Measurement and correlation of PvT data for the CO2+hydrogen+methanol+water system

NATALIA COTABARREN; PABLO E. HEGEL; FRANCISCO A. SÁNCHEZ; SELVA PEREDA

Los Cocos, Córdoba

Conferencia; VI Iberoamerican Conference on Supercritical Fluids (PROSCIBA 2023); 2023

IPQA - UNC/CONICET

CO2 hydrogenation for the synthesis of methanol (CH 3OH) is an interesting route to mitigate CO2 emissions and promote a sustainable economy considering CO 2 capture/utilization and H2 storage. Based on the current industrial methanol production from syngas (H 2+CO and minor quantities of CO2 and CH4), CO 2 hydrogenation can be carried out in gas-solid catalytic reactors at moderated pressures (50 to 100 bar) and temperatures between 490 K and 570 K. However, the current industrial method requires a large recycle flow of syngas due to the limited conversion achieved in the reactor. An interesting concept is to apply in situ conden-sation of methanol or water (subproduct) operating at higher pressures (120 to 500 bar), which helps to circumvents the costly use of adsorbents or additional coolers to increase the conversion.Volumetric properties of reactive systems are needed to elucidate kinetic mechanisms and carry out a proper design of high-pressure continuous reactors, in particular for reactors with in-situ condensation of products. To our knowledge, experimental PvT data of the system (CO2 + H 2 + CH3OH + H2O) have not been reported under the temperature (493.15 K to 563 K) and pressures (70 to 400 bar) range of interest to carry out the CO 2 hydrogenation. Also, accurately predictive modeling of the volumetric properties and phase behavior of this non-ideal system, under supercritical conditions, can be complex due to the asymmetric molecular size and polarity between reactants (CO2/H 2) and products (mainly CH3OH and H2O).In this work, we adapted a high pressure/temperature stainless-steel constant volume cell (12.76 cc) to experimentally study the pressure-temperature isochoric behavior of quaternary synthetic mixtures under different stoichiometric molar ratios. The equipment has been calibrated in the range of operating conditions using pure fluids (methanol, CO 2, water). These measurements were compared to PvT data from the National Institute of Standard and Technology (NIST). The uncertainty in the density values is about 1.2 % based on calibration studies.In this work, we report new experimental PvT data of non-reactive mixtures of H2+CO2+CH3OH+H2O in the range of temperature and pressure of industrial interest. Mixtures have been prepared considering initial molar ratios of 1:3 CO2:H2, and different hypothetical stoichiometric conversions of CO2 (60 % to 94 %) to CH3OH:H2O (1:1). Isochoric studies of the multicomponent system between 0.13 g/cc and 0.5 g/cc show evidence of the phase transition, from heterogeneous to homogeneous phase condition at temperatures and pressures higher than 530 K and 240 bar, respectively. The phase equilibria and PvT data are modeled using RK-PR, a three-parameter equation of state. We selected the RK-PR because of its simplicity and proven accuracy to represent volumetric properties of other hydrogenation reactors.