Hydroxylation of 2-methylnaphthalene to 2-methylnaphthoquinone over TI-substituted catalysis

Rose, Jamey (2010-12)

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2010.

Thesis

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.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/5192
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