(609c) Design and Control of Glycerol Tertiary Butyl Ethers Process for the Utilization of Renewable Resource

Due to the surging interest in biodiesel production in recent year, the development of a new process utilizing glycerol (as by-product in biodiesel process) becomes important. One of the various possibilities is on glycerol etherification with isobutene to produce glycerol tertiary butyl ethers (GTBEs). The products of the acid-catalyzed etherification can be a mono-ether, a di-ether, or a tri-ether, where the ?higher ethers? (di- and tri-) can be used as an octane booster for gasoline or as diesel additive. Previous investigations of this process are threefold. In the ARCO process1, large amount of mono-ether is lost through the waste water stream in an extraction column. In the Bhern and Obendorf process2, a vacuum column is necessary to prevent the cleavage of ethers. In the Di Serio, et al. process3, the design flowsheet is complex and the mono-ether is still present in the final product.

Comparing of the above three processes, Bhern and Obendorf's process, although requiring vacuum operation in a rectifying column, is the most simplified and complete design for obtaining higher ethers satisfying product specification. In this work, this conceptual design is further investigated to establish an optimized design flowsheet containing two CSTRs in series followed by an extraction column, a stripping column and a vacuum rectifying column. There are three recycle streams in the design flowsheet. Glycerol feed is introduced into extraction column to extract remaining mono-ether from the reactor effluent and then recycle back to the reaction section. Excess isobutene is recycled back to the reaction section from the top of the stripping column. The bottoms of the rectifying column containing materials not satisfying product specificaton is also recycled back to the reaction section. The overall design flowsheet is optimized to minimize the Total Annual Cost (TAC) of the overall process. This design flowsheet is further improved to avoids some dirable products to be recycled back to the reaction section, thus reduces the TAC further. The dynamics and control of the overall process are also investigated. The proposed control strategy is able to maintain product purity despite 20% production rate changes.

References:

1. Gupta, V. P. Glycerine ditertiary butyl ether preparation. U. S. Patent 5,476,971, 1995.

2. Behr, A.; Obendorf, L. Development of a process for the acid-catalyzed etherification of glycerine and isobutene forming glycerine tertiary butyl ehters. Eng. Life Sci. 2003, 2, 185-189.

3. Di Serio, M.; Casale, L.; Tesser, R.; Santacesaria, E. New process for the production of glycerol tert-butyl ethers. Energy Fuels 2010, 24, 4688.