(771d) Catalytic Dry Methane Reforming for Industrial CO2 Capture Applications & Syngas Generation

Steam Methane Reforming is the most popular process for the production of H₂ rich syngas from hydrocarbon feed such as natural gas or flare gas in refineries. Generally, the process is operated to obtain a high H₂:CO ratio around 4~7, which is further enhanced via a water gas shift reactor. However, the synthesis of hydrogen gas is accompanied by the generation of a high amount of CO₂ as well, averaging around 9 tonnes of CO₂ per tonne of H₂produced.

Syngas however can be utilized for purposes other than just hydrogen generation, in applications such as the production of synthetic crude oil (via the Fischer-Tropsch process), methanol, ethanol as well as of higher products of enhanced value such as acrylates, organic acids, ether etc. In such processes, the CO molecule is as important as the H₂ molecule. Typically, for most chemical synthesis processes the ratio of consumption of H₂:CO is between 1 â?? 2.5.

Catalytic Dry Methane Reforming¹ is a process for generation of syngas (CO + H₂), utilizing CH₄ and CO₂as feed (1). The reforming reaction is accompanied by the reverse water gas shift reaction (2).

_ �.(1)

_ �.(2)

The product syngas, with a typical composition of H₂:CO â?¤ 1, can be used to supplement the raw material for the above mentioned processes. The reaction however is highly endothermic, and requires operation at high temperatures (750-900 C). This can potentially lead to significant CO₂ emissions through fuel combustion to provide energy for the reaction. The reaction, however, has been found to consume nearly twice the quantity of CO₂that is produced by combustion of fuel, thus resulting in a carbon capture efficiency of over 50 %. This would make it a great tool to serve the dual purposes of emission reduction as well as valorization of waste greenhouse gases in industry.

Concerns over the increasing global temperatures have triggered an extensive search for viable technologies to mitigate industrial GHG emissions. Implementation of the Dry Methane Reforming process could be a viable solution to this problem for a variety of industries. However, the high temperature operation causes CH₄and CO decomposition to form carbon deposits, thus resulting in deactivation of dry reforming catalysts. The lack of a satisfactory catalyst for the DMR system has impeded the application of this process in industry.

Enerkem Inc. is a Canadian company focused on reducing the carbon footprint for cleaner chemical production. The company has developed its technology for converting municipal solid wastes to methanol, which in turn can serve as the base material for secondary chemicals, such as higher alcohols, aldehydes, acrylates etc. It is starting its first commercial operation at the Edmonton Waste Management Centre for the production of methanol. Enerkem Inc. has also developed the E20 dry reforming catalyst, which has been observed to resist deactivation when operated at over 90% CH₄ as well as CO₂conversion for more than 100 hours (Figure 1). A comparison of the emission levels for syngas production using steam methane reforming operating at equilibrium condition and the dry methane reforming using the E20 catalyst have been presented in Table 1.

Figure 1. Performance of E20 Dry reforming catalyst for 100 hour operation with CH₄:CO₂:N₂= 40:40:20, reactor temperature of 850 Ì?C and WHSV of 500 ml/min-g.cat

Kinetic experiments have been conducted on the E20 catalyst and a working kinetic model has been developed. Simulation studies performed on HYSYS® have exhibited the CO₂capture potential of the E20 catalyst when integrated with the synthesis of high value chemicals. To showcase this potential, we have considered the case of acrylic acid synthesis, using syngas as the starting material. The most commonly utilized process for the synthesis of acrylic acid is the partial oxidation of propylene. However, the pathway for synthesis from syngas can be summarized as follows:

Syngas is used to synthesize methanol via reaction 3.

â?¦.(3)

Methanol can be utilized to synthesize formaldehyde via the Formox process³ (4), as well as acetic acid via the methanol carbonylation process⁴(5).

 �.(4)

 �.(5)

The acetic acid and formaldehyde can undergo reaction via an aldol condensation route⁵to form acrylic acid (6).

 �.(6)

The overall process would allow the valorization of waste CO₂streams into high value acrylate compounds.

	SMR	SMR	DMR	DMR
Reactor Temp ( Ì?C)	1000	1000	850	850
H2O:CO2:CH4	5:0:1	3:0:1	0:1:1	0:1.67:1
H2:CO	5.5	4.3	0.84	0.71
CH4 Conversion (%)	99.2	97.2	73.8	67.8
CO2 Conversion (%)			86.5	54.7
Energy per kg H2 (kJ)	71933.4	61193.1	81392.6	95834.2
CO2 produced per kg H2 (kg)	6.5	5	-9.6	-12.6
CO2 capture efficiency (%)			68.2	70.5
Energy per kg CO (J)	28242.8	18843.7	4896.3	4841
CO2 produced per kg CO (kg)	2.5	1.6	-0.58	-0.64
CO2 capture efficiency (%)			69.1	71.1

Table 1. Comparison of Energy consumption and CO₂emission of Steam Methane Reforming (SMR) and Dry Methane Reforming (DMR) processes

References

1. Bradford, M.; Vannice, M., CO2 reforming of CH4. Catalysis Reviews 1999,41, (1), 1-42.

2. Pakhare, D.; Spivey, J., A review of dry (CO 2) reforming of methane over noble metal catalysts. Chemical Society Reviews 2014,43, (22), 7813-7837.

3. Reuss, G.; Disteldorf, W.; Gamer, A. O.; Hilt, A., Formaldehyde. Ullmann's Encyclopedia of Industrial Chemistry 2005.

4. Yoneda, N.; Kusano, S.; Yasui, M.; Pujado, P.; Wilcher, S., Recent advances in processes and catalysts for the production of acetic acid. Applied Catalysis A: General 2001,221, (1), 253-265.

5. Vitcha, J. F.; Sims, V. A., Vapor Phase Aldol Reaction. Acrylic Acid by Reaction of Acetic Acid and Formaldehyde. Industrial & Engineering Chemistry Product Research and Development 1966, 5, (1), 50-53.