(466d) Bio-Derived Gamma-Butyrolactone Production from Succinic Acid with Bio-Derived Solvents

Petrochemical resources are widely used in many industries in modern society. However, their use has caused environmental problems, such as global warming and pollution. As a result, many renewable resources are being studied as alternatives. The use of petrochemical resources can be divided into two categories: energy use and conversion to chemicals. Alternative resources for energy use include hydropower, wind power, solar power, biomass, and many others. In contrast, biomass is the only primary resource that can be used for chemical conversion. Therefore, bio-based chemicals are attracting attention. Among them, gamma-butyrolactone (GBL) is an important chemical compound with a wide range of applications in various fields, such as medicine, agriculture, and industry¹⁾. Hydrogenation using bio-succinic acid (SA) as a raw material is attracting attention as an alternative to maleic acid derived from fossil resources, which is currently used as a raw material for GBL²⁾. Since bio-succinic acid TTis an important platform chemical and is already produced on a commercial scale, this study aims to produce GBL from SA. Most of the previous studies on the SA–GBL reaction used 1,4–dioxane as a solvent^{3, 4)}. However, since 1,4–dioxane is a hazardous chemical with carcinogenic, mutagenic, and reproductive toxicity effects, its use in the production of GBL from SA is not sustainable. To achieve sustainable production, research using bio-based solvents for the generation of bio-gamma-butyrolactone from succinic acid is necessary. However, there is currently no literature available on this topic. Based on the above, in this study, we aimed to produce GBL from SA using not only raw materials, but also solvents derived from biomass. This research can contribute not only to the sustainable production of GBL but also to the production of biochemicals commonly produced by hydrogenation in industry.

2．Experimental

In this study, two types of experiments were conducted to produce GBL, Catalytic Transfer Hydrogenation (CTH) and direct hydrogenation.

The Materials were 5wt% Ru/C catalyst^*1, 5wt% Pd/Al₂O₃ catalyst^*2, SA (>99.5wt%)^*1, Solvents^*1,2, isopropanol (IPA) and tetrahydrofuran (THF), hydrogen gas (>99.999%)^*3, argon gas (>99.999%)^*3.

(*1 Fujifilm Wako Pure Chemicals Corporation, *2 Tokyo Kasei Kogyo, *3 Taiyo Nippon Sanso Gas & Welding Co.)

The reactor utilized in the experiments was a 100 mL stainless steel batch autoclave (TVS-N2 type, 100 mL, Taiatsu Techno. Corporation, Osaka, Japan).

2.1 Catalyst reduction

Ru/C catalyst or Pd/Al₂O₃ catalyst was reduced for 2.5 h at 240 °C under a hydrogen gas atmosphere.

2.2 Catalytic hydrogenation

2.2.1 Catalytic Transfer Hydrogenation (CTH)

Isopropanol (IPA) was used as the solvent and hydrogen donor in the CTH experiments. After the catalyst reduction (c.f., 2.1), the temperature was gradually lowered to room temperature, and the hydrogen gas was purged using argon gas. The hydrogenation experiments were then performed started by adding SA and IPA to the reactor followed by increasing the temperature to reaction temperature.

2.2.2 Direct hydrogenation

In the direct hydrogenation experiments, hydrogen gas was supplied externally. After the catalyst reduction (c.f., 2.1), the temperature was gradually lowered to room temperature, and the hydrogen gas was purged using argon gas. The direct hydrogenation experiments were then performed started by adding SA and the solvent to the reactor. In the direct hydrogenation process, the reactor was pressurized with hydrogen gas before the start of the temperature increase.

2.3 Analysis

After the catalytic hydrogenation reaction, the temperature was gradually lowered to room temperature, and the catalyst was filtered. Finally, the product solution was analyzed by GC-FID (Shimadzu, GC-2014).

3．Results & Discussion

In the CTH experiments conducted at 150, 180, and 200 °C with IPA, the maximum SA conversion of 98.1 mol% was achieved at 200 °C and the maximum GBL yield of 6.1mol% was achieved at 180 °C (at 79.7% SA conversion). In order to reduce the amount of SA ester produced, which was responsible for the low GBL yield, water was added. This resulted in a decrease of SA ester yield to 31.9mol%. Subsequently, the amount of water was increased to 5 and 10wt%, resulting in a decrease of SA ester yield to 24.7 and 23.0mol%, respectively. However, increasing the amount of water to 10wt% also resulted in a decrease of both SA conversion (67.4mol%) and GBL yield (5.1mol%). This indicates that while water addition greatly suppressed dehydration, it also made it difficult to suppress esterification alone.

On the other hand, in the direct hydrogenation experiment, the SA conversion and GBL yield were 57.7mol% and 9.5mol%, respectively, at a hydrogen pressure of 2.0 MPa before temperature increase and a reaction temperature of 200 °C for 4 h, using the Ru/C catalyst. However, at a reaction time of 2 h, the SA conversion and GBL yield dropped to 20.0 and 8.0mol%, respectively. At a hydrogen pressure of 1.5 MPa before temperature increase, the SA conversion and GBL yield dropped further to 17.9 and 4.7mol%, respectively. This indicates that the reaction time and hydrogen pressure have a significant effect on the conversion ratio. When the Pd/Al₂O₃ catalyst was used, the SA conversion decreased to 43.4mol%, while the GBL selectivity increased to 25.6mol%. This suggests that the Pd/Al₂O₃ catalyst forms fewer byproducts and that further improvement in GBL yield can be expected by positively influencing the SA conversion by increasing the reaction temperature and reaction time.

4．Conclusion

In this particular study, a series of experiments were carried out to produce GBL from bio-SA using a biomass-derived solvent and hydrogen. Firstly, CTH experiments were conducted using IPA at different reaction temperatures, and the maximum yield of GBL achieved was 6.1mol% at a reaction temperature of 180 °C and 79.7% SA conversion. This result indicates that SA underwent fast esterification during the CTH process.

Additionally, direct hydrogenation experiments were performed using THF as a solvent. In an experiment with THF utilizing Ru/C as catalyst, a with hydrogen pressure of 2.0 MPa before temperature increase, reaction temperature of 200 °C, and reaction time 4 h, the SA conversion reached 57.7mol%, and the corresponding GBL yield was 9.5mol%. Moreover, when the Pd/Al₂O₃ catalyst with THF as solvent was utilized under the same conditions, a high GBL selectivity of 25.6mol% was obtained. Those results indicate that further GBL yield improvement can be achieved by optimizing the reaction time and temperature.

This study about two catalytic hydrogenation approaches (CTH and direct hydrogenation) for GBL formation from bio-SA using bio-based solvents show the multiple tasks when it comes to sustainable biomass feedstock engineering, but it gives hope too, that finally we can do the transformation to a sustainable future.

References

1) Hong, U. G. et al., J. Ind. Eng. Chem., 17, 316–320 (2011).

2) C. Zhang et al., Catal. Today, 276, 55–61 (2016).

3) Hong, U.G. et al., Catal. Letters, 141(2), 332–338 (2011).

4) Shao, Z. et al., Ind. Eng. Chem. Res., 53, 9638–9645 (2014).

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