(95a) Olefins by High-Intensity Oxidation in Microchannel Reactors
AIChE Spring Meeting and Global Congress on Process Safety
Wednesday, April 25, 2007 - 9:25am to 9:50am
Ethylene is the backbone of the chemical industry, both literally and figuratively; over 120 million tons are produced annually with a value of over $100 billion, and ethylene is the basic building block of many polymers and commodity chemicals. Ethylene is the simplest olefin, a family of chemical intermediates used to produce a wide variety of plastics and end use chemicals. The conventional path to ethylene is via steam cracking, which involves heating ethane and steam in 60 foot long 4 inch diameter tubes hung in a cathedral-like furnace to form ethylene, propylene, and by-products. Despite years of incremental improvements, this approach is inefficient, and suffers from poor selectivity to ethylene and other valuable products. Velocys, Dow Chemical, Pacific Northwest National Laboratory (PNNL), and U.S. Department of Energy (DOE) are developing a process for the production of olefins via oxidative dehydrogenation in highly heat-integrated microchannels. This approach offers improved feedstock utilization and substantial energy savings due to microchannel architecture's unique ability to control reaction temperatures. Since ethylene is such a valuable commodity, it has been the focus of intense research and development. However, all attempts to improve the process, including many attempts at oxidative dehydrogenation, have failed to meet economic targets. The challenge facing all attempts to oxidize paraffins to ethylene is achieving high product yields, while overcoming the cost associated with supplying pure oxygen. At project initiation, scientists at Dow recognized that an oxidative dehydrogenation process could be commercially attractive if an improved product mix could be obtained. This has been achieved by exploiting the time-temperature-oxygen content trajectory possible only in microchannel architecture. Within a microchannel one can more effectively manage reaction time, temperature and the introduction of oxygen, by carefully controlling flow rates and reactor geometry, thus defining the time-temperature-oxygen content trajectory of the process. Breakthrough performance has been achieved with a reactor design, which was accelerated by modeling at three scales. First, a simplified kinetic model was developed from a complex reaction network of over 100 elementary steps by selecting a manageable few that account for key products and most of the energy generation and consumption. Second, the reduced network of reactions was used in a model of a slice of a commercial reactor that includes reactor hydrodynamics with detailed local mass and heat balances. Third, a global model was used to aggregate performance of many parallel reactor slices, as predicted by the intermediate model, to assess overall performance of a commercial full-scale reactor. This multi-scale modeling methodology closely predicted the experimental results of an integrated microstructured reactor with 84% ethane conversion and greater than 75% ethylene selectivity. The goal of the project is to demonstrate the economic viability of this approach. And this goal has been achieved. Although much work remains, laboratory experiments have shown that economic targets can be met in microchannel hardware with specially adapted catalysts. This presentation will describe the achievements of this DOE funded project and its implications for the broad applicability of microchannel process technology to selective oxidation processes.