A new study conducted by the Swiss Federal Institute of Technology with the support of the Swiss National Foundation discovered that mixed plastic wastes could be efficiently converted into methane using catalytic hydrocracking.
This recently developed technology can produce an ample amount of methane which can be employed as a cleaner substitute for exhaustible fuels and other chemical feedstock. Thus, using the Ru site-dominant mechanism to convert plastic wastes to natural gas can be a viable global energy source worldwide. Moreover, the utilization of ever-growing plastic wastes for gas production can solve the prevailing problem of plastic waste disposal.
Numerous types of techniques, such as fracking, pyrolysis, gasification, etc., have been developed to produce chemical derivatives and fuels from plastic wastes. Such methods are primarily based on the principle of breaking down plastic streams at high temperatures in the presence of suitable catalysts, thereby producing natural gas and a large number of wastes as the by-product. In addition, the gas obtained using these approaches requires several additional processing and purification, which makes the entire process costlier.
However, the study conducted by Lee et al. (2021) described catalytic hydrocracking as a potential alternative technology to convert plastic waste materials into clean energy. Hydrocracking uses Ru-modified zeolite as a catalyst and converts plastic wastes, such as polyethylene, polypropylene, and polystyrene into methane (>97% purity) at lower temperatures(300°C- 350°C). The methane can be fed into natural gas networks directly, thus omitting additional purification and processing. Therefore, hydrocracking can indeed be a highly effective alternative to the tedious thermal methods for recovering energy provided that an efficient catalyst is identified and used.
Figure 1: Methanation of plastic waste
The study's primary goal was to utilize the voluminous tons of plastics produced every year throughout the world as the chief raw material of the conversion process. Thus, the hydrocracking technique addresses recycling stubborn plastic materials and adds value to plastics otherwise dumped as wastes.
Bobbink, one of the co-authors of the study team, shared that the team came up with the basic idea of hydrocracking conversion of methane when working on indirect carbon dioxide methanation, an exothermic catalytic process. The significant observation made by the team was that all the carbon atoms present in a cyclic carbonate were converted to methane while the oxygen combined with the hydrogen resulting in the production of water. In furtherance, the team thus decided to work on the polycarbonates, polyesters and polyolefin.
This recently developed technology can yield 97%, 95%, and 92% of methane efficiently from polyethylene, polypropylene, and polystyrene, respectively. Furthermore, these plastics were combined to form mixed plastic waste and the catalytic conversion produced as high as 99% methane.
Lee et al., explained that the economic viability of the technique is yet to be analyzed. They further cited that ‘We are currently conducting research and study on an integrated process linked to the existing industrial systems to reduce the costs associated with thermal, logistic of feedstock, seasonal variations, and more.