Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

On the road to ANG vehicles

28.10.2015

Berkeley Lab researchers find a better way to store natural gas as a transportation fuel

With new makes of all-electric and hybrid automobiles seeming to emerge as fast as the colors of fall, it is easy to overlook another alternative to gasoline engines that could prove to be a major player in reduced-carbon transportation - cars powered by natural gas.


The cobalt-bdp MOF features flexible square-shaped pores that expand under pressure to adsorb increasing amounts of methane gas.

Credit: Jeff Long, Berkeley Lab

Natural gas, which consists primarily of methane (CH4) is an abundant, cheaper and cleaner burning fuel than gasoline, but its low energy density at ambient temperature and pressure has posed a severe challenge for on-board fuel storage in cars. Help may be on the way.

Researchers with the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab) have developed a variety of metal-organic frameworks (MOFs) - sponge-like 3D crystals with an extraordinarily large internal surface area - that feature flexible gas-adsorbing pores.

This flexibility gives these MOFs a high capacity for storing methane, which in turn has the potential to help make the driving range of an adsorbed-natural-gas (ANG) car comparable to that of a typical gasoline-powered car.

"Our flexible MOFs can be used to boost the usable capacity of natural gas in a tank, reduce the heating effects associated with filling an ANG tank, and reduce the cooling effects upon discharging the gas from the ANG tank," says Jeffrey Long, a chemist with Berkeley Lab's Materials Sciences Division and the University of California (UC) Berkeley who is leading this research.

"This ability to maximize the deliverable capacity of natural gas while also providing internal heat management during adsorption and desorption demonstrates a new concept in the storage of natural gas that provides a possible path forward for ANG applications where none was envisioned before."

Long is the corresponding author of a Nature paper that describes this work entitled, "Methane storage in flexible metal-organic frameworks with intrinsic thermal management." The lead author is Jarad Mason, a member of Long's research group. (See below for a complete list of co-authors.)

The United States holds a vast amount of proven natural gas reserves - some 360 trillion cubic feet and climbing. While compressed natural gas-fueled vehicles are already on the road, the widespread use of natural gas as a transportation fuel has been hampered by cumbersome and expensive on-board gas storage tanks and the cost of dispensing compressed natural gas to vehicles.

The storage issue is especially keen for light-duty vehicles such as cars, in which the space available for on-board fuel storage is limited. ANG has the potential to store high densities of methane within a porous material at ambient temperature and moderate pressures, but designing such high-capacity systems while still managing the thermal fluctuations associated with adsorbing and desorbing the gas from the adsorbent has proven to be difficult.

The key to the success of the MOFs developed by Long, Mason and their colleagues is a "stepped" adsorption and desorption of methane gas.

"Most porous materials that would be used as adsorbents exhibit classical Langmuir-type isotherm adsorption, where the amount of methane adsorbed increases continuously but with a decreasing slope as the pressure is raised so that, upon discharging the methane down to the minimum delivery pressure, much of it remains in the tank," Long says. "With our flexible MOFs, the adsorption process is stepped because the gas must force its way into the MOF crystal structure, opening and expanding the pores. This means the amount of methane that can be delivered to the engine, i.e., the usable capacity, is higher than for traditional, non-flexible adsorbents."

In addition, Long says, the step in the adsorption isotherm is associated with a structural phase change in the MOF crystal that reduces the amount of heat released upon filling the tank, as well as the amount of cooling that takes place when methane is delivered to accelerate the vehicle.

"Crystallites that experience higher external pressures will have a greater free energy change associated with the phase transition and will open at higher pressures," Long says. "Our results present the prospect of using mechanical pressure, provided, for example, through an elastic bladder, as a means of thermal management in an ANG system based on a flexible adsorbent."

To test their approach, Long and his colleagues used a cobalt-based MOF hybrid that goes by the name "cobalt-bdp" or Co(bdp) for cobalt (benzenedipyrazolate). In its most open form, cobalt-bdp features square-shaped pores that can flex shut like an accordion when the pores are evacuated.

Combined gas adsorption and in situ powder X-ray diffraction experiments performed under various pressures of methane at 25°C (77°F)showed that there is minimal adsorption of methane by the cobalt-bpd MOF at low pressures, then a sharp step upwards at 16 bar, signifying a transition from a collapsed, non-porous structure to an expanded, porous structure. This transition to an expanded phase was reversible. When the methane pressure decreased to between 10 bar and 5 bar, the framework fully converted back to the collapsed phase, pushing out all of the adsorbed methane gas.

Long says that it should be possible to design MOF adsorbents of methane with even stronger gas binding sites and higher-energy phase transitions for next generation ANG vehicles. He and his group are working on this now and are also investigating whether the strategy can be applied to hydrogen, which poses similar storage problems.

Moreover, Long says, "Improved compaction and packing strategies should also allow further reductions to external thermal-management requirements and optimization of the overall natural gas storage-system performance."

###

In addition to Long and Mason, other authors of the Nature paper that describes this study were Julia Oktawiec, Mercedes Taylor, Matthew Hudson, Julien Rodriguez, Jonathan Bachman, Miguel Gonzalez, Antonio Cervellino, Antonietta Guagliardi, Craig Brown, Philip Llewellyn and Norberto Masciocchi.

This research was supported by the DOE's Advanced Research Projects Agency - Energy (ARPA-E). The X-ray characterizations were carried out at synchrotron light sources that included the Advanced Light Source and the Advanced Photon Source, both DOE Office of Science User Facilities.

Lawrence Berkeley National Laboratory addresses the world's most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab's scientific expertise has been recognized with 13 Nobel prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy's Office of Science. For more, visit http://www.lbl.gov.

DOE's Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit the Office of Science website at science.energy.gov/

Lynn Yarris | EurekAlert!

Further reports about: methane gas natural gas pressure thermal management vehicles

More articles from Power and Electrical Engineering:

nachricht Agricultural insecticide contamination threatens U.S. surface water integrity at the national scale
06.12.2018 | Universität Koblenz-Landau

nachricht Improving hydropower through long-range drought forecasts
06.12.2018 | Schweizerischer Nationalfonds SNF

All articles from Power and Electrical Engineering >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Researchers develop method to transfer entire 2D circuits to any smooth surface

What if a sensor sensing a thing could be part of the thing itself? Rice University engineers believe they have a two-dimensional solution to do just that.

Rice engineers led by materials scientists Pulickel Ajayan and Jun Lou have developed a method to make atom-flat sensors that seamlessly integrate with devices...

Im Focus: Three components on one chip

Scientists at the University of Stuttgart and the Karlsruhe Institute of Technology (KIT) succeed in important further development on the way to quantum Computers.

Quantum computers one day should be able to solve certain computing problems much faster than a classical computer. One of the most promising approaches is...

Im Focus: Substitute for rare earth metal oxides

New Project SNAPSTER: Novel luminescent materials by encapsulating phosphorescent metal clusters with organic liquid crystals

Nowadays energy conversion in lighting and optoelectronic devices requires the use of rare earth oxides.

Im Focus: A bit of a stretch... material that thickens as it's pulled

Scientists have discovered the first synthetic material that becomes thicker - at the molecular level - as it is stretched.

Researchers led by Dr Devesh Mistry from the University of Leeds discovered a new non-porous material that has unique and inherent "auxetic" stretching...

Im Focus: The force of the vacuum

Scientists from the Theory Department of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science (CFEL) in Hamburg have shown through theoretical calculations and computer simulations that the force between electrons and lattice distortions in an atomically thin two-dimensional superconductor can be controlled with virtual photons. This could aid the development of new superconductors for energy-saving devices and many other technical applications.

The vacuum is not empty. It may sound like magic to laypeople but it has occupied physicists since the birth of quantum mechanics.

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

EGU 2019 meeting: Media registration now open

06.12.2018 | Event News

Expert Panel on the Future of HPC in Engineering

03.12.2018 | Event News

Inaugural "Virtual World Tour" scheduled for december

28.11.2018 | Event News

 
Latest News

A new molecular player involved in T cell activation

07.12.2018 | Life Sciences

High-temperature electronics? That's hot

07.12.2018 | Materials Sciences

Supercomputers without waste heat

07.12.2018 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>