The goal here is to establish a different chemical route for the transformation of methane into PHB, which is a biopolymer of high added value
With the use of micro-organisms, biologist Elen Aquino Perpétuo and a group of eight researchers plan to transform methane (CH4), which is present in natural gas, into PHB – a plastic of high added value. This is one of the goals of the Methane Bioconversion Project, which has already been started by the Research Centre for Gas Innovation (RCGI). Established at the end of 2015, with support from Fapesp and the BG Brazil Group, RCGI has the main purpose of investigating possible uses of natural gas to increase their participation in the country’s energy matrix and also reduce the emissions of greenhouse gases.
According to the biologist, the main aim here is to establish a non-chemical route for the transformation of methane. “There is the chemical route which involves, for example, the steam re-formation of methane. Chemical methods are more expensive and are also well established in the industry.” In her opinion, the idea is to innovate and establish a microbiological method.
“Some bacteria, which are known as methanotrophic bacteria, feed on methane and then transform it, through a series of biochemical reactions, into PHB, which is a biopolymer: a plastic of biodegradable origin”, explains Elen, who is a teacher at the Santos Lowlands campus of the São Paulo Federal University (Unifesp) and co-ordinator of the project. She explains that PHB is a “noble” kind of plastic, and is less aggressive because it is obtained from a biodegradable base. It can be used for prosthetic purposes, for example, because the adverse reactions thus caused are less. “However, its production on an industrial scale is not yet worth it, and for this reason there is no production from methane, on an industrial scale, in the whole world. Let’s see if we manage to devise a process that offers a better yield.”
Initially, the researchers shall be conducting tests with methanotrophic bacteria from genera Methylobacter sp. and Methylocystis sp. “These are better known, they are examples that have been successful. It is well established that they do indeed work, so we shall carry out our first tests using them”, says Elen. The group also plans to work with microbial consortiums arising from area which are traditional producers of methane gas, including landfills. “Normally, bacteria that produce methane are related to those that use it.”
The biologist explains that, during the tests, the bacteria are placed in a bioreactor, in a liquid medium, and then methane (CH4) and oxygen (O2) are injected. The bacteria then start consuming the methane. “The idea is that of controlling the basic variables such as temperature, pressure, and pH, until we manage to establish the best conditions for the desired reactions”, she explains.
The first test shall be conducted with pure methane. “However, we have already requested that BG provide us with a sample of the gas, which is a much more interesting idea as it is possible that there could be interfering factors in natural gas that could lead us to other results, different from those obtained exclusively through the methane test.”
Other paths – Elen reminds us that there are other projects under way at the RCGI, involving the separation of methane. “In the future, if we see that the results obtained from the reaction with methane are better, then we can consider executing the process only using the methane that has been separated using the processes that have been developed in other projects.”
It is not yet known whether this microbiological route is cheaper than the chemical process steam re-formation. “However, we do know that the yield obtained from the biotechnological process is worse than that of the chemical process. For this reason, we always look to products with high added value. At some point we shall have to make this calculation.”
Also according to Elen, the use of the microbiological method has a very strong environmental appeal. “Methane and CO2 are greenhouse gases. This means that the aim is to mitigate them in as natural a way as possible, by leaving the chemical method, which uses up many reagents and also generates toxic by-products, as well as using up a lot of energy.”
There is yet another method available, according to the researcher. This is the use of methane and CO2 mixed, in a double process involving algae and bacteria. “The algae would carry out the mitigation of CO2 and would also produce biomass that could be used for animal feed. Any methane that is left, we would place in the bioreactor so that the bacteria could produce PHB. However, we did not consider the other elements that also make up the composition of natural gas extracted from the BG reservoirs: ethane, propane, nitrogen… They are all valuable. On becoming aware of the composition of the BG gas, we even started to think about a consortium of microbes to take advantage of these other gases, in which we would have bacteria specialised in each type of gas, thereby generating different products and making full use of the gas.”