DEHYDRATION OF GLYCEROL TO ACROLEIN IN A FLUIDIZED BED REACTOR

摘要

Acrolein is a valuable chemical that can be produced by the dehydration of glycerol. The value of glycerol, as the main co-product in the process of biodiesel synthesis, has dropped considerably due to a rapid increase in biodiesel production and a lack of market for such an enormous production capacity. Therefore, the dehydration of glycerol to acrolein is one of many reactions under development, which aims to convert low cost feedstock to more valuable products. Catalyst deactivation, on the other hand, which is caused by coke formation on the surface, is a serious issue for the commercialization of this process. In the case of glycerol dehydration, although acidic sites help to enhance the acrolein selectivity, they also accelerate catalyst deactivation. Acrolein could be a source of carbon build-up, as well. Currently acrolein is produced in a single step oxidation of propylene in the presence of Bi/Mo catalyst. Most of the acrolein then converts to acrylic acid via another oxidation step in a fixed bed reactor. Replacing propylene with a bio-feedstock has been a priority for many industries due to a concern for the environment, high propylene prices and supply uncertainty as well as the low price of glycerol. In this study, we have developed a new process in which an aqueous solution of glycerol was injected directly into a fluidized bed of WO_3/TiO_2 catalyst. In order to decrease the rate of catalyst deactivation and reduce formation of hydrogenated byproducts, oxygen was co-fed with the liquid and gas feed streams. Since co-feeding of oxygen along with heating has a considerable influence on the yield of acrolein, prior to the catalytic tests, we conducted acrolein blank tests in a quartz reactor. As a result, an optimum required quantity of oxygen concentration was determined for the in-situ catalyst regeneration. The conditions under which the glycerol solution atomized, was examined qualitatively. The gas phase analysis of the products showed a selectivity of 70% towards acrolein while the catalyst was fully active. The reactor exit passed through two quenches to trap the heavy compounds such as acrylic acid, hydroxyacetone, and propionic acid. Other by-products were acetaldehyde, formaldehyde, formic acid, and acetic acid.