GB2104542A - Continuous saponification method and related system - Google Patents

Abstract

A saponification method is disclosed, in which fats and caustic soda are emulsified with 5-10% by weight of recycle liquid soap from the process itself. The emulsion is indirectly contacted with a heating agent in a form divided into plural streams, and is then separated into soap and byproducts comprising glycerine and water. Also disclosed is a saponification reactor comprising a plurality of concentrical tube pairs (31, 32) arranged inside a jacket (33). The saponification reaction mixture is caused to flow through the annular interspaces (36) between each pair of concentrical tubes (31, 32), while steam is caused to flow through the interiors of the innermost tubes (32) in each pair and through the jacket space between the outermost tubes (31). <IMAGE>

Description

SPECIFICATION Continuous saponification method and related system This invention relates to a saponification method of the continuous type and to a system for the implementation thereof.

Soap is known to be commonly prepared from a variety of animal-origin fats and vegetal oils, which are reacted with bases or salts of alkaline metals, in particular sodium ones, to obtain respective alkaline metal salts of long-chain monocarboxylic acids which are present in such fats and oils. Since long-chain monocarboxylic acids are to be found in fats and oils of natural origin in the form of terglycerides, a main byproduct of the saponification reaction is glycerine.

In addition to discontinuous soap manufacturing methods applied earlier, for some decades continuous saponification processes have been developed. The continuous saponification methods currently adopted, although developed to shorten the unduly long processing times which are typical of discontinuous methods, are still deficient from this standpoint, in that they involve production times extending from several hours to a few days. These prolonged times are economically disadvantageous and mainly due to the "incubation" time required by conventional methods to initiate the saponification reaction, as well as to the relatively low reaction rate resulting from inadequate contacting of the aqueous phase of the alkaline saponification reactant with the organic one of the fats.

Moreover, with conventional saponification methods, the recovery of glycerine only becomes feasible and economically interesting in high capacity plants, and in such cases involves additional equipment and processing steps for distillation and concentration.

Accordingly the task of this invention is to provide a novel continuous saponification method, which can obviate the drawbacks of conventional methods in that its processing times are substantially shorter than the latter times.

Within this task it is an object of the invention to provide a continuous saponification method, which allows glycerine to be recovered in a simple and effective way, without involving the use of concentrators and distillers as is typical with conventional methods, and which may be implemented not only on high output plants but also on medium and low output ones.

A further object of this invention is to provide a continuous saponification method which enables the recovery and use of any secondary products resulting from the process, as well as the utmost utilization of energy, and accordingly, can be specially advantageous from an economical standpoint.

The above task and objects as well as yet other objects, such as will be apparent hereinafter, are achieved by a continuous saponification method, according to the invention, in which starting agents including fats and a caustic soda solution are reacted together to yield soap and byproducts including glycerine and water, characterized in that it comprises the steps of mixing said starting reactants with 5-1 0% by weight, based on their combined weights, of recycle liquid soap resulting from said method to yield a starting emulsion, subjecting said emulsion to a saponification step by conveying said emulsion in indirect contact with a heating agent and in a form divided into plural streams, recycling a part of said resulting product, such as said recycle soap, to said mixing step, and subjecting the remaining part of said resulting product from the saponification step to separation, for recovering soap, and, as byproducts, glycerine and water.

For another aspect, this invention relates to a saponification system comprising at least one reactor for the continuous saponification of fats with caustic soda, characterized in that it comprises a plurality of concentrical tube pairs arranged inside a jacket, between the respective inner and outer tubes of each pair there being defined annular conduits for flowing the saponification reaction mixture therethrough, and the space inside said jacket between said tube pairs and inside the inner tubes in each said pairs of concentrical tubes defining a space for flowing a heating agent therethrough in indirect contact relationship with said reaction mixture.

Further features and advantages of the invention will be more apparent from the following description of preferred, but not limitative, embodiments thereof, with reference to the accompanying drawings, where: Figure lisa flow diagram of the saponification method according to this invention; Figure 2 is a flow diagram of further steps in the method of this invention, relating to the recovery of byproducts; Figure 3 is a longitudinal section view of a saponification reactor according to this invention; and Figure 4 is a cross-sectional, enlarged scale view of the reactor of Figure 3.

With reference to the accompanying drawings, the starting materials for implementing this method, respectively conducted from a fats reservoir 1 having a steam coil pipe for heating the fats to about 850C, and from a caustic soda reservoir also provided with a steam coil pipe for heating the reactant to 850 C, are proportioned through special proportioning pumps, respectively 3 and 4, and fed into a mixing and emulsifying chamber 6. Prior to being introduced into the mixing and emulsifying chamber, the fats are caused to undergo additional heating, in a suitable heater 5, to a temperature in the 120 to 1 500C range.

While in this description reference is made, for convenience of illustration, to fats in general, it is understood that any animal fat or vegetal oil, as commonly employed in the production of soap, may be utilized for the method according to this invention. The caustic soda is used in the form of an aqueous solution to a concentration of about 30-40 percent by weight. The proportions of said starting materials will, of course, depend on the specific composition of the fats being used, caustic soda being used in amounts equal at least to the stoichiometric amount required to neutralize the fat acids present.

The base materials described hereinabove are fed into the mixing and emulsifying chamber 6 in an atomized jet condition. Advantageously, the two jets are admitted into the chamber 6 perpendicularly to each other, so as to favor mixing of the reactants. Into the mixing and emulsifying chamber 6 is also led an amount of recycle liquid soap, through a conduit 30 which introduces said recycle soap upstream of the nozzle for atomizing the fats into the chamber 6.

The recycle soap applies an action of quick emulsion of the base material mixture, thus enabling a rapid "self-catalysis" of the saponification reaction.

Advantageously, an amount of recycle soap is used of about 5-1 0% by weight with respect to the combined weight of the fats and caustic soda solution fed into the chamber 6. The mixture, whose reaction begins already in the chamber 6, is further homogenized by flowing it through an open impeller centrifugal pump 7, and is then fed to a variable speed piston pump 8 for high pressure applications.

The emulsion is then passed to the saponification step proper, which is advantageously carried out in a set of two serially arranged reactors, 9 and 10.

According to the invention, two identical reactors of special construction are used, as shown in Figures 3 and 4. Each reactor comprises a plurality of concentrical tube pairs, each pair having a respective outer tube 31 and respective inner tube 32 concentrical to the former. Thus, there is defined between each said tube pairs an annular conduit 50 for passage of the mixture of reactants. The thickness of the annular conduits 50, understood as the difference of the respective radii of the outer tube 31 and inner tube 32, varies advantageously in the 3 to 8 mm range, and may be for example of 5 mm.

These concentrical tube pairs are arranged inside a tubular jacket 33 having conical terminating portions 34 which are formed with respective inlet and/or outlet openings 35.

The space within the jacket 33, indicated at 36 and being delimited among the plurality of tubes 31, and the space 37 within the inner tubes 32 of each pair of concentrical tubes, are intended to allow a heating agent, in particular steam, therethrough. Whereas the steam circulated through the space 36 is admitted and exhausted from the jacket through the cited openings 35, the steam circulated through the inner tubes is admitted and exhausted through special openings 38 formed in the tubular portion of the jacket 33 communicating to the spaces 37.

In the tubular portion of the jacket 33, two additional openings 39 are also provided which communicate to said annular conduits 50 for admitting and removing the reactant mixture.

Thus, a reactor structure is provided which allows a flow of saponification reaction mixture in the form of a plurality of streams configured as comparatively thin, annular films in indirect contact with a heating agent, on the inside and outside of each said annuli. In this manner, thanks to the high surface-to-volume ratio of the reactant mixture, there are achieved a perfect homogenization of the mixture itself and an intimate contact thereof with the heating agent, and hence extremely high reaction rates and substantially reduced reaction times.

The body of reactants in the emulsion form, which are fed to the first reactor 9, comprise partly saponified fats, glycerine, and water. Along its path of flow through the reactor 9, the reaction mixture reaches a temperature of 1 50250OC and a pressure of 1 5-20 kg/cm2.

Then the mixture is fed into the second reactor 10, identical to the first, where the soapy mass undergoes a further temperature increase until it reaches 260300C C, and concurrent pressure decrease down to 4-6 kg/cm2. Use is made of reactors having lengths of the respective tube nests in the 2-5 m range, e.g. 3 m. With such reactors, the residence time in the two-reactor set for completion of the saponification reaction can be reduced to 2-3 minutes.

Upon emergence from the second reactor, the saponification reaction is over. A bypass conduit 30 feeds a portion of the product from the saponification stage into the mixing and emulsifying chamber 6, as recycle soap, as explained hereinabove. The remaining saponification product is then subjected to a step of separation of the soap and resulting byproducts.

The saponification product is kept under constant control by means of a pH probe which controls, accordingly, the proportioning of soda and fats in the emulsifying chamber as a function of the values detected at the saponification stage outlet, thereby no discontinuity or delay is experienced in the saponification sequence once the latter has been initiated.

The separation step is carried out by spraying the soapy mass through two or more nozzles against the heated walls 1 2 of a flash distillation chamber 13, where a temperature of 1 50-2000C and vacuum of 20-40 mm Hg are maintained. In these conditions, there occurs instantaneous vaporization of water and glycerine, which are removed through a conduit in the upper portion of the chamber 13, while the remaining soap, which is in a semiliquid-liquid phase, flows down the walls and is collected at the bottom of the chamber, through the operation of a wide paddle stirrer performing 4-6 revolutions per minute (not shown).The almost anhydrous soap is passed to a variable speed gear pump 11 installed beneath the bottom opening of the chamber 13, and is then sprayed in a vacuumized chamber atomizer 15, wherein the soap water content is corrected to the required final values of 1030% by weight.

To this aim, at the top of the chamber-atomizer 15, upstream of the soap spraying nozzie, a specially provided metering device 14 feeds a preset amount of water to be added to the soap.

In this chamber-atomizer, a part of the water is vaporized, and the soap is cooled down to an optimum temperature for preliminary refining, so as to produce cylindrical sticks having a determined percentage of fat acids.

Special rotary scrapers (not shown) remove the soap film which deposits itself over the chamber walls, and the soap is thereafter refined in a die 1 6 and extruded in the form of cylindrical sticks, in accordance with conventional methods.

The glycerine and water vapors separated in the flash distillation chamber 13 and possibly in the chamber-atomizer 15, are transported to a glycerine and water recovery stage.

For this purpose, the glycerine and water vapors, under the suction applied by a vacuum pump the effect whereof may be further increased through the utilization of a thermal compressor, are flown through plural condensation stages; preferably two sets of air-cooled condensers are used which are serially arranged and comprise each two parallel connected units, of which only one condenser in each set are shown at 40 and 41.

During this step, glycerine condensates off in specially provided collectors 42 and 43, of which, for example, the collector tank 42 is a sealed one and has a heating pipe coil, it acting as a glycerine concentrator.

The vapors not condensed in the condensers 40 and 41 and containing mainly water and a small amount of glycerine, are conducted into a water-cooled preliminary condenser 44, wherein the remaining glycerine vapors are condensed and then passed to the concentrator-collector 42.

The residual vapors containing mainly water with possible traces of glycerine are condensed in a final condenser 45, also of the water-cooled type. The fresh water condensed therein is drained into an open collector tank 46 and utilized in the preparation of the caustic soda solution which is fed to the system during the initial stage of the process.

From the foregoing description, it will be appreciated that the method and system according to this invention achieve their objects.

In fact, the inventive method enables production of soap and concurrent recovery of glycerine in a much shorter time, on the order of a few minutes. This is the outcome, on one hand, of the good homogenization and intimate contact between the reactants during the mixing and emulsification step.

On the other hand, such significantly shorter times in the method of this invention are also the result of the perfect homogenization and enhanced contact with the heating agent during the saponification step, such as are achieved by virtue of the particular type of reactor utilized in this invention.

The apparatus for implementing the method is considerably simplified, and its starting investmerit cost reduced, because concentrators and distillers for the recovery of glycerine, which typify conventional arrangements, are effectively eliminated. Moreover, the method affords the utmost utilization of the starting materials, with remarkably high final output and no secondary products to waste. The resulting soap is of good quality, and virtually impurity-free. Also, the glycerine recovery stage is economically applicable to low throughput systems, as well as high capacity ones.

While the above description makes reference to presently preferred embodiments of the method and system according to this invention, skilled persons in the art can easily introduce modifications and variations thereof, without departing from the scope of the invention.

Claims (14)

1. A continuous saponification method, in which starting reactants including fats and a caustic soda solution are reacted together to yield soap and by-products including glycerine and water, characterized in that it comprises the steps of mixing said starting reactants with 5-1 0% by weight, with respect to their combined weights, of recycle liquid soap resulting from said method to yield a starting emulsion, subjecting said emulsion to a saponification step by conveying said emulsion in indirect contact with a heating agent and in a form divided into plural streams, recycling a part of said resulting product, such as said recycle soap, to said mixing step, and subjecting the remaining part of said resulting product from the saponification step to separation for recovering soap, and, as byproducts, glycerine and water.

2. A method according to Claim 1, wherein said mixing and emulsification step is carried out by supplying said reactants and said recycle soap in the form of jets oriented at a right angle to each other.

3. A method according to Claim 1, wherein said saponification step is carried out by supplying said emulsion through a plurality of annular conduits having each a cross-section thickness dimension of the passage opening in the 3-8 mm range, inside and outside of said annular conduits there being flown said heating agent.

4. A method according to any of the preceding claims, wherein said saponification step is carried out in two successive stages by flowing said emulsion through a first set of said annular conduits at a temperature of 150--2500C and pressure of 1 5-20 kg/cm2, and then through a second set of said annular conduits at a temperature of 260--3000C and decreased pressure of 4-6 kg/cm2.

5. A method according to either Claim 3 or 4, wherein said annular conduits have a passage opening about 5 mm thick.

6. A method according to any of the preceding claims, wherein said heating agent comprises steam.

7. A method according to Claim 1, wherein said separation step comprises flash distillation under vacuum of the product from the saponification step at 1 50-2000C and 20-40 mm Hg for the removal of glycerine and water and recovery of soap.

8. A method according to Claim 7, wherein said flash distillation is carried out by spraying said saponification product in the form of a thin layer over the walls of a chamber.

9. A method according to either Claim 7 or 8, comprising an additional step wherein said soap from said separation step is admixed with water by spraying the mixture over the walls of a vacuumized chamber to obtain a final soap having a water content of 1 0-30% by weight.

10. A method according to any of the preceding claims, further comprising the steps of subjecting the mixture of glycerine and vapor-phase water from said separation step to at least one condensation step to recover liquid glycerine, and subjecting the remaining vapor phase to at least one additional condensation step to recover fresh water.

11. A reactor for continuously saponifying fats with caustic soda, characterized in that it comprises a plurality of concentrical tube pairs arranged inside a jacket, between the respective inner and outer tubes of each pair there being defined annular conduits for flowing the saponification reaction mixture therethrough, the space inside said jacket between said tube pairs and inside the inner tubes in each said pairs of concentrical tubes defining a space for flowing a heating agent therethrough in indirect contact relationship with said reaction mixture.

1 2. A reactor according to Claim 11, wherein said annular conduits have a thickness, understood as the difference of the radius of a respective outer tube and radius of a respective inner tube concentrical to the former, in the 3-8 mm range.

13. A reactor according to Claim 12, wherein said thickness is 5 mm.

14. A saponification system comprising at least one saponification reactor according to any of Claims 11 to 13.

1 5. A saponification system according to Claim 14, comprising two such reactors serially arranged with respect to each other.

1 6. A continuous saponification method, as herein claimed, described, and illustrated.

1 7. A continuous saponification reactor, as herein claimed, described, and illustrated.