Hydroformylation of post-metathesis product using rhodium-based catalysts

Breckwoldt, Nicholas Claus Carl (2019-12)

Thesis (PhD)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: This study forms part of the overall scope of the RSA Olefins Programme for the upgrading of low-value α-alkene feedstocks to higher value detergent-range products within the South African context. The programme is motivated by the unique α-alkene market position in South Africa, as a producer of both odd- and even-numbered α-alkenes via Fischer-Tropsch conversion of syngas. Based on currently available technologies, the beneficiation of these low-value short-chain α-alkenes (C5-C9) via consecutive transition-metal-catalysed alkene metathesis and hydroformylation reactions is under consideration in South Africa. This study focused on evaluating the hydroformylation reaction within the scope of the proposed catalytic beneficiation process. The contributions of the study were thus two-fold in firstly describing the application of commercially available rhodium-based catalysts and secondly the application of non-commercial Schiff base derived rhodium-based precatalysts for the identified model hydroformylation reaction of the post-metathesis product 7-tetradecene. For both sets of catalyst systems, the study aimed to i) understand the catalytic performances of different rhodium-based catalysts for model reaction system, ii) to evaluate the effect of process conditions on the hydroformylation performance and iii) to evaluate and describe the reaction kinetics through phenomenological rate law model development that can be used in the reaction-engineering context. In terms of commercial rhodium-based catalysts: The performance of three commercially available catalyst systems, Rh-tris(2,4-ditertbutylphenyl)phosphite (1), Rh-triphenylphosphine (2) and Rh-triphenylphosphite (3) were evaluated for the model reaction by varying operating conditions such as temperature (60-90°C) and pressure (10-30 bar). Catalyst performance was characterised according to the activity (turnover numbers) and selectivity. It was found that all three commercial catalysts showed hydroformylation and isomerisation behaviour that was largely temperature- and pressure-dependent. Optimal conditions were established at 70°C (30 bar, CO:H2, 1:1) within the investigated ranges, for which 1 was exclusively hydroformylation-selective, while 2 and 3 were both hydroformylation- and isomerisation-selective. Overall, it was found that 1 was the most effective commercial catalyst system in terms of both activity (TON of 980) and regioselectivity toward targeted branched aldehyde product 2-hexylnonanal (>99%). It was further proposed and found that the reaction kinetics of the model reaction with 1 could be accurately described by a set of three interdependent first-order ordinary differential mole-balance equations. A mechanism-based rate-equation derived for bulky phosphite ligands was found to be consistent with the rate data (first-order in alkene and rhodium concentration, zero-order in hydrogen and negative order in carbon monoxide) over a wide alkene conversion range. In terms of non-commercial Schiff base derived rhodium-based catalysts: The performance of the monometallic rhodium-aryl (4) and heterobimetallic rhodium-ferrocenyl (5) Schiff base derived precatalysts bearing N’O chelate ligands were evaluated for the model reaction by varying operating conditions such as temperature (75-115°C), pressure (30-50 bar) and catalyst loading (7-tetradecene-to-precatalyst molar ratio from 1000:1 to 6000:1). It was found that the optimal reaction temperature for both 4 and 5 was 95°C (40 bar, CO:H2, 1:1). Even though precatalysts 4 and 5 were less regioselective (40:60 split in favour of isomeric aldehydes) compared to the commercial catalyst systems, significantly higher turnover numbers (up to 4310) were recorded using the Schiff base derived precatalyst systems at lower rhodium loadings. Evidence of a cooperative effect by including the second metal (ferrocene) in the heterobimetallic catalyst system was also observed due to improved catalytic activity compared to the monometallic catalyst systems under low temperature conditions. It was further found that the reaction kinetics of the model reaction with 5 could be accurately described by a set of four interdependent first-order ordinary differential mole-balance equations. A mechanism-derived rate equation derived for the hydroformylation using conventional monometallic rhodium-based catalyst was found to be consistent with the parametric influences of different reaction conditions affecting the reaction rate using the heterobimetallic precatalyst, with minor modification to account for observed fractional order dependence in precatalyst concentration. Thus, the rate of reaction was found to be first-order in alkene concentration, positive fractional-order in precatalyst concentration and first-order in both hydrogen and carbon monoxide.

AFRIKAANSE OPSOMMING: Hierdie studie vorm deel van die algehele bestek van die RSA Olefiene Program vir die opgradering van lae-graad α-alkeen voermateriaal na hoër-waarde detergentreeksprodukte binne die Suid-Afrikaanse konteks. Die program word gemotiveer deur die unieke α-alkeenmarkposisie in Suid-Afrika, as ʼn produseerder van beide onewe- en ewegetalle α-alkene via Fischer-Tropsch-omsetting van sintesegas. Gebaseer op beskikbare tegnologie tans, is die veredeling van hierdie lae-waarde kortketting α-alkene (C5–C9) via opeenvolgende oorgang-metaal-gekataliseerde alkeen metatesis en hidroformileringreaksies in oorweging in Suid-Afrika. Hierdie studie fokus op die evaluering van die hidroformileringsreaksie binne die bestek van die voorgestelde katalitiese veredelingsproses. Die bydraes van die studie was dus tweevoudig deur eerstens die toepassing van kommersieel beskikbare rodium-gebaseerde katalisators en tweedens die toepassing van nie-kommersiële Schiff-basis afgeleide rodium-gebaseerde voorkatalisators vir die geïdentifiseerde model hidroformileringreaksie van die post-metatesis produk 7-tetradeseen. Vir beide stelle van katalisatorsisteme, het die studie beoog om i) die katalitiese vermoë van verskillende rodium-gebaseerde katalisators vir die model reaksie sisteme te verstaan, ii) die effek van proses kondisies op die hidroformilering vermoë te evalueer, en iii) die reaksiekinetika deur fenomenologiese tempo wet model ontwikkeling te evalueer en beskryf wat gebruik kan word in die reaksie ingenieurskonteks. In terme van kommersiële rodium-gebaseerde katalise: Die vermoë van drie kommersieel beskikbare katalisatorsisteme, Rh(2,4-ditertbutylphenyl)fosfiet (1), Rh-triphenylfosfien (2) en Rh-triphenylfosfiet (3) is gevalueer vir die modelreaksie deur verskeie bedryfskondisies soos temperatuur (60–90 °C) en druk (10–30 bar) te varieer. Katalisator vermoë is gekarakteriseer na aanleiding van die aktiwiteit (omset nommers) en selektiwiteit. Dit is bevind dat al drie kommersiële katalisators hidroformilering en isomerisasie gedrag gewys het wat grootliks temperatuur- en drukafhanklik was. Optimale kondisies is gevestig by 70 °C (30 bar, CO:H2, 1:1) binne die nagevorste bestekke, waarvoor 1 die eksklusiewe hidroformilering-selektiewe was, terwyl 2 en 3 albei hidroformilering- en isomerisasie-selektief was. Oor die algemeen is dit gevind dat 1 die mees effektiewe kommersiële katalisatorsisteem in terme van beide aktiwiteit (TON van 980) en regioselektiwiteit na die mikpunt van uitgebreide aldehiedproduk 2-heksielnonanal (>99%), is. Dit is verder voorgestel en gevind dat die reaksiekinetika van die model reaksie met 1 akkuraat beskryf kon word deur ʼn stel van drie interafhanklike eerste-orde gewone differensiële molbalans vergelykings. ʼn Meganisme-gebaseerde tempovergelyking afgelei vir groot fosfiet ligande is bevind om in ooreenstemming met die tempo data (eerste-orde in alkeen en rodium konsentrasie, zero-orde in waterstof en negatief-orde in koolstofmonoksied) oor ʼn wye alkeen omset bestek. In terme van nie-kommersiële Schiff basis afgeleide rodium-gebaseerde katalisators: Die vermoë van die monometaliese rodium-ariel (4) en heterobimetaliese rodium-ferroseniel (5) Schiff basis afgeleide prekatalisators wat N’O chelaat ligande dra, is geevalueer vir die model reaksie deur verskillende bedryfskondisies soos temperatuur (75–115 °C), druk (30–50 bar) en katalisator lading (7-tetradeseen-na-prekatalisator mol verhouding van 1000:1 tot 6000:1) te varieer. Dit is gevind dat die optimale reaksie temperatuur vir beide 4 en 5 95 °C was (40 bar, CO:H2, 1:1). Selfs al was 4 en 5 minder regioselektief (40:60 verdeel ten gunste van isometriese aldehiedes) in vergelyking met die kommersiële katalisatorsisteme, is beduidende hoër omset nommers (tot 4310) opgeteken deur die Schiff basis afgeleide prekatalisatorsisteme by laer rodium ladings, te gebruik. Bewyse van ʼn samewerkende effek deur die insluiting van die tweede metaal (ferroseen) in die heterobimetaliese katalisatorsisteem is ook waargeneem as gevolg van die verbeterde katalitiese aktiwiteit in vergelyking met die monometaliese katalisatorsisteme onder lae temperatuurkondisies. Dit is is verder gevind dat die reaksiekinetika van die model reaksie met 5 akkuraat beskryf kan word deur ʼn stel van vier interafhanklike eerste-orde gewone differensiële molbalans vergelykings. ʼn Meganisme-afgeleide tempo vergelyking afgelei vir die hidroformilering deur konvensionele monometaliese rodium-gebaseerde katalisators te gebruik, is gevind om konsekwent met die parametriese invloede van verskillende reaksiekondisies wat die reaksie tempo affekteer, deur die heterobimetaliese prekatalisator te gebruik, met mindere wysiging om vir waargenome breukorde afhanklikheid in prekatalisator konsentrasie te reken. Dus, die tempo van reaksie is gevind om eerste-orde in alkeenkonsentrasie te wees, positiewe breukorde in prekatalisatorkonsentrasie en eerste-orde in beide waterstof en koolstofmonoksied te wees.

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