Variable, self-regulating permeate recycling in organophilic nanofiltration

Abstract

The present invention provides improvements in terms of control and process technology for a method of continuously removing components from a liquid mixture using a membrane unit comprising at least one membrane stage. The improvement is that at least a portion of the total permeate stream obtained is recirculated to a feed vessel and / or upstream of a conveyor device through the feed vessel. The method disclosed herein can be used particularly for the separation of a homogeneously dissolved catalyst from a liquid reaction mixture.

Description

Technology Field

[0001] The present invention relates to improvements in terms of control and process technology for a method of continuously removing components from a liquid mixture using a membrane unit comprising at least one membrane stage. The improvement is that at least a portion of the total permeate stream obtained is recirculated to a feed vessel and / or upstream of a conveyor device through the feed vessel. The method disclosed herein can be used particularly for the separation of a homogeneously dissolved catalyst from a liquid reaction mixture. Background Technology

[0002] For example, membrane separation methods for separating a homogeneously dissolved catalyst from a reaction mixture are known in principle in the prior art. Refer herein by example to WO 2014 / 131623 A1.

[0003] For this type of membrane separation method, improvements in control technology have already been described. International application WO 2014 / 183952 A1 discloses, for example, a membrane separation method for separating a homogeneously dissolved catalyst from a reaction mixture, wherein two control parameters, namely the volume flow rate of the membrane separation unit and the retention of the membrane separation unit, are kept constant to compensate for fluctuations in operating conditions, particularly fluctuations in the volume flow rate of the reaction mixture coming out of the reaction zone.

[0004] To maintain the aforementioned control variables constant, WO 2014 / 183952 A1 proposes a flow resistor to adjust or maintain the volume flow rate of the retained material, and closed-loop control of temperature and / or pressure in an overflow circuit to adjust or maintain the retained material constant.

[0005] The problem with the method proposed above is that maintaining a constant retention of the membrane separation unit is not productive for all methods; instead, optimization, and often maximization, of the retention of the membrane separation unit during the method is required—taking into account the plant throughput and the membrane area already installed in the membrane separation unit. Closed-loop control by a flow resistor as described in WO 2014 / 183952 A1 causes the already installed membrane area to operate at a pressure lower than the optimal transmembrane pressure. The method described above also has, based on a simple material balance considering the removed permeate stream in relation to the given total throughput of the plant and the permeate stream generated therefrom (the portion of the permeate stream discharged from the membrane separation unit onto the permeate side), the total permeate stream and the generated recirculated permeate stream (the portion of the total permeate stream recirculated to the membrane separation unit) are smaller than possible or desirable.

[0006] An additional disadvantage of the method described in WO 2014 / 183952 A1 is that both a vessel and a pump for the permeate must be planned to achieve a constant closed-loop control system on the permeate side. However, providing a pump to pump the permeate from the permeate vessel to the overflow circuit or feed vessel is associated with increased plant inventory and costs, for example, for procurement or for operation, maintenance and repair, and additionally, this can also result in plant shutdown and subsequent manufacturing shutdown.

[0007] Furthermore, the installation of the vessel generally prevents a portion of the membrane separation stage on the permeate side from being filled with hydraulic pressure, which may increase safety risks, particularly when using toxic fluids. In addition, the vessel on the permeate side, in addition to the feed vessel, creates the possibility that the closed-loop control of the two vessel states may lead to mutual fluctuations.

[0008] Accordingly, the problem to be solved by the present invention is to provide a lower-cost method for continuously separating components from a mixture, preferably for continuously separating a homogeneous catalyst from a reaction mixture. An additional problem to be solved by the present invention is to provide self-regulating permeate recirculation in a method for continuously separating components from a mixture, preferably for continuously separating a homogeneous catalyst from a reaction mixture, wherein the installed membrane area can be optimally used under different load conditions, for example, to maximize retention or yield.

[0009] The fundamental problem was solved by the method according to claim 1. Preferred configurations and embodiments are specified in dependent claims.

[0010] The method according to the present invention is a method for continuously separating components from a liquid mixture using a membrane unit comprising at least one membrane stage and supplied with a liquid mixture as a feed, and

[0011] Herein, the membrane stage comprises at least a conveyor, one or more membrane module(s), and a feed container upstream of the conveyor, wherein a mixture is guided from the feed container to one or more membrane modules as a feed by the conveyor, which in each case, based on the mixture guided to each membrane module, causes a reduction in the component to be separated from the generated permeate stream from said particular membrane module and an enrichment in the component to be separated from the generated retained stream from said particular membrane module, or the opposite case, and

[0012] A method characterized in that the entire permeate stream obtained from the final membrane stage is divided, the recirculated permeate, which is part of the entire permeate stream, is recirculated to a feed container and / or through the feed container upstream of a conveyor, and the removed permeate, which is another part of the entire permeate stream, is discharged from the final membrane stage and from the membrane unit on the permeate side, wherein the recirculation of the recirculated permeate to the feed container and / or through the feed container upstream of the conveyor is performed by hydraulic means rather than by the conveyor, that is, achieved by a pressure difference existing between the permeate side of the membrane unit and the conveyor or the suction side of the feed container. Brief explanation of the drawing

[0013] The present invention is described by the following drawings illustrating specific embodiments. The drawings are merely illustrative and should not be construed as limiting. FIG. 1 illustrates an exemplary structure of a membrane unit comprising one membrane stage. In the invention, the membrane stage consists of a feed container (B-1), a pump (P-1), and a membrane module (M-1). A liquid mixture is supplied to the feed container (B-1) as a feed (F-1) to the membrane stage. From the feed container (B-1), the liquid mixture is guided by the pump (P-1) to the membrane module (M-1) as a feed (F-2), for example, to the membrane loop where actual membrane separation takes place. Subsequently, from the membrane module (M-1), the retained material (F-3) and the total permeate (F-4) are discharged through a discharge valve (V-1). The entire permeate (F-4) is subsequently divided, so that a portion of the entire permeate (F-5) can be removed from the membrane stage and membrane unit through the discharge valve (V-2), and another portion of the permeate (F-6) can be recirculated to the feed container (B-1) through the recirculation valve (V-3). FIG. 2 illustrates an exemplary configuration of a membrane unit comprising one membrane stage but including multiple membrane modules. The membrane stage consists of a feed container (B-1), a pump (P-1), and two membrane modules (M-1 / M-2). A liquid mixture is supplied to the feed container (B-1) as a feed (F-1) to the membrane stage. From the feed container (B-1), the liquid mixture is guided by the pump (P-1) as a feed (F-2) to the first membrane module (M-1), for example, to the membrane loop where the first membrane separation occurs in this case. Subsequently, from the membrane module (M-1), a retained material (F-3) from the first membrane module and a permeate (F-4) from the first membrane module are discharged. The retained material (F-3) is guided to the second membrane module (M-2) where further membrane separation occurs, thereby generating a permeate (F-8) and a retained material (F-7) from the second membrane module (M-2). The retained material (F-7) is discharged through the discharge valve (V-1). Two permeates (F-4 / F-8) from two membrane modules (M-1 / M-2) are combined to produce a total permeate (F-14), which is then divided, so that a portion of the total permeate (F-5) can be removed through the discharge valve (V-2), and another portion of the permeate (F-6) can be recirculated to the feed container (B-1) through the recirculation valve (V-3). FIG. 3 shows an exemplary structure of a membrane unit comprising two membrane stages. Each membrane stage consists of a feed container (B-1 / B-2), a pump (P-1 / P-2) in each case, and a membrane module (M-1 / M-2). A liquid mixture is supplied to the feed container (B-1) as a feed (F-1) to the membrane stage. From the feed container (B-1), the liquid mixture is guided by the pump (P-1) to the membrane module (M-1) as a feed (F-2), for example, to the membrane loop where membrane separation occurs. Subsequently, from the membrane module (M-1), the total permeate (F-4) from the first membrane stage and the retained material (F-3) through the discharge valve (V-1) are discharged. The permeate (F-4) from the first membrane module (M-1) is guided to the feed container (B-2) of the second membrane stage, and then guided by a pump (P-2) to the membrane module (M-2) of the second membrane stage (M-2) where further membrane separation occurs as feed (F-9). From the membrane module (M-2) of the second membrane stage, the entire permeate (F-11) and retained material (F-10) from the second membrane stage (M-2) are removed. The retained material (F-10) is subsequently guided to the feed container (B-1) of the first membrane stage through the discharge valve (V-4). The entire permeate (F-11) is split after exiting the membrane module (M-2), thereby allowing a portion of the permeate (F-12) to be removed through the discharge valve (V-5) and another portion of the permeate (F-13) to be recirculated to the feed container (B-2) of the second membrane stage (M-2) through the recirculation valve (V-6). FIG. 4 is fundamentally equivalent to FIG. 1 in that it includes only one membrane stage, but includes additional indications for an example of the material balance being addressed. In this application, the term “material balance” is used based on two fundamental assumptions. The first relevant assumption is that the system is a steady-state system, which means that in the case of the present invention, no accumulation of a mixture of materials within the membrane unit occurs over time, and at most, transient fluctuations may occur. Thus, the total material in the system remains the same regardless of time. At the same time, the second assumption is that no reaction occurs in the material balance circuit of the present invention. This means that not only the total material but also the material of the individual components remains the same. The external total material balance is based on the dotted line indication in Fig. 4. The material flow rate of feed F-1 is equal to the total sum of the material flow rates of retained F-3 and permeate F-5, i.e., F-1 = F-3 + F-5. In Figure 4, the internal total material balance based on the box with the double-line dashed line around the membrane stage M-1 is correspondingly defined: the material flow rate of feed F-2 is equal to the total sum of the material flow rates of retained F-3 and the material flow rates of total permeate F-4, i.e., F-2 = F-3 + F-4. Consequently, when two streams of external material balance are specified, a third stream induces the external material balance. Thus, it is possible to determine only two of the three streams independently or to control them from the outside. It should be noted that the external material balance always defines at least one stream of the internal material balance, but the situation is the same for the internal material balance. Therefore, it is possible to fix only two streams of the external material balance and one additional stream of the internal material balance in total. From this, all other streams are generated. Specific details for implementing the invention

[0014] In the context of the present invention, the term “component to be separated” means a component intended to permeate through a membrane to a lesser extent in terms of its proportion and / or permeability, i.e., a component retained by the membrane. Thus, the component to be separated has positive retention for the corresponding particular membrane module. The component to be separated may also be a single specific chemical, or otherwise a group of chemicals that may be considered in the ordinary context for process technology purposes.

[0015] In the context of the present invention, the "membrane unit" relates to an entire membrane unit to which a liquid mixture containing a component to be separated is supplied. The membrane unit consists of at least one membrane stage. Accordingly, further processing or purification steps and any storage downstream of the permeate removed from the vessel are by definition not part of the membrane unit.

[0016] The term "membrane stage" refers to at least a part of a membrane unit and includes one or more conveying devices, e.g., a pump, and one or more membrane module(s). If there is only one membrane stage, the terms "membrane unit" and "membrane stage" should be understood as synonyms. The membrane stage has a feed vessel connected upstream of the conveying device, into which a liquid mixture, e.g., the output from a homogeneous catalytic reaction, is introduced, and from there the liquid mixture is guided to one or more membrane elements. Recirculating permeate may likewise be guided to the feed vessel. Additionally, or alternatively, rather than being guided to the feed vessel, it is possible for the recirculating permeate to be guided past the feed vessel upstream of the conveying device, i.e., to a point within the conduit between the feed vessel and the conveying device.

[0017] The term "membrane module" as used in the description of the present invention relates to a subunit of a membrane stage in terms of plant technology. Accordingly, a membrane module is an interconnection of one or more membrane element(s). A membrane module may be configured as a membrane loop or as a membrane rack. A membrane loop is understood to mean a subunit having at least one membrane element and at least one conveyor that generates a moving overflow circulation. In contrast, the term "membrane rack" means a subunit characterized by having at least one membrane element but no conveyor, and thus no moving overflow circulation is generated.

[0018] In the context of the present invention, the term “membrane element” means a membrane or a structure or device containing a membrane, wherein the desired separation of materials actually takes place, that is, a component is separated from a mixture or a homogeneous catalyst is separated from a reaction solution. These may be, for example, spiral-wound elements used in many applications in industrial membrane separation.

[0019] The basis of the present invention is that the entire permeate stream from the final membrane stage is divided into permeate that is recirculated and permeate that is removed. If only one membrane stage exists, this single membrane stage is also the final membrane stage. If there are two or more membrane stages, no division occurs at the first membrane stage; instead, the entire permeate stream is guided to the next membrane stage. Subsequently, as described above, division is performed exclusively at the final membrane stage. In the context of the present invention, the term "division" refers entirely to the amount or mass flow rate of the entire permeate and explicitly implies that there are no additional separation stages in which additional components are removed from the entire permeate, such as distillation, extraction, crystallization, and additional membrane separation stages.

[0020] One advantage of the method according to the present invention is that a portion of the entire permeate stream from the last membrane stage, i.e., the recirculated permeate, does not leave the membrane stage and / or the membrane unit, for example, rather than being recirculated first through a permeate vessel, but remains within at least one membrane stage and / or membrane unit and is recirculated thereto to a feed vessel and / or upstream of a conveyor via a feed vessel. This enables the omission of a downstream pump that pumps the permeate back into the overflow circuit or back into the feed vessel, because the permeate recirculation is self-regulated according to the load. Thus, recirculating the recirculated permeate to the feed vessel and / or upstream of the conveyor via a feed vessel is performed by hydraulic means rather than by a conveyor, that is, achieved by the pressure difference existing between the permeate side of the membrane unit and the suction side of the conveyor or feed vessel. In other words, there is no additional conveyor, in particular a pump, between the permeate side and the feed vessel.

[0021] To control the discharge flow rates of the recirculated permeate and the removed permeate, at least one adjustable flow resistor may be present on the permeate side, thereby controlling the material flow rate of the permeate. In the context of the present invention, the flow resistor is an actuator capable of controlling the material flow rate of the stream, e.g., a valve. An embodiment having at least two adjustable flow resistors on the permeate side, preferably exactly two adjustable flow resistors, is further preferred, which means that the material flow rate of the removed permeate and the permeate pressure, in particular the material flow rate and permeate pressure of the collection rail, can be adjusted. The flow resistor is, in particular, a valve.

[0022] A portion of the total permeate stream from the last membrane stage removed from the permeate-side membrane stage and from the membrane unit, i.e., the removed permeate, may be guided to a downstream process step. In the context of the present invention, the term "process step" may be understood to mean any downstream process, for example, an additional processing or purification process step or a combination thereof. This includes, in particular, purification by known methods such as (additional) reaction of the removed component, distillation, evaporation, etc. Downstream distribution or transport process steps are also possible. Prior to the downstream process step, pre-storage in a suitable container, for example, a permeate container, is also possible. If a permeate container is present, the splitting of the total permeate according to the present invention is performed upstream of the permeate container, so that only the removed permeate enters the permeate container. It will be apparent that a number of process steps through optional pre-storage, for example, the conversion of the purified component after purification and further purification of the reaction product, may also be performed sequentially.

[0023] In relation to the membrane separation method according to the present invention, a stable external material balance exists, which means that the material flow rate of the feed supplied to the membrane unit corresponds to the material flow rate of the permeate stream and / or retained stream discharged outside the membrane unit. It is possible to utilize this situation. In a preferred embodiment of the present invention, the material flow rate of one of three streams selected from the feed to the membrane unit, the permeate removed, and the retained from the membrane unit is applied in a preceding or downstream process step, and one additional stream of the three is controlled to a target value, e.g., a constant retained flow rate, a constant ratio of feed to retained, etc. Due to the external material balance, this also causes the third of the three streams to be produced. The scale and the consequent absolute material flow rates can be significantly adjusted as desired, taking into account the membrane module size and the number of membrane modules. In a preferred embodiment, the ratio of the retained material flow rate to the feed material flow rate is 1% to 99%, preferably 10% to 90%, more preferably 15% to 80%. In a further preferred embodiment, the ratio of the flow rate of the removed permeate material to the total flow rate of the permeate material is 1% to 99%, preferably 30% to 98%, more preferably 60% to 97%. In the context of the invention, "process step" refers to a plant or process unit, for example, an upstream or downstream chemical reaction in which the permeate / retainer is used, a further separation step, for example, thermal separation, such as thin film evaporation or distillation, or a combined operation, specifically an upstream or downstream tank farm or distribution operation. The upstream process step is a process step performed particularly continuously, thereby continuously providing the liquid mixture for the membrane separation process of the invention. These are preferably chemical reactions performed continuously, for example, hydroformylation or alkoxycarbonylation, which are described in detail below.

[0024] Furthermore, more specifically, a stable internal material balance also exists (where the material flow rate of the total permeate corresponds to the total sum of the material flow rates of the recirculated permeate and the removed permeate). According to the present invention, the internal material balance is preferably almost independent of the external material balance, which means that the external material balance is, in principle, merely a lower limit for the internal material balance. Accordingly, according to the present invention, the material flow rate of the recirculated permeate can be varied and is preferably established according to the material flow rate of the removed permeate, that is, without any permeate container in between. This also means that the material flow rate of the total permeate can be controlled independently of the aforementioned external material balance, regardless of technical limitations (induced by pumps, flow resistors, membrane regions, etc.), provided that the material flow rate of the total permeate is greater than the material flow rate of the removed permeate.

[0025] In the present invention, the total permeate material flow rate depends on various parameters, for example, the temperature (of the membrane module) or the concentration of components in the mixture. Accordingly, in a preferred embodiment of the present invention, to optimize the amount of the total permeate stream or to obtain a desired amount of the total permeate stream, the pressure on the holding side and / or the pressure on the permeate side or the generated transmembrane pressure (TMP = pressure difference between the permeate side and the holding side) and optionally the membrane module temperature are controlled.

[0026] The membrane separation method according to the present invention can be adjusted in various ways in terms of control technology according to each control variable, actuators present to influence the control variable, and control priority. There are various control variables for the method of the present invention, such as the filling level of the feed vessel, pressures on the retaining side and permeate side generating transmembrane pressure (TMP), and material flow rates of the retained and permeate that may be influenced by various actuators, e.g., a conveyor or one or more adjustable flow resistors.

[0027] In a preferred embodiment, the membrane separation method according to the present invention is adjusted in such a way that the material flow rate of the retained material and the TMP are kept constant from the perspective of control technology. These two parameters consequently have the highest control priority, where the exact order of the control priorities can be fixed as intended, namely that the material flow rate of the retained material may have the highest control priority and the TMP may have the second highest control priority, or vice versa.

[0028] In the method according to the present invention, the material flow rate of the feed to the (first) membrane module can be established in a manner known to those skilled in the art, for example, through a conveying device used in the (first) membrane stage. The exact embodiment for establishing the material flow rate of the feed to the (first) membrane stage is variable and typically depends on technical constraints, for example, the type of pump selected, the conveying speed, and the conveying pressure. For example, it may be possible to control the feed material flow rate using a pump directly controlled by speed, for example, a gear pump, a piston pump, a piston membrane pump, or optionally a multi-stage centrifugal pump. Another option for controlling the feed material flow rate may be to use a centrifugal pump and an adjustable flow resistor, for example, a (control) valve. An additional option may be to use a pump, for example, a gear pump, a piston pump, a piston membrane pump, or a centrifugal pump, in combination with an adjustable return flow conduit, for example, from the pressure side of the pump to the suction side.

[0029] The pressure on the retaining side (retaining pressure) may be controlled by a conveying device and / or optionally by an additional actuator, e.g., a feed pressure regulator. In the method according to the present invention, the retaining pressure may be 1 to 100 bar, preferably 10 to 80 bar, more preferably 30 to 60 bar. In the invention, the retaining pressure is greater than the pressure on the permeating side (permeate pressure). In the invention, the permeate pressure may be 0 to 50 bar, preferably 0 to 10 bar, more preferably 1 to 5 bar. In a preferred embodiment, the permeate pressures in all existing membrane modules are similar (mutual variation of 10% or less) or identical.

[0030] The transmembrane pressure formed by the difference between the retaining pressure and the permeate pressure may be 1 to 90 bar, preferably 10 to 80 bar, more preferably 30 to 60 bar. The membrane unit or individual membrane stage preferably includes closed-loop control of pressure on the retaining side comprising at least a conveyor and a pressure gauge, wherein the retaining pressure may be adjusted according to the pressure gauge. In the same invention, the retaining pressure may be controlled by adjusting the conveying volume of the conveyor according to the retaining pressure measured, for example (by the pressure gauge), and optionally by an additional actuator, for example, a feed pressure regulator, wherein the conveying volume of the conveyor is reduced when the retaining pressure increases and / or rises, and the conveying volume of the conveyor is increased when the retaining pressure decreases and / or falls, based on a predetermined target value for the retaining pressure.

[0031] Alternatively, the holding pressure may be controlled via a combination of a pressure gauge and an adjustable flow resistor, particularly a valve on the holding side. In the same invention, the holding pressure may be controlled via a valve setting, for example, according to the holding pressure measured (by the pressure gauge), wherein—based on a predetermined target value for the holding pressure—the valve is further opened when the holding pressure increases and / or rises, and further closed when the holding pressure decreases and / or falls.

[0032] In the method according to the present invention, the material flow rate of the retained material (retained material flow rate) is preferably controlled by a material flow rate controller on the retained side comprising at least one material flow meter and an adjustable flow resistor, preferably a valve. In the invention, the retained material flow rate can be controlled by adjusting the material flow rate controller according to the measured retained material flow rate, wherein—based on a predetermined target value for the retained material flow rate—the valve of the material flow rate controller is further closed when the retained material flow rate increases and / or rises, and the valve of the material flow rate controller is further opened when the retained material flow rate decreases and / or falls. Subsequently, the retained pressure can be freely selected within the minimum required and maximum possible load range of the membrane stage(s).

[0033] In another embodiment, alternatively, the holding material flow rate may be controlled by a combination of a material flow meter and a conveying device. In the present invention, the holding material flow rate may be controlled, for example, by adjusting the conveying volume of the conveying device according to the measured holding material flow rate, wherein—based on a predetermined target value for the holding material flow rate—the conveying volume of the conveying device is reduced when the holding material flow rate increases and / or rises, and / or the conveying volume of the conveying device is increased when the holding material flow rate decreases and / or falls.

[0034] Sensors and actuators for closed-loop control of the material flow rate on the holding side, comprising at least a conveyor or an adjustable flow resistor and a material flow meter, and for closed-loop control of the pressure on the holding side, comprising at least a conveyor or an adjustable flow resistor and a pressure meter, may be connected to each other in any manner desired for control technology purposes to control two control variables, the holding material flow rate and the holding pressure. The mutual priority of the two control variables, the holding material flow rate and the holding pressure, may be selected as desired in the method according to the present invention. The priority of the two control variables, the holding material flow rate and the holding pressure (and the consequent TMP), is preferably higher than the priority of all other control variables in the membrane separation stage, i.e., has the fastest response characteristics.

[0035] The material flow rate of the permeate removed (from the final membrane stage) is controlled directly or indirectly, preferably in a continuous closed-loop manner, depending on the charge level of the feed vessel, and is characterized by the fact that, based on a target value fixed in advance for the charge level of the feed vessel (wherein the target value is preferably 20% to 80% of the maximum possible charge level, more preferably 30% to 70%), the material flow rate of the permeate removed increases as the charge level of the feed vessel increases and decreases as the charge level of the feed vessel decreases. In this type of closed-loop control, the feed vessel is not fully charged, because otherwise the charge level would be at or above the upper edge of its measurement range and would be undetectable, and consequently, closed-loop control for the target value would not be possible. The material flow rate of the permeate removed is controlled, in particular, through at least one adjustable flow resistor. In the case of continuous closed-loop control, this preferably maintains the charge level of the feed vessel constant. The effect of the closed-loop control principle based on the fill level of the feed container would be, for example, that when a low level is achieved in the feed container, the material flow rate of the permeate removed is significantly reduced, and possibly no further permeate is removed.

[0036] The temperatures of the three streams of feed, retained, and permeate may vary within a wide range. The temperature of each of the three streams of feed, retained, and permeate is independently preferably -30°C to 150°C, more preferably 0°C to 100°C, and most preferably 20°C to 80°C.

[0037] In terms of control technology, the contribution to achieving the aforementioned method of execution according to the present invention is also made by the configuration of the membrane unit, which will be described in more detail below.

[0038] The membrane unit used in the method according to the present invention to separate components from a mixture comprises at least one membrane stage. Alternatively, the membrane unit may comprise a plurality of membrane stages connected in series with one another. In this case, the entire permeate stream is separated only at the last membrane stage.

[0039] The membrane stage of the membrane unit for the method according to the present invention according to the above definition includes a conveying device. The conveying device, which guides a mixture as a feed to one or more membrane modules, is preferably adjustable with respect to its conveying volume. The pressure of the feed to one or more membrane modules may be 1 to 100 bar, preferably 10 to 80 bar, more preferably 30 to 60 bar. Suitable conveying devices are, for example, pumps known to those skilled in the art, such as centrifugal pumps, piston pumps, piston membrane pumps, rotary piston pumps, or gear pumps.

[0040] The membrane stage of the membrane unit according to the present invention further comprises one or more membrane module(s). Theoretically, there is no upper limit on the number of membrane modules; instead, it depends on general process parameters and the desired membrane area. In a preferred embodiment, the membrane stage further preferably comprises a plurality of membrane modules connected in series with each other. A mixture reaching the membrane unit is guided to a (first) membrane stage, where it is guided as a feed to one or more membrane modules by a conveyor. Separation into permeate and retained is performed within the membrane stage, and the permeate stream is discharged from each existing membrane module.

[0041] Accordingly, when multiple membrane modules exist, multiple permeate streams corresponding to the number of membrane modules are generated. The membrane modules are preferably connected to each other on the permeate side, for example, via a collection rail. However, in contrast, particularly in the case of a serial connection, when only two membrane modules exist, only one permeate stream is obtained because the retained material from the first membrane module is guided to the next membrane module, additional permeate is separated from the retained material, and then the retained material from the second membrane module is guided to the next membrane module, or is discharged from the membrane stage and / or membrane unit.

[0042] In the method according to the present invention, the membrane stage includes a feed container upstream of a conveyor, from which a feed is guided by the conveyor to at least two membrane modules as feed. If there is only one membrane stage, it is possible for both the feed to the membrane stage and the permeate recirculated from the membrane stage to be introduced into the feed container, collected therein, and then guided by the conveyor to at least two membrane modules as feed. If there is more than one membrane stage, the feed to the membrane stage and the retained material from one of the subsequent stages may be collected in a feed container for the first stage, and the permeate from each preceding membrane stage and the retained material from the subsequent stage or the permeate recirculated from the last membrane stage may be collected in a feed container for the subsequent stage(s). The configuration and specifications of such feed containers are known to those skilled in the art. The feed container preferably includes a measuring unit for the filling level. In addition, in both variations, it is possible for each recirculating stream to be guided upstream of the conveyor device past the feed container rather than into the feed container.

[0043] The membrane stage may further include sensors and / or actuators to enable the aforementioned, preferably control-related, functions. These include, in particular, measurement and / or control units for parameters such as temperature, pressure, material flow rate, etc. Corresponding measurement and control units are known to those skilled in the art.

[0044] A membrane module according to the present invention, which may exist in one or more places on a membrane stage, comprises one or more membrane element(s). In principle, the membrane module may be configured as a membrane loop or as a membrane rack as mentioned. The membrane module existing according to the present invention on the membrane stage(s) is preferably a membrane loop.

[0045] The membrane loop comprises one or more membrane element(s) and at least one transport device. The membrane loop preferably comprises only one transport device. This transport device is not identical to the transport device for the corresponding membrane stage; instead, in this case, the entire system has at least two transport devices. The transport device of the membrane loop is generally responsible for the circulation of the membrane loop, whereas the transport device of the membrane stage is generally responsible for pressurizing the membrane module or the membrane loop. The transport device used may be any suitable pump. Such pumps are known to those skilled in the art. The pump used as the transport device within the membrane loop is preferably a centrifugal pump. The transport device creates a moving overflow circulation. Ideally, the overflow circulation can improve mass transfer and consequently the separation performance of the membrane. In this invention, the overflow circulation can be adjusted independently of the primary control concept and external and internal mass balance.

[0046] The membrane loop may also additionally include measurement and / or control units for parameters such as temperature, pressure difference (axial pressure drop), circulation rate, etc., for example, a heater or cooler for adjusting the temperature. Additional measurement and control units are known to those skilled in the art. In a preferred embodiment, the pressure in all membrane groups present in the membrane stage is similar (variation < 10%) or identical. Such at least similar pressures can be established without the presence of a specific control unit, but can also be established by a pressure regulator. The pressure regulator for the permeate pressure preferably has the slowest response characteristics compared to other actuators, namely, closed-loop control of the material flow rate on the permeate side, closed-loop control of the material flow rate on the retaining side, and closed-loop control of the pressure on the retaining side.

[0047] In contrast to the membrane loop described above, the membrane module configured as a membrane rack has one or more membrane elements and optionally additional measurement and control units rather than having a conveying device.

[0048] The membrane element(s) present in the membrane module, preferably in the membrane loop, are elements pre-fabricated for industrial use that contain a membrane and can be regarded as a basic unit that is no longer divisible in the membrane separation method according to the present invention. The membrane element(s) may be used as they are in the membrane module or may be placed in a pressure housing, for example, a pressure tube. The pressure tube considered in isolation may contain one or more membrane element(s), preferably up to five membrane elements. When the membrane element(s) are placed in a pressure housing, preferably a pressure tube, the membrane module may include a plurality of pressure tubes. Flow is preferably passed in series on the supply side or the holding side through the membrane elements placed in the pressure tube, which are preferably connected to the permeate side. The basic unit used as the membrane element may be a spiral-wound element known to a person skilled in the art. Subsequently, one or more spiral-wound elements may be present in the pressure housing, preferably a pressure tube.

[0049] The membrane used is preferably cellulose acetate, cellulose triacetate, cellulose nitrate, regenerated cellulose, polyimide, polyamide, polyetheretherketone, sulfonated polyetheretherketone, aromatic polyamide, polyamidoimide, polybenzimidazole, polybenzimidazolone, polyacrylonitrile, polyarylethersulfone, polyester, polycarbonate, polytetrafluoroethylene, polyvinylidene fluoride, polypropylene, terminal or lateral organically modified siloxane, polydimethylsiloxane, silicone, silicone acrylate, polyphosphazene, polyphenylsulfide, polybenzimidazole, Nylon® (Nylon-6,6), polysulfone, polyaniline, polypropylene, polyurethane, acrylonitrile / glycidyl methacrylate (PANGMA), polytrimethylsilylpropine, polymethylpentene, It has a separation-active layer made of a material selected from the group consisting of polyvinyltrimethylsilane, polyphenylene oxide, alpha-aluminum oxide, gamma-aluminum oxide, titanium oxide, silicon oxide, zirconium oxide, ceramic membrane hydrophobized with silane as described in EP 1 603 663 B1, for example, polymers having intrinsic micropority (PIM) as described in EP 0 781 166 B1, such as PIM-1, etc., or mixtures thereof. The aforementioned material may exist in a cross-linked form in the separation-active layer through the addition of an auxiliary agent, or in a form called a matrix membrane mixed with a filler, for example, carbon nanotubes, metal-organic frameworks or hollow spheres, and particles of inorganic oxide or inorganic fibers, for example, ceramic fibers or glass fibers.

[0050] It is particularly preferable to use a membrane having a polymer layer of terminal or lateral organically modified siloxane, polydimethylsiloxane, silicon acrylate, or polyimide, or a polymer layer having intrinsic micropority (PIM), e.g., PIM-1, as the separation-active layer, or for the separation-active layer to be formed by a hydrophobized ceramic membrane. It is highly particularly preferable to use a membrane formed from terminal or lateral organically modified siloxane or polydimethylsiloxane. Membranes of this type are commercially available.

[0051] In addition to the materials mentioned above, the membrane may comprise additional materials. More specifically, the membrane may comprise a support or carrier material to which a separation-active layer is applied. The selection of support materials is described in EP 0 781 166, which is incorporated by reference.

[0052] In a particularly preferred embodiment, the described method is used for membrane separation of a homogeneous catalyst. Accordingly, the component to be separated is the homogeneous catalyst, and the liquid mixture is the reaction mixture obtained from the reaction step.

[0053] Accordingly, a particularly preferred method according to the present invention is a method for continuously separating a homogeneous catalyst from a liquid reaction mixture using a membrane unit comprising at least one membrane stage and supplied with a reaction mixture containing a homogeneous catalyst coming from a reaction zone as a feed, and

[0054] Herein, the membrane stage comprises at least a carrier, one or more membrane module(s), and a feed vessel upstream of the carrier, wherein a reaction mixture is guided from the feed vessel by the carrier to one or more membrane modules as feed, which in each case, based on the reaction mixture guided to each membrane module, reduces the homogeneous catalyst in the generated permeate stream and enriches the homogeneous catalyst in the generated retained stream,

[0055] A method characterized in that the entire obtained permeate stream is divided, the recirculated permeate, which is part of the entire permeate stream, is recirculated to a feed container and / or through the feed container to the upstream of a conveyor, and the removed permeate, which is other part of the entire permeate stream, is discharged from at least one membrane stage and from a membrane unit on the permeate side.

[0056] The reaction mixture comes from a reaction zone suitable for each method, preferably one or more suitable reactors. A retained stream containing at least most of the homogeneous catalyst is preferably recirculated to the reaction zone, particularly the reactor(s), after optionally pre-purification and / or post-treatment of the catalyst. Since the material flow rate from the reaction zone may vary for manufacturing-related reasons, the control- and plant-related functions described above may also be used for the separation of the homogeneous catalyst.

[0057] In a reaction zone, preferably in a reactor(s), a homogeneous catalytic reaction is carried out accordingly. These reactions may be the following: oxidation, epoxidation, hydroformylation, hydroaminomethylation, hydrocyanation, hydrocarboxylation, hydrocarbonylation, hydrocarboxyalkylation, alkoxycarbonylation, amination, ammoxidation, oximation, hydrosilylation, ethoxylation, propoxylation, carbonylation, telomerization, metadecomposition, Suzuki coupling, and hydrogenation.

[0058] Hydroformylation is preferred. Hydroformylation is particularly the hydroformylation of an olefin having 3 to 15 carbon atoms, preferably 8 to 12 carbon atoms. Hydroformylation is preferably a homogeneous catalyzed hydroformylation in which the catalytic system is (completely) dissolved in the liquid phase of the reaction mixture. The catalytic system for hydroformylation preferably comprises a transition metal from Group 8 or 9 of the periodic table (PTE) and at least one organic phosphorus-containing ligand. Suitable phosphorus-containing ligands are known to those skilled in the art, but are preferably monodentate phosphorus-containing ligands, e.g., tris(2,4-di-tert-butylphenyl)phosphite.

[0059] The transition metal used may be, in particular, iron, ruthenium, iridium, cobalt, or rhodium, preferably cobalt or rhodium, more preferably rhodium. The catalytically active species discussed are (ligand)-carbonyl complexes of metal atoms formed in a liquid reaction mixture under increased pressure and increased temperature.

[0060] Hydroformylation may be carried out in the presence of a solvent, in which case the solvent must be compatible with the hydroformylation method. The solvent used may be a suitable solvent for hydroformylation known to a person skilled in the art, for example, alkanes, aromatic hydrocarbons, water, ethers, esters, ketones, alcohols, and reaction products or by-products of hydroformylation, such as aldehydes and condensation products of aldehydes.

[0061] In addition, hydroformylation can be performed at a pressure of 10 to 400 bar, preferably 15 to 270 bar. The temperature in hydroformylation can be 70 to 250°C, preferably 100 to 200°C, more preferably 120 to 160°C.

Claims

Claim 1 A method for continuously separating components from a liquid mixture using a membrane unit comprising at least one membrane stage and supplied with a liquid mixture as a feed, wherein the membrane stage comprises at least a conveyor, a plurality of membrane modules connected in series with respect to each other, and a feed container upstream of the conveyor, wherein the mixture is guided from the feed container to the plurality of membrane modules as a feed by the conveyor, which in each case causes the component to be separated to be reduced in the permeate stream generated from each membrane module and enriched in the retained stream generated from each membrane module, or vice versa, based on the mixture guided to each membrane module, wherein the entire permeate stream obtained from the last membrane stage is divided, and the recirculated permeate, which is part of the entire permeate stream, is recirculated to and / or through the feed container upstream of the conveyor, and the removed permeate, which is another part of the entire permeate stream, is discharged from the last membrane stage and from the permeate-side membrane unit, wherein the recirculated permeate to and / or through the feed container upstream of the conveyor is hydraulic rather than by the conveyor A method characterized by being performed by means, that is, achieved by a pressure difference existing between the permeable side of a membrane unit and the suction side of a transport device or supply container. Claim 2 A method according to claim 1, wherein one of three streams selected from a feed to a membrane unit, a permeate removed, and a retained material from the membrane unit is applied to a preceding or downstream process step, and one additional stream of the three is controlled to a target value. Claim 3 A method according to claim 1 or 2, wherein the material flow rate of the recirculated permeate may vary and is established according to the material flow rate of the removed permeate. Claim 4 A method according to claim 1 or 2, wherein, in order to obtain a desired amount of the total permeate stream, the pressure on the holding side, the pressure on the permeating side, the generated transmembrane pressure (TMP), or a combination thereof is controlled, and the membrane module temperature can be additionally controlled. Claim 5 A method according to claim 1 or 2, wherein both the material flow rate and the pressure of the permeate to be removed are controlled by an adjustable flow resistor. Claim 6 A method according to claim 1 or 2, wherein the material flow rate of the permeate to be removed is controlled in a closed-loop or continuous closed-loop manner, either directly or indirectly, depending on the filling level of the feed container, and wherein the material flow rate of the permeate to be removed is increased as the filling level of the feed container rises and the material flow rate of the permeate to be removed is decreased as the filling level of the feed container falls, based on a target value fixed in advance for the filling level of the feed container. Claim 7 A method according to claim 1 or 2, wherein the pressure on the holding side (holding pressure) is controlled by a conveying device that supplies the feed to a plurality of membrane modules, and optionally by an additional actuator or feed pressure regulator, or by a combination of a pressure gauge and an adjustable flow resistor or a valve on the holding side. Claim 8 A method according to claim 1 or 2, wherein the material flow rate on the holding side (retained material flow rate) is controlled by a closed-loop material flow controller on the holding side comprising at least a material flow meter and an adjustable flow resistor or valve, or by a combination of a material flow meter and a conveying device. Claim 9 A method according to claim 1 or 2, wherein the component is a homogeneous catalyst separated from the reaction mixture. Claim 10 A method in which the conveying device is a pump, as in paragraph 1 or 2. Claim 11 A method for continuously separating a homogeneous catalyst from a liquid reaction mixture using a membrane unit comprising at least one membrane stage and a reaction mixture from a reaction zone, wherein the membrane stage comprises at least one conveyor, a plurality of membrane modules connected in series with each other, and a feed vessel upstream of the conveyor, wherein the reaction mixture is guided from the feed vessel to the plurality of membrane modules as a feed by the conveyor, which in each case reduces the homogeneous catalyst in the generated permeate stream and enriches it in the generated retained stream based on the reaction mixture guided to each membrane module, wherein the entire obtained permeate stream is divided, the recirculated permeate, which is part of the entire permeate stream, is recirculated to the feed vessel and / or through the feed vessel upstream of the conveyor, and the removed permeate, which is another part of the entire permeate stream, is discharged from at least one membrane stage and from the membrane unit on the permeate side. Claim 12 A method according to claim 11 in which the reaction mixture is introduced from a reaction zone where a homogeneous catalytic reaction is being performed. Claim 13 A method according to claim 12, wherein the homogeneous catalytic reaction is selected from the group consisting of the following reactions: oxidation, epoxidation, hydroformylation, hydroaminomethylation, hydrocyanation, hydrocarboxylation, hydrocarbonylation, hydrocarboxyalkylation, alkoxycarbonylation, amination, ammoxidation, oximation, hydrosilylation, ethoxylation, propoxylation, carbonylation, telomerization, metalysis, Suzuki coupling, and hydrogenation. Claim 14 In paragraph 13, a method in which the homogeneous catalytic reaction is hydroformylation.

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