Negative emissions in the chemical sector

Abstract

The chemical sector is hydrocarbon intensive, using primarily fossil fuels as both fuel and feedstock. To achieve carbon-neutrality, it is likely that negative CO2 emissions will be needed to offset the carbon embodied in chemical products. This study presents first-order estimates of the decarbonization potential of combining bioenergy and biofeedstock use with carbon capture and storage (bio-CCS) for ethanol, ammonia, urea, and hydrogen. For each, net CO2 of emissions minus atmospheric removals was estimated over the whole life cycle including chemical synthesis, upstream supply chains, product use, and waste disposal. With aggressive bio-CCS using technologies that are currently commercially available, CO2 negative production was estimated to be possible for all chemicals modelled, except urea. With the use of biomass for both feedstock and fuel and capture of both high-purity and dilute CO2 streams, the estimated net CO2 was -30 g/MJ for maize bioethanol; -50 g/MJ for stover bioethanol; -50 g/MJ for merchant hydrogen; -1.2 t/t N for ammonia and 0.2 t/t N for urea. The potential for negative CO2 emissions is higher in cases where more CO2 can be captured during chemical production. However, all cases were sensitive to assumptions regarding the specific configuration and upstream supply chains.