Sintesis mangkin hetergen dengan gabungan superasid yang berprestasi tinggi bagi penghasilan monogliserid secara selektif melalui pengesteran gliserol dan asid lemak rantai panjang telah dicuba sepanjang kajian ini. Bagi mengeksploitasi keasidan 12-tungstofosforik asid (HPW), ia telah disokong kepada SBA-15 dengan kaedah pasca pengisian dan kaedah sintesis secara langsung. Sifat-sifat permukaan, struktur dan kimia mangkin telah ditafsir dan dijelas dengan bantuan pelbagai teknik pencirian. Mangkin yang disintesis melalui kaedah pasca pengisian didapati mempunyai mesoliang yang seragam (55 – 59 Å) dengan keluasan permukaan yang tinggi (323 – 600 m2/g) yang dikekalkan daripada SBA-15. Keasidan kuat yang berasal daripada HPW berstructur Keggin juga telah berjaya didepositkan dalam mesoliang. Prestasi tinggi mangkin juga dikesan dengan penukaran asid laurik (72 – 78 %) dan hasil monolaurin (46 – 54 %) yang tinggi. Sebaliknya, mangkin yang disisntesis secara langsung telah dikenalpasti sebagai bahan silika yang mempunyai keluasan permukaan yang tinggi (169 – 521 m2/g) dan mesoliang yang seragam (45 – 60 Å). Perbezaan yang ketara dari segi ciri-ciri bahan dan prestasi mangkin dapat dikenalpasti. Kekurangan penyebaran HPW telah dikesan pada mangkin yang disintesis secara langsung berbanding dengan mangkin yang disintesis secara pasca pengisian. Pembentukan tungsten oksida juga dikesan bagi 30wt% dan 40wt%-HPW/DS dan menyebabkan keasidan rendah bagi mangkin yang disintesis secara langsung tersebut. Penukaran asid laurik (71 – 75 %) dan hasil monolaurin (47 – 52 %) yang lebih rendah juga dikesan bagi mangkin yang disintesis secara langsung. Namun, semua mangkin menunjukkan potensi cerah dengan masa tindakbalas yang jauh lebih singkat (dari 20 hingga 3 jam sahaja) berbanding dengan keputusan yang pernah dilaporkan. Sebagai mangkin yang paling berpotensi, 40wt%-HPW/IM telah dipilih untuk kajian kinetik tindak balas dengan model hukum kuasa dan model berdasarkan mekanisme tertentu. Keputusan kajian tersebut mendedahkan kemungkinan laluan tindakbalas yang diselidik sebagai kombinasi penukaran nukleofilik dan mekanisme Langmuir-Hinshelwood. Malangnya, kebolehgunaan semula 40wt%-HPW/IM yang lemah telah diperhatikan. Kebolehgunaan semula mangkin yang rendah tersebut adalah disebabkan oleh kehilangan asid HPW yang telah dikuras keluar daripada mangkin. Oleh itu, mangkin telah diperbaiki melalui pengisian HPW kepada SBA-15 yang diubahsuai oleh kalsium. Dengan kaedah pengisian dua langkah, garam kalsium asid HPW yang tidak boleh larut telah dibentukkan dalam mesoliang SBA-15. Sebagaimana mangkin yang disintesis melalui kaedah pasca pengisian, HPW/CaSBA-15 terdiri daripada mesoliang yang seragam (58 – 63 Å) dengan keluasan permukaan yang tinggi (564 – 604 m2/g). Keasidan yang tinggi ((0.680 – 0.714 mmol/g) daripada HPW berstructur Keggin dapat dikesan bagi semua mangkin yang diubahsuai tersebut. Jambatan silika – kalsium – HPW di antara SBA-15 dan HPW bukan sahaja dapat mengekalkan prestasi tinggi mangkin, tetapi juga menunjukkan kebolehgunaan semula mangkin yang lebih baik tanpa kehilangan prestasi mangkin selepas 3 kitaran.
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The synthesis of highly effective superacid incorporated heterogeneous catalysts for selective monoglyceride production via esterification of glycerol with long chain fatty acid was attempted in this study. Aiming to exploit the superacidity from 12-tungstophosphoric acid (HPW), it was supported onto SBA-15 via post impregnation and direct synthesis methods. The catalysts’ surficial, structural and chemical properties were revealed and elucidated using various characterization techniques. Post impregnated catalysts showed the highly uniformed mesopores (55 – 59 Å) with high surface areas (323 – 600 m2/g) retained from the parent SBA-15. Strong acidity was exerted by the Keggin-structured HPW anions that were successfully deposited within the mesopores. High catalytic performances were detected, with high lauric acid conversions (72 – 78 %) and monolaurin yields (46 – 54 %). On the other hand, directly synthesized catalysts were identified to be silica materials with high surface areas (169 – 521 m2/g) with uniformed mesopores (45 – 60 Å). Distinct differences in terms of material characteristic and catalytic performances could be identified. Less dispersion of HPW among directly synthesized catalysts was detected when compared to those of post impregnated ones. Formation of tungsten oxides was also found for 30wt% and 40wt%-HPW/DS, ultimately causing lowered acidities found among the directly synthesized catalysts. Relatively lower lauric acid conversion (71 – 75 %) and monolaurin yield (47 – 52 %) were also detected for the directly synthesized catalysts. Nevertheless, the synthesized catalysts showed promising potential as much shorter reaction time (from 20 to 3 hours) was needed compared to those reported. With 40wt%-HPW/IM selected as the most potential catalyst, simple power law and mechanism based kinetic study was performed. Results revealed that the catalyzed reaction might follow a reaction pathway via a combination of nucleophilic substitution and Langmuir-Hinshelwood mechanism. Unfortunately, poor reusability of 40wt%-HPW/IM (up to one time only) was observed. Such poor reusability was evidently due to the heavy leaching of the HPW anions from the supports. As such, further improvement of the catalyst by impregnation of HPW onto calcium modified SBA-15 was performed. With a two-step impregnation method, insoluble calcium HPW acid salt within the mesopores of the parent SBA-15 was formed. Similar to the post impregnated catalysts earlier, HPW impregnated CaSBA-15 catalysts consisted of highly uniformed mesopores (58 – 63 Å) with high surface areas (564 – 604 m2/g). Strong acidities (0.680 – 0.714 mmol NH3 equivalent per gram), sourced from the retained Keggin HPW was found for all of the modified catalysts. The novel silica – calcium – HPW bridged between SBA-15 and HPW was found to not only able to maintain high catalytic performances, but also showed superior reusability with no apparent loss of catalytic performance after 3 cycles.
Selective esterification of glycerol with lauric acid to monolaurin using 12-tungstophosphoric acid incorporated sba-15 / Hoo Peng Yong