Steam adsorption on molecular sieve 3A for sorption enhanced reaction processes

Abstract

Steam adsorption enhanced reaction processes are a promising process intensification for many types of reactions, where water is formed as a byproduct. To assess the potential of these processes, adequate models are required that accurately describe water adsorption, particularly under the desired elevated temperatures and pressures. In this work, an adsorption isotherm is presented for H2O adsorption at 200–350 °C and 0.05–4.5 bar partial pressure on molecular sieve (LTA) 3A. The isotherm has been developed on the basis of experimental data obtained from a thermogravimetric analysis and integrated breakthrough curves. The experimental data at lower steam partial pressures can be described with a Generalized Statistical Thermodynamic Adsorption (GSTA) isotherm, whereas at higher steam partial pressures the experimental data can be adequately captured by capillary condensation. Based on the characteristics of the adsorbent particles, a linear driving force relation has been derived for the adsorption mass transfer rate and the apparent micropore diffusivity is determined. The isotherm and mass transport model presented here prove to be adequate for modelling and improved evaluation of steam adsorption enhanced reaction processes.

In Situ Conditioning of CO2-Rich Syngas during the Synthesis of Methanol

“…Catalysts 2021, 11, x FOR PEER REVIEW 10 of 18 the stationary state has been reached (this regime is akin to the experiments conducted with the double catalytic bed without H2O removal shown above). Please note that, based on recent isotherm measurements [30], a capacity of 0.1 mmol/g may be expected under these conditions leading to a breakthrough time of around 4 h. As observed in Figure 5 and Figure 7, the CO2 conversion obtained at low times on stream (TOS < 4 h) of ca. 25% is significantly higher than that obtained in either of the single-bed configurations or in the double-bed configuration without the sorbent under the same reaction conditions.…”

“…These results are discussed by considering three regimens: (i) low TOS, lower than 2 h, when the sorption capacity of the zeolite is maximum, (ii) TOS around 2-4 h, when the zeolite has lost part of its capacity, but still absorbs H 2 O, and (iii) TOS higher than 4 h, when the zeolite is fully saturated and the stationary state has been reached (this regime is akin to the experiments conducted with the double catalytic bed without H 2 O removal shown above). Please note that, based on recent isotherm measurements [30], a capacity of 0.1 mmol/g may be expected under these conditions leading to a breakthrough time of around 4 h.…”

“…In practice, this results in two times higher GHSV in the double-bed experiment than in the single-bed one, since the mass of methanol activity catalyst in the double-bed performance is the half than that in the single-bed one, which is actually consistent with the observed decreasing of methanol production. In addition, although the r-WGS has no effect in the M module of the syngas, it actually produces water, which is known to have negative impact in the performance of CZA catalysts for methanol production [22,23,30].…”

Separation enhanced methanol and dimethyl ether synthesis

“…LTA zeolites, and specically 3A, are highly selective for water due to size exclusion by the limited pore size. 14 Whereas the preferential permeation of polar molecules (water and methanol) is observed for various zeolitic membranes (FAU and MFI) and can be explained by a preferential adsorption mechanism rather than a size exclusion mechanism. 4 The recent experimental validation of pressure swing regeneration in sorption enhanced DME synthesis (SEDMES), already demonstrating a factor four increase in productivity, has opened up further process optimisation by cycle design.…”

“…11 In parallel, sorption enhanced technology for the production of DME has been developed and scaled up in recent years. 4,[12][13][14][15][16][17][18] Interestingly, the most promising materials for high temperature steam adsorption are again LTAtype zeolites. LTA zeolites, and specically 3A, are highly selective for water due to size exclusion by the limited pore size.…”