Toward Catalytic Ketonization of Volatile Fatty Acids Extracted from Fermented Wastewater by Adsorption

Abstract

Volatile fatty acids (VFA) produced by fermentation of organic-rich wastewater streams can, after efficient recovery from the dilute fermentation broth, serve as a circular source of carbon and be catalytically upgraded into various valuable platform molecules. Waste-derived VFA, that is, a mixture of acetic, propionic, and butyric acids, can thus be converted into mixed ketones, which in turn are valuable intermediates for light aromatics synthesis. Here, an integrated process is presented for the recovery and in-line catalytic conversion of VFA extracted from a fermentation broth by adsorption on a nonfunctionalized resin adsorbent. Gas-phase ketonization of the VFA was studied with and without co-fed water, which is inevitably coextracted from the broth, over TiO2 anatase catalysts to assess catalyst performance, including stability as a function of time on stream. While VFA conversion over bare TiO2 at 375 °C proceeded at 90% conversion with 100% selectivity to ketones, the presence of water in the feed resulted in an activity drop to 40%. Catalyst stability toward water could be greatly improved by dispersing the titania on a hydrophobic carbon support. The carbon-supported catalyst showed superior performance in the presence of excess water, providing a quantitative yield toward ketones at 400 °C. The approach thus allows coupling of VFA recovery from a fermentation broth with successful catalytic upgrading to mixed ketones, thus providing a novel route for the production of value-added products from waste streams.

Crystal Phase Effects on the Gas‐Phase Ketonization of Small Carboxylic Acids over TiO2 Catalysts

“…This reaction has received much interest recently as an important means for the production of transportation fuels and chemicals from biobased feedstock, such as bio‐oils [1] or, from other circular feedstock, such as fermented wastewater streams. [ 2 , 3 ] Indeed, the ketone products are versatile precursor molecules that can be further upgraded to various value‐added products, for example, to fuel components, lubricants,[ 4 , 5 , 6 ] or alkylated aromatics. [ 7 , 8 ] Amphoteric metal oxides, such as TiO 2 ,[ 9 , 10 , 11 , 12 , 13 ] ZrO 2 ,[ 13 , 14 ] CeO 2 ,[ 15 , 16 , 17 , 18 ] or Ce x Zr (1‐ x ) O 2 ,[ 19 , 20 ] have been heavily studied for this process as a result of their high ketonization activity and selectivity.…”

Evaluation of the Catalytic Activity of Metal Phosphates and Related Oxides in the Ketonization of Propionic Acid

“…Following these two systematic screenings, an increasing number of authors and inventors focused their attention on catalytic materials consisting of amphoteric and/or reducible metal oxides such as TiO 2 [35], ZrO 2 [36][37][38][39], CeO 2 and MnO 2 [24], La 2 O 3 , and other rare-earth oxides [40]. Mixed metal oxides, such as Ce/Zr/O [41], Ce/Zr/Mn/O [42], Mn/Ce/O [24,43], Ce/Fe/O [44], Mn/Zn-chromite [45], and Mg/Al/Ce/O [46] and supported catalysts such as MnO 2 /Al 2 O 3 [37], TiO 2 /C [47] and Ru/TiO 2 [25] have been claimed to be active as well.…”

Recovery Techniques Enabling Circular Chemistry from Wastewater

“…Therefore, the longer the VFA carbon chain, the stronger interaction with the resin. Non-functionalized styrene-divinylbenzene-based copolymer with the commercial name of Lewatit VP OC 1064 MD PH has shown a great potential to adsorb the VFAs from a complex mimicked fermentation broth [7,28]. Similarly, it can attract undissociated carboxylic acids via the aforementioned physical interaction mechanisms.…”

“…Whether a carboxylate salt or a carboxylic acid is to be obtained should guide the choice for the type of adsorbent and regeneration method. The main methods that have been employed to regenerate the adsorbents are thermal desorption by hot N 2 [7,28] and washing the loaded adsorbent with a basic aqueous or alcoholic solution [50,59]. In Table 2, a comparison of the advantages and limitations of these regeneration methods for various applied sorbents is given.…”

“…Although of value for our society when replacing the burning of fossil fuels, the added value of biogas is relatively small, and production of higher added value chemicals from wastewater is a topic in many research and development projects. For example, volatile fatty acids (VFAs) such as acetic acid can be produced [5], which can act as an intermediate platform chemical for a variety of other chemicals [6,7]. In addition, productions of larger carboxylic acids are known, including medium-chain carboxylic acids (MCCAs) [8][9][10][11] and even long-chain dicarboxylic acids (LCDAs), have recently been reported [12].…”