Analysis of kraft liquors

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with the aid of the following । drawings, in which:

FIG. 1 is a simplified diagrammatic flow sheet of the process of this invention; and

FIG. 2 is a graph showing the relationship between the cal: culated percent apparent causticity of various kraft cooking liquors and differential conductivity measurements determined according to the present process.

DETAILED DESCRIPTION

Kraft cooking liquor is taken from the circulating cooking liquor of a kraft mill, as for example from the causticizer, passes through conduit 10 and is pumped by pump 12 through conduit 14, valve 16, to a self-cleaning filter 18 where fibers and other debris are removed from the liquor. The liquor then passes through conduit 20, cooling coil 22, where the temperature of the liquor is cooled to a predetermined temperature, such as 25° C., and then through conduit 24 to conductivity cell unit 26. It is obvious that if conductivity unit 26 is equipped with a temperature compensator, the cooling coil 22 may be eliminated and the liquid passed from filter 18 directly to conductivity unit 26. The electrical conductivity of the liquor is measured in unit 26 and a signal, corresponding to the value of the conductivity measurement, is sent to analog computer 28 via circuit 30.

When the above conductivity measurement is completed, valve 32 is opened and the liquor passes from unit 26 to vessel 34 by way of conduit 36. Simultaneously, a barium chloride solution (preferably about 10 percent by weight) is metered from supply tank 38, passing through valve 40 and conduit 42. The barium chloride solution is supplied to vessel 34 in an amount about equal to that of the liquor, on a volume basis. The soluble carbonates, especially sodium carbonate, immediately precipitate from the liquor which is then passed to self-cleaning filter 44 by means of pump 46, conduit 48, and valve 50. The precipitated materials are removed from the liquor by filter 44, and the liquor then passes into conductivity cell unit 26 by means of conduit 52. The electrical conductivity of the liquor is measured again and a second signal is sent via circuit 30 to analog computer 28 which performs, in known manner, a subtraction of the two conductivity mea3,607,083 surements. The differential conductivity is transmitted through line 54 to recorder 56 to provide a reading of the differential conductivity. When the differential conductivity determination is complete, the liquor is drained from the unit 26 by means of valve 58 and line 60.

To those skilled in the art, it will be readily apparent that analog computer 28 controls the various valve openings and closings by means of circuits 62,64,66,68 and 70. Further, as will be understood, the conductivity cell unit 26 is standard and well known to those skilled in the art and may comprise, for example, a Beckman conductivity bridge arrangement, Model No. RD-16B2, including a Pyrex dip conductivity cell, Beckman Model No. CELBB1.

It is to be understood that FIG. 1 is diagrammatic of a flow pattern that may be utilized in practicing the present invention. Various changes may be made in the flow path. For example, filter 44 can be eliminated by routing conduit 48 back to filter 18. Obviously, the system is subject to other changes, as recognized by those skilled in the art.

The differential conductivity of a kraft cooking liquor, as determined according to the present process, has a straight line relationship with the apparent causticity of the liquor. Various samples of green and white kraft liquors were tested in the laboratory by a known analytical procedure for apparent causticity. This procedure involved dilution of a 5 ml. sample of liquor with water to 25 ml. The diluted liquor was then titrated with 0.322261 N HC1 to the phenolphthalein endpoint (A) and to the methyl orange endpoint (B). From the amounts of HC1 used for the two endpoints A and B, the apparent causticity was calculated as follows:

Percent apparent causticity =A—(B—A)/B X100 The following data was obtained from the known analytical procedure for several kraft liquor samples:

<td> Liquor No.</td><td> Percent Apparent Causticity</td>

<td> 1</td><td> 69.5</td>

<td> 2</td><td> 73.7</td>

<td> 3</td><td> 74.4</td>

<td> 4</td><td> 74.0</td>

<td> 5</td><td> 74.8</td>

<td> 6</td><td> 75.8</td>

<td> 7</td><td> 78.3</td>

<td> 8</td><td> 81.3</td>

Differential conductivity measurements were determined for the above liquors according to the process of the present invention. Conductivity measurements were made after the samples were quickly cooled to about 25° C. The complete process took only about 4 minutes. The differential conductivities were as follows:

Differential Conductivity

Liquor No. (mho/cm.)

135.0

140.0

<td colspan="4"> TABLE — Continued</td>

<td></td><td> Liquor No.</td><td> Differentia! Conductivity</td><td> (mho/cm.)</td>

<td> 5 ’</td><td> 3</td><td></td><td> 145.0</td>

<td></td><td> 4</td><td></td><td> 144.0</td>

<td></td><td> 5</td><td></td><td> 146.0</td>

<td></td><td> 6</td><td></td><td> 147.0</td>

<td></td><td> 7</td><td></td><td> 153.5</td>

<td> 10 :------</td><td> 8</td><td></td><td> 161.0</td>

’ A plot of the differential conductivities of liquors 1-8 against the calculated apparent causticities of the liquors obtained : from the known analytical procedure is shown in FIG. 2.

From the above, it can be seen that the apparent causticity of kraft cooking liquors can be determined quickly and accurately according to the process of this invention. The speed of the process allows for timely corrections to be made in a kraft liquor so as to obtain the most efficient use of the kraft process

2Q and cooking chemicals.

It is obvious that variations may be made in the process of this invention without departing from the spirit and scope thereof.