Initiatives in Process Intensification and Modular Chemical Processing

The shale gas boom in the United States provides abundant natural gas liquids (NGLs) as feedstocks to petrochemical industry¹. The major use of natural gas liquids is to produce olefins such as ethylene, propylene, and butene, which are crucial building blocks to manufacture plastic, fiber, rubber, etc. Two major bottlenecks of the conventional process framework are the conversions in reactors and the complexity of separation systems in frontend and post-reaction separation steps. Both steam cracking and catalytic dehydrogenation requires high temperatures (850°C for stream cracking and 500∼650°C for catalytic dehydrogenation of propane and butane) and low partial pressure of NGL to achieve high conversions per pass. Furthermore, steam is introduced to the steam cracker to further decrease the partial pressure of hydrocarbons; diluents such as CH₄, N₂, H₂ or steam are also sometimes introduced to catalytic dehydrogenation reactor ^2-5. However, additional separation steps to remove these diluents contribute significantly to the process complexities and the costs associated with the process. Separation units in the system, such as cryogenic demethanizer, paraffin/olefin separations are conventionally achieved through complex heat-pumped distillation configurations. More importantly, several post-reaction separations are repeated separations as they are also required in the front end. Due to this duplication of separation steps, not only more energy is consumed but more equipment is employed contributing to increased capital expenditure.

Here we propose a paradigm shift of process framework, which eliminates repeated separation units and enhances conversions in the reactors synergistically. This paradigm shift of process framework distinguishes our work from all the process intensification studies on this topic in literature, which stick to the conventional process framework and focus on the development of alternative technologies and the integration of adjacent unit operations. The benefits of the paradigm shift are illustrated through detail simulations and economic analyses of exemplary processes under the new process frameworks.

Reference

1. Siirola, J. J. The impact of shale gas in the chemical industry. AIChE Journal 2014, 60, 810–819.
2. Leonard, L. E.; Bozzano, A. G.; Towler, G. P. Hydrocarbon dehydrogenation with inert diluent. 2013; US Patent App. 13/328,931.
3. Sundaram, K.; Fernandez-Baujin, J. Effect of methane and hydrogen during thermal

cracking of light hydrocarbons. AIChE journal 1988, 34, 321–325.

4. Leesemann, C. J. Process for dehydrogenation of hydrocarbons in the presence of a

gaseous diluent. 1949; US Patent 2,461,331.

5. Gami, A. C. Use of hydrocarbon diluents to enhance conversion in a dehydrogenation

process at low steam/oil ratios. 2014; US Patent Application 14/052,949.