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New ceramic membrane enables first direct conversion of methane to liquids without CO2 emissions

A team from CoorsTek Membrane Sciences, the University of Oslo (Norway), and the Instituto de Tecnología Química (ITQ) (Spain) has developed a new process for the direct, non-oxidative conversion of methane to liquids—reducing cost, eliminating multiple process steps, and avoiding CO2 emissions.

The process uses a novel ceramic membrane that simultaneously extracts hydrogen and injects oxide ions. The resulting aromatic precursors are source chemicals for insulation materials, plastics, textiles, and jet fuel, among other valuable products. A paper describing the process is published in the journal Science.

Nonoxidative methane dehydroaromatization (MDA: 6CH4 ↔ C6H6 + 9H2) using shape-selective Mo/zeolite catalysts is a key technology for exploitation of stranded natural gas reserves by direct conversion into transportable liquids. However, this reaction faces two major issues: The one-pass conversion is limited by thermodynamics, and the catalyst deactivates quickly through kinetically favored formation of coke.

We show that integration of an electrochemical BaZrO3-based membrane exhibiting both proton and oxide ion conductivity into an MDA reactor gives rise to high aromatic yields and improved catalyst stability. These effects originate from the simultaneous extraction of hydrogen and distributed injection of oxide ions along the reactor length. Further, we demonstrate that the electrochemical co-ionic membrane reactor enables high carbon efficiencies (up to 80%) that improve the technoeconomic process viability.

—Morejudo

Methane
Current-controlled co-ionic membrane reactor. (A) CH4 is converted to benzene and hydrogen via a Mo/zeolite catalyst. H2 is transported as protons to the sweep side. Oxide ions are transported to the reaction medium to react with H2 and form steam as an intermediate before reacting with coke to form CO and H2.
(B) Scanning electron microscopy image of the membrane electrode assembly (focused ion beam section). Cathode porosity formed upon reduction of NiO can be observed beneath the dense electrolyte.

(C) Percentage of H2 extracted and O2 injected versus current density at 700 °C. The anode is swept with a 10/90 mixture of H2/CH4 and the cathode with a 3/5/92 mixture of H2O/H2/Ar. Morejudo et al. Click to enlarge.

Methane constitutes a large fraction of the world’s hydrocarbon resource, but much of this resource is stranded without economically viable paths to market. Even when available for industrial conversions, the high stability of the methane molecule leads to energy losses associated with multi-stage processing in large chemical plants which use oxygen or steam to activate the methane in what is known as synthesis gas processing.

Temperature and pressure have historically been the main parameters chemists and engineers can work with to control reactions. Catalysts can improve speed and selectivity, without promoting reactions beyond their chemical equilibrium limit. Integrating a ceramic ion-conducting membrane into the reactor enables an increase in the productivity of industrially appealing processes which are otherwise impractical due to strong thermodynamic constraints.

The ceramic membranes are made from abundant materials such as barium and zirconium found within large sand deposits, with the addition of thin electro-catalytic layers of plentiful metals like nickel and copper.

By using a ceramic membrane that simultaneously removes hydrogen and injects oxygen, we have been able to make liquid hydrocarbons directly from methane in a one-step process. As a bonus, the process also generates a high-purity hydrogen stream as a byproduct. At a macro level it is really very simple—inexpensive, abundant gas in and valuable liquid out through a clean, inexpensive process. At a nanochemistry level, however, where molecules interact with catalyst and membrane at a temperature around 700 °C, there were many factors to engineer and control in order to render just the specific valuable molecules needed to make the new process work.

—Dr. Jose Serra, Professor with ITQ

With high-volume manufacturing, we can make membrane reactors from active ceramics that are cost competitive with conventional catalytic reactors for gas processing. While the reactor costs will be similar, the results enabled by this new process have the potential to significantly improve both the financial and environmental costs of chemical production, a development CoorsTek believes will make the world measurably better.

—Per Vestre, Managing Director at CoorsTek Membrane Sciences

Engineered ceramics manufacturer CoorsTek has formulated more than 300 technical ceramic compositions over a century of experience, utilizing half the world’s elements.

Resources

  • S. H. Morejudo, R. Zanón, S. Escolástico, I. Yuste-Tirados, H. Malerød-Fjeld, P. K. Vestre, W. G. Coors, A. Martínez, T. Norby, J. M. Serra, C. Kjølseth (2016) “Direct conversion of methane to aromatics in a catalytic co-ionic membrane reactor” Science doi: 10.1126/science.aag0274

Comments

HarveyD

This could become an effective way to transform NG/methane into H2 and liquid fuels/chemicals?

With an abondant source of distributed clean H2, FCEVs could become the clean running vehicles of the future?

Engineer-Poet

Benzene is carcinogenic and aromatics tend to promote soot formation IIUC, but if methane can be electrocatalytically converted to e.g. short-chain aliphatic hydrocarbons it would be a huge advance.

mahonj

It is a pity they can't do the opposite of cracking* and make longer chain HCs like pentane or octane.
*(OK, it is called reforming as far as I can find out)

Engineer-Poet

I'm not finding anything for dearomitization.  It looks like it's a difficult thing to do, even if you have a stream of hydrogen to do it with.

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