Interplay Between Bromine and Iodine in Oxidative Dehydrogenation

Abstract

Oxidative dehydrogenation is a promising way to produce olefins, diolefins and aromatics. However, the product yield is limited by the consecutive oxidation of the product to oxygenated products. The highest yield reported for propane oxidative dehydrogenation is only about 30%. Alternatively, halogens can be used as oxidants in oxidative dehydrogenations. Although the iodine process is highly selective, it requires very high reaction temperatures (~ 900 K) to give a good yield of "C3H6+C3H7I", and iodine is too expensive for industrial deployment. Bromine is a more reactive oxidant, however, less selective towards C3H6 and C3H7Br. We show here that using bromine/iodine mixtures with low iodine content (no greater than 20%) results in up to 80% of "C3H6+C3H7X" single-pass yield at moderate reaction temperatures (< 800 K). The results are promising for developing a low temperature on-purpose propylene technology. Furthermore, the underlying chemistry might be extended to the synthesis of many other commercially desirable unsaturated hydrocarbons.

Catalytic Bromine Recovery: An Enabling Technology for Emerging Alkane Functionalization Processes

“…[1] In particular, energy-efficient and costeffective processes to selectively convert the abundant reserves of natural gas into chemical intermediates and fuels are highly sought. Pioneering work by Olah et al [2] and more recent studies by McFarland, Stucky, and co-workers [3,4] have shown that the bromination of light alkanes to the corresponding alkyl bromides followed by a catalyzed elimination reaction offers an attractive route to obtain a broad spectrum of desirable products (Figure 1). Bromine-mediated reactions of hydrocarbons are far more selective and occur under much milder conditions (typically 475 K and 100-200 kPa) than classical alkane upgrading processes (steam reforming, steam cracking, and dehydrogenation), which leads to increased product yields, energy savings, and decreased CO 2 emissions.…”

Understanding Catalytic Mechanisms of Alkane Oxychlorination from the Perspective of Energy Levels

“…In contrast, Pérez-Ramírez et al proposed that in the oxybromination of light alkanes on vanadium phosphate (VPO) catalyst, molecular O 2 oxidizes HBr into Br 2 and then molecular Br 2 activates light alkanes through radicals in the gas phase . However, an earlier study indicated that the gas-phase reaction triggered by halogen radicals can lead to uncontrolled product selectivity . Indeed, it is known that gas-phase radical chain reactions usually give a mixture of polyhalogenated hydrocarbons, which is not consistent with experimental findings for catalyzed oxychlorination .…”

“…18 However, an earlier study indicated that the gas-phase reaction triggered by halogen radicals can lead to uncontrolled product selectivity. 19 Indeed, it is known that gas-phase radical chain reactions usually give a mixture of polyhalogenated hydrocarbons, which is not consistent with experimental findings for catalyzed oxychlorination. 11 Thus, it was proposed that C−H activation processes in oxychlorination/oxybromination should confine on catalyst surfaces, instead of taking place in the gas phase.…”

Chemical Upcycling of Polyethylene to Value-Added α,ω-Divinyl-Functionalized Oligomers

“…The resulting α,ω-divinyl-functionalized oligomers have a variety of potential value-added uses, including serving as monomers in the syntheses of poly-α-olefin lubricants, polyolefins, polyethers, polyesters, and polyamides. , By tuning the degree of bromination, we demonstrate that PE can be converted selectively to α,ω-divinyl-functionalized oligomers of various chain lengths. The HBr (and, if necessary, KBr) byproducts can, in principle, be recycled by oxidation to regenerate Br 2 , − in processes that have already been demonstrated at scale. , A preliminary techno-economic assessment (TEA) suggests that the process in Scheme could be profitable on an industrial scale.…”