# The Oxidation of Isobutyraldehyde to Isobutyric Acid Using a Microenactor Technology System
## 1 Introduction  
Isobutyraldehyde is a strong-smelling, colorless liquid, commonly used as a solvent and chemical intermediate, and its derivatives have applications in pharmaceuticals, fertilizers, paints and coatings, gasoline additives, inks, fragrances, and more. Isobutyraldehyde is commonly produced from propylene and isobutene [1], and it is also primarily produced as a byproduct of the hydrogenation of propylene [2]. Recently, with the rise in environmental awareness, the shift toward bio-based alternatives and sustainable practices could influence the isobutyraldehyde market dynamics [3, 4]. Along with the production of byproducts, the treatment of surplus isobutyraldehyde has clearly become an important issue. In addition to its production as isobutanol, the process of oxidizing isobutyraldehyde to isobutyric acid is also one of the main options in the market. Isobutyric acid is a versatile chemical raw material, used as a pharmaceutical intermediate, organic synthesis intermediate, and food flavoring, among other applications. Due to its distinctive odor, isobutyric acid has been increasingly used in food, fragrances, and perfumes in recent years. In addition, the market's growing preference for environmentallyfriendly substances has significantly increased the demand for isobutyric acid [5; 6]. Isobutyric acid can be produced from renewable feedbacks and can also be generated through microbial fermentation. Furthermore, it is biodegradable. Those characteristics contribute positively to sustainable development and a green economy. Isobutyric acid is primarily produced through two methods: biological and oxidation methods. In the biological method, using sugars as raw materials for the fermentation of engineered bacteria is the dominant approach [7]. However, commercialized biological methods still face certain limitations that are difficult to overcome, such as low production capacity, sensitivity to pH value, and formation of byproducts. As a result, the oxidation method using isobutanol or isobutyraldehyde as raw materials has become the mainstream process in the global market. Companies like Oxea GmbH, Mitsubishi Chemical, Eastman Chemical, BASF SE, and Dow Chemical all utilize this oxidation method [8]. The new isobutyric acid production plants of Oxea GmbH and Eastman Chemical were completed and commissioned in 2017 and 2018, respectively. This demonstrates the growing demand for isobutyric acid in the market. The oxidation of isobutyraldehyde to isobutyric acid is typically carried out within a temperature range of 20-100 \({}^{\circ}\)C. Hydrogen peroxide, oxygen, or air can be used as oxidizing agents. The operating pressure ranges from 20 psig to 75 psig. Additionally, acetone can be used as a co-solvent, and alkaline metal catalysts may be employed [9]. Depending on the choice of oxidizing agent, the reaction can be either a gas-gas or gas-liquid reaction. In actual process cases, Mitsubishi Chemical's patented process [10] employs hydrogen peroxide as the oxidizing agent and acetone as a co-solvent. The reaction is conducted at an operating temperature of 50-70 \({}^{\circ}\)C and a pressure of 5 bar. The reaction time typically ranges from 4 to 7 h, and it is carried out as a batch production process. On the other hand, Eastman Chemical's patented process [11] uses oxygen as the oxidizing agent, with a temperature range of 20-100 \({}^{\circ}\)C and operating pressures between 1.4 bar and 3.8 bar. The reaction duration is 5-7 h, and like the Mitsubishi process, it is also conducted in batch production. These two processes highlight practical approaches to isobutyraldehyde oxidation in industrial settings as well as two issues with the existing processes: first, the relatively long reaction time, and second, the low conversion rate and poor selectivity caused by the formation of byproducts. In this study, the aim is to overcome the challenges encountered by existing processes through the use of microreactor technology.