The availability of traditional base chemicals such as ethylene, propylene and BTX aromatics is undergoing dramatic changes due to the global shift from liquid to gaseous feedstocks, fuelled by the abundance of unconventional feedstocks. Although this trend is primarily triggered by the fast growing shale gas economy in the US and cheap coal in China, other regions will follow, causing the global supply and demand situation to equilibrate across the regions. On top of the effect from lack of aromatics in the product from ethane steam cracking, BTX markets will be hit by lower demand for gasoline in key regions and consequently less aromatics-rich reformate from refineries. The tightening of aromatics markets will come at a time of healthy growth rates, however. Advantaged gaseous feedstocks such methane from shale gas or coal gasification as well as natural gas liquids (NGL), primarily propane and butanes from shale reserves or associated petroleum gas (APG), offer a great platform to make aromatics in a unconventional manner, and close the supply- demand gap, especially in regions where naphtha is in short supply. Historically, aromatization of short-chain paraffins and olefins has been used to produce aromatics-rich gasoline but it is currently being re-discovered as an attractive process for BTX aromatics, and ultimately paraxylene. Like many other processes for aromatics conversion and upgrading, aromatization makes use of the unique properties of zeolites. For C3 and C4 paraffinic feeds, Ga-MFI (ZSM-5) with Ga being incorporated in the zeolite framework has proven to be indispensable when it comes to achieving high conversion and selectivity to aromatics. The industrial record of making aromatics from synthesis gas and methanol conversion is also confined to gasoline so far (MTG process) but methanol-to-aromatics (MTA) as an aromatics- selective derivative of this process has the potential for a break-through in low-cost feed scenarios. Methanol from natural gas can be used to methylate toluene to make mixed xylenes or predominantly paraxylene, depending on the process type. All unconventional aromatics processes fit well into existing schemes of conventional aromatics production.
This paper provides an overview on the technologies used in the production of BTX aromatics from conventional (reformate, pyrolysis gasoline) and unconventional (gas-based) feeds, and elaborates on the potential benefits from alternative aromatics technologies.
