(430d) Production of Benzene, Toluene, and Xylenes from Natural Gas Via Methanol: A Process Synthesis and Global Optimization Approach

Efficient utilization of domestic resources, such as natural gas, is crucial toward meeting U.S. energy independence targets and addressing energy security, energy affordability, and the generation of lower-carbon energy. [1] As a result of the developments within the shale gas industry, recent efforts have focused on converting natural gas into more valuable products. [2,3] A subset of these valuable products are aromatics, which represent approximately one-third of the market for commodity petrochemicals. [4] Between 2005 and 2008, the global demand for benzene, para-xylene, ortho-xylene, and meta-xylene was approximately 40, 26, 6, and 0.4 million metric tons per year, respectively. [4] Benzene is a precursor to over 250 different products, including styrene and phenol. Para-xylene, the most valuable xylene isomer, is converted into polyethylene terephthalate (PET) fibers, resins and films. [5] Opportunities exist for widespread penetration of natural gas based chemical refineries, albeit with challenges associated with which types of chemicals to produce and which technologies to invest in. In order to address these challenges, we propose novel methods of producing aromatics using a combined process synthesis and global optimization approach. [6]

We present a deterministic global optimization based process synthesis framework to perform a comprehensive technoeconomic and environmental assessment of a natural gas based aromatics refinery. [6] Several direct and indirect natural gas conversion technologies, including autothermal reforming, steam reforming, and partial oxidation to methanol, are investigated. Numerous novel, commercial, and/or competing technologies are modeled within the framework, including methanol-to-aromatics, toluene alkylation with methanol, selective toluene disproportionation, toluene disproportionation and transalkylation with heavy aromatics, para-xylene separation via adsorptive separation or crystallization, isomerization of xylenes, and dehydrocyclodimerization of liquefied petroleum gas, among others. To address the economic barriers often associated with the utilization of alternative feedstocks, we develop a novel branch-and-bound global optimization algorithm that is capable of determining the optimal technologies to produce aromatics from natural gas at the highest profit. [6,7] Our approach provides an adequate baseline for comparing competing technologies and identifying bottlenecks for natural gas conversion based technologies. Several key aspects of the algorithm are discussed, multiple case studies are presented to investigate the effect of refinery capacity and product output, and the key topological decisions are described.

[1] Floudas, C. A.; Niziolek, A. M.; Onel, O.; Matthews, L. R. Multi-Scale Systems Engineering for Energy and the Environment: Challenges and Opportunities. AIChE Journal 2016, 62, 602-623.

[2] Mokrani, T.; Scurrell, M. Gas conversion to liquid fuels and chemicals: the methanol route-catalysis and processes development. Catalysis Reviews 2009, 51:1-145

[3] Baliban, R. C.; Elia, J. A.; Floudas, C. A. Novel natural gas to liquids (GTL) technologies: Process synthesis and global optimization strategies. AIChE Journal 2013, 59, 505â??531.

[4] de Klerk, A. Fischer-Tropsch Refining; Wiley-VCH Verlag & Co. KgaA: Weinheim 2011

[5] Niziolek, A. M.; Onel, O.; Elia, J. A.; Baliban R. C.; Floudas, C. A. Coproduction of Liquid Transportation Fuels and C6_C8 Aromatics from Biomass and Natural Gas. AIChE Journal 2015, 61, 831-856.

[6] Niziolek, A. M.; Onel, O.; Floudas, C. A. Production of Benzene, Toluene, and Xylenes from Natural Gas via Methanol: Process Synthesis and Global Optimization. AIChE Journal 2016, 62 (5), 1531 â?? 1556.

[7] Baliban, R. C.; Elia, J. A.; Misener, R.; Floudas, C. A. Global Optimization of a MINLP Process Synthesis Model for Thermochemical Based Conversion of Hybrid Coal, Biomass, and Natural Gas to Liquid Fuels. Computers and Chemical Engineering 2012, 42, 64-86.