FINAL TECHNICAL REPORT September 1, 2004, through August 31, 2005

Project Title: NOVEL CONCEPT FOR HYDROGEN AND CO2 SEPARATION FROM COAL GASIFICATION PRODUCTS ICCI Project Number: 04-1/3.3B-1 Principal Investigator: Tomasz Wiltowski, Southern Illinois University at

Carbondale Other Investigators: Kanchan Mondal, Southern Illinois University at

Carbondale Project Manager: Ronald H. Carty, ICCI

ABSTRACT The objective of this project is to develop a process for the separation of hydrogen from coal gasification based syngas components for end uses such as clean energy production. The research is expected to provide significant impetus to Illinois coal in finding a place in the FutureGen vision as well as tapping emerging markets for high purity hydrogen. SIU has developed a process that is capable of separating hydrogen from synthesis gas. The process is flexible such that it can be used within the gasifier to separate hydrogen or as a separate unit process, depending on the requirements of the process design. The basic idea of the research is to design and apply solids to be used in a fixed bed reactor that will increase the hydrogen yield as well as capture greenhouse gases in its matrix through reaction. The end product envisioned in this process is pure hydrogen. The spent solids would then be regenerated thermoneutrally while releasing sequestration ready carbon dioxide. The project involves the validation of this process along with the evaluation of the process parameters to maximize the hydrogen content in the product stream. The effect of sulfur (present as H2S) in the product stream on the process efficiency was also evaluated. Most importantly, the solids were designed such that they have the maximum selectivity to the beneficial reactions while maintaining their structure and activity through the reaction-regeneration cycles. Iron (created by reduction of hematite with syngas) was selected as the Boudouard catalyst and CaO was selected as the carbon dioxide removal material. Thermogravimetric and Temperature Programmed Reduction Analysis were utilized to evaluate the reaction rate parameters, and capacity for CO2. Specially synthesized CaO (wherein the surface properties were modified) was found to provide better capacity and reaction rates as compared to commercially available CaO. In addition, these specially synthesized CaO showed lower deactivation over multiple cycles. Experiments were also performed with different compositions of syngas to identify the optimal conditions for pure H2 production. Finally, simultaneous coal gasification and hydrogen enrichment experiments were conducted. It was found that for a Fe2O3: Coal ratio of 22:1, and Fe2O3: CaO ratio of 1:3, no COx was released, while for a Fe2O3: Coal ratio of 44:1, no H2S was released.

EXECUTIVE SUMMARY The objective of this research was to develop a high temperature process for the separation of hydrogen from coal derived syngas. SIUC has developed and evaluated (at atmospheric pressures) this new process utilizing the carbon formation phenomenon to the advantage of separating hydrogen from carbon monoxide. The results show enhanced enrichment of H2 along with complete depletion of CO, which is considered to be a strong poison to fuel cell catalysts and limits the wide applicability of fuel cells. The above-mentioned process involves the reaction of syngas with the two solid phases in a nearly thermoneutral process which enriches hydrogen and provides an inexpensive method for the production of sequestration ready carbon dioxide. Theoretically, the regeneration of the spent solids can be conducted thermoneutrally. The process will be conducted at pressures that would facilitate the sequestration of carbon dioxide and permit excess heat to be used for shaft work. The main goal of the research was to validate and identify the optimal conditions of this novel process using an oxygen transfer agent (that would also initiate the Boudouard reaction) and a carbon dioxide removal material to produce the hydrogen gas of the purity required for commercially available fuel cells. Based on the obtained data, the technical potential and economical applicability of the process was found to be significant. Iron derived from reduction of hematite has been identified as a suitable catalyst while surface modified CaO has been earmarked as a suitable carbon dioxide removal agent. The process has the potential of removing components such as H2S, CO, CO2 and enhances the gasification rates of methane and higher hydrocarbons. As a result, the product of this process is a pure hydrogen stream for fuel cell applications. The basic idea of the project lies in the sequential use of (a) iron oxide to oxidize carbon monoxide present in syngas and greatly enhance the Boudouard reaction for both production of CO2 and amorphous carbon and (b) capture of CO2 using an indigenously designed, high reactivity, high capacity CaO, resulting in the production of high purity hydrogen stream. Subsequently, the metallic Fe (reduction of Fe2O3) which also contains carbon is oxidized (and thus regenerated) in the presence of air/oxygen and the heat liberated via this exothermic reaction is utilized to calcine the calcium carbonate (carbonation of CaO). In the hydrogen enrichment pass, all of the carbon monoxide is converted (theoretically) to carbon dioxide (via water gas shift reaction, oxidation by iron oxide, and Boudouard reaction) and carbon (by Boudouard reaction). Thus, the operation of this system would result into three separate streams of (a) high purity hydrogen for use in fuel cells; (b) sequestration ready CO2; and (c) high temperature (pressure) oxygen depleted air for use in gas turbines. The objectives of the proposed research include i) design and fabrication of a high pressure, two reactor system that would enrich hydrogen from the coal gasification products (produced in a separate gasifier); ii) the evaluation of the oxides to optimize the efficiency of the enrichment and regeneration process at elevated pressures and identify the operating range of the process parameters; iii) determination of cycle time for enrichment and regeneration processes as well as the maximum number of enrichment – regeneration cycles; iv) development of a coherent process model; and v) establish

technical feasibility of the process. Phase composition, morphology and surface properties of the solid oxides examined were characterized using BET Quantachrome surface area analyzer, X-ray diffraction technique, Microtrac Laser Particle analyzer, energy dispersive X-ray diffraction, and scanning electron microscopy. The gaseous streams (inlet and the two effluent streams) chemical composition was analyzed using an Agilent MicroGC gas chromatograph working on-line. Task 1 Acquisition, preparation and characterization of oxides The objective of this task was the acquisition, preparation and characterization of solids, supports, and active solids on these supports. Morphologically altered high surface area CaO and Fe2O3 were synthesized in the laboratory. Monolith was acquired and wash-coated with active solids. Materials were characterized for BET surface area, pore volume, and average pore radius. The particle size distribution was evaluated using a Microtrac laser size analyzer. To check on the uniformity of the impregnation within the support, representative samples were analyzed with scanning electron microscopy with energy-dispersive X-ray methods (SEM-EDX). Task 2 Thermodynamic and Kinetic Studies The objective of this task was to analyze the thermodynamics of the process using the HSC Chemistry software. Enthalpy and free energy changes were calculated for both enrichment and regeneration reactions. Equilibrium constants were formulated over a range of temperatures (650 – 950oC) and thermodynamic analysis was used to identify favorable ranges of temperature for reaction, adsorption and regeneration to be thermodynamically feasible. Kinetic experiments were performed using a microbalance assembly consisting of a Perkin Elmer TG7A Thermogravimetric Analyzer (TGA). Reacting gas compositions were obtained by blending high purity gases using Sierra mass flow controllers. The weight change was used to determine the different reactions rate constants. The resulting solids were then analyzed using X-ray diffraction and scanning electron microscopy. Specifically, the following tasks were conducted under this section: while the TGA experiments were conducted isothermally, temperature programmed reduction studies were conducted on the various iron oxides in dilute H2 atmospheres to identify the limiting mechanisms of the reactions with the iron oxide with the reducing gases. In addition, temperature programmed oxidation of the reduced iron oxides were conducted for understanding the mechanism of regeneration.

Task 3 Hydrogen Production Experiments – Laboratory We currently possess 2 pressurized reactors (Figure 9) of 1 inch diameter and 6” and 72” long. In addition, a setup using a quartz tube of dimensions ¼ “diameter was also used.

The main aim of this task was to identify the conditions for hydrogen enrichment using known mixtures of H2 and CO under plug flow conditions. Dry runs with nitrogen at different temperatures were conducted on the system to identify any problems and to obtain data regarding pressure drop, residence time and other baseline information.

Hydrogen enrichment and regeneration experiments of key process variables including gas flow rate, syngas content, syngas composition, steam content, solids loading, and temperature were conducted. Three experiments were conducted at the given conditions to assure the reproducibility factor. The key process variables were varied to observe and quantify the effects of each variable on the concentration of the out gases and the over process efficiency.

Task 4 Hydrogen Production Experiments – Bench Scale After the initial shake-down and baseline establishment, simultaneous coal gasification and hydrogen enrichment experiments were conducted. We already have experience with the gasification of several coal samples. However, a few initial runs of coal gasification alone were conducted to establish the gas composition from gasification. The effect of temperature, steam content and coal loading on the extent of gasification was evaluated. Following this the simultaneous gasification-enrichment process was conducted using Nitrogen as the carrier gas. The effect of Fe2O3 loading and CaO loading on the purity of hydrogen, extent of CO conversion, H2S removal and coal conversion were evaluated. Task 5 Technical Feasibility analysis Mass and energy balances were carried out for estimating the system efficiency. A study was also made of the reactors and the impacts of various reactor configurations on pressure drop, heat loss, reactor size and efficiency.

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OBJECTIVES The research addresses a novel approach to the enrichment of hydrogen from syngas while providing for an inexpensive route for the generation of a sequestration ready carbon dioxide. This approach also has the potential of reducing the load for sequestration of carbon dioxide by the separation of solid carbon in addition to the removal of other trace impurities. This reduces the volume of gas that need to be cleaned and should substantially reduce pollution control costs. In addition, the approach opens up the possibility of extracting solid carbon thereby reducing the sequestration load. The flexibility of the process is such that it can be used within a gasifier or as a separate unit process next to gasification. In terms of the products, the process can adjust the CO to H2 ratios, with one extreme being pure hydrogen. The underlying concept (the reactions involved) has been demonstrated in the laboratory.

The specific objectives include fundamental understanding of the kinetics of individual reactions and their dependence on temperature, pressure and origin of the oxides in addition to demonstrating the technical feasibility of the proposed scheme at a laboratory scale and bench scale. The overall target is to achieve greater than 80 % purity with less than 15 ppm CO2 and 1 ppm CO. The main impurity in the initial stages is expected to be methane. In the later stages of the project, the goal will be to maximize methane reformation within the process such that greater than 99% pure hydrogen is obtained. The target is expected to be achieved by development of iron oxides that would provide significant Boudouard reaction. In addition, CaO-based sorbent was developed that is able to withstand several carbonation-calcination cycles. Since the porosity of the sorbent has a significant effect on its life-time due to swelling effects during reaction and change in strength inherent due to the porosity, this will be a critical variable for the optimization. The decrease in the activity of the oxides as a result of the presence of H2S was also investigated and minimized. Finally, the calcium oxide to iron oxide loading, total solids loading and the different syngas compositions were used as process variables affecting the hydrogen content in the product stream.

The research effort consisted of two major activities. The first was the fundamental study of the reactions on commercially available materials and those engineered at our laboratories. The second was the study of the underlying principles of the hydrogen enrichment process and subsequent regeneration. This should result in the further engineering development and demonstration of the overall process. Recognizing the innovative nature of the proposed technology and the technical risk inherent in the development of any novel scheme this research was mainly to provide the proof of the concept and evaluate the technical feasibility of the process for scaling up. The task structure of the research plan with a summary of the outline of each task activities are presented below.

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TASKS Task 1 Acquisition, preparation and characterization of oxides The objective of this task was the acquisition, preparation and characterization of solids, supports, active solids on these supports. Task 2 Thermodynamic and Kinetic Studies

The objective of this task was to evaluate thermodynamics of the process (such as heats of reaction, equilibrium compositions, etc) using a Chemistry Software and the kinetics of the process from the data obtained from TGA and TPR experiments Task 3 Hydrogen Production Experiments – Laboratory The objective of this task was to study and optimize the enrichment of hydrogen from syngas of various compositions. Task 4 Hydrogen Production Experiments – Bench Scale The aim of this process was to optimize conditions for simultaneous coal gasification and hydrogen enrichment in a single reactor. In addition, it was the aim of this task to evaluate the fate of H2S produced during coal gasification. Task 5 Technical Feasibility analysis The aim of this task was to summarize the data in order to evaluate the technical feasibility of the process.

INTRODUCTION AND BACKGROUND The availability of high purity hydrogen using an operationally-simple, cost-effective process can very effectively facilitate to the production of electricity via fuel cells with high efficiency as compared to other competing technologies. In addition, such a process has the potential of being virtually pollution free. As a result, it has become one of the most sought after technologies provided since there exists a cheap and readily available source for hydrogen production. With increasing energy demands and rising concerns on environmental issues, the need for high purity hydrogen from reasonable cheap sources has become critical. Based on current technologies, the most viable way to obtain this hydrogen is to separate it from syngas constituents obtained via gasification of various fossil and biomass fuels. The current technologies of cryogenic separation, absorption, adsorption, membrane separation are costly alternatives. Southern Illinois University has developed a reaction swing process for the separation of hydrogen from syngas constituents and impurities such as CO, CO2 and H2S. The main reactions in this process are the conversion of CO to CO2 by disproportionation on a

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catalyst and subsequent removal of the CO2 by a suitable CO2 removal agent. CaO has been determined to be the most suitable CO2 removal agent. Southern Illinois University has also developed a process to alter the surface characteristics of the CaO to enhance the reaction rates and its longevity over multiple carbonation calcinations cycles. The process involves the reaction of syngas with the two solid phases in a nearly thermoneutral process step which enriches hydrogen while providing for an inexpensive method for sequestration ready carbon dioxide. In addition, as a result of CO2 removal from the process stream, additional hydrogen is obtained through water gas shift reaction. Theoretically, the regeneration of the spent solids can also be conducted thermoneutrally.

(a) Hydrogen Enrichment (b) Regeneration of OTC and CDRM Figure 1 Schematic of the proposed process

A simplistic schematic of the basic idea of the proposed research is provided in Figure 1. In the hydrogen enrichment mode, the coal gasification products are passed through a bed of Fe2O3. Three major reactions take place (Eq 1-6): a) CO is oxidized to CO2; b) CO disproportionation via the Boudouard reaction resulting in carbon deposition and CO2 formation, and c) steam reforming of CH4. The products are then passed through the bed of CaO. The carbonation of CaO removes the CO2 from the stream resulting in a high purity H2 gas stream. The spent bed now contains mainly FeO, C, and Fe along with CaCO3. Oxygen/air is then passed through the bed, as shown in Figure 1b (Oxide

1. 2CO = C + CO2

2. Fe2O3 + H2 = H2O + 2FeO 3. CO + H2O = CO2 + H2 4. CO + Fe2O3 = 2FeO + CO2

FeO, Fe2O3, C

CaCO3

O2

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CO + H2

H2

CO2 + CaO = CaCO3

1. C + O2 = CO2 2. 2FeO + 1/2O2 = Fe2O3

CaCO3 = CaO + CO2

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Regeneration Mode) resulting in oxidation of FeO and Fe along with the formation/release of CO2 from the deposited C and from the calcination of CaCO3. Hydrogen Enrichment Stage:

2OFe

24 H3COOHCH 32 +⎯⎯ →⎯+ +206 kJ/mol [1] CO + H2O → CO2 + H2 (Water-Gas Shift Reaction) -42 kJ/mol [2] 2 CO → CO2 + C (Boudouard Reaction) -162 kJ/mol [3] CO + Fe2O3 → 2 FeO + CO2 +1.30 kJ/mol [4] CO + FeO → Fe + CO2 (negligible levels) [5] CaO + CO2 → CaCO3 -167.6 kJ/mol [6]

Oxide Regeneration Stage: 2Fe + O2 → 2FeO (negligible amounts) [7] 2FeO + 0.5 O2 → Fe2O3 -281.4 kJ/mol [8] C + O2 → CO2 -398.9 kJ/mol [9] CaCO3 → CaO + CO2 +167.6 kJ/mol [10]

Figure 2 Envisioned process flowsheet Preliminary calculations and experimental evidence suggest that this process has the potential to be significantly more efficient at producing hydrogen at concentrations similar to the currently available technologies with an added advantage that the reaction

F SF

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Probable solid carbon recovery

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products constitute hot working fluids that can be used to generate process steam or shaft work. This is in contrast to the conventional conversion technologies that require shaft work to compress in order to effect gas separation. A mass and energy balance on the system, assuming the absence of the Boudouard reaction, shows that only 0.68 moles of hydrogen can be produced for every mole of CO converted to CO2 because of the high energy requirement for the calcination of CaCO3. The amount of hydrogen per mole of CO reacted can be enhanced by 33% (to a value greater than 0.91) in the presence of Boudouard reaction and water gas shift reaction and subsequent oxidation of carbon. Figure 2 shows the schematic diagram of the envisioned process of hydrogen enrichment.

EXPERIMENTAL PROCEDURES Task 1 Acquisition, preparation and characterization of oxides Iron oxide and Calcium oxide were obtained from commercial sources such as GE and Mississippi Lime as well as lab grade chemical vendors such as Fisher Scientific and Sigma Aldrich. The synthesis of several specially formulated calcium oxides was completed. Surfactants were used to control the size of the particles as well as pore size distribution. Cationic surfactants were used to increase the particle size while anionic surfactants were used to decrease the particle size. The pH of the saturated solution of Ca(OH)2 was around 12. In our preparation procedure we use suspensions of CaO that are 4, 8, 16, 24 and 32 times of the suspensions density. As the carbonation takes place when CO2 was passed through the suspension, the newly formed CaCO3 precipitates from the solution. The excess of suspended CaO goes into solution maintaining the pH at around 12. Once all of the Ca(OH)2 is consumed, the pH falls rapidly to near neutral to slightly acidic pH (due to the presence of dissolved CO2 that forms carbonic acid).

Two methods of washcoating were applied to the monoliths (photo above). In the first method, aluminum nitrate and urea solution in the ratio of 2:1 was prepared at 50oC. The resulting solution was then heated to 90oC. The monoliths were immersed into the solution and withdrawn. The duration of heating the solution was varied (5 - 15 hrs) along with the contact time of the monolith with the solution (5 -15 min). This was

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followed by overnight drying of the monolith (95oC) and calcinations (400oC) for 5 hrs. In the second method, a bohemite sol was prepared by dissolving aluminum isopropoxide in hot distilled water under constant stirring and refluxed for 1 hr. Then, 0.07 mole of HNO3 was added per mole of isopropoxide to make a clear sol. The resulting solution was evaporated and concentrated to get approximately 1 M bohemite sol. When this method was used, drying process was conducted at room temperature. The washcoated monoliths were then impregnated with the active phase (Ca and Fe) by the following method. First, the reagent grade metal compound (calcium nitrate and iron nitrate) were dissolved in a suitable solvent (acetone) and mixed thoroughly with a magnetic stirrer. The monoliths were immersed into the solution of dissolved metal compound and soaked overnight at room temperature. After drying at room temperature, the monoliths were further dried in an oven at 100-110°C. Finally, such impregnated monoliths were calcined at 400°C to convert the metal complex into metal oxide distributed throughout the solid’s surface. Materials were characterized for BET surface area, pore volume, and average pore radius. The particle size distribution was evaluated using a Microtrac laser size analyzer. To check on the uniformity of the impregnation within the support, representative samples were analyzed with scanning electron microscopy with energy-dispersive X-ray methods (SEM-EDX). I Task 2 Thermodynamic and Kinetic Studies

HSC Chemistry software was used to evaluate the thermodynamics of the system. Kinetic experiments were performed using a microbalance assembly consisting of a Thermogravimetric Analyzer (TGA). Gas compositions were obtained by blending high purity gases using Sierra mass flow controllers. Carbon dioxide, carbon monoxide, hydrogen, air and nitrogen of stock gas grade (99.99%) were supplied by a gas cylinder and a pressure regulator. After loading the solids to the TGA, the sample was preconditioned and dried in flowing nitrogen by elevating the reactor temperature, followed by additional heating to achieve the temperature of interest. The sample was then allowed to come to steady state, both thermally and gravimetrically. Once the sample achieved steady state under dry nitrogen conditions, gas mixtures were introduced and nitrogen flow was ceased. The weight change vs. time curves were used to determine the various reaction constants and determine the required residence times for the lab scale experiments. The resulting solids were analyzed using X-ray diffraction and scanning electron microscopy. TPR experiments were conducted to at different heating rates at adsorbate flow rate of 60 mL/min. The samples were degassed for 3 hrs prior to TPR analysis. Task 3 Hydrogen Production Experiments – Laboratory The small scale laboratory reactor was set up for those experiments. The reactor system consist of gas supplies, water pump, steam generator, reactor system (reactor + furnace), water trap and gas collection system and the required fitting and flow measurement devices. A microGC from Agilent Technologies has been attached to the reactor system

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to provide real-time data analysis from the reactor. It consists of two separate channels, one with Plot Q column and other with Molecular Sieve 5A column and 2 TC detectors. It is capable of analyzing samples containing CO, H2, CO2, CH4, C2H6, O2 and N2 in less than 2 minutes. Figure 3 is a schematic of the setup and Figure 4 is the photograph of the components of the same. Syngas cylinders containing 20, 43 and 48 % H2 (with the balance CO) were obtained from syngas. Experiments were conducted to establish baselines such as residence time distributions for each gas at different flow rates and temperatures. Experiments with syngas were conducted to study the effect of gas flow rates (25 – 100 ml/min), syngas content (from 5 to 50 %), temperature (650 -850 oC), steam, syngas composition, solids loading (Fe2O3 loadings of 0.14 – 2 g and CaO loadings of 0.56 – 6 g) and solids ratio on the hydrogen purity and cycle time for enrichment.

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Figure 3 Schematic Diagram of the System

Steam Generator

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Figure 4 Photo of the Reactor System

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Task 4 Hydrogen Production Experiments – Bench Scale The schematic of a bench scale reactor is shown in Figure 5. Both have 1 inch diameter, however they vary in their lengths (72” and 6“ respectively, see photo below). Simultaneous coal gasification and hydrogen enrichment in a single reactor was evaluated in this phase. At the beginning of each experiment the reactor was filled with Fe2O3 and CaO carriers according to the desired ratios. Next the nitrogen flow was started and the reactor was heated up to a predetermined temperature with external furnace. Finally water was introduced into the reactor and after examining the setup of the parameters involved, coal was introduced inside the reactor through injection. The effects of temperature (700 – 850 oC), steam content (0 -91 %), iron oxide to coal ratio (0 – 44), and CaO:iron oxide ratio (0 -6) on the extent of coal conversion, hydrogen purity, CO rejection and H2S rejections were evaluated In addition, the data from this task was used to evaluate the fate of H2S produced during coal gasification.

Figure 5 Bench Scale Reactor Schematic

Steam Generator

Frit

Outer Pipe3” ID

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Task 5 Technical Feasibility analysis The aim of this task was to summarize the data in order to evaluate the technical feasibility of the process.

RESULTS AND DISCUSSION

Task 1 Acquisition, preparation and characterization of oxides Calcined limestone and hematite samples were acquired. Also alumina beads and ceramic monoliths were acquired for support materials and the active materials were deposited. Morphologically altered high surface area CaO samples were synthesized. Different surfactants were used to control the size of the particles as well as pore distribution. Cationic surfactants were used to increase the particle size while anionic surfactants were used to decrease the particle size. The pH of saturated Ca(OH)2 solution is around 12. In

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0.64 g/L1.28 g/L2.56 g/L3.84 g/L5.12 g/L

our preparation methodology we use suspensions of CaO that are 4, 8,16, 24 and 32 times the suspensions density. As the carbonation takes place due to bubbling CO2, the newly formed CaCO3 precipitates out of the solution. The excess suspended CaO goes into solution maintaining the pH at around 12. Once all of the Ca(OH)2 is consumed the pH falls rapidly to near neutral to slightly acidic pH (due to the presence of dissolved CO2 to form carbonic acid). Figures 6 a and b shows the plots of pH vs. time for various suspension densities and the presence of different surfactants. Changing the concentrations of the surfactants did not show any effect of the time for complete carbonation. Figures 7 a, b and c are the plots of cumulative pore volume vs. pore radius for samples produced using different surfactants, different suspension densities of CaO and different concentration of anionic surfactant SDS at a constant suspension density of 2.56 g/L CaO, respectively. In addition, Figures 8 a-c presents histograms of the surface areas and mean pore radii of the different samples produced by varying surfactant type, suspension density and surfactant concentrations respectively. Figure 8a contains the data for the calcium oxide prepared using 2.56 g/L of CaO in water using different surfactants, Figure 8b contains the data on surface area and mean pore size of solids obtained using different loadings of CaO in water and Figure 8c contains the data for solids obtained from different concentrations of SDS and 2.56 g/L of CaO in water. Figures 9 -12 contain the data of the cumulative size distribution of the calcium carbonates obtained after each treatment.

Figure 1 pH vs. Time (a) Different suspension densities and (b) Different surfactants

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AldrichNo SurfactantAnionic - 25R2Anionic - 31R1Anionic - SDSCationic-DDAB

(a) Different surfactants (b) Different suspension densities (c) SDS concentration Figure 7 Cumulative pore volume vs. pore size

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Figure 8: Comparison of pore size and surface area obtained for different treatments

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Figure 9. Particle size distribution for different surfactants Figure 10. Particle size distribution for different suspension densities

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Figure 11. Particle size distribution for different concentrations of surfactant SDS Figure 12. Particle size distribution for different concentrations of surfactant Pluronic 31 R1

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Task 2 Thermodynamic and Kinetic Studies The thermodynamic analysis of the system showed that the operating range for the enrichment should be between 650 oC and 850 oC. The maximum (850oC) was chosen based on the maximum temperature at which both Boudouard reaction and CO2 adsorption on CaO are thermodynamically favorable while minimum (650oC) was chosen based on the minimum temperature at which CO might be oxidized to CO2 with Fe3O4 while preventing methanation.

The TGA data (analysis) showed that at temperatures greater than 650 oC, Boudouard reaction is still significant while TPR experiments with 5 % hydrogen at different heating rates yielded the activation energies for the reduction of hematite to magnetite to wustite to iron. The activation energies are listed in Table 1. Figures 13 -15 presents the CaO conversions by CO2 at 750 oC for different synthesis routes. Figures 16 -19 shows the TGA plots of selected samples at different temperatures (namely 750, 800 and 850 oC). Of particular interest are the plots on Figure 16 (TGA profiles for the commercially available sample from Sigma Aldrich) compared with the plots on Figures 17 -19. When analyzing these data it was generalized that an increase in temperature resulted in a decrease in the extent and initial rate of carbonation. This decrease was however found relatively small as compared to that effected by commercially available dolomite which showed only 40 % conversion in the first cycle, which further reduced to 20 % by the end of 4 cycles. Figure 13 Effect of Sodium Dodecyl Sulfate Concentration on Extent of Carbonation

due to repeated Calcination and Carbonation (CaO = 2.56 % during the preparation, 800 oC during TGA, 15 minute carbonation cycle)

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Figure 14 Effect of CaO Suspension Density on Extent of Carbonation due to

repeated Calcination and Carbonation (800 oC during TGA, 15 minute carbonation cycle)

Figure 15 Effect of Pluronic 31R1TM Concentration on Extent of Carbonation due to

repeated Calcination and Carbonation (CaO = 2.56 % during the preparation, 800 oC during TGA, 15 minute carbonation cycle)

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Figure 16 Effect of Temperature on Extent of Carbonation due to repeated

Calcination and Carbonation (Aldrich CaCO3, 15 minute carbonation cycle)

Figure 17 Effect of Temperature on Extent of Carbonation due to repeated

Calcination and Carbonation (CaO = 2.56 % during preparation, no surfactant, 15 minute carbonation cycle)

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Figure 18 Effect of Temperature on Extent of Carbonation due to repeated

Calcination and Carbonation (CaO = 2.56 % during preparation, SDS = 0.001 %, 15 minute carbonation cycle)

Figure 19 Effect of Temperature on Extent of Carbonation due to repeated

Calcination and Carbonation (CaO = 2.56 % during preparation, SDS = 0.01 %, 15 minute carbonation cycle)

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21

Table 1 Reaction Activation Energy (kJ/mol) Fe2O3 → Fe3O4 7.66 Fe3O4→ FeO 8.52 FeO→ Fe 10.21

Based on the data above data analysis we selected the applicable preparation conditions: a suspension density of 3.84 g/L and an SDS concentration of 0.101 g/L. These conditions were applied when preparing solids been examined further in this study. Task 3 Hydrogen Production Experiments – Laboratory Table 2 shows the effect of temperature on the hydrogen enrichment and solids regeneration. It can be clearly seen there that hydrogen enrichment goes through a maxima around 800 oC, however due to the intensive CO2 removal the lowest gas yield was observed at that temperature. Table 2. Data on Experiments using Fe2O3 (0.5g) and CaO (0.5g)

H2 % CO % Inlet 48 52 Enrichment Regeneration

Temp Gas

Yield H2

H2 Recovery

C removed

CO2 from C

CO2 in CaCO3

oC % % % % % % 750 78 60 80 82 - - 800 48 98 95 92 35 65 850 68 72 100 54 20 80

The evaluation of the key process parameters revealed that the actual moles of syngas flowing and the amount of the active solids are the most significant factors. It was thus observed that a high residence time and high syngas content or a low residence time and low syngas content provide the optimal enrichment cycle time. A set of experiments were conducted at different iron oxide to calcium oxide ratios, ranging from 1:1 to 1:36. Figures 20 and 21 contain the plots of the gas content as a function of time for the cases of Fe2O3:CaO ratios of 1:12 and 1:36. The hydrogen content was increasing from the feed content of 48 % to nearly 80 % in both cases. The addition of steam under these conditions resulted in greater than 95 % H2 in the product for the former case while it was nearly 100 % for the latter case. Some amount of methane was observed in the absence of steam in both cases. This was found to be the result a result of methanation of the carbon deposited from the Boudouard reaction with the excess hydrogen. Figures 22 a, b, c and d show the effect of syngas content on the outlet gas composition. All the experiments were conducted with a Fe:Ca ratio of 1:3 at 750 oC. Figure 22a contains the data on the experiments conducted with 20% syngas in N2 while Figure 22b contains the data for the experiments conducted with 50 % syngas mixture in N2. Figure

22

22c and d are the outlet gas compositions of the experiments conducted at higher flow rates for feed syngas contents of 20 and 50 %, respectively. It is seen that increasing the flow rate (for a given syngas content shortens the cycling time significantly).

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Figure 20: Outlet gas Composition for Fe:Ca ratio of 1:12

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23

(a) 5 % syngas

(b) 50 % syngas Figure 22 Effect of syngas content, gas flow rate – 45 ml/min

Task 4 Hydrogen Production Experiments – Bench Scale Simultaneous coal gasification and hydrogen enrichment experiments were conducted. We already have experience with the gasification of several coal samples. However, a few initial runs of coal gasification alone were conducted to establish the gas composition from gasification. The effect of temperature, steam partial pressure, and coal loading on the conversion degree and hydrogen yield was evaluated. Following this the simultaneous gasification-enrichment processes were conducted. In this set, the reactor

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containing the iron oxide, calcium oxide containing material was introduced into the reactor. Nitrogen was used as the carrier gas. The temperature was raised to the predetermined value. Once the preset temperature is reached, the steam generator was turned on to introduce pre-heated steam into the reactor and coal was injected. The off gases were passed through a water cold trap and then through the online GC analyzer.

(a) 20 % syngas

(b) 50 % syngas

Figure 23 Effect of syngas content, gas flow rate – 100 ml/min Effect of Temperature: Table 3 summarizes the results of the coal gasification experiments conducted at different temperatures. 0.2 g of coal was gasified at different temperatures. The steam content used in these experiments was 82 %. It was observed that as the temperature is increased, the hydrogen content also increases. This increase

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was found to be the result of both – increased conversion of coal and enhanced water gas shift reaction. The latter is evident from the fact that as the temperature increased to 800 oC no carbon monoxide is observed in the resulting gases. Table 3 Effect of Temperature

Temp H2 CO CO2 CH4 Total Conversion 700 34.23 28.27 13.22 24.11 0.007 18.05 750 70.71 12.47 14.08 2.73 0.014 36.09 800 83.63 0.00 15.63 0.74 0.02 37.59 900 85.11 0.00 14.89 0.00 0.0252 41.23

Effect of Steam: Table 4 summarizes the data on the effect of steam on the coal conversion and the product gas distribution. 0.2 g of coal was gasified at 750 oC. It was seen in the table that an increase in the steam content results in a decrease in CO content (due to an increase in the degree of the water gas shift reaction) as well as a decrease in the methane content (due to steam reforming). The total amount of gases evolved also increased with an increase in the steam content. Table 4 Effect of Steam Content

Steam H2 CO CO2 CH4 Total Conversion 0 58.03 19.38 14.76 7.83 0.007 17.66

59 58.76 20.36 17.63 3.25 0.008 25.22 82 70.71 12.47 14.08 2.73 0.014 36.09 91 78.49 0.00 21.51 0.00 0.02 63.85

Effect of Coal Loading: The optimal amount of coal for maximizing the gasification yield was identified by running steam gasification experiments (82 % steam) at 750 oC. The data from these experiments are presented in Table 5. Experiments with 0.4 and 0.5 g of coal are not reported since it resulted in a large amount of tars and hydrocarbon formation. Table 5 Effect of Coal Loading

Coal H2 CO CO2 CH4 Total Conversion 0.05 59.64 22.33 15.56 2.21 0.0028 51.88 0.1 61.18 17.87 18.27 2.68 0.0085 44.05 0.2 70.71 12.47 14.08 2.73 0.014 36.09

Effect of solids addition: A comparison of pyrolysis, steam gasification, catalysts addition and catalysts and CDRM addition during steam gasification is shown in Table 6 and Figure 24. The experiments were conducted at 750 oC. 0.2 g of coal was used for these experiments. The table contains the cumulative product distribution at the end of 1 hr. It can be clearly seen there that CDRM presence increased H2 content while CO content was decreased. Effect of Iron Loading: Table 7 lists the outlet gas compositions for different amount of Fe2O3 added. No CaO was used for these experiments. It was observed that

26

an increase in iron oxide results in a decrease in the hydrogen content (initial water formation during reduction of iron oxide). However, the CO content and the H2S content also decreased with an increase in iron oxide content. The catalytic effect of iron oxide on the gasification process was also observed by the increase in the gas yield due to the addition of iron oxide. Experiments were also conducted to evaluate the effect of catalyst loading in the presence of CDRM (in the ratio catalyst:CDRM = 1:3). No CO was observed at a catalyst loading of 0.56 g, while complete H2S removal was obtained at a catalyst loading of 1.12 g. Since 0.05 g of coal was used, the catalyst to coal ratio for complete CO and H2S removal was 44:1. 99.74 % pure hydrogen was produced under these conditions. It must be noted that the use of 1.68 g of CaO with 0.05 g of coal yielded significant amount of CO and H2S. Thus, the CO2 acceptor process alone is not sufficient for complete impurity removal from coal derived syngas. Table 6 Effect of solids addition

Steam catalyst CDRM H2 CO CO2 CH4 Total Conversion 0 0 0 58.03 19.38 14.76 7.83 0.007 17.66

82 0 0 70.71 12.47 14.08 2.73 0.014 36.09 82 0.56 0 68.31 2.46 27.69 1.55 0.0252 63.32 82 0.56 1.68 80.24 0.01 18.84 0.90 0.0113 93.22

Table 7 Effect of Iron Oxide addition alone catalyst H2 CO CO2 CH4 H2S Total Conversion

0 59.64 22.33 15.56 2.21 0.26 0.0028 51.88 0.28 63.65 1.32 33.34 1.53 0.16 0.0070 79.98 0.56 52 0.19 46.123 1.68 0.007 0.006 69.84 1.12 42.72 0 55.47 1.82 0 0.0032 49.73

Table 8 Effect of iron oxide (Fe2O3:CaO = 1:3)

catalyst CDRM H2 CO CO2 CH4 H2S Total Conversion 0.28 0.84 61.53 0.42 37.13 0.83 0.086 0.0056 66.87 0.56 1.68 84.15 0 15.73 0.11 0.0017 0.0031 36.70 0.84 2.52 93.27 0 6.72 0.1 0.0005 0.0025 18.34 1.12 3.36 99.74 0 0.25 0 0 0.0023 9.25

Effect of CaO Loading: Table 9 contains the data on the cumulative outlet gas composition as a function of the CDRM loading for 0.56 g of catalyst loading. Increasing the CaO loading resulted in an increase in the hydrogen purity, however the H2S removal was not complete due to the low iron oxide loading. Table 9 Effect of CaO addition

catalyst CDRM H2 CO CO2 CH4 H2S Total Conversion 0.56 0 52 0.19 46.12 1.68 0.007 0.0062 69.84 0.56 0.56 57.65 0 40.74 1.49 0.12 0.0051 65.14 0.56 1.12 54.75 0 43.53 1.41 0.31 0.0039 44.66 0.56 1.68 84.15 0 15.73 0.12 0.0017 0.0031 36.71 0.56 3.36 97.95 0 0.22 1.74 0.0839 0.0026 10.62

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Simultaneous Regeneration Enrichment experiments were conducted for an iron oxide loading of 0.84 and a CaO loading of 1.68. The coal loading was 0.05 and the temperature and steam content were 750 oC and 82 %, respectively. One cycle of enrichment followed by regeneration in air and a second cycle of enrichment was studied. No change in the activity as evidenced by the outlet gas composition and total gas yield was observed. Pyrolysis of 0.2 g coal gasification of 0.2 g coal (82 % steam)

Steam (82 %) +Coal (0.2 g) + iron oxide (0.56 g) Steam (82 %)+Coal (0.2 g)+iron oxide(0.56 g)+CaO (1.68 g) Figure 24 Separation of coal gasification products for high purity hydrogen: Carrier Gas – N2 at 33 mL/min, Temp = 750 oC As a result of these studies the following operating conditions are suggested: Temperature – 750 oC, Steam content – 82 %, catalyst:coal ratio – 44:1, catalyst:CDRM – 1:6. In addition, it is suggested that CaO synthesized from a CaO suspension (3.84 g/L) with sodium dodecyl sulfate anionic surfactant (0.01 g/L) be used instead of the commercially available dolomite. The similar values of optimal parameters were obtained using Fe2O3 and CaO supported on the monoliths. When evaluating these data an additional advantage of applying monoliths found was greatly reduced pressure drop than observed in the fixed bed experiments.

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Task 5 Technical Feasibility analysis The studies show that this process is technically feasible. However, for industrial application extensive analysis on a larger pressurized reactor is necessary for evaluating the process.

RECOMMENDATIONS AND CONCLUSIONS The following conclusions were made from the analysis of the data

1) Iron acts as a suitable catalyst for Boudouard reaction. 2) Lab synthesized CaO performed better at all CO2 concentrations than commercially

available CaO. 3) CaO synthesized from a CaO suspension (3.84 g/L) with sodium dodecyl sulfate

anionic surfactant (0.01 g/L) is preferred 4) The use of monoliths reduce the pressure drop across the bed 5) When used as a separate unit operation, the process should be operated at 800 oC 6) High residence time and high syngas content or low residence time and low syngas

content should be used. 7) The addition of steam enhances the efficiency of CO removal. 8) The preferred catalyst to CDRM ratio is 1:3. 9) Suggested operating conditions for simultaneous gasification-enrichment:

Temperature – 750 oC, Steam content – 82 %, catalyst:coal ratio – 44:1, catalyst:CDRM – 1:6.

10) The efficiency of separation did not decrease as a result of on enrichment-regeneration cycle. It is further recommended that extensive pressurized bed studies be conducted in a larger reactor.

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DISCLAIMER STATEMENT This report was prepared by Dr T. Wiltowski and SIUC with support, in part by grants made possible by the Illinois Department of Commerce and Economic Opportunity through the Office of Coal Development and the Illinois Clean Coal Institute. Neither T. Wiltowski and SIUC nor any of its subcontractors nor Illinois Department of Commerce and Economic Opportunity through the Office of Coal Development and the Illinois Clean Coal Institute, nor any person acting on behalf of either: (A) Makes any warranty of representation, express or implied, with respect to the accuracy, completeness, or usefulness of the information contained in this report, or that the use of any information, apparatus, method, or process disclosed in this report may not infringe privately-owned rights; or (B) Assumes any liabilities with respect to the use of, or for damages resulting from the use of, any information, apparatus, method or process disclosed in this report. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring; nor do the views and opinions of authors expressed herein necessarily state or reflect those of the Illinois Department of Commerce and Economic Opportunity, the Office of Coal Development or the Illinois Clean Coal Institute. Notice to Journalists and Publishers: If you borrow information from any part of this report, you must include a statement about the state of Illinois' support of the project.