Microwave digestion instrumentThe Development and Reaction Mode of Microwave Control Technology

In 1975, the use of microwave energy as a method to accelerate acid digestion was published. This technology progressed from the open container digestion method of household microwave ovens to the instrument use in laboratories, and was equipped with a closed digestion design. People hope that microwaves can not only provide rapid heating, but also quantitatively provide energy control for reactions. Thus achieving rapid chemical process kinetics control. At first, people attempted to control the reaction to achieve stable and consistent results by fixing the microwave power/time, but it proved difficult to achieve in hardware operation and reaction due to the difficulty in quantifying the hardware emission performance indicators of microwave instruments and the inconsistency of reactant composition. It was not until the emergence of automatic frequency conversion magnetrons that the problem was finally solved, surpassing the initial unstable experimental relationship between power and reaction results, and developing into the direct quantitative relationship between thermal parameters and reaction results established today. The system with power automatic frequency conversion control response (MARS-5) that emerged won the R&D 100 Technology Invention Award in the United States in 1998. Nowadays, people do not need to set the power, and the instrument automatically controls the frequency conversion power feedback of the digestion reaction. By quantifying the thermodynamic laws of microwave chemistry, laboratory operations have found methods for reproducibility and safety, reaching a certain level. The level of microwave chemical control has gone through the following three stages:
1) No feedback fixed power/time setting
2) Fixed power/time setting switch feedback control
3) The automatic frequency conversion power feedback control has different reaction processes for certain samples under different thermal conditions. The sample digestion reaction slowly accumulates in a sealed digestion bottle, and once it exceeds its critical point at a certain stage, a large amount of gas may rapidly be generated, and its internal pressure may rise and exceed the upper pressure limit. Even releasing a large amount of heat energy makes the reaction difficult to control, causing harm. Therefore, it is necessary to carefully monitor the entire reaction process at all times and control it. The fixed power/time setting switch feedback control mode, because it is manually set for power and time, sometimes has a slow response, which can cause harm to fast critical reactions. The CEM instrument has a power frequency conversion response speed of 1/120 second, which monitors the entire process to prevent problems before they occur. It has four types of R AMP ramp response control modes:
1) Standard Control temperature/pressure control, this mode is generally only suitable for inorganic samples to be digested below 200 ℃ and for certain organic extractions. When using this mode for organic sample digestion, serious consequences may occur.
2) Ramp to Temperature is a mode of uniformly climbing at a certain temperature/hour, which can be used for controlling thermodynamic indicators of reaction kinetics. It can help chemical experimenters clearly understand the intensity of chemical reactions at various temperatures and the changes in physical equivalents, test the critical point of the reaction, and provide quantitative means. Attention: This mode is widely used in acid digestion, organic extraction, protein hydrolysis, and organic synthesis of organic/inorganic samples under high temperature and pressure.
3) Ramp to Pressure: This mode is mainly used for acid digestion, protein hydrolysis, and organic synthesis of organic samples under high temperature and pressure.