The selective synthesis of aromatics and furans from biomass-derived compounds

Mahmoud, Eyas
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University of Delaware
Chemicals provide most of the material and energy for mankind. A majority of chemicals are produced from petroleum. The field of biomass conversion seeks to develop sustainable routes to chemicals. The commercialization of these routes improves the sustainability of the chemical industry and decreases price fluctuations. In addition, the use of biomass-derived feedstocks for chemicals and fuels production could decrease global annual CO2 emissions. This thesis presents processes for the production of two classes of chemicals: aromatics and furans. ☐ The economics, practicality, feedstock availability, feedstock abundance, and environmental impact of the process were considered in the lab-scale design to convert the biomass-derived molecules to chemicals. An iterative design methodology was used that begins with a low level of detail and progressively creates more and more detail. During design development, the economic viability of the scaled-up process was considered. Lignocellulosic biomass was the chosen feedstock for chemicals production because of its abundance, its high rate of production, and because it is not consumed as a food supply. ☐ The synthesis of aromatics and furans depends on catalysts to convert biomass-derived molecules to the desired products. Catalysts materials used affected the rate of chemical reaction without being consumed by the reaction. In this thesis, zeolites Beta and faujasite, microporous molecular sieves, were the class of materials most often used to catalyze these reactions. Some dehydration reactions were performed homogeneously. ☐ A route for the production of phthalic anhydride from lignocellulosic biomass is described which uses the furfural-derived molecules. Furfural production was commercialized in the early 1900’s and it is produced at the rate of 300,000 tons per year from biomass. Furan and maleic anhydride were converted in a two-step reaction protocol of Diels-Alder followed by dehydration reactions to phthalic anhydride. A 96% yield to the Diels-Alder product, exo- 4,10-dioxa-tricyclo[]dec-8-ene-3,5-dione, was obtained after 4 h of reaction in a batch reactor initially at 25 °C. The adiabatic temperature rise, ΔTad, was calculated to be about 150 °C. The reduction of the equilibrium constant at high temperatures prevents thermal runaway. The solvent-free reaction allows for the production of the Diels-Alder product at the hundreds of thousands of tons per year scale. ☐ An important process discovery which is discussed in this thesis is the dehydration reaction of the Diels-Alder products of furans, or oxanorbornene molecules necessary for production of aromatics. The homogeneous dehydration reaction of the Diels-Alder product of furan and maleic anhydride, exo-4,10-dioxa-tricyclo[]dec-8-ene-3,5-dione, yields only a 14% selectivity to phthalic anhydride at 100% conversion after 3 h of reaction in methanesulfonic acid (MSA). Nuclear magnetic resonance (NMR) experiments were used to show that the main side reaction channels for the dehydration of oxanorbornene molecules are retro-Diels-Alder and polymerization reactions. Dehydration reactions run in a binary mixture of MSA and acetic anhydride afforded an 87% selectivity to the aromatic products phthalic anhydride and acid at 100% conversion. MSA and acetic anhydride react at 25 °C to form acetyl methanesulfonate, a strong acylating agent. In the presence of this acylating agent and acetic anhydride, it was discovered that the reaction mechanism proceeded through a different pathway when using the binary mixture of MSA and acetic anhydride as the dehydration medium as compared to reactions run in neat MSA. Following reaction, the aromatic products can be efficiently extracted using toluene as the organic phase. A technoeconomic analysis of the process demonstrated that the renewable phthalic anhydride production is cost-competitive with the synthetic route. This new chemistry can contribute to the resolution of emerging challenges in biomass conversion. ☐ A route for the production of benzoic acid from lignocellulosic biomass is described. Benzoic acid can be industrially transformed to many consumer polymers such as nylon-6, epoxy resins, phenolic resins, and carbonates. Furan and methyl acrylate or acrylic acid were converted by Diels-Alder followed by dehydration reactions to methyl benzoate or benzoic acid. Diels-Alder reactions of furan and methyl acrylate or acrylic acid run at 25 °C yielded no detectable amounts of Diels-Alder product after 24 h of reaction. Hf-, Zr-, and Sn-containing zeolite Beta were found to provide around a 50% yield of the Diels-Alder product of furan and acrylic acid and 25% yield of the Diels-Alder product of furan and methyl acrylate after 24 h of reaction at 25 °C, with no detected side products. The TOFs of these catalysts are one hundred times those of previously reported catalyst for this reaction. ☐ The Diels-Alder product was dehydrated with a 96% selectivity to methyl benzoate at 100% conversion in the binary mixture for the reaction run at 25 °C for 2 h followed by a temperature increase to 80 °C for 1 h at an endo:exo ratio of 0.43. Increasing the concentration of the reactant from 0.13 to 0.65 M at the same endo:exo ratio decreased methyl benzoate selectivity from 96 to 83% at 100% conversion. Because two stereoisomers are formed after the Diels-Alder reaction, the effect of the stereochemical composition of the reactant on the selectivity was studied. Increasing the endo:exo ratio from 0.43 to 1.89 at a 0.65 M concentration of reactant led to a 89% selectivity to methyl benzoate at 100% conversion. This indicated than a change in the stereochemical composition of the reactant does not significantly affect reaction selectivity to the aromatic product. Reactions run in neat MSA resulted in a 1.7% selectivity to methyl benzoate at 100% conversion. Running the reaction using oxanorbornene carboxylic acid, the Diels-Alder adduct of furan and acrylic acid as the reactant, led to a drop in the selectivity of aromatics from 96% to 43% at 100% conversion under identical conditions of temperature, concentration and time. The process discussed for benzoic acid synthesis is a selective pathway for the production of benzene derived polymers from molecules obtained in high yield from lignocellulosic biomass. ☐ For the solvent-free synthesis of p-xylene, metal-exchanged faujasite zeolites were used. Metal-exchanged faujasites are solid Lewis acids that can catalyze both Diels-Alder and dehydration reactions. It was found that at 250 °C, NaX catalyzes p-xylene synthesis with 96% selectivity at 10% DMF conversion. High selectivity to p-xylene (> 90%) is maintained at conversions greater than 30%. This result is a major improvement over the 35% selectivity to p-xylene obtained for HY zeolite. The experimental results indicate that the increase in p-xylene selectivity associated with Lewis acidic faujasite catalyst is due to a combination of the effects of Lewis acid type, strength, and extraframework position in the faujasite framework. ☐ An investigation of the conversion of glucose to 5-(hydroxymethyl)furfural (HMF) was performed catalyzed by heterogeneous Lewis and Brønsted acid combinations. The addition of small weight percent of water (7.5%) increased the selectivity of the glucose isomerization reaction. It was found that glucose can be converted to furans (HMF and IMF) with a selectivity of 88% at 60% glucose conversion using mixtures of Sn-Beta zeolite (Lewis acid) and Amberlyst 15 (Brønsted acid) catalysts in isopropanol. The cascade reaction was run in ethanol and isopropanol using any of the materials: Sn-MCM-41, Sn-Beta, Hf-Beta, and Zr-Beta and polymeric Brønsted acid catalysts. At larger conversion (97%), selectivity to furans decreased to 39% due to humin formation. Increasing the temperature of reaction from 120 to 140 °C in a solution of 7.5 wt. % water in isopropanol increases glucose conversion from 52 to 63% and decreases the total carbon balance from 70 to 57% after 2 h of reaction. The furans’ selectivity also decreases from 43 to 32% when the reaction is catalyzed by Sn-Beta and Amberlyst 70.
Applied sciences , Biomass-derived compounds