Hydrolysis of concentrated lignocellulose suspensions with a cumulative feeding strategy based on a critical concentration : from laboratory to pilot scale

In the context of biofuels and chemical production of petroleum substitutes from renewable carbon, bioconversion of lignocellulose biomasses is currently a major challenge. The limited knowledge of liquefaction and saccharification mechanisms stands as the main factor which penalizes bio-refinery progress. The objective of the present work was to increase the substrate concentration during hydrolysis in controlling transfer limitations by a specific strategy of substrate feeding. This concept was studied at laboratory scale and transposed into pilot scale. In-situ and ex-situ rheometry, morpho-granulometry and biochemical measurements were used to investigate transfer limitations. In a preliminary step (lab scale), rheological behaviour was modelled and a critical concentration (Ccrit ) inducing a sharp increase of viscosity was identified for Whatman paper (WP, 35 gdm.L-1) and paper pulp (PP, 31 gdm.L-1 ) [1]. Analysing hydrolysis experiments leads to assume an optimal feed rate Q* linked to this critical concentration. In a first step, cumulative feeding strategies (up to 10%w/w) were conducted for WP and PP in 2L reactor with different ratios Q/Q*. A cumulative feeding substrate strategy allows to considerably reduce the transfer limitations linked to high concentrations and to control the glucose production kinetics [2]. In the second step, the enzymatic hydrolysis (up to 20%w/w) was investigated in a 20L reactor coupled with an extruder (substrate feeding). This transposition will be discussed regarding the biochemical kinetics and physical limitations