Microscale, coke formation

Coke Formation at Microscale Effect of Acidity of Catalyst 304... 

Methanol to olefins (MTO), which provides a new route to produce light olefins such as ethylene and propylene from abundant natural materials (e.g., coal, natural gas or biomass), has been recently industrialized by the Dalian Institute of Chemical Physics (DICP), Chinese Academy of Sciences. In this contribution, the process development of MTO is introduced, which emphasizes the importance of mesoscale studies and focuses on three aspects a mesoscale modeling approach for MTO catalyst pellet, coke formation and control in MTO reactor, and scaling up of the microscale-MTO fluidized bed reactor to pilot-scale fluidized bed reactor. The challenges and future directions in MTO process development are also briefed. 

As discussed above, coke formation affects the selectivity to Hght olefins in MTO process over SAPO-34 catalyst. It has been found that at a given temperature, the ethylene-to-propylene ratio in MTO reaction is increased when coke content in catalyst increases (Barger, 2002 Song et al., 2001). Figure 18 shows the typical results in a microscale fluidized bed reactor at temperature of 450 °C and weight hourly space velocity (WHSV) of... 

The coke formation is critical for MTO reaction over SAPO-34 catalyst. The influence of coke formation is twofold a certain amount of coke deposition can prompt the selectivity to light olefins, while it also makes the catalyst deactivate rapidly. Thus, the understanding of the coke formation at microscale is extremely important for controlling coke distribution in the reactor. The influences of zeofite structure and reaction temperature on coke formation have been discussed to illustrate the essence of the mesoscale researches. However, there is still a lot of work to be explored at mesoscale concerning the coke formation. These results are eventually expected to benefit the reactor design and operation. 

The third parameter of critical importance is the catalyst-to-methanol ratio. This parameter is the key to control the circulation rate of catalyst between reactor and regenerator in pilot-scale setup. Normally it is hard to derive the relation between the catalyst-to-methanol ratio and reaction results via direct measurement in the microscale experiments as there is no circulation. However, by analyzing the coke formation in the MTO reaction, we can predict the optimal catalyst-to-methanol ratio. FromEq. (15), we can obtain the coke formation rate. We assume that the coke formation rate can be directly used in the pilot-scale experiments. Thus, the mass flow rate of catalyst required to transport this amount of coke is estimated as following ... 

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