Nitrous oxide emissions from caprolactam production

Caprolactam, a chemical compound primarily utilized in synthesizing Nylon 6 fibers and resins, plays a crucial role in various industries. These fibers are indispensable for manufacturing a wide array of textiles, including clothing, carpets, and industrial fibers. Meanwhile, the resulting resins have diverse applications across sectors such as automotive, electrical, electronic, and packaging, with the automotive sector being the largest consumer, contributing to over a third of total production.

Despite a perceived decline in the use of Nylon fibers for clothing production due to the prevalence of polyester, Nylon resins are anticipated to continue growing, particularly in tandem with the automotive sector, notably in China. Overall, global caprolactam consumption is projected to increase at an average annual rate of 2.6% (Markit, Caprolactam, 2017).

Emissions from the conventional production process of caprolactam primarily result from the release of nitrous oxide (N2O), carbon dioxide (CO2), sulfur dioxide (SO2), and non-methane volatile organic compounds (NMVOCs). Notably, N2O is the primary greenhouse gas (GHG) concern in caprolactam production. While modified processes aim to reduce ammonium sulfate by-products, they still involve NH3 oxidation and consequent N2O emissions. Global N2O-based GHG emissions from caprolactam production in 2019 were estimated to be approximately 14.3 million tons of CO2 equivalent, underscoring the significant environmental impact and the urgent need for more sustainable production methods.

Abatement of N2O emissions from Caprolactam Production

N2O emissions from caprolactam production can be abated using proven technologies similar to those employed in nitric acid N2O abatement activities. Two primary abatement techniques are recognized: secondary controls, which reduce N2O directly after its formation in the oxidation reactor, and tertiary controls, involving the installation of a catalytic reactor as an end-of-pipe application.

The most common secondary abatement technology utilizes a base metal catalyst, with an abatement efficiency that can reach up to 98% under ideal conditions. However, practical experience suggests that efficiency often ranges between 70% and 90%. Alternatively, tertiary catalyst units typically achieve a 95-98% reduction in N2O. It is crucial to note that the efficiency levels depend on specific facility conditions, and the catalyst material requires periodic replacement, with cycles ranging from 3 to 10 or more years based on technology and plant conditions.

Caprolactam production mitigation potential in ODA countries that need financial support accounts, according to computations performed by the NACAG, for up to 1,5 million tons CO2eq/year, considering a mitigation effectiveness of 95%.