Structure-performance correlations of cross-linked boronic acid polymers as adsorbents for recovery of fructose from glucose–fructose mixtures

Recovery of bio-oxygenates from reaction mixtures is one of the major challenges for future bio-refineries. Isolation of fructose produced by isomerization of glucose presents a typical example at a very early stage of the value chain. We propose to recover fructose from a solution containing a mixture of glucose and fructose by adsorption on polymers bearing phenylboronate moieties. p-Vinylphenylboronic acid was polymerized with various cross-linkers, namely polar aliphatic, low-polarity aliphatic, and aromatic. The cross-linker content was in the range 5–40 mol%. The polymers exhibit high capacities for fructose, with a maximum loading of up to 1 molFru molB−1. Fructose loading depends significantly on the length and content of cross-linker, as well as pre-treatment of the polymer. In general, the maximum fructose capacity correlates with the swelling ability of the polymers, since phenylboronate moieties become available for adsorption upon swelling. In contrast, maximum glucose loadings are much lower, in the range 0.1–0.3 molGlu molB−1, and depend only slightly on the type of cross-linker. The structures of the glucose and fructose complexes and the kinetics of their uptake were studied by in situ MAS NMR. Efficient desorption of fructose was observed in acidic medium, and more importantly, using CO2. The structures of the polymers after repeated adsorption and desorption remain unchanged, as confirmed by solid-state NMR. Adsorption-assisted isomerization of glucose catalyzed by soluble carbonates was also studied. A 56% yield of fructose was achieved after 8 successive cycles of reaction and adsorption

Respiration-based investigation of adsorbent-bioprocess compatibility

Background: The efficiency of downstream processes plays a crucial role in the transition from conventional petrochemical processes to sustainable biotechnological production routes. One promising candidate for product separation from fermentations with low energy demand and high selectivity is the adsorption of the target product on hydrophobic adsorbents. However, only limited knowledge exists about the interaction of these adsorbents and the bioprocess. The bioprocess could possibly be harmed by the release of inhibitory components from the adsorbent surface. Another possibility is co-adsorption of essential nutrients, especially in an in situ application, making these nutrients unavailable to the applied microorganism. Results: A test protocol investigating adsorbent-bioprocess compatibility was designed and applied on a variety of adsorbents. Inhibitor release and nutrient adsorption was studied in an isolated manner. Respiratory data recorded by a RAMOS device was used to assess the influence of the adsorbents on the cultivation in three different microbial systems for up to six different adsorbents per system. While no inhibitor release was detected in our investigations, adsorption of different essential nutrients was observed. Conclusion: The application of adsorption for product recovery from the bioprocess was proven to be generally possible, but nutrient adsorption has to be assessed for each application individually. To account for nutrient adsorption, adsorptive product separation should only be applied after sufficient microbial growth. Moreover, concentrations of co-adsorbed nutrients need to be increased to compensate nutrient loss. The presented protocol enables an investigation of adsorbent-bioprocess compatibility with high-throughput and limited effort

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

Structure-performance correlations of cross-linked boronic acid polymers as adsorbents for recovery of fructose from glucose–fructose mixtures

Recovery of bio-oxygenates from reaction mixtures is one of the major challenges for future bio-refineries. Isolation of fructose produced by isomerization of glucose presents a typical example at a very early stage of the value chain. We propose to recover fructose from a solution containing a mixture of glucose and fructose by adsorption on polymers bearing phenylboronate moieties. p-Vinylphenylboronic acid was polymerized with various cross-linkers, namely polar aliphatic, low-polarity aliphatic, and aromatic. The cross-linker content was in the range 5–40 mol%. The polymers exhibit high capacities for fructose, with a maximum loading of up to 1 molFru molB−1. Fructose loading depends significantly on the length and content of cross-linker, as well as pre-treatment of the polymer. In general, the maximum fructose capacity correlates with the swelling ability of the polymers, since phenylboronate moieties become available for adsorption upon swelling. In contrast, maximum glucose loadings are much lower, in the range 0.1–0.3 molGlu molB−1, and depend only slightly on the type of cross-linker. The structures of the glucose and fructose complexes and the kinetics of their uptake were studied by in situ MAS NMR. Efficient desorption of fructose was observed in acidic medium, and more importantly, using CO2. The structures of the polymers after repeated adsorption and desorption remain unchanged, as confirmed by solid-state NMR. Adsorption-assisted isomerization of glucose catalyzed by soluble carbonates was also studied. A 56% yield of fructose was achieved after 8 successive cycles of reaction and adsorption.</p