Pyrolysis of Furfural

Contrary to common belief, when submitted to nothing but thermal loading, furfural is an extremely stable compound. No gases are formed when furfural is heated to 275 °C in a sealed tube for a period of three hours. After such treatment, almost all of the fiirfural is recoverable by distillation, leaving only a tiny amount of tarry residue. 

Noteworthily, at a contact time of 0.2 seconds, only 5 percent of the furfural decomposes at 660 °C. At such elevated temperatures, furfural decomposes to furan and carbon monoxide, in complete analogy to benzaldehyde which decomposes to benzene and carbon monoxide. The best conditions for the production of furan by pyrolysis of furfural were found to be 725 °C and a contact time of five seconds. Such a process gives a furan yield of 16.5 percent. 

As all pyrolysis reactions, the decomposition of furfural to furan and carbon monoxide is accompanied by other minor reactions. Of the gases formed, only 80 percent is carbon monoxide, other gases identified being 10 percent hydrogen as well as small quantities of carbon dioxide, butadiene, propadiene, ethylene, propylene, acetylene, methylacetylene, and cyclopropene. As the quantities of carbon dioxide and butadiene are roughly equal on a molar basis, it is believed that a part of the furfural reacts with pyrolytically liberated hydrogen  

On the side of liquid products, apart from the furan, small quantities of benzene, toluene, and phenol are formed. 

---

Pyrolysis of furfural under dilute and inert conditions yields (initially) furan and CO, by unimolecular decomposition. Further processes produce a range of products including acetylene, formaldehyde and propyne. Benzaldehyde is more resistant to pyrolysis, eventually giving phenyl and hydrogen radicals plus CO, leading to benzene and CO as final products. 

---