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Title: Enhanced Hydrogen Production Integrated with CO2 Separation in a Single-Stage Reactor

Abstract

Hydrogen production from coal gasification can be enhanced by driving the equilibrium limited Water Gas Shift reaction forward by incessantly removing the CO{sub 2} by-product via the carbonation of calcium oxide. This project uses the high-reactivity mesoporous precipitated calcium carbonate sorbent for removing the CO{sub 2} product to enhance H{sub 2} production. Preliminary experiments demonstrate the show the superior performance of the PCC sorbent over other naturally occurring calcium sorbents. It was observed that the CO{sub 2} released during the in-situ calcination causes the deactivation of the iron oxide WGS catalyst by changing the active phase of the catalyst from magnetite (F{sub 3}O{sub 4}). Detailed understanding of the iron oxide phase diagram helped in developing a catalyst pretreatment procedure using a H{sub 2}/H{sub 2}O system. Intermediate catalyst pretreatment helps prevent its deactivation by reducing the catalyst back to its active magnetite (Fe{sub 3}O{sub 4}) form. Multicyclic runs which consist of combined WGS/carbonation reaction followed by in-situ calcination with a subsequent catalyst pretreatment procedure sustains the catalytic activity and prevents deactivation. The water gas shift reaction was studied at different temperatures, different steam to carbon monoxide ratios (S/C) 3:1, 2:1, 1:1 and different total pressures ranging from 0-300 psig. The COmore » conversion was found to have an optimal value with increasing pressure, S/C ratio and temperatures. The combined water gas shift and carbonation reaction was investigated at 650 C, S/C ratio of 3:1and at different pressures of 0-300 psig.« less

Authors:
; ;
Publication Date:
Research Org.:
The Ohio State Univ., Columbus, OH (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
898311
DOE Contract Number:
FC26-03NT41853
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
01 COAL, LIGNITE, AND PEAT; 08 HYDROGEN; CALCIUM; CALCIUM CARBONATES; CALCIUM OXIDES; CARBON MONOXIDE; COAL GASIFICATION; DEACTIVATION; HYDROGEN PRODUCTION; IRON OXIDES; PHASE DIAGRAMS; PRODUCTION; WATER GAS; CARBON DIOXIDE

Citation Formats

Mahesh Iyer, Shwetha Ramkumar, and Liang-Shih Fan. Enhanced Hydrogen Production Integrated with CO2 Separation in a Single-Stage Reactor. United States: N. p., 2006. Web. doi:10.2172/898311.
Mahesh Iyer, Shwetha Ramkumar, & Liang-Shih Fan. Enhanced Hydrogen Production Integrated with CO2 Separation in a Single-Stage Reactor. United States. doi:10.2172/898311.
Mahesh Iyer, Shwetha Ramkumar, and Liang-Shih Fan. Fri . "Enhanced Hydrogen Production Integrated with CO2 Separation in a Single-Stage Reactor". United States. doi:10.2172/898311. https://www.osti.gov/servlets/purl/898311.
@article{osti_898311,
title = {Enhanced Hydrogen Production Integrated with CO2 Separation in a Single-Stage Reactor},
author = {Mahesh Iyer and Shwetha Ramkumar and Liang-Shih Fan},
abstractNote = {Hydrogen production from coal gasification can be enhanced by driving the equilibrium limited Water Gas Shift reaction forward by incessantly removing the CO{sub 2} by-product via the carbonation of calcium oxide. This project uses the high-reactivity mesoporous precipitated calcium carbonate sorbent for removing the CO{sub 2} product to enhance H{sub 2} production. Preliminary experiments demonstrate the show the superior performance of the PCC sorbent over other naturally occurring calcium sorbents. It was observed that the CO{sub 2} released during the in-situ calcination causes the deactivation of the iron oxide WGS catalyst by changing the active phase of the catalyst from magnetite (F{sub 3}O{sub 4}). Detailed understanding of the iron oxide phase diagram helped in developing a catalyst pretreatment procedure using a H{sub 2}/H{sub 2}O system. Intermediate catalyst pretreatment helps prevent its deactivation by reducing the catalyst back to its active magnetite (Fe{sub 3}O{sub 4}) form. Multicyclic runs which consist of combined WGS/carbonation reaction followed by in-situ calcination with a subsequent catalyst pretreatment procedure sustains the catalytic activity and prevents deactivation. The water gas shift reaction was studied at different temperatures, different steam to carbon monoxide ratios (S/C) 3:1, 2:1, 1:1 and different total pressures ranging from 0-300 psig. The CO conversion was found to have an optimal value with increasing pressure, S/C ratio and temperatures. The combined water gas shift and carbonation reaction was investigated at 650 C, S/C ratio of 3:1and at different pressures of 0-300 psig.},
doi = {10.2172/898311},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Fri Mar 31 00:00:00 EST 2006},
month = {Fri Mar 31 00:00:00 EST 2006}
}

Technical Report:

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  • The water gas shift reaction (WGSR) plays a major role in increasing the hydrogen production from fossil fuels. However, the enhanced hydrogen production is limited by thermodynamic constrains posed by equilibrium limitations of WGSR. This project aims at using a mesoporous, tailored, highly reactive calcium based sorbent system for incessantly removing the CO{sub 2} product which drives the equilibrium limited WGSR forward. In addition, a pure sequestration ready CO{sub 2} stream is produced simultaneously. A detailed project vision with the description of integration of this concept with an existing coal gasification process for hydrogen production is presented. Conceptual reactor designsmore » for investigating the simultaneous water gas shift and the CaO carbonation reactions are presented. In addition, the options for conducting in-situ sorbent regeneration under vacuum or steam are also reported. Preliminary, water gas shift reactions using high temperature shift catalyst and without any sorbent confirmed the equilibrium limitation beyond 600 C demonstrating a carbon monoxide conversion of about 80%. From detailed thermodynamic analyses performed for fuel gas streams from typical gasifiers the optimal operating temperature range to prevent CaO hydration and to effect its carbonation is between 575-830 C.« less
  • Hydrogen production cannot be maximized from fossil fuels (gas/coal) via the WGS reaction at high temperatures as the WGS-equilibrium constant K{sub WGS} (= [CO{sub 2}][H{sub 2}]/[CO][H{sub 2}O]), falls with increasing temperatures. However, CO{sub 2} removal down to ppm levels by the carbonation of CaO to CaCO{sub 3} in the temperature range 650-850 C, leads to the possibility of stoichiometric H{sub 2} production at high temperature/pressure conditions and at low steam to fuel ratios. Further, CO{sub 2} is also captured in the H{sub 2} generation process, making this coal to hydrogen process compatible with CO{sub 2} sequestration goals. While microporous CaOmore » sorbents attain <50% conversion over cyclical carbonation-calcination, the OSU-patented, mesoporous CaO sorbents are able to achieve >95% conversion. Novel calcination techniques could lead to an ever-smaller footprint, single-stage reactors that achieve maximum theoretical H{sub 2} production at high temperatures and pressures for on/off site usage. Experimental results indicate that the PCC-CaO sorbent is able to achieve complete conversion of CO for 240 seconds as compared to only a few seconds with CaO derived from natural sources.« less
  • Hydrogen production by the water gas shift reaction (WGSR) is equilibrium limited due to thermodynamic constrains. However, this can be overcome by continuously removing the product CO{sub 2}, thereby driving the WGSR in the forward direction to enhance hydrogen production. This project aims at using a high reactivity, mesoporous calcium based sorbent (PCC-CaO) for removing CO{sub 2} using reactive separation scheme. Preliminary results have shown that PCC-CaO dominates in its performance over naturally occurring limestone towards enhanced hydrogen production. However, maintenance of high reactivity of the sorbent over several reaction-regeneration cycles warrants effective regeneration methods. We have identified sub-atmospheric calcinationmore » (vacuum) as vital regeneration technique that helps preserve the sorbent morphology. Sub-atmospheric calcination studies reveal the significance of vacuum level, diluent gas flow rate, thermal properties of diluent gas, and sorbent loading on the kinetics of calcination and the morphology of the resultant CaO sorbent. Steam, which can be easily separated from CO{sub 2}, has been envisioned as a potential diluent gas due to its better thermal properties resulting in effective heat transfer. A novel multi-fixed bed reactor was designed which isolates the catalyst bed from the sorbent bed during the calcination step. This should prevent any potential catalyst deactivation due to oxidation by CO{sub 2} during the regeneration phase.« less
  • Hydrogen production from coal gasification can be enhanced by driving the equilibrium limited Water Gas Shift reaction forward by incessantly removing the CO{sub 2} by-product via the carbonation of calcium oxide. This project aims at using the OSU patented high-reactivity mesoporous precipitated calcium carbonate sorbent for removing the CO{sub 2} product. Preliminary experiments demonstrate the show the superior performance of the PCC sorbent over other naturally occurring calcium sorbents. Gas composition analyses show the formation of 100% pure hydrogen. Novel calcination techniques could lead to smaller reactor footprint and single-stage reactors that can achieve maximum theoretical H{sub 2} production formore » multicyclic applications. Sub-atmospheric calcination studies reveal the effect of vacuum level, diluent gas flow rate, thermal properties of the diluent gas and the sorbent loading on the calcination kinetics which play an important role on the sorbent morphology. Steam, which can be easily separated from CO{sub 2}, is envisioned to be a potential diluent gas due to its enhanced thermal properties. Steam calcination studies at 700-850 C reveal improved sorbent morphology over regular nitrogen calcination. A mixture of 80% steam and 20% CO{sub 2} at ambient pressure was used to calcine the spent sorbent at 820 C thus lowering the calcination temperature. Regeneration of calcium sulfide to calcium carbonate was achieved by carbonating the calcium sulfide slurry by bubbling CO{sub 2} gas at room temperature.« less
  • High purity hydrogen is commercially produced from syngas by the Water Gas Shift Reaction (WGSR) in high and low temperature shift reactors using iron oxide and copper catalysts respectively. However, the WGSR is thermodynamically limited at high temperatures towards hydrogen production necessitating excess steam addition and catalytic operation. In the calcium looping process, the equilibrium limited WGSR is driven forward by the incessant removal of CO{sub 2} by-product through the carbonation of calcium oxide. At high pressures, this process obviates the need for a catalyst and excess steam requirement, thereby removing the costs related to the procurement and deactivation ofmore » the catalyst and steam generation. Thermodynamic analysis for the combined WGS and carbonation reaction was conducted. The combined WGS and carbonation reaction was investigated at varying pressures, temperatures and S/C ratios using a bench scale reactor system. It was found that the purity of hydrogen increases with the increase in pressure and at a pressure of 300 psig, almost 100% hydrogen is produced. It was also found that at high pressures, high purity hydrogen can be produced using stoichiometric quantities of steam. On comparing the catalytic and non catalytic modes of operation in the presence of calcium oxide, it was found that there was no difference in the purity of hydrogen produced at elevated pressures. Multicyclic reaction and regeneration experiments were also conducted and it was found that the purity of hydrogen remains almost constant after a few cycles.« less