(296d) Use of Solar Thermal Industrial Process Heat for Energy Efficient Endothermic Conversion of Ethane and Alkanes to Ethylene, Olefins and Aromatics

Highly endothermic non-oxidative dehydrogenation (NODH) is an efficient and commercially viable means to convert light paraffins ethane, propane and butane into the corresponding olefins ethylene, propylene and butylene, and under optimized process conditions, produce light aromatics including benzene, toluene and xylenes. Production of ethylene from naphtha or ethane via what is essentially modified NODH, ethane steam cracking (ESC), is the greatest consumer of energy in the petrochemical industry and as such offers a significant opportunity for improvements in terms of reducing energy demand, simplifying downstream purification processes and decreasing production costs. Solar Industrial Process Heating (SIPH), involving the use of concentrating solar power (CSP) falling particle bed receiver technology, can be used to reduce the cost and impact of hydrocarbon-based fuel combustion used as the energy source for ESC and more broadly, NODH. SIPH can operate at temperatures relevant to ESC, making this approach attractive as an alternate low impact energy source for the chemical manufacturing sector. The CSP and falling particle bed aspects of our approach to NODH are based on the performance of Sandia National Laboratories National Solar Thermal Test Facility.

We are engaged in a multi-pronged approach to addressing energy, impact and cost issues for commercial production of ethylene, light olefins, and aromatics, involving:

• Small pilot scale investigations into improvements in NODH processes including parameter tuning to optimize either olefin or aromatic yields;
• Process modeling of reactor and downstream purification unit operations for thermal recuperation and energy savings;
• Reactive computation fluid dynamics (CFD) modeling to optimize reactor designs using experimentally validated global kinetic models.;
• Use of falling particle bed solar thermal technology as the source of industrial process energy at temperatures more than 800 °C and balance of plant electric power for the NODH processes.

We have previously studied ethane NODH for ethylene production in recent projects with Sandia National Laboratories and University of New Mexico (1,2), showing that in a suitable thermal and materials environment NODH can match or exceed commercial ethane steam cracking in terms of single-pass ethylene yields, in some cases reaching 75%. In this work NODH kinetics were experimentally measured over a wide range of operating conditions and subsequently refined using reactive CFD modeling. The simplified kinetic expression involving reactions of C2H6, C2H4, CH4, H2, C3H6, C3H8, C4H8, C4H10, C6H12 and C6H6 were found to adequately model the experimental data while minimizing computational resources.

With minor adjustment to two parameter rate models for each reaction, the prior kinetic model was found to produce excellent agreement with NODH conducted for either olefin or aromatic production in the presence of solar thermal particles at temperatures from 700 to 850 °C. Conversions and product yields were measured over a range of candidate particle compositions, particle diameters and gas/particle differential flow rates using simple contactor design strategies. Particles examined included calcined aluminum hydroxide materials, alpha-alumina, quartz and yttria-stabilized zirconia, and at particle diameters from about 200 to 500 microns.

Process modeling was completed to understand how variations in product selectivities impacted energy requirements for the overall process and for product separation and purification. Aside from the reactor section, major unit operations included as part of the process model were thermal recuperation and heat exchange, compression, COX removal, product drying, BTX liquids separation, and demethanization, deethanization, and ethane splitter distillation columns to recovery fuel gas (H2, CH4), ethane recycle, C3/C4 streams, ethane for recycle and ethylene and mixed BTX product recovery.

We show that the use of CSP-based solar industrial process heating can offer reduced energy costs and process impacts while meeting or exceeding ethylene productivity of current ESC facilities. Moreover, our approach of combining CSP, SIPH and NODH can yield an economical and practical means of distributed production of valuable BTX products based on ethane hydrodearomatization. These improvements offer a new paradigm in olefin and aromatics production, enabling distributed solutions to replace highly capital-intensive centralized ESC and oligomerization facilities.

Acknowledgement: This work is supported by multiple DOE and ONR grants.

References:

1. Riley, C.R., De La Riva, A., Ibarra, I.L., Datye, A.K., and Choum S.S. "Achieving high ethylene yield in non-oxidative ethane dehydrogenation" Applied Catalysis A: General 624 (2021): 118309.

2. Weissman, J., DeCarmine, A., Datye, A., DeLaRiva, A. T., Riley, C., Brown, A., Spoerke, E. (2023, November). Reactive CFD Modeling, Experimental Validation and Scale-up of Non-Oxidative Ethane Dehydrogenation to Ethylene. In 2023 AIChE Annual Meeting. AIChE.

Keywords: Non-oxidative dehydrogenation, ethylene, aromatics