Patent Application: US-58931105-A

Abstract:
a mixing reactor for mixing efficiently streams of fluids of differing densities . in a preferred embodiment , one of the fluids is supercritical water , and the other is an aqueous salt solution . thus , the reactor enables the production of metal oxide nanoparticles as a continuous process , without any risk of the reactor blocking due to the inefficient mixing inherent in existing reactor designs .

Description:
referring first to fig2 , the aqueous stream is introduced into the bottom of the reactor , where it is cooled , preferably by a heat sink . the solution is forced under pressure in an upwards direction . the supercritical water is introduced into the reactor in the opposite direction — i . e . downwards . the sch 2 o is less dense than the aqueous stream , and thus rises upwards in the reaction chamber , becoming intimately mixed with the aqueous salt solution as it does so . this mixing is highly efficient , and results in the generation of metal oxide nanoparticles that can be separated downstream from the aqueous effluent . this design takes advantage of the density differential between the two reactant streams ( i . e . the sch 2 o and the cold aqueous salt solution ). this differential creates a strong , desirable mixing environment within the reactor and induces strong eddies downstream of the mixing point . these eddies are desirable as they help to disperse the metal oxide particles and carry them away such that they do not block the reactor . in a preferred embodiment the reactor incorporates a funnel as shown in fig3 . this aids the mixing of the reactants , and avoids a pulsing phenomenon associated with the mixing downstream . as the sch 2 o is less dense and is therefore more buoyant than the cold solution into which it is flowing a film of sch 2 o forms on the surface of the funnel . this film mixes very efficiently with the colder aqueous solution flowing past it , and this has a beneficial effect on the kinetics of the reaction between the sch 2 o and the aqueous solution . fig4 is a flow diagram of a rig incorporating the mixing reactor of the invention generally as 1 . the rig comprises a preheater oven which heats water to a temperature of 400 ° c . the water stream is then pumped from a first reservoir containing water under a pressure of 225 bar to an upper inlet by a gilson hplc pump . simultaneously , a stream of an aqueous metal salt is pumped from a second reservoir containing aqueous metal salt under a pressure of 225 bar through a lower inlet by an additional gilson hplc pump at room temperature . following mixing , the mixed streams pass through a water cooler which functions to cool the stream before being filtered under pressure by a pressure transducer 2 regulated by a tescom back - pressure regulator . following filtration under pressure , nanoparticles 3 may then be collected . the invention will now be described with reference to the following non - limiting examples : the following reaction was carried out using the mixing reactor of the invention incorporated into a rig configuration shown in fig4 . system pressure was set to 228 bar . the metal salt solution ( ce ( no 3 ) 4 , ( 0 . 2 m )) was flowed at 5 ml / min through the reactor . a total of 250 ml of the metal salt solution was used during the course of the 50 min run . the sch 2 o was flowed at 10 ml / min through the reactor at a temperature of 400 ° c . the reactor was maintained at a temperature of 370 ° c . using a band heater for the duration of the reaction . the high pressure pumps and back pressure regulator system allow the pressure to be maintained throughout the rig and then to be reduced at the end allowing liquid product to be released at ambient temperature and pressure . the rig , using the invention can be run for hours without blocking producing 2 - 5 g per hour of the metal oxide . a selection of other results obtained from the mixing reactor of the invention using similar flow and concentration conditions as described above is shown in table 1 below : fig5 shows the effect of increasing flow rate of cerium nitrate up through the reactor . clearly there is an interesting trend of increasing surface area ( from 65 m 2 / g up to 100 m 2 / g ) with increasing metal salt flow up to a value of 8 ml / min beyond which the particle size begins to decrease . it is possible that the increase is caused by the relationship between flow velocity and reaction kinetics and the decrease is caused by an ‘ excess ’ of metal salt resulting in larger particles being produced . one area of interest is the effect of the operating temperature within the reactor and it &# 39 ; s impact on surface area . the reactor can be heated externally to any given temperature sub , near or super critical , the relationship between surface area ( and indirectly , particle size ) and operating temperature can be established . even though the heated water inlet inside the reactor may be operating sub critical , the temperature differential between the metal salt and the heated water still exists and this will cause the inlet flow to turn upwards into the downstream outlet of the pipe , as shown in fig2 . fig6 is a graph showing how surface area increases significantly with operating temperature . this indicates that the particle size ( and possibly the morphology ) can be tailored by adjusting the operating conditions of the reactor . adschiri , t ., y . hakuta , et al . 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