**6. Current developments in slurry bed reactor for C1 chemistry**

Since, in a relative comparison it can be demonstrated that, the slurry bed reactors show the advantages of high efficiency of mass transfer and heat transfer, uniform reaction temperature, online replacement catalyst and low investment costs as compared to that of fixed-bed/fluidized-bed reactors [3, 6]. However, the industrialization process of the slurry bed reactor is relatively slow, it is because the enlargement of slurry bed reactor can only be achieved by increasing the diameter of the reactor, and the flow behavior in a large-scale industrial slurry bed is extremely complex under the working conditions of high temperature and high pressure. The blockage of the reactor distributor, uneven gas distribution led to the unstable operation state, which puts forward higher requirements for the rapid heat transfer of the slurry reactor [4, 39].

The process intensification is one of the methods to improve performance or solve problems in slurry bed reactors. The development of new high-efficiency internal components, the optimization of performance based on the existing internal components, and the coupling arrangement of multiple internal components can enhance the mixing and mass/heat transfer in slurry bed reactors [40]. Now, the research in slurry bed reactor mainly focuses on the fluid mechanics such as gas holdup, bubble size distribution, internal mass transfer, and heat transfer characteristics. Some or all the above problems can be solved by introduction of suitable internals into the reactor; however, the critical internals are difficult to obtain in published reports. Therefore, the structural optimization and function enhancement technology of internal components has become a challenging hot issue in the process of slurry bed design and scale-up [41]. Moreover, though the research of particle size on the effect of gas-liquid flow behavior in slurry bed reactors has been carried out earlier, however, these results in different reports are often inconsistent, which is due to the complexity of the gas-liquid-solid three-phase system, and in most cases, the influence mechanism of catalyst particles is based on analysis and prediction, without direct and sufficient proofs. Therefore, the research on the effect of particles is always the focus of attention and research.
