US3444625A - Leather dehydration in a falling film dehydrator - Google Patents

Description

May 20, 1969 G|ELLA ETAL I 3,444,625

LEATHER DEHYDRATION IN A FALLING FILM DBHYDRATOR Filed Feb. 2, i966 Sheet or 3 A rToRNE Y.

May 20, 1969 L GIELLA ET AL I 3,444,625

LEATHER DEHYDRATION IN A FALLING FILM DEHYDRATOR Filed Feb. 2, 1966 Sheet 2 of s I.\IVENIUR$. MAR/0 G/ELLA Y/PA YM ND 5". PETRAL/A A TTORNEY,

May 20, 1969 LEATHER DEHYDRATION IN A FALLING FILM DEHYDRATOR Filed Feb. 3. 1966 M. GIELLA ET AL 3,444,625

Sheet 015 INVENTORS. MAR/0 GIELLA R4 YMOND R. PETRAL/A A TTORNEY.

United States Patent 3,444,625 LEATHER DEHYDRATION IN A FALLING FILM DEHYDRATOR Mario Giella, Boston, Mass., and Raymond Rosario Petralia, Camillus, N.Y., assignors to Swift & Company,

Chicago, 111., a corporation of Illinois Filed Feb. 2, 1966, Ser. No. 524,639 Int. Cl. F26b 3/00; C14c 5/00, 11/00 U.S. Cl. 34-9 Claims ABSTRACT OF THE DISCLOSURE Sheet material is treated while suspended in a chamber containing a non-liquid environment by applying a liquid treating agent to descent along the surfaces of the material by gravity as a thin film. Treatment with solvent compositions may be utilized to extract water from the material and to apply conditioning material and the like. For instance leather may be dehydrated and also tanned.

This invention relates to processes in which water is removed from water-containing sheets of porous materials by extraction with water miscible organic solvents and to processes in which a porous sheet is treated with an agent carried by a liquid. The invention is particularly useful in dehydrating water-containing hides and skins and in tanning solvent-dehydrated hides.

Many water-containing porous materials such as paper, cloth, wood, and leather are conventionally dried by vaporizing the water in warm currents of air. Some heatsensitive materials cannot be dried using the vaporization technique because of a loss of desirable properties such as flexibility. Untanned hides and skins become hard and horny from thermal drying even at relatively low temperatures due to degradation and to the formation of new bonds as the fibers approach each other as the water is removed from the interstitial spaces.

Such heat sensitive materials may be converted to a water-free soft flexible state by means of solvent dehydration. This has been accomplished by first immersing the wet stock in successive baths of a water miscible organic solvent, such as acetone, until the equilibrium liquor has a relatively low water concentration. During the immersion procedure water contained in the wet material is displaced by the solvent, later the solvent is removed from the hide by some suitable method.

Various attempts have been made to reduce processing times and costs in the leather industry. Sol-vent processing of hides is one area which has been investigated. It has been suggested that dehaired and defleshed hides could be dehydrated by repeated immersions in a water miscible solvent and that after removal of the solvent, a dry plump hide material would result which could be easily tanned.

Leather has been produced in the laboratory using batch immersion solvent dehydration techniques and also a procedure whereby solvent is forced through thin hides by pressure, but no solvent dehydration process has proved to be commercially usable, because of economic considerations. When hides are processed using an organic solvent it is the water extraction procedure, previously accomplished by batch immersion, which is time consuming and costly. The main cost factors are the quantity of solvent required and the consequent solvent recovery requirements. Batch immersion of the hides or skins in the solvent requires a plurality of immersion steps with each step requiring from 5-8 hours to come to equilibrium. These lengthly time requirements for such a system have also discouraged commercial usage.

It is therefore an object of this invention to provide a process for economically removing water from sheets of "ice water-containing porous material with a water miscible organic solvent.

Another object of the invention is to provide a rapid method of removing water from hides and skins wherein organic solvent contacts the hides in a thin falling film.

Another object of the invention is to provide a rapid method of treating and tanning solvent-dehydrated and desolventized hides and skins with fluids.

A still further object of the invention is to provide a rapid method of tanning solvent dehydrated and desolventized hides by contact with a thin falling film of liquid tanning agent.

Other objects and advantages of the invention will become apparent upon reading the foll wing description taken in conjunction with the accompanying drawings.

Broadly, this invention relates to a method of removing water from sheets of water-containing porous material by contacting the sheets with a thin falling film of water miscible organic sol-vent. The solvent is directed to distribute itself on both surfaces of the sheet and flow by gravity in a thin falling film over the surfaces of the sheet. Minimal quantities of solvent may be employed since the solvent can be recycled. The film of solvent carries away with it water which diffuses to the surface of the sheet. After removal of water and solvent from a hide by the above procedure the hide may be tanned by applying a liquid tanning agent in a thin falling film.

Individual sheets of water-containing material are retained in a spaced apart relationship during the process. For certain solvent distribution procedures a substantially vertical sheet position is preferred. Flexible sheets may, however, be draped in loops open at the bottom and 'solvent directed at top and bottom surfaces thereof to form a thin falling film on both surfaces of the flexible sheets.

Various solvent distribution procedures may be used to obtain the falling film on the sheets. Solvent vapor can be condensed above or on the sheets in a manner to form a thin falling film. Liquid under pressure can be sprayed onto the sheets and liquid can be flowed onto the sheets.

After removal of a major amount of the water, it is usually necessary to desolventize the sheets, that is remove the residual solvent from the sheets being dehydrated. This may be accomplished by stripping the solvent from the sheets with a gas stream. The solvent may be recovered from the gas stream by condensing the solvent or by absorbing the solvent in a high boiling point liquid.

The solvent used for the extraction should be water miscible, have a low heat of vaporization, and preferably be inexpensive. Mixtures of solvents are also usable in the process.

Representative water holding substrates which can be dehydrated using the process include: limed cowhide (full thickness), bated cowhide (full thickness), chrome leather (full thickness), vegetable leather (full thickness), green cowhide (full thickness), enzyme unhaired (full thickness), limed grain splits, limed flesh splits, limed calfskin (full thickness), pickled sheepskin; depickled sheepskin; wet cardboard; and wet cloth. In general, any porous water-containing sheet can be dehydrated using the present method, which has utility for sheets of widely varying thickness.

The following drawings and description are provided by way of example and are not to be taken as a definition of the limits of the invention. In the drawings:

FIGURE 1 is a flow sheet of apparatus capable of performing the invention;

FIGURE 2 is an elevation view of a fintube distributor head;

FIGURE 3 is a sectional view taken along line 33 of FIGURE 2;

FIGURE 4 is a diagrammatic view of spray means usable in the practice of the invention; and

FIGURE 5 is a sectional view of a perforated pipe distributor head.

The method, while applicable to any porous watercontaining sheet, will for convenience hereafter be described as used on limed hides, that is, hides free of hair and flesh and comprising about 75% water. Hides to be dehydrated are retained in a spaced apart relationship in a hermetically sealed zone wherein the water removal takes place. The hides may be suspended in a substantially vertical position or draped about a retaining member to 'form an open loop.

A water miscible solvent is introduced into the hermetically sealed zone and directed to contact the hides in a thin falling film. During gravity-urged flow of the thin film down the hides the solvent flow picks up water which diffuses to the surface of the porous hide and entrains this water. Solvent and water then drop from the hides and may be recycled.

The stock is continuously bathed in a thin film of solvent which flows by gravity down the surfaces of the hide. It is necessary that the flow rate of the solvent down the stock be great enough to maintain uniform wetting of hides. The upper limit on flow rate is determined by economic factors, high flow rates requiring in general larger solvent inventories and higher pump and piping capacities.

The recycled liquid may be purified prior to reintroduction into the dehydrator or may be pumped back into the dehydrator without purification. Recycling of a particular quantity of solvent without purification may be continued until the solvent-to-water ratio of the feedbeing applied to the hides is substantially the same as the solvent-to-water ratio in the liquid draining off the hides, that is, an equilibrium point is approached.

The wet solvent may be purified by a variety of methods, either continuously or intermittently. Distillation is the most common method. Some solvents may be separated from water by salting out, phase separation on cooling, solvent extraction, chemical precipitation and freezing. The choice of method or methods used depends on the solvent employed.

A plurality of solvent feeds may be used to remove water from a given batch of hides. The term feed refers to a certain quantity of liquid which is continuously directed onto the hides in a thin falling film and is recycled without purification until equilibrium of the solvent-towater ratio is reached. The feeds may all comprise fresh solvent or a countercurrent-type procedure may be used wherein the first feed comprises a dilute solution of water in solvent and successive feeds are supplied which contain less and less water. The countercurrent-type procedure wherein previously reclaimed solvent feeds are utilized as the first feeds in a dehydration operation significantly reduces the solvent inventory required and also the quantity of solvent-water solution from which solvent must be reclaimed.

After the substantial removal of water is completed the solvent left in the hides or sheets should be recovered quantitatively for an economical process. Solvent recovery may be accomplished in several ways. One is vaporization and recondensation of the solvent by means of a hot gas stream. This procedure is described in Kremens et al., Patent No. 3,048,929. A second method of solvent recovery involves vaporization of the solvent from the hide into a low temperature gas stream followed by absorption in a high boiling absorbent from which the solvent is later stripped.

After removal of organic solvents from the hide, a soft, flexible, strong product results which weighs about 25% as much as the original limed hide. This dehydrated product can be tanned immediately without removal from the hermetically sealed zone. The tanning agent employed may be carried by a liquid or alternatively vapors may be emitted into the zone and condensed on or above the hides. If a fluid tanning agent is used the same falling film technique may be used to tan the hides.

Referring to FIGURE 1 we provide a dehydrator 10 with a steam coil 12 and including a liquid tank 14 at its lower extremity. The dehydrator 10 provides a hermetically sealed zone to prevent solvent losses.

A liquid feed line 16 directs solvent feed into the upper portion of the dehydrator 10. Solvent is initially drawn from one of a plurality of storage tanks 18 and directed through a meter 20 and forced by a liquid pump 22 through a heat exchanger 24 and into the dehydrator 10. After a selected amount of solvent is metered into the system from one of the storage tanks 18, an appropriate valve 26 is closed.

Solvent from the feed line 16 is directed onto hides contained in the dehydrator 10 to form a thin falling film of liquid on the hides. The various procedures usable in forming the thin film will be subsequently explained in de tail. During downward flow as a thin film, the solvent extracts water from the hides. The resulting solvent-water mixture drops by gravity into the bottom portion of the dehydrator 10 and may be recycled through a liquid line 28, the pump 22 and back to the top of the dehydrator. Recycle of the solvent may be continued until the solventto-water ratio of the liquid feed to the dehydrator approximates the solvent-to-water ratio of the liquid leaving the dehydrator.

After the equilibrium solvent-to-water ratio is approached or reached the feed may be fed to a column 40 for fractionation or back to the storage tanks 18. Usually a plurality of feeds are required to reach an end point after which desolventization takes place.

During desolventization of the hides there is no liquid flow in the dehydrator. A non-reactive gas such as nitrogen is fed into the system through a valved supply line 42 from a source (not shown). The gas is forced through a heater 44 and into the dehydrator 10 by a pump 46. Gascontaining solvent is exhausted from the dehydrator via a line 48 and is either recycled back to the dehydrator via a line 50 or fed to a column 52 which may be either a condenser or an absorber. FIGURE 1 illustrates piping for use of column 52 as condenser.

Non-reactive gas from the supply line 42 may also be used to purge the system before and after solvent dehydration.

Referring to FIGURES 2, 3 and 4, we show three different means for producing a thin falling film on porous sheets. Any of these means may be installed within the dehydrator 10.

Condensation of solvent vapor above stock to be dehydrated is incorporated into the method utilized by the fintube distributor head shown in FIGURES 2 and 3. A sparger tube 60 having a plurality of openings 62 distributes solvent vapor between a plurality of fins 64. A cold water pipe 66 and fins 64 condense solvent vapor above the stock 68 to be dehydrated. The fins 64 which direct the condensed vapor onto the stock to form a thin falling film are carried by the pipe 66 and are used to support the stock 68.

Referring to FIGURE 1, it can be seen that the sparger tube 61 may be attached at the terminal of a vapor line 70 off the column 40. This arrangement allows use of a minimum quantity of solvent since liquid coming off the hides can be fractionated in the column 40 and recycled over and over thus eliminating the need for a plurality of storage tanks and a large solvent inventory.

Referring to FIGURE 4, a system for spraying a thin film of liquid on a hide or skin is illustrated. A pair of bars are rigidly attachable to the interior of the dehydrator 10. Attached to the bars 80 are a plurality of spring hooks 82 which hold sheets or hides 84 in a substantially vertical position. Liquid solvent supplied by the liquid feed line 16, shown in FIGURE 1, is directed by a pair of sprayheads 86 and jets 88 onto both surfaces of a hide 84 to be dehydrated to form a thin falling film.

Another method of solvent delivery is accomplished by the means illustrated in FIGURE 5. Two horizontal perforated pipes 90 are suspended across upper portions of the dehydrator and are axially aligned with a small vertical space therebetween to permit the hides 92 to be draped over the lower pipe in the form of a loop open at the bottom. A plurality of holes 96 in the pipes 90 allow solvent to seep out of the pipe and diffuse into felt sleeves 98 which surround pipes 90 and distribute the solvent onto portions of the hide forming the bight of the open loop. A bafl'le 100 attached, to the lower pipe 90 aids in distributing solvent evenly to the underside of the hide. In using the perforated pipe distributor of FIGURE 5 the solvent may be coveniently fed into the dehydrator from a constant head reservoir (not shown) located outside and above the dehydrator.

Many commercially available organic solvents, alone and in various combinations forming azeotropic and nonazeotropic mixtures, are usable in the process. Available solvents which alone or in combination are capable of removing water from a porous substrate include: formal; acetone; chloroform; methanol; ethanol; tetrahydrofuran; acetonitrile; dichloromethane and ethylenediamine; dichloromethane and methanol; dichloromethane and acetone; formal and acetone; formal and methanol; methylformate and methanol; methylformate and acetone; chloroform and methanol; acetone and hexane; acetone and carbondisulfide; acetone, dichloromethane and n-hexane; acetone; dichloromethane and methanol; and acetone and formal. Acetone, methanol, ethanol, acetonitrile, formal and tetrahydrofuran are all eflicient solvents. Acetone will remove the highest percentage of water from hides under given conditions as shown by the following table.

Pieces of limed cowhide were selected of as nearly the same dimensions and weight as possible. The dehydration was carried out by allowing solvent to flow down both sides of the vertically suspended limed cowhide at .04 lb. per linear foot of falling film per minute for each solvent evaluated and only fresh solvent was fed onto the hides. The following table shows the dehydration rates of a few of the solvents.

Percentage of original water left at- The process may in general be practiced on any porous sheet which is capable of holding Water. The following table shows some of the porous substrates which have successfully been dehydrated using the present method. These materials were dehydrated by continuously recycling multiple feeds of fresh material as a thin falling film at a rate of about 0.4 lb. per linear foot per minute to substantial equilibrium. The end point of each feed was determined by checking the specific gravity of wet solvent off the stock. All materials were dehydrated until the specific gravity of the last feed was brought below 0.802.

Several variables including sheet thickness, solvent-tohide ratio and solvent purity affect the dehydration rate. For a given type of material, the dehydration rate is inversely related to sheet thickness as can be seen by the above table.

As previously mentioned, the solvent-water mixture which is drained off the hides after extraction by the thin film may be recycled and again distributed over the hides in a thin film either with in-line purification of the solvent or without in-line purification.

From the standpoint of minimizing solvent-water fractionation requirements, it is preferable to use a plurality of feeds. The solvent-to-hide weight ratio of each feed affects the dehydration rate. Higher solvent-to-hide ratios result in fewer feeds and less time required to reach an end point. On the other hand, the lower the solvent-tohide ratio, the less solvent is required.

The effect of different solvent-to-hide ratios is shown by the following table wherein the amount of fresh acetone per feed, number of feeds, dehydration time and total amount of acetone required per pound of limed cowhide to dehydrate to the same end point are listed. Each feed used in these tests was fresh acetone and was distributed onto suspended limed cowhides by spray heads. Each feed was recirculated until the acetone-water ratio in the dehydrating solvent reached a constant value.

Solvent/hide ratio Lbs. fresh Sp. gr. of (lbs. acetone/feed N 0. of Dehydi'aacetone/lb. final feed at per lb. of hide) feeds tion time of hide 20 C./20 C Falling film dehydration of porous sheets offers several advantages relating to process flexibility. A plurality of independently operated and self-contained processing chambers can be built above ground. Each dehydrating chamber has its own condenser and fractionating column. It is not necessary to design dehydration chambers to withstand hydrostatic pressures as in a fully submerged liquid immersion process. The above-ground dehydration chambers may be serviced through a gasketed door by a monorail system.

Different kinds of stock such as grain or flesh splits, limed, pickled, chrome, and other types of hides and skins can be processed simultaneously in different processing chambers. Also, desolventizing and tanning operations can be carried out simultaneously in different chambers. Another important feature of the process is its adaptability to hides of widely varying thickness. Hides graded for thickness may be processed together for cutting processing times to a minimum.

The products resulting from the dehydration and desolventization of untanned hides can be directly converted into leather in the dehydrator 10 shown in FIGURE 1. Tanning fluid may be placed in the tank 14 at the bottom of dehydrator 10 for vaporization by steam coils 12. The vapors produced come into contact with the hide and react with it. The following tanning agents produce significant increases in shrink temperature of the hides: formaldehyde, acrolein, toluenediisocyanate, dichlorobutene, p-benzoquinone, terephthalaldehyde, monoethylene, glycolbischloroformate, epichlorohydrin.

A dehydrated and desolventized hide can also be tanned in dehydrator 10 by dissolving tanning agent in a solvent and contacting the hide with a thin falling film of tanning solution. The distributing apparatus illustrated in FIGURES 2-5 may be used to produce the thin falling film. Advantages of using the falling film technique include rapid tanning and a reduction in the inventory of tanning fluid necessary. Conventional tanning procedures may also be used to tan hides dehydrated by the instant method.

The following examples are set forth to illustrate specific embodiments of the invention and should not be construed as placing any limitation on the scope thereof.

Example I.-Limed cowhide, acetone, and spray heads Freshly limed cowhide from the beam house was suspended in the dehydrator between jet spray heads. The system was purged with nitrogen gas from a cylinder, and then a wet acetone feed (about 21% water) was introduced onto the hides by jet spray heads similar to the apparatus shown in FIGURE 4. This feed was recycled onto the hides for about 2% hours and then drained from the system. A more pure solvent solution, the fourth feed from the previous run containing about 12% water was introduced into the system and circulated for 1 /2 hours. This procedure was repeated with the fifth, sixth and seventh feeds from the previous run, the feeds having water compositions respectively of 9%, 5%, and 4%, with recirculation for l, /2 and /2 hours, respectively. The procedure was again repeated using two feeds of fresh acetone which were recirculated for /2 hour each. The final feed resulted in a solution draining off the hides having a specific gravity of about .802.

Without moving the stock, a nitrogen gas stream at 74 F. was circulated about the suspended hides; through a condenser at 35 F., through a heat exchanger, and back to the dehydrating chamber at a linear rate of flow through the dehydrating chamber of about 35 feet per minute. At the end of 80 minutes the stock had a very white appearance, indicating almost complete desolventization. The dry hide was soft, flexible, strong, porous, and free from hard spots. The weight of the dehydrated and desolventized product was about 25% of the original limed weight.

Example II.Fintube distributor, acetone vapor and unhaired cowhide Enzyme unhaired cowhide containing 76% water was hung in the tube slot of a fintube distributor head. The dehydration chamber was sealed and acetone vapor from the fractionator operating at a 3/1 reflux ratio was allowed to enter and condense on the upper portions of the cooled fins. The liquid at 35 C. was distributed evenly across the hide and ran down both surfaces to extract the water. A solvent flow rate of 120 milliliters/minute/foot of horizontally exposed hide resulted in a uniform thin falling film down both surfaces of the hide and in five hours produced hides having a moisture content of 8%. The hides after desolventizing were of a white color and were flexible and had no residual hard spots.

Example lII.Perforated pipe distributor, pumped acetone, and limed cowhide Limed cowhide was hung from the bottom distributor pipe of an apparatus similar to FIGURE 5. Acetone feeds comprising fresh acetone with a solvent-to-hide weight ratio of about 0.3 were recirculated over the stock at a rate suflicient to maintain good wetting on both surfaces thereof. After attainment of equilibrium for each feed, which was shown by no further change in the specific gravity of the circulating solvent, the feed of wet solvent was replaced with a fresh charge of acetone and recirculation resumed. Nine feeds of fresh acetone produced about 3 water in the final feed.

Example IV.-Condenser pipe head, volatile solvent pool, and limed split hide Strips of limed split cowhide were draped over the lower of two half-inch diameter condenser pipes aligned axially one over the other with a space of one-half inch between the two pipes, the lower pipe having a baflle to distribute the condensed solvent. The bottom of the dehydrator was filled with three pounds of a solvent solution per pound of hide. The solvent solution comprised three parts by weight of methyl formate and one part methanol and was heated to 37 C. to continuously vaporize the solvent. The solvent vapors which formed condensed on the pipes and ran down the stock. After four hours of vaporizing the solvent and after desolventizing, the hides were White and flexible.

Example V.Perforated pipe distributor, condensed ethanol, and chrome leather Strips of full thickness chrome leather containing 55% water were draped over the lower perforated pipe of an apparatus similar to that shown in FIGURE 5. Ethanol at 50 C. from a constant head supply tank was used to form a thin falling film having a flow rate of about 25 ml./min./foot of perforated pipe. The wet alcohol was continuously sent to the fractionator where an azeotropic mixture was recovered and sent back to the constant head supply tank. The ethanol was recirculated for about three hours. After desolventization the hides were smooth, flexible, and were free of any noticeable hard spots on their surface.

Example VI.-C0ndenser pipe, gas saturated with methanol, and green hide Strips of hair-on-hide containing 64% water were suspended from fintube distributor heads similar to those illustrated in FIGURES 2 and 3. A methanol-saturated stream of gas at 35 C. was introduced into the distributor head. The solvent condensation formed on the condenser pipes ran down the hide in a thin falling film extracting the water, and then dropped into a tank at the bottom of the dehydrator. The gas stream was resaturated by warming it and passing it through liquid methanol. After operating for 12 hours the solvent-to-water ratio of the liquid dropping off the hide was 99/1.

Example VIl.Liquid tanning, quebrancho in acetone Full grain limed cowhide which had been previously dehydrated and desolventized was suspended in the dehydrator between spray heads similar to those illustrated in FIGURE 4. Crushed quebrancho, a vegetable extract, was dissolved in acetone (about lb. of quebrancho per pound of acetone). The tanning material was distributed onto the hide in a thin falling film by the same spray heads used in the water removal process. Tanned leather, as shown by coloration of the hide cross section and increase in shrinkage temperature, resulted after 2 hours recirculation keeping the temperature of the solution at 100 F.

Example VIII.Tanning with chromium chloride in methanol Full grain limed cowhide which had been previously dehydrated and desolventized was suspended in the dehydrator between spray heads. A 16% solution of chromium chloride hexahydrate in methanol was distributed onto the hide in a thin falling film for 15 minutes. The solvent was removed by a nitrogen gas stream, and then a 1% solution of sodium methylate in methanol was distributed onto the hide by the same falling film technique for one aninute. Again the solvent was removed by a nitrogen gas stream. The resulting leather had a shrinkage temperature of 170 F. as contrasted to the starting li med stock with a shrinkage temperature of F.

Example IX.-Tanning with glutaraldehyde in acetone Full grain enzyme unhaired cowhide which had been previously dehydrated and desolventized was suspended in the dehydrator between spray heads. A 28% solution of aqueous glutaraldehyde25% in acetone was distributed onto the hide in a thin falling film for one hour. The resulting leather had a shrinkage temperature of 173 F.

Example X .-p-Quinone in acetone tanning Full grain limed cowhide which had been previously dehydrated and desolventized was suspended in the dehydrator between spray heads. A 10% solution of pquinone in acetone was distributed onto the hide in a thin falling film for 15 minutes. The resulting yellow-surfaced leather had a shrinkage temperature of 170 F.

Example Xl.lmpregnatin with a resin in acetone Full grain lirned cowhide which had been previously dehydrated and desolventized was suspended in the dehydrator between spray heads. A 40% solution of Dymerex resin, a hard thermoplastic resin comprising dimerized resin acids, in acetone was distributed onto the hide in a thin falling film for 30 minutes. More specifically, Dyrnerex is a pale, acidic, thermoplastic, high-softening point resin. It consists of approximately 80% resin acid dimers and 20% monomeric resin acids and neutral material. Dymerex resin has high resistance to oxidation and does not crystallize from solutions or from solid compositions containing it. It is compatible with many natural and synthetic film-formers and rubbers. Being an acidic resin, it reacts readily with polyalcohols or hydrated lime to produce high-melting derivatives. It is available in flake and lump forms. It has the following properties:

Softening point (Hercules drop method), C. 145-158 Color (U.S. rosin grade) K Acid number 131-150 Saponification number 145 Unsaponifiable material, percent 8 Gasoline insoluble, percent Nil Molecular weight, average 502 Density at 20 C 1.069

It is soluble in alcohols, esters, ketones, hydrocarbons, chlorinated solvents and mineral oils. It is insoluble in water.

The solvent was removed from the coated hide by a nitrogen gas stream and the resulting product showed a 50% increase in Weight over the dry limed stock. In 24 hours the impregnated product increased in weight by 32% when immersed in water at 80 F. as compared to an increase of about 250% by an untreated piece.

Obviously many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof.

We claim:

1. A method for treating sheets of porous material comprising: retaining the sheets of porous material within a non-liquid environment in a spaced apart relationship; directing a liquid treating agent at the upper portions of both surfaces of the sheets to form thin falling films of liquid over both surfaces of each of the sheets; treating the sheets during the downward movement of the liquid agent over the sheets; and removing excess liquid treating agent from the sheets.

2. The method of claim 1 wherein the sheets are hides or skins.

3. The method of claim 1 wherein the liquid treating agent comprises a water miscible organic liquid solvent and water is extracted from these sheets during the downward movement of the solvent.

4. The method of claim 3 wherein the sheets are retained in a vertical spaced apart relationship beneath a zone of condensing water miscible solvent vapor and the condensed vapor is directed to form said thin falling film.

v5. The method of claim 4 wherein the sheets are hides or skins.

6. The method of claim 3 wherein the sheets are retained in a spaced apart relationship by draping the sheets in loops, said loops being open at the bottom and said liquid is directed at top and bottom portions of the sheet, said portions forming the bight of said loop, to form said thin falling film on both surfaces of the sheet.

7. The method of claim 6 wherein the sheets are hides or skins.

8. An improved method for removing water from flexible porous sheets comprising: suspending the sheets in vertical spaced apart relationship in a hermetically sealed zone; purging said zone with a non-reactive gas; continuously directing liquid at the upper portions of both surfaces of the sheets to form a thin falling film of liquid over the sheets, said liquid originally comprising a dilute solution of water in a water miscible organic solvent; varying the composition of said liquid by periodically supplying a solvent containing less water; extracting water from the sheets during downward movement of said thin falling film; and removing the solvent and extracted water from the sheets.

9. The method of claim 8 wherein the sheets are hides or skins.

10. The method of claim 9 wherein the water miscible organic liquid is selected from the group consisting of acetone, acetonitrile, ethanol, methanol, tetrahydrofuran, and formal and mixtures thereof.

11. The method of claim 10 wherein the water miscible organic liquid is acetone.

12. The method of claim 1 wherein hides are suspended in a hermetically sealed zone and the liquid treating agent is a thin falling film of tanning liquid.

13. The method of claim 12 wherein the hides are suspended in a substantially vertical spaced apart relationship and said tanning liquid is sprayed onto the hides to form said thin falling film.

14. The method of claim 12 wherein the hides are suspended in spaced apart relationship beneath a zone of condensing tanning agent vapor, and the condensed vapor is directed to form a thin film of tanning liquid over both surfaces of the hides to tan the hides.

15. The method of claim 12 wherein the hides are suspended by draping the hides in loops, said loops being open at the bottom.

References Cited UNITED STATES PATENTS 1,338,308 4/1920 Krouse. 3,048,929 8/1962 Kremen et a1. 349

JOHN I CAMBY, Primary Examiner.

US. Cl. X.R.

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