METHOD OF PRODUCTION OF SULFONATED HEAT-RESISTANT POLYMERIC MATERIALS

Abstract: A sulfonated heat-resistant polymeric material containing at least 1 % by weight (in terms of sulfur content) of sulfone groups and an ammonia adsorption capacity of at least 10 mg/ g, which is produced by heat-treating at 250 to 500°C a starting material composition mainly comprising a sulfonated aromatic polymeric compound containing an aromatic sulfonic acid or its salt as the repeating unit and being soluble in aqueous solvents.

Description: Technical Field This invention relates to a sulfo-group-containing heat-resistant high-molecular material which has a high heat resistance and a large specific surface area and which can be used in a wide variety of fields such as adsorbents, deodorants, filter mediums and flame retardants. Background Art Among various high-molecular materials which are industrially useful, carbon materials are excellent generally in such characteristics as heat resistance, corrosion resistance and lubricating property. Further, since they can be imparted with a variety of functions by the adequate control of production conditions and additional treatment conditions, they are being used in various fields as fibers or moldings of desired shapes depending on the individual use purposes. Of these carbon materials, fibrous materials are usually produced by heat-treating their precursor fibers to make them infusible, followed by carbonization and graphitization at higher temperatures. However, this process involves complex production steps and moreover requires carbonization and graphitization treatments at high temperatures, so that the resulting carbon materials are relatively expensive and therefore have had limited uses insite of their excellent characteristics. Hence, in the field where a high strength or high-temperature heat resistance is not particularly demanded, it has been proposed to use fibrous carbon materials in the form of the so-called flame resistant fibers not completely carbonized, which are formed by burning organic fibers at comparatively low temperature. Further, it has been attempted to introduce sulfo groups into organic high-molecular materials with a view to imparting functionalities to the materials. For instance, copolymers of styrene and divinylbenzene having sulfo groups introduced by means of sulfuric acid, chlorosulfonic acid, etc. have been used as cation exchange resins of strong acid type, and polystyrenes sulfonated by a similar method have been used as surface active agents. It has also been known to produce fibrous adsorbents by forming side chains such as styrene on a base material such as polypropylene fiber by radiation graft copolymerization and sulfonating the resulting side chains. It has been reported that among the above-described flame resistant fibers, those of polyacrylonitrile origin contain carbonyl groups of acridone type, and that active carbon fibers of high hydrogen sulfide adsorptivities can be obtained by activating them at 800 - 1,000°C. However, the fibers do not have functionalities such as absorptivity and ion exchange ability, when they have only undergone a flame resisting treatment of oxidation at 250 - 300°C. Sulfonated products of styrene-divinylbenzene copolymers are insoluble in water but are partially soluble in organic solvents such as quinoline and DMSO. Sulfonated polystyrenes are also soluble in water. Moreover, these sulfonated polymers have low heat resistances of 100°C or below as well as low strengths. Further, in the case of the radiation graft copolymers, their preparation has to be done by a particular process using radiation and, in addition, the heat resistance of the resulting fibers is no more than that of the substrate fibers. Disclosure of the Invention The object of the present invention is to provide a process for the heat treatment of a formaldehyde condensation product of ammonium β-naphthalene-sulfonate, which is a mixture of monomer and various polymers having polymerization degrees of up to 200, and has a number-average molecular weight of 800 to 50,000, a condensation product of a sulfonated creosote oil, which is a mixture of monomer and various polymers having polymerization degrees of up to 40, and has a number-average molecular weight of 2,000 to 5,000 or a condensation product of phenanthrenesulfonic acid, which is a mixture of monomer and various polymers having polymerization degrees of up to 30, and has a number-average molecular weight of 2,500 to 5,000, consisting of either heat treating the polymers in a non oxidizing atmosphere at a temperature between 250°C and 500°C or heat treating the polymers in an oxidizing atmosphere at a temperature between 250°C and 400°C and if necessary heat treating the resulting composition in a non-oxidizing atmosphere at a temperature between 250°C and 500°C. The inventive process provides an industrially useful high-molecular material which can be prepared by a relatively simple process, has a high heat resistance and specific surface area. The present inventors have made investigations into high-molecular materials which have specific functionalities such as adsorptivity and deodorizing property as well as excellent heat resistance and strength, and finally found that a highly functional heat-resistant high-molecular material is obtained by heat-treating a sulfo-group-containing aromatic high-molecular compound under suitable conditions, leading to completion of the present invention. The process of the invention provides a sulfo-group-containing heat-resistant high-molecular material containing not less than 1 wt.% of sulfo groups in terms of sulfur content and having an ammonia adsorptivity of not less than 10 mg/g, formed by heat-treating at a temperature of 250 - 500°C a starting composition composed mainly of a sulfo-group-containing aromatic high-molecular compound as indicated above which comprises unit constituents of an aromatic sulfonic acid compound or a salt thereof and is soluble in aqueous solvents. The sulfo-group-containing heat-resistant high-molecular material obtained according to the process of the present invention exhibits a high heat resistance which enables the material to be used at a temperature in the range of 150 - 350°C as well as a good thermal conductivity and ion exchange capacity. Further, it has a large specific resistance and also a specific surface area as large as 40 m 2 /g measured by the CO 2 BET method. Therefore, it has a good adsorptivity characteristically, particularly for alkaline components including ammonia due to the presence of sulfo grous. As described above, the sulfo-group-containing heat-resistant high-molecular material obtained according to the process of the present invention incorporates a high heat resistance and a sufficient strength for practical use as well as high functionalities, so that it can be used in a variety of industrial fields as adsorbents, deodorants, filter mediums, flame retarding materials, ion exchangers and heat reserving materials or as components for miscellaneous composite materials. In particular, it is preferably used as members required to have heat resistance, corrosion resistance (chemical resistance) and flexibility as well as non-electroconductivity, that is, as members to be used in the area where synthetic resins are insufficient in heat resistance or carbon materials are inadequate due to their electroconductivity, for example, as materials for a spacer of electrodes in a fuel cell. The preparation process of the present invention offers an industrially advantageous process for producing materials having the foregoing characteristics. Brief Description of the Drawings Figures 1 to 3 are graphs in each of which an example of variation in a physical property is illustrated upon heating a starting composition prepared by forming a formaldehyde condensation produce of ammonium β-naphthalenesulfonate into a fibrous material. Figure 1 is a graph illustrating the relationship between the heat treatment temperature and the contents of carbon, nitrogen and sulfur in the treated product. Figure 2 is a graph illustrating the relationship between the heat treatment temperature and the strength of the treated product. Figure 3 is a graph illustrating the relationship between the heat treatment temperature and the specific resistance of the treated product. Best Mode for Carrying Out the Invention As a raw material for the sulfo-group-containing heat-resistant high-molecular material of the present invention, there is used a sulfo-group-containing aromatic high-molecular compound with a structure in which unit constituents each comprising an aromatic sulfonic acid compound, which is formed by replacing an average of 1 or 2 hydogen atoms in an aromatic ring such as benzene or naphthalene with sulfo group, or a salt thereof, are linked successively via a certain bonding group. As the cation moieties to form the aromatic sulfonates may be mentioned Na + , K + , Ca +2 , NH 4 + , etc. Of these sulfonates, the ammonium salts are preferred in view of the ease of handling in the heat treatment subsequent to spinning or molding. The preferred salts are dependent on the kind of the desired high-molecular materials. For instance, for the production of high-molecular materials requiring to have high strengths, the ammonium salts are preferred, whereas in the production of porous adsorbents or deodorants, the salts of sodium, potassium, iron, calcium, etc. may be used in addition to the ammonium salts. These sulfo-group-containing aromatic high-molecular compounds can be obtained with a variety of properties depending on the kind of the aromatic compounds used as the raw material and the conditions of the sulfonation and condensation or polymerization reactions, and hence can be selectively used at will according to the characters of the intended sulfo-group-containing heat-resistant high-molecular materials. The above mentioned sulfo-group-containing aromatic high-molecular compounds may be used not only as a single composition but also in the form of a mixture of two or more of the condensation products, or copolymerization or copolycondensation products thereof. The formaldehyde condensation product of ammonium beta-naphthalene sulfonate is a solid at room temperature, soluble in organic solvents such as benzene, toluene and acetone at low concentrations and easily soluble in aqueous solvents. The 60 wt.% aqueous solution has a viscosity of about 10 - 20,000 poise at 60°C and has a sufficient spinnability and moldability. The yield in the heat treatment of the condensation product at 250 - 500°C is approximately 95 - 55 wt.%. When the condensation product of a sulfonated creosote oil or the condensation product of phenanthrenesulfonic acid are used, these sulfo-group-containing aromatic high-molecular compounds are dried and, if necessary, ground and graded, followed by heat treatment or dissolution or dispersion in solvents. The solutions or suspensions thus obtained are adjusted in viscosity as required by way of dilution, concentration, etc., and then spinned into fibers or molded into any desired forms such as bulky, columnar, tabular, film-like and honeycomb forms. Thereafter, they are treated with heat to obtain sulfo-group-containing heat-resistant high-molecular materials in desired forms. The solvents used herein may preferably include water, alcohols such as methanol, organic acids such as acetic acid and polar solvents such as acetonitrile, in view of the characteristics of the sulfo-group-containing aromatic high-molecular compounds. Among others, water or aqueous solvents formed by mixing water and other water-soluble solvents are most suitable. When fibrous or molded products are to be obtained in the preparation process of the present invention, it is useful to add a water-soluble high-molecular compound in an amount of from 0.02 to 20 parts by weight based on 100 parts by weight of the starting sulfo-group-containing aromatic high-molecular compound as a spinning or molding auxiliary. Thus, the spinnability or moldability of the starting composition can further be improved. The water-soluble high-molecular compounds used herein are those which are soluble in water or miscellaneous aqueous solvents or dispersible therein as colloid. They may preferably include polyalkylene oxide type compounds such as condensation products of ethylene oxide, propylene oxide, etc. and condensation products of these compounds with alcohols, fatty acids, alkylamines or alkylphenols, polyvinyl compounds such as polyvinyl alcohol and polyvinyl pyrrolidone, polyacrylic acid type compounds such as polyacrylic acid, polyacrylamide, acrylic acid-acrylamide copolymers, etc. Among the sulfo-group-containing aromatic high-molecular compounds used as the principal raw material in the process of the present invention, polystyrenesulfonic acid and the like, which are highly soluble in water, may be used as the water-soluble high-molecular compound mentioned above. The addition of these water-soluble compounds may effectively acccelerate the rate of spinning, facilitate the handling of spinned fibers or moldings prior to the heat treatment, and increases the strength of the resulting fibrous or molded high-molecular materials. When the amount of the water-soluble high-molecular compound added exceed 20 parts by weight, an additional infusibilizing step will unfavorably be necessary because the fibers or the like are liable to fuse upon raising temperature or heating during the heat treatment. Since the sulfo-group-containing aromatic high-molecular compounds used as a raw material in the preparation process of the present invention have such a character as can be heat-treated without need for a prior infusibilizing treatment, they are particularly suitable for use in the production of fibrous heat-resistant high-molecular materials. The starting composition composed of the above mentioned sulfo-group-containing high-molecular compound is subjected to a heat treatment as granules or after being formed into fibrous or other desired shapes. The heat treatment is conducted by heating the composition in a non-oxidizing atmosphere in such a range that the highest temperature attains 250 - 500°C, preferably 350 - 400°C. Upon heating the starting composition, elimination of the sulfo groups begins to take place at a temperature in the vicinity of 250°C, and the starting composition that is soluble in solvents such as water is converted into a high-molecular material that is insoluble in the solvents and infusible and has a strength enough to withstand handling as well as a high specific surface area and adsorptivity. It is assumed that during the heat treatment, three dimensional crosslinking and improvement of surface properties proceed following the elimination of volatile matters, and the presence of the sulfo groups promotes these proceedings. The variations of the physical properties upon heating the starting composition composed mainly of the sulfo-group-containing aromatic high-molecular compound are as illustrated in Figures 1 to 3 typically with respect to a starting composition of a fibrous form prepared from a formaldehyde condensation product of ammonium β-naphthalenesulfonate. As will be discussed below, since the chemical reaction taking place upon heating is endothermic and the variations of the physical properties are hardly affected by the rate of raising temperature, the drawings are given in terms of the relationship between the temperature of the heat treatment or carbonization and each of the physical properties. Figure 1 is a graph illustrating the variations of the contents of carbon, nitrogen and sulfur in a material. As seen in the graph, the contents of carbon, nitrogen and sulfur in the material become practically constant at a heat treatment temperature of between 600 and 700°C, and the further heating causes a gradual increase of carbon and a gradual decrease of nitrogen and sulfur owing to the progress of carbonization. Figure 2 shows the variations of the strength caused by the heat treatment, illustrating that the exhibition of the strength of the material occurs in two stages. The first stage takes place primarily with the progress of three dimensional crosslinking in the heat treatment at 300 - 500°C, while the second stage is exhibited by the carbonization above 600 - 700°C. Figure 3 is a graph showing the variation of the specific resistance with the heat treatment temperature. From this drawing, it is found that since carbonization does not take place in the heat treatment below 600°C, the resulting material is a non-conductor with little ability of conducting electricity, but by heating above 700°C, carbonization proceeds to transform the material to a good conductor. As described above, the propeties of the material obtained by heat-treating a sulfo-group-containing aromatic high-molecular compound vary significantly at around 600°C. The heat-resistant high-molecular materials of the present invention which are formed by the heat-treatment below 500 *) exhibit the properties of organic matters and hence differ from the carbides obtained by the heat treatment at higher temperature. Further, the heating up to 400°C of the starting composition conducted in an oxygen-containing atmosphere accelerates the formation of functional groups such as carbonyl and carboxyl on the surface of the material, thus efficiently imparting the material such functionalities as adsorptivity and deodorizing property. The optimum heat treatment conditions vary with the properties of the starting composition and the desired sulfo-group-containing heat-resistant high-molecular material. However, they may properly be determined in such a way that the highest temperature lies between 250°C and 500°C and the product still holds 10 - 90% of the sulfo groups contained in the starting composition and hence contains sulfo groups in an amount of not less than 1 wt.% in terms of sulfur content. If the highest temperature is less than 250°C, the heat treating effects will be insufficient and the strength will also be undesirably low. If the starting composition is heat-treated beyond 400°C in an oxygen-containing atmosphere or beyond 500°C even in a non-oxidizing atmosphere, the strength of the product increases. However, most of the sulfo groups contained in the starting composition are stripped off during the heat-treatment, and the product does not exhibit the characteristic effects of sulfo groups. The chemical reaction in the heat treatment step of the present invention is endothermic and hence does not impose any particular limitations on the raising rate of temperature during the heat treatment. However, when the water formed by thermal decomposition attaches to the starting composition, the composition becomes liable to partial dissolution, adhesion, deformation, etc. Therefore, it is desirable to carry out the heat treatment under the conditions capable of rapid removal of the thermal decomposition gas, for example, in a stream of a carrier gas or under reduced pressure. When a fibrous product is produced, it is effective for the improvement of the strength to exert a tensile force on the composition during the heat treatment. The sulfo-group-containing heat-resistant high-molecular materials obtained according to the process of the present invention are those containing sulfo groups in an amount of not less than 1 wt.% in terms of sulfur content and having a specific surface area of not less than 40 m 2 /g measured by the CO 2 BET method, have an ammonia adsorptivity of not less than 10 mg/g and do not cause substantial weight reduction up to 250°C. They are lustrous, yellow or black, and highly heat-resistant and corrosion-resistant (chemical-resistant) high-molecular materials. Another characteristic of the sulfo-group-containing heat-resistant high-colecular material is that its electric conductivity is low owing to its large specific resistance of 10 8 Ω·cm. These natures make it possible to provide a material which is required to have a high heat resistance up to 250°C and corrosion resistance and is suitable for members that should not have electric conductivity. It is also possible to impart flexibility to the material by forming it into a fibrous product. However, when as the raw material a salt of aromatic sulfonic acids, the cationic moiety of which does not volatilize during the heat treatment, e.g., a Na salt, is used, the resultant material sometimes has a hygroscopic property and exhibits a lower specific resistance on account of the water adsorbed. These physical properties vary in accordance with the kind of the starting compositions, the heat treatment conditions, the shape of the products, etc. An example of the fibrous products teaches that the strength increases with a rise in the heat treatment temperature, giving a value of 15 - 50 kg/mm 2 by the heat treatment at 350 - 450°C in a stream of nitrogen. The specific surface area of the fibers also increases with increasing heat treatment temperature, giving a value of 50 - 200 m 2 /g for a 350°C-heat-treated product and approximately 250 m 2 /g for a 450°C-heat-treated product, as measured by the CO 2 BET method. The present invention will be illustrated more specifically with reference to the following examples. Example 1: To 1,280 g of refined naphthalene was added 1,050 g of 98% sulfuric acid, and the naphthalene was sulfonated by reaction at 155°C for 3 hours. The resulting mixture was distilled under reduced pressure to remove the unreacted naphthalene and the water formed by the reaction out of the system. The composition of the sulfonated product was: β-naphthalenesulfonic acid = 96.2 wt.%; α-naphthalenesulfonic acid = not detected; naphthalaenepolysulfonic acid = 3.0 wt.%; and unreacted naphthalene = 0.8 wt.%. Thereafter, the sulfonated product was added with 1,000 ml of water and then with 857 g of 35% aqueous formaldehyde. They were reacted at 105°C for 8 hours and neutralized with ammonia. Insoluble matters were separated therefrom by filtration and the filtrate was concentrated to obtain an aqueous solution of a formaldehyde condensation product of β-naphthalenesulfonic acid with a number average molecular weight of 3,820, the solution containing 45 wt.% of water and having a viscosity of 1,000 poise at 32°C. The aqueous solution as a raw material was subjected to dry spinning using spinneret of 0.1 mm diameter. The resulting spum fiber was put in a vessel at a bulk density of 0.025, *) charged in a furnace kept at 250°C, and raised in temperature in a stream of nitrogen at a rate of 20°C/min. to a predetermined temperature, at which it was kept for a predetermined period of time for its heat treatment. The properties of the heat-treated products thus obtained are given in Table 1. The 375°C-heat-treated product given in Table 1 was allowed to adsorb ammonia, then to desorb the ammonia at 180°C, and to adsorb ammonia again at room temperature. Ammonia was adsorbed therein in an amount of 34.3 mg/g. The same sample was then allowed to desorb the ammonia at 250°C, and to adsorb ammonia again, with the result that 34.9 mg/g of ammonia was adsorbed. Thus, it was found that repeated use of the products was feasible by heat regeneration. Example 2: To 1,420 g of naphthalene oil (composition: a lower boiling distillate than naphthalene boiling point = 4.2 wt.%; naphthalene = 28.4 wt.%; β-methylnaphthalene = 49.0 wt.%; α-methylnaphthalene = 12.1 wt.%; an intermediate boiling distillate between naphthalene and α-methylnapthahlene = 4.0 wt.%; and a higher boiling distillate than α-methylnaphthalene boiling point = 4.3 wt.%) was added 1,200 g of 98% sulfuric acid. The naphthalene oil was sulfonated by reaction at 150°C for 3 hours. The resulting mixture was distilled under reduced pressure to remove the unreacted oil and the water formed by the reaction out of the system. Thereafter, the sulfonated oil was added with 500 g of water and then with 857 g of 35% aqueous formaldehyde. They were reacted at 105°C for 15 hours, and then calcium hydroxide was added thereto in an amount of 0.9-equivalent to the residual sulfuric acid, thereby removing the sulfuric acid as gipsum by filtration. The filtrate was neutralized with ammonia and subjected to evaporation at 105°C for 2 hours. Based on the solid residue thus obtained, 0.5 wt.% of polyethylene glycol (manufactured by Seitetsu Chemical Industries Co., Ltd.; trade name: PEO-3; average molecular weight: 600,000 - 1,100,000) was added as an aqueous solution. The resultant mixture was adjusted in water content to obtain a starting composition containing 38 wt.% of water and having a viscosity of 10,000 poises at 80°C, the composition being composed mainly of a formaldehyde condensation product of sulfonated naphthalene oil, the solid matter of which composition contains 13.6 wt.% of sulfo groups in terms of sulfur content. The starting composition was subjected to an extruder at 80°C to form it into a honeycomb-shaped molded article. The molded article was then raised in temeprature at a rate of 10°C/min. in a stream of air under a reduced pressure of 50 Torr from room temperature to 375°C, at which it was kept for 15 minutes for its heat treatment. The honeycomb molded article thus obtained was black and contained 4.4 wt.% of sulfo groups in terms of sulfur content. It was insoluble in solvents and infusible and had a surface area of 1.0 m 2 /g according to the N 2 BET method and that of 75 m 2 /g according to the CO 2 BET method. Its adsorption of ammonia was 35 mg/g, while the specific resistance was 10 8 Ω·cm or more, at room temperature. The honeycomb molded article was immersed in a 1 wt.% aqueous NaCl solution in an autoclave and treated under the conditions of 20 atmospheres and 150°C. Its ion exchange capacity was measured to be 2.4 meq/g, showing a good performance as an ion exchanger. Example 3: The 325°C-heat-treated black fiber obtained in Example 1 was packed in a 120 x 40 x 40 mm mold at a density of 0.136 g/cm 2 *) and treated with heat for 5 minutes in a furnace at 350°C. The resulting molded article was a rectanglar parallelopiped with dimensions of 120 x 40 x 38 mm and a density of 0.134/cm 2 **) and contained 5.2 wt.% of sulfo groups in terms of sulfur content. Its heat conductivity was 0.045 W/m·k, exhibiting a good performance of thermal conduction, while the specific resistance was 10 8 Ω·cm or more.

Claims: A process for the heat treatment of a formaldehyde condensation product of ammonium β-naphthalene-sulfonate, which is a mixture of monomer and various polymers having polymerization degrees of up to 200, and has a number-average molecular weight of 800 to 50,000, a condensation product of a sulfonated creosote oil, which is a mixture of monomer and various polymers having polymerization degrees of up to 40, and has a number-average molecular weight of 2,000 to 5,000 or a condensation product of phenanthrenesulfonic acid, which is a mixture of monomer and various polymers having polymerization degrees of up to 30, and has a number-average molecular weight of 2,500 to 5,000, consisting of either heat treating the polymers in a non oxidizing atmosphere at a temperature between 250°C and 500°C or heat treating the polymers in an oxidizing atmosphere at a temperature between 250°C and 400°C and if necessary heat treating the resulting composition in a non-oxidizing atmosphere at a temperature between 250°C and 500°C.

Inventors: SAKATA KOJI, SAKAWAKI KOUJI, SAKATA, KOJI, SAKAWAKI, KOUJI
Applicants: MITSUI MINING CO LTD, MITSUI MINING COMPANY, LIMITED
Application year: 1990
Main classification: C08J3
IPC codes: B01J20, C08J7, C08G16, C08J3, D01F6