Study of catalyst deactivation during 1,3-butanediol dehydration to produce butadiene

Abstract

Catalyst deactivation and mechanism of coke formation during the gas phase dehydration of 1,3-butanediol were studied on solid acids of different nature: Al2O3, SiO2/Al2O3, HZSM5 and tungstophosphoric acid (TPA) supported on SiO2. All the catalysts deactivated on stream with a significant coke content ranged between 9% and 14% C. Fresh and spent catalysts as well as carbonaceous deposits were thoroughly characterized using different techniques such as N2 physisorption, FTIR spectroscopy, FTIR of adsorbed pyridine, DSC-TGA, GC-MS and MALDI-TOF MS (matrix-assisted laser desorption/ionization time of flight mass spectrometry). The IR spectra of spent and washed (after direct extraction with CH2Cl2) samples and the superficial soluble coke characterized by MALDI-TOF MS showed the different nature of coke formed in each catalyst with carbonaceous products of higher molecular weights on HZSM5 and TPA/SiO2 than on Al2O3 and SiO2/Al2O3. After catalyst dissolution using hydrofluoric acid and extraction with CH2Cl2 both total soluble and insoluble coke were analyzed. Insoluble coke was only detected on TPA/SiO2 and it was attributed to the strength of its Brønsted acid sites. GC-MS chromatograms of total soluble coke showed the presence of aromatic and polyromantic species, that were very alkylated in the case of HZSM5. Particularly, the well differentiated nature of coke on HZSM5 including alkylnaftalenes and alkylantracenes suggested the coke formation by a shape selectivity mechanism.