Benzaldehit-metanol tepkimesinin amberlit IR-120 katalizör varlığında kinetik incelenmesi

Abstract

Benzaldehit-Metil Alkol tepkime kinetigi asidik formdaki katyon degistirici reçine (Amberlit IR-120) varlıgında çalısıldı. Çözücü olarak 1,4-dioksan kullanıldı. Bir denge tepkimesi olan asetal olusumunun, hidrolizine oranla yavas olması nedeniyle, ileri tepkime olarak hidroliz tepkimesi çalısıldı. Benzaldehit dimetilasetalin hidrolizine ait denge sabiti 298-328 K sıcaklık aralıgında Kd= exp(8,67-1880/T) olarak bulundu. Burada T, Kelvin olarak mutlak sıcaklıktır. Amberlit IR-120 katalizör varlıgında gerçeklestirilen deneyler sonucunda, hidroliz tepkimesinin adsorplanmıs su molekülleri ile yıgın içindeki asetal molekülleri arasında gerçeklestigi (Eley-Rideal modeli) ve tepkimenin “yüzey tepkimesi basamagı kontrollü” oldugu gösterildi. Tepkime hızının ise; 2 ( ) 1 BA M A W e W BA BA W W m C C k C C V K r K C K C − − = + + seklinde verilebilecegi bulundu. Burada derisimler mol L-1’dir. Asetal hidrolizi yönündeki hız sabitinin sıcaklıga baglı olarak k = exp(9,4- 4915/T) L2 ( g-kuru reçine) -1.mol -1.dakika -1 esitliginden hesaplanabilecegi gösterildi. Benzaldehit ve suya ait adsorpsiyon denge sabitleri ise KBA = exp (7292/T-24,9) L.mol-1 KW = exp(1296/T-4,4) L.mol-1 seklinde bulundu.

The kinetics of acetalisation of benzaldehyde with methyl alcohol has been studied in the presence of a cation exchanger in its acidic form (Amberlite IR-120). 1,4- Dioxane has been used as solvent. Acetalisation is an equilibrium reaction, and it was found that the rate of acetal formation is much slower than that of acetal hydrolysis. Hence hydrolysis, rather than acetal formation, was choosen as forward reaction. In the temperature range 298-328 K, the equilibrium constant for hydrolysis of benzaldehyde dimethyl acetal was found to be Kd= exp(8,67-1880/T) Where, T is absolute temperature in Kelvin. In the presence of catalyst, the reaction has been found to be occured between an adsorbed water molecule and a molecule of acetal in the bulk phase (Eley-Rideal model). From this model it was concluded that the reaction is “surface reaction control” and its rate will be given by expression 2 ( ) 1 BA M A W e W BA BA W W m C C k C C V K r K C K C − − = + + Where, concentration are in the unit of mol L-1. It was shown that temperaure dependency of hydrolysis rate constant can be given by k = exp(9,4- 4915/T) L2 ( g-dry resin) -1.mol -1.minute -1 The adsorption equilibrium constants related to benzaldehyde and water were also calculated to be KBA = exp (7292/T-24,9) L.mol-1 KW = exp(1296/T-4,4) L.mol-1 respectively.