Liquid purification or separation – Processes – Including controlling process in response to a sensed condition
Reexamination Certificate
1999-01-13
2001-03-20
Drodge, Joseph W. (Department: 1723)
Liquid purification or separation
Processes
Including controlling process in response to a sensed condition
C210S800000, C210S805000, C585S250000, C585S502000, C585S709000
Reexamination Certificate
active
06203712
ABSTRACT:
The present invention relates to polyphase liquid mixtures in which the phases are at least partially non miscible. More particularly, the invention relates to separating the different phases of such a mixture.
Separating at least two liquid phases which are at least partially non miscible is usually carried out by settling. The mixture is sent to a vessel termed a settler where separation takes place under gravity. Phases with different densities separate out, and the different phases form layers which are superimposed in order of density. The most dense phase, i.e., the heaviest phase, occupies the bottom of the settler; the least dense phase, i.e., the lightest phase, is located above the other phases in the upper portion of the settler. Clear phase separation is often observed. In practice, two-phase liquid-liquid mixtures are usually treated.
In the present description, the abbreviation “&mgr;m” is used for “micrometer”, i.e., 10
−6
meters.
Depending on the settler used, settling can be more or less efficient. In the least efficient settlers, large droplets of one phase will be permitted in a given phase. The term “large droplets” means droplets with a diameter of about 100 &mgr;m to 10
−3
m. In the most efficient settling steps, the maximum diameter of the droplets of another phase in a given phase is about 50 &mgr;m to 200 &mgr;m. This thus defines a specification for the size of droplets which will be permitted.
The present invention provides a process for separating at least two liquid phases which are at least partially non miscible, characterized in that after reacting, a polyphase effluent is settled in at least two distinct settling zones arranged in parallel, each of these settling zones containing at least one settler.
The present invention also provides an apparatus for carrying out the separation process.
The advantages of the present invention over the prior art include the fact that this process enables smaller settlers to be used, and these settlers are thus easier to use and take up a smaller ground surface area. Thus if the specifications for size of droplets obtained with two settlers each 1 m in diameter are to be reproduced in a single settler—the sum of the inlet and outlet flow rates otherwise being equal in the two embodiments—, it would be necessary to use a settler with a diameter of about three times that of the settlers used in the process of the invention. Further, when fluids are treated under pressure, the larger the settler size, the thicker the settler wall has to be, and thus material is saved when several smaller settlers rather than a single large settler are used. Further, for the reactions to which the process of the invention can be applied and where cooling using an external and/or internal coil is not efficient, sufficient cooling is obtained by re-circulating the light phase from at least one settling zone.
The present invention provides a process for separating liquid phases which are at least partially non miscible of a polyphase reaction effluent in at least two distinct settling zones arranged in parallel, each of the settling zones containing at least one settler, preferably each settling zone comprising a single settler.
The two phases are separated in at least two distinct settling zones a) and b) arranged in parallel. A number of implementations of the invention are possible: in one particular implementation, the light phase from settling zone a) is recycled to the reaction zone after settling, and the light phase from settling zone b) is evacuated.
In a further implementation of the invention, the heavy phase from at least one settler is recycled to the reaction zone after settling.
In a preferred implementation of the process of the invention, the light fraction from settling zone a) is recycled to the reaction zone after settling, the light fraction from settling zone b) is evacuated and the heavy phases from the settlers are recycled to the reaction zone.
The separation process of the invention can be applied to any chemical reaction where the effluent is a polyphase mixture at the reactor outlet. Frequently, one of the phases, generally the densest phase, contains a liquid catalytic composition. This reaction can, for example, be a reaction which is catalysed by a liquid catalytic composition with an ionic nature which is slightly or non miscible with an organic phase.
The separation process of the invention can, for example, be applied to reactions in which the effluent is a two-phase liquid-liquid type effluent such as, for example, oligomerisation, hydroformylation or hydrogenation reactions, in particular oligomerisation, hydroformylation or hydrogenation of olefins; the process is also applicable to alkylation reactions, in particular aliphatic alkylation.
In the process of the invention, the polyphase effluent is sent to at least two settling zones after reacting. In a preferred embodiment of the invention, the effluent enters the settler in a direction which is approximately horizontal and approximately tangential to the arc of the circle described by the settler wall. This thus produces a vertical effluent velocity of almost zero. In each settler of these settling zones, the temperature and pressure conditions are preferably the same as the temperature and pressure conditions inside the reactor. Further, the dimensions of these settlers are selected depending on the degree of settling which is desired at the given inlet and outlet effluent flow rates. Thus a maximum diameter for droplets of another phase which is permitted in a given phase is selected. After settling, the settled liquids are extracted, the phase containing the desired products from settling zone a) is recycled to the reaction zone and the phase containing the desired products from settling zone b) is recovered.
In continuous mode, the light phase is recovered using an effluent recovery means placed in the highest portion of the settler; simultaneously the heavy phase is recovered by an effluent recovery means placed in the lower portion of the settler. The scope of the present invention encompasses treating a polyphase mixture containing three or more phases in which each phase is of a different density. After settling, as many superimposed layers of liquid are obtained as there are phases. Each phase is then extracted from the settler by an effluent recovery means placed in the portion of the settler corresponding to the level of that phase.
The settling process can particularly be applied to separating constituents of the effluent from a catalysed olefin oligomerisation reaction in a two-phase liquid-liquid medium. The catalytic composition used in this type of process is dissolved in a polar phase which is not miscible with the organic phase.
Descriptions of the prior art concerning homogeneous oligomerisation processes carried out in a two-phase liquid-liquid medium propose the use of different types of catalysts depending on the olefins to be treated and on the product which is selected; such catalysts all contain at least one metal compound, preferably a nickel compound, and an alkylaluminium halide. The medium with an ionic nature comprises at least one salt with formula Q
+
A
−
, where Q
+
is normally a quaternary ammonium or phosphonium cation or a mixture of the two, or a lithium cation, and A
−
is a co-ordinating or non co-ordinating anion normally selected from the group formed by halogenoaluminates, organohalogenoaluminates, organogallates, organohalogenogallates or a mixture of at least two of those compounds. The reaction temperature is about −40° C. to +100° C., the pressure is such that the reactants are at least partially, preferably mainly in the liquid phase and the stirring conditions are those required to convert at least a portion of the feed. Examples of olefins which can be treated by such a process are olefins containing 2 to 8 carbon atoms per molecule. Examples are ethylene, propylene, 1- and 2-butenes, styrene, pentenes or mixtures of those compounds.
Applying the pr
Bronner Charles
Forestiere Alain
Hugues Francois
Drodge Joseph W.
Institut Francais du Pe'trole
Millen White Zelano & Branigan P.C.
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