• Safe procedure for catalyst filtration from the Autoclave
• There is no spillage of expensive catalyst
• Closed circuit operation avoids fire hazards in case of pyophoric catalysts

• High efficiency candles result in very low losses, which are often below measurable limits
• The filtration system pays for itself through high rate of catalyst recovery

Catalyst filtration is an important aspect of a Hydrogenation system. Omega ‐ Kemix supplies a cost effective system, which incorporates complete filtration, operational safety, full backwash, as well as minimal holdup of the reaction mass

At the completion of hydrogenation reaction, balance Hydrogen gas in reactor headspace is vented, and the Reactor is purged with Nitrogen, to eliminate all traces of remaining Hydrogen. Subsequently, the Reactor is pressurized to about 1 bar with Nitrogen, through Valve V₁ Valves V₂, V₃ and V₄ are opened. All othe valves (V₅ to V8) are in closed position. Nitrogen is continuously fed through Valve V1, so that Reactor pressure is maintained around 1 bar.

Typically, if the catalyst is noble metal on a carrier, e.g., Pd/C, the entire mass is filtered. In this case, it is advisable to stir the reaction mass at around 50 RPM, and the dip pipe or blow leg should extend to the lowest possible point in the Reactor.

For heavy metal catalysts like Raney Nickel, the bulk of the catalyst settles within a very short time, typically 30 minutes after cessation of stirring. In this case, a common practice is to filter the supernatant liquid (through a dip pipe terminating just below the lower tan line of the Reactor).

Nitrogen pressure in the Reactor headspace forces the liquid‐catalyst slurry into the Main Filter through Valve V₃. This filter is fitted with sintered SS 316 L candles, suspended from a tubesheet.

Initially, the Filter body fills up with Liquid‐catalyst slurry. When it is full, filtration commences. Catalyst cake accumulates outside the candles. Clear filtrate enters the candles, and flows out through Valve V₄. Filtrate flow can be observed through Sight Flow Indicator (FI).

Once the Reactor contents are entirely displaced by Nitrogen, gas will flow into the Filter through V₃. The Filter Candles are fitted with an inner Siphon Tube. Gas entering the Filter displaces the slurry, so that clear liquid is siphoned out through Valve V₄ due to action of siphon tubes in the candles. Due to this action, slurr level in the Filter falls to the lower end of the candles. In effect, the filter cone and lower parts are full of unfiltered slurry (also known as "Heel"), and candles are coated with wet cake.

At this point, only gas flows through the Sight Flow Indicator

A Zero Holdup Filter is fitted at the lower end of the Main Filter, below the conical portion. This is a Jacketed Sintered pipe (or Lower Candle), around 125 mm inside diameter, suitable for inside to outside filtration. Please refer Drawing 2 for details of the Zero Holdup Filter.

When gas flow (i.e., no liquid flow) is observed through the Sight Flow indicator as described above, Valve V₄ is closed, and V₉ is opened. Nitrogen gas entering the Filter cone forces filtrate through the Lower Candle, so that slurry in the Filter Cone and lower parts is filtered through the Zero Holdup Filter. Heel filtrate is observed flowing through the Sight Flow Indicator FI.

Once the entire heel slurry is filtered, no further liquid flow is observed through the Sight Flow Indicator. All the slurry has been filtered. At this stage, outer surfaces of the upper candles, and inner surface of the lower candle are covered with wet cake. Valves V₉, V₃ and V₂ and V₁ are now closed, and the Reacto vented to atmospheric pressure, by opening Valve V₁₀. Solvent/feed for the next batch, or Nitrogen at 1 to 5 bar is introduced at Valve V₅, located at the top of the Filter. Keeping Valve V₁₀ open, Valve V₈ and then Valve V₆ is opened, so that catalyst adhering to candle surfaces gets back‐flushed into the Reactor.

For best results, Valve V₆ should be a Solenoid operated ball valve, so that there is a pressure pulse while opening this valve. This ensures effective dislodgement of catalyst cake from the Candles.

This procedure ensures a safe procedure for catalyst filtration from the Autoclave. There is no spillage of expensive catalyst. The closed circuit operation avoids fire hazards, as many catalysts are pyrophoric, and can spontaneously ignite when exposed to air. High efficiency candles result in very low losses, which are often below measurable limits. The filtration system pays for itself.

After several batch cycles, it may be necessary to remove catalyst from the system, and send it for disposal or regeneration. In this case, Valve V₇ is opened instead of V₈, during back flushing operation, and spent catalyst collected in the Recycle Drum.