(734a) Direct Non-Oxidative Conversion of Shale Gas to Aromatics: Dynamic Data Reconciliation, Parameter Estimation, and Dynamic Modeling of a Fixed-Bed Reactor

Majority of the BTX is produced from either petroleum naphtha, pyrolysis gasoline by-product, and/or coal liquids from coke-oven [1]. However, the abundant availability of small and large shale gas reserves in the United States, at easily accessible and remote locations, has significantly increased the interest in development of new reaction pathways for BTX production. For example, the Cyclar process developed by BP and UOP uses C₃-C₄ feed on a H-ZSM-5 catalyst for production of aromatics [1–3]. Other existing routes involve a multi-step process in which synthesis gas (syngas) must be first produced from the shale gas through steam reforming, partial oxidation, or autothermal reforming reaction. In these multi-step processes, the syngas generation step accounts for half of the plant capital, and a large share of the plant operating costs [4]. The carbon utilization efficiency is low (<50%), and the valuable H₂ product is also lost because CO or H₂ needs to be added to remove the oxygen when producing aromatics. Oxygen is removed in form of CO₂ or H₂O, as a result the energy penalty and capital cost increase due to the requirement for separation and disposal of CO₂.

One way to overcome these drawbacks is to directly convert methane, the main component in the shale gas, to aromatics. One of the key technologies for direct conversion of methane to aromatics is the non-oxidative methane dehydroaromatization (DHA) [5]. The DHA technology can lead to high conversion of methane with reasonable selectivity. Due to coke formation, conversion and yield from the DHA reactor keep changing with time making it difficult to develop an accurate kinetic model and estimate its parameters. Existing works in this area have assumed that the reactor operates under a pseudo-steady state condition thus ignoring the catalyst deactivation. Li et al. [6] have performed optimization of catalyst and membrane reactors for non-oxidative methane conversion process at a single temperature without considering the catalyst deactivation effect. Kaidi et al. [7] have proposed a set of 3 global reactions where the parameters of their rate model were estimated using the experimental data under assumed pseudo steady state region. Iliuta et al. [8], Fayzullaev et al. [9], and Yao et al. [10] have performed parameter estimation for methane DHA reaction system assuming steady state operation thus ignoring the catalyst deactivation effect.

In this work, reaction rate models including a deactivation model are proposed and their parameters are estimated using the in-house experimental data from a novel Mo/HZSM-5 catalyst. As the transient change in the amount and composition of the coke is not available and the experimental data do not satisfy carbon and hydrogen balances, a two-stage dynamic data reconciliation and parameter estimation problem is solved while simultaneously estimating the unknown initial state of the reactor. The kinetic model is then used to develop a multi-tubular multiscale first-principles dynamic fixed bed reactor model considering heat and mass transfer resistances. This model is used to simulate the cyclic reactor operation and techno-economic optimization.

References

[1] Niziolek AM, Onel O, Floudas CA. Production of Benzene, Toluene, and Xylenes from Natural Gas via Methanol: Process Synthesis and Global Optimization. AIChE 2016;62:1531–56.

[2] Treese SA, Pujadó PR, Jones DSJ. Handbook of petroleum processing. 2015. https://doi.org/10.1007/978-3-319-14529-7.

[3] Sweeney WA, Bryan PF. BTX Processing. Kirk-Othmer Encycl. Chem. Technol., 2007. https://doi.org/10.1002/0471238961.02202419230505.a01.pub2.

[4] Wilhelm DJ, Simbeck DR, Karp AD, Dickenson RL. Syngas production for gas-to-liquids applications: Technologies, issues and outlook. Fuel Process Technol 2001. https://doi.org/10.1016/S0378-3820(01)00140-0.

[5] Alvarez-Galvan MC, Mota N, Ojeda M, Rojas S, Navarro RM, Fierro JLG, et al. Direct methane conversion routes to chemicals and fuels. Catal Today2 2011;171:15–23.

[6] Li L, Borry RW, Iglesia E. Design and optimization of catalysts and membrane reactors for the non-oxidative conversion of methane. Chem Eng Sci 2002. https://doi.org/10.1016/S0009-2509(02)00314-7.

[7] Gao K, Yang J, Seidel-Morgenstern A, Hamel C. Methane Dehydro-Aromatization: Potential of a Mo/MCM-22 Catalyst and Hydrogene-Selective Membranes. Chemie-Ingenieur-Technik 2016. https://doi.org/10.1002/cite.201500139.

[8] Iliuta MC, Iliuta I, Grandjean BPA, Larachi F. Kinetics of methane nonoxidative aromatization over Ru-Mo/HZSM-5 catalyst. Ind Eng Chem Res 2003. https://doi.org/10.1021/ie030044r.

[9] I. Fayzullaev N. Kinetics and Mechanism of the Reaction of Catalytic Dehydroaromatization of Methane. Int J Oil, Gas Coal Eng 2017. https://doi.org/10.11648/j.ogce.20170506.11.

[10] Yao B, Chen J, Liu D, Fang D. Intrinsic kinetics of methane aromatization under non-oxidative conditions over modified Mo/HZSM-5 catalysts. J Nat Gas Chem 2008. https://doi.org/10.1016/S1003-9953(08)60027-4.