When applying for a patent, an inventor naturally wants to cast a net wide enough to cover not only what the inventor has actually done but also all variations that utilize the invention’s core innovation. A claim that is too wide, however, can run into resistance at the U.S. Patent and Trademark Office (USPTO). A recent case regarding a process for the simultaneous production of ethylene and benzene illustrates how these two concerns can conflict with each other.
Ethylbenzene is an important precursor to many engineering materials, including polystyrene. It is traditionally made by the alkylation of benzene with ethylene in the vapor phase at 750°F. This process requires the use of high-purity benzene, because the nonaromatic impurities typically associated with benzene tend to crack at high temperatures and form cumene and other alkylates. Conventional distillation is not effective for removing these contaminants, since they form azeotropes with benzene. Therefore, extractive distillation, i.e., the separation of components by differences in their solubilities using a high-boiling-point solvent, is commonly used to purify benzene.
Extractive distillation is a well-known process widely used by Shell, UOP, Lurgi, and Uhde for a variety of separations, including benzene purification. Shell developed its own...
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