Патент USA US2119132код для вставки
May 3l, 1938. ì J. <3` HATMAN RECOVERY OF TAR ACIDS Filed April 15, 1935 Y '2,119,132v *2,119,132l Patented May 31, 1938 UNITED STATES ArsN'r OFFICE 2,119,132 RECOVERY or TAR ACIDS Julius George Hatman, Elkins Park, Pa., assignor to The Sharples Specialty Company, Philadel phia, Pa., a corporation of Delaware Application April 13, 1935, Serial No. 16,240' 8 Claims. This invention relates to- the art of recovering tar acids from tar and particularly to a process by which the tar acids may be separated in a simple, economical manner from the tar pro duced incidental to the manufacture of coke. An arrangement of apparatus that it has been found advantageous to use in the performance of the new process is also a part of this invention. In accordance with the usual process of manu facturing coke, a. quantity of tarry material re sults as a by-product. This tarry material, or crude tar as it will hereafter be called, has a speciñc gravity of around 1.06 to 1.18 and ordi narily contains from 21/2 to 6% of tar acids and up to about 10% of water. The tar acids, which consist mainly of phenol and its homologues, such as the cresols and xylenols, are valuable commer cially but are quite diliìcult to isolate according to known procedures. The practice heretofore has usually been to dehydrate the crude tar either by evaporating off the water or centrifuging. After dehydrating, the crude tar is distilled in a tar still and separated into two fractions, the fraction boiling below 25 270° C. being known as tar oil and the remain der simply as tar, or as tar residue. The tar acids are substantially wholly contained in the tar oil and are present thereinin a concentration of between 15 and 25%. This tar oil fraction is subjected to further 30 treatment to separate these acids. Such treat ment ordinarily consists in intermixing the tar oil with an aqueous caustic soda solution of a concentration suiîlcient to convert the tar acids into phenolates, cresolates and the like. These compounds, which will hereafter be referred to generally as phenolates, dissolve readily in the caustic solution and are subsequently separated from the tar oil by allowing the mixture to settle into an aqueous layer and an oil layer and then (Cl. 7260-154) these refineries must be equipped to carry out the relatively long and involved process outlined above. The present process has been conceived to overcome difficulties involved in the practice of >the process now in use and to produce relatively pure tar acids simply and expeditiously, directly from the original tarry material as it is pro duced by the coke plant. According to an appli cation Serial No. 754,718, filed by Charles M. 10 Ambler, Jr. and-Charles E. Underwood on No vember 26, 1934 which has matured into Patent #2,081,692, it has been found that if this original tarry material is mixed directly with a basic solution such as an aqueous solution of caustic 15 soda or caustic potash, capable of converting the tar acids into the corresponding phenolates, and thereafter separated from such solution with sufñcient promptness to avoid emulsion difficul ties, such separation can be effected and the sepa rated solution will contain substantially all of the tar acids in the form of soluble phenolates. These compounds may thereafter be reconverted into tar acids by the addition of acid, and sepa rated. 25 The present invention is an improvement upon the process and apparatus described in the Ambler et al. application and provides a modified proc ess according to which the aqueous solution of phenolates formed by the action of water and 30 caustic soda upon the tar, is recycled until the concentration of phenolates therein isv greatly increased and-'the eii'ìciency with which these phenolates may be separated from the aqueous solution is materially bettered. Furthermore, the g5 present invention provides a system of apparatus by which this novel process may be performed either continuously or by the batch. Further de tails that add to the efüciency or desirability of the new process and apparatus will appear more A through it, or may be treated with an acid, usu fully from a consideration of the following de tailed description of the preferred mode of prac ticing the invention and of the system of appa ally sulphuric, to convert the dissolved com The tar acids, being insoluble, are thereafter separated from the re sulting solution of sodium carbonate or sodium ratus which has been found especially adapted for the performance of this process. 45 In the drawing, forming a part of this applica tion, the new process and system of apparatus decanting. The aqueous solution so obtained is thereafter treated by blowing carbon dioxide gas 45 pounds back into tar acids. sulphate by gravity settling. for performing it are illustrated in their pre ferred form by a flow sheet. According to this 50 quires a dehydration and. distillation of the heavy ` ilow sheet the original raw materials are water, tarry material which is difñcult and troublesome tar, caustic soda solution and stack gas from the and which many coke plants are not equipped coke ovens. In place of at least part of the water, to accomplish. Hence the tar must often be after the process has been started in operation, sold without extracting the tar acids therefrom, a solution of phenolates from previously extract The difficulty with such a process is that it re to refineries especially equipped for this work and ed tar is supplied. ' 2 2,119,132 According to illustrated process, a caustic soda solution, usually of a concentration of about 8% by weight is supplied to the mixer through a constant head pump and a proportioningfmeter in approximately the ratio of one gallon of caus tic solution to each iive or six gallons of tar, the tar also being fed through a constant head pump and the proportioning meter. At the same time an aqueous liquid, either Water or pheno 10 late solution from a previous extraction or a mixture of the two, is fed through another` con stant head pump and the proportioning meter into the mixer. The aqueous liquid may either enter the mixer with the caustic solution and the tar or may be supplied to theseconstituents after they have been partially mixed, in accord ance with the process described in the above mentioned application. The ratio of the aque ous liquid to the tar is usually about 2 to l by volume but may be as low as 1 to 1. The ratio of caustic solution to tar is preferably adjusted so that approximately 1.4 pounds of caustic soda are added for every gallon of tar acids in the tar. After the mixing has been completed, prefer ably in the manner described by the above men tioned application, although it may be done in any other manner found convenient, the mix ture is brought to a temperature of around 80° C. and centrifuged to separate the tar from the aqueous solution of phenolates formed by the reaction of the caustic soda solution upon the tar acids in the tar. The resulting aqueous solution of phenolates t-n LA is passed into a storage tank from which it may be returned by a pump and be recycled through the same process. As this recycling is continued the supply of water to the system may be d_i minished or stopped altogether, with the result 40 that the concentration of phenolates in the so lution increases until a concentration is reached at which the phenolate solution contains a suf ficient percentage of phenolates to enable their recovery to be efliciently made. At that time the whole of the phenolate solution may be di rected into other apparatus for recovering the tar acids therefrom, or a portion of the pheno lates may be directed into such apparatus and the remainder recycled to collect more tar acids. The concentration of phenolates in the solution will not increase indefinitely, for the caustic soda solution added tends to dilute the phenolate solution and thus to reduce the concentration and in addition a certain amount of water is ex tracted from the tar itself. Usually there is around six to ten percent of water in the tar as it is originally received and of this all but about 0.5 to 1.5 percent is extracted and passes into the phenolate solution. As the phenolate solution is recycled, the ad 60 dition of caustic soda solution may be discon tinued, if desired, and sufficient caustic soda, in solid form, added to the phenolate solution to maintain the desired concentration. Alterna tively the addition of the caustic soda solution may be continued and the rate of addition ad justed to maintain the proper concentration, namely, around 1.4 pounds ofcaustic soda per the phenolates in the phenolate solution Will be substantially constant. A point of equilibrium will also be reached if water is added at a deli nite rate with the recycled phenolate solution and a suflicient quantity of the phenolate solu tion is Withdrawn continuously to balance this water, as well as the water taken from the tar and the caustic solution. The phenolate solution taken from the above described section of the system passes through a pump and suitable heating apparatus which raises its temperature to around 90° C. to a springing tower where it passes countercurrent to gas from coke oven stacks. In so doing the phenolate solution absorbs carbon dioxide and 15 the tar acids are re-formed. Some of the water and a portion of the tar acids are Volatilized and pass off through the top of the tower, but these are condensed in a suitable condenser and passed to a settling tank together with the portion of 20 the tar acids and water solution that remains liquid. In the settling tank the re-formed tar acids separate from the aqueous solution of car bonates formed in the springing tower. The carbonate solution is passed to suitable appa 25 ratus where it is regenerated into caustic soda by treatment with lime. The tar acids, which still contain some residue and some Water are distilled to obtain three por tions, residue, dry tar acids and a mixture of 30 tar acids and water. The residue is discarded, and the tar acid and water mixture permitted to settle. Upon settling a quantity of water is recovered which may be discarded or added back to the phenolate solution being recycled. There 35 remains crude tar acids which together with the tar acids recovered directly from the distilla tion, may be treated in any suitable manner to further refine them or to separate them into the individual tar acids. 40 While the process and system of apparatus described above are the preferred form, it is to be understood that considerable modifications may be made in both the process and the appa ratus without departing from the principles of 45 this invention. For example, any suitable device may be substituted for the constant head pumps and the proportioning meter, for feeding accu rately-proportioned amountsrof caustic soda so lution, tar and phenolate solution or water to 50 the mixer, The phenolate solution or Water may be added at any time during the mixing and the constituents may be heated either before or after mixing to a temperature of around 80° C‘., or the process may be performed without the 55 application of heat to the constituents prior to the centrifuging. Also, although it is definitely preferred to use a centrifuge to separate the phenolate solution from the tar, other means of separation, such as gravity or filtration may con 60 ceivably be employed. As has already been indicated, the phenolate solution resulting from the treat-ment is re cycled either in whole or in part and this re cycling may be carried out to any desired ex 65 tent, thus building up a concentration of pheno lates in the solution of anywhere from 5 to 40% or even greater. Preferably, in order to make If an amount of phenolate solution equal to the amount of caustic added plus the amount of water extracted from the tar, is removed to the recovery apparatus continuously and no addi tional water is added, the system will‘reach an the process economical, the concentration is built up to at least 15 or 20% and may be much higher. 70 1f the process is to be performed by the batch, all ofthe phenolate solution or at least a major part of it will ordinarily be drawn> off at one time, whereas> if the process is to be performed equilibrium point at which the concentration of continuously a smaller portion, usually from 5 , gallon of tar.- Y ` 2,119,132 to 15%, by volume will be removed to the re covery apparatus continuously. In the recovery of the tar acids from the phenolate solution the steps and the apparatus may also be modiñed. Thus, the phenolate so lution may be passed to the springing tower with out previous heating or the phenolate solution may be treated with sulphuric acid instead of stack gas to liberate the tar acids. If desired, 10 the tar acids may be taken directly from the ñrst settling tank without any further distillation and used in this condition or passed to other appa ratus for puriiication. I claim: 15 l. A process of removing tar acids from tar that comprises separately mixing with the tar 3 phase to the process to be mixed with the tar; and continuously withdrawing a portion of the aqueous phase and recovering tar acids there from. 6. A process for the recovery of tar acids from tar that comprises mixing with tar an aqueous caustic soda solution containing about 8% caustic soda by weight and in such proportion that ap proximately 1.4 pounds of caustic soda are added for each gallon of tar acids in the tar, mixing 10 with these two constituents water in the propor tion of approximately two gallons of the aqueous liquid to each gallon of tar, heating the mixture to approximately 80° C., centrifuging to resolve a constant proportion of an aqueous caustic soda solution and a constant proportion of water, cen the mixture into a tarry portion and an aqueous 15 portion, recycling the aqueous portion as at least a part of the aqueous liquid added to the tar and caustic soda solution, and thereafter passing the trifuging the resulting mixture to remove the tar, said aqueous portion into contact with a gas con 20 recycling the aqueous liquid recovered from the taining carbon dioxide whereby the tar acids are centrifuge by mixing it with additional tar and recovering the tar acids from the recycled aqueous liquid. 2. A process of removing tar acids from tar 25 that comprises separately mixing with the tar a precipitated therefrom, settling to separate the constant proportion of an aqueous caustic soda solution and a constant proportion of water, centrifuging the resulting mixture to remove the tar, recycling the aqueous liquid recovered from 30 the centrifuge by mixing it with additional tar and additional caustic soda solution, and recover ing the tar acids from the recycled aqueous liquid. 3. A process of removing tar acids from tar that comprises mixing with the tar a constant propor 35 tion of caustic soda and a constant proportion of Water, centrifuging the resulting mixture to re move the tar, recycling the aqueous liquid re covered from the centrifuge a plurality of times by mixing it with additional tar and recovering 40 the tar acids from the recycled aqueous liquid. 4. A process of removing tar acids from tar that comprises separately mixing with the tar a constant proportion of an aqueous caustic soda solution and a constant proportion of water, tar acids from the aqueous solution and distilling the tar acids so separated. '7. A continuous process for the removal of tar acids from crude undistilled tar having a speciiic 25 gravity in excess of 1.06 that comprises continu ously mixing the crude tar with an aqueous al kaline solutionv to convert the tar acid content of said crude tar into the corresponding salts of said tar acids, passing the mixture of crude tar 30 and the aqueous solution of said salts formed by a reaction of the alkaline solution with said tar acids continuously through a centrifugal sepa rator and thereby separating the mixture into a tarry and an aqueous phase, continuously re 35 turning a portion of the aqueous phase sepa rated from the centrifugal separator into con fluence with alkali and a further quantity of said crude tar and continuously withdrawing a portion of the aqueous phase and recovering tar 40 acids therefrom. 8. A process for the removal of tar acids from crude undistilled tar having a speciñc gravity in excess of 1.06 that comprises mixing the crude 45 heating the mixture to around 80° C., centrifuging tar with an aqueous alkaline solution to con the resulting mixture to remove the tar, recycling the aqueous liquid recovered from the centrifuge a plurality of times by mixing it with additional tar and additional caustic soda solution, and re 50 covering the tar acids from the recycled aqueous vert the tar acid content of said crude tar into liquid. 5. A continuous process for the removal of tar acids from tar that comprises continuously and separately mixing with tar an aqueous caustic 55 soda solution and water in predetermined pro portions, heating the mixture to around 80° C., continuously centrifuging to separate the mix ture so formed into a tarry and an aqueous phase, ' continuously returning a portion of the aqueous 45 the corresponding salts of said tar acids, passing the mixture of crude tar and the aqueous solu tion of said salts formed by a reaction of the alkaline solution with said tar acids through a 50 centrifugal separator and thereby separating the mixture into a tarry and an aqueous phase, returning a portion of the aqueous phase sepa rated from the centrifugal separator into con fluence with alkali and a further quantity of said 55 crude tar and withdrawing a portion of the aqueous phase and recovering tar acids there from. JULIUS GEORGE HATMAN.