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8Journal of Siberian Federal University. Chemistry 1 (2010 3) 3-11
УДК 630.863.+663.534
Influence of Preliminary Mechanical Treatments on Acidic Hydrolysis of Aspen Wood
Sergei V. Baryshnikova, Victor I. Sharypova, Boris N. Kuznetsov a,b, Anatoly M. Zhyzhaevaand Yuriy D. Alashkevichc *
a Institute of Chemistry and Chemical Technology SB RAS,
Krasnoyarsk, RUSSIA b Siberian Federal University, Krasnoyarsk, RUSSIA c Siberian State Technological University, Krasnoyarsk, RUSSIA 1
Received 5.03.2010, received in revised form 12.03.2010, accepted 19.03.2010
For the mechanical activation of aspen wood in aqueous medium the cuttery, jet, vibratory rod mills and mechanochemical activator were used. The influence of treatment conditions on wood structure and on activated wood acidic hydrolysis was studied.
It was found that the preliminary mechanical activation on aspen wood increases the yield of easy -hydrolyzed polysaccharides and the rate of their hydrolysis to sugars with 2 % HCl. The higher influence on the reaction ability in hydrolysis process was observed after aspen wood treatment in a planetary activator mill AGO - 2.
Keywords: aspen wood, mechanical treatment, structure, acidic hydrolysis, intensification.
Mechanicalandmechanochemicalprocessing is widely used in technologies of lignocellulosic raw materials conversion to target materials and chemical products. A variety of equipments like machine of knife grinding, jet grinding, vibrating mills, mechanochemical activators of centrifugal and planetary types, cavitational devices and etc. which differ in nature of action on crushed materials was applied with this purpose.
Theoreticalbasisofgrindingprocessoffibrous materials are considered in monograps [1-4]. Milling of wood biomass in aqueous medium is a complicated mechanical process which resulted in
* Corresponding author E-mail address: [email protected]
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the water-fibrous suspension formation. Treatment in disk knife mills can be considered as a set of mechanical and hydrodynamic action on wood biomass which lead to the changes in dispersion of water suspensions and to the disintegration of wood fibers [2]. It is been shown [8], that the destruction and compression of external P and S1 layers of a wood cell, which prevent swelling and fibrillation of fibers take place in the process of knife grinding [5]. Destruction of these layers uncovers bulk structure of a secondary wall of a cell - layer S2, and facilitate the consumption of water. The processes of fibrillation swelling and
plasticization of fibers are started. These factors result in an increasing of fibers external surface and content of hydroxyl groups, which adsorb water [2].
Preliminary treatment of cellulose in knife mills is widely used in industry for production of a paper with required structure and physical properties [6, 7]. It is perspective to apply for this purpose the apparatus of jet grinding in which a stream of suspension is throw out under a pressure from a nozzle to barriers of various configurations (stream-barrier method). During this process a several forces act on fibrous suspension like tangent shearing force, the normal shear arising at pressure of a stream, forces of cavitation phenomena [8, 9]. The ground cellulose has high degree of fibrillation at the minimum shortening of fibers and it is used for production of a paper with high resistance to rupture [9].
Crushing of samples with vibrating mill is occurring at collision of steel cylinders (crushing bodies freely move in a drum) among themselves, and when they strike to a wall. Treatment of lignocellulosic materials with vibrating mills finds wide application in research practice and in industry. Preliminary activation of a larch wood intensifies the process of arabinogalactan isolation [10]. The treatment of aspen, pine, birch wood in a vibrating mill accelerates the process of its sulfoalkylation, which increases solubility of products and viscosity of suspensions on their basis [11]. The grinding of cellulose in vibrating mills increases a speed of cellulose bleaching by 30 % [12]. Activation of lignocellulose by rolling and treatment in a vibrating mill intensifies its degradation to soluble sugars during acidic hydrolysis. The rate of hydrolysis depends on the duration of crushing process [13].
During the mechanochemical activation of wood material with centrifugal and planetary power intense mills, along with crushing process some reactions of biomass degradation and its
interaction with water are initiated [13-15]. At some conditions the reactions, which can be realized only at higher temperature and pressure, can proceed during mechanochemical activation of different kinds of plant materials [13-15].
Mechanochemical treatment intensifies the saccharification of the lignocellulose starchy raw materials, barley, corn [13, 16].
In the present work the influence of different methods of preliminary mechanical treatment of aspen wood on its structure and reaction ability in acidic hydrolysis was investigated.
Experimental
The aspen wood was crushed to particles size less then 4 mm and dried at 100oC till the moisture content was less 0.1 wt.%. Some characteristics of the initial aspen wood are given in Table 1.
The samples of wood were mixed up with necessary quantity of the distilled water and then were treated in different apparatus.
Knife grinding was carried out with a disk mill of type LDM-74 [2] at concentration of wood in water suspension 1.8 wt.% during 30 minutes. The degree of a grinding at these conditions was defined according to Shopper - Rigler method.
Jet grinding was realized with original laboratory installation [2], in which the water suspension containing 1.8 wt % of the wood was threw out of nozzles with diameter 2mm under the pressure of 16 MPa to barrier of special configuration. The speed of suspension stream was 145 m/s. For 15 minutes of work of installation, 30 running cycles were accomplished and the degree of grinding 77 ° ShR was reached.
Mehanochemical activation with tensile energy planetary activator mill AGO-2 was carried out at the acceleration developed by grinding bodies 60 g during 30 minutes. Concentration of wood in water suspension was 8 wt. %.
Vibrating grinding was accomplished with vibrating installation SVU-2 during 15 minutes 4 -
Table 1. Some characteristics of the aspen wood
Wood composition, wt. % Ash content, wt. %
Cellulose Lignin Hemicellulose Water-soluble substances Resins Extractive substances
46.3 20.4 24.1 3.6 0.9 4.3 0.5
Table 2. Content of solid and water-soluble products in the initial and mechanically treated samples of aspen wood
Sample № Method of wood treatment Solid lignocellulose material, wt.% Water solub Total * le products, wt.% Reducing products
1 Without mechanical treatment 96,4 3,6 0,3
2 Vibrating grinding 93,9 6,1 0,5
3 Knife grinding 89,2 10,8 2,5
4 Jet grinding 88,8 11,2 4,6
5 Mechanochemical activation 87,2 12,8 5,7
* The total yield of water soluble products of wood was calculated as a difference of weights of the loaded initial aspen wood and the solid product after wood treatment.
for a grinding degree 77 ° ShR. Concentration of wood in water suspension was 8 wt.%
After the mechanical treatment the activated samples were filtered, the residue on the filter was washed with distilled water and dried at 100 °C. The content of easily hydrolysed polysaccharides (EHPS) in a solid product of the wood treatment was determined by hydrolysis in 2 % HCI according to standart method [17]. Contents of hardly hydrolysed polysaccharides (HHPS) and Klason lignin were determined by standard techniques [17, 18]. The content of reducing substances in the water fraction after filtering of suspension of the treated wood was determined according to [17].
Samples of initial and mechanically treated wood were investigated with scanning microscope TM-1000 «Hitachi».
Results and discussion
Treatment of wood samples by all studied methods leads to increase of the yield of water-soluble products (Table 2). The maximum yield of these products (12.8 wt. %, including reducing substances 5.7 wt. %) was observed
after mehanochemical treatment of wood in AGO- 2. Yields of water-soluble products and reducing substances from mechanochemically treated wood are higher, accordingly by 3.6 times and 19 times as compared to initial wood.
Results of scanning electron microscopy study show that the variations in wood structure depend on the type of treatment (Fig. 1). Sample of an initial aspen wood (Fig. 1(1)) has the insignificant deformation changes when wood was desintegrated to particles less 4 mm. Traces of chips breaking and insignificant deformation of the top of cellular layer were visible. In general, the initial structure of wood was remained. After grinding in a vibrating mill the deep longitudinal splitting of a wood material was observed. Lumens of large vessels and the open and perforated ends of smaller pores got imperceptible, that specifies in squashing action of a vibrating mill (Fig. 1 (2)).
Treatment of the aspen wood by a method «stream-barrier» (Fig. 2(3)) and knife grinding (absent in figure) results in more essential changes in the structure of treated wood. The intensive fibrillation of large bunches of a wood 5 -
Fig.1. Scanning microscope images of the samples of aspen wood: 1 - initial, 2 - after vibrating grinding
fibers was observed, along with the leaching of some part of lignin and hemicelluloses. The most considerable changes in structure of wood occur after its treatment in mill-activator AGO-2. The considerable destruction and deformation of walls of large vessels, rupture and deformation of fibers and tracheid, separate unstructured fragments and fibrillation of separate bunches of fibers were observed. Besides, the considerable leaching of lignin and hemicelluloses from intercellular space (Fig. 2(4)) took place.
Mechanical treatments of the wood influence significantly on composition of the wood samples. Figure 3 shows that the all used methods of treatment increase the amount of easily hydrolyzed polysaccharides and decrease the content of highly hydrolyzed polysaccharides. These results denote the partial destruction of cellulose. Simultaneously the amount of residual lignin was considerably decreased. The obtained data correspond to results of papers [12, 13, 15] in which it was shown that the mechanochemical treatment of cellulose accelerates its hydrolysis.
In the present work a greatest effect was observed after mechanochemical activations of wood in AGO - 2. In this case the yield of easily hydrolyzed substances from treated wood was by 1.7 times higher in the comparison with initial wood.
The treatment of wood not only increases the yield of easy hydrolyzed polysacharides but also the rate of their hydrolysis to sugars with 2 % hydrochloric acid (Fig.4). The highest rate of hydrolysis reaction was observed after wood activation in AGO-2 (sample 5, Fig.4). For samples of activated wood 2, 3, 5 the maximal rates of hydrolysis were observed at the first hour of hydrolysis process. For sample 1 of non-treated wood and sample 4 the maximal rates were displaced towards the second hour of hydrolysis process.
Conclusions
The preliminary treatment of aspen wood in aqueous medium with the use of knife, jet, vibrating mills and mechanochemical activator results in the deformation and
60
50
1 2 3 4 5
number of sample
Fig. 3. Composition of aspen wood hydrolysis products: a - residual lignin; 6 - EHPS, (acid hydrolysis in 2 % HCl, 10 hours); b - HHPS, c - water-soluble not reduced substances (1, 2, 3, 4, 5 - numbers of samples are given according to Table 1)
Fig. 4. Dynamics of sugars concentration changes during the hydrolysis of aspen wood by 2 % HCl (1, 2, 3, 4, 5 - numbers of samples are given according to Table 1)
partial destruction of the basic mechanical tissue of wood, with simultaneous dispersion of its substructure. Under the action of mechanochemical activation a deformation, splitting and destruction of cellular walls, partial fibrillation of bunches of fibers as well as leaching of lignin and hemicelluloses were observed.
The used methods of mechanical activation of aspen wood increase the yield of easily hydrolyzed substances and the rate of their hydrolysis to sugars in the presence of 2 % HCl. The maximal yield of easily hydrolyzed substances (by 1.7 times higher as compared to non-activated wood) was observed after wood treatment in planetary type mill AGO-2.
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Влияние различных механических обработок древесины осины
на ее реакционную способность в кислотном гидролизе
С.В. Барышников3, В.И. Шарыпов1, Б.Н. Кузнецов8 5. А.М. Жижаева, Ю.Д. Алашкевичв,
а Институт химии и химической технологии СО РАН, Россия 660049, Красноярск, ул. К. Маркса, 42 б Сибирский федеральный университет, Россия 660041, Красноярск, пр. Свободный, 79 в Сибирский государственный технологический университет,
Россия 660049, Красноярск, пр. Мира, 82
Изучено влияние механической обработки древесины осины в аппаратах ножевого и струйного, вибрационного помолов и механохимического активирования в водной среде на ее строение и реакционную способность в процессе кислотного гидролиза.
Показано, что используемые способы воздействия на древесину приводят к увеличению выхода легкогидролизуемых веществ и скорости их гидролиза в 2 % HCl. Наибольшее влияние оказывает механохимическая обработка древесины в мельнице-активаторе центробежно -планетарного типа АГО - 2.
Ключевые слова: древесина осины, механическая обработка, структура, кислотный гидролиз, интенсификация.
