Separation in Biorefineries by Liquid Phase Adsorption: Itaconic Acid as Case Study

In biorefinery processes often the downstream processing is the technological bottleneck for an overall high efficiency. On the basis of recent developments, the selective liquid phase adsorption applying highly hydrophobic porous materials opened up new opportunities for process development. In this contribution, the efficiency of selective liquid phase adsorption is demonstrated for the separation and purification of itaconic acid from aqueous solutions for the first time. A wide range of different adsorbents was screened, revealing the surface polarity as well as textural properties as critical parameters for their performance. Adsorption from mixed solutions of itaconic acid and glucose exhibited extraordinary high selectivities for adsorbents with highly hydrophobic surfaces, especially certain activated carbons and hyper-cross-linked polymers. Evaluation of the pH dependence showed that the respective molecular species of itaconic acid/itaconate has a major impact on the adsorption performance. Additionally, experiments on a continuously operated fixed-bed adsorber were carried out, and the desorption behavior was evaluated. Overall, the technical feasibility of the selective adsorptive removal of itaconic acid from aqueous solutions with hydrophobic adsorbents is demonstrated as a model system for an alternative technology to conventional separation strategies in biorefinery concepts

Nanoporöse hochvernetzte Polymere und Aktivkohlen in selektiven Adsorptions- und Nanofiltrationsprozessen zur Anwendung in biogenen Wertschöpfungsketten

Hypercrosslinked porous polymers (HCP) from aromatic building blocks and polymer based spherical activated carbons (PBSAC) create a promising material basis for usage in a variety of separation processes. Especially adsorption and membrane processes. Biobased value chains on the other hand often create challenging separation processes, in which classical approaches face certain limitations. In this context the presented work delivers exemplary solutions in such fields of application. Initially a novel way of synthesizing a variety of HCP using conventional brønsted acids is developed. The obtained materials are then characterized with focus on the textural properties showing high hydrophobic surfaces and specific surface areas with above 1800 m² g-1. The HCP as well as PBSAC were then tested in adsorption processes with focus on 5-hydroxymethylfurfural (5-HMF)/fructose as well as itaconic acid/glucose. Both batch and continuous sorption experiments show high selectivities towards 5-HMF and itaconic acid by using HCP and PBSAC. Even the use of real fermentation broths contained the selectivity. Studies on the surface polarity furthermore enabled the description of the adsorption behaviour which was enabled through the targeted correlation between adsorption experiments and the polarity of different carboxylic acids. A reversed trend between the capacity of the adsorption and the dipole moment were observed presenting a semi quantitative way on estimating sorption selectivities. Lastely, the use of the mixed matrix membrane concept was used to develop HCP based membranes. Their usability was shown in nanofiltration applications on water based systems. Moderate rejections were presented through different dyes

Solvent-Responsive and Switchable Nanofiltration Membranes based on Hypercrosslinked Polymers with Permanent Porosity

Porous organic framework materials such as hypercrosslinked polymers (HCP) show a high chemical stability and dynamic behavior in a variety of solvents while their pore properties exhibit great potential for mixed matrix membrane (MMM) applications. However, their influence as porous filler in MMMs, especially for applications in liquid-phase filtration is still unexploited. Herein, we demonstrate an HCP-based MMM for molecular separation in the liquid phase by nanofiltration (NF). Depending on the solvent, the membrane changes its fractional free volume by shrinking or swelling. In connection to that, the pore size is also influenced, hence, providing a tunable permeance and molecular cut-off. The reduction of the pore volume and size directly correlates to the improvement of the NF performance, while the volume increase completely diminishes it. The extraordinary flexibility and high degree of crosslinking assure permanent porosity and render the dynamic behavior fully reversible. Thereby, a solvent-responsive “on” and “off” switching of the NF properties is enabled and was experimentally proven. Overall, this provides alternative strategies regarding the fouling and regeneration of membranes as well as the inhibition of pore blocking in membrane-derived processes by a tunable separation performance

Separation in Biorefineries by Liquid Phase Adsorption: Itaconic Acid as Case Study

In biorefinery processes often the downstream processing is the technological bottleneck for an overall high efficiency. On the basis of recent developments, the selective liquid phase adsorption applying highly hydrophobic porous materials opened up new opportunities for process development. In this contribution, the efficiency of selective liquid phase adsorption is demonstrated for the separation and purification of itaconic acid from aqueous solutions for the first time. A wide range of different adsorbents was screened, revealing the surface polarity as well as textural properties as critical parameters for their performance. Adsorption from mixed solutions of itaconic acid and glucose exhibited extraordinary high selectivities for adsorbents with highly hydrophobic surfaces, especially certain activated carbons and hyper-cross-linked polymers. Evaluation of the pH dependence showed that the respective molecular species of itaconic acid/itaconate has a major impact on the adsorption performance. Additionally, experiments on a continuously operated fixed-bed adsorber were carried out, and the desorption behavior was evaluated. Overall, the technical feasibility of the selective adsorptive removal of itaconic acid from aqueous solutions with hydrophobic adsorbents is demonstrated as a model system for an alternative technology to conventional separation strategies in biorefinery concepts

Aromatisation of bio-derivable isobutyraldehyde over HZSM-5 zeolite catalysts

An efficient route to obtain aromatic products based on biomass feedstock is a challenge for future biorefineries. Isobutyraldehyde is a promising feedstock available via biotechnological routes based on both carbohydrates and the direct bioconversion of CO2. Herein, we report an efficient process for the aromatisation of isobutyraldehyde over zeolite catalysts in a continuous fixed bed reactor to provide value-added aromatic compounds with a yield of 93%. Benzene, toluene and xylenes are the major compounds formed with 79% yield and a productivity of 65 mmol g(cat)(-1) h(-1). Zeolite Y, Beta and Mordenite and ZSM-5 of different modules were studied. Comprehensive catalyst characterisation using XRD, NH3-TPD, N-2-physisorption, and ICP-OES enabled establishing structure-performance relationships with a major role of zeolite structure, density of strong acid sites and mesoporosity, respectively. HZSM-5 with Si/Al ratios of 15 to 49 proved effective at the aromatisation possessing a comparable density of strong acid sites of 0.37-0.52 mmol g(-1). Superior stability was observed for HZSM-5 zeolites with higher mesopore volumes. The reaction is suggested to mainly proceed via catalytic cracking to C-1-C-4 alkanes/alkenes, which undergo further oligomerisation, cyclisation, and aromatisation to form the observed alkyl-aromatics. Emphasizing the potential of the concept, long term continuous operation was carried out by alternating 10 hours time on steam operation and catalyst regeneration via in situ calcination