DE102006061477B4 - Process for separating and purifying solids from suspensions - Google Patents

Abstract

Process for separating and purifying solids from suspensions, comprising the steps of:
a) providing a suspension;
b) introducing the suspension into filter chambers of a filter press to form a filter cake;
c) introducing a stream of a washing medium into the filter chambers so that the filter cake is rinsed with the washing medium;
d) stopping the flow of the washing medium for at least 10 seconds;
e) resuming the introduction of the washing medium into the filter chambers;
f) repeating steps (d) and (e);
g) stopping the flow of the washing medium;
h) removing the filter cake from the filter chamber.

Description

The invention relates to a process for the separation and purification of solids from suspensions.

Filter presses are used for the industrial processing of sludges or suspensions from the most diverse areas. Such filter presses comprise vertically arranged filter plates whose main surfaces are each covered with a filter cloth. The filter plates are each combined to form a filter plate stack, wherein the stack comprises, depending on the field of application, a different number of filter plates, for example 50 filter plates. The filter plates each have a recess on their major surfaces. If the filter plates combined to form a filter plate stack, so formed between adjacent filter plates from a filter chamber, which is lined by the filter cloth. The filter plate stack is compressed by a hydraulic, so that during the filtration process, the filter chambers can not be opened by the pressure of the medium flowing into the filter chamber. The aufarbeitende suspension is introduced into the filter chamber, wherein the liquid phase flows through the filter cloth and is led out of the filter chamber, while solid portions are retained in the filter chamber and build there a filter cake. During filtration, the back pressure, which must overcome the liquid phase, increases by building the filter cake constantly. If the pressure exceeds a certain limit, or if the filter chamber is completely filled by the filter cake, the introduction of the suspension to be worked up is interrupted. In a particular embodiment of such filter presses, so-called membrane filter presses, the filter cake can be further dehydrated. For this purpose, a membrane is provided on the main surface of the filter plate. The membrane may be pressurized by a suitable medium, generally compressed air or water, so that it may bow away from the main surface of the filter plate, thereby reducing the volume of the filter chamber. The filter cake is thereby squeezed out so that a filter cake with a higher solids content is obtained. To empty the filter chambers, the filter plates are moved apart. The filter plates are movably mounted in a frame. In principle, a distinction is made between side rail filter presses and bridge rail filter presses ("overhead press"). In the Seitenholmausführung spars are arranged on both sides of the filter plate stack, in which the filter plates are slidably mounted. This has the advantage that when the filter plates are moved apart, the space between adjacent plates is accessible from the top of the plate filter press. In the Brückenholmausführung the filter plates are movably latched in a guided over the plate stack spar. If the filter plates are moved apart to empty the filter chambers, the gap is accessible from the side.

For example, in the DE 43 07 601 Cl a filter press with monitoring device described. On the filter plates of the filter press pivotable frames are provided which are pivotable about a lower horizontal axis of an operating position in which the frame substantially on the main surface of the respective filter plate, away from this in a discharge position. Filter cloths are attached to the frame, so that the filter cloths rest against the filter plate in the operating position and can be pivoted away from it in the emptying position. The pivotable frames are biased in the sense of a pivoting movement towards the associated filter plate with a torque which is smaller than the torque exerted by the total weight of the pivotable frame, the associated filter cloth and a filter cake adhering thereto.

In the DE 103 31 383 A1 is an apparatus for filtering fluids having an inlet for the unfiltered and an outlet for the filtrate and with a plurality of stackable frame parts, in particular in the form of filtrate plates and filter frame, wherein the respective filter frame limits a Filtratraum for receiving a forming filter cake, which is described on its one, the next frame part in the stack facing side of a laminated filter is completed. The Filtratraum with the recordable filter cake is limited on its, the layer filter opposite side of another filter medium through which a further fluid can be supplied, which leaves after passing through the filter cake and the adjacent layer filter, the device via its output.

In the JP 2002 186 804 A there is described a filter press having a supply channel for supplying a solution and an outlet channel for discharging a filtrate solution or washing solution. In addition, an operating method for a filter press is described in which the interior of the filter press is prewashed prior to replacement of the filter medium, the inside of the filter press is washed with an additional washing liquid and subsequent recovery of the washing liquid, which is recovered from the outlet channel liquid of the washing liquid and the interior of the filter press after the recovery of the washing liquid is dried in order to use the filter medium after drying in a further filtration can.

In the US 4,317,734 A There is described a filter press having a fixed end plate, a movable end plate, and compression filter plates interposed therebetween. Each filter plate comprises a base plate having two flexible, fluid-tight plates which are respectively applied to the front and back of the base plate and have uneven filter surfaces on which a filter cloth is applied to a pressure space between the base plate and each of the two adjacent plates and a Filtration chamber to form between adjacent filter plates. The filter plate has a supply channel for fluids communicating with the pressure space, a filtrate outlet channel open to its filter surface, and a supply channel open to the filtration chamber. The filter plate is also provided with another fluid supply channel which is open to its filter surface and has a bypass channel communicating with the former fluid supply channel. A supply line for fluids and a connecting line are provided with valves.

In the EP 0 208 899 A1 a filter press with spreading device will be described. Also in this plate filter press two mutually at least the upper portion of the filter plate are provided on each filter plate on both sides pivotable frame. To empty the filter chamber, the frames are pivoted away from the main surface of the filter plate, so that the filter cloth is inclined with respect to the main plane of the filter plate. The frames of adjacent filter plates can be connected together at their upper edge by means of a bolt. If the filter plates are moved apart for emptying the filter chamber, the frames therefore form a roof-shaped structure.

Filter presses as described above are used, for example, in the synthesis of catalysts to separate the solid catalyst from catalyst suspensions obtained in the synthesis.

In the production of alcohols from carbon monoxide and hydrogen on a large industrial scale catalysts are often used, which are based mainly on copper and zinc. With such catalysts, short-chain alcohols, such as methanol and ethanol, as well as longer-chain alcohols are prepared, such as hexanol, octanol or decanol. Such longer-chain alcohols are further processed, for example, into detergents. The catalysts used for the synthesis usually contain other components, such as alumina, through which the temperature stability of the catalyst can be improved. For the preparation of such catalysts, for example collodially dissolved, dispersed aluminum hydroxide is used. This is mixed with an acid copper / zinc solution and precipitated the copper or zinc on the colloidal silica. A suspension is obtained which contains, in addition to the catalyst or a catalyst precursor, even larger amounts of dissolved salts. From the suspension, the catalyst precursor can then be filtered off with the aid of a filter press described above.

The US Pat. No. 4,598,061 A describes the preparation and use of a Cu / Zn / Al catalyst for the preparation of methanol and mixtures of higher alcohols. To improve the temperature stability, the catalyst contains not only the catalytically active material copper and zinc but also aluminum oxide. Furthermore, the catalyst contains at least one alkali carbonate or alkali oxide for accelerating the reaction. The concentration of alkali salt should be in the range of 50-100 ppm. Otherwise, at higher concentrations of alkali metal salt ions, the reaction rates and yield decrease significantly.

The DE 101 60 486 A1 describes a Cu / Zn / Al catalyst for the production of methanol. The catalyst has an atomic ratio of copper to zinc of less than 2.8. This allows for higher specific activity and selectivity at temperatures below 250 ° C. For the preparation of the catalyst, the corresponding hydroxocarbonates or hydroxides are precipitated from a solution of Cu and Zn salts and part of the Al salts with an alkali carbonate or alkali aluminate solution. Either the solution of the Cu and Zn salts or the alkali metal carbonate or alkali aluminate solution contains an aluminum hydroxide sol. The resulting precipitate is separated from the precipitation solution, for which the filter presses described above are used in an industrial production. The precipitate is washed, dried and calcined. For conversion into the active form, the catalyst stage is then reduced.

The activity of the Cu / Zn / Al catalyst in methanol synthesis is strongly influenced by the concentration of alkali metal salt ions remaining in the catalyst after synthesis. Small alkali metal salt concentrations significantly increase the reaction rate of methanol formation. As the concentration increases, however, the alkali metal ions simultaneously block the active centers of the Cu / Zn catalyst. As the alkali metal salt concentration increases, therefore, the rate of reaction of the alcohol synthesis above a threshold is significantly slowed. During the preparation of the catalyst, high alkali metal salt concentrations enter the catalyst precursor. The Cu / Zn / Al catalyst precursor must therefore After separation from the synthesis mixture to be washed. In general, however, it is not possible to lower the alkali metal salt concentration in the catalyst to below the required threshold with only one wash step. In preparing the catalyst on an industrial scale, the catalyst precursor separated from the synthesis mixture is generally not reslurried in water and the purified catalyst is then separated from the suspension in a filter press. Usually, the procedure is that the crude catalyst precursor is first separated in a filter press from the resulting in the synthesis of suspension suspension. Subsequently, wash water is passed through the filter chamber, so that the filter cake is rinsed with wash water. The rinsing time can be determined, for example, by measuring the alkali metal concentration in the wastewater. If the alkali metal concentration falls below a certain threshold value, the flow of wash water is stopped and the purified catalyst precursor is removed from the filter chamber.

During rinsing, the water-soluble portions of the filter cake, for example alkali metal salts, are discharged from the filter chamber. As a result, the solids volume of the filter cake decreases. Cracks form in the filter cake, through which the wash water flows more easily than through more compact areas of the filter cake. Therefore, as the rinsing step progresses, the worse the residual compact portions of the filter cake are rinsed. With very high proportions of water-soluble constituents in the filter cake, it may therefore be necessary to interrupt the rinsing process and remove the filter cake from the filter chambers. The filter cake still containing soluble salts must then be reslurried in water or other suitable washing medium and the resulting suspension pumped again into the filter press to continue the rinsing step.

There is therefore the problem that, although only small amounts of alkali metal ions can be detected in the wastewater, the catalyst precursor often still contains relatively large amounts of alkali metal compounds after removal from the filter press. This is due to the fact that the filter cake is traversed unevenly across its volume by the wash water and in the worst case arise areas that are not or only slightly rinsed by the wash water. To be sure that the catalyst precursor contains only at most the required maximum amount of alkali metal ions, therefore, even if no or only very small amounts of alkali metal can be detected in the wastewater of the filter press, the filter cake often for a long time be rinsed with fresh water. This results in large amounts of wastewater, which must be disposed of. This is particularly problematic if the wastewater contains ions that can not be released without further into the environment. For example, wastewater containing nitrate ions should not simply be discharged into, for example, a body of water because of the risk of over-fertilization. The nitrate ions must first be removed from the wastewater by biological or physical processes. A further disadvantage is that the production time for the catalyst is prolonged by the long rinsing times, so the separation and purification of the catalyst precursor forms a kind of bottleneck in the preparation of the catalyst.

The invention was therefore based on the object to provide a method using a filter press with which the concentration of water-soluble salts in the filter cake can be lowered efficiently with a smaller compared to the prior art wastewater quantity reliably to a low, preferably negligible residual concentration.

This object is achieved by a method using a filter press having the features of claim 1. Advantageous embodiments of the method according to the invention are the subject of the dependent claims.

The filter press used in the method according to the invention differs from the previously known filter presses in that the liquid supply to the filter chambers and the liquid discharge from the filter chambers is regulated by means of a control device interval. During operation of the filter press, therefore, the flow of a washing medium which flows through a filter cake arranged in the filter chamber can be switched on and off. It has been shown that when using the filter press much smaller amounts of wash water are needed and within shorter flushing times, the concentration of water soluble ions remaining in the filter cake can be reliably pressed below a predetermined threshold.

In the following description, a liquid is understood as meaning both a suspension of a solid in a liquid and a pure liquid, for example washing water.

The filter press used in the method according to the invention comprises a plurality in the form of a filter plate stack juxtaposed, vertically aligned, between an operating position and a discharge position horizontally displaceable filter plates which form a filter chamber in the operating position between major surfaces of adjacent filter plates. At least a part of the filter plates has a liquid supply and / or - derivative. According to the invention, the filter press used in the method comprises a control device, by means of which a flow in the liquid supply and / or discharge can be controlled at intervals.

In conventional filter presses, the suspension to be separated and the wash water are passed successively through a supply line continuously into the filter chamber. If a suspension is introduced, a filter cake first builds up. If a water-soluble impurity, for example an alkali metal salt, is to be removed from the filter cake by rinsing with washing water, then the flow rate of the washing water at different points of the filter chamber differs depending on the distance to the inflow opening and local inhomogeneities of the filter cake. When rinsing therefore does not reach all points of the filter cake, the same amount of washing water. Rather, there are areas in the filter chamber, for example in the corners of the filter chamber, get to the only small amounts of washing water and in which therefore relatively high salt concentrations remain even with long flushing times.

The control device makes it possible to carry out the flow of washing water at intervals, so for example to stop the washing water flow after a predetermined flow period t ₁ for a predetermined rest period t ₂ or to change the flow rate in a pulsed manner. For example, after a first volume of wash water has flowed into the filter chamber, the flow of wash water is stopped. The inventors assume that during this flowless time, the water-soluble ions, in particular alkali metal ions, first dissolve in the washing water. Since the dissolution process takes place in the flowless state, the interfering ions dissolve essentially equally well at all locations of the filter cake. Subsequently, the ions can diffuse from high concentration sites to low ion concentration sites. This dissolves a total of a larger amount of salts in the wash water contained in the filter chamber. If again fresh wash water is led into the filter chamber, the salt solution is displaced from the filter chamber and replaced by salt-free wash water. If the washing water flow is stopped again, the ions to be removed dissolve uniformly in the washing water in all sections of the filter cake. The change of switching on and off the flow of wash water through the filter chamber is repeated several times during the washing step. With the filter press used in the method according to the invention inhomogeneities in the filter cake or in the flow profile of the wash water over the volume of the filter cake can be compensated to a high degree, so that the volume of wash water used can be used much more efficiently. In the filter press used in the method according to the invention, therefore, smaller amounts of wash water are required, for example, to lower the concentration of alkali metal ions in a catalyst precursor, as obtained in the synthesis in the form of a suspension, reliably below a predetermined limit.

The effect achievable with the filter press used in the method according to the invention, the reliable removal of interfering ions from a solid by a rinsing step in which the flow of washing water is stopped at intervals, can in itself be achieved with a filter press comprising only one filter chamber. However, the filter press used in the method according to the invention preferably comprises a plurality of filter chambers, preferably more than 10 filter chambers, more preferably more than 30 filter chambers, in particular more than 50 filter chambers. A filter chamber is formed by two vertically suspended filter plates. In the space between the frame of the filter plate and the respective main surface of the filter chamber, for example, the suspension obtained from the synthesis of a catalyst is introduced. For this purpose, at least one liquid supply and / or discharge is arranged in a section of the filter plates. About this, both the suspension and in a subsequent rinsing step, a washing medium, such as washing water, are introduced. The solids contained in the suspension are retained in the filter chamber by a suitable filter device. For this purpose, for example filter cloths may be attached to the filter plates. The liquid phase can pass through the filter cloths and drain off the filter chamber while the solids are retained in the filter chamber where they build up a filter cake. The filter cloths may for example be attached to a pivotable frame, so that when emptying the filter chamber, the filter cloth can be pivoted away from the main surface of the respective filter plate.

To empty the filter chambers adjacent filter plates are moved apart in the horizontal direction. The filter cake can then be removed, for example, by falling down from the filter plate. If the filter press has filter cloths attached to swiveling frames, then the Filter cloths are lifted from the main surfaces of the associated filter plates and pivoted into the space between two adjacent filter plates. The hanging in the frame filter cloths hang through like a bulb, so that the filter cake by its weight usually completely detached from the filter cloths.

The control device of the filter press allows an interval-like liquid supply and discharge into and out of the filter chambers. In particular, the control device makes it possible to periodically stop the flow of liquid through the filter chamber. This is particularly advantageous when rinsing the filter cake. Intermittent flushing improves the absorption of soluble constituents into the wash medium throughout the entire volume of the filter cake. Thus, the existing amount of washing medium is used optimally and for a given amount of washing medium, the content of soluble salts in the filter cake compared to a filter press without control device, i. with a continuous washing water flow, significantly lowered.

The control device may be, for example, a clock through which a valve in the supply line for the wash water is opened or closed at predetermined time intervals. However, a computer may be used as the controller, allowing a more complex control of the washing process. For example, the duration for which the washing water flow is stopped at the beginning of the washing step, if the filter cake still contains large amounts of soluble salts, be chosen shorter and at the end of the washing step, when only small amounts of salts are released from the filter cake need, longer. Further, suitable measuring instruments may be provided on the filter press, for example for determining the flow rate, pressure or conductivity of the washing medium which provide data to the computer to optimize or automate the washing step.

According to a preferred embodiment, each filter chamber has at least one drainage opening. The drainage opening is preferably arranged in one of the filter plates, which together form the filter chamber, at an arbitrary location. According to one embodiment of the filter press used in the method according to the invention, a plurality of drainage openings may be provided per filter chamber. If several drainage openings per filter chamber provided, this allows a more uniform flow through the filter cake and thus a further improvement of the cleaning effect.

The liquid supply or discharge to or from the filter chamber preferably comprises a valve with which the liquid flow introduced into the filter chamber can be stopped. This allows in particular a simple control of the flow of wash water.

Preferably, a common supply line and / or a common discharge to or from the filter chambers is provided, with which the individual filter chambers are supplied centrally with suspension or washing medium, or which receives the wastewater from the filter chambers. Preferably, the valve for controlling the washing water flow is provided in the common supply line, so that the washing water flow can be stopped centrally or resumed in all filter chambers by a switching operation of a single valve.

However, it is also possible to assign the drainage openings of the filter plates each individual valves. By this measure, the flow conditions in the filter chamber can be influenced. The wash water can be passed through a different circuit of the valves on different paths through the filter cake. Since a more uniform flow through the filter cake can be achieved in this way, the amount of wash water or the time required for the rinsing step can be further reduced.

To adapt the flow conditions in the filter chamber, the valves can be controlled jointly or individually, for example, by a central control unit.

In the filter press used in the method according to the invention, at least one supply opening is provided per filter chamber. The at least one inlet opening, like the drainage opening, is preferably provided in at least one of the filter plates, which together form a filter chamber. The inlet opening can serve both for the supply of the suspension as well as the washing medium, in particular washing water. However, it is also possible to provide separate supply openings for the suspension and the washing water. Preferably, several supply openings per filter chamber are provided. This allows a more uniform filling of the filter chamber or a more efficient flow through the filter cake with the wash water.

The feed opening may be arranged at any point on the main surface of a filter plate. Preferably, the feed opening, in particular a feed opening for the supply of the suspension, is arranged centrally on the main surface of the filter plate. This allows a uniform distribution of the suspension in the filter chamber and thus a more homogeneous structure of the filter cake. When rinsing a uniform flow through the filter cake can then be achieved with washing water.

In the supply line for the suspension and / or the washing medium, a pump is preferably provided. The control of the flow can then be carried out, for example, in such a way that the pump is switched on or off. The pump is connected to the control device.

In the filter press used in the method according to the invention, the filter plates are preferably arranged in the form of a filter plate stack. Each filter plate is therefore arranged between two adjacent filter chambers. Preferably, at least every second filter plate is designed as a membrane filter plate with a membrane which can be pressurized by a pressure medium. If the membrane of the filter plate is pressurized, it bulges into the filter chamber and thereby reduces its volume. After completion of the filling of the filter chamber, the filter cake can therefore be further pressed to remove a portion of the mother liquor or the washing medium, so that a filter cake is obtained with a reduced moisture content.

The filter plate may be provided with a membrane on only one or preferably on both main surfaces. With a single filter plate then two adjacent filter chambers can be pressed.

1. a) Bereitstellen einer Suspension;
2. b) Einleiten der Suspension in Filterkammern einer Filterpresse unter Ausbildung eines Filterkuchens;
3. c) Einleiten eines Stroms eines Waschmediums in die Filterkammern, sodass der Filterkuchen mit dem Waschmedium gespült wird;
4. d) Anhalten des Stroms des Waschmediums für mindestens 10 Sekunden;
5. e) Wiederaufnehmen des Einleitens des Waschmediums in die Filterkammern;
6. f) Wiederholen der Schritte (d) und (e);
7. g) Anhalten des Stroms des Waschmediums;
8. h) Entnehmen des Filterkuchens aus der Filterkammer.

The filter press used in the process according to the invention enables the separation of solids from suspensions and the efficient purification of the separated solids. The invention therefore relates to a process for the separation and purification of solids from suspensions. The method according to the invention comprises the following steps:

1. a) providing a suspension;
2. b) introducing the suspension into filter chambers of a filter press to form a filter cake;
3. c) introducing a stream of a washing medium into the filter chambers so that the filter cake is rinsed with the washing medium;
4. d) stopping the flow of the washing medium for at least 10 seconds;
5. e) resuming the introduction of the washing medium into the filter chambers;
6. f) repeating steps (d) and (e);
7. g) stopping the flow of the washing medium;
8. h) removing the filter cake from the filter chamber.

In the method according to the invention, a suspension is first introduced into filter chambers of a filter press, so that a filter cake can build up in the filter chambers. The solids concentration of the suspension is chosen in the usual ranges. For example, the suspension should advantageously still be pumpable with a pump. The delivery rate of the suspension depends on the dimensioning of the filter press and can be determined by the skilled person by appropriate preliminary tests.

After a filter cake has built up in the filter chambers, the introduction of the suspension is stopped. The time at which the introduction of the suspension is terminated in the filter chamber, for example, can be determined by the back pressure generated in the filter chamber. After filling, a washing medium is passed through the filter chambers. The washing medium used is preferably water. The delivery rate of the washing medium into the filter chambers in turn depends on the dimensioning of the filter press and the available equipment, such as pumps, and the packing density of the filter cake. The suitable flow rate can be determined by the skilled person by means of appropriate preliminary tests.

After a predetermined period of time, the flow of the washing medium is stopped. The period of time is suitably chosen so that the volume of the filter chamber at least once through the washing medium is exchanged. Preferably, the time period is selected so that the volume of the filter chamber is replaced several times, preferably at least ten times, in particular at least fifty times through the washing medium. The time required for the replacement of the washing medium depends on the dimensioning of the filter chamber. Preferably, the time interval between 30 seconds and 10 minutes, more preferably between one and five minutes is selected.

Subsequently, the flow of the washing medium is stopped by the filter chamber. The filter chamber now contains first the solid separated from the suspension and fresh washing medium. In the washing medium, soluble impurities now dissolve out of the solid. Depending on the local concentration of the contaminant and the duration for which the wash medium remains in the filter chamber, more concentrated solutions of the contaminants in the wash medium may result. The contaminants dissolved in the wash medium may diffuse in the wash medium during the time that the flow of wash medium is stopped by the filter chamber, so that dissolved contaminants can move from high concentration areas to low concentration areas.

The period of time for which the flow of the washing medium through the filter chamber is stopped is preferably chosen to be sufficiently long that the contaminants may dissolve in a higher concentration in the washing medium and may possibly diffuse into areas of lower concentration. The time period is selected to be at least 10 seconds, preferably at least 30 seconds, more preferably at least 1 minute. As the concentration of the impurity in the washing medium increases, the amount of impurity dissolved in the washing medium per unit time decreases. In order to achieve efficient cleaning of the filter cake, it is therefore not necessary to choose the period during which the flow of the washing medium is stopped until a saturated solution of the impurity in the washing medium is obtained. In most cases it is advantageous that only up to about 50%, preferably up to about 40%, of the maximum attainable concentration of the impurity is dissolved in the washing medium. Preferably, the period of time for which the flow of the washing medium is stopped is chosen to be shorter than 10 minutes, advantageously shorter than 5 minutes.

Subsequently, the influx of fresh washing medium in the filter chamber is resumed. As a result, the contaminated with impurities from the solid washing medium is displaced from the filter chamber and replaced by fresh washing medium.

Subsequently, the above-described process is repeated. The change of introducing the washing medium into the filter chamber and interrupting the flow of the washing medium is repeated at least once. The number of repetitions depends on the solubility of the impurity, the concentration of impurity in the filter cake and the required purity of the filter cake. Preferably, steps (d) and (e) are repeated at least five times, more preferably at least ten times. Preferably, the process is repeated until the desired degree of purification of the solid is reached.

To complete the purification of the solid, the flow of the washing medium is stopped, the filter chamber is opened and the purified solid is removed from the filter chamber.

According to one embodiment of the method according to the invention, a part of the washing medium still present in the filter cake can be removed before the removal of the solid from the filter chamber by a gas, for example compressed air or nitrogen gas, is pressed through the filter chamber.

The period of time during which the flow of washing medium is stopped may be the same or different for successive steps. If the time span for which the flow of the washing medium is stopped is selected to be constant, this advantageously facilitates the regulation of the cleaning process. But it is also possible to make the period of time for which the flow of the washing medium is stopped, variable. For example, at the beginning of the cleaning, when high concentrations of impurities are still present in the filter cake, the period of time can be selected shorter, while at a later stage of the cleaning, when only small amounts of impurities are contained in the filter cake, the period is longer.

According to a preferred embodiment, the concentration of an impurity is measured in the flow of the washing medium leaving the filter chamber. With ionic impurities, this can be done, for example, by measuring the conductivity of the washing medium leaving the filter chamber. Depending on the concentration of the impurity in the washing medium, it may then be controlled whether steps (d) and (e) are repeated again.

According to a further embodiment, the filter cake is pressed out between steps (d) and (e). In this way, some of the contaminated with impurities wash medium is already removed from the filter cake before fresh wash medium can flow into the filter chamber. For this purpose, the filter press can be equipped, for example, with membrane filter plates, which allow the filter cake to be pressed out.

According to a further preferred embodiment, the filter cake is pressed out of the filter chamber before the filter cake is removed. This can be done for example by means of membrane filter plates.

According to another embodiment, the volume of the filter chamber during the washing process can be continuously reduced. This can be done continuously or step by step. For this purpose, the filter press may be equipped with membrane filter plates, for example. If these are pressurized, the membranes bulge into the filter chamber and thus reduce their volume. In this way, the volume loss of the filter cake can be collected, which it suffers from the discharge of the contaminant, so that cracking in the filter cake can be prevented.

The washing medium occurs in the inventive method, for example, through an inlet opening which is arranged in the lower portion of the filter chamber in the filter chamber to then flow against the force of gravity through the filter cake and the filter chamber through an outlet opening, which is arranged in an upper portion of the filter chamber is to leave again. In order to achieve a uniform flow through the filter cake via successive steps (e), in one embodiment of the method according to the invention, the washing medium in the filter cake has a flow direction and the flow directions are selected differently in successive steps (e). For this purpose, for example, two inlet openings may be provided, for example in the lower portion of the filter chamber at opposite outer portions of the main surfaces of a filter plate, and the washing medium are introduced once through the one inlet port and once through the other inlet port into the filter chamber. By this measure, areas which are less well flowed through by the washing medium, largely pushed back.

According to a particularly preferred embodiment, the process according to the invention is used for working up suspensions which are obtained in the preparation of Cu / Zn (Al) catalysts. Such catalysts are, as described in the introduction, for example, for the production of alcohols from carbon monoxide and hydrogen used industrially.

• - eine Kupfer/Zinknitratlösung bereitgestellt wird;
• - eine Sodalösung bereitgestellt wird;
• - eine Natrium/Aluminiumnitratlösung bereitgestellt wird;
• - die Lösungen vereinigt werden, wobei die Suspension aus der Herstellung von Cu/Zn-Katalysatoren erhalten wird.

According to a particularly preferred embodiment, the suspension is provided from the preparation of Cu / Zn catalysts by:

• providing a copper / zinc nitrate solution;
• a soda solution is provided;
• a sodium / aluminum nitrate solution is provided;
• - The solutions are combined, wherein the suspension is obtained from the production of Cu / Zn catalysts.

In the preparation of this suspension can be moved in such a way that first a soda solution is prepared. For this Na ₂ CO _{3 is} preferably stirred at elevated temperature, for example about 50 ° C in distilled water. To prepare the copper / zinc nitrate solution, for example, Cu (NO ₃ ) ₂ × 3 H ₂ O can be dissolved in distilled water. To this solution may then be added zinc oxide dispersed in nitric acid. The mixture is preferably stirred until a clear solution is obtained. This solution is very acidic due to the nitric acid contained.

For the preparation of the Al / Na nitrate solution, NaAlO _{2 is} preferably added to distilled water at room temperature. Nitric acid is added to this mixture so that the precipitate dissolves. The Al / Na nitrate solution can then be added to the copper / zinc nitrate solution. For precipitation, the soda solution is added to the metal ion solution prepared as described above. For this, the soda solution can be added to the solution of the metal ions. But it is also possible to pump the two solutions together in a precipitation tank. The precipitation of the Cu / Zn / Al-containing solid can be carried out at room temperature or else at elevated temperature. Preferably, the precipitation is carried out at elevated temperature, in particular at temperatures in the range of 50 to 90 ° C. The resulting precipitate can be aged afterwards. The duration of aging can be chosen arbitrarily. Preferably, the aging is chosen for a duration in the range of 30 to 120 minutes. The aging can be carried out at room temperature or preferably at elevated temperature. Preferably, the temperature in the range of 50 to 90 ° C is selected. In particular, the aging is carried out at a temperature at which the precipitation was carried out. The resulting suspension is then filtered and washed as described above.

Particularly preferably, the cleaning is continued until the effluent from the filter chamber washing medium has an alkali content of less than 700 ppm, preferably less than 500 ppm.

The filter cake obtained after the cleaning can be dried. Preferably, the filter cake is dried by spray drying.

To remove impurities, the dried solid can still be calcined. The calcination is preferably carried out at temperatures in the range of 250 to 450 ° C for a period of 2 to 4 hours.

In order to convert the Cu / Zn catalyst into the active form, the calcined solid can still be reduced. For the final reduction, a reducing gas can be used, which consists for example of 98% N ₂ and 2% H ₂ . The reduction is preferably carried out at temperatures in the range of 180 to 250 ° C.

The filter press used in the method according to the invention will be explained in more detail with reference to the accompanying figures. The same objects are provided with the same reference numerals.

• 1: eine schematischen Darstellung einer Seitenansicht der in dem erfindungsgemäßen Verfahren verwendeten Filterpresse;
• 2: eine Detailansicht einer Filterplatte mit schwenkbarem Rahmen in der Entleerungsstellung;
• 3: ein Schema der Herstellung eines in der Filterpresse gefilterten und gewaschenen Cu/Zn/(Al)-Katalysators

The figures show in detail:

• 1 a schematic representation of a side view of the filter press used in the method according to the invention;
• 2 : a detailed view of a filter plate with a pivotable frame in the emptying position;
• 3 FIG. 2: a schematic of the preparation of a filtered in the filter press and washed Cu / Zn / (Al) catalyst

1 shows an embodiment of a filter press used in the method according to the invention. The design of the filter press is substantially similar to the construction of known filter presses, but with an additional control device is provided, with which the flow of wash water can be controlled. The filter press comprises a certain number of filter plates 1 , which together form a filter plate stack. The filter plates 1 are about a suspension 2 in a bridge spar 3 movably mounted. On one side of the filter plate stack is a solid abutment 4 arranged and to the other side of the filter plate stack a movable abutment 5 , which by means of a hydraulic cylinder 6 can be moved in a horizontal direction. For filtration, the filter plate stack by means of the movable abutment 5 pushed together until this at the fixed abutment 4 comes to the plant. Through the hydraulic cylinder 6 This creates a pressure through which the individual filter plates 1 the filter plate stack are sealingly abutting each other. Between adjacent filter plates 1b , c are each filter chambers (not shown) formed. For working up a suspension, the suspension is first passed through the supply line 7 introduced into the filter chambers. The supply line 7 is with a three-way valve 8th provided and connected in the embodiment shown with all filter chambers of the filter press. About the three-way valve 8th can in the supply line 7 via wire 9 a suspension or via line 10 Wash water are introduced. The three-way valve 8th is via lines 12 with a control unit 13 connected. The three-way valve is controlled by the control unit 13 first switched so that over line 9 Suspension in the supply line 7 and further introduced into the filter chambers. The solid phase of the suspension remains in the filter chamber, while the liquid phase via a drain 11 is led out of the filter chamber again. After a filter cake has built up in the filter chambers, the introduction of the suspension is terminated. This is done with the help of the control unit 13 the three-way valve 8th closed. In the filter chambers washing water is introduced in the next step. This is done with the help of the control unit 13 the three-way valve 8th so open that over line 10 Wash water in the supply line 7 and further introduced into the filter chambers. The valve remains open for a predetermined time t ₁ , during which the filter chambers are traversed with wash water. After the expiration of t ₁ , with the help of the control unit 13 the three-way valve 8th closed, so that the flow of wash water is stopped. Impurities, for example alkali metal salts, dissolve in the washing water contained in the filter chambers. Of the Wash water flow is stopped for a predetermined period of time t ₂ . After the expiration of t ₂ is the control unit 13 a pulse to the three-way valve 13 given so that this is opened and again over line 10 Wash water in the supply line 7 and continues to flow into the filter chambers. Subsequently, the process is repeated, ie the washing water flow is maintained for t ₁ and then stopped again for a time t ₂ . In addition to the three-way valve 8th For example, a pump (not shown) may be provided which coordinates with the three-way valve 8th promotes the suspension or the wash water. This pump can also be via the control unit 13 to be controlled.

After the cycle of introducing wash water into the filter chambers and stopping the wash water flow has been passed through several times, so that the concentration of soluble impurities in the filter cake or the effluent has dropped below a certain threshold, the filter cake may optionally with the aid of filter membranes (not shown) be squeezed out. The filter chambers are then opened one after another by first moving the abutment 5 by means of the hydraulic cylinder 6 moved away from the filter plate stack, leaving between the filter plates 1 a gap 14 is trained. In the gap 14 become frames 15a . 15b pivoted, each to filter plates 1a . 1b are pivotally mounted in the lower region. The frames 15a . 15b can at their upper cross member (not visible) by means of a cable tie 16 be connected. In the space 14 form the hinged frame 15a . 15b therefore a roof-shaped structure. To the frame 15a . 15b are each filter cloths 17a . 17b attached. The attachment to the side rails of the swiveling frame 15a . 15b takes place by means of cable ties 16 , which on the one hand by a at the edge of the filter cloths 17a . 17b provided opening and around the side spar of the pivotal frame 15a . 15b are guided around. In the emptying position hang the filter cloths 17a . 17b through belly. Under its own weight, therefore, the filter cake dissolves 18 from the filter cloths 17a . 17b down and down. He falls on a conveyor belt 19 from which it is transported to the next processing station. Below the plate filter stack is a light path 20 intended. This is done by a laser 21 a beam of light emitted to a receiver 22 meets. Through the falling filter cake 18 becomes the light path 20 interrupted. This will trigger a signal. By suitable control electronics, the filter plate 1b in the example shown then moved to the left, so that the gap 14 is closed and between the adjacent two filter plates 1b . 1c forms a gap. In this intermediate space, as described above, the filter cake is then ejected.

In the 2 is the in 1 illustrated gap 14 shown in more detail. The gap 14 is from a filter plate 1a limited, on their main surfaces 23 each swiveling frame 15a . 15b . 15c are arranged. The swiveling frame 15 are each in a warehouse 24 pivoted. Over the narrow side 25 the filter plate la spans a spring 26 which the side rails 27 surrounds, so the swiveling frame 15a . 15c towards the main surface 23 the filter plate 1 be tense. The filter plate 1 is in a suspension 2 hung, over which the filter plate movable in the in 1 illustrated bridge spar 3 is mounted. On the main surface 23 the filter plate 1 is a large-scale depression 28a provided, which corresponds to one half of the filter chamber. On the surface of the depression 28a is the opening 29 a derivative provided over which the filtrate is discharged. Next is the area of the depression 28a with pimples 30 occupied, so that between the surface of the depression 28a and the filter cloth placed above 17 Form channels, through which the filtrate to the derivative 29 can flow. At its outer edge is the main surface 23 with a circumferential frame surface 31 provided so that when forming the plate filter stack, the frame surfaces 31 adjacent filter plates 1 sealingly reach each other to the plant. The swiveling frame 15a . 15b are at their upper end by means of cable ties 16 connected. The cable ties 16 are each around the upper cross member 32 the hinged frame 15a . 15b looped, each passing through the space between the filter cloth 17 and side rail 27 are guided. The width of the cable tie 16 formed loop is chosen so that the pivoting frame 15a . 15b have a certain play. In the frame 15a . 15b are each filter cloths 17a . 17b hooked. The filter cloths 17a . 17b are on the side rails 27 each with cable ties 16 attached. At the upper end of the swiveling frame 15a . 15c is the filter cloth 17 each around the upper cross member 32 guided around and in projecting bolts 33 hooked. In the emptying position shown hang the filter cloths 17a . 17b therefore belly-like. The filter chamber is filled via a feed opening (not visible). This is on top of the main area 23 the filter plate, for example, arranged in the lower right corner, so that they are as large a distance to the left upper corner arranged derivative 29 occupies.

3 shows the schematic course of producing a Cu / Zn / (Al) suspension, as obtained in the preparation of a Cu / Zn / Al catalyst. In a first step, a soda solution is produced. For example, 141 liters of distilled water and 25.15 kg of Na ₂ CO _{3 are} mixed at 50 ° C. After that For example, the preparation of a copper / zinc nitrate solution is followed by mixing 20.23 kg of Cu (NO ₃ ) ₂ .3H ₂ O in a 50 liter container with 24.2 kg of distilled water. To this is added 4.43 kg of ZnO powder dispersed in 6.3 kg of H ₂ O and 10.08 kg of 86% HNO ₃ in a 300 liter container and completely dissolved. This is followed by the production of an Al / Na nitrate solution. For this purpose, for example, in a 30-liter container, 1.63 kg NaAlO ₂ at room temperature in 7.5 kg of distilled water. To this is stirred 6.4 kg of 68% HNO ₃ . After a slight browning of the solution, it is pumped into the Cu / Zn nitrate solution. To this solution is added a solution of 1.63 kg of NaAlO ₂ in 7.5 kg of distilled water. The total solution is made up to a volume of 84.6 L with distilled water and heated to 74 ° C. The initially prepared soda solution serves to precipitate the catalyst. For this purpose, it is pumped at a temperature of 74 ° C simultaneously with the main solution in the precipitation tank. The resulting precipitate is then aged at 70 ° C for 60 min. The resulting suspension is then used for the following purification experiments. In this case, a filter press is used, as described above.

Comparative test

The catalyst suspension prepared as described above was fed via the central turbidity channel into the filter chambers of the filter press. After the filter chambers were filled, the membranes of the filter plates were subjected to 3 bar pressure for 5 minutes to squeeze out the filter cake and remove a portion of the mother liquor. After the pressure on the membranes was relaxed again, the filtrate was drained from the filter press for an additional 8 minutes.

To wash the filter cake, deionized water was passed through the filter chambers. The inlet of the wash water was via an opening in the lower left corner of the filter plate and the discharge via an opening in the upper right corner. At the beginning, the membrane was operated without pressure. In order to avoid cracking in the filter cake, the membrane pressure was increased to 3 bar and the filter cake was washed continuously for a further 53 minutes with distilled water. During the washing process, the conductivity of the running wash water was checked. However, a desired conductivity of <700 μS / cm could not be achieved.

After completion of the washing process, the filter cake was squeezed out by first increasing the membrane pressure to 5 bar. This pressure was maintained for 4 minutes and then increased to 10 bar for an additional 4 minutes.

After pressing, the filter cake was blown out for 9 minutes with compressed air at 5 bar.

Trial 1

The catalyst suspension prepared as described above was introduced into the filter chambers of the filter press up to a back pressure of 4 bar. In this case, 1387 kg of mother liquor were separated. It was then rinsed with 161 kg of deionized water to remove residues of the suspension from the feed lines of the filter press. The filter cake was squeezed out by applying a pressure of 4 bar to the membranes of the filter plates for 2 minutes.

For washing, the wash water was passed at a pressure of 3.5 bar through the filter chambers of the filter press. In order to avoid cracking in the filter cake, the membranes of the filter plates were subjected to a pressure of 4 bar. The wash water was introduced through an opening in the lower left corner of the filter plate in the filter chamber and discharged through an opening in the upper right corner of the filter plate. After washing water had been passed through the filter chambers for 6 minutes, the flow of wash water was stopped and waited until no more filtrate drained from the chambers. The pressure of the wash water was then increased to 4 bar and the washing started again. Washing water was passed through the filter chambers for a further 6 minutes, and then the supply line of the washing water was stopped again until no more filtrate ran out of the filter chambers. This process was repeated a total of 6 times.

To dry the filter cake, the membrane pressure was first increased to 6 bar for 2.5 minutes and then to 8 bar for a further 1.5 minutes. Finally, the filter cake was blown dry for 3 minutes with compressed air at a pressure of 6 bar.

Trial 2

The catalyst suspension prepared as described above was introduced into the filter chambers of the filter press up to a back pressure of 1 bar. In this case, 521 kg of mother liquor were separated. It was then rinsed with 110 kg of deionized water to remove residues of the suspension from the feed lines of the filter press. The filter cake was squeezed out by subjecting the membranes of the filter plates to a pressure of 2.5 bar for 2 minutes.

For washing, the wash water was passed through the filter chambers for 4 minutes at a pressure of 1 bar, the wash water being introduced through an opening in the lower left corner of the filter plate into the filter chamber and out through an opening in the upper right corner of the filter plate Filter chamber was derived. The flow of wash water was stopped and the pressure on the membranes of the filter plates increased to 2.5 bar. It was waited until no more filtrate expired, the pressure on the membranes relaxed and then washed in reverse flow direction at a pressure of 1 bar again with washing water. The washing process was interrupted twice every 4 minutes during which the filter cake was squeezed out by applying a pressure of 2.5 bar to the membranes of the filter plates.

Finally, the pressure on the membranes was increased to 8 bar for 3 minutes and, after no more filtrate expired, the filter cake was blown dry by blowing compressed air through the filter cake for 3 minutes at a pressure of 4.5 bar.

Trial 3

The catalyst suspension prepared as described above was introduced into the filter chambers of the filter press up to a back pressure of 1 bar. Subsequently, the lower filtrate channel was additionally opened and further suspension introduced into the filter chambers. In this case, 1108 kg of mother liquor were separated. It was then rinsed with 118 kg of deionized water to remove residues of the suspension from the feed lines of the filter press. The filter cake was squeezed out by subjecting the membranes of the filter plates to a pressure of 2 bar for 3 minutes.

For washing, the wash water was introduced into the chambers at a pressure of 3.0 bar. In order to avoid cracking, the pressure on the membranes of the filter plates was increased to 2 bar. The inlet of the wash water was via an opening at the bottom left corner of the filter plate while the drain was via an opening in the upper right corner of the filter plate. For this first wash cycle, 350 kg of recycled wash water from a previous filtration having a conductivity of 3.3 Ms / cm was used. The stream of wash water was stopped and the filter cake was squeezed out by increasing the membrane pressure to 2.5 bar. The filter cake was blown dry with compressed air at 4 bar.

Subsequently, the filter cake was washed twice for 4 minutes each with washing water, whereby the filter cake was pressed in between by the filter membranes were subjected to a pressure of 2.0 bar. Subsequently, the filter cake was blown dry with compressed air at a pressure of 4 bar. It was then washed again with wash water until the conductivity of the effluent filtrate had dropped to a value of <700 μS / cm.

After completion of the washing, the membranes of the filter plates were first pressurized for 2 minutes with a pressure of 6 bar and then for 2 minutes with a pressure of 8 bar. Finally, the filter cake was blown dry with compressed air (4.5 bar).

The data obtained for the experiments described above are summarized in Table 1. Table 1: Water consumption and cleaning effect with continuous and periodic rinsing attempt Mother liquor + wash water (kg) Dry matter final product (kg) Mother liquor + wash water (kg) / dry matter final product (kg) Na (ppm) in the final product comparison 2,038.0 48.2 42.3 973.0 1 2,462.0 99.3 24.8 395.0 2 1,108.2 41.9 26.4 265.0 3 2,103.80 76.9 27.35 343.0

Claims (9)

Process for separating and purifying solids from suspensions, comprising the steps of: a) providing a suspension; b) introducing the suspension into filter chambers of a filter press to form a filter cake; c) introducing a stream of a washing medium into the filter chambers so that the filter cake is rinsed with the washing medium; d) stopping the flow of the washing medium for at least 10 seconds; e) resuming the introduction of the washing medium into the filter chambers; f) repeating steps (d) and (e); g) stopping the flow of the washing medium; h) removing the filter cake from the filter chamber. Method according to Claim 1 , characterized in that the time interval in step (d) is chosen to be constant for successive steps in which the flow of the washing medium is stopped. Method according to one of Claims 1 or 2 , characterized in that in the stream of the washing medium leaving the filter chamber, the concentration of an impurity is measured. Method according to one of Claims 1 to 3 , characterized in that between the steps (d) and (e) the filter cake is pressed out. Method according to one of Claims 1 to 4 , characterized in that the washing medium in the filter cake has a flow direction and the flow directions in successive steps (e) is selected differently. Method according to one of Claims 1 to 5 , characterized in that the filter chambers are reduced in size during washing in their volume. Method according to one of Claims 1 to 6 , characterized in that the suspension is a suspension from the production of Cu / Zn catalysts. Method according to one of Claims 6 or 7 , characterized in that the filter cake is dried after cleaning. Method according to Claim 8 , characterized in that the drying is carried out as spray drying.

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