Industrial Crops and Products 32 (2010) 349–352
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
Kinetic study on the liquefaction of cornstalk in polyhydric alcohols
Yongbin Yan a ,Mingming Hu a ,Zhihua Wang b ,∗
a School of Chemistry and Materials Science,Xiaogan University,Xiaogan,Hubei 432000,China b
School of Life Science and Technology,Xiaogan University,Xiaogan,Hubei 432000,China
a r t i c l e i n f o Article history:
Received 8February 2010
Received in revised form 21May 2010Accepted 23May 2010
Keywords:Kinetic
Liquefaction Cornstalk
Polyhydric alcohols
a b s t r a c t
The powders of cornstalk were liquefied in polyhydric alcohols using sulfuric acid as catalyst at 130–190◦C for different reaction times.The kinetics along with liquefaction ratio was analyzed using kinetic models under different reaction temperatures.The result indicated that the liquefaction of corn-stalk in polyhydric alcohols was multilevel.The apparent reaction rate constants increased with the increase of reaction temperatures.The apparent activation energy (E )was 73.6kJ mol −1and the appar-ent frequency factor (A )was found to be 8.8×105S −1.According to transition-state theory,the apparent activation free enthalpy ( G ),apparent activation enthalpy ( H ),and apparent activation entropy ( S )of liquefaction reaction slightly changed with temperature.With regards to apparent activation enthalpy,the result indicated that the liquefaction of cornstalk in polyhydric alcohols was predominantly an endothermic reaction in nature.
© 2010 Elsevier B.V. All rights reserved.
1.Introduction
The conversion and effective utilization of lignocellulosic biomass,which is abundant and reproducible,is increasingly received interest due to the perceived need for the reduction of consumption of fossil energy and environmental protection.Espe-cially for China,which is an agricultural country,there are nearly 7×108ton crop byproducts,such as sugarcane bagasse,cornstalk,wheat straw,and wood wastes,which are abundantly reproducible resource in nature (Sun and Sun,2006).Thus,it is significant for energy strategy to use these crop byproducts efficiently for our country.However,lignocellulosic biomass is composed mainly of cellulose,hemicellulose and lignin,which are of thermosetting polymer,and therefore cannot be processed easily like thermoplas-tic polymer,glasses and metal.In the past decades,many attempts and efforts have been made to utilize lignocellulosic biomass much more efficiently by applying chemical and biochemical tech-niques,such as pyrolysis (Sharma and Rao,1999),modification (Nakano,1994),hydrolysis (Chio and Mathews,1996)and lique-faction (Kurimoto et al.,1999;Pu and Shiraishi,1993;Yamada and Ono,1999;Yao et al.,1993,1994).Especially for liquefaction in solvents,biomass could be decomposed into liquid at mild tem-perature and atmospheric pressure,which could be used as fuel and chemical raw materials.
∗Corresponding author.Tel.:+867122345490;fax:+867122345484.E-mail address:wangzhihuay@126.
com (Z.Wang).There were two kinds of liquefaction solvents in common use,which were polyhydric alcohols (Kurimoto et al.,1999;Yamada and Ono,1999;Yao et al.,1993)and phenol (Pu and Shiraishi,1993).Accordingly,the liquefaction reactions involving the two kinds of solvents were called alcoholysis and phenolysis,respectively.The liquefied products could be used to prepare polyurethane,phenolic resin (Lin et al.,1995)and corresponding materials,such as foam (Yao et al.,1995),film (Kurimoto et al.,2000,2001)and adhesive (Alma and Basturk,2006).In order to use liquefied products more effectively,it was of great importance to identify liquefied products and analyze reaction mechanisms.Because of the complexity of the components of biomass,it was mainly focused on using cellulose and lignin models to analyze the liquefaction reaction pathways (Lin et al.,1997a,b,c,2001a,b;Yamada et al.,1996;Yamada and Ono,1999,2001;Zhang et al.,2006).
Renewed interest in the utilization of lignocellulosic biomass as sources of energy and chemicals has necessitated an under-standing of the liquefaction reaction kinetics,which is helpful in investigating the effect of experimental variables on liquefaction reaction rate.Alma and co-workers had studied the kinetics of wood phenolysis,using hydrochloric acid and sulfuric acid as cata-lysts (Acemioglu and Alma,2002;Alma and Acemioglu,2004).And also the kinetics of pyrolysis and hydrolysis had been investigated (Chio and Mathews,1996;Sharma and Rao,1999).However,there w
as no kinetic study on the liquefaction of lignocellulosic biomass in polyhydric alcohols.In the past,we had prepared biomass-based polyurethane foams successively,using the liquefied products of cornstalk and sugarcane bagasse in polyhydric alcohols (Yan et al.,2008,2009).In this paper,the liquefaction reaction kinetics
0926-6690/$–see front matter © 2010 Elsevier B.V. All rights reserved.doi:10.1016/j.indcrop.2010.05.015
350Y.Yan et al./Industrial Crops and Products32 (2010) 349–352 in polyhydric alcohols was studied,using cornstalk as raw mate-
rial.顶真联
2.Methods
2.1.Materials
Cornstalk power(20–80mesh)was used as raw material,which
was dried in an oven at105◦C for24h and kept in a desiccator at
room temperature before use.Polyethylene glycol(PEG,M n,400)
and glycerine were used as liquefaction solvents in the alcoholysis
of cornstalk;98wt.%sulfuric acid was used as catalyst;1,4-dioxane
was used as solvent to dissolve the liquefied products and in deter-
mining the residue content.All these chemicals were of analytical
reagent grades,which were obtained from commercial sources,and
used without further purification.
2.2.Liquefaction of cornstalk
The liquefaction was carried out in a three-neckflask equipped
with a stirrer,refluxing condenser and thermometer.Theflask
charged with the mixture of liquefaction solvents(PEG/glycerine,
4/1,w/w)and sulfuric acid(3wt.%)was immersed into an oil bath
and preheated at certain temperature.Quantitative cornstalk(liq-
uid/solid,10/3,w/w)was then added to theflask under stirring.
The liquefaction was conducted under constant stirring and reflux
罗增刚at the certain temperature.After the presetting time,theflask was
immersed in ice water to quench the liquefaction reaction.
2.3.Measurement of liquefaction ratio
The resultant product was diluted with a large excess(about
20times of liquefied product)of dioxane/water(80/20,v/v)binary
solvents,which had been recommended as the universal diluent
for liquefied biomass(Kurimoto et al.,1999;Yao et al.,1993,1994),
and stirred with a magnetic stirrer for more than4h.Thereafter the
diluted resultant wasfiltrated usingfilter paper under vacuum to
separate residue from the liquefied cornstalk.The insoluble residue
was rinsed thoroughly with the dioxane/water binary solvents until
协方差colorlessfiltrate was obtained,and then dried in an oven at105◦C
to constant weight.The liquefaction ratio,which was defined as
the percent weight of the dioxane soluble liquefied cornstalk to
the total cornstalk charged and used as an index of the extent of
liquefaction efficiency,was calculated as follows:
Liquefaction ratio˛=W0−W
W0
(1)
Residue content1−˛=W
W0
(2)
where W and W0were the weights of insoluble cornstalk residue, cornstalk sample before liquefaction,respectively.
3.Kinetic models
The components of cornstalk are complex,and therefore it is almost impossible to measure the liquefaction rate like an indi-vidual reaction because of the chemical complexity of liquefaction reaction.Furthermore,it is difficult to isolate an individual reac-tion and measure its rate when one takes into considering the chemical complexity of the heterogeneous reactions occurring dur-ing biomass liquefaction.Nevertheless,it is possible to measure the concentration of liquefied products as a function of time,and the amount of liquefied products formed may be modeled using apparent reaction rate constants which could provide a better understanding of overall reaction process.Thus i
t is desirable
to
Fig.1.Effects of reaction temperature on the liquefaction of cornstalk.
get a physical model describing the liquefaction process of corn-stalk in polyhydric alcohols in terms of the changes of liquefaction ratio occurring in the system.
According to the previous studies about liquefaction reaction mechanisms(Lin et al.,1997a,b,c,2001a,b;Pu and Shiraishi,1993; Yamada and Ono,1999,2001;Yao et al.,1993),the liquefaction of biomass in organic solvents was a solvolysis process,and the solvents mainly solved and dispersed the liquefied products,and prevented the re-condensation of the degraded and modified com-ponents.On the other hand,the solvents in the liquefaction systems were more out and away than biomass,and so it could be seen that the solvents were superfluous.Thus for the liquefaction of corn-stalk in this study,the concentration of polyhydric alcohols,which acted as liquefaction solvents,could be considered constant.And so the reaction rate was only in relation to the residue content,and the kinetic equation could be written as the follows:
d˛
dt
=kf(˛)(3) In this equation,k was the apparent reaction rate constant, which measured up to the Arrhenius equation,k=Ae−E
⁄RT;f(˛)was the liquefaction reaction function.It was assumed that f(˛)was only in relation to the residue content(1−˛)at any time,and not in relation to reaction temperature and other conditions.And so the liquefaction reaction function could be simplified as follows, f(˛)=(1−˛)n,where n was the apparent reaction order.There-fore,the kinetic equation was taken as the following forms:
d˛
dt
=k(1−˛)n(4) Thus,in association with Eqs.(1)and(2),the logarithmic form of the kinetic equation above was:
ln
−1
W0
dW
dt
=ln k+n ln
W
W0
(5) 4.Results and discussion
4.1.Apparent reaction rate constant,reaction order and
activation energy of the liquefaction of cornstalk
For the liquefaction of cornstalk,the liquefaction efficiency was influenced with liquefaction solvents,catalyst and its content,reac-tion temperature,reaction time,etc.(Kurimoto et al.,1999;Pu and Shiraishi,1993;Yamada and Ono,1999;Yao et al.,1993,1994;Yan et al.,2008).The time-dependence of the liquefaction curves for cornstalk under different reaction temperatures is shown in Fig.1. It could be seen that,with the increase of reaction temperature,
Y.Yan et al./Industrial Crops and Products32 (2010) 349–352
351
Fig.2.Relation between liquefaction reaction rates and residue contents. the reaction rate increased and also the liquefaction efficiency was enhanced(Yan et al.,2008).
According to the kinetic equation(5),the liquefaction curves in Fig.1.were analyzed by differential,and the liquefaction reaction rates were got at different temperatures and reaction times.There-after,the relation of the liquefaction reaction rates and residue contents is shown in Fig.2,using the logarithm of the reaction rates and residue contents as ordinate and abscissa,respectively. The result indicated that the logarithm of reaction rates was directly proportional to that of residue contents at different times under the same temperature,which corresponded well to the kinetic equa-tion(5).By linearfitting,the apparent reaction rate constants and apparent reaction orders at different temperatures could be got in Table1.Based on the kinetic data,it could be seen that the appar-ent reaction rate constant increased with the increase of reaction temperature,which indicated that the increase of reaction temper-ature could accelerate the liquefaction of cornstalk in polyhydric alcohols.The apparent reaction rate constant increased by two and a half times when the reaction temperature increased from130◦C to150◦C.A further increase in temperature to170◦C resulted in lit-tle increase in apparent reaction rate constant indicating that the maximum liquefaction extent of cor
nstalk could not be improved significantly by increasing reaction temperature because of the pro-moting re-condensation reaction at the same time(Yao et al.,1993). But when the reaction temperature increased to190◦C further,the apparent reaction rate constant was the4.2times of that at170◦C, which could be due to the pyrolysis of cornstalk at high tempera-ture.On the other hand,the apparent reaction orders were close and between two and three,signifying that the liquefaction reaction of cornstalk was very complex.
According to Arrhenius equation,the relation between reaction rate constants and reaction temperatures was listed as the follow-ing equation:
ln k =ln A −E
R
1
钢领圈>dsj
T
(6)
For the liquefaction of cornstalk in polyhydric alcohols,the rela-tionship between ln k and1/T in Table1is essentially linear with a correlation coefficient of0.95as shown in Fig.3.From Fig.3,
the
Fig.3.Arrhenius plot of the liquefaction of cornstalk in polyhydric alcohols. apparent activation energy(E )value was73.6kJ mol−1and the apparent frequency factor(A )was8.8×105S−1,which were deter-mined from the slope and intercept of the Arrhenius plot of ln k versus1/T.So,it was shown that the liquefaction reaction of corn-stalk in polyhydric alcohols with high apparent activation energy was quite sensitive to temperature.
4.2.Apparent activation free enthalpy,activation enthalpy and activation entropy of the liquefaction of cornstalk
Furthermore,a more detailed explanation concerning the trans-formation of reactants into liquefied products could be expressed by the transition-state theory.According to the theory,the reac-tants were quickly degraded into unstable intermediate state called “activated complexes”atfirst and then spontaneously transformed into condensed products as follows:
A+B AB∗→condensed products
Where AB*was the intermediate state of the liquefaction of corn-stalk in polyhydric alcohols.
In fact,the formation of intermediate state was so rapid that there existed in equilibrium with the reactants at all the reac-tion time.It has not been fully understood how it was formed, but the probability of the occurrence of intermediate state could be estimated by Eyring equation,which described the relationship between apparent reaction rate constant and apparent activation free enthalpy( G )as showed in equation below(Acemioglu and Alma,2002;Alma and Acemioglu,2004):
k =
k B T
h
·e− G /RT(7)
where k was the apparent reaction rate constant(S−1),k B was the Boltzmann constant(1.381×10−23J K−1),and h was the Planck constant(6.626×10−34J S).
In addition,the apparent activation enthalpy( H )and appar-ent activation entropy( S )were calculated from the following
Table1
Apparent reaction rate constants and apparent reaction orders under different temperatures.
Temperature(◦C)Linear equation Apparent reaction rate constant k ×10−4(S−1)Apparent reaction order(n)R2
130y=−8.3+2.4x 2.6 2.40.87 150y=−7.0+2.4x9.1 2.40.94 170y=−6.7+2.2x12.8 2.20.92 190y=−5.2+2.6x54.1 2.60.84
352Y.Yan et al./Industrial Crops and Products32 (2010) 349–352
Table2
Apparent activation free enthalpy( G ),apparent activation enthalpy( H ),and
apparent activation entropy( S )of the liquefaction of cornstalk in polyhydric
alcohols under different temperatures.
Temperature(◦C) G (kJ mol−1) H (kJ mol−1)− S (J mol−1K−1)
130127.466.9150.2
150129.566.5148.8
170134.566.2154.2
190135.265.9149.7
equations,respectively:
H =E −2RT(8)
and
S = H − G
T
(9)
The values of apparent activation free enthalpy( G ),activation enthalpy( H ),and activation entropy( S )of cornstalk alcoholy-sis under different reaction temperatures are listed in Table2.The apparent activation free enthalpy( G )for the liquefaction reac-tion went up steadily with the increase of reactio
n temperature,but the increasing extents were low.From Table2,the fact that G has a higher positive value of131.6kJ mol−1on average demonstrated that the activated complexes were very unstable,and the second step was likely to be the rate-controlling step.As a result,the major-ity of degraded cornstalk components reacted each other,resulting in condensed products.
It can also be drawn from Table2that the apparent acti-vation enthalpy( H )was partially influenced by the reaction temperature.A20◦C increase in reaction temperature resulted in a0.3–0.4kJ mol−1decrease in H ,which indicated the cornstalk alcoholysis process was dominantly an endothermic reaction.
5.Conclusions
Cornstalk powders could be successfully liquefied in polyhydric alcohols in the presence of sulfuric acid as catalyst at different reac-tion temperatures,and the typical liquefaction kinetic parameters were studied.Through kinetic analysis,the study presented the following postulations.
Cornstalk alcoholysis in polyhydric alcohol was a multistage reaction,and the liquefaction reaction was of complex process. Increase in reaction temperature was found to increase the appar-ent reaction rate constant.However,the process has a negative effect because of promoting the re-conde
nsation reaction with the increase of reaction temperature.As a result,the maximum lique-faction extent of cornstalk could not be improved significantly by an increase in reaction temperature.
According to Arrhenius equation,the apparent activation energy (E )was found to be73.6kJ mol−1and the apparent frequency factor(A )was8.8×105S−1when the liquid ratio was10/3.Appar-ent activation free enthalpy( G ),activation enthalpy( H ),and activation entropy( S )of cornstalk alcoholysis slightly changed with temperature.Furthermore,the results of apparent activation enthalpy( H )indicated that the liquefaction of cornstalk in poly-hydric alcohols was of endothermic process dominantly.
Acknowledgments
This study was supported by contract grant:Scientific Research Project of Hubei Provincial Department of Education of China(No. Q20102709).References
Acemioglu,B.,Alma,M.H.,2002.Kinetics of wood phenolysis in the presence of HCl as catalyst.J.Appl.Polym.Sci.85,1098–1103.
Alma,M.H.,Acemioglu,B.,2004.A kinetic study of sulfuric acid catalyzed liquefac-tion of wood into phenol.Chem.Eng.Commun.190,968–980.
Alma,M.H.,Basturk,M.A.,2006.Liquefaction of grapevine cane waste and its application to phenol–formaldehyde type adhesive.Ind.Crop.Prod.24,171–176.
Chio,C.H.,Mathews,A.P.,1996.Two-step acid hydrolysis process kinetics in the saccharification of low-grade biomass.1.Experimental studies on the formation and degradation of sugars.Bioresour.Technol.58,101–106.
Kurimoto,Y.,Doi,S.,Tamura,Y.,1999.Species effects on wood liquefaction in poly-hydric alcohols.Holzforschung53,617–622.
Kurimoto,Y.,Takeda,M.,Koizumi,S.,Yamauchi,S.,Dio,S.,Tamura,Y.,2000.Mechan-ical properties of the polyurethanefilms prepared from liquefied wood with polymeric MDI.Bioresour.Technol.74,151–157.
Kurimoto,Y.,Takeda,M.,Dio,S.,Tamura,Y.,Ono,H.,2001.Network structures and thermal properties of polyurethanefilms prepared from liquefied wood.
Bioresour.Technol.77,33–40.
Lin,L.Z.,Yoshioka,M.,Yao,Y.G.,Shiraishi,N.,1995.Preparation and properties of phenolated wood/phenol/formaldehyde cocondensed resin.J.Appl.Polym.Sci.
手冢治虫怎么读
58,1297–1304.
Lin,L.Z.,Yao,Y.G.,Yoshioka,M.,Shiraishi,N.,1997a.Liquefaction mechanism of lignin in the presence of phenol at elevated temperature without catalysts.Study on-o-4lignin model compound.I.Structural characterization of the reaction products.Holzforschung51,316–324.
Lin,L.Z.,Yoshioka,M.,Yao,Y.G.,Shiraishi,N.,1997b.Liquefaction mechanism of lignin in the presence of phenol at elevated temperature without catalysts.
Study on-o-4lignin model compound.II.Reaction pathway.Holzforschung 51,325–332.
Lin,L.Z.,Yoshioka,M.,Yao,Y.G.,Shiraishi,N.,1997c.Liquefaction mechanism of lignin in the presence of phenol at elevated temperature without catalysts.
Study on-o-4lignin model compound.III.Multi-condensation.Holzforschung 51,333–337.
Lin,L.Z.,Yao,Y.G.,Shiraishi,N.,2001a.Liquefaction mechanism of-o-4lignin model compound in the presence of phenol under acid catalysts.Part1.Identification of the reaction products.Holzforschung55,617–624.
Lin,L.Z.,Nakagame,S.,Yao,Y.G.,Yoshioka,M.,Shiraishi,N.,2001b.Liquefaction mechanism of-o-4lignin model compound in the presence of phenol under acid catalysts.Part 2.Reaction behavior and pathways.Holzforschung55, 625–630.
Nakano,T.,1994.Mechanism of thermoplasticity for chemically-modified wood.
Holzforschung48,318–324.
Pu,S.,Shiraishi,N.,1993.Liquefaction of wood without a catalyst.I.Time course of wood liquefaction with phenols and effects of wood/phenol ratios.Mokuzai Gakkaishi39,446–452.
Sharma,A.,Rao,T.R.,1999.Kinetics of pyrolysis of rice husk.Bioresour.Technol.67, 53–59.
Sun,Z.J.,Sun,Y.M.,2006.Situation and development of agricultural residues as energy resource utilization in rural areas in China.Rev.China Agric.Sci.Technol.
8,6–13.
Yamada,T.,Ono,H.,Ohara,S.,Yamaguchi,A.,1996.Characterization of the products resulting from direct liquefaction of cellulose.I.Identification of intermediates and the relevant mechanism in direct phenol liquefaction of cellulose in the presence of water.Mokuzai Gakkaishi42,1098–1104.
Yamada,T.,Ono,H.,1999.Rapid liquefaction of lignocellulosic waste by using ethy-lene carbonate.Bioresour.Technol.70,61–67.
Yamada,T.,Ono,H.,2001.Characterization of the products resulting from ethylene glycol liquefaction of cellulose.J.Wood Sci.47,458–464.
Yan,Y.B.,Pang,H.,Yang,X.X.,Zhang,R.L.,Liao,B.,2008.Preparation and character-ization of water-blown polyurethane foams from liquefied cornstalk polyol.J.
Appl.Polym.Sci.110,1099–1111.
Yan,Y.B.,Xu,J.W.,Pang,H.,Zhang,R.L.,Liao,B.,2009.Thermal decomposition and kinetics of rigid polyurethane foams derived from sugarcane bagasse.J.Wuhan Univ.Technol.Mater.Sci.Ed.24,776–780.
Yao,Y.G.,Yoshioka,M.,Shiraishi,N.,1993.Combined liquefaction of wood and starch in a polyethylene glycol/glycerine blended solvent.Mokuzai Gakkaishi 39,930–938.
Yao,Y.G.,Yoshioka,M.,Shiraishi,N.,1994.Soluble properties of liquefied biomass prepared in organic solvents.I.The soluble behavior of liquefied biomass in various diluents.Mokuzai Gakkaishi40,176–1
84.
Yao,Y.G.,Yoshioka,M.,Shiraishi,N.,1995.Rigid polyurethane foams from com-bined liquefaction mixtures of wood and starch.Mokuzai Gakkaishi41,659–668.
Zhang,Y.C.,Ikeda,A.,Hori,N.,Takemura,A.,Ono,H.,Yamada,T.,2006.Characteriza-tion of liquefied product from cellulose with phenol in the presence of sulfuric acid.Bioresour.Technol.97,313–321.
豫公网安备41160202000603
站长QQ:729038198
关于我们
投诉建议