Fischer-Tropsch Synthesis in a Microchannel Reactor: The Influence of Co/SiO2 Catalyst Structure on FTS Performance

Abstract

Abstract Conversion of synthesis gas into clean diesel fuel from natural gas (Gas-to-Liquids - GTL) via a Fischer-Tropsch synthesis (FTS) process can provide an economical way to create value from unconventional, remote and problem gas. However, conventional processes, fixed-bed and slurry phase, are not economically viable for the smaller plants required for processing stranded natural gas fields. On the other hand, a microchannel reactor for FTS offers the opportunity for a small, modular, less expensive and high efficiency facility. Over the past several years Velocys has been engaged in not only the development of microchannel reactor technology for FTS, but also supported cobalt catalysts that provide the necessary level of C5+ productivity for an economically viable process. The influence of support properties, synthesis methodology, cobalt loading and promoters on catalyst performance has been studied. For example, it has been determined that both the support surface chemistry and the Co particle size distribution have a strong effect on the rate of catalyst deactivation for Co loadings >40%. In this presentation the authors will show how the structural properties of a Co/SiO2 catalyst are influenced by both the surface chemistry of the support and the method of synthesis. Catalyst characterization data will be used to explain observed FTS performance in a microchannel reactor. Introduction For most of its nearly 100 year history, the considerations for deployment of the Fischer-Tropsch (FT) synthesis have focused on either conventional multi-tube fixed-bed or slurry bubble-column reactors. As catalyst development offered catalysts with increasing activity, the need to shed the high heat of the hydrogenation reactions was a much greater focus of process designers. Dramatic advances in metal fabrication techniques in recent decades have now allowed for a further reactor option for deploying FT technology, the microchannel fixed-bed reactor. In such microchannel devices, both process and coolant channels have dimensions which are factors of 10–100 smaller than their traditional technology counterparts. [1] These short transport distances make it possible to remove much higher heats of reaction per unit area of cooled wall, thereby making it possible to shrink the overall dimensions of the process reactors quite dramatically. Velocys was founded on the basis of innovative microchannel reactor designs for process technologies where heat transfer is a critical aspect of process and has been a leader in the deployment of such reactors for application to the FT synthesis. Successful and cost-effective deployment of a FT process requires more than just the microchannel reactor itself. At every step of the process design, attention must be paid to the particular characteristics of the microchannel reactor environment. These microchannel systems are ideal platforms for the development of highly modularized process designs, since capacity can be tailored by discreet units of output. Velocys has brought together companies which are leaders in their market areas in order to provide customers with smaller gas holdings plant designs which achieve favorable economic returns at production scales well below those required by conventional reactor technologies. An example is shown in Figure 1 using a range of potential costs for microchannel-based installations. While the microchannel and slurry reactor facility costs per unit of output converge at larger capacity, the microchannel-based facility achieves significant advantages at lower capacity. Even more importantly, the rate at which costs rise as capacity decreases is sufficiently modest that even much smaller plants can potentially meet the requirements for market-based economic returns. This opens a much wider range of gas sources to potential development than would be possible using only traditional slurry or tubular reactor designs.