Process intensification of the ionoSolv pretreatment: effects of biomass loading, particle size and scale-up from 10 mL to 1 L

Abstract

The ionoSolv process is one of the most promising technologies for biomass pretreatment in a biorefinery context. In order to evaluate the transition of the ionoSolv pretreatment of biomass from bench-scale experiments to commercial scale, there is a need to get better insight in process intensification. In this work, the effects of biomass loading, particle size, pulp washing protocols and 100-fold scale up for the pretreatment of the grassy biomass Miscanthus giganteus with the IL triethylammonium hydrogen sulfate, [TEA][HSO₄], are presented as a necessary step in that direction. At the bench scale, increasing biomass loading from 10 to 50 wt% reduced glucose yields from 68 to 23% due to re-precipitation of lignin onto the pulp surface. Omitting the pulp air-drying step maintained saccharification yields at 66% at 50 wt% loading due to reduced fiber hornification. 100-fold scale-up (from 10 mL to 1 L) improved the efficacy of ionoSolv pretreatment and increasing loadings from 10 to 20 wt% reduced lignin reprecipitation and led to higher glucose yields due to the improved heat and mass transfer caused by efficient slurry mixing in the reactor. Pretreatment of particle sizes of 1-3 mm was more effective than fine powders (0.18-0.85 mm) giving higher glucose yields due to reduced surface area available for lignin re-precipitation while reducing grinding energy needs. Stirred ionoSolv pretreatment showed great potential for industrialization and further process intensification after optimization of the pretreatment conditions (temperature, residence time, stirring speed), particle size and biomass loading. Pulp washing protocols need further improvement to reduce the incidence of lignin precipitation and the water requirements of lignin washing.

Figure 1

Comparison of the key pretreatment parameters—pulp yield, lignin and saccharification yields and delignification- after pretreatment of Miscanthus with [TEA][HSO₄] (water content of 20 wt%) for 6 h at 120 °C at different biomass loadings, ranging from 2 to 50 wt%. Errors were calculated as standard deviation across triplicates.

Figure 2

Total component mass balance for experiments conducted at 10 wt% and 50 wt% biomass loading. Results are shown per 100 g of starting material on a dry basis, assuming no IL losses.

Figure 3

Glucose yields obtained after four ethanol washes (ethanol wash) and four ethanol washes plus one DMSO wash (DMSO wash) of air-dried pretreated Miscanthus pulps at various biomass loadings. Enzymatic hydrolysis was carried out for 7 days and glucose yields are shown relative to the amount of glucan in untreated biomass. Percentage increase following DMSO wash relative to ethanol wash is shown inset.

Figure 4

Photographs of (above) untreated biomass and (below) recovered pulps after pretreatment of Miscanthus with [TEA][HSO₄] at 120 °C for 6 h at bench scale using a biomass loading of 20 wt%.

Figure 5

Effect of particle size of Miscanthus on key indicators for ionoSolv pretreatment, after pretreatment with [TEA][HSO₄] at 120 °C for 6 h at bench scale using a biomass loading of 20 wt%.

Figure 6

Comparisons of total solids (i.e. pulp), glucan, hemicellulose and lignin recovered in the pulp, and lignin precipitate yield (a) upon 100-fold scale-up for 10 and 20 wt% solid loading. Results shown as a proportion of component amount in untreated Miscanthus; (b) for fine, medium and coarse particle sizes. Results shown as a proportion of component amount in untreated Miscanthus; (c) for fine, medium and coarse particle sizes as a function of stirring speed. Results shown as a proportion of component amount in untreated Miscanthus.