Lynne Wong's PhD thesis

More documents

Recommendations

Info

6.5 THE NET ISOSTERIC HEAT OF SORPTION q st , THE TOTAL ISOSTERIC HEAT OF SORPTION Q st AND THE ENTROPY OF SORPTION S d The net isosteric heat of sorption q st is defined as the total heat of sorption Q st in the food or fibre minus the latent heat of vaporisation of water H L , at the system temperature (Tsami et al., 1990). Conventionally, q st is a positive quantity when heat is evolved during adsorption and negative when heat is absorbed during desorption. It is indicative of the intermolecular attractive forces between the sorption sites and water vapour (Wang and Brennan, 1991). The values of the net isosteric heat of sorption q st are obtained from the slopes of ln a w versus 1/T plots by linear regression analysis with the assumption that they are constant over the temperature range studied. According to the differential form of the Clausius Clapeyron equation (Labuza, 1984): ⎡ ⎢ ⎣ d d ( ln aw ) ⎤ qst = − ( 1/ T) ⎥ R ⎦ m (3) where a w is the water activity, T is the Kelvin temperature (K), m is the equilibrium moisture content, q st is the net isosteric heat of sorption (kJ mol -1 ), and R is the universal gas constant (8.314 J mol -1 K -1 ). Since equation (3) holds only for constant moisture content, values of the water activity a w at specified moisture contents need to be evaluated from the best-fit isotherm equation (Hailwood-Horrobin model in this case). In this study the water activity at 18 fixed moisture values (namely 0.01, 0.05, 0.1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30 and 35 g/g db) were calculated. In order to do this, the Hailwood-Horrobin equation: aw m = b + c a w + d( a w ) 2 was written in the form of a quadratic equation: d a 2 w 1 + ( c − ) aw + b = m 0 and solved for a w at the chosen values of m. Only the positive values of a w are taken. This was effected at four temperatures (i.e. 30, 45, 55 and 60 °C) for the same chosen values of the moisture content. For each moisture content, ln a w calculated for the four temperatures are plotted as ordinate against 1/T as 249
abscissa. For each moisture level (18 in all), a straight line was obtained, the slope of which equals -q st /R, from which the net isosteric heat of sorption q st could be calculated at that particular moisture level (Wang and Brennan, 1991). This procedure was repeated for each of the nine cane components of R 570 aged 52 and 36 weeks. This approach assumes that q st is independent of temperature; although this is not always true, it has been accepted as such (Iglesias et al., 1989). The application of this method requires the measurement of sorption isotherms, at no less than three temperatures. The total isosteric heat of sorption Q st , is a measure of the interaction (binding energy) between water vapour and the adsorbent material; in this work, sugar cane fibre. It is the sum of the net isosteric heat of sorption q st and the latent heat of vaporisation of pure water, H L : Q st = q st + H L The latent heat of vaporisation of pure water H L at various temperatures can be interpolated from Table 5.3. Thus, H L values at 30, 45, 55 and 60 °C are 43.47, 44.53, 46.03 and 47.01 kJ mol -1 respectively, but the average value of H L for the temperature range may be used (Sanchez et al., 1997), and can be taken as constant at 43 kJ mol -1 . The relationship between the total isosteric heat of sorption Q st and the entropy of sorption S d is given by (Aguerre et al.,1986): - ln a w = Qst S − d (4) RT R where a w is the water activity, Q st is the total isosteric heat of sorption (kJ mol -1 ), R is the universal gas constant (J mol -1 K -1 ), T is the Kelvin temperature (K) and S d is the entropy of sorption (J mol -1 K -1 ). The entropy of sorption S d is proportional to the number of available sorption sites at a specific energy level (Madamba et al., 1996). If ln a w is plotted against 1/T, for a constant moisture content, the intercept yields S d /R. An example of a Clausius Clapeyron plot for stalk fibre aged 52 weeks is shown in Fig 6.5. The calculated net isosteric heat of sorption q st is plotted against moisture level for all nine cane components of R 570 aged 52 and 36 weeks in Fig 6.6, and the corresponding entropy of sorption is shown in Fig 6.7. 250
Page 1 and 2:
THE BRIX-FREE WATER CAPACITY AND SO
Page 3 and 4:
dissolved and hydrated waters, and
Page 5 and 6:
ACKNOWLEDGEMENTS I am particularly
Page 7 and 8:
Page 1.5 THE DELETERIOUS EFFECTS OF
Page 9 and 10:
Page 2.2 THE PHENOMENON OF BRIX-FRE
Page 11 and 12:
Page 3.4.3.3 Cane tops 83 3.4.4 Cha
Page 13 and 14:
4.3.3 Temperature at which Brix-fre
Page 15 and 16:
4.6.1 Materials 143 4.6.1.1 Samples
Page 17 and 18:
CHAPTER 6. PROPERTIES OF THE SORBED
Page 19 and 20:
APPENDIX 3. CALCULATIONS LEADING TO
Page 21 and 22:
LIST OF FIGURES Page Figure 1.1. Fi
Page 23 and 24:
Figure 3.1. Glucose and fructose an
Page 25 and 26:
Figure 5.11. Residual plots for the
Page 27 and 28:
total adsorbed water (m) and the pr
Page 29 and 30:
Table 2.18. Moisture content in sug
Page 31 and 32:
Page Table 4.4. Results of the dete
Page 33 and 34:
Page Table 4.24. Analysis of varian
Page 35 and 36:
Page Table 5.13. Table 5.14. Equili
Page 37 and 38:
Table 6.3. Heat of sorption of the
Page 39 and 40:
GLOSSARY OF TERMS Absorption is the
Page 41 and 42:
Filterability of a raw sugar is mea
Page 43 and 44:
Sorption is the generic term used w
Page 45 and 46:
LIST OF MAIN SYMBOLS Symbol Descrip
Page 47 and 48:
s c s Slope of Caurie I isotherm pl
Page 49 and 50:
number of 255, and cane land covere
Page 51 and 52:
Nouvelle Mon In Trésor ustrie and
Page 53 and 54:
Figure 1.3. Cane sampling by core s
Page 55 and 56:
In Mauritius, most of the sugar fac
Page 57 and 58:
are: cane tops, dry and green leave
Page 59 and 60:
1.4 TRENDS IN CANE QUALITY RECEIVED
Page 61 and 62:
campaign was launched to encourage
Page 63 and 64:
The level of extraneous matter in c
Page 65 and 66:
In Australia (Cargill, 1976), cane
Page 67 and 68:
The effect of soil on factory perfo
Page 69 and 70:
leaves increased the level of impur
Page 71 and 72:
• From 1976 to 1980, when the pro
Page 73 and 74:
Clerget purity of molasses 40 Clerg
Page 75 and 76:
CHAPTER 2. IMPACT OF EXTRANEOUS MAT
Page 77 and 78:
Since the extrapolated purity of mo
Page 79 and 80:
Figure 2.1. Jeffco cutter grinder.
Page 81 and 82:
2.1.4 Results The analytical result
Page 83 and 84:
Table 2.3. Analytical results of re
Page 85 and 86:
Table 2.5. Composition of dry trash
Page 87 and 88:
Table 2.7. Predicted factory perfor
Page 89 and 90:
Boiling house recovery 91.0 89.8 89
Page 91 and 92:
0 5 10 15 20 % EM in cane y = 0.572
Page 93 and 94:
% EM in cane 0 5 10 15 20 0 -2 -4 -
Page 95 and 96:
1 y = 0.020 (% D) R 2 = 1.00 = 0.03
Page 97 and 98:
% EM in cane 0 5 10 15 20 0 -2 y =
Page 99 and 100:
esulting in 0.015 unit sucrose loss
Page 101 and 102:
2.2.1 Experimental procedure Cane m
Page 103 and 104:
filter paper, rejecting the first f
Page 105 and 106:
Table 2.9. Effect of increased addi
Page 107 and 108:
Table 2.11. Effect of increased add
Page 109 and 110:
Table 2.13. Effect of increased add
Page 111 and 112:
various components such as stalk fi
Page 113 and 114:
in the presence of dry leaves, if c
Page 115 and 116:
Table 2.17. Moisture content in sug
Page 117 and 118:
CHAPTER 3. SEPARATION OF THE SUGAR
Page 119 and 120:
Table 3.1. It can be seen that the
Page 121 and 122:
Table 3.2. Fibrous physical composi
Page 123 and 124:
R 579 R 570 M 1557/70 M 1400/86 74
Page 125 and 126:
loosen the fibre. The woody core is
Page 127 and 128:
agitate the mixture in the pot, and
Page 129 and 130:
Figure 3.7. Custom-built fibre-pith
Page 131 and 132:
The extraction of fibres starting f
Page 133 and 134:
pre-treatment in a Jeffco cutter-gr
Page 135 and 136:
Figure 3.19. Stalk cake washed free
Page 137 and 138:
not have many dry leaves attached t
Page 139 and 140:
Table 3.5. Masses of cane samples a
Page 141 and 142:
Table 3.7. Masses of cane samples a
Page 143 and 144:
Table 3.9. Masses of cane component
Page 145 and 146:
3 57.6 126.3 23.7 97.2 31.1 53.8 11
Page 147 and 148:
Table 3.12. Material loss (%) from
Page 149 and 150:
3.5.3 Fibre/pith ratios in cane com
Page 151 and 152:
Table 3.15. Effect of extraneous ma
Page 153 and 154:
Snow (1974) investigated the season
Page 155 and 156:
from Figure 2.9 that the change in
Page 157 and 158:
Table 3.18. Fibre % cane results by
Page 159 and 160:
110
Page 161 and 162:
(a). Dry leaf (b). Green leaf (c).
Page 163 and 164:
dry fibre, or a factor, is used in
Page 165 and 166:
Steuerwald (1912) applied sucrose s
Page 167 and 168:
solution/fibre ratio was lowered fr
Page 169 and 170:
leave some residual moisture on the
Page 171 and 172:
instead of 150 g of 10° Brix sucro
Page 173 and 174:
Table 4.2. Determination of Brix-fr
Page 175 and 176:
Table 4.3. Comparison of Brix-free
Page 177 and 178:
Table 4.4. Results of the determina
Page 179 and 180:
In order to test for homogeneity of
Page 181 and 182:
Table 4.7. Results of the repeat de
Page 183 and 184:
The experiment was repeated with th
Page 185 and 186:
e any residual moisture in the samp
Page 187 and 188:
By means of the same technique, Won
Page 189 and 190:
was still hot. Since the filter was
Page 191 and 192:
value determined could be corrected
Page 193 and 194:
Qin and White’s finding was confi
Page 195 and 196:
A sample size of 3.5 g with 75 g co
Page 197 and 198:
Figure 4.4. Fibre samples drying in
Page 199 and 200:
- One large fibre sample (rind) of
Page 201 and 202:
Table 4.18. Brix-free water values/
Page 203 and 204:
Table 4.20. Brix-free water values/
Page 205 and 206:
4.7.3 Statistical analysis It is es
Page 207 and 208:
Table 4.23. Analysis of variance (B
Page 209 and 210:
pointing out that at 52 weeks old,
Page 211 and 212:
The crop of R 570 sampled in 2001 w
Page 213 and 214:
4.7.4. Estimated Brix-free water co
Page 215 and 216:
The main difference in the two sets
Page 217 and 218:
Table 4.27. Predicted Brix-free wat
Page 219 and 220:
4.8 SUMMARY AND CONCLUSIONS An anal
Page 221 and 222:
component parts, and verify the Bri
Page 223 and 224:
3) Thermodynamic, water in equilibr
Page 225 and 226:
Langmuir (1916, 1917, 1918) propose
Page 227 and 228:
to determine the moisture sorption
Page 229 and 230:
Table 5.1. Some commonly used isoth
Page 231 and 232:
Lomauro et al. (1985) found that wi
Page 233 and 234:
and on agricultural products such a
Page 235 and 236:
Bruijn (1963) studied the mass incr
Page 237 and 238:
After measuring the EMC of dry corn
Page 239 and 240:
approached, that is, either by adso
Page 241 and 242:
Table 5.4. Water activity (a w ) of
Page 243 and 244:
5.6.3 Procedure to determine equili
Page 245 and 246:
5.6.4 Results and discussion An exa
Page 247 and 248:
Table 5.8. Equilibrium moisture con
Page 249 and 250:
Table 5.10. Equilibrium moisture co
Page 251 and 252: Table 5.12. Equilibrium moisture co
Page 253 and 254: 30 o C 45 o C 55 o C 60 o C Water w
Page 255 and 256: m/m of 96% activity, a w (g/100g dr
Page 257 and 258: vaporisation generally decreases fr
Page 259 and 260: 30 o C isotherm 45 o C isotherm 55
Page 261 and 262: 4 0 Stalk fibre 5 0 Stalk pith 5 0
Page 263 and 264: 5.6.4.4 Fitting of sorption models
Page 265 and 266: Table 5.19. Parameters of the sorpt
Page 275 and 276: Modified GAB Kuhn Iglesias - Chirif
Page 277 and 278: Table 5.28. Classification of resid
Page 279 and 280: Stalk fibre Stalk pith Rind fibre 4
Page 281 and 282: 5.6.4.5 Calculated EMC values of re
Page 283 and 284: Table 5.30. Calculated equilibrium
Page 285 and 286: m/m of 96% Table 5.32. Calculated e
Page 287 and 288: Table 5.33. Parameters of the Hailw
Page 289 and 290: CHAPTER 6. PROPERTIES OF THE SORBED
Page 291 and 292: where m is the equilibrium moisture
Page 297 and 298: 6.2 THE NUMBER OF ADSORBED MONOLAYE
Page 299 and 300: 6.3 TOTAL SOLID SURFACE AREA AVAILA
Page 301: Thus, for each cane component of ea
Page 307 and 308: A similar procedure was followed to
Page 309 and 310: 10 0 Stalk fibre Stalk pith Rind fi
Page 311 and 312: Moreover, if T β > T hm the proces
Page 313 and 314: Table 6.5. Characteristic parameter
Page 315 and 316: Binding energy/kJ (kg mol) -1 2 0 0
Page 317 and 318: 6.8 CALCULATION OF BOUND WATER AND
Page 319 and 320: The values of K 1 , K 2 and W were
Page 321 and 322: Table 6.7. Separation of the total
Page 323 and 324: Table 6.7. (Contd.) Sample 30 o C 4
Page 325 and 326: 3 0 S talk fibre 4 0 Stalk pith 3 0
Page 327 and 328: 3 0 Reconstituted cane at 30 o C 3
Page 329 and 330: when water is added to dry wood, wh
Page 331 and 332: It is evident that in some cases ma
Page 333 and 334: The number of adsorbed monolayers,
Page 335 and 336: Data in Tables 2.9 and 2.11 show th
Page 337 and 338: particular fibre is systematically
Page 339 and 340: Anon. (1985b). Laboratory manual fo
Page 341 and 342: Blanchi R.H. and A.G. Keller (1952)
Page 343 and 344: Day D.L. and G.L. Nelson (1965). De
Page 345 and 346: Heyrovsky J. (1970). Determination
Page 347 and 348: Kuhn I.J. (1964). A new theoretical
Page 349 and 350: Madamba P.S., R.H. Driscoll and K.A
Page 351 and 352: Prinsen Geerligs, H.C. (1897). Stud
Page 353 and 354:
Sing K.S.W., D.H. Everett, R.A.W. H
Page 355 and 356:
Van der Pol C., C.M. Young and K. D
show all

Lynne Wong's PhD thesis

Create successful ePaper yourself

Delete template?

Save as template?