JPS6259610B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for separating lower alcohols from lower alcohol-containing aqueous solutions by reverse osmosis. [Conventional technology] Conventionally, liquid separation technology using the reverse osmosis principle is an energy-saving separation technology that does not involve phase or chemical changes, and has been used in fields such as desalination of can water and seawater, recovery and purification of useful substances, etc. Various studies and developments are underway. This kind of reverse osmosis separation technology has the following advantages: (1) resource conservation through the recovery and reuse of useful materials; (2) energy conservation by reducing the cost of unit operations such as concentration, recovery, and purification compared to conventional evaporation methods (3) ) It has the characteristic of being able to prevent pollution through a closed system in the collection of useful materials and wastewater treatment, and its practical application is attracting attention, but the focus is on desalination of can water and seawater. In reverse osmosis separation technology for inorganic salts such as table salt, many proposals have been made regarding the various membrane materials and membrane configurations used in this field, but there are no methods for separating useful substances such as lower alcohols. There have been few proposals for practical use. In other words, reverse osmosis separation technology for water-soluble useful substances is
Like lower alcohols, their interaction or affinity with membranes is different from that of salt, etc., and even if the membrane is effective for reverse osmosis separation of seawater, etc., it has no or almost no separation performance for separating lower alcohols. This is thought to be largely related to the individual characteristics of separation performance, such as the fact that the membrane itself lacks chemical stability, so there is a risk that its separation properties will rapidly be lost over time. By the way, today's depletion of petroleum resources has created a strong social need for the development of alternative energy sources.As an alternative energy source to replace petroleum, lower alcohols such as methanol and ethanol can be produced in large quantities at low cost. Possible methods are being investigated, one of which is biomass, viz.
Technologies that convert natural resources such as cellulose, corn, and sugar cane into lower alcohols such as methanol and ethanol by fermenting and decomposing them are attracting attention. However, one of the key points for using alcohol obtained from this biomass as fuel is to recover it under energy-saving conditions. In other words, the lower alcohol obtained from this biomass is an aqueous solution containing at most a few percent of alcohol, and recovering or concentrating alcohol from this low-concentration aqueous alcohol solution requires a huge amount of energy and is costly. Its recovery plays a large role in its use as a fuel that can replace petroleum. On the other hand, membranes that are capable of reverse osmosis separation of these lower alcohols include single crosslinked polymer membranes made of furfuryl alcohol and composite membranes with semipermeable polyamide membranes. The rejection rate (hereinafter referred to as Rej) is about 60 to 90%, and moreover, for alcohols useful as fuel such as methanol and ethanol, Rej is low and is only 80% at most. Therefore, an aqueous solution containing a relatively high concentration of alcohol, for example, about 6 to 8%, is prepared under high pressure, for example, 40 to 70 kg/cm ²
The separation and concentration of alcohol in the biomass-based alcohol manufacturing technology does not have much merit in terms of energy saving. Known membrane materials related to the present invention include JP-A-Sho
No. 54-107882, but this film lacked a protective film over the active layer, so there was a problem in durability. [Problems to be Solved by the Invention] Under the current circumstances, the present inventors have proposed a reverse osmosis separation membrane that is industrially advantageous in terms of efficiency and energy saving from aqueous solutions containing lower alcohols, particularly methanol and ethanol. As a result of intensive research, it was discovered that the barrier layer material of a composite membrane for reverse osmosis separation, the thickness of the barrier layer, and the protective film layer are closely related to the practical application of a reverse osmosis separation membrane for lower alcohols, and the present invention This is what we have come to do. That is, an object of the present invention is to provide a reverse osmosis separation method for separating alcohol components from an aqueous solution containing a high concentration of lower alcohol under advantageous operating conditions. Furthermore, it is an object of the present invention to provide a durable separation membrane that is not easily damaged even during module production or high-pressure operation, and can be operated stably for a long period of time. [Means for Solving the Problems] In order to achieve the above object, the present invention has the following configuration. "A crosslinked polymer having a thickness of at least 150 Å and consisting of furfuryl alcohol containing 30 to 70% by weight of a hydrophilic crosslinked polymer and 70 to 30% by weight of a monomer copolymerizable with the furfuryl alcohol. A lower alcohol characterized by concentrating and separating a highly concentrated lower alcohol from an aqueous solution containing 1 to 15% lower alcohol using a reverse osmosis membrane comprising a reverse osmosis membrane and having a protective layer thereon. In other words, it is known that even in conventional reverse osmosis separation membranes for can water and seawater, the semi-permeable ultra-thin barrier layer controls the Rej for water. In reverse osmosis separation membranes for water and seawater, the thickness of the barrier layer is made as thin as possible, and Rej
It is normal to maintain the barrier layer at a high level and increase the flux as much as possible.Also, as described later, it is possible to increase the thickness of the barrier layer, but as the thickness increases, water Increasing the thickness of semipermeable membranes has rarely been considered because the permeation rate may decrease and the uniformity of the membrane thickness as a semipermeable membrane may decrease, leading to a decrease in performance. I can say that. However, in the present invention, in order to efficiently separate lower alcohols by reverse osmosis, it is necessary to use a polymer that exhibits at least optimal performance for reverse osmosis separation of lower alcohols, although this differs depending on the type of polymer constituting the barrier layer. In the case of the hydrophilic crosslinked polymer of the invention,
The thickness of the barrier layer needs to be at least 150 Å or more. Of course, if this film thickness becomes too thick, the flux will decrease, so it is desirable that the film thickness is less than 500 Å, although it varies depending on the type of polymer. Here, the raw material of the hydrophilic crosslinked polymer constituting the barrier layer of the composite membrane for reverse osmosis separation of the present invention is a water-soluble monomer and/or a synthetic polymer thereof, and these water-soluble monomers and/or The crosslinked polymer formed from the polymer must maintain its hydrophilicity, be insoluble in water and alcohol, and be chemically stabilized. In other words, if the membrane made of the crosslinked polymer is soluble in water and alcohol, or is not chemically stabilized and, for example, swells, the initial selective separation performance of the composite membrane will simply be low. However, this is not preferable because the performance deteriorates over time and the layer becomes susceptible to peeling from the support layer and mechanical damage. As the hydrophilic crosslinked polymer of the present invention, there are various known monomers and polymers, but preferably an FA-based polymer mainly composed of furfuryl alcohol (hereinafter abbreviated as FA), especially a copolymer of FA. An FA-based copolymer having a proportion within the range of about 30 to 70% by weight is preferred. Examples of copolymerization components for FA include tris(hydroxyalkyl)isocyanurate, inositol, tris(diglycidyl)isocyanurate, and especially tris(hydroxyethyl)isocyanurate and tris(hydroxypropyl)isocyanurate. A crosslinked product of an FA copolymer copolymerized with about 70 to 30% by weight of (alkyl) isocyanurate forms an excellent reverse osmosis separation membrane for lower alcohols. That is, in the case of the above FA-based polymer, the copolymerization ratio of FA or its copolymer component is about 30% or less or 70% or less.
% or more, the selective separation property, especially the permeation rate of water, becomes insufficient. On the other hand, if the proportion of the FA or its copolymerized component is about 70% or more or less than 30%, it becomes difficult to separate alcohols, especially methanol and ethanol.
This is not preferred because selective separation becomes insufficient. Next, the protective layer of the present invention will be explained. A protective layer is provided on the active layer, and such a protective layer has the effect of greatly improving durability. Polyvinyl alcohol is preferred as the protective layer. In order to provide this material, it is preferable to make it into an aqueous solution in advance, apply it on the active membrane, and then dry and heat-treat it to make it insoluble in water. The support membrane constituting the composite membrane of the present invention includes:
Any form of porous film, sheet, tube, or hollow fiber made of hydrophobic polymers such as polysulfone, chlorinated polyethylene, polyvinyl chloride, polycarbonate, cellulose acetate, and cellulose nitrate can be used. The porous structure is anisotropic, preferably one surface of the support has micropores with a diameter of about 10 to 100 angstroms, and the pore size gradually increases toward the other surface (inside). good. A more specific method for producing a porous support is described in “Office of Saline Water Research.
and Development Progress Report No. 359 (1968).Next, the method for separating lower alcohols using the composite membrane for reverse osmosis separation of the present invention is described in %, preferably 4 to 12% by weight, of a lower alcohol-containing aqueous solution, and although it varies depending on the operating conditions, the concentrated liquid separated by the composite membrane has a high alcohol concentration. At least 2 times higher than the concentration of the stock solution
%, and by controlling the operating conditions, a concentrated solution with a high concentration of about 10 to 20% can be easily obtained. Therefore, even if such a highly concentrated alcohol-containing aqueous solution is further concentrated and separated using the conventional evaporation method, the energy consumption is much lower than when concentrating and separating the raw stock solution itself using the evaporation method. It is highly effective in recovering alcohol from aqueous solutions containing low concentrations of alcohol, such as biomass. Here, the operating conditions for the composite membrane include a pressure of about 30 to 100 Kg/cm ² , preferably 50 to 90 Kg/cm ²
For reverse osmosis separation under such pressure conditions, especially at 60 kg/cm ² or less, the composite membrane of the present invention has a Rij of at least 90%, has excellent heat resistance, and has a temperature of the feed stock solution. is high temperature, for example 15~60℃
This is because it shows stable reverse osmosis separation performance even within the range of . In addition, examples of the lower alcohol of the present invention include methanol, ethanol, butanol, benzyl alcohol, phenol, propyl alcohol, furfuryl alcohol, and cyclohexanol.
An example of this is a alcohol with a certain alcohol content. Among these, ethanol is particularly preferred. [Example] Hereinafter, the present invention will be specifically explained with reference to Examples. In the examples, the thickness of the semipermeable membrane layer constituting the composite membrane is a value measured by the following method. Ultrathin sections were prepared from the sample (composite membrane), the sections were stained with osmic acid, and observed and measured using transmission electron microscopy. In addition, the ethanol separation performance and durability of the separation membrane are as follows:
Supply liquid 6% ethanol, pressure 60Kg/m ² , temperature 25℃
Performance was measured 24 hours after the start of measurement and 500 hours later. Example 1 [Manufacture of polysulfone support membrane] Taffeta made of rectangular polyester fibers with a size of 20 cm x 30 cm (multifilament of 150 denier for both warp and weft yarns, weave density of 90 pieces/inch vertically and 67 pieces/inch horizontally) , 160μ thick) on a glass plate, and then a 15% by weight dimethylformamide (DMF) solution of polysulfone (Udel P-3500 manufactured by Union Carbide) was fixed on the glass plate to a thickness of 200μ at room temperature (15-30℃). ) and immediately cast in sodium dodecylbenzenesulfonate 0.5 at room temperature.
A fiber-reinforced polysulfone support (hereinafter abbreviated as FR-PS support) is prepared by immersing it in an aqueous solution containing % by weight, leaving it for 5 minutes, and washing it with pure water for 1 hour. The pure water permeability coefficient of this FR-PS support (thickness: 200 μm) was 0.01 to 0.020 g/cm ² ·sec·atm when measured at a pressure of 1 Kg/cm ² and a temperature of 25°C. [Coating of semi-permeable membrane] Tris hydroxyethyl isocyanurate (hereinafter abbreviated as THEIC) 1% by weight, furfuryl alcohol (hereinafter abbreviated as FA) 2% by weight (THEIC/FA)
Molar ratio = 16/84), 2% by weight of sulfuric acid, 1% by weight of sodium dodecyl sulfate, and isopropyl alcohol
An aqueous solution containing 20% by weight is prepared, and the FR-PS support wetted with water is immersed in this aqueous solution at 15° C. for 5 minutes. Next, take out the FR-PS support and sandwich both long sides between 2cm wide iron plates (150g/plate) at 20℃.
After hanging it for 1 minute and holding it vertically, I put it in a hot air dryer and dried it at 130℃ for 3 minutes.
Subsequently, heat treatment is performed at 150°C for 5 minutes. [Coating of protective film] Next, this film was fixed on a glass plate, and polyvinyl alcohol (NM- manufactured by Nippon Gosei Kagaku Co., Ltd.) with a degree of saponification of 100 mol% and a degree of polymerization of 1500 was applied on the surface of the film.
14) was coated with a 1% by weight aqueous solution at room temperature (20°C) to a thickness of 50μ using a doctor knife.
Place in a hot air dryer and heat treat for 2 minutes. Interference fringes due to the polyvinyl alcohol thin film were observed on the surface of the resulting composite film. In addition, when the thickness of each layer of the composite membrane was measured by electron microscopy, the thickness of the barrier layer (semi-permeable membrane) was 300 Å, and the thickness of the protective film layer was 0.4 Å.
It was 0.5μ. The results of ethanol separation performance are shown in Table 1. Example 2 In Example 1, the same amount of inositol was used instead of THEIC, and a film was formed under the same conditions. The thickness of the barrier layer of this film was 250 Å.
The results of ethanol separation performance are shown in Table 1. Comparative Example 1 In Example 1, the steps of applying the polysulfone support membrane and the protective film were the same, but in the step of applying the semipermeable membrane, THEIC was changed to 0.75% by weight, FA to 1.5% by weight, and sulfuric acid to 1.5% by weight. However, an aqueous solution having the same composition as the other components was prepared, and a film was formed using the same method. The barrier layer of this composite film was 100 Å and the protective film was 0.4 to 0.5 μ. Comparative Example 2 Using the same polysulfone support as in Example 1, a composite semipermeable membrane was obtained by applying a semipermeable membrane using an aqueous solution containing 2% by weight of epiamine and not containing ethylenediamine, but in the same manner as in Example 1. The gel layer of this membrane is 0.9μ
The barrier layer had a thickness of 100 Å, and the protective film had a thickness of 0.4 to 0.5 μ. The results of the above Examples and Comparative Examples are shown in Table 1.

[Table] As seen in Table 1, composite semipermeable membranes with a barrier layer of 150 Å or less have poor performance after 24 hours and also have poor durability. Comparative Example 3 In Example 1, ethanol separation was carried out under the same conditions as in Example 3, except that no protective film was provided on the surface of the composite membrane. As a result, Rej after 24 hours is 93
%, Flux is ^0.21m3 / ^m2・day, Rij after 500 hours is 89
%, Flux was 0.22 m ³ /m ² ·day, and the durability was significantly inferior to that of Example 1. [Effects of the Invention] The present invention has the following remarkable effects. Highly durable. Since this is a composite membrane that exhibits a Rej of at least 90% relative to lower alcohols, reverse osmosis separation can be performed by directly using lower alcohol aqueous solutions with low alcohol concentrations, such as biomass, as the feed stock solution. There is no fluctuation or decline in reverse osmosis separation performance, which is the most problematic issue when processing large amounts of alcohol-containing aqueous solutions. Since reverse osmosis separation of lower alcohols is possible over a wide range of operating pressures and temperatures of 30 to 100 Kg/cm ² and 15 to 60°C, various stock solutions with different alcohol concentrations can be used.

Claims (1)

[Scope of Claims] 1. Furfuryl alcohol having a thickness of at least 150 Å and containing 30 to 70% by weight of a hydrophilic crosslinked polymer, and 70 to 30% by weight of a monomer copolymerizable with the furfuryl alcohol. Concentrating and separating a high concentration of lower alcohol from an aqueous solution containing 1 to 15% lower alcohol using a separation membrane that is a reverse osmosis membrane made of a crosslinked polymer consisting of 1% to 15% and has a protective layer thereon. A reverse osmosis separation method for lower alcohols. 2. The reverse osmosis separation method for lower alcohols according to claim 1, characterized in that the pressure of the lower alcohol-containing aqueous solution is maintained within a range of about 30 to 100 Kg/cm ² . 3. The method for reverse osmosis separation of lower alcohols according to claim 1, characterized in that the lower alcohol is ethyl alcohol. 4. The reverse osmosis separation method for lower alcohols according to claim 1, wherein the protective layer is polyvinyl alcohol.