Improved variable and self-regulating permeate recirculation in organophilic nanofiltration

Abstract

The invention relates to improved variable and self-regulating permeate recirculation in organophilic nanofiltration, providing improvements in control and process technology for methods for continuous removal of components from liquid mixtures using membrane units comprising at least one membrane stage. The improvement is that a part of the total permeate stream is recirculated to the feed vessel and / or outside the feed vessel but upstream of the delivery device, and the remainder of the total permeate stream is removed, wherein the recirculated permeate has a higher concentration of the component to be separated than the removed permeate. The disclosed method is particularly useful for separating homogeneously dissolved catalysts from liquid reaction mixtures.

Description

Technical Field

[0001] This invention relates to improvements in 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 lies in recirculating a portion of the total permeate stream to a feed container and / or upstream of the conveying device but outside the feed container, and removing the remainder of the total permeate stream, wherein the recirculated permeate has a higher concentration of the component to be separated compared to the removed permeate. The method disclosed herein is particularly useful for separating homogeneously dissolved catalysts from liquid reaction mixtures. Background Technology

[0002] Membrane separation methods, such as those for separating homogeneously dissolved catalysts from a reaction mixture, are known in principle in the prior art. Reference is made herein by way of example to WO 2014 / 131623 A1.

[0003] Improvements in control techniques have been described for this type of membrane separation method. For example, International Application WO 2014 / 183952 A1 discloses a membrane separation method for separating homogeneously dissolved catalysts from a reaction mixture, wherein two parameters, namely the permeate volume flow rate of the membrane separation unit and the retention of the membrane separation unit, are controlled to remain constant in order to compensate for fluctuations in operating conditions, particularly fluctuations in the volumetric flow rate of the reaction mixture from the reaction zone.

[0004] To keep the aforementioned controlled variables constant, WO 2014 / 183952 A1 proposes a flow resistor for regulating or keeping constant the volumetric flow rate of residual material, as well as closed-loop control of temperature and / or pressure in the overflow loop to regulate or keep constant the retention.

[0005] One problem with the proposed methods is that not all methods are effective at maintaining a constant retention rate in the membrane separation unit; rather, given the equipment throughput and the membrane area already installed in the membrane separation unit, what is needed is to optimize, and typically maximize, the retention rate of the membrane separation unit during the proposed method. Closed-loop control via a flow resistor, as described in WO 2014 / 183952 A1, may have the effect that the installed membrane area is not operating at the optimal transmembrane pressure but below that optimal transmembrane pressure. The methods described therein may also have the effect that, for a given total throughput of the equipment and the resulting permeate stream removed from it (the portion of the permeate stream exported from the membrane stage or membrane separation unit on the permeate side), based on a simple mass balance and taking into account the removed permeate stream (the portion of the total permeate stream recirculated back into the membrane separation unit), the total permeate stream and the resulting recirculated permeate stream will be smaller than possible and / or desired.

[0006] Another drawback of the method described in WO 2014 / 183952 A1 is that it considers both the container and the pump used for the permeate to achieve a closed-loop control system with constant permeate on the permeate side. However, the provision of pumps to pump the permeate from the permeate container to the overflow loop or feed container is associated with increased equipment inventory and costs, such as for procurement or for operation, maintenance and repair, which may also lead to additional equipment downtime and thus production stoppage.

[0007] Furthermore, the installation of containers often results in a portion of the membrane separation stage on the permeate side not being hydraulically filled, which can increase safety risks, especially when using toxic fluids. Additionally, besides the feed container, the container on the permeate side creates the possibility that closed-loop control of these two container states could lead to opposite fluctuations. Summary of the Invention

[0008] Therefore, the problem solved by the present invention is to provide a cheaper method for the continuous separation of components from a mixture, preferably for the continuous separation of a homogeneous catalyst from a reaction mixture. Another problem solved by the present invention is to provide a self-regulating permeate circulation in the method for the continuous separation of components from a mixture, preferably for the continuous separation of a homogeneous catalyst from a reaction mixture, wherein the installed membrane area can be optimally utilized under different loading conditions, for example, for maximizing the yield.

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

[0010] The method according to the invention is a method for continuously separating components from a liquid mixture using a membrane unit comprising at least one membrane stage and fed with the mixture as feed, wherein the membrane stage comprises at least a conveying device, at least two membrane modules connected in series, and a feed container upstream of the conveying device.

[0011] The method includes the following steps:

[0012] The mixture from the feed container is directed as feed to the first of the at least two membrane modules via a conveying device, which in each case depletes the component to be separated in the resulting permeate stream from the first membrane module based on the mixture directed to the first membrane module and enriches it in the resulting residual stream from the first membrane module.

[0013] The permeate from the first membrane module is directed to the second membrane module, which in each case depletes the component to be separated in the resulting permeate stream from the second membrane module based on the permeate from the first membrane module and enriches it in the resulting permeate stream from the second membrane module.

[0014] Its features

[0015] The at least two membrane modules are connected to each other on the permeate side in such a way that each of the at least two permeate streams is directed into a common conduit, which generates a total permeate stream in the conduit.

[0016] The at least two membrane modules are connected to a common conduit in opposite directions on the permeate side, such that a portion of the total permeate stream, i.e., the recirculated permeate, is at least partially recirculated to the feed container and / or upstream of the conveying device but outside the feed container, while the remainder of the total permeate stream, i.e., the removed permeate, is at least partially guided out of the membrane stage, wherein the recirculated permeate has a higher concentration of the component to be separated than the removed permeate.

[0017] In the context of this invention, the term "component to be separated" refers to a component that permeates through the membrane to a lesser extent in proportion and / or according to permeability, i.e., a component retained by the membrane. Therefore, for the particular membrane module in question, the component to be separated has a positive retention. The component to be separated may also be a single specific chemical substance or a group of chemical substances considered to have commonalities for process technology purposes.

[0018] The method according to the invention may also include more than two membrane modules. If three or more membrane modules are present, it is preferable to direct the permeate from the previous membrane module to the subsequent membrane module (not applicable to the last membrane module), resulting in that, in each case, based on the permeate from the previous membrane module, the component to be separated is depleted in the resulting permeate stream from the subsequent membrane module and enriched in the resulting permeate stream from the subsequent membrane module.

[0019] In the context of this invention, "membrane unit" refers to the entire membrane separation unit supplied with a liquid mixture containing components to be separated. A membrane unit consists of at least one membrane stage. Therefore, as the name suggests, downstream further processing or purification steps and any storage of removed permeate in a container are not part of the membrane unit.

[0020] The term "membrane stage" refers to at least a portion of a membrane unit and includes at least one delivery device (e.g., a pump) and at least two membrane modules. If only a single membrane stage exists, the terms "membrane unit" and "membrane stage" should be understood as synonyms. A membrane stage has a feed container connected upstream of the delivery device, into which a liquid mixture (e.g., an output from a homogeneous catalytic reaction) is introduced and guided from the feed container to the one or more membrane elements. Recirculated permeate may also be guided into the feed container. Additionally or alternatively, recirculated permeate may not be guided into the feed container but rather upstream of the delivery device, i.e., at a location in a conduit between the feed container and the delivery device.

[0021] In terms of equipment technology, the term "membrane assembly" used to describe the present invention refers to a sub-unit of the membrane level. Therefore, a membrane assembly is an interconnection of one or more membrane elements. A membrane assembly can be configured as a membrane ring or a membrane frame. A membrane ring is understood to refer to a sub-unit in which at least one membrane element and at least one conveying device are present, through which a moving overflow circulation is generated. In contrast, the term "membrane frame" refers to a sub-unit having the characteristic of having at least one membrane element but no conveying device and therefore not generating a moving overflow circulation.

[0022] In the context of this invention, the term "membrane element" refers to a membrane or a structure or device containing a membrane, where the desired separation of a substance actually occurs, i.e., the separation of the component from a mixture or the separation of a homogeneous catalyst from a reaction solution. These can be, for example, helical wound elements used in many applications of industrial membrane separation.

[0023] The basis of this invention is that the total permeate stream from the final membrane stage is split only into recirculated permeate and removed permeate. If there is only one membrane stage, that single membrane stage is also the final membrane stage. If there are two or more membrane stages, no splitting occurs in the first membrane stage; instead, the entire permeate stream is directed to the next membrane stage. Then, as described above, splitting occurs only in the final membrane stage. In the context of this invention, the term "split" refers only to the amount or mass flow rate of the total permeate and explicitly indicates that there are no additional separation steps to remove other components from the total permeate, i.e., no distillation, no extraction, no crystallization, no adsorption, and no further membrane separation steps.

[0024] One advantage of the method according to the invention is that a portion of the total permeate stream from the last membrane stage, i.e., the recirculated permeate, does not leave the membrane stage and / or membrane unit until then, for example, via a permeate container for recirculation, but remains within the at least one membrane stage and / or membrane unit and is thus recirculated to the feed container and / or upstream of the feed container but outside the feed container. This eliminates the need for a downstream pump to return the permeate to the overflow loop or to the feed container, since permeate recirculation is self-regulating according to the load. Therefore, the recirculation of the recirculated permeate to the feed container and / or upstream of the feed container but outside the feed container is achieved not by a conveying device but by hydraulic means (i.e., by the pressure difference existing between the permeate side of the membrane unit and the feed device or the suction side of the feed container). In other words, there is no additional conveying device, particularly no pump, between the permeate side and the feed container.

[0025] The portion of the total permeate stream removed from the membrane stage or membrane unit (i.e., the removed permeate) can be directed to downstream process steps. In the context of this invention, the term "process step" can be understood to refer to any downstream process, such as further processing or purification process steps or combinations thereof. This particularly includes (further) reactions of the removed components, purification by known methods (such as distillation, evaporation), etc. Downstream distribution or transport process steps are also possible. The permeate can also be pre-stored in a suitable container, such as a permeate container, prior to downstream process steps. If a permeate container is present, the splitting of the total permeate according to the invention occurs upstream of the permeate container, such that only the removed permeate enters the permeate container. It is evident that multiple process steps, optionally via pre-storage, can be carried out sequentially, for example, purification, followed by conversion of the purified components and further purification of the reaction products.

[0026] According to the invention, at least two membrane modules are connected to a common conduit in opposing directions on the permeate side, such that at least a portion of the total permeate (recirculated permeate) from the last membrane module is at least partially circulated to the feed container and / or upstream of the conveying device but outside the feed container, while the remaining portion of the total permeate (removed permeate) from the first membrane module is at least partially guided out of the membrane stage on the residue side. Thus, permeate from all membrane modules present in such a membrane stage is guided to the common conduit and separated therein. In the common conduit, between the connection of the first membrane module to the conduit and the connection of the last membrane module to the conduit, preferably no control actuators, such as valves or separation units, are present. However, this does not preclude the presence of non-regulating actuators, i.e., actuators that exist but do not interfere with the process, such as constantly and fully open valves. In terms of equipment technology, what is achieved simply by the concept of the invention is that the recirculated permeate has a higher concentration of the component to be separated than the removed permeate. In the unfavorable situation where there is no feed from upstream process steps to the feed container, the functions associated with these devices and controls have the effect of completely recycling permeate from all components into the feed container or membrane unit.

[0027] This method ensures that the different permeates from the at least two membrane modules are not completely mixed, meaning that a mixture with the same concentration of the component to be separated is formed in a common channel. The ultimate goal is for the recirculated permeate to have a higher concentration of the component to be separated than the removed permeate, which is impossible with complete mixing. This can also be achieved by… Figure 1To illustrate: For example, in the process of the present invention, the result must be that the concentration of the component to be separated in the recirculated permeate is greater than the concentration of the component to be separated in the removed permeate. Therefore, based on the concentration of the component to be separated, there is always a case where F-11>F-12. A preferred additional result is that the concentration of the component to be separated in the recirculated permeate is greater than the concentration in the common conduit between the connection point of the first membrane module and the connection point of the last membrane module, wherein the concentration of the component to be separated is greater than the concentration of the component to be separated in the removed permeate. Based on the concentration of the component to be separated, the corresponding case is F-11>F-10>F-12. Complete mixing can be prevented in various ways by device technology. A preferred option according to the invention is that the characteristics of the common conduit (e.g., length, diameter, etc.) can be adjusted to avoid complete mixing of the total permeate.

[0028] To control the outlet flow rates of the recirculated permeate and the removed permeate, at least one adjustable flow resistor can be present on the permeate side to control the mass flow rate of the permeate. In the context of this invention, a flow resistor is an actuator capable of controlling the mass flow rate of the flow, such as a valve. A further preferred embodiment is one in which at least two adjustable flow resistors, preferably exactly two, are present on the permeate side. This means that the mass flow rate of the removed permeate and the permeate pressure, particularly in a common conduit, can be adjusted. These at least two adjustable flow resistors are, in particular, valves. The valves are preferably not located between the connection between the first membrane assembly and the conduit and the connection between the last membrane assembly and the conduit, but rather outside the connection with the conduit in the direction of flow of the recirculated or removed permeate.

[0029] Regarding the membrane separation method according to the invention, a stable external mass balance exists, meaning that the mass flow rate of the feed supply to the membrane unit corresponds to the mass flow rate of the permeate and / or residual streams exiting the membrane unit. This can be utilized. In a preferred embodiment of the invention, the mass flow rate of one of the three streams selected from the feed to the membrane unit, the removed permeate, and the residual stream from the membrane unit is defined by preceding or downstream process steps, and another of the three streams is controlled to a target value, such as a constant residual stream rate, a constant feed to residual stream ratio, etc. This also results in the third of the three streams due to the external mass balance. The absolute mass flow rate can be adjusted substantially by scaling and thus by referring to the membrane module size and the number of membrane modules as needed. In a preferred embodiment, the ratio of the residual mass flow rate to the mass flow rate is 1% to 99%, preferably 10% to 90%, and more preferably 15% to 80%. In a further preferred embodiment, the ratio of the mass flow rate of removed permeate to the total permeate mass flow rate is 1% to 99%, preferably 30% to 98%, more preferably 60% to 97%. In the context of this invention, a "process step" refers to equipment or process unit, such as upstream or downstream chemical reactions using permeate / residue, further separation steps, such as thermal separations like membrane evaporation or distillation, or logistics, i.e., especially upstream or downstream tank farms or distribution operations. Upstream process steps are particularly continuous process steps through which a liquid mixture is continuously supplied to the membrane separation process of this invention. These process steps are preferably continuous chemical reactions, such as hydroformylation or alkoxycarbonylation, as detailed below.

[0030] Furthermore, more specifically, there exists a stable internal mass balance (the total permeate mass flow rate, i.e., the sum of all permeate streams from the membrane module, corresponding to the sum of the mass flow rates of the recirculated permeate and the removed permeate). According to the invention, the internal mass balance is preferably largely independent of the external mass balance, meaning that the external mass balance is, in principle, merely a lower limit of the internal mass balance. Therefore, according to the invention, it is preferred that the mass flow rate of the recirculated permeate can fluctuate and be established based on, preferably directly based on (i.e., without any permeate container in between) the mass flow rate of the removed permeate. This also means that the total permeate mass flow rate can be controlled independently of the aforementioned external mass balance without considering technical limitations (caused by pumps, flow resistors, membrane area, etc.), provided that the total permeate mass flow rate is greater than the removed permeate mass flow rate.

[0031] The total permeate mass flow rate depends on various parameters, such as the temperature (of the membrane module) or the concentration of each component in the mixture. Therefore, in a preferred embodiment of the invention, the pressure on the permeate side and / or the pressure on the permeate side, or the resulting transmembrane pressure (TMP = pressure difference between the permeate side and the permeate side), and optionally the membrane module temperature, are controlled to optimize the amount of total permeate flow or to obtain the desired amount of total permeate flow.

[0032] The membrane separation method according to the invention can be adjusted in various ways in terms of control technology based on the respective controlled variables, the actuators present that influence the controlled variables, and the control priority. Various controlled variables exist in this method, such as the filling level of the feed container, the pressures on the permeate and residue sides, resulting in their differences in transmembrane pressure (TMP), and the mass flow rates of the residue and permeate, which may be affected by various actuators such as conveying devices or one or more adjustable flow resistors.

[0033] In a preferred embodiment, the membrane separation method according to the invention is regulated in terms of control technology in such a way that the mass flow rate of the permeate and the total mass flux (TMP) remain constant. Therefore, these two parameters have the highest control priority, wherein the exact order of control priority can be fixed as needed, i.e., the mass flow rate of the permeate may have the highest control priority, while TMP has the second highest control priority, and vice versa.

[0034] In the method according to the invention, the mass 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 via a conveying device for the (first) membrane stage. Specific embodiments for establishing the mass flow rate of the feed to the (first) membrane stage are variable and generally depend on technical limitations, such as the type of pump selected, the delivery rate, and the delivery pressure. For example, pumps with direct speed control, such as gear pumps, piston pumps, piston diaphragm pumps, or optionally multistage centrifugal pumps, can be used to control the feed mass flow rate. Another option for controlling the mass flow rate is to use a centrifugal pump and an adjustable flow resistor such as a (control) valve. Another option is to use a pump, such as a gear pump, piston pump, piston diaphragm pump, or centrifugal pump, in conjunction with, for example, an adjustable return conduit from the pressure section to the pump suction side.

[0035] The pressure on the permeate side (permeate pressure) can be controlled by a delivery device and / or optionally, other actuators such as a pressure regulator. The permeate pressure in the method according to the invention can be 1 to 100 bar, preferably 10 to 80 bar, and more preferably 30 to 60 bar. The permeate pressure is greater than the pressure on the permeate side (permeate pressure). The transmembrane pressure formed by the difference between the permeate pressure and the permeate pressure can be 1 to 90 bar, preferably 10 to 80 bar, and more preferably 30 to 60 bar.

[0036] The permeate pressure can then be 0 to 50 bar, preferably 0 to 10 bar, and more preferably 1 to 5 bar. In a preferred embodiment, the permeate pressures of all membrane modules are similar (differences of no more than 10%) or identical, which can be further preferably established via a pressure regulator on the permeate side. This is because the pressure of each membrane module is preferably independent of the total pressure on the permeate side, such as the common conduit, and is not controlled.

[0037] The membrane unit or individual membrane stages preferably include a closed-loop control system for the pressure on the permeate side, which includes at least a delivery device and a pressure gauge, wherein the permeate pressure can be adjusted according to the pressure gauge. Here, the permeate pressure can be controlled based on the permeate pressure measured (by the pressure gauge) by adjusting, for example, the delivery volume of the delivery device and optionally by another actuator (e.g., a pressure regulator), wherein, based on a pre-fixed target value for the permeate pressure, the delivery volume of the delivery device decreases when the permeate pressure increases and / or rises, and increases when the permeate pressure decreases and / or falls.

[0038] Alternatively, the residual pressure can be controlled via a combination of a pressure gauge on the residual side and an adjustable flow resistor, particularly a valve. The residual pressure can be controlled here based on the residual pressure measured (via the pressure gauge), for example via valve settings, wherein, based on a pre-fixed target residual pressure value, the valve is further opened when the residual pressure increases and / or rises, and further closed when the residual pressure decreases and / or falls.

[0039] In the method according to the invention, the mass flow rate of the permeate (permeate mass flow rate) is preferably controlled by a mass flow regulator on the permeate side, the mass flow regulator comprising at least one mass flow meter and an adjustable flow resistor, preferably a valve. Here, the permeate mass flow rate can be controlled by adjusting the mass flow regulator according to the measured permeate mass flow rate, wherein, based on a pre-fixed target value for the permeate mass flow rate, the valve of the mass flow regulator is further closed when the permeate mass flow rate increases and / or rises, and the valve of the mass flow regulator is further opened when the permeate mass flow rate decreases and / or falls. The permeate pressure can then be freely selected within the range of the minimum necessary load and the maximum possible load of the membrane stage.

[0040] In another embodiment, alternatively, the mass flow rate of leachate can be controlled by a combination of a mass flow meter and a conveying device. Here, the mass flow rate of leachate can be controlled, for example, by adjusting the conveying volume of the conveying device according to the measured mass flow rate of leachate, wherein, based on a predetermined target value for the mass flow rate of leachate, the conveying volume of the conveying device decreases when the mass flow rate of leachate increases and / or rises, and increases when the mass flow rate of leachate decreases and / or falls.

[0041] Sensors and actuators for the aforementioned closed-loop control of mass flow rate (including at least a conveying device or adjustable flow resistor and mass flow meter) on the residue side and for the aforementioned closed-loop control of pressure (including at least a conveying device or adjustable flow resistor and pressure gauge) on the residue side can be connected to each other in any desired manner for control purposes, in order to control the two controlled variables, residue mass flow rate and residue pressure. In the method according to the invention, the relative priorities of the two controlled variables, residue mass flow rate and residue pressure, can be selected as needed. The priority of these two controlled variables (and therefore TMP) is preferably higher than the priority of all other controlled variables in the membrane separation stage, i.e., having the fastest response characteristics.

[0042] The mass flow rate of permeate removed (from the final membrane stage) directly or indirectly depends on the fill level of the feed container, preferably under continuous closed-loop control. This is characterized by a pre-fixed target fill level for the feed container, preferably 20% to 80%, more preferably 30% to 70% of the maximum possible fill level. The mass flow rate of the removed permeate increases as the fill level of the feed container increases and decreases as the fill level decreases. In this type of closed-loop control, the feed container is not fully filled because if it were, the fill level would be at or above the upper edge of its measurement range and therefore unknown, making closed-loop control at the target value impossible. The mass flow rate of the removed permeate is regulated, in particular, via at least one adjustable flow resistor. In the case of continuous closed-loop control, this preferably maintains a constant fill level for the feed container. Depending on the fill level of the feed container, the effect of the closed-loop control principle is, for example, that when a low level is reached in the feed container, the mass flow rate of the removed permeate decreases even further and possibly no more permeate is removed.

[0043] The temperatures of the feed, residue, and permeate streams can vary over a wide range. The temperature of each of the feed, residue, and permeate streams is preferably -30°C to 150°C, more preferably 0°C to 100°C, and most preferably 20°C to 80°C.

[0044] The above-described mode of execution of the method according to the invention also contributes to the control technology through the construction of the membrane unit, which will be described in more detail below.

[0045] In the method according to the invention, the membrane unit for separating components from the mixture comprises at least one membrane stage. Alternatively, the membrane unit may comprise multiple membrane stages connected in series with each other. In this case, the total permeate stream is diverted only in the last membrane stage.

[0046] Based on the above definition, the membrane stage of the membrane unit used in the method according to the invention includes a conveying device. The conveying device that guides the mixture as feed to the at least two tandemly connected membrane modules is preferably adjustable in terms of its conveying volume. The feed pressure of the at least two membrane modules can be from 1 to 100 bar, preferably from 10 to 80 bar, and more preferably from 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 diaphragm pumps, rotary piston pumps, or gear pumps.

[0047] The membrane stage of the membrane unit according to the invention further includes at least two membrane modules connected in series. The number of membrane modules is theoretically unlimited; rather, it depends on general process parameters and the required membrane area. In a preferred embodiment, the membrane stage includes more than two membrane modules, more preferably connected in series. The mixture arriving at the membrane unit is directed to the (first) membrane stage, where it is fed as feed to the one or more membrane modules via a conveying device. Within the membrane stage, permeate and residue are separated, with the permeate stream discharged from each present membrane module.

[0048] Therefore, in the at least two membrane modules present, a number of permeate streams corresponding to the number of membrane modules are generated. As described above, the membrane modules are connected to a common conduit in opposite directions on the permeate side. In contrast, only one residual stream is obtained because the residual from the first membrane module is directed to the next membrane module, from which further permeate is separated, and then the residual from the second membrane module is directed to the next membrane module, or, if only two membrane modules are present, it is discharged from the membrane stage and / or membrane unit.

[0049] The membrane stage in the method according to the invention includes a container upstream of the conveying device, from which feed is directed as feed to the at least two membrane modules. If only one membrane stage exists, both the feed of the membrane stage and the recirculated permeate from the membrane stage can be introduced into and collected in a feed container, and then directed as feed to the at least two membrane modules via the membrane device. If more than one membrane stage exists, both the feed of the first membrane stage and the permeate from one of the subsequent membrane stages can be collected in the feed container of the first stage, while permeate from the corresponding previous membrane stage, and permeate from the subsequent stage or the recirculated permeate from the last membrane stage can be collected in the feed containers of the (one or more) subsequent stages. The construction and specifications of such feed containers are known to those skilled in the art. The feed container preferably includes a measuring unit for the fill level. In those variations, the corresponding recirculated flow may also be directed upstream of the conveying device but outside the feed container, instead of into the feed container.

[0050] The membrane stage may also include sensors and / or actuators to enable the aforementioned preferred control-related functions. These control-related functions particularly include measurement and / or control units for parameters such as temperature, pressure, mass flow rate, etc. The corresponding measurement and control units are known to those skilled in the art.

[0051] According to the invention, at least two membrane modules are present in the membrane stage, comprising one or more membrane elements. In principle, as described above, the membrane module can be configured as a membrane ring or a membrane frame. The membrane module present in the membrane stage according to the invention is preferably a membrane ring.

[0052] A membrane ring includes one or more membrane elements and at least one delivery device. Preferably, the membrane ring includes only one delivery device. This delivery device differs from the delivery device of the corresponding membrane stage; conversely, in this case, the entire system has at least two delivery devices. The delivery device of the membrane ring is typically responsible for circulating the membrane ring, while the delivery device of the membrane stage is typically responsible for pressurizing the membrane module or membrane ring. The delivery device used can be any suitable pump. Such pumps are known to those skilled in the art. The pump used as a delivery device within the membrane ring is preferably a centrifugal pump. The delivery device generates a moving overflow circulation. Overflow circulation can ideally improve mass transfer and thus improve the separation performance of the membrane. Overflow circulation can be regulated here independently of this most important control concept and external and internal mass balance.

[0053] The membrane ring may also additionally include measurement and / or control units for parameters such as temperature, differential pressure (axial pressure drop), circulation rate, etc., such as heaters or coolers to regulate temperature. Other measurement and control units are known to those skilled in the art. In a preferred embodiment, the pressures present in all membrane rings of the membrane stage are similar (deviation <10%) or identical. This at least similar pressure can be established without a specific control unit, but can also be established by a pressure regulator. The pressure regulator for permeate pressure preferably has the slowest response characteristics compared to other actuators, i.e., closed-loop control of permeate-side mass flow rate, closed-loop control of residual mass flow rate, and closed-loop control of residual pressure.

[0054] Compared to the membrane rings described above, membrane modules configured as membrane frames do not have a conveying device, but instead have one or more membrane elements and optional additional measurement and control units.

[0055] The membrane element, present in the membrane module, preferably in the membrane ring, is a membrane-containing element prefabricated for industrial use and can be considered a basic unit that cannot be further separated in the membrane separation method according to the invention. The membrane element can be used as is in the membrane module or can be disposed in a pressure housing, such as a pressure tube. A pressure tube, considered in isolation, can contain one or more membrane elements, preferably up to five. If the membrane element is disposed in a pressure housing, preferably a pressure tube, the membrane module can include multiple pressure tubes. Fluid preferably passes in series through the membrane element disposed in the pressure tube on the feed or permeate side, and is preferably connected on the permeate side. The basic unit used as the membrane element can be a helical wound element known to those skilled in the art. One or more helical wound elements can then be present in the pressure housing, preferably a pressure tube.

[0056] The membranes used are preferably those having a separation active layer made of materials selected from: cellulose acetate, cellulose triacetate, cellulose nitrate, regenerated cellulose, polyimide, polyamide, polyetheretherketone, sulfonated polyetheretherketone, aromatic polyamide, polyamidoimide, polybenzimidazole, polybenzimidazole ketone, polyacrylonitrile, polyarylethersulfone, polyester, polycarbonate, polytetrafluoroethylene, polyvinylidene fluoride, polypropylene, terminally or side-position organically modified siloxanes, polydimethylsiloxane, organosilicon, organosilicon acrylates, polyphosphazene, polyphenylene sulfide, polybenzimidazole, etc. Nylon 6,6, polysulfone, polyaniline, polypropylene, polyurethane, acrylonitrile / glycidyl methacrylate (PANGMA), polytrimethylsilylpropyne, polymethylpentyne, polyvinyltrimethylsilane, polyphenylene ether, α-alumina, γ-alumina, titanium dioxide, silicon dioxide, zirconium oxide, silane-hydrophobic ceramic membranes as described in EP 1 603 663 B1, polymers (PIMs) with inherent microporous properties as described in EP 0 781 166 B1 such as PIM-1 and others, or mixtures thereof. The above substances can be cross-linked in the separation active layer by adding additives, or in the form of a so-called mixed matrix membrane with fillers such as carbon nanotubes, metal-organic frameworks or hollow spheres, and inorganic oxides or inorganic fiber particles (e.g., ceramic fibers or glass fibers).

[0057] Particularly preferred are membranes having a polymer layer formed from a polymer (PIM) with inherent micropority, such as PIM-1, with terminal or side-position organic modification of the siloxane, polydimethylsiloxane, organosilicone acrylate, or polyimide, as the separation active layer, or wherein said separation active layer is formed from a hydrophobic ceramic membrane. Membranes formed from terminal or side-position organic modification of the siloxane or polydimethylsiloxane are very particularly preferred. Such membranes are commercially available.

[0058] In addition to the materials mentioned above, the membrane may also include other materials. More specifically, the membrane may include a support or carrier material to which a separation active layer has been applied. The selection of the carrier material is described in the explicitly cited document EP 0 781 166.

[0059] In a particularly preferred embodiment, the method is used for membrane separation of a homogeneous catalyst. The components to be separated are the homogeneous catalyst, and the liquid mixture is a reaction mixture obtained from the reaction stage.

[0060] Therefore, a particularly preferred method according to the 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 fed with a reaction mixture containing the homogeneous catalyst from the reaction zone, wherein the membrane stage comprises at least a conveying device, at least two membrane modules connected in series, and a feed container upstream of the conveying device.

[0061] The method includes the following steps:

[0062] The reaction mixture from the feed container is directed as feed to the first of the at least two membrane modules via a conveying device, which in each case depletes the homogeneous catalyst in the resulting permeate stream from the first membrane module based on the mixture directed to the first membrane module and enriches it in the resulting residual stream from the first membrane module.

[0063] The permeate stream from the first membrane module is directed to the second membrane module, which in each case depletes the homogeneous catalyst in the resulting permeate stream from the second membrane module based on the permeate from the first membrane module and enriches it in the resulting permeate stream from the second membrane module.

[0064] Its features

[0065] The at least two membrane modules are sequentially connected to each other on the permeate side in such a manner that the at least two permeate streams form a total permeate stream in which complete mixing of the individual permeate streams does not occur, and

[0066] A portion of the total permeate stream, namely the recirculated permeate, is recycled to the feed container and / or upstream of the conveying device but outside the feed container, and the remainder of the total permeate stream, namely the removed permeate, is removed from the membrane stage, wherein the recirculated permeate has a higher homogeneous catalyst concentration than the removed permeate.

[0067] The reaction mixture originates from a reaction zone suitable for the corresponding method, preferably one or more suitable reactors. Optionally, after pre-purification and / or post-treatment of the catalyst, the permeate stream containing at least a majority of the homogeneous catalyst is preferably recycled back to the reaction zone, particularly the reactor. Since the mass flow rate from the reaction zone can vary for production-related reasons, the aforementioned control and equipment-related functions can also be used for the separation of the homogeneous catalyst.

[0068] Homogeneous catalytic reactions are carried out accordingly in the reaction zone, preferably in one or more reactors. These reactions can be the following: oxidation, epoxidation, hydroformylation, hydroamination, hydroaminomethylation, hydrocyanation, hydrocarboxylation, alkylation, hydrocarboxylation, alkoxycarbonylation, amination, ammoxidation, oximeation, hydrosilylation, ethoxylation, propoxylation, carbonylation, telomerization, substitution, Suzuki coupling, and hydrogenation.

[0069] Hydroformylation is preferred. Hydroformylation is particularly the hydroformylation of alkenes having 3 to 15 carbon atoms, preferably 8 to 12 carbon atoms. Hydroformylation is preferably homogeneous catalytic hydroformylation, wherein the catalyst system is (completely) dissolved in the liquid phase of the reaction mixture. The catalyst system used for hydroformylation preferably comprises a transition metal from Group 8 or Group 9 of the Periodic Table (PTE) and at least one organophosphorus-containing ligand. Suitable phosphorus-containing ligands are known to those skilled in the art, but monodentate phosphorus-containing ligands are preferred, such as tris(2,4-di-tert-butylphenyl phosphite).

[0070] The transition metal used may be, in particular, iron, ruthenium, iridium, cobalt, or rhodium, preferably cobalt or rhodium, and more preferably rhodium. The catalytically active material discussed is typically a metal atom (ligand)-carbonyl complex formed in a liquid reaction mixture under elevated pressure and elevated temperature.

[0071] Hydroformylation can be carried out in the presence of a solvent, in which case the solvent should be compatible with the hydroformylation method. The solvent used can be a suitable solvent for hydroformylation known to those skilled in the art, such as alkanes, aromatics, water, ethers, esters, ketones, alcohols, and the reaction products or byproducts of hydroformylation, such as aldehydes and condensation products of aldehydes.

[0072] Furthermore, hydroformylation can be carried out at a pressure of 10 to 400 bar, preferably 15 to 270 bar. The temperature of hydroformylation can be 70 to 250°C, preferably 100 to 200°C, more preferably 120 to 160°C. Attached Figure Description

[0073] The present invention is described with reference to the following drawings, in which specific embodiments are illustrated. These drawings are illustrative only and should not be considered as limiting.

[0074] Figure 1An exemplary configuration of a membrane unit is shown, comprising a membrane stage having two membrane modules. The membrane stage consists of a feed container (B-1), a pump (P-1), and two membrane modules (M-2 / M-3). The feed container (B-1) is fed with a liquid mixture that serves as feed (F-1) to the membrane stage. The liquid mixture is directed from the feed container (B-1) as feed (F-5) to a first membrane module (M-2), such as a membrane ring, via the pump (P-1), where a first membrane separation occurs. Residue (F-6) and permeate (F-8) from the first membrane module are then discharged from the membrane module (M-2). Residue (F-6) is directed to a second membrane module (M-3), where further membrane separation occurs, producing permeate (F-9) and residue (F-7) from the second or final membrane module (M-3). Residue (F-7) is discharged via a drain valve (V-2). The two permeates (F-8 / F-9) from the two membrane modules (M-2 / M-3) are directed into a common conduit (F-10). In the context of this invention, these two permeates (F-8 / F-9) produce a total permeate (dashed rectangle), which exists at least as a calculation variable even if not completely mixed. Two permeate streams are discharged from the common conduit (F-10): a recirculated permeate stream (F-11) and a removed permeate stream (F-12). The removed permeate (F-12) is removed via a discharge valve (V-4), and the recirculated permeate (F-11) is sent to the feed container (B-1) via a return valve (V-3). It is also conceivable that the recirculated permeate (F-11) is not fed into the feed container (B-1) but rather between the feed container (B-1) and the pump (P-2) (not shown).

[0075] Figure 2An exemplary configuration of a membrane unit is shown, 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 one or two membrane modules (M-1 / M-2 / M-3). The feed container (B-1) is fed with a liquid mixture that serves as feed (F-1) to the membrane stage. The liquid mixture is guided from the feed container (B-1) as feed (F-2) to the membrane module (M-1), such as a membrane ring, by the pump (P-1), where membrane separation occurs. The permeate (F-4) and residue (F-3) from the first membrane stage are then discharged from the membrane module (M-1) via a drain valve (V-1). Permeate (F-4) from the first membrane module (M-1) is directed to the feed container (B-2) for the second membrane stage and subsequently fed as feed (F-5) to the first membrane module (M-2) of the second membrane stage via a pump (P-2), where membrane separation occurs. Residual permeate (F-6) and permeate (F-8) from the first membrane module are then discharged from the membrane module (M-2). Residual permeate (F-6) is directed to the second or final membrane module (M-3) of the second membrane stage, where further membrane separation occurs, producing permeate (F-9) and residual permeate (F-7) from the second membrane module (M-3). Residual permeate (F-7) is then directed via a discharge valve (V-2) to the feed container (B-1) of the first membrane stage. Both types of permeate (F-8 / F-9) from the two membrane modules (M-2 / M-3) are directed to a common conduit (F-10). Two permeate streams are discharged from a common conduit: a recirculated permeate stream (F-11) and a removed permeate stream (F-12). The removed permeate (F-12) is removed via a discharge valve (V-4), while the recirculated permeate (F-11) is sent to the feed container (B-1) via a return valve (V-3). Alternatively, the recirculated permeate (F-11) may not be fed into the feed container (B-1) but rather into a space between the feed container (B-1) and the pump (P-2) (not shown).

Claims

1. A method for continuously separating components from a liquid mixture using a membrane unit, said membrane unit comprising at least one membrane stage and used as a feed for the mixture, wherein the membrane stage comprises at least a conveying device, at least two membrane modules connected in series, and a feed container upstream of the conveying device. The method includes the following steps: The mixture from the feed container is directed as feed to the first of the at least two membrane modules via a conveying device, which in each case depletes the component to be separated in the resulting permeate stream from the first membrane module based on the mixture directed to the first membrane module and enriches it in the resulting residual stream from the first membrane module. The permeate from the first membrane module is directed to the second membrane module, which in each case depletes the component to be separated in the resulting permeate stream from the second membrane module based on the permeate from the first membrane module and enriches it in the resulting permeate stream from the second membrane module. Its features The at least two membrane modules are connected to each other on the permeate side in such a way that each of the at least two permeate streams is directed into a common conduit in which a total permeate stream is generated, and The at least two membrane modules are connected to a common conduit in opposite directions on the permeate side, such that a portion of the total permeate stream, i.e., the recirculated permeate, is recirculated to the feed container and / or upstream of the conveying device but outside the feed container, while the remainder of the total permeate stream, i.e. the removed permeate, is guided out of the membrane stage, wherein the recirculated permeate has a higher concentration of the component to be separated than the removed permeate.

2. The method of claim 1, wherein the concentration of the component to be separated in the recirculated permeate is greater than the concentration of the component to be separated in the common conduit between the connection of the first membrane module and the connection of the last membrane module, and wherein the concentration of the component to be separated in the common conduit is greater than the concentration of the component to be separated in the removed permeate.

3. The method according to claim 1 or 2, wherein there is no control actuator in the common conduit between the connection of the first membrane module to the conduit and the connection of the last membrane module to the conduit.

4. The method according to any one of claims 1-2, wherein the recirculated permeate is recirculated to the feed container and / or outside the feed container but upstream of the conveying device is done by hydraulic means rather than by the conveying device.

5. The method according to any one of claims 1-2, wherein the mass flow rate of one of the three streams selected from the feed of the membrane unit, the removed permeate, and the residual permeate from the membrane unit is defined by an preceding or downstream process step, and the other of the three streams is controlled to a target value.

6. The method according to any one of claims 1-2, wherein the mass flow rate of the recirculated permeate can fluctuate and is determined according to the mass flow rate of the removed permeate.

7. The method according to any one of claims 1-2, wherein in each case the mass flow rate of the permeate removed and the permeate pressure are both determined by an adjustable flow resistor.

8. The method according to any one of claims 1-2, wherein the mass flow rate of the removed permeate, which depends directly or indirectly on the filling level of the feed container, is continuously controlled in a closed loop, characterized in that: based on a pre-fixed target value for the filling level of the feed container, the mass flow rate of the removed permeate increases as the filling level of the feed container increases and decreases as the filling level of the feed container decreases.

9. The method according to any one of claims 1-2, wherein the pressure on the permeate side is controlled by a feed supply to one or more membrane modules and optionally additional actuators, or by a combination of a pressure gauge and an adjustable flow resistor on the permeate side.

10. The method according to any one of claims 1-2, wherein the mass flow rate on the residue side is controlled by a closed-loop mass flow control system on the residue side comprising at least one mass flow meter and an adjustable flow resistor, or by a combination of a mass flow meter and a conveying device.

11. The method according to any one of claims 1-2, wherein the component is a homogeneous catalyst separated from the reaction mixture.

12. The method according to any one of claims 1-2, wherein the conveying device is a pump.

13. A method for continuously separating a homogeneous catalyst from a liquid reaction mixture using a membrane unit, said membrane unit comprising at least one membrane stage and fed with a reaction mixture containing the homogeneous catalyst and originating from a reaction zone, wherein the membrane stage comprises at least a conveying device, at least two membrane modules connected in series, and a feed container upstream of the conveying device. The method includes the following steps: The reaction mixture from the feed container is directed as feed to the first of the at least two membrane modules via a conveying device, which in each case depletes the homogeneous catalyst in the resulting permeate stream from the first membrane module based on the mixture directed to the first membrane module and enriches it in the resulting residual stream from the first membrane module. The permeate from the first membrane module is directed to the second membrane module, which causes the homogeneous catalyst to be depleted in the resulting permeate stream from the second membrane module and enriched in the resulting permeate stream from the second membrane module in each case, based on the permeate from the first membrane module. Its features The at least two membrane modules are sequentially connected to each other on the permeate side in such a manner that the at least two permeate streams form a total permeate stream in which complete mixing of the individual permeate streams does not occur, and A portion of the total permeate stream, namely the recirculated permeate, is recycled to the feed container and / or upstream of the conveying device but outside the feed container, and the remainder of the total permeate stream, namely the removed permeate, is removed from the membrane stage, wherein the recirculated permeate has a higher homogeneous catalyst concentration than the removed permeate.

14. The method of claim 13, wherein the reaction mixture is taken from a reaction zone in which a homogeneous catalytic reaction is taking place.

15. The method of claim 14, wherein the homogeneous catalytic reaction is selected from the following reactions: oxidation, hydroformylation, hydroaminomethylation, hydrocyanation, hydrocarboxylation, alkylation, hydrocarboxylation, alkoxycarbonylation, amination, ammoxidation, oximeation, hydrosilylation, ethoxylation, propoxylation, telomerization, substitution, Suzuki coupling, and hydrogenation.

Images