Renewable butadiene: A case for hybrid processing via bio- and chemo-catalysis

Abstract

1,3-butadiene (butadiene) is a by-product produced during naphtha steam cracking, predominantly used in tyre manufacturing. Recently, steam crackers have converted to using more cost effective, lighter feedstocks such as shale gas, yielding less butadiene. The potential shortfall, coupled with concerns around increasing greenhouse gas emissions, provides a unique opportunity for renewable production. This study investigated the techno-economics and greenhouse gas emissions associated with renewable butadiene production routes within the context of a China located pulp mill. A hybrid bio-catalytic route, utilising black liquor, was compared against two chemo-catalytic routes using forestry residues and pulpwood. The hybrid bio-catalytic route uses a novel aerobic gas fermentation platform, employing heat integrated supercritical water gasification and aerobic gas fermentation to produce acetaldehyde, followed by chemo-catalytic upgrading (Acet-BD). The two chemo-catalytic routes catalytically upgrade biomass derived syngas; where one route (Eth-BD) passes through an ethanol intermediate, and the other (Syn-BD) utilises a series of commercialised catalytic technologies with propene as an intermediate. The hybrid bio/chemo-catalytic route, Acet-BD, was the only route profitable using the nominal techno-economic inputs, producing a Net Present Value of $2.8 million and Minimum Selling Price of $1367 tn−1. In contrast, the two chemo-catalytic routes produced Minimum Selling Prices of $1954 tn−1 (Eth-BD) and $2196 tn−1 (Syn-BD), demonstrating the competitiveness of this novel platform. Sensitivity analyses highlighted the equipment capital as the main contributor to increased Minimum Selling Price for all cases, and the Acet-BD route presented a 19% probability of achieving a positive net present value. Moreover, owed to the low process emissions and sequestration of biogenic carbon, all routes produced net negative emissions within a cradle-to-gate framework. As such, renewable butadiene production has potential as a net carbon sink for pulp mill residues conventionally destined for energy recovery.