Carbon-negative hydrogen: aqueous phase reforming (APR) of glycerol over NiPt bimetallic catalyst coupled with CO2 sequestration

Abstract

Herein we report the production of high-pressure (19.3 bar), carbon-negative hydrogen (H₂) from glycerol with a purity of 98.2 mol% H₂, 1.8 mol% light hydrocarbons (mainly methane), and 400 ppm of CO. Aqueous phase reforming (APR) of 10 wt% glycerol solution was studied with a series of NiPt alumina bimetallic catalysts supported on alumina. The Ni₈Pt₁-450 catalyst had the highest hydrogen selectivity (95.6%) and the lowest alkanes selectivity (3.7%) of the tested catalysts. The hydrogen selectivity decreased in the order of Ni₈Pt₁-450 > Ni₈Pt₁-260 > Ni₁Pt₁-260 > Pt-260. The CO₂ was sequestered with CaO adsorbent which formed CaCO₃. We measured the adsorption capacity of the CaO adsorbent at different temperatures. Life cycle analysis showed that the APR of glycerol coupled with CO₂ capture has net negative CO₂ equivalent greenhouse gas emissions. The CO₂ emissions are −9.9 kg CO₂ eq./kg H₂ and −50.1 kg CO₂ eq./kg H₂ when grid electricity and renewable electricity are used, respectively, and the CO₂ is allocated respectively to the mass of products produced. The cost of this H₂ (denoted as “green-emerald”) was estimated to be 2.4 USD per kg H₂ when grid electricity is used and 2.7 USD per kg H₂ when using renewable electricity. The cost of glycerol has the highest contribution of 1.71 USD per kg H₂. Participation in the carbon credit markets can further decrease the price of the produced H₂.