# The Oxidation of Isobutyraldehyde to Isobutyric Acid Using a Microenactor Technology System
## 3 Results and Discussion  
### Laboratory-Scale Experiments with Hydrogen Peroxide as Oxidizing Agent  
The batch experiments for this study were conducted in a beaker prior to the microreactor system experiments. In the batch experiments, 120 mL of isobutyraldehyde was placed  
Figure 1: Experimental flowchart for oxidation of isobutyraldehyde by hydrogen peroxide. in a beaker, and hydrogen peroxide was fed at a rate of 2 mL per minute using a pump for the oxidation reaction. The hydrogen peroxide was stored at 0 \({}^{\circ}\)C, while the beaker containing the reaction mixture was maintained at approximately 25 \({}^{\circ}\)C. After 3 h of operation, the conversion rate of isobutyraldehyde was only around 15%, with almost no formation of isobutyric acid. It is presumed that the reaction performance in the batch beaker setup was very limited. Therefore, to achieve better reaction performance and optimize conditions, subsequent experiments will be conducted using a microreactor system. For microreactor system, the MMRS Miprowa modular reactor will be used as the main reactor for the reaction. The reactor is equipped with an external jacket through which liquid is passed for temperature control. A LH-25 mixer will be installed before the reactor to pre-mix the two feedstreams. The system is also equipped with a backpressure valve at the downstream section for pressure control. Before exiting the reactor, the pipeline will pass through an ice bath for cooling. Samples will be taken for analysis using GC and GC-MS. A simplified experimental flowchart is shown in Figure 1.  
In the experimental design, the primary objective is to determine the appropriate experimental temperature. The feed ratio of isobutyraldehyde/acetone/hydrogen peroxide is 1:1:1, with isobutyraldehyde and acetone pre-mixed. The total feed flow rate is 5 mL/min, and the reaction time is 6 min. The experimental operating pressure is 10 bar, and the operating temperature is designed between 20 \({}^{\circ}\)C and 80 \({}^{\circ}\)C. The experimental results are shown in Figure 2.  
The experimental results indicate that the optimal condition is 20 \({}^{\circ}\)C, which is close to room temperature. There are two main reasons for this outcome. First, the reaction is exothermic, and according to Le Chatelier principle, an increase in temperature will hinder the progress of the oxidation reaction. Second, an increase in temperature will cause the decomposition of hydrogen peroxide, leading to a loss of its oxidizing ability. Therefore, 20 \({}^{\circ}\)C will be selected as the testing temperature for subsequent experiments. Figure 2: Percentage conversion/selectivity vs. temperature plot for oxidation of isobutyraldehyde by hydrogen peroxide. In the experimental results of Figure 2, although the optimal conversion rate of isobutyraldehyde (iHBu) reaches nearly 50%, the selectivity for isobutyric acid (iHOBu) does not exceed 10%. Therefore, the next step is to modify the feed ratio. The system design still follows the process outlined in Figure 1. As for the experimental conditions, the total liquid feed flow rate is 5 mL/min, the reaction time is 6 min, the experimental operating pressure is 10 bar, and the operating temperature is 20 \({}^{\circ}\)C. The feed ratio of isobutyraldehyde to hydrogen peroxide is operated between 2:1 and 1:8. The experimental results are shown in Figure 3.  
In the experimental results of Figure 3, when the isobutyraldehyde to hydrogen peroxide ratio exceeds 1:4, the conversion rate reaches a critical value of 90%. However, the selectivity for isobutyric acid remains very low, staying around 5% regardless of the ratio. Although the addition of acetone as a co-solvent did indeed address the challenges of the heterogeneous reaction between isobutyraldehyde and hydrogen peroxide, it still could not direct the reaction towards the synthesis of isobutyric acid.