Catalyst performance testing recycle operation

The ROTOBERTY internal recycle laboratory reactor was designed to produce experimental results that can be used for developing reaction kinetics and to test catalysts. These results are valid at the conditions of large-scale plant operations. Since internal flow rates contacting the catalyst are known, heat and mass transfer rates can be calculated between the catalyst and the recycling fluid. With these known, their influence on catalyst performance can be evaluated in the experiments as well as in production units. Operating conditions, some construction features, and performance characteristics are given next. 

These tests were performed to establish the limits in flexibility and operability of a methanation scheme. The two demonstration plants have been operated in order to determine the optimum design parameters as well as the possible variation range which can be tolerated without an effect on catalyst life and SNG specification. Using a recycle methanation system, the requirements for the synthesis gas concerning H2/CO ratio, C02 content, and higher hydrocarbon content are not fixed to a small range only the content of poisons should be kept to a minimum. The catalyst has proved thermostability and resistance to high steam content with a resultant expected life of more than 16,000 hrs. 

The feedstock used in this study was a hydrodesulfurized straight-run naphtha recovered from an industrial naphtha HDS unit. The catalyst used in this investigation was a conunercial available Pt-Re reforming sample (Pt 0.29 wt%. Re 0.29 wt%). The tests were performed in a fixed-bed pilot plant with H2 recycle. The unit consists of a stainless-steel reactor (internal diameter of 2.5 cm and length of 25 cm), which was operated in isothermal mode by independent temperature control of a three-zone electric furnace. 

The most effective molybdenum-based oxide catalyst for propane ammoxidation is the Mo-V-Nb-Te-0 catalyst system discovered and patented by Mitsubishi Chemical Corp., Japan, U.S.A. (140). Under single-pass process conditions, acrylonitrile yields of up to 59% are reported, whereas under recycle process feed conditions, the acrylonitrile selectivity is 62% at 25% propane conversion (141). Although the latter results show that the catalyst operates effectively under recycle feed conditions, the catalyst system was originally disclosed for propane ammoxidation under single-pass process conditions. The catalyst was derived from the Mo-V-Nb-0 catalyst developed by Union Carbide Corp. for the selective oxidation of ethane to ethylene and acetic acid (142). The early work by Mitsubishi Chemical Corp. used tellurium as an additive to the Union Carbide catalyst. The yields of acrylonitrile from propane using this catalyst were around 25% with a selectivity to acrylonitrile of 44% (143). The catalyst was also tested for use in a regenerative process mode much like that developed earlier by Monsanto (144) (see above and Fig. 8). Operation under cyclic reduction/reoxidation conditions revealed that the performance of the catalyst improved when it was partially reduced in the reduction cycle of the process. Selectivity to acrylonitrile reached 67%, albeit with propane conversions of less than 10%, since activity in... 

The data in Table 9.2 showthat catalysts based on POL-TPP exhibit roughly the same catalytic performance as the TPP system. (In Ref. [21], systems are also documented in which the POL-based catalysts exhibit better performance.) Especially important is the robustness of these properties when the catalysts are recycled. The results from [21] would suggest that it is possible to reuse the catalyst several times with no adverse effects on performance. However, as far as we know, there have been no results published from long-term tests in continuously operating mini-plants. 

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