Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Partially oxygenated aromatic compounds, e.g. quinones, hydroquinones and cresols, play a vital
role in the fine chemical industry and were initially prepared by stoichiometric oxidation processes
that produce toxic products that are hazardous towards the environment. As a result, it was
important to investigate environmentally friendly processes for the hydroxylation of aromatic
compounds. This resulted in newer methods using Ti-substituted microporous zeolites as catalysts
with hydrogen peroxide as oxidant in the presence of a solvent.
However, the methods were found to be ineffective for large, bulky substrates due to the small pore
structure. This led to using Ti-mesoporous materials as catalysts but suffered from two drawbacks;
the hydrophilic nature and low hydrothermal stability of the catalyst structure. Ti-microporous and
Ti-mesoporous materials acting as catalysts for the oxidation of bulky substrates achieved
environmentally friendly processes but obtained low conversions and quinone yields. Therefore, the
challenge has been to develop a process that is environmentally friendly, achieves high conversions,
where the catalyst acts truly heterogeneous and obtains high quinone yields for the hydroxylation of
bulky substrates. Recently, micropores/mesopores catalysts incorporating advantages of both
micropores and mesopores materials were synthesised and seemed promising for the hydroxylation
of bulky substrates.
This study focuses on synthesising and evaluating the feasibility of various Ti-substituted catalysts for
improving the hydroxylation of the bulky substrate, 2-methylnaphthalene (2MN) with hydrogen
peroxide as oxidant in the presence of a solvent, acetonitrile. The oxidation of 2MN produces
2-methyl-1,4-naphthoquinone (2MNQ). 2MNQ is also known as menadione or Vitamin K3 and acts as
a blood coagulating agent. The catalysts synthesised for this study were mesoporous catalysts, Ti-
MCM-41 and Ti-MMM-2 and microporous/mesoporous catalysts, Ti-MMM-2(P123) and a highly
ordered mesoporous material. The main objective of this study was to design an efficient process
that is environmentally friendly and achieves high 2MN conversions and 2MNQ yields. This was
achieved by evaluating the various catalysts synthesised, reaction conditions, testing if the catalyst
was truly heterogeneous and identifying the products formed from the process.
The designed process was proved to be environmentally friendly because the system did not
produce products that were harmful towards the environment. The products identified in this study
were 2MNQ, 2-methyl-1-naphthol, 2-naphthaldehyde, 3-ethoxy-4-methoxybenzaldehyde and
menadione epoxide. An investigation was conducted to determine which catalyst synthesised
favoured this process by quantifying the effect reaction conditions have on the various catalysts. The
reaction conditions were defined in terms of the hydrogen peroxide volume, catalyst amount,
solvent volume, substrate amount, reaction time and reaction temperature. The desired catalyst for
this study obtained the highest 2MN conversions in comparison with the other catalysts and
favoured the formation of 2MNQ. The catalyst achieving the highest conversions and favouring
2MNQ in most cases for this investigation was the highly ordered mesoporous material. Improving operating conditions to obtain high 2MNQ yields for the oxidation of 2MN to 2MNQ over
the highly ordered mesoporous material was determined by varying the reaction conditions with the
one factor at a time approach and a factorial design. The one factor at a time approach showed that
best 2MNQ yields were obtained at 1 g substrate when investigating a change in substrate amount
between 0.5 g and 2 g. Best 2MNQ yields were obtained at 10 ml solvent when investigating a
change of solvent volume between 5 ml and 20 ml. The 2MNQ yield increased with increasing the
catalyst amount (50 mg to 200 mg), hydrogen peroxide volume (1 ml to 6 ml) and increasing the
reaction times (2 hour to 6 hours) at reaction temperatures, 120°C and 150°C. The yield decreased
with increasing the reaction time (2 hours to 6 hours) at reaction temperature, 180°C. A preliminary
2 level factorial design was prepared to observe if there were any important interactions affecting
the 2MNQ yield. The results from the factorial design indicated that the hydrogen peroxide volume
had the most influence on the 2MNQ yield followed by the reaction time-reaction temperature
interaction and reaction temperature. From the factorial design, the yield increased by increasing
the hydrogen peroxide volume and reaction temperature whilst decreasing the reaction
temperature-reaction time interaction. The highest 2MNQ yields and 2MN conversions obtained for
the hydroxylation of 2MN to 2MNQ over the highly ordered mesoporous material in this study were
in the ranges 48-50 % and 97-99 %, respectively.
This study indicates that the process system, reaction conditions and catalyst type have an impact on
the products formed, 2MN conversion, 2MNQ selectivity and 2MNQ yield. The highly ordered
mesoporous material was found to be truly heterogeneous because no leaching occurred and the
catalyst could be recycled without losing its catalytic activity and selectivity for at least two catalyst
cycles. It can be concluded that the highly ordered mesoporous material is therefore a promising
catalyst for the selective oxidation of bulky substrates with aqueous H2O2 because it produces an
environmentally friendly process, achieves high conversions, obtains high quinone yields and the
catalyst truly acts heterogeneous. / AFRIKAANSE OPSOMMING: Gedeeltelik geoksideerde aromatiese verbindings (bv. kinone, hidrokinone en kresole) speel ‘n
belangrike rol in die fynchemiebedryf. Hierdie verbindings is aanvanklik voorberei deur
stoïchiometriese oksidasie prosesse wat gifstowwe nadelig vir die omgewing veroorsaak. Daarom is
dit belangrik om omgewingsvriendelike prosesse vir die hidroksilering van aromatiese verbindings te
ondersoek. Hierdie ondersoeke het gelei tot nuwe metodes wat Ti-vervangde mikroporeuse seoliete
as katalisator met waterstofperoksied as oksideermiddel in die teenwoordigheid van ʼn oplosmiddel
benut.
Dit is egter gevind dat hierdie metodes oneffektief is vir groot, lywige substrate weens die fyn
poriestruktuur van die katalisator. Dit lei tot die gebruik van Ti-mesoporeuse materiale as
katalisators, maar toon twee tekortkominge, naamlik die hidrofiliese aard en lae hidrotermiese
stabiliteit van die katalisatorstruktuur. Ti-mikroporeuse en Ti-mesoporeuse materiale benut as
katalisators vir die oksidasie van lywige substrate lewer omgewingsvriendelike prosesse, maar
vermag lae omsetting en kinoonopbrengs. ʼn Uitdaging is dus om ʼn omgewingsvriendelike proses te
ontwikkel met hoë omsetting, waar die katalisator werklik heterogeen optree en hoë
kinoonopbrengs lewer vir die hidroksilering van lywige substrate. Katalisators vir die hidroksilering
van lywige substrate wat die voordele van beide mikroporieë/mesoporieë ten toon stel is onlangs
gesintetiseer, met belowende resultate.
Hierdie studie is ingestel op die sintetisering en evaluering van uitvoerbaarheid van verskeie Tivervangde
katalisators vir die optimering van die hidroksilering van die lywige substraat, 2-
metielnaftaleen (2MN), met waterstofperoksied as oksideermiddel met asetonitriel as oplosmiddel.
Die oksidering van 2MN produseer 2-metiel-1,4-naftokinoon (2MNK), ook bekend as vitamien K3, ʼn
bloedstollingsmiddel. Die katalisators vervaardig vir hierdie studie was die mesoporeuse katalisators,
Ti-MCM-41 en Ti-MMM-2, en die mikroporeuse/mesoporeuse katalisor Ti-MMM-2(P123), sowel as ʼn
hoogs geordende mesoporeuse materiaal. Die hoofdoel van hierdie studie was om ʼn doeltreffende,
omgewingsvriendelike proses met hoë 2MN omsetting en 2MNK opbrengs te ontwerp.
Voorgenoemde is vermag deur verskeie gesintetiseerde katalisators en reaksiekondisies te evalueer,
om te toets of katalisators werklik heterogeen is, en om die prosesprodukte te identifiseer.
Die ontwerpte proses kan beskou word as omgewingsvriendelik, aangesien die stelsel geen produkte
lewer wat skade aan die natuur kan veroorsaak nie. 2MNK, 2-metiel-1-naftol, 2-naftaldehied, 3-
etoksi-4-metoksibensaldehied en menadioonepoksied is in hierdie studie geïdentifiseer as
prosesprodukte. Om te bepaal watter gesintetiseerde katalisators hierdie proses begunstig, is ʼn
ondersoek geloods om die effek van reaksiekondisies op die verskeie katalisators te kwantifiseer. Die
reaksiekondisies is omskryf in terme van waterstofperoksiedkonsentrasie, katalisatorhoeveelheid,
oplosmiddelvolume, substraathoeveelheid, reaksietyd en reaksietemperatuur. Die gewenste
katalistor vir hierdie proses was die katalisator wat die hoogste 2MN omsetting lewer en die vorming van 2MNK bevorder. Die hoogs geordende mesoporeuse materiaal was in hierdie ondersoek die
katalisator met die hoogste omsetting wat ook 2MNK-vorming bevorder het in die meeste gevalle.
Om die beste bedryfstoestande vir hoë 2MNK opbrengs vanaf die oksidering van 2MN oor hoogs
geordende mesoporeuse materiaal te bepaal, is die reaksiekondisies verander deur met een faktor
op ʼn slag te verander, sowel as faktorverandering volgens ʼn faktoriaalontwerp. Die een-faktor-op-‘nslag
benadering het getoon dat die 2MNK opbrengs ʼn maksimum bereik waar die
substraathoeveelheid tussen 0.5 g en 2 g wissel, met die oplosmiddelvolume tussen 5 ml en 20 ml.
Die opbrengs het ietwat verbeter met ʼn groter hoeveelheid katalisatorhoeveelheid (van 50 mg na
200 mg), terwyl die opbrengs drasties verbeter het waar die waterstofperoksiedvolume van 3 ml tot
6 ml verhoog is. Die opbrengs het ook verbeter met ʼn styging in reaksietemperatuur (van 120°C tot
180°C) met reaksietydintervalle van 1 tot 6 ure. Die opbrengs het egter gedaal by 180°C waar
reaksietye langer as 2 ure.
Volgens die resultate van die een-faktor-op-‘n-slag benadering blyk dit dat reaksietemperatuur,
waterstofperoksiedvolume, katalisatorhoeveelheid en reaksietyd faktore is wat verhoogde 2MNK
opbrengs bevorder. Hierdie reaksiekondisies is geselekteer vir die faktoriaalontwerp. ʼn Voorlopige 2-
vlak faktoriaalontwerp is voorberei om te bepaal of daar enige belangrike interaksies is wat die
2MNK opbrengs beïnvloed. Die resultate van die faktoriaalontwerp het aangetoon dat
waterstofperoksiedvolume die grootste invloed op 2MNK opbrengs het, gevolg deur die interaksie
van reaksietyd en reaksietemperatuur, en dan reaksietemperatuur. Die faktoriaalontwerp resultate
toon verder dat opbrengs verhoog met toenemende waterstofperoksiedvolume en
reaksietemperatuur, terwyl die opbrengs verlaag soos wat die reaksietyd-reaksietemperatuur
interaksie toeneem. Hierdie studie het hoogste 2MNK opbrengs van 48-50% en 2MN omsetting van
97-99% vir die hidroksilering van 2MN na 2MNK oor hoogs geordende mesoporeuse materiale
behaal.
Hierdie studie bevestig bevindinge van die literatuur dat die prosesstelsel, reaksiekondisies en
katalisatortipe ʼn groot impak het op prosesprodukte, 2MN omsetting, 2MNK selektiwiteit en 2MNK
opbrengs. In hierdie navorsingstudie is bevind dat hoë 2MN omsetting en 2MNK opbrengs behaal
word by hoë reaksietemperature met kort reaksietye en hoë waterstofperoksiedvolumes. Dit is
gevind dat die hoogs geordende mesoporeuse materiaal werklik heterogeen is, aangesien geen
loging plaasgevind het nie, en aangesien die katalisator hergebruik kon word sonder verlies aan
katalisatoraktiwiteit en –selektiwiteit, vir ten minste twee katalisatorsiklusse. ʼn Gevolgtrekking kan
gemaak word dat die hoogs geordende mesoporeuse materiaal ʼn belowende katalisator vir die
selektiewe oksidering van lywige substrate met waterige H2O2 is, aangesien dit ʼn
omgewingsvriendelike proses lewer met hoë omsetting, hoë kinoonopbrengs en katalisatorgedrag
wat waarlik heterogeen is.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/5192 |
| Date | 12 1900 |
| Creators | Rose, Jamey |
| Contributors | Callanan, L. H., University of Stellenbosch. Faculty of Engineering. Dept. of Process Engineering. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 138 p. : ill. |
| Rights | University of Stellenbosch |
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