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Industrial Crops and Products 33 (2011) 734–738
Contents lists available at ScienceDirect
Industrial Crops and
Products
j o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /i n d c r o
p
Isolation of cellulo with ionic liquid from steam exploded rice straw
Man Jiang,Mengmeng Zhao,Zuowan Zhou ∗,Ting Huang,Xiaolang Chen,Yong Wang
Key laboratory of Advanced Technologies of Materials,Ministry of Education,School of Materials Science &Engineering,Southwest Jiaotong University,610031Chengdu,Sichuan,China
a r t i c l e i n f o Article history:
Received 17November 2010Received in revid form 29December 2010
Accepted 13January 2011
Available online 12 February 2011Keywords:Rice straw
Cellulo isolation Ionic liquid
Hydrogen peroxide Ozone
a b s t r a c t
Isolation of cellulo from straw is a bottleneck for exploiting such biomass resources.In recent years,considerable concerns have arin over new efficient and environmentally friendly way for this purpo.A novel method for cellulo isolation has been propod by dissolving steam exploded rice straw in 1-allyl-3-methylimidazolium chloride ionic liquid (IL),following regeneration of crude cellulo by diluting the cellulo-ionic liquid solution adequately after paration of insoluble residues.The crude cellulo was then bleached by 2%hydrogen peroxide aqueous solution with low-flux ozone blowing into.No acid-insoluble lignin and only 0.85%hemicellulos were detected in the bleached cellulo.The isolated cellulo was analyzed by SEM,FT-IR,13C CP/MAS solid state NMR,XRD spectroscopes,and the results indicated that high quality cellulo preparation could be isolated in this manner from rice straw.
© 2011 Elvier B.V. All rights rerved.
1.Introduction
Cellulo is the most abundant biopolymer on the earth and is widely ud in commercial materials due to its attractive proper-ties such as biocompatibility,biodegradability,renewable,thermal and chemical stability.Agriculture residues are important ligno-cellulosic material,however,cellulo accompanies with other structural biopolymers,primarily hemicellulos and lignin,which compri 20–35and 5–30%of plant dry weight,respectively (Lynd et al.,2002).Efficient paration of constitutive biomass components constitutes one of the major obstacles to efficient utilization of the renewable resource.Under such circumstances,novel environmentally friendly process have been developed continuously to isolate cellulo from biomass,such as:steam explosion (Montane et al.,1998;Sun et al.,2005a ,2005b;Chen and Liu,2007),organosolv process (Sun et al.,2004),chlorine-free method (Sun et al.,2005a ,2005b ),combined chemical and enzymatic extraction (Reddy and Yang,2006),etc.However,ionic liquids (ILs)have opened a completely new way for this rearch field,which is comprid of discrete cations and anions.The most attractive characteristic of IL is the adjustability of its physical,chemical and even biological properties by independent modi-fication of the cation and anion (Swatloski et al.,2002).Having been described almost a century ago (Walden,1914),ionic liq-uids reignited tremendous interest,not only as new alternatives to
∗Corresponding author.Tel.:+862887600454;fax:+862887600454.E-mail address:zwzhou@at-c (
Z.Zhou)anic solvents in numerous synthesis and polymerization pro-cess (Seddon,1997;Welton,1999;Rogers and Seddon,2003;Li et al .,2005;Plechkova and Seddon,2008),but also in the para-tion/extraction chemistry (Zhang et al.,2005).
After veral kinds of ionic liquids have been found to be non-derivatizing solvents for cellulo,which have begun to be applied in such rearch fields as capturing the portrait of single cellu-lo molecule (Wan et al.,2008),chemical modification of cellulo (Abbott et al.,2005;Äinen et al.,2007;Xie et al.,2007)and develop-ing micro-and nano-porous composite materials (Tsioptsias et al.,2008).Still,no rearch work has been reported on directly isola-tion of cellulo from biomass with ionic liquids to the best of our knowledge.
Steam explosion has been a well known pretreatment for parating lignocellulosic material to obtain the parated main components.It is pointed to be a physic-chemical process:(a)the rapid pressure releasing caud mechanical action on the texture of the straw;(b)the steaming led to hemicellulos autohydrolyzing and lignin depolymerizing partially (Sun et al.,2005a ,2005b ).
Enlightened by the reports that ionic liquids were found to be nonderivatizing solvents for cellulo (Wan et al.,2008;Abbott et al.,2005;Äinen et al.,2007;Xie et al.,2007;Tsioptsias et al.,2008),for the firs
t time,we adopted ionic liquid in isolation of cellulo from steam exploded rice straw,and proved it was an efficient and environmentally safe way in isolating cellulo from rice straw.Comparing to other procedures that focud mainly on removing non-cellulo components to leave the cellulo,we pro-pod a direct way to dissolve the cellulo by lected ionic liquid from steam exploded rice straw.
0926-6690/$–e front matter © 2011 Elvier B.V. All rights rerved.doi:10.1016/j.indcrop.2011.01.015
M.Jiang et al./Industrial Crops and Products33 (2011) 734–738735
Table1
Solubility of the four ILs for cellulo and lignin.a
I L AMIMCl BMIMCl BnMIMTFA BnMIMCl
Cellulo 5.2% 4.9%––
Lignin–– 4.9% 3.9%
a Cellulo and lignin ud in this experiment are samples parated from rice straw in other procedure by ourlves;“–”reprents nearly no sample can be dissolved.
2.Experimental
2.1.Main materials
Air-dried rice straw was collected in suburb of Deyang City of Sichuan Province,China.It was cut into about200mm in length. The chemical composition of the rice straw was determined to be: 35.06%cellulo,17.98%pentosans,15.24%acid-insoluble lignin, 14.9%ash,and9.55%moisture content.
1-Butyl-3-methylimidazolium chloride(BMIMCl),1-allyl-3-methylimidazolium chloride(AMIMCl),1-benzyl-3-methyl-imidazolium chloride(BnMIMCl)and1-benzyl-3-methyl-imidazolium trifluoroacetate(BnMIMTFA)ionic liquids were synthesized according to literature(Dyson et al.,1997,their structures had been confirmed by1H NMR and FT-IR spectra and not given here.).The four ionic liquids were put to the dissolving experiment and the results were shown in Table1.
2.2.Analysis methods for raw material and cellulo preparation
The chemical composition of raw material and cellulo prepa-ration was analyzed according to TAPPI Standard Methods,2009. The pentosans contents in raw material and steam exploded rice straw were analyzed in respon to T223cm-01.The cellulo in raw material and steam exploded rice straw was measured by using the method of T203cm-99.The acid-insoluble lignin content in crude and bleached cellulosic preparations was determined accord-ing to T222om-06.The hemicellulos contents of the purified cellulosic preparation were analyzed with reference to gamma-cellulo content in pulp(test method T203cm-09,TAPPI).The SCAN viscosity of the cellulo preparation was measured by using a Ubbelohde viscometer in cupri-ethylenediamine(CED).The DP (degree of polymerization)of the cellulo was calculated by the equation of DP0.76=(SCAN viscosity)/2.28(Ziaie-Shirkolaee et al., 2008).Cellulo preparation yield was determined gravimetrically after drying in an oven at105±2◦C for12h.
Morphological and structural characteristics of the cellulo preparation have also been analyzed by SEM(Fei Quanta200, Holand,20kV),FT-IR(Nicolet5700,KBr),CP/MAS13C solid-state Table3
Whiteness of the crude cellulo and bleached cellulo samples.
Sample
Crude cellulo Bleached cellulo
Bleaching reagent H2O2O3H2O2/O3 Whiteness12.8315.8013.1282.40
NMR(Bruker Avance III,100.6MHz,25◦C),and X-ray diffraction (XRD,DX-2500SSC,copper target,40kV and25mA).The whiteness degrees of the samples were measured on a whiteness apparatus (YQ-Z-48A,BaO).
2.3.The pretreatment and isolation process
The rice straw was pretreated with steam explosion at a bench scale equipment with a10L reactorfitted with a quick-opening aerodynamic butterfly valve in the procedure as:rice straw was steamed at2.5MPa with a solid to liquid ratio of3:1(w/w)for 25min and then exploded.(The optimum condition was deter-mined according to a group of experiments as shown in Table2.) The collected steam-exploded rice straw was soxhlet extracted with water and ethanol quentially,and then completely dried in an oven under105±2◦C for6h.The dried sample was stored in an exsiccator for further u.The completely dried SE-rice straw1.5g was added to20g the ionic liquid(AMIMCl)in a three-neckedflask with magnetic stirring at40–60◦C for2–3h under anhydrous con-dition,worked up immediately byfiltering off through a screener (pore size:38m)and adding adequate distilled water t
o the solu-tion to precipitate cellulo sufficiently.
2.4.The bleaching process
The isolated crude cellulo was charged into a three-necked flask contained2%H2O2aqueous solution,cooking at50–60◦C for 12h under magnetic stirring with(or without)ozone blowing into (about3.4g/h generated in an SZH5ozone apparatus,Peking).After filtration,the solid cellulo preparations were dried in an oven under105±2◦C for12h and the whiteness were measured(shown in Table3).
3.Results and discussion
3.1.Preparation of crude cellulo from SE-rice straw
Generally,as mentioned above,the ionic liquids were ud to dissolve the cellulo for chemical modification or nano-composites preparation,as well as the straws pretreatment.We
Table2
Characteristics of the samples under different steam-explosion conditions.
Experiment number Conditions lg R0a Cellulo%Hemicellulos%[ŋ]DP Pressure(MPa)Steaming time(min)何川洋
1 3.015 5.956.511.3296.1604
2 3.020 6.065.0 3.8198.4357
3 3.025 6.170.
4 3.0224.9421
4 2.51
5 5.672.3 5.4281.4565
5 2.520 5.864.
6 3.9206.6376
6 2.525 5.971.8 1.1270.3536
7 2.015 5.371.213.8251.4577
8 2.020 5.467.6 5.3230.1434
9 2.025 5.569.98.7288.8585
10 1.515 5.085.6 6.2384.4852
11 1.520 5.177.98.1444.81033
12 1.525 5.274.117.4459.51078
a lg R0(treatment verity,R0=t exp(T−100)/14.75).
736M.Jiang et al./Industrial Crops and Products33 (2011) 734–738
Table4
Main components and whiteness of the original rice straw and the treated samples.a
Sample
Component Original rice straw(%)Steam-exploded rice straw(%)Crude cellulo(%)Bleached cellulo(%)wapi
Cellulo35.0664.8095.58
Pentosans17.98 1.100.85
Acid-insoluble lignin15.2414.760.90–
Ash14.90 3.57
Moisture9.55–––
DP b1123536508484
Whiteness––12.8382.40
a“–”reprents none of the component was detected;Blank space reprents the component was not analyzed.
b DP:degree of polymerization.
tried to apply the ionic liquid to extract the cellulo from the rice straw.The solubility of the synthesized four kinds of ionic liquids was evaluated,and the results indicated that BnMIMCl or BnMI
MTFA displayed good efficiency in dissolving lignin,while each of BMIMCl and AMIMCl was a good solvent of cellulo(shown in Table1).In this work,we lected AMIMCl as the solvent to isolate cellulo becau it was the best one in lective dissolv-ing cellulo other than lignin.In order to elevate the efficiency, the steam explosion pretreatment was employed.The contents of pentosans and cellulos of the steam exploded rice straw(SE-rice straw)were analyzed to be1.10%and64.8%respectively.After iso-lation with AMIMCl,the isolated crude cellulo was detected only 0.9%acid-insoluble lignin contained.
Compared with the original rice straw,different size of micro-pore formed in the straw organization after steam-explosion pretreatment,which was attributed to the hydrolyzation and dis-solving out of the hemicellulos and degradation of the little portion of lignin by breaking the ether bonding to hemicellulos (Schmidt and Thomn,1998).This was very benefit to further iso-lation of cellulo.Swatloski and coworkers(Tsioptsias et al.,2008) proved that chloride containing ILs bad on imidazole appeared to be the most effective solvents for cellulo,presumably through hydrogen-bounding of hydroxyl and anions of the ILs.ILs with longer-chain-alkyl substituted cations appeared to be less efficient at dissolving cellulo,which might be due to the relatively reduced effective chloride concentration.However,such kind of IL was pointed out to be ineffective for lignin.When the
cationic moiety of IL possd an electron-rich aromatic-system,it might create strong interactions with the polymers though–and n–inter-actions to dissolve lignin.The prence of moisture in this process could significantly decrea the solubility,which was in accordance with the reports(Seddon,1997;Welton,1999;Rogers and Seddon, 2003;Li et al.,2005;Plechkova and Seddon,2008;Tsioptsias et al., 2008;Wan et al.,2008).So,AMIMCl ionic liquid was ud to conduct the isolation of cellulo from the SE-rice straw which contained very small amount of hemicellulos under anhydrous condition.
3.2.Bleaching process of the crude cellulo
Although the as-isolated crude cellulo preparation was detected only0.9%acid-insoluble lignin,and the steam-explosion pretreatment eliminated almost all hemicellulos,the sample’s color was still yellow,and it could not meet the requirement of further application such as spinning or pulping.We bleached the parated crude cellulo by immersing into hydrogen peroxide aqueous solution together with ozone blowing.It had been gen-erally accepted that the hydro-peroxide anion(HOO−)formed in alkaline media was the primary species responsible for bleach-ing,which was generated from the reaction between H2O2and alkali(such as:NaOH or cyanamide,Montane et al.,1998;Sun et al.,2005a,2005b).In the light of environment protection,we introduced ozone to assist
the generation of HOO−from the H2O2aqueous solution via the reaction between H2O2and oxygen radi-cal relead from the ozone.Additionally,ozone could degrade the residual lignin through ozonolysis(Liyama et al.,1991).It indicated, as shown in Table3,that only H2O2aqueous solution or O3blowing into water could not bleach the crude cellulo.
3.3.Components analysis and morphological structure of the bleached cellulo
Cellulo was obtained in yield of30.73%from completely dried rice straw and the component analysis(TAPPI,method T222om-06,and T203cm-09)indicated that no detectable acid-insoluble lignin and only0.85%of hemicellulos in the obtained cellulo sample.The average degree of polymerization(DP)by viscosity measurement of the prepared highly purified cellulo was484. The components analysis of the original rice straw and the sam-ples during the process were given in Table4.The SEM image of the obtained cellulo was shown as Fig.1,Cellulofibers could be obrved clearly in the SEM picture with average lengths more than100m.
3.4.Spectroscopic analysis of the highly purified cellulo from
rice straw
forever at your feet
The FT-IR spectra of the as-bleached cellulo preparation and the original rice straw as well as SE-rice straw had been illustrated in Fig.2.The spectrum c prents the bleached cellulo:the very strong absorption at3402cm−1belongs to the OH stretch and the bands at2919and2887cm−1reprent C–H anti-symmetric and symmetric stretch respectively.The absorption at1635cm−1is principally associated with the adsorbed water,since the pure cel-lulo has strong affinity for water.The weak absorptions at1417, 1374and1317cm−1reprent C–H stretch and C–H or O–H
bend-Fig.1.SEM image of bleached rice straw cellulo.
M.Jiang et al./Industrial Crops and Products 33 (2011) 734–738
737
Fig.2.FT-IR spectra of original rice straw (a),steam exploded rice straw (b)and bleached rice straw ce
llulo (c).
ing.The strong absorption at 1054cm −1attributes to the C–O–C stretch.The sharp band at 892cm −1corresponds to the C-1group frequency or ring frequency,which is characteristic absorption of -glycosidic linkages between the sugar units (Chaikumpollert et al.,2004).As compared with the spectra of the original (spec-trum a in Fig.2)and the steam exploded rice straw (spectrum b in Fig.2),the absorptions at 1510,1465and 1423cm −1,correspond-ing to the skeleton stretch of the benzene ring,were disappeared.The related peaks were also weakened in spectrum b comparing with spectrum a .
smm
The CP/MAS 13C solid-state NMR spectrum of the bleached cel-lulo is shown in Fig.3.The chemical shifts at 62and 64ppm are assigned to C6of the primary alcohol group.The next cluster of resonances at 71and 74ppm are attributed to C2,C3and C5,the ring carbons other than tho anchoring and glycosidic linkage.The chemical shifts at 83and 88ppm are associated with C4and,that at 104ppm is associated with C1(R.Atalla and Vanderhart,1999).The signals at 173and 20ppm may be attributed to carbonyl and methyl resonances respectively,the very weak signals indicate trace amount of residual carboxylic acids or esters in the sample resulting from the degradation of lignin or cellulo.
on the way什么意思
The physical structure of the isolated cellulo has been studied by X-ray diffraction and shown in Fig.4.As en from the XRD
pat-
Fig.3.CP/MAS13C solid-state NMR spectrum of isolated rice straw
cellulo.
Fig.4.XRD profile of bleached cellulo.
tern,the isolated rice straw cellulo has the prominent cellulo peak at 22◦,denoting the (002)reflection,however,the charac-teristic (101)and (10¯1)
peaks (2Âbetween 15◦and 17◦)are not distinct as tho in cotton (Reddy and Yang,2007),but combine into one broad peak at 16◦.This is suggested to be due to the prence of noncellulosic substances in the sample,which is in accordance with the CP/MAS solid-state 13C NMR spectrum.The value of crystalline index (CI)is about 74%according to the X-ray diffraction analysis.4.Conclusions
In summary,this rearch work has proved that 1-allyl-3-methylimidazolium chloride (AMIMCl)is effective for isolating cellulo from steam explosion pretreated rice straw on the ba of its strong lective solubility for cellulo other than lignin.Perox-ide hydrogen aqueous solution assisted by ozone blowing is found to be an effective way for bleaching the crude cellulo,which is a fairly more
environmentally friendly and efficient way than alka-line activated peroxide hydrogen popular adopted at the prent time.No volatile organic solvent has been introduced in the pro-cess,and what is more,the ionic liquid can be recovered by vacuum distillation to remove water,and no pollutant has been discharged into the environment during the whole procedure.Acknowledgements
The authors are grateful for the financial support of this rearch from the National Natural Science Foundation of China (90305003),the National Hi-tech Program of China (No.2008AA030705)and Sichuan Province Science and Technology Plain Foundation (09GG1632).References
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