TC
TC
Feed
TC
Reactor
Inlet zone α-Al O
Catalyst zone Catalyst + α-Al O
Outlet zone α-Al O
Thermowell
Inert
CeO
CuO Cr O
CuCrO
CuO Cr O diluted
CuCrO diluted
1
2
3
4
5
Figure 2 Reactor packing design of the 16-fold high throughput unit, catalysts (a) CeO₂ (b) CuO∙Cr₂O₃ (c) CuCrO₂ at different residence times and inert dilutions
Most of the state-of-the-art testing equipment oper- ates single stage. There are only a few high throughput approaches for catalyst deactivation research. However, they work without online analytics. Furthermore, experi- mental programmes are often limited to mild conditions (high O₂ or N₂ dilution) and low catalyst mass or runtime.⁶ We have designed a tailored 16-fold high throughput unit to accelerate the assessment of activity, selectivity, and decay for catalysts in the field of chlorine chemistry at industrially relevant conditions. It can process corrosive gases at a high hydrogen chloride intake and extended runtime that also includes off-gas treatment on a kg scale. Figure 1 shows a simplified scheme of the 16-fold high throughput unit. The contrast of chemical versus mechanical resistance is one of the core issues that must be overcome for the high throughput testing of chlorine chemistry HCl, pure oxygen, internal standard, and nitrogen are dosed by Coriolis and mass flow meters and distributed at equal flow into 16 channels by a controlled pressure drop. The entire upstream section is made of stainless steel parts, and the feed gas was dried to work absolutely water free. Up to 16 catalysts can be screened in parallel, operating at reaction temperatures up to 410°C and pres- sures of 4 barg. Reactors are made of quartz glass with a maximum catalyst volume of 1 ml (operation at +/-2K temperature deviation). Depending on the material type, up to 2g of Deacon catalyst can be loaded per position. Online temperature profiles can be measured using a movable thermocouple placed inside a quartz thermowell. The reactor pressure is
controlled by a customised membrane pressure controller. The reactor effluent can be diluted with an inert gas to pre - vent condensation. Subsequently, one of the channels can be selected for analysis. The composition of the product stream is analysed by an online-FTIR developed by Gasmet Technologies. This device allows the measurement of water and HCl in a nitro- gen matrix by means of robust detection even at volume per cent concentration levels above 50% HCl at a maxi- mum sampling frequency of 1 data point/second. This analytical method provides an efficient alternative to conventional gravimetric titration, where a poor perfor- mance differentiation between several catalysts is obtained. The entire downstream section was designed by a modular combination of polymer, alloys, and coated materials, com- bined in a way that temperature and elevated pressure can be run, even in a wet gas environment. To comply with environmental standards, HCl and chlo- rine need to be fully neutralised. This is achieved in a multi- stage scrubbing unit equipped with temperature and pH control. Two CSTR trains can be run in alternating opera- tion, each capable of removing several kilograms of chlo- rine, to reach a runtime of up to several months, depending on the amount of HCl fed to the unit. From a technical point of view, experimental protocols for the Deacon reaction require, on the one hand, the right equipment; on the other hand, a lot of operational expe- rience is also necessary to prevent severe corrosion and improve overall unit availability. The most critical corrosion issues are briefly investigated, as follows. When processing iron or iron-rich alloys (Fe >5% w/w), the feed needs to be dried carefully since water impuri- ties above the ppb range can form liquid clusters, resulting in severe liquid phase corrosion. This especially concerns the tube wall, where the gas velocity is zero and local cold spots may occur. Heat loss during wall contact and water condensation cannot essentially be excluded. Once a liquid phase is formed, either oxygen or HCl can diffuse inside
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PTQ Q4 2022
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