretreatment of rice straw that are microwave/alkali, microwave/acid/alkali, and microwave/acid/alkali/H2O2 for its enzymatic hydrolysis and for xylose recovery from the pretreatment liquid. They found that xylose could non be recovered during the microwave/alkali pretreatment procedure, but could be recovered as crystalline wood sugar during the microwave/acid/alkali and microwave/acid/alkali/H2O2 pretreatment. The enzymatic hydrolysis of pretreated rice straw showed that the pretreatment by microwave/acid/alkali/H2O2 had the highest hydrolysis rate and glucose content in the hydrolysate.In our group, Ploypradith P. ( 2010 ) studied the NaOH pretreatment with microwave on corn cob.

The optimal conditions were found at 2 % NaOH at 100 A°C for 30 min which could cut down lignin by 66.27 % and increse in surface country by 38.31 % . And the highest glucose concentration can make up to 32.53 g/l and entire sugar of 42.93 g/l was released. Furthermore, microwave aids NaOH can bring forth entire sugar concentration at shorter pretreatment clip and lower pretreatment temperature compared with sterilizer. In add-on, entire sugar concentration of microwave was higher than that of conventional warming.

Wanitwattanarumlug B. ( 2011 ) besides studied the pretreatment of corn cob utilizing microwave and K hydrated oxide. The highest sugar output of 34.79 g/l was obtained from the maize hazelnut pretreated by microwave and 2 % KOH at 120 A°C for 25 min.

The consequences indicated that microwave-assisted base intervention was an efficient manner to better the enzymatic hydrolysis handiness.There are many research work related with pretreatment methods to better its transition. Among them, the microwave-assisted chemical pretreatment is a more effectual to heighten the enzymatic hydrolysis by speed uping the reaction. In this survey, The combined pretreatment of corn cob with microwave was conducted. A two-stage pretreatment utilizing 2 % NaOH at 100 A°C for 30 min the optimum status of NaOH from Ploypradith P. ( 2010 ) and followed by H2SO4 pretreatment. In this work NaOH was used to divide lignin in the first phase and the consequence of temperature, abode clip and solid burden were determined in the 2nd phase of two-stage pretreatment.


4 Inhibitors from Biomass Pretreatment

The pretreatment procedure generates legion byproducts that inhibit the growing of micro-organism and agitation. However, the coevals of byproduct depends on feedstock and pretreatment method ( Jonsson et al. , 2013 ) . Particularly, acerb pretreatment that solubilizes hemicellulose taking to the formation of pentoses, hexoses, and inhibitors such as feruric acid, acetic acid, 2-furaldehyde ( furfural ) , formic acid, and furoic acid. Furthermore, cellulose besides degrades hexoses to 5-hydroxymethylfurfural ( HMF ) , and levulinic acid. Other aldehydes and phenol can be formed by degration of lignin.

Figure 2.9 showed the inhibitors that are generated during pretreatment ( Liu and Blaschek, 2010 ) . Although more than 100 compounds were detected as inhibitors, many have non been good studied ( Liu et al, 2004 ) .Levulinic acidHMFHexosesCelluloseDehydrationFurfuralLignocellulosicBiomassFormic acidPentosesHemicelluloseFuroic acidAcetic acidOther aldehydesFerulic acidLigninOther phenolsOther acidsFigure 2.9 The debasement merchandise of lignocellulosic biomass during pretreatment ( Liu and Blaschek, 2010 ) .Inhibitors can be classified base on chemical functional groups into 4 groups as aldehydes, ketones, phenols, and organic acids.

Some surveies have investigated that the low molecular weight compounds have more toxic to microbes than high molecular weight due to easier to transport ( Sierra et al, 1991 ) .2.4.

1 Aldehyde inhibitorsAldehyde inhibitors are compounds with one or more aldehyde functional groups with a furan ring, a benzine ring or a phenol construction. For illustration, furfural and HMF which contain a furan ring and an aldehyde functional group. Other aldehyde inhibitors include 4-hydroxyA­benzaldehyde, vanillin ( Klinke et ai. , 2002 ) , syringaldehyde, and other compounds holding a benzine ring or a phenol-based construction including isovanillin, ortho-vanillin, and coniferylaldehyde ( Liu and Blaschek, 2010 ) .

The construction of aldehyde inhibitors are showed in Figure 2.10.Figure 2.10 The construction of aldehyde inhibitors ( Liu and Blaschek, 2010 ) .2.

4.2 Ketone inhibitorsKetone inhibitors include 4-hydroxyacetopheone and the closely related compounds acetovanillone and acetocsyringone. These compounds all portion a common ketone functional group ( Klinke et al. , 2003 ) . The construction of ketone inhibitors are showed in Figure 2.

11.Figure 2.11 The construction of ketones inhibitors ( Liu and Blaschek, 2010 ) .2.

4.3 Phenol-based inhibitorsPhenol-based inhibitors are grouped together including phenol, benzene-l,2-diol ( catechol ) , benzene-1,4-diol ( hydroquinone ) , 4-ethylbenzene-l,2-diol ( ethy1catechol ) , 2-methylphenol, 3-methylbenzene-l,2-diol ( methy1catechol ) , 2-methoxyphenol ( guaiacol ) , 4- ( hydroxymethyl ) A­2-methoxyphenol ( vanillyl intoxicant ) , and 2,6-dimethoxybenzene-1,4-diol ( Klinke et al. , 2002 ) . The construction of phonols inhibitors are showed in Figure 2.12.Figure 2.12 The construction of phenols inhibitors ( Liu and Blaschek, 2010 ) .2.

4.4 Organic acid inhibitorsOrganic acid inhibitors include simple acids every bit good as furoic acid with a furan ring that was considered as being a furan inhibitor. Furthermore, many antecedently recognized phenolic compounds are now grouped as members of the organic acid inhibitor category based on their functional construction. Inhibitory compounds of this category all contain a carboxyl functional group and include acetic acid, formic acid, levulinic acid, caproic acid, furoic acid, 4-hydroxybenzoic acid, 3-hydroxybenzoic acid, 2-hydroxybenzoic acid, 2,5-dihydroxybenzoic acid, protocatechic acid, vanillic acid, Gallic acid, syringic acid,4A­hydroxycinnarnic acid, ferulic acid, homovanillic acid, guaiaclyglycolic acid, and sinapic acid. These inhibitors are thought to be exert their repressive actions via their carboxyl functional groups. The construction of organic acid inhibitors are showed in Figure 2.13.Figure 2.

13 The construction of organic acid inhibitors ( Liu and Blaschek, 2010 ) .

2.5 Butanol Fermentation Inhibitors

Pretreatment has been seen as a preferable method that make the enzyme in enzymatic hydrolysis measure extremely digests biomass in order to bring forth high sum of cut downing sugar for farther ABE agitation. However, the toxic compounds including weak acids, furan derived functions, phenolic compounds, vanillic aldehyde, and tannic acid are generated during pretreatment ( Eva and Barbel, 2000 ) ; hence, no micro-organism can efi¬?ciently bring forth butyl alcohol from lignocellulosic biomass ( Weber et al. , 2010 ) due to the inhibitors affect cell growing and ABE production.Ezeji et Al. ( 2007 ) studied the impact of inhibitors that generated from H2SO4 pretreatment on ABE concentrations.

The consequences showed that syringaldehyde, ferulic, and I?-coumaric acids were powerful inhibitors of ABE production by Clostridium beijerinckii BA101 as shown in Figure 2.14. In general, ferulic and coumaric acids inhibit micro-organism by damaging the hydrophobic sites of the bacteriums cells because ferulic and coumaric acids are phenolic acids and phenolic compounds that affect membrane permeableness ( Heipieper et al.

, 1994 ) . Furthermore, the writers observed that furfural and HMF ( 3 g/l ) were non inhitory to Clostridium beijerinckii BA101. However, the combination of furfural and HMF affects the civilization negatively.

In add-on, the production of salt, sulphate, which is consequence of sulphuric acid used for pretreatment was besides toxic to Clostridium beijerinckii BA101.Figure 2.14 The consequence of inhibitors generated during 0.

5 % H2SO4 pretreatment of maize fibre on ABE concentrations ( Ezeji et al. , 2007 ) .2.

6 Detoxification Method ( Chandel et al. , 2011 )Since inhibitors from pretreatment procedure can be debatable for agitation, the remotion of inhibitors from hydrolysates is necessary to heighten microbic growing and agitation efficiency. Nevertheless, inhibitors depend on type of pretreatment and feedstock. The most detoxification methods are physical, chemical, and biological ( Chandel et al.

, 2011 ) .2.6.1 Physical Methods2.6.

1.1 VaporizationThe vaporization under vacuity can take volatile compounds for illustration, furfural, acetic acid, and vanillin from hydrolysate of lignocellulosic biomass. However, vaporization retains the non-volatile toxic compounds such as lignin derived functions and extractives in the hydrolysates.

A survey by Wilson et Al. ( 1989 ) found a lessening in the concentration of furfural, vanillin, and acetic acid by 100 % , 29 % and 54 % , severally, compared with the concentrations in the hydrolysate. Likewise, Larsson et Al. ( 1999 ) studied the remotion of furfural and HMF utilizing vacuum vaporization from wood hydrolysate. The consequences showed that furfural and HMF were reduced 90 % , 4 % , severally. Membrane separationsAdsorbent micro porous membranes have surface functional groups attached to their internal pores, that remove the cell wall derived inhibitors from acerb hydrolysates. Grzenia et Al. ( 2010 ) applied the membrane extraction for inhibitors removal from sulphuric acerb hydrolysate of maize stover. The consequences showed that acetic acid, formic acid, levulinic acid, HMF, and furfural was eliminated.2.

6.2 Chemical Methods2.6.2.1 NeutralizationThe neutralisation of acid hydrolysates is needed measure before agitation because of low pH. Alkali ( Ca ( OH ) 2 or NaOH ) is used for hydrolysates neutralisation ( pH in the scope of 6-7 ) . Phenolics and furfural may be removed by precipitation. OverlimingIt was reported that overliming is the most cost effectual method for detoxicating soft wood hydrolysates. Detoxification after pretreatment and enzymatic hydrolysis or before agitation by alkali intervention Begins by adding calcium hydroxide ( NaOH or Ca ( OH ) 2 ) to set the pH of the hydrolysate to a high value ( in the scope of 9-11 ) followed by pH readjustment to 6.

6 with H2SO4. Adjustment of pH with Ca ( OH ) 2 has been reported to increase the fermentability more than that with NaOH. The entire sum of phenolic compounds was more expeditiously decreased by Ca ( OH ) 2.

However, it has been shown that monovalent ions such as Na+ affect the ethanol productiveness negatively, whereas Ca2+ does non. However, acetic acid and sugars were non removed by intervention procedure with NaOH or Ca ( OH ) 2. Furthermore, a heating measure in the overliming process ( taking to some vaporization ) improves fermentability ( Larsson, 1999 ) . Furthermore, Ethanol productiveness was more than twice as high after intervention with Ca ( OH ) 2 compared with NaOH. The entire concentration of phenolic compounds was affected by overliming detoxification due to phenoplasts were most expeditiously removed with this method ( Larsson, 1999 ) .2.6.

2.3 Activated Charcoal TreatmentActivated wood coal is a cost effectual method with high capacity to absorb compounds without impacting the sum of sugar in hydrolysate ( Chandel et al. , 2007 ) . The activated wood coal intervention efficiency depends on pH, temperature, contact clip, and the activated wood coal taken and the liquid hydrolysate volume ratio ( Prakasham et al. , 2009 ) .2.6.2.

4 Ion Exchange ResinsIon exchange rosins intervention was applied to take lignin-derived inhibitors, acetic acid and furfurals. The ion-exchange rosins based separation of fermentative inhibitors may non be cost effectual ( Lee et al. , 1999 ) .2.

6.3 Biological MethodsThe biological methods for detoxification are more executable, environmental friendly, with fewer side-reactions and less energy demands ( Parawira and Tekere, 2011 ) . The micro-organism and/or the enzymes have possible to change the chemical nature of inhibitors. However, the slow reaction clip and the loss of fermentable sugars make this methods unattractive ( Yang and Wyman, 2008 ) .2.7 Response Surface Methodology ( RSM ) ( Carley et. al. , 2004 )Response Surface Methodology ( RSM ) is a statistical and mathematical techniques good for developing, bettering, and optimising procedures.

A low-order multinomial is appropriate to utilize. In many instances, either a first-order or a second-order theoretical account is used. The first-order theoretical account is suited when the experimenter is interested in come closing the true response surface over a comparatively little part of the independent variable infinite.In general, the first-order theoretical account is expressed as following equationWhere Yi is the response ; xi is the input variables, which influence the response variable Yi ; a0 is the offset term ; ai is the ith additive coefficient.The curvature in the true response surface is frequently strong plenty that the first-order theoretical account is unequal.

A second-order theoretical account will be required. The undermentioned equation was used to correlate the dependant and independent variables of second-order theoretical account.Where Yi is the response ; xi, xj are the input variables, which influence the response variable Yi ; a0 is the offset term ; ai is the ith additive coefficient ; aii is the quadratic coefficient and aij is the ijth interaction coefficient.The second-order theoretical account is widely used in response surface methodological analysis for several grounds:1. The second-order theoretical account is really flexible due to a broad assortment of functional signifiers ; therefore it will frequently work good as an estimate to the true response surface.2.

It is easy to gauge the parametric quantities in the second-order theoretical account. The method of least squares can be used for this intent.3. There is considerable practical experience bespeaking that second-order theoretical accounts work good in work outing existent response surface jobs.


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