Adipic Acid Production: Bottlenecks and Viability Conditions of the Conventional, Electrochemical, and Biomass-Based Routes under European Market and Policy Scenarios

Abstract

Adipic acid is a large-volume chemical, used mainly for nylon, and about 95 % of world production runs through nitric-acid oxidation of benzene-derived intermediates, a route whose nitrous oxide by-product dominates the product's emissions and whose benzene ties it to a fossil supply chain. Electrochemical oxidation and a biomass route via electrochemical hydrogenation are proposed against both problems, and all three are modelled together in Yeo (2025), the one published baseline that spans them in Aspen Plus at a consistent scale and boundary. This thesis re-evaluates that baseline under the European market and policy conditions it holds fixed, not to rank a fixed winner, but to establish the bottlenecks and viability conditions that decide each route.

The re-evaluation is built on one basis for a 100 kt/a European plant: a full pinch analysis on each flowsheet, cell degradation over service life, carbon priced under the EU ETS, and electricity charged at each Antwerp-Rotterdam-Rhine-Ruhr (ARRRA) country's tariff and grid carbon intensity in place of a single price and an assumed renewable supply. Around that basis every input the published work holds fixed is swept rather than assumed: the conventional route's N2O destruction efficiency, the carbon price, each country's grid intensity and electricity price, cell performance and degradation, feedstock prices and procurement, load factor, and both biomass endpoints, trans-3-hexenedioic acid (t3HDA) and adipic acid. Each is varied alone and in combination.

On central inputs the conventional route reaches a levelised cost of adipic acid (LCOA) of 1.87 $/kg at a cradle-to-gate greenhouse-gas (GHG) intensity of 3.39 kgCO2e/kg; the electrochemical route 2.19 $/kg at 3.79 kgCO2e/kg; and the biomass route 4.03 $/kg at 2.34 kgCO2e/kg to t3HDA, or 4.34 at 2.56 once catalytically hydrogenated to adipic acid. Against that baseline the electrochemical route's cost premium over the conventional route narrows from 47 to 17 %, and its GHG position reverses, from 54 % below the conventional route to 12 % above. No route is best on both measures.

The binding constraints differ by route. The conventional route turns mainly on the destruction efficiency it sustains and the carbon price on its residual N2O, the electrochemical route on the carbon intensity and price of its electricity, and the biomass route on the cost of a muconic-acid broth no market yet quotes and on whether a buyer pays for non-fossil origin or for the reactive double bond t3HDA retains. Both alternatives also rest on electrochemical cells demonstrated only in the laboratory. Across every case assessed here, abating the conventional process's N2O costs orders of magnitude less per tonne of CO2-equivalent than any change of route, which points to unabated capacity, most of it outside Europe, as the larger near-term lever on the adipic-acid sector's GHG emissions.