Integrated Humin Formation and Separation Studied In Situ by Centrifugation.

We present a novel method for studying the integrated formation and separation of humins formed during the Brønsted acid-catalyzed conversion of fructose (here, at 90 °C with 20 wt % fructose and 5 wt % sulfuric acid). For the first time, we report the reaction carried out in situ during systematic centrifugation experiments, which allows combining humin formation and separation along with investigation of the phase behavior of humins. Analysis of the formed humin deposits employing scanning electron microscopy reveals deposits that are formed from a layer of monodisperse microspheres with a narrow diameter range of 0.9-1.9 µm. In the centrifugal force field, the microspheres partially coalesce, which increases with time and relative centrifugal force up to the formation of a thin and uniform layer of microspheres covering a continuous humin bulk phase with 80-90 µm thickness. These findings give evidence that humin spheres are highly viscous droplets rather than solid particles during formation. Our result is in line with the often-reported spherical and planar deposits formed during acidic carbohydrate conversion in technical systems and supports the development of strategies for deposit prevention, on the one hand, and humin preparation for material utilization, on the other hand.

In situ adsorption of itaconic acid from fermentations of Ustilago cynodontis improves bioprocess efficiency.

BACKGROUND: Reducing the costs of biorefinery processes is a crucial step in replacing petrochemical products by sustainable, biotechnological alternatives. Substrate costs and downstream processing present large potential for improvement of cost efficiency. The implementation of in situ adsorption as an energy-efficient product recovery method can reduce costs in both areas. While selective product separation is possible at ambient conditions, yield-limiting effects, as for example product inhibition, can be reduced in an integrated process. RESULTS: An in situ adsorption process was integrated into the production of itaconic acid with Ustilago cynodontis IAmax, as an example of a promising biorefinery process. A suitable feed strategy was developed to enable efficient production and selective recovery of itaconic acid by maintaining optimal glucose concentrations. Online monitoring via Raman spectroscopy was implemented to enable a first process control and understand the interactions of metabolites with the adsorbent. In the final, integrated bioprocess, yield, titre, and space-time yield of the fermentation process were increased to values of 0.41 gIA/gGlucose, 126.5 gIA/L and 0.52 gIA/L/h. This corresponds to an increase of up to 30% in comparison to the first extended batch experiment without in situ product removal. Itaconic acid was recovered with a purity of at least 95% and high concentrations above 300 g/L in the eluate. CONCLUSION: Integration of product separation via adsorption into the bioprocess was successfully conducted and improved the efficiency of itaconic acid production. Raman spectroscopy was proven to be a reliable tool for online monitoring of various metabolites and facilitated design and validation of the complex separation and feed process. The general process concept can be transferred to the production of various similar bioproducts, expanding the tool kit for design of innovative biorefinery processes.

Holistic Approach to Process Design and Scale-Up for Itaconic Acid Production from Crude Substrates.

Bio-based bulk chemicals such as carboxylic acids continue to struggle to compete with their fossil counterparts on an economic basis. One possibility to improve the economic feasibility is the use of crude substrates in biorefineries. However, impurities in these substrates pose challenges in fermentation and purification, requiring interdisciplinary research. This work demonstrates a holistic approach to biorefinery process development, using itaconic acid production on thick juice based on sugar beets with Ustilago sp. as an example. A conceptual process design with data from artificially prepared solutions and literature data from fermentation on glucose guides the simultaneous development of the upstream and downstream processes up to a 100 L scale. Techno-economic analysis reveals substrate consumption as the main constituent of production costs and therefore, the product yield is the driver of process economics. Aligning pH-adjusting agents in the fermentation and the downstream process is a central lever for product recovery. Experiments show that fermentation can be transferred from glucose to thick juice by changing the feeding profile. In downstream processing, an additional decolorization step is necessary to remove impurities accompanying the crude substrate. Moreover, we observe an increased use of pH-adjusting agents compared to process simulations.

Investigation of the elution behavior of dissociating itaconic acid on a hydrophobic polymeric adsorbent using in-line Raman spectroscopy.

The use of adsorption for the purification of dicarboxylic acids is rather limited and currently predominantly confined to ion-exchange chromatography. A promising, but less regarded alternative is the use of hydrophobic adsorbents. Regarding hydrophobic absorbents, the literature focuses on screenings of adsorbents for purification of (di)carboxylic acids with regard to adsorption equilibria. The investigation of dynamic phenomena in the column received only minor attention. In this contribution, this knowledge gap is addressed. First, the adsorption behavior of itaconic acid species on the hydrophobic, highly-crosslinked polymeric adsorbent Chromalite™ PCG1200C is investigated. For this purpose, adsorption isotherms are determined via frontal analysis at pH values of 2, 3, 4.5, 6.5, and 8 to evaluate the dependency of the adsorption capacity on the dissociation state. Capacities above 150 g Lads-1 at liquid phase concentrations of 70 g L-1 are observed at a pH of 2. A strong decrease of capacity with increasing pH value, i.e., with increasing fraction of dissociated negatively charged acid species, is observed. Second, pulse experiments at aforementioned pH values are performed. Thereby, in-line Raman spectra are recorded at the column outlet, which allows the direct differentiation of the acid species state of dissociation. The spectral information is evaluated for quantitative concentration profiles of itaconic acid species using Indirect Hard Modeling with mixture hard models that are calibrated subject to ideal as well as non-ideal thermodynamics. In-line measurement errors of ≤ 3.5 g L-1 are achieved for the itaconic acid species. In dependency of the pH of the feed solution, a separation of the individual acid species within the pulse experiments is observed. It is conjectured that the process is dominated by a superposition of species-dependent adsorption characteristics and dissociation reactions.

Designed to Be Green, Economic, and Efficient: A Ketone-Ester-Alcohol-Alkane Blend for Future Spark-Ignition Engines.

Model-based fuel design can tailor fuels to advanced engine concepts while minimizing environmental impact and production costs. A rationally designed ketone-ester-alcohol-alkane (KEAA) blend for high efficiency spark-ignition engines was assessed in a multi-disciplinary manner, from production cost to ignition characteristics, engine performance, ecotoxicity, microbial storage stability, and carbon footprint. The comparison included RON 95 E10, ethanol, and two previously designed fuels. KEAA showed high indicated efficiencies in a single-cylinder research engine. Ignition delay time measurements confirmed KEAA's high auto-ignition resistance. KEAA exhibits a moderate toxicity and is not prone to microbial infestation. A well-to-wheel analysis showed the potential to lower the carbon footprint by 95 percent compared to RON 95 E10. The findings motivate further investigations on KEAA and demonstrate advancements in model-based fuel design.

Inline Raman Spectroscopy and Indirect Hard Modeling for Concentration Monitoring of Dissociated Acid Species.

We propose an approach for monitoring the concentration of dissociated carboxylic acid species in dilute aqueous solution. The dissociated acid species are quantified employing inline Raman spectroscopy in combination with indirect hard modeling (IHM) and multivariate curve resolution (MCR). We introduce two different titration-based hard model (HM) calibration procedures for a single mono- or polyprotic acid in water with well-known (method A) or unknown (method B) acid dissociation constants pKa. In both methods, spectra of only one acid species in water are prepared for each acid species. These spectra are used for the construction of HMs. For method A, the HMs are calibrated with calculated ideal dissociation equilibria. For method B, we estimate pKa values by fitting ideal acid dissociation equilibria to acid peak areas that are obtained from a spectral HM. The HM in turn is constructed on the basis of MCR data. Thus, method B on the basis of IHM is independent of a priori known pKa values, but instead provides them as part of the calibration procedure. As a detailed example, we analyze itaconic acid in aqueous solution. For all acid species and water, we obtain low HM errors of < 2.87 × 10-4mol mol-1 in the cases of both methods A and B. With only four calibration samples, IHM yields more accurate results than partial least squares regression. Furthermore, we apply our approach to formic, acetic, and citric acid in water, thereby verifying its generalizability as a process analytical technology for quantitative monitoring of processes containing carboxylic acids.

Direct Monitoring of Microgel Formation during Precipitation Polymerization of N-Isopropylacrylamide Using in Situ SANS.

Poly(N-isopropylacrylamide) microgels have found various uses in fundamental polymer and colloid science as well as in different applications. They are conveniently prepared by precipitation polymerization. In this reaction, radical polymerization and colloidal stabilization interact with each other to produce well-defined thermosensitive particles of narrow size distribution. However, the underlying mechanism of precipitation polymerization has not been fully understood. In particular, the crucial early stages of microgel formation have been poorly investigated so far. In this contribution, we have used small-angle neutron scattering in conjunction with a stopped-flow device to monitor the particle growth during precipitation polymerization in situ. The average particle volume growth is found to follow pseudo-first order kinetics, indicating that the polymerization rate is determined by the availability of the unreacted monomer, as the initiator concentration does not change considerably during the reaction. This is confirmed by calorimetric investigation of the polymerization process. Peroxide initiator-induced self-crosslinking of N-isopropylacrylamide and the use of the bifunctional crosslinker N,N'-methylenebisacrylamide are shown to decrease the particle number density in the batch. The results of the in situ small-angle neutron scattering measurements indicate that the particles form at an early stage in the reaction and their number density remains approximately the same thereafter. The overall reaction rate is found to be sensitive to monomer and initiator concentration in accordance with a radical solution polymerization mechanism, supporting the results from our earlier studies.

Multi-scale processes of beech wood disintegration and pretreatment with 1-ethyl-3-methylimidazolium acetate/water mixtures.

BACKGROUND: The valorization of biomass for chemicals and fuels requires efficient pretreatment. One effective strategy involves the pretreatment with ionic liquids which enables enzymatic saccharification of wood within a few hours under mild conditions. This pretreatment strategy is, however, limited by water and the ionic liquids are rather expensive. The scarce understanding of the involved effects, however, challenges the design of alternative pretreatment concepts. This work investigates the multi length-scale effects of pretreatment of wood in 1-ethyl-3-methylimidazolium acetate (EMIMAc) in mixtures with water using spectroscopy, X-ray and neutron scattering. RESULTS: The structure of beech wood is disintegrated in EMIMAc/water mixtures with a water content up to 8.6 wt%. Above 10.7 wt%, the pretreated wood is not disintegrated, but still much better digested enzymatically compared to native wood. In both regimes, component analysis of the solid after pretreatment shows an extraction of few percent of lignin and hemicellulose. In concentrated EMIMAc, xylan is extracted more efficiently and lignin is defunctionalized. Corresponding to the disintegration at macroscopic scale, SANS and XRD show isotropy and a loss of crystallinity in the pretreated wood, but without distinct reflections of type II cellulose. Hence, the microfibril assembly is decrystallized into rather amorphous cellulose within the cell wall. CONCLUSIONS: The molecular and structural changes elucidate the processes of wood pretreatment in EMIMAc/water mixtures. In the aqueous regime with >10.7 wt% water in EMIMAc, xyloglucan and lignin moieties are extracted, which leads to coalescence of fibrillary cellulose structures. Dilute EMIMAc/water mixtures thus resemble established aqueous pretreatment concepts. In concentrated EMIMAc, the swelling due to decrystallinization of cellulose, dissolution of cross-linking xylan, and defunctionalization of lignin releases the mechanical stress to result in macroscopic disintegration of cells. The remaining cell wall constituents of lignin and hemicellulose, however, limit a recrystallization of the solvated cellulose. These pretreatment mechanisms are beyond common pretreatment concepts and pave the way for a formulation of mechanistic requirements of pretreatment with simpler pretreatment liquors.

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.

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.