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A study published in , and supported by funding from the , describes greenhouse gas (GHG) benefits of substituting pyrolysis oil from post-use plastic for naphtha and fossil fuel gases in steam cracking operations.

The study considers two types of facilities, pioneer facilities with a capacity of less than 50,000 tons/year and “Nth” facilities, with capacity greater than 50,000 tons/year. The scaling factor is significant, the use of pyrolysis oil in pioneer facilities increases GHG emissions, while GHG emissions from Nth facilities are lower than that of conventional operations.

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Cracking operations produce monomers for plastic production. In the United States, crackers are fed with an average of 6% naphtha and 94% gases. Substitution of naphtha with pyrolysis oil provides the greatest benefit in terms of GHG emissions. Photo Credit: National Library of Medicine

The study also considers two substitution ratios, 5% and 20%. When substituting only 5% pyrolysis oil for naphtha and gases, the elimination of chlorides and other contaminants by hydrotreatment is not necessary. Hydrotreatment contributes significantly to the GHG emissions of using pyrolysis oil. At a substitution ratio of 20%, hydrotreatment is necessary to protect equipment, bringing down the GHG benefit on a per kilogram basis.

From the recycler’s perspective, the substitution of pyrolysis oil provides a 23% reduction for HDPE production and an 18% reduction for LDPE production. However, these numbers set aside the 95% of production still being carried out by traditional means in this scenario. The producer still needs to source the other 95% (from fossil fuels) in order to make the 5% recycled material, so from the cracker’s perspective the benefit is around 1%.

Expanding the system boundaries to include end-of-life disposal increases the GHG benefit further, especially when compared against incineration.

The authors identified the availability of operational data on steam cracking and hydrotreatment processes as a limitation of the study. Detailed information is considered proprietary, and values were based on available literature and discussions with industry partners.