Hydrolysis of Potassium Borohydride using Formic Acid Catalyst

Abstract

Nowadays, in parallel with the increasing energy requirements, especially with the depletion of fossil fuels, the trend towards alternative renewable energy sources is rapidly increasing. With this increasing trend, hydrogen, an important energy carrier source, comes to the fore. Borohydrides provide the opportunity to obtain hydrogen easily, reliably and quickly by hydrolysis. However, since the hydrolysis of borohydrides in aqueous solutions is slow, catalysts have to be used to accelerate the reaction. While these catalysts can be homogeneous or heterogeneous, homogeneous catalysts have more advantages in industrial applications. In this study, in the presence of formic acid, an acid-based homogeneous catalyst, the hydrolysis reaction of potassium borohydride (KBH4) was investigated. The kinetic behavior of the examined reaction was determined depending on formic acid amount, temperature, and potassium borohydride concentration. Based on different temperature data and reaction rate equations, the hydrolysis reaction rate is found as around 5 liters of H2/gcatmin, the reaction rate is 1.1, the activation energy is 57.92 kJ/mol, the reaction enthalpy is 55.32 kJ/mol, and the entropy decrease is 58.11 J/molK. The Gibbs free energies of the hydrolysis reaction were calculated as 72.35, 72.93, 73.51, 74.67 kJ/mol for 20, 30, 40 and 60 °C, respectively. As a result, it is understood from the hydrolysis reaction rate that the hydrogen obtained at the end of potassium borohydride hydrolysis is sufficient to meet the needs of small-scale PEM fuel cells.

Keywords

• Formic acid
• homogeneous catalyst
• hydrolysis
• kinetics
• potassium borohydride

Potasyum Borhidrürün Formik Asit Katalizörü Varlığındaki Hidrolizi

Abstract

Günümüzde artan enerji ihtiyacına paralel olarak özellikle fosil yakıtların tükenmesiyle birlikte alternatif yenilenebilir enerji kaynaklarına yönelim hızla artmaktadır. Artan bu eğilim ile birlikte, önemli bir enerji taşıyıcı kaynağı olan hidrojen öne çıkmaktadır. Hidroliz ile kolay, güvenilir ve hızlı bir şekilde hidrojen elde edebilme imkânı sağlayan borhidrürler bu kaynakların başında gelir. Ancak borhidrürlerin sulu ortamdaki hidrolizleri oldukça yavaş olduğundan reaksiyonu hızlandırmak amacıyla katalizörlerin kullanılması gerekir. Bu katalizörler homojen veya heterojen olabilirken, homojen katalizörlerin endüstriyel uygulamalarda daha fazla avantajı bulunur. Bu çalışma kapsamında potasyum borhidrürün (KBH4) asit bazlı homojen bir katalizör olan formik asit varlığında hidroliz reaksiyonu ele alınmıştır. Reaksiyonun kinetik davranışı formik asit miktarı, sıcaklık ve potasyum borhidrür konsantrasyonu parametreleri incelenerek belirlenmiştir. Farklı sıcaklık verilerinden yola çıkılıp reaksiyon hız eşitlikleri kullanılarak potasyum borhidrürün formik asit varlığında hidroliz reaksiyonunun hızı 5 litre H2/gkatdk civarında, reaksiyon hız derecesi 1.1, aktivasyon enerjisi 57.92 kJ/mol, reaksiyon entalpisi 55.32 kJ/mol, entropi azalışı 58.11 J/molK olarak bulunmuştur. Hidroliz reaksiyonuna ait Gibbs serbest enerjileri ise 20, 30, 40 ve 60 °C için sırasıyla 72.35, 72.93, 73.51, 74.67 kJ/mol olarak hesaplanmıştır. Sonuç olarak potasyum borhidrürün hidrolizi sonucu elde edilen hidrojenin, küçük ölçekli PEM yakıt hücrelerinin ihtiyacını karşılamak için yeterli seviyede olduğu, hidroliz reaksiyonunun hız değerlerinden anlaşılmaktadır.

Keywords

• Formik asit
• hidroliz
• homojen katalizör
• kinetik
• potasyum borhidrür

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