GB2064994A - Process for classification of carbon black - Google Patents

Abstract

In a process for the classification of carbon black, powdered carbon black from a feeder is entrained in air at a concentration of 0.01-1.0 Kg/m<3>, and preferably passed through a blower, before being fed into a pneumatic classifier.

Description

SPECIFICATION Process for classification of carbon black The present invention relates to a process of classification of carbon black. More particularly, it relates to a process of classification of carbon black for separating impurities from carbon black.

Carbon black is produced by a thermal decomposition of hydrocarbons. In the production of carbon black, hard gritting carbon material is produced in the furnace used for the thermal decomposition. In the collection of the resulting carbon black, iron powder formed by corrosion of the apparatus contaminates the carbon black.

In the foregoing, the grit, iron powder etc. are referred to simply as 'impurities'. In order to use carbon black in various fields, it is necessary to separate out the impurities.

In order to separate the impurites from carbon black, a gravity separation, a magnetic separation and floatation have been known. The carbon black is fine and scatterable to be inconvenient for handling. The carbon black has the chain structure connecting many fine carbon particles which forms a coagulate in the intertwined structure, whereby it is difficult to substantially separate the fine impurities entangled in the coagulate.

The impurities in the carbon black are measured as a content rough particles by the Japanese Industrial Standard K-1469. In accordance with the conventional process for separation of the impurities, it is difficult to reduce the content of the rough particles to less than 0.002 wt. %. The carbon black having a content of the rough particles of about 0.01 wt. % has been used for most of fields, however, it has been required to use carbon black having less content of rough particles in the special fields requiring electric conductivity such as carbon black blended to a resin for coating a high voltage cable.

An object of the present invention is to overcome these disadvantages and to provide a process for producing carbon black having remarkably small content of the rough particles by feeding air entraining carbon black at a specific concentration to a pneumatic classifier.

The present invention is to provide a process of classification of carbon black by feeding carbon black into a pneumatic classifier by a powder feeder which comprises feeding air between said powder feeder and said pneumatic classifier to entrain carbon black in air at a concentration of 0.01 to 1.0 kg ./m3.

The process of the present invention will be illustrated in detail.

Figure lisa block diagram showing steps of the embodiment of the present invention.

The carbon black obtained by the conventional separation and collection from gaseous products discharged from a carbon black furnace shown in Figure 1 is fed through a carbon black inlet passage (6) into a tank (1). The carbon black stored temporarily in the tank (1) is entrained in air (suction or compression) fed through the air inlet passage (7) into a carbon black powder feeder (2) and is fed through a blower (3) into a pneumatic classifier (4).

The blower (3) makes excellent dispersibility of carbon black in the air flow by the mechanical function. The concentration of carbon black in the air flow is controlled by feeding a desired rate of air through an air passage (8) equipped in the suction side of the blower (3), into the air flow entraining carbon black fed from the powder feeder (2) in the floating condition. The impurities separated by the pneumatic classifier (4) are discharged through the impurity discharge passage (9). The carbon black treated by the classification is fed together with air entraining the carbon black, into the separationcollector (5). The carbon black separated by the separation-collector (5) is discharged through the carbon black outlet passage (11) and air is discharged through the air outlet passage (10).

A concentration of carbon black in the air entraining carbon black fed into the pneumatic classifier (4) is in a range of 0.01 to 1.0 kg./m3 preferably 0.03 to 0.5 kg./m3.

When a concentration of carbon black fed into the pneumatic classifier, is more than 1.0 kg./m3, the floating dispersibility of carbon black is not satisfactory to cause the unsatisfactory separation of the impurities. When it is less than 0.01 kg./m3, the separation of the impurities is effective, however, the amount of carbon black treated in unit capacity by the classifier is disadvantageously low.

In the process of the present invention, various kinds of powder feeders can be used. For example, suction nozzle type, rotary feeder type or ejector type feeder is preferably used. The pneumatic classifier can be centrifugal pneumatic classifiers such as all peripheral feed type, classiclone type, microsepar atortype, microplextype centrifugal pneumatic classifiers; lower type, Vantongeren type inertia pneumatic classifiers; and gravity type pneumatic type classifiers. The principles of these pneumatic classifiers are described in Kagaku Kogaku Binran fourth edition published by Maruzen in 1978.

In accordance with the process of the present invention, the concentration of carbon black is controlled and air entraining carbon black is passed through the blower, to improve dispersibility of carbon black to impart the separation oftheimpuri- ties.

As described in Example 1 and Reference 1, bulk densities of carbon blacks separated and collected through the classifier, are respectively 0.015 g./ml.

and 0.023 g./ml. Therefore, it is understood that the dispersibility of carbon black is improved by passing through the blower.

The effects of the process of the present invention are as follows: (1) The impurities contained in carbon black can be reduced to be less than 0.0002 wt. % as the rough particles which could not be succeeded by the conventional process.

(2) The apparatus is simple and the operation is easy.

(3) The maintenance is easy.

The present invention will be further illustrated in detail by certain examples.

Example 7 In the steps of classification of carbon black shown in Figure 1,carbon black containing impurities at a content of 0.024 wt. % as rough particles was fed into air flow at a rate of 150 kg./hr. to give an average concentration of carbon black of about 0.6 kg./m3 by an ejector type powder feeder (2). The air flow entraining carbon black was sucked by a centrifugal blower (3) and simultaneously air was fed through an air inlet (8) placed at the suction inlet of the blower (3) thereby controlling the concentration of carbon black at the inlet of the pneumatic classifier (4) to be 0.065 kg./m3. The air entraining the carbon black was passed through Vantongeren type pneumatic classifier (4) thereby separating the impurities through an outlet passage (9). The carbon black was separated and collected by a cyclone and a bag-filter.As a result, a content of the rough particles in the carbon black was reduced to 0.0003 to 0.0001 wt.%.

As a reference, the apparatus of Example 1 was used and carbon black having a content of rough particles of 0.024 wt. % was fed into air flow to entrain in it at a rate of 150 kg./hour by an ejector type powder feeder to give an average concentration of carbon black of 0.065 kg./m3. The air entraining carbon black was directly fed into Vantongeren type pneumatic classifier to classify it without passing through a blower and carbon black was separated and collected by a cyclone and a bag-filter. As a result, a content of rough particles in carbon black was 0.0028 to 0.0016 wt. %.

Example 2 In the apparatus of Example 1, carbon black containing impurities at a content of 0.024 wt. % as rough particles was fed into air flow as a rate of 150 kg./hour to give a concentration of 0.6 kg./m3 by an ejector type powder feeder and the air entraining carbon black was fed through the blower into Vantongeren type pneumatic classifier and the carbon black was separated and collected by a cyclone and a bag-filter. As a result, a content of rough particles in carbon black was 0.0008 to 0.0004 wt. %.

Claims (3)

1. A process for the classification of carbon black by feeding carbon black into a pneumatic classifier by a powder feeder, which process comprises feeding air between said powder feeder and said pneumatic classifier to entrain carbon black in gas at a concentration of from 0.01 to 1.0 kg./m3.

2. A process according to Claim 1 wherein said carbon black in air is passed through a blower before feeding it into said pneumatic classifier.

3. A process according to Claim 1 or Claim 2 substantially as herein described with reference to either of the Examples.