US1815328A - Process of recovering and utilizing the valuable compounds in spent cooking liquors - Google Patents

Description

July 21, 1931. A mgm-ER 1,815,328

. PROCESS OF RECOVERING AND UTILIZING THE VALUABLE COMPOUNDS IN SPENT COOKING LIQUORS Original Filed Nov. 23, 1927 Patented July 21, 1931 UNITED STATES PATENT oFFicE GEORGE A. RICHTER, OF BERLIN, NEW HAMPSHIRE, ASSIGNOR TO BROWN COMPANY, OF BERLIN, NEW HAMPSHIRE, A kCORPORATION OF MAINE `:PROCESS OF RECOVERING AND UTILIZING THE VALUABLE COMPOUNDS IN SPENT i COOKING LIQUORS 'Original application iiled November 23, 1927, Serial No. 235,335. Divided and this application filed January This invention relates to a process of recovering and utilizing valuable compounds in spent cooking liquors, and more especially liquors of the class containing sodium-sulphur compounds.

Various liquors of both acid and alkaline character containingV sodiumnsulphur compounds as the fiber-liberating agents have been proposed and are now being utilized for the production of pulp from raw cellulosic materials, a typical alkaline liquor of this class being kraft or sulphate liquor, so

called, and a typical acid liquor being sodiy water, and converting the smelt solution to a fresh cooking liquor. When the inorganic content of spent liquors containing sodium-sulphur compounds is smelted, a smelt consisting of a mixture of essentially onlyvtwo sodium compounds is produced, one bering sodium carbonate, and the other being` Thus, if the smelta sodium-sulphur salt. ing takes place in a reducing atmosphere, a smelt containing sodium carbonate and sodium sulphide results; but if the smelting takes place in an oxidizing atmosphere, a

, smelt containing sodium carbonate and sodium sulphate results.

I have found that it is often advantageous to remove sodium carbonate from the rest of the smelt before preparing fresh cooking In accordance with the present invention, theV removal of sodium carbonate from the rest of the smelt is effected either by taking advantage of the difference in solubility between the sodium carbonate and the rest of the smelt, or by converting it into the relatively insoluble bicarbonate. Thus,

Serial N0. 332,724.

if the smelthas been produced in a reducing atmosphere and contains sodium carbonate and sodium sulphide, separation of sodium carbonate may be effected by taking advantage of the marked difference in water solubility between sodium carbonate and sodium sulphide, the sodium sulphide being quite soluble even under conditions when sodium carbonate is relatively quite insoluble and crystallizes out of solution. If the smelt has been produced in an oxidizing atmosphere and contains sodium sulphate rather than sodium sulphide, separation of a substantial amount of the sodium carbonate may be effected by crystallizing it out.

of the solution while permitting most of the sodium sulphate to remain in solution. Or the smelt solution may be carbonated to convert a portion or all of the sodium carbonate into insoluble bicarbonate and the insoltain instrumentalities which mayl be e1n' ployed when smelting is effected inA an .oxidizing atmosphere.

Referring to the drawing, 20 represents a storage tank containing the concentrated spent liquor, which may, for example, be concentrated spent kraft liquor, sulphite liquor, or mixtures thereof. The liquor is fed into a smelting furnace 30, in which an oxidizing atmosphere is maintained so as to produce a smelt containing sodium sulphate and sodium carbonate. The smelt is run into a body of water maintained in a dissolving tank 31, to form an aqueous smelt solution.

A substantial amount of sodium carbonate may then be crystallized out of the smelt solution while permitting most of the sodium sulphate to remain in solution. Thus, a smelt solution comprising 29 parts of sodium carbonate and 13 parts of sodium sulphate at a temperature of, say, 300 C., may be cooled to, say, 20@ C., to form a crystalline precipitate of sodium carbonate containing but a relatively very small amount of sodium sulphate. After the removal of the crystalline material, the mother liquor contains 1G parts of sodium carbonate and 12 parts of sodium sulphate, indicating a substantial removal of sodium carbonate and a relatively lowv removal of sodium sulphate. Or I may deliver the smelt solution (or the mother liquor) into a carbonating tower 32, as shown, wherein it is treated with carbon dioxide, thereby precipitating the relatively insoluble sodium bicarbonate. The precipitated sodium bicarbonate may be removed as by passing the solution and precipitate into a. rotary filter 33. rl`lie removed sodium carbonate or bicarbonate may be acidified to produce an acid sulpliite cooking liquor,V While the sodium sulphate-.containing mother liquor may be delivered to a kraft mill to replace the salt-cake ordinarily there employed to compensate for losses. Or only a portion of the mother liquor may be used for this purpose in a kraft mill, the rest being mixed With the sodium bicarbonate and the mixture acidilied with sulphur dioxide to produce an acidV cooking liquor wherein the ratio of sulphite to sulphate` is higher than Would be the case if the smelt solution Were acidified Without previous separation of bicarbonate. During` acidification of the bicarbonate to produce sodium sulpliite, carbon dioxide is liberated. This carbon dioxide may be recovered and used for the carbonation of otliersmelt solutions.

Having thus described certain embodiments of this invention, it is evident to those skilled in the art that various changes and n iodiiications might be made therein Without departing` from the spirit or scope of invention as defined in the appended claims. Y

I claim: l. A process which vcomprises smelting the inorganic content of spent cooking liquor containing sodium-sulphur duce a smelt containing sodium carbonate and sodium sulphate, forming an aqueous smelt solution, carbonating the smelt solution to precipitate sodium bicarbonate, and removing the precipitated bicarbonate.

2. A process which comprises smelting the inorganic content of spent cooking` liquor containing sodium-sulphur compounds in an oxidizing atmosphere to produce a smelt containing sodium carbonate and sodium sulphate, forming an aqueous smelt solution, carbonating the smelt solution to precipitate sodium bicarbonate, re-

moving the precipitated bicarbonate, and

acidifying the bicarbonate to produce an acid cooking` liquor.

compounds in an oxidizing atmosphere to pro-A 3. A process which comprises smelting the inorganic content of spent cooking liquor containing sodium-sulphur compounds in an oxidizing atmosphere to produce a smelt containing sodium carbonate inorganic compounds from spent cooking liquor containing sodium-sulphur compounds for use in both acid and kraft cooking, which comprises smelting the inorganic content of suoli spent cooking liquor in an oxidizing atmosphere to produce a smelt@ containing sodium carbonate and sodium sulphate, forming an aqueous smelt solution, carbonating the smelt solution to precipitate sodium bicarbonate, removing the precipitated bicarbonatev and convertingv the Same into acid sulpliite cooking liquor, and smelting the inorganic content of the remaining smelt solution along With the inorganic content of spent kraft liquor for the production of fresh kraft cooking liquor.

A process of recovering the valuable inorganic compounds from spent. cooking liquor containing sodium-sulphur compounds for use in both acid and kraft cooking, which comprises smelting the inorganic content of such spent cooking liquor in an oxidizing atmosphere to produce a smelt containing sodium carbonate rand sodium sulphate, forming an aqueous smelt solution, carbonating the smelt solution toV vprecipitate sodium bicarbonate, removing the precipitated bicarbonate, smelting the inorganic content of a portion of the remaining smelt solution along with the inorganic content of spent kraft liquor for the production of fresh kraft cooking liquor, mixing the rest of the smelt solution With the bicarbonate, and converting the mixture into an acid cooking liquor.

6. A process Which comprises smelting the inorganic content of spent cooking liquor containing sodium-sulphur compounds in an oxidizing atmosphere to produce a smelt containing sodium carbonate and sodium sulphate, and removing sodium carbonate from the smelt.

7. A process Which comprises smelting the inorganic content of spent cooking liquor containing sodium-sulphur pounds in an oxidizing atmosphere to produce a smelt containing sodium carbonate and sodium sulphate, forming an raqueous smeltsolution, andcrystallizing out a substantial amount of sodium carbonate from the smelt solution while permitting most of the sodium sulphate to remain in solution.

8. A process which comprises smelting the inorganic content of spent cooking liquor containing sodium-sulphur compounds in an oxidizing atmosphere to produce a smelt containin sodium carbonate and sodium sulphate, orming an aqueous smelt solution, crystallizing out a substan tial amount of sodium carbonate from the smelt solution While permitting most of the sodium sulphate to remain in solution, removing the crystallized carbonate, and acidifying the carbonate to produce an acid cooking liquor.

In testimony whereof I have aiixed my signature.

GEORGE A. RICHTER.

Images