Transcript Kinetics of a solid-liquid extraction of water

Kinetics of a solid-liquid extraction of water-soluble compounds of
Tilia sapwood
Kun-Yung Tsai#, Wen-Ta Chiu and Yuh-Shan Ho*
Taipei Medical University - Wan-Fang Hospital
Introduction
The Tilia sapwood, contains many molecules in particular sugars, lipids, catechic and gallic tanins, polyphenolic compounds, organic acids,
mineral salts, amino acids, vitamins, and essential oils. Tilia has been known for its pharmacological properties and is used in medicines.
The molecules involved in these activities are present in the flowers and sapwood. These compounds are obtained by a succession of
operations, which always begins with a solid-liquid leaching with the accurate solvent. The aim of this study was to determine the influence of
temperature on the extraction of water-soluble compounds of Tilia sapwood in a batch reactor in order to explain the mechanism of the
operation. A method is presented for determining the activation energy of extraction and the initial extraction rate based on a second-order
extraction process. Rate parameters were defined and are used to describe the phenomenon and to predict the weight of aqueous extracted
dry matter of Tilia sapwood.
Methods
Seven hundred ml of deionized water was initially introduced into the reactor and then
heated to the study temperature. An amount of the particles was added to have the
solid/water ratio 0.14 then introduced into the medium, and the mixture was stirred at this
temperature during the study period. The experimental set-up of the process is shown in
Fig. 1. Experiments were carried out with a solids/water weight ratio of 0.14, a particle size
of 0.286 - 0.348 mm, and a stirring speed of 100 rpm at 313, 333, 353, and 363 K.
Figure 1. Experimental set-up of the process
T: Thermal probe
C: Condenser
S: Stirrer
H: Heater
S
C
C T°
Kinetic Model
Tilia sapwood ( s )  water(l ) 
water - soluble compounds ( aq)
T
T
S
A second-order kinetic rate equation can be written as follows:
dCt
2
 k Cs  Ct 
dt
H
where k is the second-order extraction rate constant (L/g min), Cs is the extraction capacity which is the concentration of water-soluble
compounds at saturation (g/L), and Ct is the concentration of water-soluble compounds of Tilia sapwood in the solution at any time, t (min).
A second-order kinetic rate equation linear form:
Figure 1. Plot of water-soluble dry matter of Tilia sapwood versus
time at various temperatures.
1.6
t
1
t


Ct kCs2 Cs
Results
1.4
Table 1. Linearization of the kinetic model of the second-order
leaching at various leaching temperatures of Tilia sapwood by water
1.2
Ct (g/L)
1
T
Cs
k
h
K
g/L
L/g min
g/L min
313
1.17
0.0141
0.0193
0.999
0.6
323
1.31
0.0202
0.0345
0.999
0.4
T = 353K
333
1.38
0.0242
0.0459
0.998
1.43
0.0352
0.0719
0.998
0.2
T = 363K
353
363
1.45
0.0486
0.103
1.000
r
2
T = 313K
0.8
T = 323K
T = 333K
0
0
Figure 2. Predictive model for water-soluble compounds
of Tilia leached at any leaching time and temperature.
1.4
1.2
Ct (g/L)
200
300
Time (min)
400
500
Conclusions
 The kinetics of leaching of water-soluble compounds of the sapwood of Tilia
were based on the assumption of a mechanism of a second-order leaching
that was developed to predict the rate constant of leaching, the saturated
capacity of the leaching, and the initial leaching rate.
1.6
1
 The leaching rate increases with temperature.
0.8
 An activation energy of leaching was evaluated to be 21.9 kJ mol-1 watersoluble compounds with the second-order leaching rate constants.
0.6
0.4
 A saturated leaching capacity was also evaluated with the second-order
leaching rate equation.
0.2
0
310
100
480
320
T (K)
330
340
350
360
120
0
240
360
Time (min)
 A three-dimensional predictive model was developed to evaluate the
capacity of leaching at all times and temperatures of leaching.