全 文 ：№.5　　　　　　　　　　　　　　　 　　　　陕西科技大学学报　　　　　　　　　　　　　　　　　　Oct.2007
Vol.25 　　　　　　JOURNAL OF SH AANXI UNIVERSIT Y OF SCIENCE &T ECHNOLOGY　　　　　　·1·
＊　文章编号:1000-5811(2007)05-0001-05
DIRECTLY DELIGNIFYING AUTO-CATALYZED
ETHANOL WHEAT STRAW PULP WITH OZONE
XU Yong-jian , PU Wen-juan , ZHANG Mei-yun
(Schoo l of Pape rmaking Eng ineering , Shaanxi Univ ersity o f Science &Techno log y , Shaanxi P ro vince Key Lab
of Pampering Technolo gy and Specialty Paper , Xi′an 710021 , China)
Abstract:This pape r describes the extent to w hich lignin in unw ashed auto-catalyzed ethanol
w heat st raw pulp is removed directly by ozone , based on kappa number analy ses.For com-
parison , ozone bleaching OP pulp w as also studied.The results show that lignin precipitates
on the w ashed pulp fiber surfaces in a heterogeneous and sphe rical w ay and tha t lignin par ti-
cle can be seen using light micro scopy.The lignin remaining in the unw ashed pulp w as effec-
tively removed direct ly by ozone , and the kappa number dramatically decreases f rom 128 to
34.This is much more than that of the OP pulp bleached w ith ozone , which depends on the
deox idization substance in ethanol pulp , the lignin-adso rbed mo rpholog y , and the location of
the residual lignin.New ideas and technolog ie s w ere int roduced concerning the production of
auto-cataly zed ethano l w hea t st raw pulp w ith comparable kappa number.
Key words:o zone;delignification;kappa number
CLC Number:TS745　　　Document Code:A
0　Introduction
O rgano solv pulping technolo gy aim s at the environmental concerns related to sulfur emission , and i t
has been found to be sui table for seve ral w ood species wi th a bro ad range o f o rg anic solvents.Ethanol al-
cohol is the preferable o rg anic solvent , which can dissolve lignin molecules wi th slight degradat ion.Eth-
anol pulping technolo gy has at t racted many scho lars f rom Japan , America , Russia , Canada and China ,
e tc.because of i ts advantages including lower co st , better st reng th , lower po llution , and good bleacha-
bility compared w ith the conventional pulping technolog y.However , there sti ll remain some obstacles
that rest rain the development of this technology and are required to be elucidated.Firstly , the kappa
number of ethanol pulp is highe r than that of conventional bleachable chemical pulps , but ethano l pulp
show s a good bleachability ;secondly , compared w ith conventional chemical pulps , the adso rption of lig-
nin and hemicellulose is obvious based on lab studies conce rning ethanol pulping and w ashing w hich are
dif ferent from K raf t pulping〔1-5〕 .In other wo rds , ethanol-pulping techno logy should be improved in or-
der to produce ethanol pulp w ith comparable kappa number.
TCF is a development trend of bleaching.Ozone is a particular TCF bleaching chemical〔6〕 , which
takes part in a react ion in cationic form under acidic conditions.It s poo r selectivi ty is responsible fo r lig-
nin and carbohydrate oxidation , and cel lulo se fibers w ith low st reng th and viscosi ty.Measures must be
taken to prohibi t more carbohydrates from deg radation.One effect ive method is to add some chemicals ,
and ethanol alcohol could act as this job.The adsorbed lignin on ethano l pulp f ibers may cause cellulose
to become encompassed , which ef fectively protects carbohydrates during o zone delignification.Acco rd-
ingly , the goal o f this paper w as to study the ef fect of adsorbed lignin on ozone deligni ficat ion , and of o-
zone delignification on kappa number.Compared to ozone-bleached pulp , te sts w ere conducted to analyze
＊ 收稿日期:2006-06-22
作者简介:徐永建(1970-),男 ,陕西省西安市人,副教授 ,在读博士生 ,研究方向:低污染/溶剂制浆技术
基金项目:国家自然科学基金项目“非木材料纤维乙醇法制浆区域化学行为及表面木素的研究 , 20577032”
陕西科技大学学报 第 25 卷
the ef fect on the decrease in kappa number af ter OP sequence.
1　Experimental
1.1　Materials
Wheat st raw , o rig inated f rom Liquan County , Shannxi Province , was cut into 20 ～ 30 mm in
leng th.
1.2　Equipment
Oil bath is made o f gly cerine loaded in a ro tary elect ro-thermal 15 L-digester.Wheat st raw w as
charged in 4 1.0 L-stainless-tubes , and then placed into the oi l bath to gether to cook.XF-3 ozone gener-
a to r made in Shanghai w as used to produce o zone.ZQYC (oil-press machine)made in Shannxi U niversi-
ty of Science &Technolog y w as ut ilized for dew atering the pulp.Light micro scope made in M otec Com-
pany w as employed to observe pulp fibers.
1.3　Pulping
Pulp w as prepared under the cooking condit ion〔2〕 , and then unw ashed pulp w as direct ly condensed
wi th the oil-press machine to 35%～ 40%dryness.Finally , the pulp w as completely f luf fed using a fo od
pro cessor fo r ozone delignif icat ion.
1.4　Ozone yield
The amount of ozone w as measured using the following procedure:20 mL KI(10 moL/ L)was add-
ed to 500 mL gaseous-adso rbed bo t tle , and then diluted 10 times.After dilution , 5 mL H 2SO4(2 moL/
L)was added.2 L ozone entered into the bo tt le at a rate of 1 L/min , whereupon the solution was ti t ra-
ted by 0.2 moL/ L Na2S2O 3 , and 2 drops of starch indicator w ere added to determine the end o f tit ration
reaction.
Ozone concentration (CZ )was calculated w ith the fo llow ing equation:
CZ =NV ·48·100/(2·2·100)
　　Where N is Na2S2O 3 concentration in moL/L and V is ti trated volume of Na2S2O 3 in milliliter.
1.5　Ozone delignification
Unw ashed ethanol w heat st raw pulp(10 g)was dew atered to 35%～ 40%dryness w ith the oil press
machine.Without pre-acidif icat ion , the high-consistency pulp w as fully f luf fed in a fo od processo r w ith a
dull plastic blade.The f luffed pulp w as t ransferred to a 200 mL multiporous w ashing bo t tle fo r delignifi-
cation.Ozone w as introduced in gaseous phase in carrier O 2 through a tube that reached to the bo ttom o f
the bo t tle.The bot tle w as agitated on a w rist-action shake r during o zonation to provide mixing.After o-
zone t reatment , the pulp w as removed from the bot tle , brought immediately to pH 11 wi th NaOH , and
then w ashed w ith ethanol-water follow ed by w ater to neutrality.
1.6　Calculation o f decrease rate in kappa number
Decrease rate in kappa number w as calcula ted using the fo llow ing formula:
R =[(k1 -k2)/k1] ·100%
　　Where R is the decrease ra te in kappa number;k1 i s the kappa number o f the untreated pulp;k2 is
the kappa number of the pulp af ter delignif ication.
2　Results and Discussion
2.1　Lignin-adso rbed in ethano l w heat st raw pulp
High kappa number of ethano l pulp has been emphatical ly considered , which leaves lignin dist ribu-
tion in fibers to be dete rmined.The one-stage w ashed ethano l w heat st raw pulp f ibers w ere observed u-
sing light microscopy af ter stained by Herzberg dyeing agent.Fo r comparison , soda-AQ wheat st raw
pulp fibers w ere also imaged , and thei r image s are show n in Fig.1 and Fig.2.It is obvious that lignin lo-
cates on the fibe r surfaces as granules , as show n in Fig.1 , while soda-AQ pulp fiber surfaces are
smooth , as show n in Fig.2.Resea rch reported that lignin w as adso rbed on kraft and soda pulp fibers;
however adso rbed lignin canno t be detected under the view of light microscope.Some literature has re-
vealed that lignin exists as g elatinous g ranules during the ethanol cooking process , which proves that in-
teraction betw een liquor and lignin during ethanol pulping w as great ly dif ferent f rom that o f conventional
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第 5 期 徐永建等:乙醇麦草浆洗涤前后臭氧脱木素菜对比研究
chemical pulping.Lignin precipi tates w ithout ef fectively w ashing o r separating w aste liquo r f rom pulp ,
as ethano l concentration is low ered due to the addit ion of w ate r.O n the o ther hand , the cleavage o fα-ar-
y l ether o r α-alky l ether linkage in the pheno lic lignin occurs during alkaline pulping , and β-aryl ether
bond can also be broken when a ttacked by OH- , o r especially by SH -.Consequently , lignin macromol-
ecules are broken into small pieces and disso lved into black liquo r〔7〕 .However , only ethano l alcohol and
w ater are used in ethanol pulping to dissolve lignin instead o f deg rading st rong ly as in alkaline puling.
Ethano l lignin has good solubi li ty in an ethanol wa ter solution but no t in pure w ater.The increase in a-
cidity is found in cooking sy stem during pulping , based on chemical research on the ethanol pulping
mechanism〔2 , 9〕 , and lignin condensation could take place at a low pH condit ion.Furthermo re , once the
condensation occurred , lig nin could no t dif fuse into e thano l-water phase.Cooking and w ashing w ere car-
ried out at 195℃ and 145℃, respect ively.T here w as a quenching cooling process af ter cooking and
w ashing due to high pressure before pulp w as moved out of the stainless tubes.During the process , dis-
solved lignin could precipi tate/adso rb on the fiber surfaces w hen temperature and ethanol concentration
were reduced.For tunately , hemicellulose hydroly zed during the cooking , and many micropo res emerged
in the cell w all , which w as responsible fo r easier lignin diffusion.During quenching coo ling , lignin g ran-
ules moved into cell w al l through micropores o r by adsorbing onto fibe rs due to the decrease in lignin sol-
ubi li ty.Washing temperature is low er than cooking temperature;in turn that lignin solubi li ty decrease ,
which makes lignin dissolve dif ficul tly .After pulp being w ashed tw o times w ith ethanol-water , follow ed
by w ater w ashing stage , the result w as that lignin could not be effectively separated f rom pulp but in-
stead deposited on the fiber surfaces.
　　Fig.1　Ethanol wheat straw pulp　　　Fig.2　Soda-AQwheat straw pulp(Objective lens=100)
2.2　Effect o f ozone delignification on the kappa number of unwashed pulp
Ozone is a kind of bleaching chemical w ith poo r selectivi ty , and it strong ly and simultaneously re-
acts w ith lignin and carbohydrate.The react ion occurs rapidly at the interface be tw een gaseous ozone
and so lid lignin in cellulo se f ibers , but the t ranspor t of ozone to the fiber surfaces is cont rol led by gas-
phase convection and dif fusion.In addi tion , gaseous pre ssure and solid dispersibi li ty cont rols the gas-
solid react ion〔6〕 , so it w as evident that lignin morpho logy as w ell as it s dist ribut ion inf luences the ozone
dif fusion rate and delignification rate.These facto rs also have an important influence on the react ion:as
stated above , lig nin w as adsorbed on fiber surfaces of the ethano l w heat st raw pulp , and more ozone re-
acted w ith lignin loca ted outermost o f the f iber surface instead of carbohydrate.
Howeve r , ozone is ve ry reactive and i ts stability decreases w ith increasing pH value.A prominent
characteristic o f auto-cataly zed e thano l pulping is tha t the increase in acidi ty could occur during cooking
because o f acety l hydroly sis.The pH value in the sy stem is low er than 7 af ter cooking , even down to
3.5〔2〕 .Acco rding to literature〔1 , 2 , 5〕 , ethano l pulp requires w ashing w ith ethanol-water.Gene rally , i t
w as necessary to w ash ethanol pulp wi th w ater to remove the residual ethano l and ace tic acid.While o-
zone dilignification could proceed unde r acidic conditions , the residual acetic acid in pulp made acidi ty op-
timum fo r o zone deligni fica tion , the refore there is no requirement to adjust acidity.Conve rsely , some
studies indicate that ozone bleaching routinely used acetic acid to adjust the pH value , and ethanol acted
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陕西科技大学学报 第 25 卷
i s used as a reactive agent.Given these results the re are tw o advantages:when pulp w as t reated direct ly
by ozone after cooking , one is to adjust acidi ty wi thout acid , the o ther is that the residual ethanol acted
as reactive agent for ozone delignif ication.The purpose of this pape r is to directly remove lignin re-
mained in w heat st raw pulp by ozone fol lowed by ethanol-water w ashing , and compare this data w ith
w heat st raw pulp w ashed w ith aqueous ethanol and w ater.The resul ts show that the kappa number o f
e thano l w heat st raw pulp is higher , even though the pulp is w ashed at 140℃with 70%(v/v)ethano l.In
order to decrease kappa number , unw ashed pulp w as treated direct ly by ozone , and the resul t may be
seen in Tab.1.It can be seen that kappa number decreases dramat ically dow n to 34 af ter the pulp w as
deligni fied direct ly by ozone.The decrease rate in kappa number is 73%, which show s that kappa num-
ber could be reduced when unw ashed e thano l pulp is delignif ied direct ly by ozone fo llow ed w ith ethano l-
water w ashing.However , the pulp′s kappa number changes indistinctively as the w ashing stages in-
crease g radually af te r being t reated direct ly by ozone.This suggests that most ozonized residual lignin is
deg raded , which could be separated f rom pulp only by w ashing wi th w ater.
Tab.1　The results of ethanol pulp delignification by ozone
stag es kappa numbe r after treating decrease rate in kappa number/ % no te
1
2
3
4
34.8
34.2
34.1
34.0
73.02
73.49
73.57
73.64
Wash w ith ethano l-w ater
af te r delignified by o zone
　　No te:Ethanol concentration is 50%～ 60%, w ashing tempera tur e is 140℃, ozone dosage is 0.5%, kappa number of
unw ashed pulp is 129
2.3　Ozone bleaching OP pulp
The oxygen-diligni fied pulp(OP)was bleached by ozone under condit ions of pH 2.5 , pulp consis-
tency 45%, and room tempe rature.Tests were perfo rmed to study the influence of v arious o zone dosa-
ges on the brightne ss and the kappa number , and the results are show n in Fig.3.As can be seen from
Fig.3 , the kappa number and the brightness markedly change when o zone dosage s vary f rom 0.2% to
0.5%, but they reach a plateau f rom 0.5% to 0.8%.On the othe r hand , the decrease in pulp yield oc-
curs w ith increasing o zone dosage , which indicates that serious damage to cellulose f ibers could occur af-
ter bleached by ozone.As stated above , ozone is a poo rly selective bleaching agent , so w hen the residual
lignin content in pulp w as low , whe reupon carbohydrate lo st the protection f rom lignin.
Fig.3　The effect of ozone dosage on bleaching
(Note:OP pulp bright-nes s:58% SBD;kappa:9.7)
2.4　Comparison o f tw o kinds of pulps
Unwashed pulp and OP pulp w ere delignified by o-
zone , and the resul ts are show n in Tab.2.It is apparent
that the decrease rate in kappa number o f the former is
higher than that of the lat ter.There are tw o reasons for
this:f irst , ethanol pulp could po ssess o ther reducible
substances o ther than lignin;second , lignin adsorption
during ethano l pulping and washing could occur on f iber
surface s , which is responsible for the lignin enrichment
on fiber surfaces.As fo r lignin-adso rbed content , lignin
distribution , lig nin morpho logy and chem ical properties
of fiber surface s , extensive research should be carried
out.It is assumed that ozone could react to o ther reducible substances in addi tion to lignin in unw ashed
e thano l pulp , which is the reason that kappa numbe r is st rongly decreased;while the lat ter pulp is delig-
nified by oxygen enhanced w ith hydro gen pero xide , so it w as hard to remove the residual lignin.
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第 5 期 徐永建等:乙醇麦草浆洗涤前后臭氧脱木素菜对比研究
Tab.2　Compare the results of different ethanol pulp treated by ozone
pulp
kappa numbe r
befo re trea ting
kappa number
after t reating
decrease rate in
kappa numbe r/ %
unw ashed pulp 128 34 73
OP pulp 9.7 3.7 61.9
　　No te:Bleaching conditions:ozone do sage 0.5%, pH value 2.5 , pulp concentra tion 45%, r oom tempera tur e
3　Conclusions
After a quench-coo ling w ashing process , many g ranular lignin part icles located on fiber surfaces o f
e thano l w heat st raw pulp obse rved using light microscopy .Unwashed ethanol pulp w as delignif ied di-
rect ly by ozone , and kappa number dramatically decreases from 128 to 34.The decrease rate in kappa
number of OP pulp t reated by ozone reaches 61.9%, and is low er than that of unw ashed e thanol pulp
t reated direct ly by ozone.
References
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乙醇麦草浆洗涤前后臭氧脱木素的对比研究
徐永建 , 蒲文娟 , 张美云
(1.陕西科技大学造纸工程学院 , 陕西省造纸技术及特种纸品开发重点实验室 , 陕西 西安　710021)
摘　要:本试验主要对未洗乙醇浆直接臭氧脱木素 ,然后再经过乙醇水洗涤后纸浆卡伯值的变
化进行了初步研究 ,并和洗涤后纸浆臭氧处理进行比较.结果表明:未洗乙醇浆直接臭氧脱木
素对降低卡伯值非常有效 ,用 0.5%的臭氧即可将卡伯值从 128降低到 34 ,这对于制取低卡伯
值乙醇浆提出了新的思路和工艺.并与臭氧处理 OP 浆进行了对比 ,初步证明前者卡伯值降低
率大于后者的原因除与乙醇浆中的还原性物质有关外 ,也与吸附木素形态及木素在纤维中的
存在位置有关.
关键词:臭氧;脱木素;卡伯值
中图分类号:TS745　　　文献标识码:A
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