# The Oxidation of Isobutyraldehyde to Isobutyric Acid Using a Microenactor Technology System
## 4 Conclusions  
In this study, hydrogen peroxide was first tested as the oxidant. Although a conversion rate of nearly 90% for isobutyraldehyde was achieved in the Miprowa process, it was almost impossible to control the reaction to proceed towards isobutyric acid, with the selectivity for the product being less than 10%. Moreover, the hydrogen peroxide process is originally a heterogeneous reaction, requiring the addition of acetone as a co-solvent, which significantly increases the cost of subsequent separation. Therefore, it was decided to abandon the use of hydrogen peroxide as the oxidant for this study and switch to using oxygen for the oxidation process.  
The experimental results of the oxygen-based process showed that in the laboratory-scale process, with an isobutyraldehyde flow rate of 5 mL/min, an air flow rate of 1 SLPM, a process back pressure of 10 bar, and a reaction time of 1 h, the optimal isobutyraldehyde conversion rate of 90% and the isobutyric acid selectivity of 95% were achieved. In the pilot-scale system, with an isobutyraldehyde flow rate of 20 mL/min, an air flow rate of 4 SLPM, a process back pressure of 10 bar, and a reflux time of 3 h, the optimal isobutyraldehyde conversion rate of 91% and the isobutyric acid selectivity of 97% were achieved. Under the optimal experimental conditions, a single custom-built microreactor system can achieve an annual production of 7-8 tons of isobutyric acid.  
However, microreactor technology still has certain limitations in practical use. Firstly, the cost is relatively high. For instance, the Ehrfeld MMRS system used in this study costs over USD 300,000, which poses a significant financial burden for research laboratories and small to medium-sized enterprises. Secondly, microchannels are highly prone to clogging.  
Figure 12: Results for pilot-scale experiment.  
The formation of solid precipitates or crystal deposits from reaction products can lead to an increase in system pressure, ultimately causing the experiment to halt.  
Therefore, this study attempted to use a custom-built microreactor system to reduce the cost to below USD 100,000. In addition, catalysts were deliberately avoided in the experimental setup to minimize the risk of channel clogging during the reaction. This study demonstrates a value-added process by converting isobutyraldehyde (valued at USD 0.8-1.0/kg) into isobutyric acid (valued at USD 1.3-1.6/kg). Through technology transfer, the process is expected to be scaled up to a hundred-ton level and developed into a commercial-scale mass production process.  
In summary, this study has improved the isobutyraldehyde oxidation process using microreactor technology, achieving better production efficiency and demonstrating that there is no scaling-effect in the amplification of the process using custom-built MRT. Furthermore, the patent for this study has been successfully filed, and efforts are actively being made to scale up the production process to a hundred-ton level. It is hoped that this environmentally friendly and efficient process will be realized in the industry.  
C.-Y.W.: data curation, methodology, writing--original draft preparation. W.-Y.C.: data curation, reviewing and editing. L.-T.Y.: data curation, reviewing and editing. C.-H.C.: methodology, reviewing and editing. Y.-H.T.: conceptualization, supervision. All authors have read and agreed to the published version of the manuscript.  
This research was funded by National Science Council under the Grant No. NSC-112-2622-E-011-012. The results of this study have been granted a patent in Taiwan (No. I872292).  
Not applicable.  
Informed Consent Statement: Informed consent was obtained from all subjects involved in the study.  
The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.  
The authors declare no conflict of interest.