**3.4 Synthetic natural gas synthesis**

Slurry bed reactor is suitable for the strongly exothermic methanation reactions (3H2 + CO = CH4 + H2O, <sup>Θ</sup> ∆H298K = − 206 kJ/mol) [25]. The Chemical Systems Inc.


#### **Table 2.**

*Comparison of industrialization Technology of Dimethyl Ether Production in slurry bed [24].*

*Review of Slurry Bed Reactor for Carbon One Chemistry DOI: http://dx.doi.org/10.5772/intechopen.109094*

**Figure 4.** *Liquid phase methanation concept, adapted from [26].*

(United States) developed a liquid-phase methanation process [26], as shown in **Figure 4**. The syngas produced in a coal gasifier was introduced into the catalytic liquid phase methanation reactor (LPM) along with a circulating process liquid (mineral oil), which absorbs the heat of reaction. The product gas was separated in a liquid phase separator and in a product gas separator. The process liquid was pumped through a filter to remove any catalyst fines and recirculated back to the LPM reactor. After a methanation reaction time for more than 300 h, the results showed low conversion and high catalyst loss, and thus the LPM-project was terminated in November 1981.

Taiyuan University of Technology and SEDIN Engineering Co., Ltd. have jointly developed a slurry-bed process for syngas methanation [27], as shown in **Figure 5**. The generated methanation gas together with the catalyst and the liquid-phase components enters through a gas-liquid separator, where the gas-phase product was condensed to produce synthetic natural gas, the liquid-phase product is mixed with fresh catalyst in the storage tank and added into the slurry bed methanation reactor to preheat the fresh catalyst. Due to the excellent heat transfer performance of the slurry bed, the adaptability of the feed gas for methanation of slurry bed is stronger, and the content of CO in feed gas can be adjusted within a wide range of 2–30%. The results show that the CO conversion for methanation reached 96% at the reaction temperature of 280°C in a slurry bed reactor.

For industrial fixed-bed methanation technology, the commercial catalysts are Ni-based catalyst, which is due to its cheap and excellent catalytic activity at high temperatures. However, the traditional industrial Ni-based catalysts exhibit poor catalytic performance in slurry bed reactors [28]. By optimizing the preparation method and conditions [29], adding additives, a slurry bed methanation catalyst with a high CO or CO2 conversion of more than 99.5% can be obtained.

#### **Figure 5.**

*Flow diagram of slurry-bed methanation for coal to synthetic natural gas. 1. Methanation reactor, 2. heat exchanger, 3. gas-liquid separator I, 4. gas-liquid separator II, 5. fresh catalyst storage tank, 6. heat exchanger II, 7. circulation pump, p1-p9 pipeline [27].*
