US541147A - blackman - Google Patents

Description

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H.. BLAGKMAVN. PROCESS or AND APPARATUS FOB. BLnAcHme,

Patented June 18,- 1895.

FIG. 1.

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H. BLACKMAN PROCESS OI AND APPARATUS FOR BLEAGHING.

No. 541,147. Patented June 18, 1895.

FIG. 2.

FIG. 4.

WITNESSES: INZENTOR:

By his Attorneys,

(No Model.) 3 Sheets-Sheet 3.

H-QBLAGKMAN.

PROCESS OF AND APPARATUS FOR BLEAGHING.'

No. 541,147. Patented June 18, 1895.

FIG. 7.

WITNESSES: A INVENTO'R:

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UNITED STATES PATENT OFFICE.

HENRY BLACKMAN, OF NEW YORK, N. Y.

PROCESS OF AND APPARATUS FOR BLEACHING.

SPECIFICATION forming part of Letters Patent No. 541,147, dated June 18, 1895.

Application filed June 28, 1894. Renewed April 27, 1895. Serial No. 547,414- (No model.)

To all whom it may concern:

Be it known that I, HENRY BLACKMAN, a citizen of the United States; residing in the city, county, and State of New York, have invented certain new and usefullmprovements in Processes of and Apparatus for Bleaching, of which the following is a specification.

This invention relates to bleaching by an electrolytically prepared bleaching agent, and has particular reference to the bleaching of paper pulp and analogous materials, although applicable generally for bleaching textile fibers, fabrics, &c.

When an aqueous solution of for example sodium chloride is subjected to electrolysis, the sodium chloride is decomposed, the so-, dium liberated at the cathode in turn decomposing the water, combining with one equivalent of hydrogen and the oxygen to form sodium hydrate, the other equivalent of hydrogen being set free and escaping in bubbles, while the chlorine which appears at the anode will, unless in some way prevented from so doing, combine with the sodium hydrate, which undergoes a new reaction and produces sodium hypochlorite NaCaO. This hypochlorite constitutes a valuable bleaching agent. The same essential reaction will occur by the use of a chloride of any of the alkalies or alkaline earths, as for example if magnesium chloride be thus electrolyzed, there results magnesium hypochlorite. Efforts have heretofore been made to practice bleaching by generating these hypochlorites electrolytically. The instability of the hypochlorites, however, in connection with the difiiculty of electrolyzing a sufficient percentage of the electrolyte to afiord other than a very weak bleaching solution, has rendered these efforts to great extent futile from the 'point of View of practical economy. It is found that if the electrolysis be continued sufficiently to produce other than a weak solution of sodium hypochlorite (for example), this hypochlorite by reason of its great instability degenerates into sodium chloride and sodium chlorate, both of which are devoid of bleaching prop erties. A weak solution 0t sodium hypochlorite which it is feasibleto produce by electrolysis of brine, is found to bleach very slowly, the time required being such that the process ofiers no economic advantage over the ordinary method of bleaching by chlorine or chloride of lime.

My invention is based. upon a discovery which I have made, namely, that upon heating such a weak solution of sodium hypochlorite to a sufficient temperature, its activity as a bleaching agent is many times intensified.

According to my invention I electrolyze an aqueous solution of sodium chloride (or other alkali or alkaline earth) and after drawing off the electrolyte from the electrolytic cell, I heat it to the required high temperature, and maintain it at such temperature during the bleaching. The temperature which is most advantageous is that which gives the maximum activity of bleaching with the minimum conversion of sodium hypochlorite into sodiumchlorate. Inasmuch as only from five to ten per centof the electrolyte can be advantageously decomposed for the formation of the hypochlorite, it is desirable after the bleaching operation to return the electrolyte to the electrolytic cell and further electrolyze it, in order thereby to thoroughly utilize the brine or other solution and render the process a continuous one; but to return the hot electrolyte to the cell, would both impair the electrodes and decrease the efiiciency of the electrolytic decomposition.

A second feature of my inventiontheret'ore consists in removing the spent bleaching agent, cooling it to a normal or sufficiently low temperature, and subjecting it again to electrolysis to again generate the hypochlorite and reconstitute it a bleaching agent, whereby the process is made continuous, fresh brine being added from time to time as may be found necessary.

For effectively carrying out my said process, I have devised the combination of apparatus shown in the accompanying drawings, wherein- Figure 1 is a plan view. Fig. 2 is a sectional elevation. Fig. 3 is a transverse section of the electrolytic cell. Fig. 4 is a plan of this cell. Fig. 5 is a transverse section of the cooler. Fig. 6 is a plan of the cooler. "Fig. 7

is a vertical section showing a modified construction of apparatus.

Referring to Figs. 1 to 6, letA designate an electrolytic cell or electrolyz'er; B, a suitable heater; 0, a bleaching tank of any suitable sort; D, a circulating pump, and E, a cooler.

The electrolyzer A may be of any suitable construction, of which the one form shown is an example. It is constructed with an inclosing box or tank a, a perforated pipe I) for admitting the brine or other electrolyte, a perforated pipe 0 for removing the electrolyte, alternate electrodes or plates, preferably of zinc and platinum d and e respectively, all the anode plates 61 at being connected to a conducting rod 01' at one side, and all the cathode plates 9 e being connected to a conducting rod 6 at the other side. These plates are so arranged that the liquid circulating from the pipe to the pipe 0 shall flow in thin streams between the respective plates, and shall be thereby subjected to the electrolytic action of electric currents flowing from the anode plates toward the adjacent cathode plates. The outlet pipe 0 is extended upward at c in order to maintain the liquid at a level sufficient to keep the plates submerged, as shown in Fig. 3. A pipef connects thence with the heaterB and bleaching tank 0, the flow of liquid being con trolled by a valve f.

The heater B may be variously constructed,

the particular construction shown consisting of a steam pipe 9 extended within the pipef in which the electrolyzed brine flows. The steam entering the pipe 9 radiates heat to the surrounding column of brine, and the steam thereby is or may be more or less condensed, any remaining steam, and any water of condensatio'n that are formed, being discharged from the lower end of the pipe into the brine, so that all the heat of the steam is communicated to the brine. The temperature may be regulated by adjusting the flow of steam by means of a valve g.

In lieu of or in addition to the heater B, the liquid may be heated in the tank 0 by means of a heater B, shown best in Fig. 1. consisting of a coil of pipe laid in the lower portion of the tank and through which steam is circulated, controlled by a valve g*, the water of condensation produced in this coil being removed by a trap 9 Either or both these means of heating may be employed, it being a matter of little importance whether the bleaching liquid is heated before its introduction into the bleaching tank or afterward.

The particular construction of bleaching tank 0 shown in the drawings, is designed especially for the treatment of paper pulp, being what is known to paper makers as a beater engine. It is constructed as usual with a heater cylinder 0 formed with knives or paddles working against the fixed knives C beneath, and throwing the pulp up over a dam C from which it flows down the back fall in the usual manner. In order to remove the bleaching liquid from the tank in the same proportion as the new liquid that isv introduced, the tank is provided with a revolving washer or strainer F consisting of a wire gauze cylinder or octagonal prism, through the meshes of which the liquid can flow, but not the fibrous matter, and having internal blades or dippers which scoop up the entering liquid and direct it out through a discharge pipe F, from which it falls into the hopper F and descends into the tank G of suitable capacity. This tank may be employed for originally. mixing the brine. is pumped by a pump D through a pipe h and through the cooler E. This cooler may be of any suitable construction, of which that shown in Figs. 5 and 6 is an example, consisting of a tank containing cold water and having rows or sections of horizontal pipes t' extended through it, through which the warm brine flows back and forth, cold water being introduced by a pipe-j, and caused by vertical partitions k k to flow in a zigzag course as indicated by the arrows in Fig. 6, the water thus flowing generally in the opposite direction to the brine, and beingfinally discharged bya pipe j. As it passes through the coils of pipe 1', the brine or electrolyte is cooledand flows thence by a pipe h to the plectrolyzer, which it enters by the perforated pipe b as before described, and flows again in parallel currents between the adjacent electrodes or plates. Thus the brine is first electrolyzed in the electrolyzer A for generating sodium I hypochlorite. The bleachingliquid thus produced then flows by its own weight through the pipef to the heater B, where it is heated and is discharged through the nozzle 1 into the [COL bleaching tank 0. The pulp to be bleached is placed in this tank, the operations of bleaching and beating by the beater engine going on simultaneously, the beater cylinder 0' being driven by any suitable power, and the washer F being continuously revolved. The bleaching liquid'and pulp are kept heated by introducing steam to the heaters'B and B' (one or both) to maintain the pulp at the required temperature. The exact temperature which should be employed is that which gives 1 the maximum activity of bleaching, with the minimum conversion of sodium hypochlorite into sodium chlorate. I have found a temperature of from to Fahrenheit to give good results, being as nearly as I have been able to ascertain, sufficiently close for practical purposes. At these temperatures the bleaching proceeds rapidly, the strength of the bleaching agent being continually fortified by drawing ofi a quantity of it by means of the strainer cylinder F, the liquid thus removed descending to the tank G, and being again pumped up passed through the cooler E to reduce it again to a normal temperature,

and again passed through the electrolyzerA, by which a further quantity of brine is converted into sodium hypochlorite.

entire quantity of pulp in the beater engine has been sufficiently bleached, it is run out into a drainer, where the bleaching liquor-is strained out of it, this liquor being-then pumped back to the tank G, or some other not When the Y 130];

1s From this tank the brine.

tank in connection with the described circuit. The pulp is finally washed in a percolator to expel the remaining quantity of bleaching liquid. 7 I

In practicing my process, the brine may advantageously have a density of upward of 2 Baum, or preferably 4 to 6, and of this brine the electrolyzer may convert from five to ten per cent. into hypochlorite of sodium. The electric energy required will depend upon circumstances, as to the size of the electrolyzer, the number of plates employed,-and the distances of the plates apart, and other conditions. I have successfully employed a pressure of from four to five volts.

My invention may be variously modified without departing from its essentialfeatures. For example the apparatus shown in Fig. 7 maybe substituted for that already described. Here the cooler and electrolyzer are combined in one by placing cooling pipes m m in the upper part of the electrolyzer tank so as to cool the electrolyte before or during the electrolysis. Through these pipes on cold water, or salt Water made by mixing ice with salt, or cold brine or other noncongealable liquid from an ice machine, may be circulated. The heater B here consists of a chamber to which steam is admitted, and a pipe f conducting the brine from the electrolyzer to the bleaching tank, extendedwithin this'chamber in the form of a coil. The condensed steam is carried off by a trap g The bleaching tank lettered G is a simple tank in which is placed the material 19 to be bleached, the bleaching liquor being taken out as it overflows from the tank through a pipe F which runs it into a receiving tank G. From this tank it is pumped by the pump D through a pipe 71. up to a brine percolator H, in which the brine is strengthened by causing it to percolate through a mass of salts. The refortified brine then descends through the pipe t to the electrolyzer, being cooled by the cooling pipes m.

It is not essential to my invention that a continuous circulation should be maintained in the manner described, although this is practically preferable. In lieu thereof a given quantity of brine may be sufiiciently electrolyzed and then run into a tank containing material to be bleached, being heated either before or after it enters the tank, and may remain in contact with the material until the latter is sufficiently bleached without undergoing any circulation.

I claim as my invention the following-defined novel features,-substantially as hereinbefore specified, namely: 1. The process of bleaching consisting in first electrolyzing a solution of achloride of an alkali or alkaline earth, heating the electrolyte containing the resulting hypochlorite and bleaching with it while at an elevated temperature, then cooling it and again electrolyzingit, whereby the bleaching is performed at a high temperature and the electrolysis at a low temperature.

2. The described continuous electrolytic bleaching process consisting in first electrolyzing a solution of a chloride of an alkali or alkaline earth by circulating it through an electrolyzer, heating the electrolyte containing the resulting hypochlorite, bleaching with it while at an elevated temperature, continuously drawing ofithe electrolyte from the material being bleached, cooling it, and returning it to the electrolyzer.

3. The improved bleaching apparatus consisting of the combination of an electrolyzer, a bleaching tank, a heater, a cooler, a circulating pump, and connecting pipes constituting a circuit, whereby the bleaching liquid will be cirlcuated through the electrolyzer to the heater and bleaching tank, and thence through the cooler back to the electrolyzer.

4. The improved apparatus for bleaching electrolyzer, a heater, a pipe leading from the electrolyzer to the heater and from the heater to the bleaching tank, a cooler, pipes leading from the tank to the cooler and thence to the electrolyzer, and a circulating pump in the circuit of pipes.

In witness whereof I have hereunto signed my name in the presence of two subscribing witnesses.

HENRY BLAOKMAN.

Witnesses:

- ARTHUR G. FRASER,

GEORGE H. FRASER.

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