Biomass conversion to H₂ with substantially suppressed CO₂ formation in the presence of Group I & Group II hydroxides and a Ni/ZrO₂ catalyst

Abstract

Combination of hydroxides and metal catalysts enables the conversion of cellulose to high purity H2 and solid carbonates.

Investigation of the role of Ca(OH)2 in the catalytic Alkaline Thermal Treatment of cellulose to produce H2 with integrated carbon capture

“…Acharya et al found that for the gasification of sawdust at 943 K the conversion to H 2 was enhanced to approximately 20% at a CaO/Biomass ratio of 2 [21] . This ratio is similar to that used in our previously published study [12] ; yet, their gaseous product still contained approximately 20% CO 2 [21] . Toshiaki et al also investigated the effect of Ca(OH) 2 at similar loadings on the gasification of Japanese oak at 923 K. Their results indicated that a biomass to H 2 conversion of 38% could be achieved while simultaneously suppressing CO 2 [22] .…”

“…A reaction scheme that can avoid these issues is the Alkaline Thermal Treatment (ATT) reaction, which is capable of producing H 2 by reacting cellulose with a metal hydroxide at moderate temperatures, while simultaneously capturing the carbon as a thermodynamically stable carbonate [10][11][12] . The stoichiometry is given in Eqs.…”

“…(1 )) due its relatively low melting point and high alkalinity. Ca(OH) 2 on the other hand, has lower solubility, lower basicity, a tendency to decompose (as opposed to melt), and therefore a lower activity for producing H 2 via the ATT reaction [12] . However, Ca(OH) 2 is chemically safer to handle and could be produced from waste alkaline streams containing CaO, such as steel slag [13][14][15] .…”

“…Our group has shown that a mixture of Ca(OH) 2 and 10% Ni/ZrO 2 could achieve H 2 yields similar to NaOH [12] , yet it required that cellulose be intimately mixed with Ca(OH) 2 and 10% Ni/ZrO 2 . The scalability and sustainability of such a process is hindered due to several practical challenges: (1) mixing large quantities of solids uniformly presents a design challenge, (2) the products (bio-char, CaCO 3 , spent catalyst) would require several steps to separate, and (3) the presence of carcinogenic nickel is an environmental hazard [16] .…”

Gasification characteristics of hydrochar and pyrochar derived from sewage sludge

“…Based on WGS, an enhanced hydrogen concentration can be accomplished if CO 2 is removed. For example, Stonor et al [35] investigated the production of H 2 from the steam gasification of cellulose with substantially suppressed CO 2 formation using Group I and II hydroxides (e.g. NaOH, Ca(OH) 2 ) and a Ni/ZrO 2 catalyst.…”