VARIABLE, SELF-REGULATING PERMEATE RECYCLE IN ORGANOPHILEN NANOFILTRATION

Description

[0001] The present invention relates to a control and process engineering improvement for a method for the continuous separation of a component from a liquid mixture using a membrane unit comprising at least one membrane stage. The improvement consists in the fact that at least a portion of the total permeate stream obtained is returned to the feed vessel and / or downstream of the feed vessel but upstream of the conveying device. The method described herein can be used, in particular, for separating a homogeneously dissolved catalyst from a liquid reaction mixture.

[0002] Membrane separation processes, for example for the separation of homogeneously dissolved catalysts from a reaction mixture, are generally known in the art. Reference is made, by way of example, to WO 2014 / 131623 A1.

[0003] Control engineering improvements have already been described for membrane separation processes of this type. For example, international patent application WO 2014 / 183952 A1 discloses a membrane separation process for separating a homogeneously dissolved catalyst from a reaction mixture, in which two parameters, the retentate volume flow rate of the membrane separation unit and the retention of the membrane separation unit, are kept constant by the control engineering system in order to compensate for fluctuating operating conditions, in particular fluctuations in the volume flow rate of the reaction mixture originating from the reaction zone.

[0004] To keep the aforementioned control variables constant, WO 2014 / 183952 A1 proposes a flow resistance to adjust or maintain the retentate volume flow rate and a control of the temperature and / or pressure in the overflow circuit to adjust or maintain the retention.

[0005] One problem with the proposed method is that maintaining a constant retention value of the membrane separation unit is not advantageous for all processes. Instead, considering the plant throughput and the already installed membrane area of ​​the separation unit, optimization, and often maximization, of the retention value of the membrane separation unit during the process should be the goal. A control system using a flow resistance, as described in WO 2014 / 183952 A1, may result in the already installed membrane area operating below the optimal transmembrane pressure.The procedure described there can also lead to a situation where, given the total throughput of the plant and the resulting discharged permeate flow (part of the permeate flow that is discharged from the membrane separation unit on the permeate side), the total permeate flow and the resulting recycled permeate flow (part of the total permeate flow that is recycled into the membrane separation unit) calculated using a simple mass balance taking into account the discharged permeate flow are smaller than would be possible and / or desirable.

[0006] Another disadvantage of the method described in WO 2014 / 183952 A1 is that it requires both a permeate tank and a pump to maintain a constant permeate control system. However, providing a pump to transfer permeate from the permeate tank to the overflow circuit or feed tank entails increased equipment inventory and costs, for example, for acquisition, operation, maintenance, and repair, which can also lead to system downtime and thus production losses.

[0007] DE 10 2013 113 641 A1 describes a process or a plant for membrane-based separation of a liquid mixture, in which flows within a membrane unit are guided with recirculation (recycle) to enable continuous operation with stable separation conditions.

[0008] Furthermore, the installation of a tank typically results in the permeate-side section of the membrane separation stage not being hydraulically filled, which can lead to increased safety risks, particularly when using toxic fluids. Additionally, the presence of a tank on the permeate side, alongside the feed tank, creates the possibility that the control of the two tank levels could cause fluctuations in each other.

[0009] The object of the present invention was therefore to provide a more cost-effective method for the continuous separation of a component from a mixture, preferably for the continuous separation of a homogeneous catalyst from a reaction mixture. Furthermore, the object of the present invention was to provide a self-regulating permeate recirculation system for the method of continuously separating a component from a mixture, preferably for the continuous separation of a homogeneous catalyst from a reaction mixture, in which the installed membrane area can be optimally utilized under different load conditions, for example, to maximize retention or yield.

[0010] The underlying problem was solved by the method according to claim 1. Preferred embodiments and configurations are specified in the dependent claims.

[0011] The method according to the invention is a method for the continuous separation of a component from a liquid mixture using a membrane unit comprising at least one membrane stage and fed with the mixture as feed. wherein a membrane stage consists of at least a conveying device, one or more membrane module(s) and a feed container upstream of the conveying device, and wherein the mixture from the feed container is conveyed by means of the conveying device as feed to the one or more membrane modules, whereby the component to be separated is depleted in the resulting permeate stream of this respective membrane module and enriched in the resulting retentate stream of this respective membrane module, or vice versa, characterized in that the total permeate stream obtained from the last membrane stage is divided and a part of the total permeate stream, the recycled permeate, is recycled to the feed container and / or downstream of the feed container but upstream of the conveying device, and the other part of the total permeate stream, the discharged permeate,The permeate is discharged from the last membrane stage and from the membrane unit, whereby the recycling of the returned permeate to the feed container and / or behind the feed container but before the conveying device is not carried out by means of a conveying device, but hydraulically, i.e. by a pressure difference existing between the permeate side of the membrane unit and the suction side of the conveying device or the feed container.

[0012] In the context of the present invention, the term "component to be separated" refers to the component that, proportionally and / or according to its permeability, intentionally permeates less through the membrane, i.e., the component that is retained by the membrane. The component to be separated thus exhibits a positive retention effect for the respective membrane modules under consideration. The component to be separated can be a single specific chemical substance or a group of chemical substances considered within a common process engineering context.

[0013] A membrane unit within the meaning of the present invention relates to the entire membrane separation unit to which the liquid mixture containing the component to be separated is fed. A membrane unit consists of at least one membrane stage. Downstream processing or purification steps, as well as any storage of the discharged permeate in a container, are therefore, by definition, not part of the membrane unit.

[0014] The term membrane stage refers to at least one part of the membrane unit and includes at least one conveying device, such as a pump, and one or more membrane modules. If there is only a single membrane stage, the terms membrane unit and membrane stage are used synonymously. The membrane stage has a feed vessel upstream of the conveying device, into which the liquid mixture, for example, the discharge from a homogeneously catalyzed reaction, is fed and from which it is conveyed to the one or more membrane elements. The recirculated permeate can also be fed into the feed vessel. Additionally or alternatively, the recirculated permeate can be routed not into the feed vessel, but downstream of the feed vessel but upstream of the conveying device, i.e., to a point in the line between the feed vessel and the conveying device.

[0015] The term membrane module, used to describe the present invention, refers to a subunit of the membrane stage. A membrane module is therefore an assembly of one or more membrane elements. Membrane modules can be configured either as a membrane loop or as a membrane rack. A membrane loop is understood to be a subunit containing at least one membrane element and at least one conveying device that generates a moving overflow circuit. In contrast, the term membrane rack refers to a subunit characterized by the presence of at least one membrane element but no conveying device, and consequently, no moving overflow circuit.

[0016] In the context of the present invention, the term membrane element refers to the membrane, the structure, or the device containing the membrane where the desired separation of substances actually takes place, i.e., where the component is separated from the mixture or the homogeneous catalyst is separated from the reaction solution. These can be, for example, so-called spiral-wound elements, as used in many industrial membrane separation applications.

[0017] The invention is based on the fact that only the total permeate flow from the last membrane stage is divided into the recycled and the discharged permeate. If there is only one membrane stage, this single membrane stage is also the last membrane stage. If there are two or more membrane stages, no division takes place in the first membrane stage(s), but the total permeate flow is completely routed to the next membrane stage. The division then takes place as described above exclusively in the last membrane stage. The "division" within the meaning of the present invention refers exclusively to the quantity or mass flow of the total permeate and explicitly excludes any additional separation step in which further components are removed from the total permeate, i.e., no distillation, extraction, crystallization, or further membrane separation steps.

[0018] An advantage of the method according to the invention is that a portion of the total permeate flow from the last membrane stage, i.e., the recirculated permeate, does not leave the membrane stage and / or the membrane unit and then, for example, be recirculated via a permeate container, but remains within the at least one membrane stage and / or the membrane unit and is recirculated from there to the feed container and / or behind the feed container but before the conveying device. This makes it possible to dispense with a downstream pump that pumps permeate back into the overflow circuit or back into the feed container, since the permeate recirculation is self-regulating depending on the load. The recirculation of the permeate to the feed container and / or behind the feed container but before the conveying device is therefore not carried out by means of a conveying device, but hydraulically, i.e.,This is caused by a pressure difference between the permeate side of the membrane unit and the suction side of the conveying device or the feed container. In other words: There is no other conveying device, in particular no pump, between the permeate side and the feed container.

[0019] To control the outflow of the recirculated and discharged permeate, at least one adjustable flow resistance can be provided on the permeate side, via which the mass flow of the permeate is regulated. A flow resistance within the meaning of the present invention is an actuator with which the mass flow of a flow can be regulated, for example, a valve. A further preferred embodiment is one in which at least two adjustable flow resistances, preferably exactly two adjustable flow resistances, are provided on the permeate side, with which the mass flow of the discharged permeate, as well as the permeate pressure, particularly of the busbar, can be adjusted. The flow resistances are, in particular, valves.

[0020] The portion of the total permeate flow from the last membrane stage that is discharged from the membrane stage and the membrane unit, i.e., the discharged permeate, can be directed to a subsequent process step. For the purposes of this invention, the term "process step" can be understood to mean any subsequent process, such as further processing or purification steps, or combinations thereof. This includes, in particular, (further) conversion of the separated component, purification by known methods such as distillation, evaporation, or similar processes. Subsequent filling or transport process steps are also possible. Prior storage in a suitable container, for example, a permeate container, is also possible before the subsequent process step.If a permeate tank is present, the division of the total permeate according to the invention takes place upstream of the permeate tank, so that only the discharged permeate reaches the permeate tank. It is understood that several process steps can also be carried out sequentially, optionally via prior storage, for example, purification, followed by a reaction of the purified component and an additional purification of the reaction product.

[0021] With regard to the membrane separation process according to the invention, a balanced external mass balance exists, meaning that the mass flow rate of the feed supplied to the membrane unit corresponds to the mass flow rates of the permeate and / or retentate flows discharged from the membrane unit. This fact can be utilized. In a preferred embodiment of the present invention, the mass flow rate of one of the three flows—selected from the feed to the membrane unit, the discharged permeate, and the retentate of the membrane unit—is predetermined by a preceding or subsequent process step, and a further of the three aforementioned flows is regulated to a setpoint, for example, a constant retentate flow rate, a constant feed-to-retentate ratio, etc. This results in the third of the three aforementioned flows being determined by the external mass balance.The scale, and thus the absolute mass flow rates, can be adjusted largely arbitrarily based on the membrane module size and number. In a preferred embodiment, the ratio of the retentate mass flow rate to the feed mass flow rate is 1 to 99%, preferably 10 to 90%, and particularly preferably 15 to 80%. In a further preferred embodiment, the ratio of the mass flow rate of the discharged permeate to the total permeate mass flow rate is 1 to 99%, preferably 30 to 98%, and particularly preferably 60 to 97%. A process step within the meaning of the present invention is a plant or process unit, for example, an upstream or downstream chemical reaction in which the permeate / retentate is used, a further separation step, for example, a thermal separation such as thin-film evaporation or distillation, or logistics, i.e., in particular upstream or downstream tank storage facilities or filling.Upstream process steps are, in particular, continuously performed process steps that continuously provide a liquid mixture for the present membrane separation process. Preferably, these are continuously performed chemical reactions, for example, the hydroformylation or alkoxycarbonylation described in more detail below.

[0022] Furthermore, a balanced internal mass balance is present (the mass flow rate of the total permeate corresponds to the sum of the mass flow rates of the recycled and discharged permeate). According to the present invention, the internal mass balance is preferably largely independent of the external mass balance, i.e., the external mass balance essentially only represents the lower limit for the internal mass balance. It is therefore preferred according to the invention that the mass flow rate of the recycled permeate can fluctuate and adjusts itself depending on, preferably directly dependent on, i.e., without an intermediate permeate container, the mass flow rate of the discharged permeate. This also means that, apart from technical limitations (due to pumps, flow resistance, membrane area, etc.), the mass flow rate of the total permeate can be adjusted.) can be regulated independently of the above-mentioned external mass balance, as long as the mass flow rate of the total permeate is greater than the mass flow rate of the discharged permeate.

[0023] The mass flow rate of the total permeate depends on various parameters, such as the temperature (of the membrane module) or the concentration of the components in the mixture. In a preferred embodiment of the present invention, the pressure on the retentate side and / or the pressure on the permeate side, or the resulting transmembrane pressure (TMP = pressure difference between the permeate and retentate sides), and optionally the membrane module temperature, are therefore controlled in order to optimize the total permeate flow rate or to obtain a desired total permeate flow rate.

[0024] The membrane separation process according to the invention can be controlled in various ways, depending on the respective controlled variable, an actuator available for influencing the controlled variable, and the control priority. For the present process, there are various controlled variables, such as the fill level of the feed container, the pressure on the retentate side and on the permeate side, the difference of which yields the transmembrane pressure (TMP), as well as the mass flow rates of retentate and permeate, which can be influenced by various actuators, for example, the conveying device or one or more adjustable flow resistances.

[0025] The control engineering embodiments described below refer – insofar as they concern the active conveying of permeate flows by means of conveying devices – to comparative or background designs that are not in accordance with the invention.

[0026] In a preferred embodiment, the membrane separation process according to the invention is controlled such that the mass flow rate of the retentate and the TMP are kept constant. These two parameters therefore have the highest control priorities, whereby the exact order of the control priorities can be arbitrarily defined, i.e., the mass flow rate of the retentate can have the highest control priority and the TMP the second-highest control priority, or vice versa.

[0027] The mass flow rate of the feed to the (first) membrane module can be adjusted in a manner known to those skilled in the art in the invention, for example, via the conveying device used in the (first) membrane stage. The exact embodiment for adjusting the mass flow rate of the feed to the (first) membrane stage is variable and usually depends on technical boundary conditions such as the type of pump selected, the flow rate, and the delivery pressure. Control of the feed mass flow rate could, for example, be implemented with a pump directly controlled by speed, e.g., a gear pump, a piston pump, a piston diaphragm pump, or possibly a multi-stage centrifugal pump. Another possibility for controlling the feed mass flow rate could be to use a centrifugal pump and an adjustable flow resistance, such as a (control) valve. A further possibility would be to use a pump, e.g.,a gear pump, a piston pump, a piston diaphragm pump or a centrifugal pump, in combination with an adjustable return line, for example from the pressure side to the suction side of the pump.

[0028] The retentate-side pressure can be regulated by the conveying device and / or optionally by an additional actuator, for example, a pressure regulator. In the process according to the invention, the retentate pressure can be 1 to 100 bar, preferably 10 to 80 bar, and particularly preferably 30 to 60 bar. The retentate pressure is greater than the permeate-side pressure. The permeate pressure can be 0 to 50 bar, preferably 0 to 10 bar, and particularly preferably 1 to 5 bar. In a preferred embodiment, the permeate pressure of all existing membrane modules is similar (with a maximum deviation of 10% from each other) or the same.

[0029] The transmembrane pressure formed from the difference between retentate pressure and permeate pressure can be 1 to 90 bar, preferably 10 to 80 bar, and particularly preferably 30 to 60 bar in the process according to the invention. The membrane unit or the individual membrane stages preferably comprise a retentate-side pressure control system, which includes at least the pumping device and a pressure gauge, wherein the retentate pressure can be adjusted depending on the pressure gauge reading.The retentate pressure can be regulated by adjusting, for example, the delivery volume of the conveying device and optionally by an additional actuator, such as a pre-pressure regulator, depending on the retentate pressure measured (by the pressure gauge), whereby - relative to a previously defined setpoint for the retentate pressure - the delivery volume of the conveying device is reduced when the retentate pressure is increased and / or rising, and the delivery volume of the conveying device is increased when the retentate pressure is decreased and / or falling.

[0030] The retentate pressure can also be regulated by a combination of a pressure gauge and an adjustable flow resistance, in particular a valve on the retentate side. In this case, the retentate pressure can be regulated, for example, by the valve position depending on the measured retentate pressure (by the pressure gauge), whereby – relative to a predefined setpoint for the retentate pressure – the valve opens further when the retentate pressure increases and / or rises, and closes further when the retentate pressure decreases and / or falls.

[0031] In the inventive method, the retentate mass flow rate is preferably controlled by a retentate-side mass flow control system comprising at least one mass flow meter and an adjustable flow resistance, preferably a valve. The retentate mass flow rate can be controlled by adjusting the mass flow controller as a function of the measured retentate mass flow rate. Relative to a predetermined setpoint for the retentate mass flow rate, the valve of the mass flow controller closes further when the retentate mass flow rate increases and / or rises, and opens further when the retentate mass flow rate decreases and / or falls. The retentate pressure can then be freely selected within the limits of the minimum necessary and maximum possible load on the diaphragm stage(s).

[0032] According to another embodiment, the retentate mass flow rate can also be controlled by a combination of a mass flow meter and the pumping device. The retentate mass flow rate can be controlled, for example, by adjusting the pumping device's delivery volume as a function of the measured retentate mass flow rate. Relative to a predetermined setpoint for the retentate mass flow rate, the pumping device's delivery volume is reduced when the retentate mass flow rate increases and / or rises, and conversely, the pumping device's delivery volume is increased when the retentate mass flow rate decreases and / or falls.

[0033] The sensors and actuators of the retentate-side mass flow control, which comprises at least the conveying device or an adjustable flow resistance and a mass flow meter, and of the aforementioned retentate-side pressure control, which comprises at least the conveying device or an adjustable flow resistance and a pressure gauge, can be interconnected in any configuration to control the two control variables, retentate mass flow and retentate pressure. The priority of the two control variables, retentate mass flow and retentate pressure, can be freely selected in the method according to the invention. Preferably, the priority of the two control variables, retentate mass flow and retentate pressure (or, consequently, the TMP), is higher than that of all other control variables of the membrane separation stage, thus exhibiting the fastest response time.

[0034] The mass flow rate of the discharged permeate (from the last membrane stage) can be directly or indirectly dependent on the fill level of the feed vessel by a preferably continuous control, characterized in that – relative to a predetermined setpoint for the fill level of the feed vessel, where the setpoint is preferably 20 to 80%, particularly preferably 30 to 70% of the maximum possible fill level – the mass flow rate of the discharged permeate is increased when the fill level of the feed vessel rises and decreased when the fill level of the feed vessel falls. With this type of control, the feed vessel is not completely filled, as otherwise the fill level would be at or above the upper limit of its measuring range and thus unknown, making control to a setpoint impossible.The mass flow rate of the discharged permeate is adjusted, in particular, by means of at least one adjustable flow resistance. In the case of continuous control, the fill level of the feed container is preferably kept constant as a result. A control principle based on the fill level of the feed container would, for example, cause the mass flow rate of the discharged permeate to be continuously reduced when a low level is reached in the feed container, and potentially no permeate would be discharged at all.

[0035] The temperatures of the three streams, feed, retentate, and permeate, can vary over a wide range. The temperature of each of the three streams, feed, retentate, and permeate, is preferably -30 °C to 150 °C, more preferably 0 °C to 100 °C, and most preferably 20 °C to 80 °C.

[0036] The construction of the membrane unit, which will be described in more detail below, also contributes to the realization of the aforementioned control engineering implementation methods of the method according to the invention.

[0037] The membrane unit used in the inventive process for separating the component from the mixture comprises at least one membrane stage. However, the membrane unit can also comprise several membrane stages connected in series. In this case, the division of the total permeate flow takes place only in the last membrane stage.

[0038] A membrane stage of the membrane unit of the method according to the invention comprises, as defined above, a conveying device. The conveying device, which feeds the mixture to the one or more membrane modules, is preferably adjustable with respect to its conveying volume. The pressure of the feed to the one or more membrane modules can be from 1 to 100 bar, preferably from 10 to 80 bar, and particularly preferably from 30 to 60 bar. Suitable conveying devices include, for example, pumps known to those skilled in the art, such as centrifugal pumps, piston pumps, piston diaphragm pumps, rotary piston pumps, or gear pumps.

[0039] A membrane stage of the membrane unit according to the invention further comprises several membrane modules. The number of membrane modules is theoretically not limited upwards, but depends on the general process parameters and the desired membrane area. According to the invention, the membrane stage comprises several membrane modules which are further connected in series. The mixture arriving at the membrane unit is fed to the (first) membrane stage, where it is conveyed by means of the conveying device as a feed to one or more membrane modules. Within the membrane stage, the mixture is separated into permeate and retentate, with a permeate stream being drawn from each existing membrane module.

[0040] When multiple membrane modules are present, a number of permeate streams corresponding to the number of membrane modules is generated. The membrane modules are preferably connected to each other on the permeate side, for example via a busbar. In contrast, particularly in series connection, only one retentate stream is obtained, since the retentate from the first membrane module is passed to the next membrane module, a further permeate is separated from the retentate, and the retentate from the second membrane module is then passed to the next membrane module or, if only two membrane modules are present, is routed out of the membrane stage and / or the membrane unit.

[0041] A membrane stage according to the inventive method comprises a feed container upstream of the conveying device, from which the feed is conveyed by the conveying device to the at least two membrane modules. If only one membrane stage is present, both the feed to the membrane stage and the recycled permeate from the membrane stage can be introduced into the feed container and collected there before being conveyed by the conveying device to the at least two membrane modules. If more than one membrane stage is present, the feed to the first membrane stage and a retentate from one of the subsequent stages can be collected in the feed container of the first stage, while the permeate from the preceding membrane stage and either the retentate from the subsequent stage or, in the last membrane stage, the recycled permeate can be collected in the feed container of each subsequent stage(s).The design and specifications of such a feed container are known to those skilled in the art. The feed container preferably includes a level measuring unit. In both variants, it is also possible that the respective returned flows are not routed into the feed container, but rather behind the feed container and in front of the conveying device.

[0042] The membrane stage may further include sensors and / or actuators to meet the aforementioned preferred control requirements. These include, in particular, measuring and / or control units for parameters such as temperature, pressure, mass flow, etc. Such measuring and control units are known to those skilled in the art.

[0043] A membrane module according to the present invention, one or more of which may be present in the membrane stage, comprises one or more membrane elements. As mentioned, membrane modules can generally be configured either as a membrane loop or as a membrane rack. Preferably, the membrane modules present in the membrane stage(s) according to the invention are membrane loops.

[0044] A membrane loop comprises one or more membrane elements and at least one pumping device. Preferably, a membrane loop comprises only one pumping device. This pumping device is not identical to the pumping device of the corresponding membrane stage; rather, the entire system then has at least two pumping devices. The pumping device of the membrane loop is typically responsible for circulating the membrane loop, while the pumping device of the membrane stage is typically responsible for pressurizing the membrane modules or the membrane loop. Any suitable pump can be used as the pumping device. Such pumps are known to those skilled in the art. The pump used as the pumping device within a membrane loop is preferably a centrifugal pump. The pumping device creates a moving overflow circuit. Ideally, this overflow circuit improves the mass transport and thus the separation efficiency of the membrane.The setting of the overflow circuit can be adjusted independently of the overall control concept and the external and internal mass balance.

[0045] A membrane loop can also include measuring and / or control units for parameters such as temperature, differential pressure (axial pressure drop), flow rate, etc., for example, a heater or cooler to regulate the temperature. Other measuring and control units are known to those skilled in the art. In a preferred embodiment, the pressure of all membrane loops in a membrane stage is similar (deviation < 10%) or identical. This at least similar pressure can be set automatically without a specific control unit, but can also be set using a pressure regulator. The pressure regulator for the permeate pressure preferably has the slowest response time compared to the other actuators, i.e., the permeate-side mass flow control, the retentate-side mass flow control, and the retentate-side pressure control.

[0046] In contrast to the previously described membrane loop, a membrane module designed as a membrane rack does not have a conveying device, but rather one or more membrane elements and, if necessary, additional measuring and control units.

[0047] The membrane element(s) present in the membrane module, preferably in the membrane loop, are pre-assembled elements for technical use, containing the membrane and which can be considered the indivisible basic unit of the membrane separation process according to the invention. The membrane element(s) can be used as such in the membrane module or arranged in a pressure housing, for example, a pressure tube. The pressure tube, considered individually, can contain one or more membrane element(s), preferably up to five membrane elements. If the membrane element(s) are arranged in a pressure housing, preferably a pressure tube, a membrane module can comprise several pressure tubes. The membrane elements arranged in a pressure tube are preferably flowed through serially on the feed or retentate side and are connected on the permeate side.Basic units that can be used as membrane elements include spiral winding elements known to those skilled in the art. One or more spiral winding elements can then be located in a pressure housing, preferably a pressure tube.

[0048] Membranes are preferably those having a separation-active layer made of a material from the group consisting of cellulose acetate, cellulose triacetate, cellulose nitrate, regenerated cellulose, polyimides, polyamides, polyetheretherketones, sulfonated polyetheretherketones, aromatic polyamides, polyamideimides, polybenzimidazoles, polybenzimidazolones, polyacrylonitrile, polyarylethersulfones, polyesters, polycarbonates, polytetrafluoroethylene, polyvinylidene fluoride, polypropylene, terminally or laterally organomodified siloxane, polydimethylsiloxane, silicones, silicone acrylates, polyphosphazenes, polyphenyl sulfides, polybenzimidazoles, 6.6. Nylon®, polysulfones, polyanilines, polypropylenes, polyurethanes, acrylonitrile / glycidyl methacrylate (PANGMA), polytrimethylsilylpropyne, polymethylpentyne, polyvinyltrimethylsilane, polyphenylene oxide, alpha-aluminum oxides, gamma-aluminum oxides, titanium oxides, silicon oxides, zirconium oxides, ceramic membranes hydrophobized with silanes as described in EP 1 603 663 B1, polymers with intrinsic microporosity (PIM) such as PIM-1 and others as described, for example, in EP 0 781 166 B1, or mixtures thereof. The above-mentioned substances may be present in the release layer cross-linked by the addition of excipients or as so-called mixed matrix membranes with fillers such as carbon nanotubes, metal-organic frameworks or hollow spheres, as well as particles of inorganic oxides or inorganic fibers, such as... B. be provided with ceramic or glass fibers.

[0049] Membranes are particularly preferred that comprise a polymer layer of terminally or end-organized siloxane, polydimethylsiloxane, silicone acrylates, or polyimide as the separation layer, which are composed of polymers with intrinsic microporosity (PIM) such as PIM-1, or wherein the separation layer is composed of a hydrophobic ceramic membrane. Membranes made of terminally or end-organized siloxanes or polydimethylsiloxanes are especially preferred. Such membranes are commercially available.

[0050] In addition to the materials mentioned above, the membranes may contain other materials. In particular, the membranes may have support or carrier materials onto which the separation layer is applied. A selection of support materials is described in EP 0 781 166, to which explicit reference is made.

[0051] In a particularly preferred embodiment, the described method is used for membrane separation of a homogeneous catalyst. The component to be separated is then the homogeneous catalyst, and the liquid mixture is the reaction mixture obtained from a reaction stage.

[0052] A particularly preferred method according to the present invention is therefore a method for the continuous separation of a homogeneous catalyst from a liquid reaction mixture using a membrane unit comprising at least one membrane stage and fed with the reaction mixture containing the homogeneous catalyst originating from a reaction zone. wherein a membrane stage consists of at least a conveying device, one or more membrane module(s) and a feed vessel upstream of the conveying device, and wherein the reaction mixture is conveyed from the feed vessel by means of the conveying device as feed to the one or more membrane modules, whereby the homogeneous catalyst is depleted in the resulting permeate stream and enriched in the resulting retentate stream, in each case with respect to the reaction mixture conveyed to the respective membrane module, characterized in that the total permeate stream obtained is divided and a part of the total permeate stream, the recycled permeate, is recycled to the feed vessel and / or downstream of the feed vessel but upstream of the conveying device, and the other part of the total permeate stream, the discharged permeate, is discharged from the at least one membrane stage and from the membrane unit on the permeate side.

[0053] The reaction mixture originates from a reaction zone suitable for the respective process, preferably one or more suitable reactors. The retentate stream, containing at least a large proportion of the homogeneous catalyst, is preferably recycled to the reaction zone, in particular to the reactor(s), optionally after prior purification and / or work-up of the catalyst. Since the mass flow rate from the reaction zone can fluctuate due to production requirements, the control and plant engineering specifications described above can also be applied to the separation of the homogeneous catalyst.

[0054] In the reaction zone, preferably the reactor(s), a homogeneously catalyzed reaction is carried out. This can include the following reactions: oxidations, epoxidations, hydroformylations, hydroaminations, hydroaminomethylations, hydrocyanations, hydrocarboxylations, hydroxycarbonylations, hydrocarboxyalkylations, alkoxycarbonylations, aminations, ammonium oxidation, oximations, hydrosilylations, ethoxylations, propoxylations, carbonylations, telomerizations, methatheses, Suzuki couplings, and hydrogenations.

[0055] Preferably, the reaction is a hydroformylation. In particular, the hydroformylation is a hydroformylation of olefins with 3 to 15 carbon atoms, preferably 8 to 12 carbon atoms. The hydroformylation is preferably a homogeneously catalyzed hydroformylation in which the catalyst system is (completely) dissolved in the liquid phase of the reaction mixture. The catalyst system of the hydroformylation preferably comprises a transition metal from group 8 or 9 of the periodic table of elements and at least one organic phosphorus-containing ligand. Suitable phosphorus-containing ligands are known to those skilled in the art, but preferably they are monodentate phosphorus-containing ligands, for example, tris(2,4-di-tert-butylphenyl)phosphite.

[0056] Suitable transition metals include, in particular, iron, ruthenium, iridium, cobalt, or rhodium, preferably cobalt or rhodium, and especially rhodium. The catalytically active species are typically (ligand) carbonyl complexes of the metal atoms, which form in the liquid reaction mixture under elevated pressure and temperature.

[0057] Hydroformylation can be carried out in the presence of a solvent, which should be compatible with the hydroformylation process. Suitable solvents known to those skilled in the art can be used for hydroformylation, for example, alkanes, aromatic hydrocarbons, water, ethers, esters, ketones, alcohols, and the reaction or byproducts of hydroformylation such as aldehydes and condensation products of aldehydes.

[0058] Furthermore, the hydroformylation can be carried out at a pressure of 10 to 400 bar, preferably 15 to 270 bar. The temperature during the hydroformylation can be 70 to 250 °C, preferably 100 to 200 °C, and particularly preferably 120 to 160 °C.

[0059] The present invention is described with reference to the following figures, which show certain embodiments. The figures are for illustrative purposes only and are not to be understood as limiting.

[0060] Fig. 1 Figure 1 shows an exemplary setup of a membrane unit comprising a membrane stage. The membrane stage consists of a feed vessel (B-1), a pump (P-1), and a membrane module (M-1). The feed vessel (B-1) is supplied with the liquid mixture as feed to the membrane stage (F-1). From the feed vessel (B-1), the liquid mixture is pumped by the pump (P-1) as feed (F-2) to the membrane module (M-1), for example, a membrane loop, where the actual membrane separation takes place. The retentate (F-3) and the total permeate (F-4) are then removed from the membrane module (M-1) via the outlet valve (V-1). The total permeate (F-4) is subsequently divided, whereby a part of the total permeate can be discharged from the diaphragm stage and the diaphragm unit via the outlet valve (V-2) (F-5) and the other part of the permeate (F-6) can be returned to the feed container (B-1) via the return valve (V-3).

[0061] Fig. 2 Figure 1 shows an exemplary setup of a membrane unit comprising one membrane stage but several membrane modules. The membrane stage consists of a feed vessel (B-1), a pump (P-1), and two membrane modules (M-1 / M-2). The feed vessel (B-1) is supplied with the liquid mixture as feed to the membrane stage (F-1). From the feed vessel (B-1), the liquid mixture is pumped by the pump (P-1) as feed (F-2) to the first membrane module (M-1), for example, a membrane loop, where the first membrane separation takes place. From the membrane module (M-1), the retentate (F-3) and the permeate (F-4) of the first membrane module are then extracted. The retentate (F-3) is fed to the second membrane module (M-2), where further membrane separation occurs, producing the permeate (F-8) and the retentate (F-7) of the second membrane module (M-2). The retentate (F-7) is removed via the outlet valve (V-1).The two permeates (F-4 / F-8) from the two membrane modules (M-1 / M-2) are combined to form a total permeate (F-14) and then split, allowing part of the total permeate (F-5) to be discharged via the outlet valve (V-2) and the other part of the permeate (F-6) to be returned to the feed container (B-1) via the return valve (V-3).

[0062] Fig. 3 Figure 1 shows an exemplary setup of a membrane unit comprising two membrane stages. Each membrane stage consists of a feed vessel (B-1 / B-2), a pump (P-1 / P-2), and a membrane module (M-1 / M-2). The feed vessel (B-1) is supplied with the liquid mixture as feed to the membrane stage (F-1). From the feed vessel (B-1), the liquid mixture is pumped (P-1) as feed (F-2) to the membrane module (M-1), for example, a membrane loop, where membrane separation takes place. The total permeate (F-4) from the first membrane stage and the retentate (F-3) are then removed from the membrane module (M-1) via the outlet valve (V-1). The permeate (F-4) of the first membrane module (M-1) is directed to the feed container (B-2) of the second membrane stage and from there is conveyed by means of a pump (P-2) as feed (F-9) to the membrane module (M-2) of the second membrane stage (M-2), where further membrane separation takes place.The total permeate (F-11) and the retentate (F-10) are drawn from the membrane module (M-2) of the second membrane stage. The retentate (F-10) is then routed via the outlet valve (V-4) to the feed reservoir (B-1) of the first membrane stage. After exiting the membrane module (M-2), the total permeate (F-11) is split, with one portion (F-12) being discharged via the outlet valve (V-5) and the other portion (F-13) being returned to the feed reservoir (B-2) of the second membrane stage (M-2) via the return valve (V-6).

[0063] Fig. 4 This generally corresponds to the Fig. 1 The diagram therefore contains only one membrane stage, but includes additional markings to clarify the mass balances discussed. The term "mass balance" is used in this application based on two fundamental assumptions. The first relevant assumption is that a steady-state system exists, which in this case means that no accumulation of the mixtures occurs within the membrane unit over time, but at most temporary fluctuations. The total mass in the system thus remains constant regardless of time. Simultaneously, and this is the second assumption, no reaction takes place in our mass balance circuit. This means that not only the total mass, but also the masses of the individual components remain constant.

[0064] The external total mass balance refers to the dotted marking in Fig. 4 The mass flow of feed F-1 is equal to the sum of the mass flow of retentate F-3 and the mass flow of permeate F-5, i.e., F-1 = F-3 + F-5.

[0065] The internal total mass balance, which relates to the double-dashed box around the membrane stage M-1 in Fig. 4 The mass flow of feed F-2 is defined accordingly: The mass flow of feed F-2 is equal to the sum of the mass flow of retentate F-3 and the mass flow of total permeate F-4, i.e., F-2 = F-3 + F-4.

[0066] It follows that if two flows of the external mass balance are specified, the third flow of the external mass balance results. Therefore, only two of the three flows can be determined independently or externally controlled. The same applies to the internal mass balance, although it should be noted that the external mass balance always specifies at least one flow of the internal mass balance. Consequently, only two flows of the external mass balance and one additional flow of the internal mass balance can be defined. All other flows result from these.

Claims

1. Method of continuously separating a component from a liquid mixture using a membrane unit which comprises at least one membrane stage and is fed with the mixture as feed (F-1), wherein a membrane stage consists at least of a conveying device(P-1), a plurality of mutually series-connected membrane modules (M-1, M-2), and a feed vessel (B-1) upstream of the conveying device, and wherein the mixture is guided from the feed vessel (B-1) by means of the conveying device (P-1) as feed (F-2) to the plurality of membrane modules (M-1, M-2), which results in reduction of the component to be separated off, based in each case on the mixture guided to the respective membrane module (M-1, M-2), in the resulting permeate stream from this respective membrane module (M-1, M-2) and enrichment in the resulting retentate stream from this respective membrane module (M-1, M-2) or vice versa, characterized in that the overall permeate stream (F-14) obtained from the last membrane stage is divided and a portion of the overall permeate stream (F-6), the recycled permeate, is recycled to the feed vessel (B-1) and / or beyond the feed vessel (B-1) but upstream of the conveying device (P-1) and the other portion of the overall permeate stream (F-5), the removed permeate, is conducted out of the last membrane stage and out of the membrane unit on the permeate side, wherein the recycling of the recycled permeate (F-6) to the feed vessel (B-1) and / or beyond the feed vessel (B-1) but upstream of the conveying device (P-1) is not by means of a conveying device (P-1) but by hydraulic means, i.e. by means of a pressure differential existing between the permeate side of the membrane unit and the suction side of the conveying device (P-1) or the feed vessel (B-1).

2. Method according to Claim 1, wherein the mass flow rate of the recycled permeate (F-6) can fluctuate and is established depending on the mass flow rate of the removed permeate (F-5).

3. Method according to Claim 1 or 2, wherein the pressure on the retentate side and / or the pressure on the permeate side or the resulting transmembrane pressure (TMP) and optionally the membrane module temperature are controlled in order to obtain a desired amount of the overall permeate stream (F-14).

4. Method according to any of the preceding claims, wherein both the mass flow rate of the removed permeate (F-5) and the permeate pressure are controlled by means of an adjustable flow resistor.

5. Method according to any of the preceding claims, wherein the mass flow rate of the removed permeate (F-5), depending directly or indirectly on the fill level of the feed vessel (B-1), is subject to preferably continuous closed-loop control, a feature of which is that - based on a target value fixed beforehand for the fill level of the feed vessel (B-1) - the mass flow rate of the removed permeate (F-5) increases with rising fill level of the feed vessel (B-1) and the mass flow rate of the removed permeate (F-5) decreases with falling fill level of the feed vessel (B-1).

6. Method according to any of the preceding claims, wherein the pressure on the retentate side (retentate pressure) is controlled by means of the conveying device (P-1) with which the feed (F-2) is fed to the plurality of membrane modules (M-1, M-2), and optionally a further actuator, for example a supply pressure regulator, or by means of a combination of a manometer and an adjustable flow resistor, especially a valve (V-1) on the retentate side.

7. Method according to any of the preceding claims, wherein the mass flow rate on the retentate side (retentate mass flow rate) is controlled by means of a closed-loop mass flow controller on the retentate side comprising at least a mass flow meter and an adjustable flow resistor, preferably a valve (V-1), or by means of a combination of mass flow meter and conveying device.

8. Method according to any of the preceding claims, wherein the component is a homogeneous catalyst which is separated from a reaction mixture.

9. Method according to any of the preceding claims, wherein the conveying device (P-1) is a pump.