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STUDY OF THE CHEMICAL COMPOSITION OF GRAPE STALKS – FEEDSTOCK FOR BIOREFINERY
SÓNIA O. PROZIL , JOANA A. MENDES ‡, DMITRY V. EVTUGUIN , LUÍSA P. CRUZ LOPES ‡
CICECO and Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal ‡ CI&DETS and Department of Environment, Polytechnic Institute of Viseu, 3504-510 Viseu, Portugal
Email: [email protected]
PRODUCTS
Pulp, oils, ethanol, bioplastics,
adhesives, composites, etc.
PROCESSING TECHNOLOGIES
Bio-processes, Chemical processes,
Thermal and Physical processes
Continued to wine
process
1. Introduction
Vineyard culture is widely spread across all Continents, in
which the European Union (EU) represents 60% of the
world production of wine. The treatment of winemaking by-
products is receiving more attention, both to facilitate its
recovery and/or protection of the environment. The wine
industry produces a large amount of by-products which, in
most cases, are not highly valued, and constitute
enormous waste. Grape stalks are an important by-product
of the wine sector. Since this is a by-product of
lignocellulosic nature, renewable character and not
competitive with food and industrial use, grape stalks are
an excellent biomass that fits with biorefinery concept. As
both aiming for a better understanding of grape stalks and
the evaluation of their potential as a source of new
materials are essencial, particularly for the acquisition of
thermomechanical pulp, the general chemical composition
has been evaluated.
FEEDSTOCK
Lignocellulosic material [1]
Figure 1: The integrated grape stalks biorefinery concept.
2. Experimental and Results
Parameters Content (%)
Ashes (Tappi T 211 om-93) 7.0
Extractives
(Tappi T 204 om-88)
2.3
1.0
23.7
Proteins 6.1
Tannins 15.9
Klason Lignin (Tappi T 204 om-88) 17.4
Cellulose Kürscher and Höffer 30.3
Hemicelluloses 21.0
Pulping Conditions
Pulp yeld
% wt.
Residual
Lignin
% wt.*
Alcali active
%
Sulfidity
%
Temperature
ºC
Time
min
20 28 165 120 48.1 33.5
2. Experimental and Results
General chemical composition
Cellulose Characterization
Xylans Characterization Lignin Characterization
Kraft pulping of grape stalks
The cellulose determined using the Kürscher and Höffer
method [2] and was analyzed by X-ray scattering [3].
0
10000
20000
30000
40000
50000
60000
70000
10 15 20 25 30 35 40
2q, deg
Rela
tive i
nte
nsit
y,
a.u
.
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O=93º
c=
10.3
Å
a=7.9
Å
b=8.0 Å
101101
002
002
101101
040Iam
IcrIcr
040
0
10000
20000
30000
40000
50000
60000
70000
10 15 20 25 30 35 40
2q, deg
Rela
tive i
nte
nsit
y,
a.u
.
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O=93º
c=
10.3
Å
a=7.9
Å
b=8.0 Å
101101101
002
002
101101101
040Iam
IcrIcr
040
Figure 3: X-ray scattering diffractogram of cellulose from grape
stalks. Unit Cell Dimensions: a - 7.9 nm; b - 8.0 nm; c - 1.03 nm
and angle γ = 93º. Degree of cristallinity = 75.4%
Polymorph Cellulose I
The xylans were extracted with DMSO from the holocellulose
obtained by deslignification (85 ºC, 30 min, 14% AcOOH) of
the grape stalks with peracetic acid [4]. The isolated xylans
were analysed by 1H NMR in D2O.
Xylans Characterization
ppm (t1)
4.505.00
H3 in X
yl -2
,3 A
c
H1 in M
eG
lcA
H3 in X
yl -3
Ac-2
Glc
A
H3 in X
yl-3
Ac
H1/H
2 in X
yl-2
Ac
H1
in X
yl
Degree of acetylation 0.49
Figure 4: 1H NMR spectrum of expanded
region of anomeric protons of xylan from
grape stalks.
Mw = 19.0 kDa
Lignin Characterization
Lignin content in grape stalks free of extractives, proteins and tannins
was determined by Klason method with 72% H2SO4 (according to Tappi
T 222 om-88) and characterized by 13C CP/MAS NMR.
ppm (t1)050100150200
OCH3
-CH2OH
-CH2- -CH< >CH-O-
=CH-
=C<
=C-O-
COOH >C=O
Figure 5: 13C CP-MAS NMR spectrum of Klason
lignin from grape stalks.
3:71:26
Nitrobenzene oxidation products
H:G:S
Table 3: Results of kraft pulping of grape stalks.
* residual lignin is assessed as acid insoluble residue; acid insoluble residue in initial
grape stalks was 35.4% wt.
Low selectivity in delignification of grape stalks under alkaline conditions.
3. Conclusions 4. References
Acknowledgements
The authors wish to thank Portuguese Foundation for Science and Technology (FCT project PTDC/AGR-AAM/104911/2008) and the
Operation Program of Competitive Factors COMPETE, ref. FCOMP-01-0124-FEDER-008734) for the financial support of this work.
The grape stalks contained a rather significant amount of ash (7.0%) and extractives soluble in hot water (ca 23%).
The cellulose content in grape stalks was relatively low (ca 30%) though an unusually high degree of crystallinity was
detected (75.4%). The heteroxylan was the second most abundant polysaccharide in grape stalks, after cellulose.
The grape stalks lignin is an HGS type with a predominance of G units. This lignin is apparently highly condensed
and structurally associated with other macromolecular components of grape stalks. The kraft pulping of grape stalks
showed serious limitations to obtain well-delignified fibers. This fact was attributed to specific lignin structure and
eventual interaction with other macromolecular components upon kraft pulping.
[1] - Prozil, S.O., Evtuguin, D.V., Cruz Lopes, L.P. Chemical Composition of Grape Stalks of Vitis vinifera L. from Red Grape
Pomaces, Industrial Crops &Products, 2011, doi:10.1016/j.indcrop.2011.06.035.
[2] - Browning, B.L., 1967. Methods in 481 Wood Chemistry, vol. II. John Wiley & Sons, New York, USA, 482 pp. 406–727.B
[3] - Figueiredo, A., Evtuguin, D.V., Saraiva, J., 2010. Effect of high pressure treatment 506 on structure and properties of
cellulose in eucalypt pulps. Cellulose 17, 507 1193–2122.
[4] - Evtuguin, D., Tomás, J., Silva, A., Neto, C. P., Characterization of an acetylated heteroxylan from Eucalyptus globulus
Labill. Carbohydr. Res. 2003, 338 (7), 597-604.
Table I: Chemical composition of grape stalks (% dry material).
Table I presents the grape stalks’ chemical composition and Figure 2 presents the results of sugars’
analysis. Grape stalks are a lignocellulosic material (cellulose – 30.3%; hemicelluloses – 21%; lignin –
17.4%). Taking into account the monosaccharide’s analysis (Figure 2), it can be verified that, after
cellulose, xylans are the second major polysaccharide component present in grape stalks (with around
12%).
Acetone
Dichloromethane
Hot water <0.2%
62.7%
1.7%5.5%
4.9%4.8%
20.4%
Rhamnose Fucose Glucose
Xylose Mannose Galactose
Arabinose
Figure 2: Composition of monosaccharide’s (% wt)
in grape stalks.
SEC
Xyl 57
Xyl-2Ac 14
Xyl-3Ac 19
Xyl-2,3Ac 6
Xyl-3Ac-2GlcAc 4
GlcA 4
Short designation Relative abundance
(per 100 Xylp units)
Table 2: Relative content of acetyl groups
in structural units of xylan from grape stalks.
