Jörn Viell

Is biomass fractionation by Organosolv-like processes economically viable? A conceptual design study

In this work, the conceptual designs of the established Organosolv process and a novel biphasic, so-called Organocat process are developed and analyzed. Solvent recycling and energy integration are emphasized to properly assess economic viability. Both processes show a similar energy consumption (approximately 5 MJ/kg(dry biomass)). However, they still show a lack of economic attractiveness even at larger scale. The Organocat process is more favorable due to more efficient lignin separation. The analysis uncovers the remaining challenges toward an economically viable design. They largely originate from by-products formation, product isolation, and solvent recycling. Necessary improvements in process chemistry, equipment design, energy efficiency and process design are discussed to establish economically attractive Organosolv-like processes of moderate capacity as a building block of a future biorefinery.

Disintegration and dissolution kinetics of wood chips in ionic liquids

Abstract Ionic liquids are able to dissolve polysaccharides and lignin, but there is only scarce knowledge about the dissolution of native wood. In the present paper, wood was dissolved by the ionic liquid 1-ethyl-3-methylimidazolium acetate (EMIMAc). A quantitative balance of the dissolved compounds is presented and the investigations are complemented by in situ microscopy of native wood in EMIMAc. The resulting dissolution kinetics in EMIMAc reveals distinct differences between spruce and beech. While particles of 0.1–0.5 mm of spruce dissolve slowly (up to 40% after 24 h), beech is dissolved more efficiently (75% after 24 h and 90% after 72 h). Wood chips of 10 mm length show similar dissolution kinetics and lignin yields of up to 10%. Microscopic studies reveal a disintegration of wood in EMIMAc into cells with large specific surface area, and differences in dissolution between spruce and beech were observed. These findings explain the size-independent dissolution of wood in EMIMAc and may open up new opportunities for the pretreatment of wood in ionic liquids.

Fractionation of lignocellulosic biomass using the OrganoCat process

The fractionation of lignocellulose in its three main components, hemicellulose, lignin and cellulose pulp can be achieved in a biphasic system comprising water and bio-based 2-methyltetrahydrofuran (2-MeTHF) as solvents and oxalic acid as catalyst at mild temperatures (up to 140 °C). This so-called OrganoCat concept relies on selective hemicellulose depolymerization to form an aqueous stream of the corresponding carbohydrates, whereas solid cellulose pulp remains suspended and the disentangled lignin is to a large extent extracted in situ with the organic phase. In the present paper, it is demonstrated that biomass loadings of 100 g L−1 can be efficiently fractionated within 3 h whereby the mild conditions assure that no significant amounts of by-products (e.g. furans) are formed. Removing the solid pulp by filtration allows to re-use the water and organic phase without product separation in repetitive batch mode. In this way, (at least) 400 g L−1 biomass can be processed in 4 cycles, leading to greatly improved biomass-to-catalyst and biomass-to-solvent ratios. Economic analysis of the process reveals that the improved biomass loading significantly reduces capital and energy costs in the solvent recycle, indicating the importance of process integration for potential implementation. The procedure was successfully scaled-up from the screening on bench scale to 3 L reactor. The feedstock flexibility was assessed for biomasses containing moderate-to-high hemicellulose content.

An efficient process for the saccharification of wood chips by combined ionic liquid pretreatment and enzymatic hydrolysis

A process concept combining pretreatment of wood in ionic liquids and subsequent enzymatic hydrolysis to sugars is herein investigated to identify operating conditions which allow for (i) the processing of larger wood chips of 10 mm length, (ii) low temperature, (iii) high sugar yield, and (iv) short processing time. A careful quantitative study of the interaction of pretreatment and hydrolysis reveals that hydrolysis is most effective if beech chips are first disintegrated in [EMIM][Ac] at 115 °C for 1.5 h. The cellulose conversion varies between 70.5 wt% and 90.2wt% for hydrolysis times between 5 h and 72 h. A complete recovery of cellulose and xylan resulting in a total saccharification of 65 wt% of the wood chips could be demonstrated. It is shown that short pretreatment times are required to enable high sugar yield as well as to limit product degradation.

Concentration Measurements in Ionic Liquid–Water Mixtures by Mid-Infrared Spectroscopy and Indirect Hard Modeling

An analytical method for the quantitative characterization of binary mixtures of water and ionic liquids (ILs) is presented. Mid-infrared (mid-IR) spectroscopy in combination with indirect hard modeling (IHM) is employed to quantify the water content in 1-butyl-3-methylimidazolium chloride (BMIMCl), 1,3-dimethylimidazolium dimethylphosphate (DMIMDMP), and 1-ethyl-3-methylimidazolium acetate (EMIMAc). Despite significant nonlinear shifts of the spectral bands, a good spectral fit with calibration errors of less than 2.3 wt % can be achieved almost over the whole concentration range. A profound analysis of the spectral models including peak assignment substantiates the physico-chemical foundation of the spectral models. Furthermore, the shift of peak functions in the spectral models is shown to provide a measure of molecular interaction in IL–water mixtures, which can also be utilized quantitatively. The vibrational bands of the water dipole reveal differences in the strength of hydrogen bonding with water in the IL studied. These properties of the spectral hard models demonstrate their quantitative analytical potential and set the stage for multiway calibration in comprehensive reaction monitoring in these highly interacting mixtures of IL and water.

Systematic Screening of Fermentation Products as Future Platform Chemicals for Biofuels

The production of biofuels must be economically and ecologically viable, in particular due to the competition with existing mature fossil-based fuels. There are many alternative products and pathways to generate biofuels. Hence, focusing on the most promising products and process alternatives requires identification of corresponding pathways from biomass to biofuel candidates using scarce data of high uncertainty. This contribution presents a methodology for i) process evaluation of fermentation and downstream processing (DP) in terms of costs and primary energy demand (PED) as main sustainability criteria and ii) identification of the most promising platform chemicals gained by fermentation for a biofuel production. The methodology considers the energy requirement already at an early design stage bridging the gap between performance screenings solely based on reaction stoichiometry and time-consuming process design, enabling an early process analysis, detection of bottlenecks and ranking of various processes. The focus herein is on lignocellulosic biomass.

Systematic approach for modeling reaction networks involving equilibrium and kinetically-limited reaction steps

Abstract Chemical systems often exhibit dynamics in different time scales owing to fast and slow reactions. Thus deriving models suitable for computation with standard numerical methods is challenging. In this tutorial we present a systematic approach for modeling chemical reaction systems including (known) slow reactions and fast reactions that can be assumed at equilibrium. The presented approach consists of the following steps: (i) identifying an independent set of reactions; (ii) writing the overall mass balance; (iii) writing a species balance for each species; (iv) writing the species transformation rates as a function of the net reaction rates; (v) introducing a constitutive equation for each reaction (either kinetic rate or equilibrium condition); (vi) performing index reduction of the differential-algebraic-equation (DAE) system. The resulting reduced system can be readily solved with standard DAE integrators. We discuss the number of initial conditions to be specified and illustrate the method through simple examples: methane reforming, Michaelis–Menten reaction and hydrogen-deuterium exchange.

Correction: Fractionation of lignocellulosic biomass using the OrganoCat process

Correction for ‘Fractionation of lignocellulosic biomass using the OrganoCat process’ by Philipp M. Grande et al., Green Chem., 2015, 17, 3533–3539.