Adsorption followed by stepwise desorption to concentrate volatile fatty acids (VFAs) from very dilute aqueous streams is challenging and only a limited amount of VFAs can be collected at high concentration using N2-stripping. Here, we describe the preparation and use of superparamagnetic porous adsorbents to recover much larger fractions of VFAs in highly concentrated form from dilute aqueous streams than with the state-of-the-art N2-stripping technique. Our system is based on poly(divinylbenzene) (PDVB) impregnated with superparamagnetic magnetite nanoparticles (MNPs) synthesized by coprecipitation and functionalized with oleic acid (OA). The OA grafted MNPs (OA-MNPs) were embedded in the matrix of the polymer during suspension polymerization. The porous particles had an average size of 222 ± 40 µm with a surface area of 496 ± 10 m2/g and contained 11 ± 1 wt% MNPs with an average core size of 10 nm. VFAs adsorption from a dilute aqueous solution (containing 0.25 wt% of each acid) reached a saturation capacity of 43 g carboxylic acid per kg adsorbent,. The two-stage desorption was started with alternating magnetic field (AMF) heating at 25 mT and 52 kHz, followed by a hot N2 stripping stage removed 90 ± 9% of the water that had physically filled the pores during adsorption, and only 11 ± 2% of the loaded VFAs. Subsequently, 89 ± 3% of the VFAs were recovered almost water free using hot N2 stripping. Compared to sorbent regeneration and vapor fractionation by nitrogen stripping with a temperature gradient only, this new approach offers a much sharper acid fractionation from water, facilitating large energy savings in downstream operations.
Searching for renewable alternatives to produce platform chemicals, various biomasses have shown great potential as feedstock for value-added chemicals. For instance, biomass obtained by aerobic digestion of wastewater is rich in the copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). Pyrolysis of PHBV yields a mixture of crotonic acid (CA) and 2-pentenoic acid (2-PA). Application of CA and 2-PA as bio-based monomers requires purification. Purification by distillation is challenging as the high melting point of CA (72 °C) in combination with the high polymerization potential limits the temperature window for distillation severely. This study has experimentally explored the use of a spinning band distillation column (SBC) under vacuum operation to separate these acids. The thermodynamic feasibility for distillation was first studied by measuring vapor–liquid equilibrium data at relevant pressures of 50 and 100 mbar. The separation in the SBC was accomplished at 50 mbar and 40–110 °C for about 5 h. A successful recovery of CA with a high purity of >98% was achieved using a synthetic mixture of acids with a mass ratio of 80/20 (CA/2-PA). Actual pyrolyzate mixtures obtained by pyrolysis of the biomass and extracted pure PHBV were also fed to the distillation column and resulted in separation of CA with purities of 96 and 93%, respectively.
In an era where it becomes less and less accepted to just send waste to landfills and release wastewater into the environment without treatment, numerous initiatives are pursued to facilitate chemical production from waste. This includes microbial conversions of waste in digesters, and with this type of approach, a variety of chemicals can be produced. Typical for digestion systems is that the products are present only in (very) dilute amounts. For such productions to be technically and economically interesting to pursue, it is of key importance that effective product recovery strategies are being developed. In this review, we focus on the recovery of biologically produced carboxylic acids, including volatile fatty acids (VFAs), medium-chain carboxylic acids (MCCAs), long-chain dicarboxylic acids (LCDAs) being directly produced by microorganisms, and indirectly produced unsaturated short-chain acids (USCA), as well as polymers. Key recovery techniques for carboxylic acids in solution include liquid-liquid extraction, adsorption, and membrane separations. The route toward USCA is discussed, including their production by thermal treatment of intracellular polyhydroxyalkanoates (PHA) polymers and the downstream separations. Polymers included in this review are extracellular polymeric substances (EPS). Strategies for fractionation of the different fractions of EPS are discussed, aiming at the valorization of both polysaccharides and proteins. It is concluded that several separation strategies have the potential to further develop the wastewater valorization chains.
(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) obtained from waste/wastewater using a mixed microbial culture (MMC) usually varies in its properties due to daily variation in the waste/wastewater composition applied as feedstock. In the current study, the average molecular weight (MW) of PHBV was purposely reduced from about 1 MDa to about 200 kDa by drying the PHBV-rich biomass at elevated temperature of 120 °C for 18 h to ease extraction and handling. Furthermore, conversion into value-added chemicals such as trans-crotonic acid (trans-CA) and trans-2-pentenoic acid (2-PA) by thermal decomposition (pyrolysis) benefits from the lower MW. For the extraction of low MW PHBV, the use of the bio-based solvents 2-methyltetrahydroxyfuran (2-MTHF) and dihydrolevoglucosenone (cyrene) was studied. The maximum extraction yield of 62 ± 3 % with purity of > 99 % was achieved with 2-MTHF at 80 °C for an hour with high biomass to solvent ratio of 5 % (g/mL). Cyrene-based extractions resulted in the highest yield of 57 ± 2 % with purity of > 99 % at 120 °C in 2 h with 5 % (g/mL) biomass to solvent ratio. The mass balance closure over the extraction process indicated that about 15 % and 10 % of polymer has remained in the residual biomass after extraction by 2-MTHF and cyrene, respectively. The performance of these new solvents to extract polymers with various average MW was compared to the benchmark extractions using chloroform and dimethyl carbonate (DMC). It was found that for the polymers with low average MW the extraction efficiency of the proposed solvents exceeds the benchmark solvents.
There is a pronounced growth in industrial interest for renewable and environmentally sustainable pathways to produce chemicals. Driven by the desire to move away from linear economic models based on the supply of fossil fuel-based materials, renewable sources for chemicals are being explored. In this thesis, a multistep process to produce crotonic acid (CA) from a waste/wastewater is studied. CA is used in textile, cosmetic, painting, and coating applications and as building block in the synthesis of co-polymers, for example by copolymerization with vinyl acetate. Regardless of its wide range of application, the current production pathway of CA through a petrochemical route is neither renewable nor straightforward. Thus, this research was focused on providing a bio-based pathway to produce CA using a waste/wastewater as a feedstock. First, the waste/wastewater was subjected anaerobic fermentation to produce volatile fatty acids (VFAs). We examined adsorption as an affinity separation technique to recover these VFAs from the fermentation broth using a novel superparamagnetic polymer. Then, the VFAs were fed into an aerobic bio-reactor in which the microorganisms converted the VFAs into an intracellular co-polymer, called poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). After production of the PHBV, we investigated the application of bio-based solvents to extract the PHBV from the cells. Afterwards, the thermal degradation of PHBV towards CA was studied. Pyrolysis of the PHBV results in not only CA, but also in various side products. Therefore, the last step was focused on the purification of the produced bio-based CA.
In this research, the 80S bioactive glass with different Ca/P ratios was prepared by the sol-gel route. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and Fourier transforms infrared spectroscopy (FTIR) were used to study the apatite structure and shape. According to the results, the 78SiO2–17P2O5–5CaO bioglass showed a higher rate of crystalline hydroxyapatite (HA) on its surface in comparison with the other bioglasses. After 3 days of immersion in the SBF solution, spherical apatite was formed on the 78SiO2–17P2O5–5CaO surface, which demonstrated high bioactivity. A statistically significant promotion in proliferation and differentiation of G292 osteoblastic cells was also observed. Regarding its optimal cell viability and bioactivity, the 78SiO2–17P2O5–5CaO bioactive glass could be offered as a promising candidate for bone tissue applications.
Crotonic acid (CA) and trans-2-pentenoic acid (2-PA) can be obtained from renewable resources by pyrolysis of the bio-based poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) copolymer. In this study, direct pyrolysis of the PHBV-enriched biomass into CA and 2-PA was studied under an inert atmosphere and N2 carrier gas flow, aiming at obtaining high acid yields from mixed microbial cultures (MMCs). The highest yields of 80 ± 2% for CA and 67 ± 1% for 2-PA were obtained at conditions of 240 °C, 1 h, and 0.15 L/min nitrogen flow rate, corresponding to a mean hot vapor residence time of 20 s. A similar acid yield was achieved when the pyrolysis was performed under reduced pressure (150 mbar) instead of using nitrogen gas. The combined pyrolysis of extracted PHBV at 220 °C and 90 min with vapor fractionation by distillation resulted in yields of 81 and 92% for CA and 2-PA, respectively.
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