US3080206A - Treatment of chrome leather and preparation of vegetable retanning material used in the process - Google Patents

Description

United States Patent Oflfice 3,080,206. Patented Mar. 5, 1963 TREATMENT OF CHROME LEATHER AND PREP- ARATEGPJ 6F VEGETABLE RETANNHNG MATE- REAL USED IN THE PRQQESS Carl G. Telander, Ashtabula, @hio, and Melvin L. Herman, Sheboygan, Wis assignors, by mesne assignments, to Armour a Company of Delaware, (Ihicago, 11]., a corporation of Deiaware No Draw "ting. Continuation of application Ser. No. 442,896, Early 12, 1954. This application Feb. 11, 1959, Ser. No. 792,461

12 Claims. (Cl. 84-.26)

This invention relates generally to the tanning of leather. More particularly, this invention relates to an improved process of retanning chrome tanned leather in the manufacture of retan leathers. This invention also relates to the processing of runaway liquor in preparing novel vegetable retanning compositions for the treatment of chrome leather.

Vegetable tannage or mineral tannage have long constituted the major tanning processes in the manufacture of leathers of different types. Each process has its advantages as Well as limitations and the choice of method is necessarily determined on the basis of the properties of the leather desired and other considerations such as cost, availability of reagents, etc.

The vegetable tanning process, for example, is desirable particularly in the tanning of heavy leathers such as sole leather since superior Plumping and fullness is obtained thereby accounting for high yields of leather from the hide or skin stock. The rate of diffusion of vegetable tannin into hides, however, is very slow and a long time is required to sufficiently tan the hide. The use of concentrated vegetable tanning liquors to circumvent the slow diffusion has not proven successful since the rate of combination of the tannin with the protein of the hide is greater than the rate of diffusion of the tannin into the interior of the hide. Consequently, the outer layers of the hide become contracted to a greater extent than the inner layer and a distortion results which detracts from the appearance and value of the leather. To overcome this difiiculty, tanners are compelled to use a multiple step process when tanning with vegetable tannins which involves the moving of the hides or skins into progressively stronger tanning liquors until they are completely tanned. In some cases, as in the tanning of sole leather, months may be required to complete the tanning of the leather.

Mineral tannage, on the other hand, the most Widely used process being chrome tanning, is capable of drastically reducing the period required for tanning the hide or skin stock. Chrome tanning also imparts to the leather the properties of greater resistance to heat and abrasion than does vegetable tanning. Although a good portion of the worlds supply of light leathers is tanned by means of chromium salts, the chrome tanning processes are incapable of producing the properties of plumpness, fullness, and other characteristics required for many specific uses for leather.

Several approaches have been used in attempting to overcome the above difiiculties and limitations. One approach has been the search for new types of tanning materials commonly referred to as syntans. Another has been the use of combined chrome and vegetable tannage using, for example, a chrome tanning operation first and then vegetable tannage or vice versa to supplement or combine the characteristics or results inherent in each tanning process. The products from such combination type of tanning process are called retan leathers.

In effect, the chrome tanning step when used in combination with a vegetable tanning step makes it possible to more or less average the advantages and disadvantages of both tanning procedures. The chrome tanning or pretanning thus enables a rapid penetration of the mineral tanning liquor into the entire mass and imparts to the leather the improved resistance to heat and abrasion. The chrome leather is then subjected to the action of fresh vegetable tanning liquors to permit the desired degree of retanning to occur whereby a plumper and fuller retanned product is obtained. Other changes such as properties pertinent to tooling "and embossing the leather are also significantly improved by the retanning.

One basic disadvantage of the combination tannage is the increased cost of tanning reagents inasmuch as both the chrome tanning and vegetable tanning reagents are necessarily involved in the process. The cost of the relatively expensive vegetable tannin materials is a particularly important factor in the production of retan leathers.

We have now found that chrome leather can be retanned by treating the same with concentrated runaway liquor. Surprisingly enough, this spent vegetable tanning liquor which heretofore has been considered to be of no value for further vegetable tanning purposes has now been found to be an excellent retanning agent for chrome leather. Until the present discovery, the discarding of this runaway liquor has constituted a major waste disposal problem. In addition to eliminating this waste disposal problem, the newly discovered utility of this formerly rejected material now makes possible the retanning of chrome leather at a substantially lower cost. The retan leather made in accordance with the present invention is not only as good as the chrome leather conventionally retanned with fresh vegetable tanning liquor but is actually superior in so far as qualities and properties such as grain texture and strength, yield of leather breaking characteristics, feel, etc., are concerned. The runaway liquor concentrate described hereinafter in detail has also been found to be highly desirable as a color mordant for chrome-tanned leather.

It is therefore an object of this invention to provide a process for retanning chrome leather without requiring the use of fresh vegetable tannin liquors heretofore used in the process for vegetable retanning of chrome leather. It is another object to provide a process for retanning chrome leather wherein runaway liquor extract can be utilized as a complete or partial replacement for natural vegetable tanning substances as the retanning agent. It is another object to provide novel retanning mixtures useful in the treatment of chrome leather. It is a further object to provide a process for retanning chrome leather at a substantially reduced cost. It is yet another object of this invention to provide a process for applying spent vegetable tanning liquors after treatment of the same to retanning and mordanting of chrome leathers thereby eliminating a Waste disposal problem. Yet another object is to provide a chrome leather retanning process which results in the production of retan leathers having superior tooling and embossing characteristics as well as improved grain texture and strength, yield, feel, appearance, etc. Yet another object is to provide a process for treating runaway liquor for converting the same to a desirable form for utilization as a vegetable retanning and mordanting agent for chrome leathers. Further objects ment.

and advantages will appear as the specification proceeds. Conventional vegetable tannery liquor is made up of extracts from quebracho, chestnut, wattle, valonia, myrobalons, spruce, gambier, divi-divi, and other nut, wood, root or bark concentrates. Following its conventional use in vegetable tannery operations wherein the active tannin content is considered substantially exhausted to a degree wherein the liquor is of no further use for tanning purposes, this material depending upon its initial composition and the vegetable tanning process in which it has been used has the following approximate composition:

Total solids percent 2.8-3.6 Soluble solids do 2.63.1 Insolubles do 0.2-0.5 Non-tannin do 2.02.3 Tannin do 0.6-0.9 Purity 23-28 pH 5.0-5.5

The spent vegetable tanning liquor constitutes the socalled runaway liquor the bulk of which is routinely discharged to sewers thereby creating a serious disposal problem. Usually, active remedial steps involving substantial cost must be taken to eliminate odor and pollution problems created by the waste disposal. Some limited uses of the material have been heretofore made as, for example, in connection with the treatment of boiler water, oil well applications, leather dressing, etc., but such uses have resulted in the utilization of only small quantities of the available runaway liquor resulting from vegetable tanning operations.

This invention is based in part on the discovery that runaway liquor concentrates prepared in accordance with the process hereinafter described in detail can be used as a retanning and mordanting agent for chrome leather. Although this material is by no means a suitable substitu te for fresh vegetable tanning liquors in so far as vegetable tanned leather is concerned, it has now been found to be an excellent vegetable retanning agent for chrome leather in place of the fresh vegetable tanning liquor heretofore required for the purpose. In other words, despite the fact that the components in the concentrate are substantially rejected in conventional vegetable tanning operations, in the case of chrome leather, an almost complete takeup of the tannin, insolubles and non-tannin occurs. Thus, the processed runaway liquor when used for retanning chrome leather functions in a manneli similar to fresh vegetable tanning liquors'resulting in an almost complete exhaustion of the liquor- In .the case of the runaway extract, the non-tannins appear to be taken up by the leather to an even greater degree than the non-tannins of natural vegetable tanning extracts. The mechanism for this phenomenon is not clear-;

1y understood but the'specificity of the action as being related to the prior chrome tanning treatment of the leather is clearly established.

' This discovery is of great importance since in addition to virtually eliminating a serious waste disposal problem, a much more inexpensive retanning and mordanting liquor is made readily available for the treatment of chrome leather. Atthe same time, chrome leather treated with the runaway liquor extract is of better quality than when retanned with natural vegetable tanning agents in accordance with conventionalpractice. This improve ment of quality of the finished leather is particularly evident in the flanks and heads as compared to leather retanned with conventional fresh vegetable extracts. The, treatment of runaway liquor or vegetable tanning sewer liquor prior to its utilization as a retanning or rnorda nting agent for chrome leather can be readily achieved on a commercial basis in conventional equip- Prior to the processing of the waste liquor, the discharge liquor from thevegetable tanning rocker sec tions is collected in a tank and allowed to settle for a brief period. Prolonged standing and the use of dirty tanks should be avoided to prevent excessive contamination and bacterial decomposition which cause undesirable odor development. Solid materials of relatively large particle size such as fibrous flesh materials, bark fragments, etc., are easily removed by screening the liquor. The next step of the treatment comprises concentrating the total solids content of the runaway liquor from the previously indicated 2 to 4% level to any desired value dependent upon the requirements of the subsequent retanning or mordanting procedure in which the concentrate is to be used. For most chrome leather retanning processes, it is desirable to have retanning liquors containing total solids ranging from 20 to 45% by weight or more depending upon the fluidity, ratio of tannins to non-tannins present, insolubles, etc. In order to reduce handling and shipping costs, it may be desirable to evaporate the runaway liquor extract to complete dryness or powder form by conventional spray or flash drying methods. The concentrate in either the liquid or powder form can be readily reconstituted or adjusted to any desired total solids level prior to its mordanting and retanning usage without any loss or. impairment of the retanning or mordanting properties of the material.

For evaporating or condensing runaway liquor, conventional equipment such as single stage, double stage or multiple stage evaporators can be used. Triple effect vacuum evaporators have been found to be especially practical for processing runaway liquor in commercial quantities.

The condensation or evaporation treatment produces certain changes in the non-tannin content of the liquor. Although the mechanism for the changes is not fully understood, it can be readily determined by standard tannin analyses and evaluation of the purity that a conversion of non-tannins to tannin actually occurs. If no changes in non-tannins and insolubles took place, the composition of the tannin in the concentrate would vary only in proportion to the extent of concentration. Such is not the case, however, as seen from the following data which are representative of the values at various stages of the treatment of runaway liquor as compared to calculated values which would otherwise be expected if no conversion of non-tannin to tannin occurred:

Although the conversion of insolubles and non-tannins materials varies somewhat depending upon the starting material as determined by the composition and usage of the original vegetable tanning solution, the increase in active tannin is nevertheless consistently obtained by virtue of the evaporation process. The more pronounced conversion of non-tannins to tannin is indicated by the relatively higher total solids levels as compared to concentration of total solids to below 20% or thereabouts.

In view of the enhanced conversion of insolubles and non-tannin substances in the liquor to tannin previously described, however, it is accordingly preferred to concentrate the total solids at least to 20% and preferably to about 35 to 45%. The tannin content of concentrates of about 42% total solids on the basis of overall composition ranges from about 8 to 15% by weight of the total solids therein and the concentrate in this form provides an excellent vegetable retanning liquor for chrome leather.

As previously indicated, the non-tannins and insolubles present in the concentrate are also consumed in the retanning process. Therefore the high degree of retanning action achieved by the use of runaway extract cannot be explained solely on the basis of the tannin content alone. Although the mechanism of the retanning action is not clearly understood, it is believed that the non-tannin content acts as a buffer thereby preventing drawing of the grain of the leather particularly in the neck and flank portion of the hides.

The use of the concentrates prepared from difierent sources in accordance with the method herein disclosed occasionally results in considerable variation of the color of the finished leather when applied to the retanning of chrome leather. For eliminating or minimizing this difficulty, changing the dyes used in coloring the leather has been found to be helpful. Color improvement may be more effectively achieved however, by lowering the pH of the concentrate. Further improvement of coloring properties and characteristics is obtained by adding a sequestering agent which modifies the effect of iron and other metal salts present in the concentrate through its chelating action. The use of both measures are preferred for establishing a firmer combination of the retanning ingredients in the leather and improving the coloring properties of the concentrate.

The acids which may be used for lowering the pH may be either organic or mineral acids including acetic, oxalic, lactic, formic, citric, hydrochloric, sulfuric, phosphoric acids, etc., or mixtures thereof. Very good results are obtained, for example, by the use of combinations of acids such as acetic-hydrochloric or sulfuric-oxalic, etc.

The amount of acid to be used can be varied rather broadly but the pH adjustment should not be excessively low (below 4.0) since the penetration of the concentrate is adversely affected. The use of runaway concentrate at a pH below about 4.0 also causes a pile-up on the grain resulting in a dry crust break of the leather. The adjustment of pH between the range 4.1 and 5.8 is generally satisfactory but it is preferred to adjust the pH to between 4.5 and 5.5 with about 4.7 being the optimal pH value. The acid or acids used for adjusting the pH of the extract may be incorporated into the concentrate either during the condensation process or prior to the utilization of the concentrate in the retanning or mordauting process.

sequestering agents of various types can be used for improving the coloring properties of the concentrate. Commercially available sequestering agents of the ethylenediamine tetraacetic acid type and its salts are especially desirable. Excellent results are obtained by the use of the various sodium salts thereof. The quantity of sequestering agent to be added to the concentrate can be varied broadly as from .05 to 2% by weight based on the weight of the concentrate in either liquid or powder form. Good results are obtained when from .1 to .2% by weight of the sequestering agent is added to the evaporated extract containing about 4045% total solids.

In a preferred process for preparing the concentrate of extract from vegetable tanning runaway liquor, the accumulated liquor is screened and evaporated in a tripleefiect evaporator to concentration of approximately 20 to 30% by weight of total solids. This concentrate referred to as first run extract is allowed to settle in a tank whereby the coarser insoluble particles become separated and are removed. The first run extract is then further evaporated to about 42% total solids (second run extract) after which the pH is adjusted to approximately 5.0 by the addition of hydrochloric acid. Sufficient acetic acid is then added along with about .15 of sequestering agent (based on the weight of the second run extract) to adjust the pH of the concentrate to about 4.7.

During the evaporation process, conventional antifoaming agents can be used if desired to eliminate or minimize losses of the material caused by excessive foaming. A further modification consists of the addition of a masking agent to improve the odor characteristics of the product. Preferably, the masking agent should also possess bactericidal properties for improving the keeping qualities of the concentrate. Silicofiuoride salts, phenolic compounds, mercurials and other preservatives can be used but it is preferred to use phenolic compounds such as phenol, cresol, etc. Mixed cresols or cresylic acid are particularly desirable when added in concentrations up to about 0.5% by weight with the preferred concentration of masking agent being within the range of from 0.03 to 0.1% by weight.

It is to be understood that the preferred embodiment for preparing the concentrate containing about 42% total solids disclosed above merely relate-s to a desirable composition and to a convenient procedure for purposes of handling, shipping, fluidity, etc. Accordingly, it is not intended to be limited thereby as to the specific degree of concentrations of the runaway liquor and to the manner in which the concentration is achieved. The two-step evaporation, for example, is not essential since the evaporation to any desired level of total solids can be achieved directly or in a single step and, as previously indicated, the evaporation can be continued until a solid material is produced as by spray or drum drying without adversely aifecting the efiicacy of the concentrate in the retanning and/or mordanting processes for chrome leather.

For treating chrome leather with runaway liquor concentrate or extract, any of the conventional vegetable retanning procedures for chrome leather can be used. The concentrate may be used as is, depending upon its total solids content as determined by the degree of concentration or it may be diluted or reconstituted for use in the retanning process. The extract can also be used alone or with other materials as a vegetable retanning and mordanting material on chrome leather. The pH of the leather can be adjusted during the course of the retanning procedure as desired without impairing the retanning properties of the extract or causing undesirable pile-up of the grain. Organic acids such as acetic, formic, lactic, oxalic, etc. are conventionally used for this purpose.

The quantity of runaway concentrate to be used in treating chrome leather can be varied considerably depending upon the degree of retanning desired in the leather and also upon the total solids content of the specific run away liquor extract being used in the process. As a mordant for the dyeing of chrome leather, for example, only a light surface treatment is usually involved and the quantity of total solids absorbed by the leather during such treatment is about 2 to 6% by weight based on the weight of the shaved chrome stock. Thus the total amount of the concentrate can be readily calculated on the basis of its known total solids content in any given case thereby making available to the chrome leather the predetermined amount of total solids.

The quantity of run-away concentrate to be used for retanning chrome leather is similarly calculated on the basis of the weight of the shaved stock. Depending upon the degree of retanning desired and also upon the source and quality of the leather stock being treated, extensive variation as to the quantity of retanning agent are necessarily involved. In terms of absorbed total solids by chrome leather, the uptake of the tannins, non-tannins and insolubles can vary from as little as 6 to 15% of its weight to as high as about 25% in the case of heavy retannage of sole leather. Whereas the tannin content of the natural vegetable liquors heretofore used for retanning chrome leather is determinative of the amount to be used in a given retanning process, the method of determining the amount of concentrates should take into consideration the non-tannins and insolubles in view of the importance of these components in the retanning process. By way of illustration, if a heavy degree of retanning is desired,

proximately 42% by weight of total solids.

.about 60% by weight of-runaway liquor extract containthe retanning mixture about 25% total solids on the basis of the weight of the shaved chrome leather. Lesser quantities or diluted solutions can be used depending upon the required specifications of the finished leather and the type of chrome leather being treated. Thus it is seen that the techniques and procedures for retanning chrome leather in accordance with conventional practices involving vegetable retanning of chrome stock are generally applicable to the retanning process herein disclosed, the essential difference being the utilization of the runaway extract as a complete or at least a partial replacement for new natural vegetable retanning materials.

The retanning procedure can be further modified to include the use of both the runaway concentrate and fresh vegetable tannin liquor by either utilizing a mixture of the two retanning agents or by subjecting the chrome leather to the action of each in separate processing steps. For preparing the mixture for simultaneous use in a onestep process, the quantity of each retanning agent can be varied from a small proportion of runaway liquor extract up to a point where practically none of the natural vegetable tannins are present. By way of illustration, a highly satisfactorily finished leather can :be obtained by treating chrome leather in one operation with a retanning blend consisting of 75% by weight of the concentrate (42% T.S.), the balance of the material being fresh vegetable tanning liquor prepared from wattle or quebracho, etc. The total quantity of the blend to be used depends merely upon the degree of retannage desired for the finished leather.

The two-step procedure can likewise be varied broadly as to the ratio of the concentrate to fresh vegetable tanning liquor to be used. In this procedure, it is preferred to subject the chrome leather to the retanning action of the concentrate and after a light washing, the leather is further treated with fresh vegetable tanning liquor. One embodiment of this process involves treating chrome leather successively with equal weights of the concentrate (about 42% T5.) and fresh vegetable tanning liquor respectively.

The general method of application of the runaway liquor concentrate as a retanning agent for chrome leather is to add it in a suitable dilution to the drained and shaved chrome stock in a revolving drum. The quantity will vary with the type of leather produced but may reach up to about 50 to 60% of the leather weight on the basis of runaway liquor concentrate containing ap- As previously stated, the retanning may be carried out exclusively with the concentrate or it may be effected by supplementing the same with varying amounts of fresh'vegetablev tanning liquor either in admixture therewith or used separately as a two-step retanning operation. In either event, there is no specific limitation upon the quantity of runaway liquor concentrate or upon the ratio of the same to fresh vegetable tanning materials which can be used other than the individual requirements of any given retanning process as determined by the degree of retanning desired in the treatment of chrome leather.

For a fuller understanding of the nature and objects of the invention, reference should be made to the following examples which are given to illustrate the invention:

EXAMPLE I In a series of runs involving the daily supply of runaway liquor made available from conventional vegetable tanning operations, the liquor was evaporated in a tripleeifect evaporator to concentrate the total solids content to approximately to 30% total solids and at this stage was held in a tank to permit settling and removal of the coarser insoluble particles. The material was then further evaporated to yield the finished extract (untreated) the compositions of which are indicated in Table I.

'lbs. of concentrate (untreated).

Table I Run Total Soluble solu- Non- Tannin Purity pH Ash solids solids bles tannin Percent tannin X 100 Percent soluble solids Percent tannin X 100 Percent non-tannins percent tannin EXAMPLE II Runaway liquor concentrate prepared in accordance with the procedure set forth in Example I was further processed following the second evaporation step by the addition of hydrochloric acid with stirring to bring the pH between 5.1 to 5.0. Sufficient acetic acid was then added to further lower the pH to 4.7 after which 0.15% by weight of the sequestering agent (sodiumsalt of ethylenediamine tetraacetic acid) was added. Finally, while still stirring the mixture .05% by weight of cresylic acid was added to produce the treated concentrate.

When used in mordanting or retanning chrome leather, the treated concentrates as opposed to the untreated concentrates showed considerably improved coloring properties. The odor of the material itself as well as that of the finished leather was also substantially improved. A further advantage consisted of vastly improved keeping qualities of the material when kept under typical conditions of storage.

EXAMPLE III A tank car of runaway liquor amounting to 67,300 lbs. of liquid after separation of sediment was processed in a triple-effect evaporator to yield approximately 5000 A small portion of the concentrate was kept for analysis and evaluation and the balance was pumped into a mixing unit. A sequestering agent was added to a concentration of .4% by weight a (205* of sodium salt of ethylenediamine tetraacetic acid) based on the Weight of the concentrate and the mixture was stirred 15 minutes. The pH was then lowered by the gradual addition with stirring of hydrochloric acid,

about 60 lbs. being required to bring the pH to 5.05.

Acetic acid (80%) was then added to further lower the pH and following the use of 75 lbs. the pH reached 4.55. The mixer was run for an additional 15 to 30 minutes to insure thorough mixing.

The data in Table II summarizes the analytical data for the runaway liquor, the concentrate (untreated) prepared therefrom and the acid and sequestering agent treated concentrate.

Tablet]! Mois- Total 801- In- Non- Tan- Purture solids uble soltannins ity pH solids ubles nin Runaway liquor 96.27. 3.73 3.44 0.29 2.16 1.28 37.2 5.2 Concentrate (untreated)- 56.73 43.27 40. 79 2.48 24.17 16.62 40.7 5.6 Concentrate (treated) 57.26 42.74 40.74 2.00 23.38 17.36 42.6 4.6

EXAMPLE 1V 5(quebracho) and (b) the runaway liquor concentrate added to the revolving drum and run for 30 minutes.

Analysis of both retanning agents before and after use gave the following results:

Spent runaway liquor concentrate trate New quebracho Moisture percent.

EXAMPLE V In a conventional retanning process for the treatment of chrome leather wherein fresh vegetable tanning substances are used, the natural vegetable extract can be substituted on an equal weight basis when it is desired to use runaway liquor concentrate (40-45% by weight total solids) as a 100% replacement therefor. As in usual practice, the chrome tanned stock is loaded in a revolving drum and washed or neutralized depending upon the desired pH. The skins are covered with water (80 F.) and the desired quantity of the runaway liquor concentrate is introduced and drummed into the stock until the total solids ar spent to about 1 to 1.5%. Thereafiter the stock is further treated in accordance with conventional practices for the production of retan leather.

EXAMPLE VI Blend 1 Blend 2 Blend 3 Parts vegetable extract 25 Parts runaway liquor concentrate.

Instead of using the blend, the retanning agents can be used separately in the two-step retanning process in which event the runaway liquor cooncentrate is first drummed into the stock using the process set forth in Example V. The stock is washed for 5 minutes and again covered with water (80 F The natural vegetable extract is added to complete the retanning and the leather is fat-liquored and further treated in accordance with conventional practice.

This application is a continuation of patent application Serial No. 442,896, filed July 12, 1954, by the same coinventors, and now abandoned.

While in the foregoing specification the novel retanning and mordanting materials and methods of preparing and applying the same have been described in considerable detail by reference to specific embodiments thereof, it will be apparent to those skilled in the art that the invention is susceptible to other embodiments and that many of the details set forth can be varied widely without departing from the basic concepts of the invention.

We claim:

1. In a process for treating animal hides wherein chrome tanned leather is contacted with fresh natural vegetable tanning materials to retan said leather, the improvement characterized by the step of substituting for at least a portion of said fresh vegetable tanning materials a spent vegetable tanning liquor concentrated by evaporation at reduced pressure to at least 20% by weight of total solids.

2. The process of claim 1 wherein the spent vegetable tanning liquor concentrate is substituted as a complete replacement for the natural vegetable tanning materials and the chrome tanned leather is contacted therewith until said leather has absorbed from 6 .to 25% of its weight of total solids from the concentrate.

3. In a process for retanning chrome tanned leather the improvement which comprises the steps of partially retanning said leather with spent vegetable tanning liquor concentrated by evaporation at reduced pressure to at least 20% by weight of total solids and thereafter completing the retanning with fresh natural vegetable tanning materials.

4. In a process for retanning chrome tanned leather, the step of treating said leather with spent vegetable tan ning liquor concentrated by evaporation at reduced pressure to contain from 20 to 45% by weight of total solids.

5. In a process for preparing a vegetable tanning and mordanting agent for chrome tanned leather from spent vegetable tanning liquor, the steps comprising concentrating said liquor by evaporation at reduced pressure to increase the total solids content thereof and adjusting the pH of the concentrate to between 4.0 and 5 .8.

6. In a process for preparing a retanning substance for chrome tanned leather from spent vegetable tanning liquor, the steps comprising evaporating said liquor at reduced pressure to concentrate the total solids therein to between 20% and 45 by Weight, adjusting the pH of the concentrate to a pH between 4.5 and 5.5 and adding a sequestering agent thereto.

7. In a process for preparing a retanning substance for chrome tanned leather from spent vegetable tanning liquor, the steps comprising evaporating said liquor at reduced pressure to a total solids content of about 20% to 45 by weight, adjusting the pH of the concentrate to between 4.0 and 5.8 and adding a sequestering agent and an odor masking agent thereto.

8. In a process for treating spent vegetable tanning liquor to prepare a retanning and mordanting agent for chrome tanned leather, the steps comprising evaporating said liquor at reduced pressure to increase the total solids content thereof to at least 20% by weight of total solids, adding acid to lower the pH of the concentrate, and adding to said concentrate a sequestering agent and an odor masking agent to improve the coloring and odor characteristics thereof. 7 v

9. In a process for preparing a retanning substance for chrome tanned leather from spent vegetable tanning liquor, the steps comprising evaporating said liquor at reduced pressure to about 35% to 45% total solids by weight, adding suflicient mineral acid thereto to adjust the pH to about 5.0, further lowering the pH to about 4.7 by the addition of an organic acid, and adding sufiicient amounts of a sequestering agent and an odor masking agent thereto to improve the coloring and Odor characteristics of the product.

10. The process of claim 9 wherein the sequestering agent is .a sodium salt of ethylenediamine tetraacetic acid and the quantity used ranges from 0.05 to 2.0% by weight based on the weight of the finished product.

11. In a process for preparing a vegetable retanning substance for chrome tanned leather from spent vegetable tanning liquor, the steps comprising evaporating said liquor at reduced pressure to produce a first run extract containing about 20% to 30% by weight of total solids, further evaporating said extract at reduced pressure to obtain -a second run extract containing about 42% by weight of total solids, adjusting the pH of said second extract to about-5 .0 with a mineral acid selected from the group consisting of hydrochloric, sulfuric and phosphoric acids, further lowering the pH of the mixture to about 4.7 by the addition of an organic acid selected from the group consisting of acetic, oxalic and lactic acids, adding about .15 byweight of a sodium salt of ethylenediamine tetraacetic acid to improve the coloring characteristics thereof .and adding about .05% by Weight of an odor masking and .from said liquor to produce a powder suitable upon reconstitution with Water for use in treatment of chrome tanned leather.

12 References Cited in the file of this patent UNITED STATES PATENTS 1,065,168 Nance June 17, 1913 1,149,298 Shaw Aug. 10, 1915 1,953,968 Merritt Apr. 10, 1934 OTHER REFERENCES McLaughlin et al.: The Chem. of Leather Manufac- 10 ture, 1945, Reinhold Publ. Co., New York, pp. 568 and R.T.D.T.D.C., Vol. 45, N0. 9, September 1953, pp. 176- Progress in Leather Science, 1920-1945, London, 1948,

Claims (1)

1. IN A PROCESS FOR TREATING ANIMAL HIDES WHEREIN CHROME TANNED LEATHER IS CONTACTED WITH FRESH NATURAL VEGETABLE TANNING MATERIALS TO RETAIN SAID LEATHER, THE IMPROVEMENT CHARACTERIZED BY THE STEP OF SUBSTITUTING FOR AT LEAST A PORTION OF SAID FRESH VEGETABLE TANNING MATERIALS A SPENT VEGETABLE TANNING LIQOUR CONCENTRATED BY EVAPORATION AT REDUCED PRESSURE TO AT LEAST 20% BY WEIGHT OF TOTAL SOLIDS.