GB2236107A - Natural rubber serum concentrate - Google Patents

Abstract

Serum concentrates consisting essentially of 30 to 80 per cent of non-rubber solids are prepared by coagulation, separation and concentration of natural rubber latices. The non-rubber component includes proteins, saccharides and other important materials. The concentrate product is applied particularly to fertilizers, rubber additives and bacterial culture media.

Description

NATURAL RUBBER SERUM CONCENTRATE AND METHOD OFT MAKING THE SAME This invention relates to natural rubber serum concentrates and more particularly to a serum concentrate having specified contents of non-rubber components. The invention is also directed to a method for the production of such serum concentrate.

A wide variety of rubber plants are known among which a rubber tree called Hevea brasiliensis has been cultivated on a commercial basis. Contained in a latex or milky liquid tapped from the rubber tree are about 35% by weight of rubber hydrocarbons, about 5% by weight of non-rubber components and the balance of water. The non-rubber components include for example proteins, saccharides and the like. Such natural rubber latex is of a hydrophobic colloidal sol having a rubber hydrocarbon as a disperse phase and water as a continuous phase.

Natural rubbers such as ribbed smoked sheet (RSS), brown crepe and the like may be formed usually by diluting a natural rubber latex in water to remove foreign matter therefrom and subsequently by coagulating all rubber hydrocarbons with the addition of an acid such as formic, acetic, sulfuric or similar acid, followed by dewatering and drying of the coagulum and by subsequent smoking of the same against bacterial attack.

By the term serum is meant an aqueous solution byproduced upon separation of a rubber coagulum from a natural rubber latex. Serums have in most instances been disposed as wastes. This has posed an environmental pollution problem in those countries and territories producing natural rubber latices because the serum readily develops malodor upon decomposition of its non-rubber components including proteins, saccharides and the like. To cope with this problem, many attempts have been made with costly disposal equipment but with little success.

As disclosed in Japanese Patent Laid-Open Publication No. 61-293201, it has been proposed that a natural rubber serum be spray-dried into a particulate product formulated for use in certain sectors of industry. This product is of a non-rubber composition including proteins, saccharides and the like and having an average particle size of 10 to 100 Vm. It is applicable as a starting material to fertilizers, vulcanization accelerators, surface treatments, feeds, pharmaceuticals, cosmetics and the like. Such product is easy to handle as it is in powdery form.

The above particulate product is rather hygroscopic in nature and often liable to get agglomerated while in prolonged storage. This will in turn render the non-rubber components decomposable and hence malodorous.

With the foregoingodifficulties of the prior art in view, the present invention seeks to provide a serum concentrate which is free from denaturation and decomposition, storable over long periods of time at room temperature and even in an open state, easy to handle and economical of transport. The invention further seeks to provide a method of producing such serum concentrate.

The serum concentrate according to the invention finds application to fertilizers, animal feeds, rubber additives such as vulcanization agents, vulcanization accelerators, dispersants, surface treatments and the like, bacterial culture media and the like.

The above and other objects and advantages of the invention will become better understood from the following description taken in conjuction with the accompanying drawings.

More specifically, the invention provides a serum concentrate consisting essentially of (a) an aqueous solution resulting from coagulation of and separation of substantially all rubber hydrocarbons from a natural rubber latex and (b) a non-rubber component remaining in the aqueous solution and having a solids content of 30 to 80 percent by weight.

The invention also provides a method of producing a serum concentrate comprising (a) collecting an aqueous solution resulting from coagulation of and separation of substantially all rubber hydrocarbons from a natural rubber latex, (b) standing the aqueous solution for 12 to 72 hours to thereby remove floating solid matter and (c) subsequently concentrating a non-rubber component remaining in the aqueous solution to a solids content of 30 to 80 percent by weight by evaporation at a temperature of 60 to 950C and at a vacuum pressure of 600 to 670 mmHg.

Figure 1 is a graphic representation of a serum concentrate embodying the present invention but showing the correlation between the solids content and the specific gravity.

Figure 2 is a view similar to Figure 1 but illustrative of the correlation between the solids content and the viscosity.

Figure 3 is a diagramatic representation showing an apparatus for performing the method of the invention.

Suitable serums used for purposes of the present invention are, without limitation, those collected from aqueous solutions byproduced upon coagulation of and separation of all rubber hydrocarbons from natural rubber latices. The starting solution is hereunder referred to simply as a natural rubber serum (NRS) and the final product as a natural rubber serum concentrate (NRSC).

Importantly, NRSC should have a solids content in the range of 30 to 80% by weight. NRSC if lower in solids content than 30% mould be too abundant in water and hence spacious for storage and also uneconomical of transport in terms of net concentrate. Moreover, NRSC's non-rubber components would become decomposable even at room temperature.

Higher solids contents than 80% would render NRSC excessively viscous for stirring or dispersion, leading to handling inconveniences. Another difficulty would be that the final product deposits on the wall of the apparatus employed.

The composition of NRSC is dependent upon the kind of NRS and hence difficult to define with accuracy. The serum product of the invention, however, has now been found to be predominant of the following components expected in the art as commercially useful.

1. Proteins such as a-globlin, herein and the like.

2. Amino acids such as glutamic, aspartic and like acids.

3. Ashes such as sulfur, potassium, magnesium and the like.

4. Fatty acids such as lauric, palmitic and like acid.

5. Ammonium salts such as ammonium sulfate and the like.

In accordance with another aspect of the invention, there is provided a method of the production of NRSC. An aqueous solution is collected as NRS which is derived by coagulating and separating all hydrocarbons from a natural rubber latex. The aqueous solution should thereafter be allowed to stand at room temperature for 12 to 72 hours and preferably 16 to 24 hours so that any remaining rubber hydrocarbons and other solid materials are made floatable for removal. Shorter periods than 12 hours would be responsible for insufficient separation of the remaining rubber hydrocarbons and hence objectionable deposit of the same on the apparatus. Longer periods than 72 hours should be avoided to preclude NRSC of quality deterioration as the non-rubber components would be likely to commence decomposition. When it is found desirable, heating or cooling may be effected in the course of standing of NRS.

The starting serum thus treated may be preheated at from 50 to 700C and preferably from 60 to 650C, thereby improving the efficiency of subsequent concentration. Lower temperatures than 500C would not be effective for preheating with the decline in temperature within the apparatus and hence in speed of concentration. Higher temperatures than 70"C would require bulked heat source, entailing reduced economy.

In preheating NRS, it is preferable to utilize excessive heat available from subsequent concentration.

Preheating may be done while NRS is being disposed standstill.

The starting serum after being preheated may be concentrated to a solids content of 30 to 80% by weight.

Concentration may be effected at a temperature of 60 to 950C and at a gauge vacuum pressure of 600 to 670 mmHg equivalent to an absolute pressure of 160 to 90 mmHg.

Lower temperatures than 600C would be only timeconsuming and less effective, and higher temperatures than 950C would make the non-rubber components decomposable, resulting in NRSC of poor quality. To this end temperature conditions are preferred to be in the range of 65 to 94.50C.

The vacuum pressures if lower than 600 mmHg would need high temperatures in concentrating NRS. Higher vacuum pressures than 670 mmHg would cause foaming of NRS, failing to adjust temperature and pressure.

Particularly preferred is a vacuum pressure in the range of 640 to 650 mmHg.

The method of the invention may preferably be effected by a two- or three-stage mode of operation from the economical point of view.

In adjudging that the targeted serum concentrate has reached the above specified range of solids contents, it is convenient to measure the specific gravity or viscosity of NRSC.

In Figure 1 there is shown a product of NRSC provided in accordance with the invention, the specific gravity being plotted against the solids content.

Figure 2 is similar to Figurel but illustrative of the plot of the viscosity against the solid content at varying temperatures. The specific gravity of Figure 1 is as determined at 280C by a gravimeter, whereas the viscosity of Figure 2 results from measurement at 30, 50 and 700C on a Brookfield type viscometer at 60 rpm. As appears clear from Figures 1 and 2, both curves of NRSC have a conspicuous point of turn at a solid content between 60 and 70%, which unique properties will aid in quality control and in process control.

Turning next to Figure 3, there is shown diagrammatically at 10 one preferred form of apparatus used to accomplish the method according to the invention. For purposes of convenience, the flow of NRS and NRSC is indicated by the solid line, the flow of vapor and drain by the dot line and the electrical control system of valves and pumps by the dash and dot line.

The apparatus 10 is constructed essentially with a reservior 12, three sets of evaporators 14, 16, 18, a steam generator 22 located to generate vapor as a heat source for NRS concentration, three sets of air-liquid separators 20, 30, 36 adapted to separate heating vapor and concentrated vapor from NRS mist and concentrated liquid, and vacuum means equipped with a vacuum pump VP and arranged to bring those evaporators and separators into reduced pressure at from 600 to 670 mmHg.

In the reservior 12 is stored NRS from which any floating solid matter has been removed by standing for a predetermined length of time. Mounted on the reservior 12 is a jacket 12a for entry of waste vapor conveyed after successive heating of the evaporators 14, 16, 18 so that NRS is preheated at about 450C in the reservior 12. NRS may if necessary be let to stand and then solid matter be removed in the reservior 12.

NRS thus preheated, after being taken into a supply tank 24, is fed by a pump 13 into the third evaporator 18 and thereafter into the second evaporator 16 and finally into the first evaporator 14. In this course of flow and prior to entry into the evaporator 14, NRS is preheated at about 650C.

Disposed in the evaporator 14 are a multiplicity of vertical pipes of small diameter for passage of vapor fed via a steam booster 26 from the steam generator 22.

The evaporator is thus maintained at 94.50C. NRS is allowed to flow through the evaporator 14 from top to bottom and over those pipes during which the starting serum is concentrated in vacuo and collected at the bottom at about 900C. The first concentrated NRS portion hereunder called NRS-I is then conveyed by a pump 28 to the second evaporator 16.

The first evaporator 14 is provided at its bottom with a level meter 14L held in association with a valve 28a. Upon sensoring by the level meter 14L of a given amount of NRS-I has been gathered in the evaporator 14, the valve 28a is opened to transport NRS-I by the pump 28 to the evaporator 16. The pump 28 is continuously operative, even while in closing of the valve 28a, for circulation from bottom to top of the evaporator 14.

Heating vapor, fed via the steam booster 26 into the evaporator 14, is put into the air-liquid separator 30 together with NRS vapor after which only pure vapor is conveyed as a heat source to the evaporator 16.

Concentrated liquid and NRS mist separated from the separator 30, coupled with NRS-I, are transferred by the pump 28 to the evaporator 16. Because of its structural similarity to the first evaporator, the second evaporator is maintained at 88.50C with the entry of the above pure vapor fed from the separator 30. NRS-I is subjected to concentration in the evaporator 16 and gathered at the bottom at about 82.50C as is in the evaporator 14.

The evaporator 16 is provided with a level meter 16L associated with a valve 32a, which level meter is devised to act like the level meter 14L. Sensoring by the level meter 16L enables the valve 32a to open to transport the second concentrated NRS portion by a pump 32 to a circulation path between the evaporator 18 and the separator 20. The second NRS portion is hereunder called NRS-II. The pump 32 is of a type similar to the pump 28 and while in closing of the valve 32a is applicable to a bottom to top circulation in the evaporator 16.

Vapor fed in the evaporator 16 is transported together with NRS-II mist to the air-liquid separator 36. From this separator only pure vapor is supplied as a heat source to the third evaporator 18. In the apparatus illustrated an excessive portion of pure vapor is designed to recirculate into the steam booster 26.

Concentrated liquid and NRS mist separated by the separator 36 are conveyed together with NRS-II to the circulation path 34. NRS-II is forced to circulate by a pum? 37a between the evaporator 18 and the separator 20 and heated at 800C in the evaporator 18 on contact with vapor fed from the separator 20, followed by vacuum concentration to a predetermined solids content.

A level meter 20L is mounted on the separator 20 for association with a pump 37b and a valve 37c. On sensoring by the level meter 20L, the valve 37c is opened to cause the pump 37b to drive thereby transporting an NRSC product into a tank 40.

The whole apparatus 10 may be so structured in conventional manner as to control and adjust NRSC in its concentration to a predetermined solids content when a given amount of the product has been collected in the separator 20.

Designated at 38 is a densitometer held in associated-relation to the valve 26a located adjacent to the steam booster 26. This densitometer has a role to control the feed of vapor depending upon the concentration of NRS-II. The concentration of NRSC may be determined at the densitometer 38 as by differential pressure, specific gravity and viscosity.

Vapor used to heat the evaporator 18 is transported as waste vapor by a pump 41 to a drain tank 42. Part of the waste vapor is returned to the jacket 12a of the reservior 12 for preheating NRS at above 450C. This contributes to great economy of heat energy.

The apparatus 10 may be modified to place the separator 20 in vacuo by the action of the pump VP to thereby hold all the evaporators and the other separators at reduced pressure. Alternatively, each such constituent part may be connected to an individual vacuum path. A cold trap may be mounted on the pump VP.

When the method of the invention is conducted with NRS of about 4% in solids content fed from the reservior 12 to the supply tank 24 and with the lengths of the evaporators 14, 16 set to 14 m and at a flow speed of about 10.5 t/hr, it has now been found that NRSC of 70% in solids content can be obtained at a production rate of about 600 kg/hr.

Although the use of three evaporators has been described, a single-, four- or multi-stage mode of concentration may suitably be employed in the practice of the invention. Particularly preferred is a two- or three-stage operation with energy efficiency, production rate and product quality and overall economy in view.

The following examples are given to further illustrate the invention.

Group I: Evaluation of NRSC A serum, NRS, was collected from a natural rubber latex by coagulation of and separation of all rubber hydrocarbons with the addition of sulfuric acid. NRS was let to stand at room temperature for 24 hours to thereby remove floating solid matter. NRS was thereafter preheated at 650C and concentrated at 950C and at 645 mmHg to thereby provide a serum concentrate according to the invention, NRSC of 71.8 wt% in solids content.

The properties of NRS and of NRSC are shown in Table 1. The data are as measured at 280C.

NRSC, though relatively great in COD and BOD, is smaller in BOD/COD than NRS. This is interpreted to mean that lesser decomposition is involved in NRSC than in NRS.

The compositions of NRSC and of a similar product in particulate form, NRSP, are enumerated in Table 2, and the materials typically contained in both products are given in Table 3. Identified among the amino acids of Table 3 are glutamic acid, aspartic acid, alanine, glycine, leucine, lysine, cysteine, serine, valine, thyroxine, proline, tryptophan, threonine, histidine, arginine, phenylalamine and isoleucine.

Examination of Tables 2 and 3 shows that NRSC representing the invention contains a variety of components of industrial value.

Group II: Examples 1 to 5 Comparative Examples 1 to 4 The procedure of Group I was followed in preparing different NRSC and NRSP products. Storage, handling and economy were examined with the results shown in Table 4.

Less contents than 30% were almost ineffective in quality improvement by concentration and rather comparable to NRS. Higher contents than 75% invited viscosity buildup and hence handling inconvenience.

NRSC products of the invention become less viscous on heating and hence sufficient to handle. With respect to the efficiency of stirring, the maximum possible viscosity and solids content are usually up to 1,000 cp and up to 80%, respectively, as is apparent from Figure 2.

NRSP of a particulate type may be increased in its solids content to about 95% as taught by the foregoing prior publication. The particulate product has been proved hygroscopic in nature and sensitive to agglomeration and hence prone to get difficult to handle with time. Hydroscopicity is likely to lead to decomposition and hence malodor.

Group III: Example 6 Comparative Examples 5 and 6 The procedure of Group I was followed except that NRS was allowed to stand at room temperature for from 12 to 72 hours. There was obtained an inventive NSRC product of 71.8 wt% in solids content. Controls were also prepared. Decomposition, solid matter removal and standing were evaluated with the results shown in Table 5.

Shorter standing than 12 hours revealed insufficient removal of solid matter. Prolonged standing caused decomposition.

Group IV: Example 7 Comparative Examples 7 and 8 The procedure of Group III was followed except that NRS was let to stand for 24 hours and that NRS was preheated at varied temperatures. The resulting samples were tested for foaming, decomposition and economy with the results shown in Table 6.

Insufficient preheating below 500C was susceptible to foaming at the feed of NRS into air-liquid separators. Excessive preheating above 700C resulted in decomposed NRS.

Group V: Example 8 Comparative Examples 8 and 9 The procedure of Group III was followed except that NRS disposition was effected for 24 hours and that varying concentration temperatures were used.

Decomposition, standing, economy and handling were adjudged with the results given in Table 7.

Lower temperatures than 600C revealed too slow a speed of concentration and lesser production. Higher temperatures than 950C made NRS decomposable and adherent to the inner walls of the apparatus.

Group VI: Example 9 Comparative Examples 10 and 11 The procedure of Group III was followed except that NRS was let to stand for 24 hours and that the vacuum degree was varied. The samples were tested for foaming and economy with the results shown in Table 8.

Below 600 mmHg was unacceptable in production rate. Above 670 mmHg rendered NRS foamable and hence difficult to concentrate with control.

Group VII: Example 10 Comparative Examples 12 and 13 The procedure of Group III was followed except that NRS was allowed to stand for 24 hours and that the stage number of evaporators was changed. Economy and decomposition were determined with the results shown in Table 9.

A single stage mode of operation took too much time in concentrating NRS to a given solids content, causing decomposition. the use of four or more evaporators will not be economical in respect of energy efficiency, concentration speed and other parameters.

Table 1

NRS NRSC pH 3.29 4.39 specific gravity 1.06 1.43 solids content (%) 4.5 71.8 COD (ppm) 26350 666500 BOD (ppm) 19300 398000 BOD/COD (%) 73.24 59.71 COD : chemical oxygen demand BOD : biochemical oxygen demand BOD/COD : bacterial decomposition rate Table 2

NRSC NRSC* NRSP solids content (%) 7.30 - 94.5 water (%) 26.7 - 5.5 nitrogen compound (%) 39.6 54.0 47.2 quebrachitol (%) 15.8 21.7 22.7 saccharide** (%) 7.0 9.6 7.4 fatty acid (%) 1.4 1.9 0.5 ash (%) 9.4 12.8 16.7 * : on dry basis ** : other than quebrachitol Table 3

ash fatty acid sulfur 8.1 lauric acid 1.52 potassium 6.5 palmitic acid 0.02 phosphorus 0.7 stearic acid 51 ppm chlorine 0.5 oleic acid 113 ppm zinc 0.4 linolenicacid 78 ppm magneisum 0.1 sodium 0.02 nitrogen compound calcium 0.02 ammonium salt 23.4 iron 0.01 protein and 23.6 aluminum 0.01 amino acid rubidium 0.01 unit: wt% other than ppm Table 4

- - - - B -- P 3 a Comparative Exam les t S x les s s a aE Z Q\ tl me t) 3 1 2 3 4 5 NRS NRSC NRSP solids X sC g Q 13.2 fi L, Srpl a, nr c, L( not decompose at X O q)- q) C - room k aru c IW kC mP L) E ct V: rcl - c, C m ..

decomposed after not decomposed at temperature storage of 3 days at room room temperature - < to agglarrated 0 0 0 reci itate x > OI x x 0 x highly easy E O P m J CIQri a handle due to Q) &commat; a) v C :> m Z L of low to h D3 a) with heat mm m m m a oL) ,p u c -- U of transport economical of Fuzztransport and transport and acce tabl s licable U h ~ x x x A x x A 0 Live evaluation ur m P ci O p a . Qz O O n v7 v > < v O : > , &commat; c X < > N W v v h , U o > 8 H v ~~ ~ v oz v O u7 a) ~ . ~ U a) cs s X: O W U N n &commat;U v x &commat;X &commat; o x x v v E ~ o U > o- < > O 8 x ~ e S O . Hs za > ~ Hv ~ UX - o X X OC 3 m O ~ tr s n v X .H X O O O X X u vU na v' 44 C v < W O H C: O O v S o U - O v Q .< dP O C O X V v O .~, A U < c 3 U < - < : e v cJ xn U C H H H O uz C uz U A zo O v U h ss > tn z S Z $ U Q} Table 5

ive Exam les Comparative Samples Example 6 5 6 more than less than standing of NRS (hr) 12 - 72 72 than 12 decomposition of NRS x separation of rubber hydrocarbon from NRS uz uz X deposit on apparatus X evaluation x x note: see footnote to Table 4 Table 6

Com arative Examples Example 7 7 8 lower than higher tha preheating of NRS (OC) 50 - 70 50 70 foaming of NRS x O decomposition of NRS uz uz X efficiency A A evaluation x x note: see footnote to Table 4 Table 7

Comparative Examples Example 8 9 10 higher than lower tha concentration of NRS (OC) 95 - 60 95 60 decomposition of NRS x deposit on apparatus uz X efficiency X handling O evaluation x A note: see footnote to Table 4 Table 8

Ccmparative Examples Example 9 11 12 concentration of NRS 600 - 670 foaming of NRS X efficiency X O evaluation X x note: see footnote to Table 4 Table 9

Comparative Examples Example 10 13 1 ~ 14 apparatus (stage) 2 - 3 more than 3 1 efficiency x decomposition of NRS X evaluation (9 A X note: see footnote to Table 4

Claims (8)

CLAIMS:

1. A serum concentrate consisting essentially of: (a) an aqueous solution resulting from coagulation of and separation of substantially all rubber hydrocarbons from a natural rubber latex; and (b) a non-rubber component remaining in said aqueous solution and having a solids content of 30 to 80 percent by weight.

2. The concentrate according to claim 1 wherein said non-rubber component includes proteins, amino acids, ashes, fatty acids and ammonium salts.

3. A method of producing a serum concentrate which comprises: (a) collecting an aqueous. solution resulting from coagulation of and separation of substantially all rubber hydrocarbons from a natural rubber latex; (b) standing said aqueous solution for 12 to 72 hours to thereby remove floating solid matter; and (c) subsequently concentrating a non-rubber component remaining in said aqueous solution to a solids content of 30 to 80 percent of by evaporation at a temperature of 60 to 95"C and a vacuum degree of 600 to 670 mmHg.

4. The method according to claim 3 wherein said aqueous solution is cooled or heated while in disposition.

5. The method according to claim 3 wherein said aqueous solution is preheated, prior to concentration, at a temperature of 50 to 700C.

6. A serum concentrate substantially as hereinbefore described.

7. A method of producing a serum concentrate substantially as hereinbefore described.

8. Any novel integer or step, or combination of integers or steps, hereinbefore described and/or as shown in the accompanying drawings, irrespective of whether the present claim is within the scope of, or relates to the same or a different invention from that of, the preceding claims.