Thermal (non-catalytic) HDA — broad aromatics feedstock

A real thermal-HDA licensor's process (non-catalytic, tolerant of a mixed aromatics feedstock and inert impurities) modeled as a genuine competing-and-sequential reaction network in a real plug-flow reactor, not a fixed-Keq equilibrium reactor like the simpler hda-toluene-dealkylation example. The main toluene dealkylation (toluene + H2 -> benzene + methane) uses real published kinetics: (-r_toluene) = k0*exp(-Ea/RT)C_tolueneC_H2^0.5 (order 1 in toluene, order 0.5 in H2, the classic 1.5-order thermal-HDA rate law), k0 = 5.67e9 (m3/mol)^0.5/s, Ea = 228,200 J/mol, heat of reaction -49,000 J/mol -- transcribed from Shull & Hixon (Ind. Eng. Chem. Process Des. Develop. 5, 147, 1966) as tabulated in Rase, H.F., 'Chemical Reactor Design for Process Plants, Vol. 2: Case Studies and Design Data' (Wiley-Interscience, 1977), Case Study 104 'Toluene Dealkylation', pp. 36-42 (unit-converted from the source's imperial (ft, lb-mol, degR) basis to SI). That same source explicitly states 'rate equations for the side reactions have not been reported' -- so the coking/heavies side reaction (2 toluene -> biphenyl + H2, the real reaction that caps aromatic yield below 100% and drives decoking intervals) and the xylene demethylation feeding the shared toluene pool (o-xylene + H2 -> toluene + methane -- the real single-methyl-loss pathway, not a lumped double-dealkylation straight to benzene, so this is a genuine reactions-in-series-and-parallel network, not three independent reactions) both stay illustrative order-of-magnitude Arrhenius parameters, tuned only to land in the source's cited ~98% main-reaction selectivity at 2:1 H2:toluene -- honestly labeled as such, not fabricated citations. H2S/CO2/ammonia ride through the flowsheet as inert impurities -- exactly what 'impurity tolerance' means in a mass balance, not a special chemistry path. A real fired heater (rigorous combustion stoichiometry + stack energy balance, the same unit op used in the naphtha-steam-cracker example) brings the mixed fresh-plus-recycle feed up to reaction temperature -- not a feed specified as already at 950 K. The H2-rich high-pressure separator vapor is a real recycle loop: fresh feed joins recycled gas at a mixer ahead of the furnace, and past the separator the vapor splits into a recompressed recycle (85%) and a genuine purge (15%) that bleeds off the methane a single pass could never consume -- the same role a purge plays in the ammonia-synthesis-loop example. Quench, the high-pressure separator, and a letdown-valve-plus-flash stabilizer strip dissolved H2/methane before the aromatics split. The reactor is genuinely adiabatic, not isothermal: temperature is a real energy-balance-coupled ODE state (kinetic_reactor.py's adiabatic PFR mode) that rises along the reactor length as the exothermic reactions release heat -- starting from the furnace's real ~900 K outlet (in the source's cited 894-922 K inlet range) and climbing as the reaction proceeds, self-consistent to within ~0.01% of the reactor's own required external duty (which should be ~0 for a truly adiabatic reactor -- verified, not assumed). One honest simplification remains: the final benzene/toluene/xylene-derived-benzene split still uses a shortcut separator rather than a rigorous column, for the same documented reason as hda-toluene-dealkylation: trace H2/methane corrupts the column's wide-boiling initial-guess classification, and a fix narrowed to just that seed broke the shipped methanol-synthesis example when tried previously.