Technical feasibility

SECTION 1: Testing

1 Has the R & D result been tested? YES
1a In what mode has the result been tested? 

•           Prototype

•           Pilot Application

•           Alpha/BETA testing

The R&D result has already been tested. The prototype material’s performance was investigated in the Lab of Petrochemical Technology, Department of Chemical Engineering, Aristotle University of Thessaloniki, Greece. The Sorption Enhanced Reforming (SER) experiments were performed at atmospheric pressure in the laboratory unit equipped with a mass flow controlled system for the incoming gases, a fixed bed quartz reactor, and an online gas chromatograph. An HPLC pump was used for the admission of the distilled water to the reactor through a preheater. The fixed bed quartz reactor was equipped with a coaxial thermocouple for monitoring the temperature in the middle of the solid bed. Minor variations in the reactor temperature were observed during the reforming/sorption period. This is because the heat requirements for the endothermic reforming were almost balanced by the heat generated from the exothermic carbonation under the conditions studied. The reactor was heated electrically by a tubular furnace, with three independentlycontrolled temperature zones. The hot gases exiting the reactor were cooled to condense the unreacted steam. The gas phase products were analyzed with an online gas chromatograph equipped with TCD. The CO2 concentration in the reactor exit was also monitored by a CO2 analyzer.
1b. Please describe and discuss the testing results
The carbonation conversion of CaO-Ca12Al14O33 (85:15) was tested in a TGA apparatus. The weight increase of CaO-Ca12Al14O33 (85:15) recorded in atmospheric experiments with constant CO2 partial pressure (15% CO2 in N2) at various temperatures (500-690 °C) is presented in Fig 3. The selected partial pressure of CO2 simulates the typical CO2volumetric concentration at the reformer reactor exit which does not surpass 15%. The effect of temperature on the carbonation is positive in the range of 500-650 °C as the overall kinetics is favored at higher temperatures. The results indicate the temperature 650 °C as the optimal, ensuring high reaction rates and the highest weight increase of the material, 50%, corresponding to almost 75% molar CaO carbonation conversion for 30 min treatment. Further increase in temperature leads to lower weight increase. The reason is that the reverse reaction, calcination, is progressively favored by thermodynamics due to the exothermicity of the forward carbonation reaction. 

Fig 3. Effect of temperature on sorption capacity of CaO-Ca12Al14O33 (85:15) at constant CO2 partial pressure (0.15 atm)

 

On account of the complete study of the new CO2 sorbent, CaO-Ca12Al14O33 (85:15 wt), SER of natural gas was studied. An admixture of a commercial nickel-based catalyst and CaO-Ca12Al14O33 was used for the experiments. Approximately 1.5 g of the catalyst and 3g of the sorbent was added to the reactor. The catalyst loading was selected so as to ensure equilibrium conversions of conventional SR under all the specified conditions.  The total inlet flow of methane and helium was 36-144 cm3/min (CH4/He:1/2.3), and the steam to methane molar ratio was equal to 3.4. The reactions were studied at 650 °C. Steam reforming (SR) experiments without a sorbent were also carried out to test the activity of the commercial catalyst at 650 0C and were used as a reference for the experiments with a mixed bed of catalyst and sorbent.

Fig 4. H2 and CO2 outlet concentration (% dry basis) response curve for sorbent and catalyst loadings equal to 3 g and 1.5 g,respectively. Reaction conditions: 1 atm, 650 °C, H2O/CH4 = 3.4

 

Fig 4 presents the experimental results of SR (open symbols), SER (closed symbols), and the equilibrium concentrations (solid lines). The SR results are close to the equilibriumvalues, indicating that the catalyst activity at the relevant conditions is high enough. The effluent gas composition indicates constant hydrogen concentration at near 77% and a CO2 concentration at 10-11% throughout the course of the experiment. The new sorbent material CaO-Ca12Al14O33 (85:15) was then mixed with the reforming catalyst and introduced to the reactor (SER). As it is readily deduced, there are three discrete regimes, related to the progressive saturation of the sorbent. During the first period (prebreakthrough) , the CO2 separation proceeds with maximum efficiency shifting the reforming and water gas shift reactions. Hydrogen concentration is maximum (92-93%), while CO2 is minimum (2-3%), both approaching SER equilibrium predictions (solid lines). The prebreakthrough period is followed by the breakthrough period during which hydrogen concentration, gradually decreases from 92-93% to 77-78%. The reason for this is that CaO-Ca12Al14O33 is progressively saturated in CO2 resulting in a decrease of the enhanced reforming extent. Therein, the concentration of the gases pass from the steadystate (prebreakthrough), through the unsteady-state period (breakthrough), to the steady-state period (postbreakthrough), where the CO2 separation is no longer effective. At this point, only the reforming and shift reactions are active and the experimental product gas concentrations conform with the conventional SR equilibrium. This explains why CO2 follows, opposite to hydrogen, an increasing course with CO2 becoming about 4 times higher (from 3% to almost 12%). It is to be noted that the amount of CO2 emitted during the prebreakthrough period of the first cycle of this SER experiment is 67% less than the amount of total CO2 that would have been emitted in conventional steam reforming. Therefore, the application of this SER process not only increases the hydrogen purity but also reduces the number of necessary downstream processing steps.

Long-term experiments of CaO-Ca12al14O33 (85:15 wt) were also conducted , under the selected conditions. The sorbent regeneration was conducted at 850 °C, in 100% He flow. The new material was tested for 13 consecutive cycles (SER absorption – desorption), resulting in high (>92%) hydrogen concentration revealing its high potential for industrial applications. The hydrogen concentration during the prebreakthrough period of the first, third, and 13th cycles is shown in Figure 5. The minor differences in the profiles between the first and the13th cycles point indirectly to the adequate stability of the sorbent and the catalyst under the examined conditions. The durations of the prebreakthrough and breakthrough periods also provide an indication of the stability of the sorbent. Overall, after 13 cycles, i.e. 60 h on stream, only part of the sites was permanently lost, resulting in a moderate loss of CaO-Ca12Al14O33 sorption capacity (12%).

Fig 5. Prebreakthrough and postbreakthrough hydrogen concentration(dry basis) for the 1st, 3rd, and 13th reforming regeneration cycles in SER. Reaction conditions: 1 atm, 650 °C

SECTION 2: Current Stage of Development

2a To what extent does the development team have technical resources for supporting the production of a new product? (Researchers, human resources, hardware, etc.)
Angeliki Lemonidou is Professor of Chemical Engineering at the Aristotle University of Thessaloniki and Head of the Petrochemical Technology Laboratory. The research interests of the group mainly lie in the area of applied catalysis and the development of active and selective nano-structured materials for reactions related to transformation of hydrocarbons and bio-based compounds. Target reactions currently studied are the selective oxidation of alkanes, the steam reforming of natural gas with in-situ CO2 capture, the steam reforming of bio-oil components and recently the hydrogenolysis of glycerol. Expertise lies in the preparation of nanomaterials via advanced preparation techniques, structural and morphological characterization using various physicochemical techniques, as well as detailed kinetic measurements of catalytic materials under reaction conditions. Professor A. Lemonidou has published numerous scientific papers in Journals (>65) and conference proceedings (>120) in these areas. Prof. Lemonidou served as a member the Editorial Board of the Journal Applied Catalysis A General (2004-2007) and as Guest Editor of a special issue in Catalysis Today. She has a hybrid background in Chemistry and Chemical Engineering (PhD, Chemical Engineering Department, 1990).

 

2b What are the technical issues that need to be tackled for full deployment, if needed?
The material is ready for upscaling and testing in pilot and demo scale experimental units under industrially relevant conditions. Further research could be carried out regarding sorbent regeneration in 100% CO2 flow, in order to  attain a 100 % CO2  stream in the reactor exit, which will be thereupon stored permanently in underground tanks. However, regeneration in CO2 flow usually takes place at higher temperatures ( > 800 °C) and could induce the agglomeration of CaO particles through sintering effect and consequently the reduction of the sorption ability of the material.

 

2c What additional technical resources are needed for the production of this new product?
A ‘Service Level Agreement’ (SLA) is needed in order for the R&D result to be used. A SLA is an agreement between two parties where one is the customer and the other is the product provider. This can be a legally binding formal or informal contract, which will include a defiition of services, performance measurement, problem management, customer duties, warranties, disaster recovery and termination of agreement.

 

2d Overall assessment of the current stage of technical development.
This innovative sorbent material is the outcome of an integrated study and aims at boosting the efficiency of the hydrogen production Steam Reforming systems. The research team disposes all available technical equipment and expertise to further improve this material with the purpose to achieve better efficiency, reduced capital cost and CO2 emissions in large petrochemical industries.

SECTION 3: Deployment

3a Define the demands for large scale production in terms of
  • Materials
The raw materials required for the synthesis of this innovative solid, are calcium acetate monohydrate, Ca(CH3COO)2 *H2O and aluminum nitrate enneahydrate, Al(NO3)3 *9H2O. Ca(CH3COO)2 *H2O is a snow-white powder, hazardous in case of skin contact (irritant), of eye contact (irritant), of ingestion, of inhalation. and slightly hazardous in case of skin contact (permeator). Al(NO3)3 *9H2O is a moisture-sensitive, white crystalline powder. It is irritating to eyes and skin and contact with combustible material may lead to fire.
  • technologies, tools, machineries
An open box type furnace is required for the calcination of the mixture of Ca(CH3COO)2 *H2O and Al(NO3)3 *9H2O
  • Staff effort
No special staff effort will be needed

SECTION 4: Overall Assessment

1 What is you overall assessment of the technical feasibility of the research result?
CaO-Ca12Al14O33 (85:15wt) is a promising CO2 sorbent for high purity hydrogen productionvia SER process. About 95% of the methane is converted at the low temperature of 650 °C and 1 bar of pressure. The high hydrogen purity, >92 %, of the reforming outlet stream compared to the 77% hydrogen concentration in the case of the conventional steam reforming reveals the high importance of the sorbents’ presence. At the same time, with the use of CaO-Ca12Al14O33, the necessity of downstream purification steps decreases due to the low CO2 (3-4%) content at the reformer exit. Moreover, the stability of the material in multiple cycles of reforming –regenerations reveals its high potential for industrial application. Additional research could be carried out, in order to further decrease the process energy requirements and the complexity of the unit.

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Description

The present industrial production of hydrogen, based on fossil fuels, contributes in green-house gas ( CO2) emissions and in wasteful energy consumption. Research has been recently focused to an alternative concept, which combines both reforming reaction and in situ CO2 separation in order to increase the efficiency of the current process. Such process is known as Sorption Enhanced Reforming (SER). The presence of a CO2 sorbent material in the reformer reactor boosts the feedstock (natural gas) conversion and leads to higher product quality. Development of a sorbent material with constant capture and regeneration ability is the key point for the economical and waste management efficiency of the process.

The scientific result focuses on the development of a CaO-based CO2 sorbent with high sorption capacity and long life-time for high temperature applications, such as SER. The optimum CO2 sorbent was found to be CaO-Ca12Al14O33 (85-15 wt%). The active component of the material is CaO while Ca12Al14O33 provides a stable framework inhibiting deactivation of CaO.

A Scanning Electron Microscopy, SEM, study of CaO-Ca12Al14O33 (85:15) revealed that this sorbent material can be visualized as consisting of a number of small grains (Fig 1). The macropores surrounding these grains facilitate the gas diffusion to the various grains.

Fig 1. SEM micrograph of the CO2 sorbent material CaO-Ca12Al14O33 (85:15)

 

X-ray Diffraction, XRD, was also employed to study the crystal phases which are present in this new sorbent material. The XRD pattern is shown in Figure 2. All characteristic peaks of CaO (2θ = 32.2, 37.35, 53.85, 64.15, 67.3) and Ca12Al14O33 (2θ = 33.41, 41.21, 55.22, 57.52) were clearly detected. The absenceof any other Ca-Al mixed phases or hydrated mixed structures proved the formation of the desired CaO-Ca12Al14O33.

Fig 2. XRD pattern of the CO2 sorbent material CaO-Ca12Al14O33 (85:15)

The concept of Sorption Enhanced Reforming,SER, is based on Le Chatelier’s principle, according to which the conversion of reactants to products and the rate of the forward reaction in an equilibrium controlled reaction can be increased by selectively removing some of the reaction products from the reaction zone.

In SER this principle is applied by using a CO2 sorbent (e.g. CaO) (reaction 3) in order to shift reaction (2) and consequently reaction (1) to hydrogen production side. As the sorbent is effectively consumed in reaction 3, the process is inherently dynamic in operation, requiring a regeneration step. In addition, the sorbent must maintain its activity through many cycles for the process to be economically viable.

 

CH4 + H2O -> CO + 3H2     ΔH298K  = 206,2kJ / mol (1)

CO + H2O – >CO2 + H2    ΔH298K = – 41,2 kJ / mol (2)

CaO + CO2 -> CaCO3   ΔH298K =- 178 kJ / mol  (3)

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