AB 140 oC 107 0.19 66.4 AB 150 oC 172 0.48 106.8 AB 160 oC 171 0.40 85.8 AB 170 oC 162 0.38 92.8 AB 180 oC 121 0.31 94.3 AB 190 oC 101 0.26 96.3 AB 200 oC 44 0.13 98.4 Table 3. Textural properties of mesoporous cellulose from orange peel with different extraction temperatures. According to the porosity data the textural property of the sample indicates that the samples are mesoporous, with negligible microporosity ( which possibly reflects the relatively low degassing temperatures to be used i.e. oC ) and possess a high surface area (AB 150 oC, 172.4 m2 g-1). Thus the materials have potential use as adsorbents. The porosity comes from the structured cellulose present in orange peel and is increased by the removal of the other structural non-porous components due to the hydrothermal treatment. Also, it is possible that the microwave irradiation opens up the linear cellulose structure giving rise to porous solid. But also the porosity decreased significantly, from 100.5 m2 g-1 to 44.3 m2 g-1, as the temperature was raised from 180 oC to 200 oC, respectively. This is probably due to the fact that the acidic conditions of orange peel and microwave irradiation leads to the thermal decomposition and depolymerisation of cellulose to give acetic acid, formic acid or even hydroxymethylfurfural (HMF). The pore volume also significantly drops due to treatment at 180 oC to 200 oC.
(°C) region remarks Commercial orange pectin RT ester: ~171 ppm acid: ~175 ppm ~53 ppm Data Ms Lucie Pfaltzgraff Enzymatic treatment RT 172.8 ppm (very broad) 168.4 ppm (defined shoulder) 164.3 ppm (defined standalone peak) ~54 ppm The enzymatic treatment has not removed all the pectin Enzymatic + microwave 140 173.8 ppm (very broad) Hint for a shoulder ~ 168 ppm but unclear weak and peaks the impression exists that there are no methyl ester groups but there are clearly some residual carbonyl groups Enzymatic + microwave treatment seems to give cleaner materials at 140 °C compared to only microwave treatment at 140 °C Treatment at 180 °C, irrespective the exact method, gives cleaner materials in which more pectin has been removed Note that the 13C solid state NMR spectra of all these materials are taken making that the should be bigger than the CO-O-CH3 peak. 180 173.8 ppm (broad but smaller compared to 140 °C) 168.3 ppm (distinct peak) absent (or at maximum a shoulder) Microwave treatment 140 173.6 ppm (broad peak) 168.4 ppm (more defined) broad peak at ~54 ppm microwave treatment at 140 C still leaves some methyl esters. 180 172.7 ppm (broad peak) 168.3 ppm (more defined peak) Absent microwave treatment at 180 C seems to have eliminated all methyl esters. Yet some carbonyl groups are remaining. Table 6. Summary of CPMAS NMR signals of cellulose extracted by different methodologies based on the prior removal of pectin
acidic hydrolysis, and the production of (bio)ethanol by hydrolysis with cellulases.,,, According to the literature grapefruit peels contains about 27 % of pectin. Based on the results described in Chapters 3 and 4, optimized conditions were used for the extraction of mesoporous cellulose from virgin citrus peels: grapefruit; lemon, and ;lime without any pre-treatment or addition of any mineral acid in order to further understand the variation in textural properties and degree of crystallinity with respect to processing conditions. Within the context of biorefinery it is important that it can operate with different feedstocks depending regardless of security of supply, i.e., if orange peel becomes limited then biorefinery can switch to different citrus waste without compromising productivity. 5.2 Results and Discussion The yields of cellulosic matter post microwave treatment at 180 oC were: grapefruit peel, 5.1% (dark-grey brown); lemon peel, 5.1% (dark grey), and; lime peel, 4.9% (grey). 5.2.1 ATR-IR Spectroscopic analysis Figure 42 shows the ATR-IR spectra of the cellulosic matter derived from microwave hydrothermal treatment at 180 oC of lime-, lemon-, and grapefruit-peel compared with that of cellulosic matter from orange peel under the same extraction conditions to draw a parallel amongst the different fruits belonging to the same family. From the IR spectra shown in Figure 42 no significant difference in the spectra was observed thus the process was feedstock independent and based on Table 2 (Chapter 3, section 3.2.2), the absorption bands of the samples were in complete accordance with the reference absorption bands found for micro-crystalline cellulose. Figure 42. ATR-IR spectra of cellulosic matter derived from different citrus peels at 180 oC compared with the commercial cellulose For further clarity and to show that pectin has been removed very efficiently (significant decrease in absorption bands between 1700 – 1630 cm-1), the ATR-IR spectra of grapefruit