Differences in Product Distribution Measured with Flame Ionization Detector Gas Chromatography and Thermal Conductivity Detector Gas Chromatography during the Dimethyl Ether-to-Olefins and Methanol-to-Olefins Processes

• Published in: Energy & fuels 2017-12, Vol.31 (12), p.13266-13272
• Main Authors: Gao, Yuli, Cao, Yingqian, Chen, Sheng-Li, Wang, Ya, Zhu, Ruyue, Sun, Wei, Zhang, Qi, Fan, Yu
• Format: Article
• Language: English
• ISSN: 0887-0624; 1520-5029
• DOI: 10.1021/acs.energyfuels.7b02145

It is generally accepted that the products of dimethyl ether (DME)-to-olefins (DTO) and methanol-to-olefins (MTO) processes are hydrocarbons; therefore, gas chromatography (GC) equipped with a flame ionization detector (FID) rather than a thermal conductivity detector (TCD) is usually used to measure their product distribution for the higher response sensitivity of FID than TCD. Product distributions of DTO and MTO processes over SAPO-34 and metal-oxide-modified SAPO-34 catalysts were measured in this research work with GC equipped with FID and TCD. Results showed that product distribution over SAPO-34 measured with FID GC alone was similar to that measured with TCD + FID GC when the DME or methanol conversions were close to 100% and the main products were hydrocarbons, with only trace amounts of H2 and carbon oxides in the products. When using metal-oxide-modified SAPO-34 as the catalyst, it was found that the product distribution measured by TCD + FID GC was greatly different from that measured by FID GC alone. A lot of H2 and carbon oxides were detected with TCD + FID GC, which are missed when using the sole FID GC to analyze the products. The accurate measurement of the complete product distribution spectrum is of importance for not only the calculation of product yields, mass balance, and reaction heat but also the investigation of reaction mechanisms and reaction kinetics. It is strongly suggested that TCD + FID GC be used to analyze the product distribution of DTO and MTO processes, especially when SAPO-34 is promoted with other components.