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PhD Defence Vahideh Elhami | Bio-based Crotonic Acid Production from Wastewater

Bio-based Crotonic Acid Production from Wastewater

The PhD Defence of Vahideh Elhami will take place in the Waaier building of the University of Twente and can be followed by a live stream.
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Vahideh Elhami is a PhD student in the department Sustainable Process Technology. (Co)Supervisors are prof.dr.ir. B. Schuur, prof.dr. G.J. Vancso and dr. M.A. Hempenius from the faculty of Science & Technology.

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.

To separate VFAs from the fermentation broth, a superparamagnetic polymer was synthesized, aiming at enhancing the fractionation of water and acids during the thermal regeneration of the adsorbent and recovering the loaded VFAs in highly concentrated solution. Loading the adsorbent with superparamagnetic nanoparticles provides an opportunity to generate heat inside the particles by applying an alternating magnetic field (AMF). The basis of the superparamagnetic beads was poly(divinylbenzene) (PDVB) incorporated with oleic acid grafted superparamagnetic magnetite nanoparticles (OA-MNPs). The MNPs were synthesized by the co-precipitation method and functionalized with oleic acid (OA). Following this step, the OA-MNPs were embedded in the matrix of the polymer during suspension polymerization. Using the synthesized beads in a packed bed column. Desorption was performed in two steps, starting with AMF heating at 25 mT and 52 kHz, followed by a hot N2 stripping stage. During AMF heating, it was found that 90 ±10% of the water in the pores was removed which physically filled the pores during adsorption of VFAs, while only 11% of total loaded VFAs were removed by AMF heating. Subsequently, the remaining VFAs were completely recovered in concentrated form using hot N2 stripping.

The bio-based solvents namely 2-methyltetrahydrofuran (2-MTHF) and dihydrolevoglucosenone (cyrene) were used to extract PHBV from the biomass. Moreover, the performance of these proposed bio-based solvents was compared with chloroform and dimethyl carbonate (DMC) as benchmark solvents using different batches of the PHBV-enriched biomass. The extraction with 2-MTHF and cyrene was optimized to recover the PHBV with the lowest average molecular weight. 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 2h with 5% [g/mL] biomass to solvent ratio. According to the mass balance closure over the extraction process, about 15% and 10% of polymer has remained in the residual biomass after extraction by 2-MTHF and cyrene, respectively. Performing two-stages cross-current extraction using fresh solvent did not significantly enhance the extraction yield, meaning that a fraction of the polymer was not extractable.

In this thesis, aiming at obtaining high yields of both CA and 2-pentenoic acid (2-PA) from MMC, direct pyrolysis of the PHBV-enriched biomass into CA and 2-PA was studied either under an inert atmosphere using N2 carrier gas flow or under reduced pressure using a custom-designed oven pyrolyzer. Applying nitrogen as a carrier gas enabled to experimentally optimize thermal depolymerization of the PHBV towards CA and 2-PA by manipulating the mean residence time of the hot vapor phase. The highest yields of 80±2% for CA and 67±1% for 2-PA were obtained at 0.15 L/min nitrogen flow rate corresponding to a mean residence time of 20 s, 240 ˚C for 1 hour. When the pyrolysis was conducted at a reduced pressure of 150 mbar instead of using nitrogen gas, a comparable acid yield was obtained. Overall, the custom-built pyrolysis set-up displayed an excellent operation performance using both N2 flow and reduced pressure.

Pyrolysis of PHBV yields a mixture of CA and 2-PA, originating from hydroxy butyrate (HB) and hydroxy valerate (HV) monomers, respectively. Aiming to use CA and 2-PA as bio-based monomers, requires a purification step to obtain the pure acids. In this study, we have experimentally explored the use of a spinning band distillation column (SBC) under vacuum operation to separate these acids. The thermodynamic feasibility for the distillation was first studied by measuring VLE-data of the mixture at process-relevant pressures of 50 and 100 mbar using a custom-designed VLE set-up. According to VLE data obtained by this equilibrium cell, there is a reasonable relative volatility and no sever pinch points for CA/2-PA mixture which indicate that separation is achievable by distillation. Thus, SBC was employed to further examine the separation of CA/2-PA by distillation.

For distillation feed in SBC, a mixture of acids with a mass ratio of 80/20 (CA/2-PA) was used. The separation in SBC was studied at 50 mbar and about 110˚C. In the experiments with synthetic mixtures, it was found that a successful recovery of CA can be achieved with high purity of >98% using a laboratory SBC. Furthermore, applying the actual pyrolyzate mixtures obtained by pyrolysis of the biomass and extracted pure PHBV as a feed for distillation column resulted in separation of CA with relatively high purity of 96% and 93%, respectively.