Scientists have combined 3D printed polymers with methane-eating bacteria to create the first reactor that can produce methanol from the greenhouse gas, an advance that may lead to a more efficient energy production.
The researchers removed enzymes from methanotrophs, bacteria that eat methane, and mixed them with polymers that they printed or molded into innovative reactors.
"Remarkably, the enzymes retain up to 100 per cent activity in the polymer," said Sarah Baker, from the Lawrence Livermore National Laboratory in the US.
"The printed enzyme-embedded polymer is highly flexible for future development and should be useful in a wide range of applications, especially those involving gas-liquid reactions," Baker said.
Advances in oil and gas extraction techniques have made vast new stores of natural gas, composed primarily of methane, available.
A large volume of methane is leaked, vented or flared during these operations, partly because the gas is difficult to store and transport compared to more-valuable liquid fuels.
Methane emissions also contribute about one-third of current net global warming potential, primarily from these and other distributed sources such as agriculture and landfills.
Current industrial technologies to convert methane to more valuable products, like steam reformation, operate at high temperature and pressure, require a large number of unit operations and yield a range of products.
The only known catalyst to convert methane to methanol under ambient conditions with high efficiency is the enzyme methane monooxygenase (MMO), researchers said.
The reaction can be carried out by methanotrophs that contain the enzyme, but this approach inevitably requires energy for upkeep and metabolism of the organisms.
Instead, the team separated the enzymes from the organism and used the enzymes directly.
The team found that isolated enzymes offer the promise of highly controlled reactions at ambient conditions with higher conversion efficiency and greater flexibility.
"Up to now, most industrial bioreactors are stirred tanks, which are inefficient for gas-liquid reactions," said Joshuah Stolaroff, an environmental scientist on the team.
"The concept of printing enzymes into a robust polymer structure opens the door for new kinds of reactors with much higher throughput and lower energy use," said Stolaroff.
The team found that the 3D-printed polymer could be reused over many cycles and used in higher concentrations than possible with the conventional approach of the enzyme dispersed in solution.
The research was published in the journal Nature Communications.
