RU2096319C1 - Method for producing carbon articles having controllable characteristics and porous structure - Google Patents

Abstract

FIELD: production of filtering elements both for micro- and ultrafiltration processes using baromembranes, and for conventional filtration operations; production of porous carbon articles for electrode industry and electrical engineering. SUBSTANCE: first filler of narrow fractions is taken in amount 40-66% and mixed at temperature 120 C with corresponding amount of binder. Latter is constituted by medium-temperature coal-tar pitch (grade A) and polyethylene wax used as pore-forming agent. Latter is waste product resulting from production of low-density polyethylene. Mixture thus-formed is subjected to pressing by broaching press, die of which has temperature 77 - 103 C. Finally, articles are subjected to roasting by steps of temperature rises at rate not greater than 3 deg/min up to 1000 C. EFFECT: method makes it possible to turn out high-quality filtering carbon elements. 5 dwg

Description

 The invention relates to chemical technology, namely to the production of porous carbon materials, and can be used mainly in the production of filter elements for both baromembrane micro and ultrafiltration processes, and for the traditional filtering process, as well as in the preparation of porous carbon products in the electrode and the electrical industry.

A known method for the production of porous carbon products, which include mixing a carbon filler with a binder phenol-formaldehyde resin and pitch, molding the resulting mixture and subsequent corbonization when stuffing workpieces up to 1000 ^o C and above for 240 300 h [1] The formation of pores in the carbon material when this The method occurs due to the removal of gaseous products released from the binder during the firing of a carbon product. However, the use of phenol-formaldehyde resin leads to an increase in the proportion of closed pores in the calcined product.

 A known method of obtaining a porous carbon material, including the preparation of the current casting slip based on a liquid dispersion phase, mixing a pre-homogeneous dispersed organic binder of a liquid porophore and a dispersed agent, casting blanks from a slip, curing them to a self-supporting state, removing liquid dispersion phases from the blanks and subsequent heat treatment to high temperatures [2] The disadvantages of this method include the high complexity of technological operations and low pr productivity.

The present invention is to develop a method for producing porous carbon materials, which allows to control both the value of open porosity and pore size in the finished product. This problem is achieved by modifying the binder by adding an organic blowing agent into it, which is homogeneously distributed in it and decomposes with the formation of a minor coke residue, as well as by using a filler of narrow fractions. The proposed method involves mixing at a temperature of 120 ^o C of the filler of narrow fractions in an amount of from 40 to 66% with an appropriate amount of a binder, consisting of medium-temperature coal tar pitch grade A and blowing agent of polyethylene wax (PV), which is a waste product of the production of low density polyethylene (PV content in a modified binder from 20 to 60 wt.% pressing the mixture on the piercing press at the temperature of the mouthpiece (die) from 77 to 103 ^o C, and firing when raising the temperature at a speed of no higher than 3 deg / min to 1000 ^o C.

 The use of coal tar pitch modified with polyethylene wax makes it possible to reduce the yield of coke residue during the roasting of a product as compared to using the same amount of unmodified binder. The advantage of this method of regulating porosity is that with virtually lower binder content, the rheological properties of the mixture do not deteriorate, which is especially important for piercing molding. In addition, the maximum value of porosity can reach the filler voidness, which, as we have found, for narrow fractions is practically independent of the average particle size and is approximately 50%. Moreover, the particle size, as was shown in a number of works, determines the average size then in fired products. Thus, the use of a modified binder allows under certain conditions to simultaneously control both open porosity and the predominant pore size in the calcined product. The above process parameters limits provide optimal characteristics of the porous structure of products, their strength properties and geometric dimensions, as illustrated by the following examples.

 Example 1

In a heated mixer load 60 wt. coke KNPS fractions 32 microns, 28 wt. crushed coal tar pitch and 12 wt. shredded polyethylene wax. Stir at room temperature for 30 minutes. Then, with constant stirring, the temperature in the mixer is raised to 120 ^° C. and stirring is continued for 60 minutes. The mixture is cooled, discharged and molded in a hydraulic press in the form of tubular elements with a diameter of 10 mm with a wall thickness of 2 mm and a length of 1000 mm at a die temperature of 90 ^o C. The cooling field of the product is placed in a protective coke charge and fired, raising the temperature to 1000 ^o C speed 2 deg / min. The resulting material has the following characteristics: open porosity - 43.5% radius (and proportion) of the predominant pores 0.2 μm (70%); tensile strength 3.5 MPa.

 Example 2

The cooking sequence as in example 1, characterized in that the crushed wax and pitch are preloaded into the mixer in the indicated proportions, heated with stirring to 120 ^° C and heated coke is added (to avoid clumping of the mass). The resulting material has the same characteristics as in example 1.

 Example 3

Mine, consisting of 44.5 wt. coke KNPS fraction -36; +32 microns. 26.1 wt. pitch and 29.4 wt. the blowing agent, mixed as described in example 1 or 2. Form at a temperature of 77 ^o C and burn, raising the temperature to 1000 ^o C at a speed of 1 deg / min. The resulting material has the following characteristics: open porosity 55.5%, the radius of the predominant pores is 21.0 μm; tensile strength 2.25 MPa.

 Example 4

61.5 wt. coke KNPS fraction -36; +32 μm, 28.1 wt. coal tar pitch and 10.4 wt. polyethylene wax is mixed as described in example 1 or 2. It is molded at a temperature of 103 ^o C and fired, raising the temperature to 1000 ^o C at a speed of 1 deg / min. The resulting material has the following characteristics: open porosity 45% radius of the predominant pores (and their fraction) 0.2 μm (78%); tensile strength 2.5 MPa.

 Example 5

53 wt. coke KNPS fraction -50; +36 μm, 37.6 wt. coal pitch and 9.4 wt. polyethylene wax is mixed as described in example 1 or 2. It is molded at a temperature of 90 ^o C and fired, raising the temperature to 1000 ^o C at a speed of 1 deg / min.

The resulting material has the following characteristics: open porosity
29.6% radius of the predominant pores 1 μm; tensile strength 3.5 MPa.

 The scope of the invention is limited by the following parameters.

 When coke is added to the composition in an amount exceeding 66%, piercing molding cannot be used due to the “rigidity” of the mass.

 When the coke content in the composition is less than 40%, the product is destroyed during the firing process.

When using the compositions indicated in the claims, the composition is not formed using piercing molding if its temperature is below 70 ^° C. If the molding temperature exceeds 110 ^° C, then the product is deformed when it leaves the mouthpiece (die) of the press.

Claims (1)

A method of producing carbon products with controlled characteristics of the porous structure, including mixing calcined petroleum coke of narrow fractional composition with coal tar pitch, piercing molding and firing in a protective backfill at 1000 ^° C, characterized in that polyethylene wax in the amount of 9 36 wt. coke is served in an amount of 40 to 66 wt. the components are mixed at 120 ^o C, and molding is carried out at 70 110 ^o C.