CN107176708B - Method for separating cellulose ether residues from cellulose ether production wastewater - Google Patents
Method for separating cellulose ether residues from cellulose ether production wastewater Download PDFInfo
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Abstract
The invention provides a method for separating cellulose ether residues from cellulose ether production wastewater, relates to the field of chemical production, also belongs to the field of water treatment and environmental protection, and comprises the following steps: the first procedure, high-viscosity cellulose ether in the cellulose ether production wastewater is separated, wherein, when the cellulose ether is in a water-soluble state, the cellulose ether is treated by a sedimentation method; when the cellulose ether is in a micelle state, treating by adopting an air floatation and vacuum filtration method; and a second step of separating the low and medium viscosity cellulose ether from the wastewater treated in the first step by a membrane separation method to obtain fresh water. The invention combines the sedimentation method/air flotation and vacuum filtration method with the membrane separation method, so that the cellulose ether recovery rate is high, the wastewater treatment process is simple, and the process method which has low cost and simple and feasible process is obtained.
Description
Technical Field
The invention relates to the field of chemical production, belongs to the field of water treatment and environmental protection, and particularly relates to a method for separating cellulose ether residues from cellulose ether production wastewater.
Background
Cellulose ether production wastewater, a high-salt, high-concentration organic wastewater, has Chemical Oxygen Demand (COD) components generally exceeding 5 ppm, even exceeding 10 ppm. The composition of the waste water from cellulose ether production is very complicated, and it contains more than 1% of cellulose ether residue, and also contains a large amount of inorganic salts such as sodium nitrate, sodium chloride, etc., and ethylene glycol, propylene glycol and condensates formed therefrom, polyol, etc.
The traditional wastewater treatment method, including a biochemical method, is difficult to treat the wastewater from cellulose ether production to reach the standard. The only viable method is to separate the various contaminant components of the wastewater and recover them as a useful resource. Therefore, on one hand, the resources can be recycled, and on the other hand, the pollutant level of the wastewater can be reduced to the level that the conventional method can effectively treat the wastewater. Two purposes are achieved at one stroke. However, the recovery of these contaminant components is premised on the separation of residual cellulose ether from the waste water, otherwise the other components cannot be purified to the product quality level. The reason is that cellulose ether is a sticky substance, and its presence causes the separation and purification of other components including inorganic salts, organic salts and alcohols, etc. to become extremely difficult, and thus the process cannot be achieved.
Disclosure of Invention
In view of the above problems, there is a need for a process for separating macromolecular cellulose ether residues from cellulose ether wastewater. The core of the method is that the residual cellulose ether macromolecules in the wastewater are separated out by the sedimentation and membrane separation technology, and the process foundation is laid for the recovery of various resources in the wastewater.
The above-mentioned technological process is a whole technological process. The process comprises two implementation procedures, and each procedure comprises a plurality of implementation steps. The first step is the separation of high viscosity cellulose ethers, which means cellulose ether molecules having a molecular weight of 5 kilodaltons or more. The second step is the separation of cellulose ethers of medium to low viscosity, by which is meant cellulose ether molecules having a molecular weight below 5 kilodaltons.
The invention aims to provide a method for separating cellulose ether residues from cellulose ether production wastewater, and provides a low-cost and feasible process method for separating and removing the cellulose residues from the cellulose ether production wastewater.
The invention is realized by the following steps: a process for separating cellulose ether residue from waste water from cellulose ether production comprising the steps of:
the first procedure, high-viscosity cellulose ether in the cellulose ether production wastewater is separated, wherein, when the cellulose ether is in a water-soluble state, the cellulose ether is treated by a sedimentation method; when the cellulose ether is in a micelle state, treating by adopting an air floatation and vacuum filtration method;
and a second step of separating the low and medium viscosity cellulose ether from the wastewater treated in the first step by using a membrane separation method to obtain fresh water.
The sedimentation method is a wastewater treatment method in which after wastewater enters a sedimentation tank, components with lower viscosity are deposited on the upper layer, and components with high viscosity are collected at the bottom in a concentrated manner.
The air floatation and vacuum filtration method is a method for collecting cellulose ether in a colloidal state on the water surface of wastewater by an air floatation machine and then filtering the cellulose ether in the colloidal state by a filter to obtain a cellulose ether filter cake.
The membrane separation method is a method which adopts a molecular sieve structure of a membrane stack, only allows small molecules to pass through, but does not allow large molecules to pass through, thereby achieving the purpose of separation.
By adopting the technical scheme, the cellulose ether production wastewater is divided into different procedures for treatment according to different molecular weights, the treatment method of each procedure is different, and the treatment methods are all common technologies in the wastewater treatment method. The purpose of separating and removing the high-viscosity cellulose ether in the first process is to reduce the viscosity of the waste water and avoid blockage caused by overhigh viscosity in the membrane separation of the next process. The combined treatment of the treatment methods has the advantages of high recovery rate of cellulose ether, simple wastewater treatment process, low cost and simple and feasible process.
As a further improvement of the present invention, the sedimentation process comprises the steps of:
step A1, pumping the cellulose ether production wastewater into a settling tank through a lift pump;
step A2, after sequentially settling through a plurality of settling tanks, collecting supernatant discharged from an outlet in a water collecting tank to obtain wastewater treated in the first procedure;
step a3, cellulose ether is intermittently collected from a stickies drain at the bottom of the settling tank.
The settling method achieves the purpose of separating high-viscosity cellulose ether from the cellulose ether production wastewater through sequential settling of a plurality of settling tanks, and is suitable for separating the cellulose ether which is in a water-soluble state due to continuous improvement of solubility when the temperature is below 45 ℃. The technical scheme is that the high-viscosity cellulose ether is separated and removed in the first process so as to reduce the viscosity of the wastewater and avoid blockage caused by overhigh viscosity in the membrane separation of the next process.
As a further improvement of the invention, the air floatation and vacuum filtration method comprises the following steps:
b1, air floating, namely scraping off cellulose ether suspended on the water surface and glued into a cellulose ether collecting tank by using an air floating machine through a scraper rotating on the air floating machine under the aeration condition;
step B2, performing vacuum filtration, namely performing vacuum filtration on the micelle-containing aqueous solution in the cellulose ether collecting tank by using a vacuum rotary drum filter, scraping a filter cake attached to the surface of a rotary drum filter screen by a scraper in the continuous rotation of a rotary drum, and allowing the filter cake to enter a slag collecting tank to obtain the wastewater treated in the first procedure;
and step B3, collecting filter cakes, and treating the filter cakes as waste residues or recovering cellulose ether.
The air floatation and vacuum filtration method is suitable for cellulose ether which is in a micelle shape and floats on the water surface due to the reduction of solubility at the temperature of below 45 ℃. The technical scheme is that the high-viscosity cellulose ether is separated and removed in the first process so as to reduce the viscosity of the wastewater and avoid blockage caused by overhigh viscosity in the membrane separation of the next process.
As a further improvement of the present invention, the membrane separation method comprises the steps of:
step C1, pre-filtering, namely pumping the wastewater treated in the first procedure into a filter by using a filter pump, and feeding the filtrate passing through the filter into a pre-filtering liquid storage tank to obtain pre-filtered wastewater;
step C2, membrane separation, namely pumping the pre-filtered wastewater into a membrane system by using a high-pressure pump for separation, collecting the fresh water from which the cellulose ether is removed in a fresh water tank after separation, and collecting the concentrated water containing the cellulose ether in a concentrated water tank;
and step C3, backwashing the membrane, pumping clean water in the backwashing tank into the membrane system in the reverse direction by using a backwashing pump, and refluxing the clean water to the backwashing tank to form circular cleaning until the cleaning is finished.
The membrane separation method refers to an ultrafiltration or nanofiltration technology, and the principle of ultrafiltration and nanofiltration membrane separation is that a membrane forms a molecular sieve in different density structures, only small molecules are allowed to pass through, but large molecules cannot pass through, so that the purpose of separation is achieved. The critical molecular weight that cannot pass is called the molecular weight cut-off. The molecular weight cut-off of the membrane adopted by the invention is 150-300 daltons.
By adopting the technical scheme, the membrane separation method is suitable for separating the cellulose ether with medium and low viscosity in the cellulose ether production wastewater.
As a further improvement of the present invention, the membrane system comprises at least two membrane stacks connected in series, each membrane stack comprises at least two membrane groups connected in parallel, each module comprises a membrane shell and a membrane member installed inside each membrane shell, the first membrane stack is connected with the high pressure pump, and the last membrane stack is respectively connected with the fresh water tank and the concentrated water tank.
Furthermore, each membrane group is provided with an outer water channel and an inner water channel, and wastewater enters the inner water channel after being subjected to membrane separation from the outer water channel in the same membrane group.
Furthermore, the outer water channels of all membrane groups of the same membrane stack are connected in parallel and then connected in series with the outer water channels of the adjacent membrane stacks to form a common outer water channel; the inner water channels of all membrane groups of the same membrane stack are connected in parallel and then connected in series with the inner water channels of the adjacent membrane stacks to form a common inner water channel.
Furthermore, an outer water channel of the first membrane stack is connected with the high-pressure pump, a public outer water channel of the last membrane stack is connected with the concentrated water tank, and a public inner water channel of the last membrane stack is connected with the fresh water tank.
Further, the pressure of the pre-filtered wastewater is 0.9-1.6Mpa, and the temperature of the pre-filtered wastewater is not more than 45 ℃.
Further, in the step C3, clean water enters each membrane stack from the common outer water channel of the last membrane stack, and finally flows back to the backwashing tank from the common inner water channel of the membrane stack.
The invention adopts a membrane stack serial system, each membrane stack comprises one or more parallel membrane shells, and each membrane shell comprises one or more serial membrane pieces. By adopting the technical scheme, the separation effect of the medium-low viscosity cellulose ether is the best.
Compared with the prior art, the invention has the beneficial effects that: through the combined treatment of the sedimentation method/air flotation and vacuum filtration method and the membrane separation method, the recovery rate of the cellulose ether is high, the wastewater treatment process is simple, and the process method which is low in cost and simple and feasible in process is obtained.
Drawings
FIG. 1 is a flow chart of a process for separating cellulose ether residue from wastewater from cellulose ether production provided by the present invention.
FIG. 2 is a partial schematic view of the structure of a process for separating cellulose ether residue from wastewater from cellulose ether production according to the present invention.
Description of the drawings: 1-membrane stack, 2-module, 3-outer water channel, 4-inner water channel, 30-public outer water channel, 40-public inner water channel, 100-high pressure pump, 200-concentrated water tank, 300-fresh water tank and 400-backwashing tank.
Detailed Description
In order to more clearly describe the embodiments of the present application or the technical solutions in the prior art, the present invention is further described below with reference to the accompanying drawings and specific embodiments.
Example 1
This embodiment will further explain the present invention with reference to fig. 1 and fig. 2.
A method for separating cellulose ether residue from waste water of cellulose ether production, which is characterized by comprising the following steps:
the first procedure, high-viscosity cellulose ether in the cellulose ether production wastewater is separated, wherein, when the cellulose ether is in a water-soluble state, the cellulose ether is treated by a sedimentation method; when the cellulose ether is in a micelle state, treating by adopting an air floatation and vacuum filtration method;
and a second step of separating the low and medium viscosity cellulose ether from the wastewater treated in the first step by using a membrane separation method to obtain fresh water.
The first step is the separation of high viscosity cellulose ethers, which means cellulose ether molecules having a molecular weight of 5 kilodaltons or more. The second step is the separation of cellulose ethers of medium to low viscosity, by which is meant cellulose ether molecules having a molecular weight below 5 kilodaltons.
The sedimentation method is a wastewater treatment method in which after wastewater enters a sedimentation tank, components with lower viscosity are deposited on the upper layer, and components with high viscosity are collected at the bottom in a concentrated manner.
The air floatation and vacuum filtration method is a method for collecting cellulose ether in a colloidal state on the water surface of wastewater by an air floatation machine and then filtering the cellulose ether in the colloidal state by a filter to obtain a cellulose ether filter cake.
The membrane separation method is a method which adopts a molecular sieve structure of a membrane stack, only allows small molecules to pass through, but does not allow large molecules to pass through, thereby achieving the purpose of separation.
By adopting the technical scheme of the embodiment 1, the cellulose ether production wastewater is divided into different procedures for treatment according to different molecular weights, the treatment method of each procedure is different, and the treatment methods are all common technologies in the wastewater treatment method. The purpose of separating and removing the high-viscosity cellulose ether in the first process is to reduce the viscosity of the waste water and avoid blockage caused by overhigh viscosity in the membrane separation of the next process. The combined treatment of the treatment methods has the advantages of high recovery rate of cellulose ether, simple wastewater treatment process, low cost and simple and feasible process.
Example 2
Example 2 is a preferred embodiment of the settling and air flotation plus vacuum filtration process of example 1.
On the basis of example 1, the sedimentation process comprises the following steps:
step A1, pumping the cellulose ether production wastewater into a settling tank through a lift pump;
step A2, after sequentially settling through a plurality of settling tanks, collecting supernatant discharged from an outlet in a water collecting tank to obtain wastewater treated in the first procedure;
step a3, cellulose ether is intermittently collected from a stickies drain at the bottom of the settling tank.
Further, the air floatation and vacuum filtration method comprises the following steps:
b1, air floating, namely scraping off cellulose ether suspended on the water surface and glued into a cellulose ether collecting tank by using an air floating machine through a scraper rotating on the air floating machine under the aeration condition;
step B2, performing vacuum filtration, namely performing vacuum filtration on the micelle-containing aqueous solution in the cellulose ether collecting tank by using a vacuum rotary drum filter, scraping a filter cake attached to the surface of a rotary drum filter screen by a scraper in the continuous rotation of a rotary drum, and allowing the filter cake to enter a slag collecting tank to obtain the wastewater treated in the first procedure;
and step B3, collecting filter cakes, and treating the filter cakes as waste residues or recovering cellulose ether.
In the first process two different process methods are used for the difference of the physical state of different cellulose ethers under different temperature conditions.
As shown in fig. 1, for the wastewater in the first state, i.e. the cellulose ether in a water-soluble state due to the continuous increase of solubility at a temperature below 45 ℃, a technical scheme of sedimentation is adopted, and a tandem combined type sedimentation tank is adopted for the sedimentation process, such as a triple-combined mode or a quadruple-combined mode. The concrete technological process is that the water pipe is first connected from the waste water tank to the lift pump and then to the water inlet of the combined apparatus, and the water outlet of the combined apparatus is connected to the water collecting pond. After the lift pump is started, the process wastewater is sent into the serial combined settling tank through the lift pump, the wastewater sequentially passes through all the tanks and is discharged from the water outlet, the effluent automatically flows into the water collecting tank, and meanwhile, high-viscosity cellulose ether residues are collected from the bottom of the settling tank in a staged manner.
Aiming at the wastewater in the second state, namely the cellulose ether which is in a micelle shape due to the reduction of solubility at the temperature below 45 ℃ and floats on the water surface, the technical scheme of an air floatation and vacuum method is adopted, and the specific steps are as follows: b1, air flotation, namely scraping off cellulose ether suspended on the water surface and in the form of a dough by using a scraper rotating on the air flotation machine under the aeration condition and feeding the cellulose ether into a cellulose ether collecting tank; step B2, vacuum filtration, namely, a vacuum drum filter is utilized to carry out vacuum filtration on the micelle-containing aqueous solution in the cellulose ether collecting tank, and during the continuous rotation of the drum, the cellulose ether slag cake attached to the surface of the drum filter screen is scraped off by a scraper and enters a slag collecting tank; and step B3, collecting filter cakes, and treating the filter cakes as waste residues or recovering cellulose ether. The temperature conditions of the above two physical states are also the temperature conditions under which the membrane separation process of the next process is operated.
By adopting the technical scheme of the embodiment 2, the purpose of separating and removing the high-viscosity cellulose ether in the first process is to reduce the viscosity of the wastewater and avoid blockage caused by overhigh viscosity in the membrane separation of the next process.
Example 3
Example 3 is a preferred embodiment of the membrane separation method based on example 1 or example 2.
The membrane separation method comprises the following steps:
step C1, pre-filtering, namely pumping the wastewater treated in the first procedure into a filter by using a filter pump, and feeding the filtrate passing through the filter into a pre-filtering liquid storage tank to obtain pre-filtered wastewater;
step C2, membrane separation, namely pumping the pre-filtered wastewater into a membrane system by using a high-pressure pump for separation, collecting the fresh water from which the cellulose ether is removed in a fresh water tank and collecting the concentrated water containing the cellulose ether in a concentrated water tank after separation;
and step C3, backwashing the membrane, pumping clean water in the backwashing tank into the membrane system in the reverse direction by using a backwashing pump, and refluxing the discharged water to the backwashing tank to form circular cleaning until the cleaning is finished.
Further, as shown in fig. 2, the membrane system includes four membrane stacks 1 connected in series, each membrane stack 1 includes three membrane groups 2 connected in parallel, each module 2 includes a plurality of membrane shells and membrane elements installed inside each membrane shell, the first membrane stack is connected to the high-pressure pump 100, and the last membrane stack is connected to the fresh water tank 300 and the concentrated water tank 200, respectively.
Furthermore, each membrane group 2 is provided with an outer water channel 3 and an inner water channel 4, and wastewater enters the inner water channel 4 after being subjected to membrane separation from the outer water channel 3 in the same membrane group 2. Specifically, a fresh water outlet is respectively arranged on the axis lines of two ends of each membrane shell, a concentrated water inlet is arranged at one side of each membrane shell close to one end, and a concentrated water outlet is arranged at the other side of each membrane shell close to the other end, the membrane groups are connected in parallel in such a way that the concentrated water inlets at the same side of each membrane shell are connected together through a connecting pipe A, the concentrated water outlets at the same side of each membrane shell are connected together through a connecting pipe B, and wastewater enters from the connecting pipe A and exits from the connecting pipe B after passing through each module to form an outer water channel 3; and fresh water outlets at the same end of all the membrane shells are connected together through a connecting pipe C to form an inner water channel 4.
Further, the outer water channels 3 of all membrane groups of the same membrane stack are connected in parallel, and then are connected in series with the outer water channels 3 of the adjacent membrane stacks to form a common outer water channel 30; the inner water channels 4 of all membrane groups of the same membrane stack are connected in parallel and then connected in series with the inner water channels 4 of the adjacent membrane stacks to form a common inner water channel 40.
Further, the first membrane stack is connected to the high pressure pump 100, the outer water channel 3 of the last membrane stack is connected to the concentrate tank 200, and the common inner water channel 40 of the last membrane stack is connected to the fresh water tank 300.
Further, the pressure of the pre-filtered wastewater is 0.9-1.6Mpa, and the temperature of the pre-filtered wastewater is not more than 45 ℃.
Further, in the step C3, clean water enters each membrane stack from the common outer water channel 30 of the last membrane stack, and finally returns to the backwash tank 400 from the common inner water channel 40 of the membrane stack.
The membrane separation process refers to an ultrafiltration or nanofiltration technique, wherein the membrane refers to a polymer membrane product that is made of various chemical raw materials and has been widely commercialized. In the using process, membrane sheets are combined into a unit in a rolling mode or a flat mode, the unit is called a membrane piece, and a plurality of membrane pieces are connected in series or in parallel to form a membrane system. The invention adopts a membrane stack serial system, each membrane stack comprises one or more parallel membrane shells, and each membrane shell comprises one or more serial membrane pieces. The principle of ultrafiltration and nanofiltration membrane separation is that a membrane forms a molecular sieve with different density structures, only small molecules are allowed to pass through, and large molecules cannot pass through, so that the purpose of separation is achieved. The critical molecular weight that cannot pass is called the molecular weight cut-off. The molecular weight cut-off of the membrane adopted by the invention is 150-300 daltons.
As shown in fig. 1, the second process includes three steps: step C1 is a pre-filtration process, which is intended to remove suspended matter and cellulose ether residues with excessive viscosity from the wastewater before the wastewater enters the membrane system, so as not to clog the membrane system and affect the operation thereof. The process is completed by a filter pump and a filter, and the filter pump belongs to a self-priming centrifugal pump. The filter used for pre-filtration can be a bag filter, a filter element filter or a ceramic filter, and the filtration precision is 1 micron. Starting a filter pump, pumping the wastewater treated by the first procedure into a filter, and collecting filtrate in a pre-filtrate storage tank after filtering; step C2 is membrane separation, which is performed by a high pressure pump belonging to a multi-stage high pressure centrifugal pump and a membrane system. The high-pressure pump is connected with the pre-filtering liquid tank and the membrane separation system through pipelines, and a positive one-way valve is respectively arranged at the inlet end and the outlet end of the high-pressure pump. The motor power of the high-pressure pump is controlled by a frequency converter, so that the water inlet pressure of the membrane separation system is controlled. The specific separation process is that after the separation program is started, the high-pressure pump sends the wastewater in the pre-filtering liquid storage tank into the first membrane stack of the membrane separation system, and the inlet water sequentially enters other membrane stacks along with the public external water channel. The water inlet pressure is maintained at 0.9-1.6 mpa. The fresh water permeating the separation membrane enters a public internal water channel and flows into a fresh water tank, and finally the water reaching the standard is obtained through evaporation and desalination. And the concentration of the cellulose ether of the concentrated water which does not permeate the separation membrane is sequentially increased along with the stage number of the concentrated water flowing through the membrane stack and reaches the highest value when the concentrated water flows through the last stage of membrane stack, and then the concentrated water automatically flows into the concentrated water tank. The cellulose ether residue collected in both processes can be used to recover the cellulose ether product; step C3 is a backwash of the membrane system. The water permeability of the membrane system is reduced after the membrane system is continuously used for a certain time, and in order to ensure the stability of the long-term performance of the membrane system, backwashing is carried out once after the continuous separation operation is carried out for a certain time. The process is completed by a backwashing system, the backwashing system is specifically a loop consisting of a backwashing pump, a membrane system and a backwashing circulation tank, the backwashing pump belongs to a centrifugal pump, and the specific process is that after a backwashing program is started, the backwashing pump pumps clean water in the backwashing tank into the membrane system, the clean water enters the membrane system from a water channel on the outer side of the membrane and from the opposite direction of the water inlet of a separation program, the discharged water flows back to the circulation tank, continuous circulation cleaning is carried out for 30 minutes, and then the separation program is recovered.
The method for separating the cellulose ether residues from the cellulose ether production wastewater is suitable for water-soluble cellulose ether, can effectively remove the cellulose ether residues in the wastewater, has reliable process and low cost, and has important significance for treating the cellulose ether high-concentration wastewater: on one hand, the method can be directly used for recovering cellulose ether, and on the other hand, conditions are created for the recovery and utilization of other components in the wastewater.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (7)
1. A method for separating cellulose ether residue from waste water of cellulose ether production, which is characterized by comprising the following steps:
the first procedure, high-viscosity cellulose ether in the cellulose ether production wastewater is separated, wherein, when the cellulose ether is in a water-soluble state, the cellulose ether is treated by a sedimentation method; when the cellulose ether is in a micelle state, treating by adopting an air floatation and vacuum filtration method;
a second step of separating the low and medium viscosity cellulose ether in the wastewater treated in the first step by using a membrane separation method to obtain fresh water;
wherein, the high viscosity cellulose ether refers to cellulose ether molecules with molecular weight more than 5 ten thousand daltons, the medium and low viscosity cellulose ether refers to cellulose ether molecules with molecular weight less than 5 ten thousand daltons, the water soluble state refers to cellulose ether which shows water soluble state due to the increasing solubility when the temperature is below 45 ℃, and the micelle state refers to cellulose ether which is in micelle state and floats on the water surface due to the decreasing solubility under the temperature condition below 45 ℃;
wherein the membrane separation method comprises the following steps:
step C1, pre-filtering, namely pumping the wastewater treated in the first procedure into a filter by using a filter pump, and feeding the filtrate passing through the filter into a pre-filtering liquid storage tank to obtain pre-filtered wastewater;
step C2, membrane separation, namely pumping the pre-filtered wastewater into a membrane system by using a high-pressure pump for separation, collecting the fresh water from which the cellulose ether is removed in a fresh water tank after separation, and collecting the concentrated water containing the cellulose ether in a concentrated water tank;
step C3, backwashing the membrane, pumping the clean water in the backwashing tank into the membrane system in the reverse direction by using a backwashing pump, refluxing the clean water to the backwashing tank,
forming circular cleaning until the cleaning is finished;
the membrane system comprises at least two membrane stacks connected in series, each membrane stack comprises at least two membrane groups connected in parallel, each membrane group comprises a membrane shell and a membrane piece arranged in each membrane shell, the first membrane stack is connected with the high-pressure pump, and the last membrane stack is respectively connected with the fresh water tank and the concentrated water tank; the pressure of the pre-filtered wastewater is 0.9-1.6Mpa, and the temperature of the pre-filtered wastewater is not more than 45 ℃;
the membrane separation method refers to an ultrafiltration or nanofiltration technology, and the adopted membrane has the molecular weight cutoff of 150-300 daltons.
2. The process of separating cellulose ether residue from cellulose ether production wastewater as claimed in claim 1, characterized in that the settling process comprises the steps of:
step A1, pumping the cellulose ether production wastewater into a settling tank through a lift pump;
step A2, after sequentially settling through a plurality of settling tanks, collecting supernatant discharged from an outlet in a water collecting tank to obtain wastewater treated in the first procedure;
step a3, cellulose ether is intermittently collected from a stickies drain at the bottom of the settling tank.
3. The method of claim 1, wherein the air flotation and vacuum filtration method comprises the following steps:
b1, air floating, namely scraping off cellulose ether suspended on the water surface and glued into a cellulose ether collecting tank by using an air floating machine through a scraper rotating on the air floating machine under the aeration condition;
step B2, performing vacuum filtration, namely performing vacuum filtration on the micelle-containing aqueous solution in the cellulose ether collecting tank by using a vacuum rotary drum filter, scraping a filter cake attached to the surface of a rotary drum filter screen by a scraper in the continuous rotation of a rotary drum, and allowing the filter cake to enter a slag collecting tank to obtain the wastewater treated in the first procedure;
and step B3, collecting filter cakes, and treating the filter cakes as waste residues or recovering cellulose ether.
4. The process for separating cellulose ether residues from cellulose ether production wastewater as claimed in claim 1, wherein each membrane module is provided with an outer waterway and an inner waterway, and wastewater enters the inner waterway after being subjected to membrane separation from the outer waterway in the same membrane module.
5. The process for separating cellulose ether residue from cellulose ether production wastewater as claimed in claim 4, wherein the outer waterways of each membrane group of one membrane stack are connected in parallel to each other and then connected in series with the outer waterways of adjacent membrane stacks to form a common outer waterway; the inner water channels of all membrane groups of the same membrane stack are connected in parallel and then connected in series with the inner water channels of the adjacent membrane stacks to form a common inner water channel.
6. A process for separating cellulose ether residue from cellulose ether production wastewater as claimed in claim 5, characterized in that the outer waterways of the first membrane stack are connected to a high pressure pump, the common outer waterways of the last membrane stack are connected to a concentrate tank, and the common inner waterways of the last membrane stack are connected to a fresh water tank.
7. The process for separating cellulose ether residues from cellulose ether production wastewater as claimed in claim 1, wherein in said step C3, fresh water enters each membrane stack from the common external waterways of the last membrane stack and finally returns to the backwash tank from the common internal waterways of the membrane stacks.
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