GB2181665A - A plant for the continuous hydrolysis of fats - Google Patents

Abstract

To improve the cracking degree of an installation for continuous cracking of fats comprising in a tubular column counter-flowing currents of ascending fats and falling water, to increase the glycerin concentration and reduce the retention time, packing sections (16) and heating sections (17) are alternatively arranged in the tubular column (15), in its longitudinal direction. The packing sections contain filler bodies with at least 90% free volume.

Description

SPECIFICATION A plant for the continuous hydrolysis of fats This invention relates to a plant for the continuous hydrolysis of fats comprising a tube, designed for water descending in countercurrentto ascending fat at around 5 MPa/260"C, of a splitting column which comprises at its sump a fat inlet and a glycerol water outlet and at its head a water inlet and a fatty acid outlet, the inlets being preceded by heating means and a pressure pump and the outlets being followed by expansion and cooling means. The invention also relates to a processforthe continuous hydrolysis offats. In the context of organic chemistry, the expression "fat" also covers oils.

In general, only native fats are used for hydrolysis in the way described. The fats are hydrolized by water to glycerol and fatty acid. Hydrolysis may be carried out discontinuously in stirrer-equipment autoclaves or continuously in splitting columns with or without a catalyst. Today, hydrolysis is carried out above all in splitting columns through which the two liquid reactants, namelywaterandfat, are passed in countercurrent.

The first continuous countercurrent processes are described in US-PS 2 156863 and 2 159397 and in DE-PS 657938. According to FR-PS 924906, a few plates may be provided at the fatty acid outlet for heat recovery.

Splitting columns of the described type operate in accordance with the specifications in "Bailey's Industriai Oil and Fat Products",John Wiley & Sons, New York, Vol.2,4th Edition, pp. 108 to 110, at 5 MPa and at around 260with residence times in the column of from 2 to 3 h ou rs. Th e wate r-to-fat rati o is ofthe order of 40 to 50%. The columns may range from 500 to 1200 mm in diameterandfrom 18to 24 m in height.They are heated by the injection ofdirectsteam. In columns such as these, degrees of hydrolysis offrom 97to 99% and glycerol concentrations offrom 13 to 18% can be achieved according to the journal "J.Am. Oil. Chem. Soc." 29(1952),490to495.

The object ofthe present invention in general terms is to improve the hydrolysis of fats by higher degrees of hydrolysis, a smaller excess of water and a shorter residence time. Higher degrees of hydrolysis mean a correspondingly improved yield of the process. The fatty acid processing steps following hydrolysis, namely distillation, fractionation and esterification, are also favorably influenced with a smaller percentage of unhydrolyzed material. A smaller excess of water leadsto higherconcentrations of glycerol and henceto lowerworking-up costs forthe glycerol to be produced. A shorter residence time provides for an increase in throughput in existing splitting columns and for smaller dimensions and hence for lower building costs for the columns.

Forthe plant comprising a splitting column mentioned atthe beginning,thesolution provided by the invention is characterized in that packing sections with packings consisting of packing elements with a free volume of at least 90% and heating sections for heating the reactants moved through the column in countercurrent follow one another substantially vertically in the longitudinal direction ofthe column tube. For the process according to the invention,the solution is characterized in that the water droplets falling through the column are permanently deflected, split up and recombined and in thatthefat ascending through the column-with longitudinal mixing suppressed- is permanently radially mixed with thewaterdroplets.

The invention is based on the observation that, due above all to the improvements in high-pressure hydrolysis afforded by the temperature program with a reduction in the residence time to around 2.5 hours, the velocity of the mass transfer of water into the fat phase and of glycerol into the water phase has become more important than the actual reaction velocity.Whereas, therefore, under the reaction conditions hitherto applied in regard to temperature and pressure the masstransfermay be regarded as a slow and hence velocity-determining step, it is possible in accordance with the invention sufficiently to intensify the mass transfer by permanent deflection, splitting up and recombination and by permanent renewal of the interface ofthe water droplets on the one hand and the fat particles on the other hand and furtherto establish an ideal counterflow of aqueous and organic phase and to avoid axial back-mixing in the column. Accordingly, it is possible where the invention is applied simultaneously to adjust a more favorable water-to4at ratio, to shorten the residence time and to increase the degree of hydrolysis.

The use of packing elements and packing of which the gap volume occupies only a very small part of the reactorvolume is of cnicial importance to the effect of the column packings according to the invention.

According to anotheraspectofthe invention, the packings installed in the columns may consist of irregular dumped tower packings, of sieve plates orof regular packings. The only importantfactor is the effect on the two reactants. The packings must bring about a permanent deflection, splitting up and recombination of water and fat and avoid back-mixing in order to obtain the greatest possible, driving concentration gradient between aqueous and organic phase.

According to another important aspect of the invention, the packing sections are followed in the column by heating sections and/or vice versa. The heating sections may be provided either with a heat-exchange system, for example with indirect heating by heat carrier oil, or with a heating system using directly injected steam. The injection of steam creates high turbulence and provides for a fine droplet spectrum and hence for an extremely large interface between the two phases. The use of heat exchangers using heat carrier oil enables the plant to be built even at locations where high-pressure steam is not available and where nevertheless the optimally high hydrolysis temperature has to be established and maintained.

Finally, according to another aspect of the invention, it is advantageous to associate with the column packings and/orwith one of the liquids orwith both liquids moved in counter-current means for pulsating the movement of the reactants in orderfurtherto accelerate the permanent changing of the interface between the liquids.

The invention is described in more detail in the following with reference to the accompanying drawings, wherein: Figure lisa flowsheet of a hydrolysis plantforfats.

Figure2 shows part of a column with a heating section.

Figure 3 shows part of a column with moving sieve plates.

Figure4shows a column sumpwith a pulsation pump coupled thereto.

In theflowsheetofthe hydrolysis plant shown in Figure 1, starting fat 1 from a tank (not shown) is pumped by a pressure pump 2through a heatexchanger3 in which it is preheated under 5.0to 5.5 MPa by glycerol water4and after heating bya peak heater5to a temperature offrom 230 to 240"C is fed intothesump 6 of a splitting column generally denoted by the reference 7. Likewise, hydrolysis water8, i.e. fully deionized water orcondensate, is pumped by another pressure pump 9tothe head 1 O 10 ofthesplitting column 7. The sensible heat of the fatty acid 12 produced is used to preheatthe water in a heat exchanger 11.Bubble plates 14 are provided in the upper part 13 of the splitting column 7 to enable heat to be directly exchanged between the watered in and the fatty acid produced. Atemperature of from 240 to 250"C is reached. Alternatively, the hydrolysis water 8 may also be indirectly heated in an additional heat exchanger (not shown).

The water heated in the upper part 13 ofthe column 7 is fed in the form of droplets from the bubble plates 14 orvia a sprinkler ring (not shown) into the column tube 15 filled with fat. The tube 15 contains packing sections 16 and heating sections 17 optionally comprising heat exchangers following one another in the longitudinal direction, as shown in Figures 1 and 2. The packing sections 16arefilled with regularpackings or with irregulardumped packings having a gap volume of at least 90%.

In the packing sections 16, the droplets of water sink downwards through the fat phase because of their greater density and, in the process, are deflected, split up and recombined at the packing elements. In this way, the interface is permanently renewed and the swarm of droplets transversely mixed. The droplets are collected in the sump 6 and are removed via a separation layer regulator 18. After passing through the heat exchanger3, the glycerol water4 is optionally delivered via a reducing valve 19to a vessel 20 and expanded to normal pressure. On leaving the vessel 20, the glycerol water passes through the pipe 21 into following tanks (not shown). The vapors from the vessel 20 are condensed in the condenser 22 and reused as hydrolysis water.

Thefat phase ascendsthrough the column 7 in counter-currentto the water droplets. Underthe influence of the packing sections 16, the fat particles are also radially mixed, longitudinal mixing being suppressed. At the head 10 of the column tube 15, the fatty acid 12formed by hydrolysis is removed through a pressure regulating valve 23, optionally after passing through the heat exchanger 11, and expanded in a vessel 24.

Aftercooling in a heat exchanger 25, the fatty acid formed passes through a pipe 27 to a tank. The vapors from the vessel 24 are condensed in the condenser 26 and flow into a separation pit.

The splitting column shown in Figure 1 operates under a pressure of 5.0 to 5.5 MPa and at a temperature of from 255 to 265"C. Since the inflowing streams of water and fat are heated to a maximum temperature of only 24000, the splitting column has to be additionally heated. To this end, high-pressure stream 28 is directly injected into the heating sections 17 in the embodiment illustrated. Depending on the iength ofthe column, a heating section 17 should be provided at least in the middle and, preferably, also adjoining the head 10 and thesump 6 ofthe column tube 15. High turbulence and a finedropletspectrum are produced bythe injection of high-pressure steam.Alternatively, however, the heating section 17 may even be indirectly heated with steam or heat carrier oil (cf. Figure 2) by installing heat exchangers 29 in the heating sections 17 or at their periphery. Indirect heating is particularly advantageous at locations where no high-pressure steam is available but where, nevertheless, the optimally high hydrolysis temperature has to be reached.

To intensify mass transfer, it is advantageous to enlarge the phase area and permanently to renew the phase interface. These objectives are preferably supported by mechanical pulsation ofthe reactants. To this end, sieve plates 31 to be shaken in the direction of the arrow 30 may be provided in the extraction column as shown in Figure 3. However, the mechanical energy may also be applied to the reactants by means offluids.

As shown in Figure 4, for example, a pulsation pump 32 with a piston 34 reciprocating in the direction of the arrow 33 may be coupled via a socket 35 to the column sump 6.

The results of hydrolysis tests carried out in columns with and without packing sections are presented in the following.

The principal influence factors forthe hydrolysis of fats are temperature, water-to-fat ratio and residence fomed from the total quantity of water, including the injected steam, and from the quantity of fat. The expression "residence time" is understood to mean the quotient of reaction volum between entry of the fat phase and entry of the water phase and the volume flow of both phases, including the direct steam. The degree of hydrolysis is the quotient of acid number and saponification number. All the tests were carried out with a tallow containing 10% free fatty acids. The initial degree of hydrolysis was of the order of 10%.

Table Test No. 1 2 3 4 5 6 7 Packings no no yes no yes no yes Temperature 'C 255 256 259 265 264 256 260 Water/fat% 51 43 46 57 58 54 60 Residencetimeh 2.4 0.9 1.0 1.3 1.3 1.1 1.0 Degree of hydrolysis % 99.0 94.5 98.8 96.2 99.4 96.2 98.3 Glycerolconcentrat.% 17 19 19 15 15 16 15 The test resu Its show the fol lowi ng: Without packings, i.e. without the packing sections 1 6 of the column 7, a residence time of 2.4 his required to obtain a degree of hydrolysis of 99%. Where packing sections are used, a residence time of 1.3 h is sufficient to obtain a degree of hydrolysis of 99.4% (cf.tests Nos. 1 or4 and 5).

For a residence time ofca. 1 h, a degree of hydrolysis higher by 2to 4% is obtained where the packings are used (cf. tests Nos. 2 to 7).

For a residence time ofca. 1 the reduction in the water-to-fat ratio is less noticeable in its effect in columns comprising packing sections than in columns with no packing sections (cf. tests Nos. 3 and 5 and also 2 and 4).

The point of entry into the splitting column is crucially important to the smooth operation of the column and for obtaining a high degree of hydrolysis and minimal oil losses in the hydrolysis water where neutral oils of diminishing quality are used for hydrolysis.

In known processes, the point of entry of the neutral oil is situated beneath the separation layer in the splitting column (7).

In this case, the neutral oil (temperature approx. 80"C) accommodated in a holding tank is brought by a pressure pump (2) to the operating pressure of the column and introduced into the column. By positioning the inletforthe neutral oil at a corresponding distance down from the separation layer, an internal heat exchange is established between the neutral oil ascending in the column and the descending hydrolysis water. In this way, the hydrolysis water is cooled from the operating temperature (approx. 260"C) to approx. 150"C while the neutral oil is correspondingly heated.

The disadvantage of known processes is that neutral oils of diminishing quality promote the formation of emulsions as they ascend through the separation layer, thus disrupting the stationary operation of the column. This results in a reduction in the degree of hydrolysis and in the entrainment of neutral oil into the hydrolysis water.

According to the invention, therefore, the point of entry forthe netural oil is arranged above the separation layer regulatorto preventthe neutral oil from ascending through the separation layer. In orderto obviate the disadvantage of no internal heatexchangewhich would result in doubling ofthe energy consumption, an external heat exchanger(3) was installed; by passing through this heat exchanger, the hydrolysis water issuing from the column is also cooled from approximately 260"Cto around 1 10-170"Cwhilethe neutral oil passing through this external heat exchanger is correspondingly heated from approximately 80"C.

Since both the hydrolysis water and the neutral oil lead to scaling of the heat-exchanger surfaces, the heat exchanger has to be designed in such a way that both surfaces can be cleaned.Where atube-type heat exchanger suited to these working conditions is used, closeable cleaning openings allowing the use of a high-pressure water jet cleaning system to be used should be provided for example around the outside of the tubes.

Claims (17)

1. A plantforthe continuous hydrolysis offats comprising a tube, designed forwaterdescending in countercurrentto ascending fat at around 5 MPa/260 C, a splitting column, which comprises at its sump a fat inletand a glycerol water outlet and at its head, a water inlet and afattyacid outlet, the inlets being preceded by heating means and a pressure pump and the outlets being followed by expansion and cooling means, characterized in that packing sections with packings consisting of packing elements with a free volume of at least 90% and heating sections for heating the reactants moving countercurrentlythrough the column are arranged sequentially in the longitudinal direction ofthetube.

2. A plant as claimed in Claim 1, characterized in that the heating sections comprise means for injecting steam for directly heating the reactants.

3. A plant as claimed in Claim 1, characterised in thatthe heating sections contain heat exchangers for indirectly heating the reactants.

4. A plant as claimed in one or more of Claims 1 to 3, characterized inthatthe packings ofthe packing sections consist of dumped tower packings.

5. A plant as claimed in one or more of Claims 1 to 3, characterized in thatthe packings of the packing sections are regular packings.

6. A plant as claimed in one or more of Claims 1 to 3, characterized in thatthe packings ofthe packing sections consist of sieve plates.

7. A plant as claimed in one or more of Claims 1 to 6, characterized in that means for pulsating the movement of the reactants are associated with at least one ofthe two liquids moved in countercurrent either directly orviathe packings.

8. A plant as claimed in one or more of Claims 1 to 7, characterized in that the inlets for neutral oil are situated above the separation layerof the splitting column.

9. A plant as claimed in one or more of Claims 1 to 8, characterized by a heat exchanger preferably of the tube type, ofwhich the two pressure chambers are accessible for mechanical cleaning by water under high pressure.

10. A plantsubstantially as herein described with reference to the drawings.

11. A process for the continuous hydrolysis of fats in a tube designed for water descending in countercurrentto ascending fat at around 5 MPa/260 C, of a splitting column, characterized in that the water droplets falling through thetube are permanently deflected, split up and recombined and inthatthefat ascending through the tube will longitudinally mixing suppressed, is permanently radially mixed with the water droplets.

12. A process as claimed in Claim 11, characterized in thatthe contents ofthecolumn are heated in sections.

13. A process as claimed in Claim 12, characterized in that the turbulence of the reactants is increased together with the temperature by the injection of steam under high pressure into the heating sections.

14. A process as claimed in one or more of Claims 11 to 13, characterized in that a pulsating movement is imparted to the reactants.

15. A process as claimed in one or more of Claims 11 to 14, characterized in the art a heat exchanger heats the neutral oil underthe operating pressure of the column by cooling the hydrolysiswater underthe operating pressure ofthe column.

16. A process as claimed in Claim 11 substantially as herein described with reference to the drawings.

17. The products of the hydrolysis of fats when recovered by a process as claimed in any of claims 11 to 16.