Production of formic and acetic acids from phenol by hydrothermal oxidation

Abstract

Hydrothermal technology is a core environmental-protection technique which can be used for waste water treatment and biomass conversion. In this paper a novel idea, alkaline hydrothermal oxidation, is proposed for producing formic and acetic acids from wastewater containing phenolic compounds. The effects of the most important conditions-reaction temperature, reaction time, oxygen supply, and type of alkaline catalyst-on yields of formic and acetic acids were investigated. The results indicated that the optimum conditions for production of formic and acetic acids were: reaction temperature 300°C, reaction time 90 s, H 2 O 2 equivalent to 60% oxygen, and NaOH concentration 1.5 mmol. Under the optimum conditions the yields of formic and acetic acids reached 4.8 and 23.5%, respectively. In addition, the effect of different alkalis on yields of formic and acetic acids was also investigated. The results showed that compared with use of NaOH addition of KOH had a more pronounced effect on improving the yield of acetic acid. This research indicated that high-value-added formic and acetic acids can be recovered as resources by hydrothermal oxidation of phenolic wastewater, and thus hydrothermal oxidation has high potential for converting phenolic compounds in wastewater into value-added products.

Hydrothermal Conversion of Catechol into Four-Carbon Dicarboxylic Acids

“…In addition, it seems that KOH is more effective than NaOH at promoting the production of carboxylic acids, and a similar result was also observed in our previous research. 8,31 Since the radius of K + is larger than that of Na + , it is proposed that KOH has a greater alkalinity, as well as a greater tendency than NaOH to react with the H in the OH groups of catechol to form o-quinone. Consequently, studies with KOH were conducted to optimize the production of C4-DCAs.…”

“…8 Since a lower H 2 O 2 supply is helpful to easily get the initial oxidation products, 9 a H 2 O 2 supply of 20−60% (H 2 O 2 concentration varies from approximately 0.65 to 1.95 mol/L) was selected in this study to produce C4-DCAs with larger molecular weights. As shown in Figure 5a, the yield of total C4-DCAs increased with the increase of H 2 O 2 supply, reached a maximum of 31.4% with 50% H 2 O 2 supply, and then decreased sharply with the H 2 O 2 supply increased to 60%.…”

“…5 Our previous research on the hydrothermal conversion of lignin and its models into formic (HCOOH) and acetic (CH 3 COOH) acids has shown that phenolics were first oxidized to unsaturated six-carbon dicarboxylic acids by ring-opening reactions, then to four-carbon dicarboxylic acids (C4-DCAs) by double bond cleavage, and finally to formic and acetic acids. 5,8,9 C4-DCAs, such as tartaric (HOOC−CH(OH)−CH(OH)− COOH), malic (HOOC−CH 2 −CH(OH)−COOH), and fumaric (HOOCCHCHCOOH) acids, are not only essential industrial materials with extensive applications in food, chemical, pharmaceutical, and cosmetic industries but also potential platform chemicals. 10,11 These C4-DCAs currently are produced through the catalytic oxidation of petroleum-based feedstocks, and noble metal catalysts are usually required.…”

Selective Conversion of Glucose into Lactic Acid with Transition Metal Ions in Diluted Aqueous NaOH Solution

“…In addition, it is known that the constant ionization (k w ) of high temperature water is the maximum at near 300 °C at saturated vapor pressure. 35 The highest yield of lactic acid obtained at 300 °C may be related to the fact that the maximum ion product (k w ) of high temperature water occurs at about 300 °C. However, the yield of lactic acid further decreased with increasing reaction time from 1 to 5 min at 325 °C.…”

Production of Acrylic Acid from Biomass-Derived Fumaric Acid under Hydrothermal Conditions

“…Therefore, fairly high-purity fumaric acid is used in this study. Recently, many works have demonstrated that lignin models could also be oxidized into fumaric acid under hydrothermal conditions [26][27][28][29][30]. As a building block, fumaric acid has been widely studied [31].…”