WO2014069979A1 - An improved method of recovering rubber from skim natural rubber latex - Google Patents

An improved method of recovering rubber from skim natural rubber latex Download PDF

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Publication number
WO2014069979A1
WO2014069979A1 PCT/MY2013/000070 MY2013000070W WO2014069979A1 WO 2014069979 A1 WO2014069979 A1 WO 2014069979A1 MY 2013000070 W MY2013000070 W MY 2013000070W WO 2014069979 A1 WO2014069979 A1 WO 2014069979A1
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WO
WIPO (PCT)
Prior art keywords
latex
potassium hydroxide
membrane module
skim
retentate
Prior art date
Application number
PCT/MY2013/000070
Other languages
French (fr)
Other versions
WO2014069979A8 (en
Inventor
Kumar Veelu JAYA
Abdullah Zainan
Jaril Asis Ahmad
Putri Ahmad Sabri Maizatul
Muis Mohamed Yusof Khairul
Meriam Binti Nik Sulaiman Nik
Original Assignee
Sime Darby Malaysia Berhad
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Sime Darby Malaysia Berhad filed Critical Sime Darby Malaysia Berhad
Priority to CN201380056669.6A priority Critical patent/CN104903355B/en
Publication of WO2014069979A1 publication Critical patent/WO2014069979A1/en
Priority to PH12015500908A priority patent/PH12015500908A1/en
Publication of WO2014069979A8 publication Critical patent/WO2014069979A8/en
Priority to HK15111223.9A priority patent/HK1210485A1/en

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08C—TREATMENT OR CHEMICAL MODIFICATION OF RUBBERS
    • C08C1/00—Treatment of rubber latex
    • C08C1/02—Chemical or physical treatment of rubber latex before or during concentration
    • C08C1/075—Concentrating
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08C—TREATMENT OR CHEMICAL MODIFICATION OF RUBBERS
    • C08C1/00—Treatment of rubber latex
    • C08C1/02—Chemical or physical treatment of rubber latex before or during concentration
    • C08C1/075—Concentrating
    • C08C1/08—Concentrating with the aid of creaming agents
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08C—TREATMENT OR CHEMICAL MODIFICATION OF RUBBERS
    • C08C1/00—Treatment of rubber latex
    • C08C1/02—Chemical or physical treatment of rubber latex before or during concentration
    • C08C1/075—Concentrating
    • C08C1/10—Concentrating by centrifugation
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L17/00—Compositions of reclaimed rubber

Definitions

  • the present invention relates to an improved method of recovering rubber from skim natural rubber latex. More particularly, the present invention relates to an improved method of recovering rubber from skim natural rubber latex and converting the rubber into latex concentrate using a combination of membrane filtration and centrifugal separation techniques.
  • Skim natural rubber latex or skim latex is produced as a by-product in the process of concentrating natural rubber latex involving separation of the rubber latex into a concentrate and skim latex by centrifugation. Skim latex generally contains only about 5% of dry rubber and it is usually recovered as skim crepe rubber.
  • skim rubber can be recovered from skim latex by coagulation using sulphuric acid. The recovered rubber is then dried in the open before the rubber is sold as skim rubber.
  • the skim rubber obtained from this coagulation method is of an inferior quality as it contains a high proportion of entrained non-rubber constituents and acid content.
  • the skim rubber also possesses undesirable physical properties, including the generation of obnoxious odor, leading to low economic value in skim rubber.
  • the method also produces highly acidic effluent which may cause pollution to the environment if the effluent is not treated in a proper manner before being discharged to the environment.
  • Coagulation of skim latex can also be performed by using proteolytic enzymes where enzymatic deproteinization of skim latex is achieved. This process however is not economical as it requires the use of large quantity of enzymes and involves deammoniation and acid coagulation steps in the process. Consequently, there is a need in the art to provide a method for recovering rubber from skim natural rubber latex that addresses at least one of the problems described above, or at least to provide an alternative.
  • the method is performed in the following manner.
  • the method begins by pre-treating the skim latex.
  • the pre- treated skim latex then passes through a membrane module repeatedly with addition of potassium hydroxide or a solution containing ammonium laurate and potassium hydroxide at intervals to obtain a retentate and a permeate.
  • the retentate is blended with a fresh field latex and centrifuged to obtain a latex concentrate.
  • the latex concentrate is further blended with a fresh latex concentrate and treated with ammonia to obtain the final latex concentrate.
  • the method further comprises treating the retentate with a tetramethylthiuramdisulphide (TMTD) and zinc oxide (ZnO) dispersion prior to the step of blending the retentate with a fresh field latex.
  • TMTD tetramethylthiuramdisulphide
  • ZnO zinc oxide
  • the method further comprises subjecting the retentate to a second stage concentration prior to blending the retentate with the fresh field latex.
  • the second stage concentration is carried out by passing the retentate through a second membrane module repeatedly with addition of further potassium hydroxide or solution containing ammonium laurate and potassium hydroxide to obtain a second retentate and a second permeate.
  • the second retentate is optionally chemically treated and controllably blended with fresh field latex.
  • the blended second retentate is centrifuged to obtain a latex concentrate.
  • the latex concentrate then undergoes further control blending with fresh latex concentrate to obtain the final latex concentrate.
  • the method further comprises pre-treating the retentate with potassium hydroxide or a solution containing ammonium laurate and potassium hydroxide prior to passing the retentate through the second membrane module.
  • the potassium hydroxide or the solution containing ammonium laurate and potassium hydroxide is added to the pretreated skim latex at intervals of 10 to 30 minutes until about 80% to 90 % by weight of the permeate is obtained.
  • the potassium hydroxide or the solution containing ammonium laurate and potassium hydroxide is added to the pretreated skim latex at intervals of 10 to 30 minutes until about 60% to 70% by weight of the permeate is obtained. Further potassium hydroxide or the solution containing ammonium laurate and potassium hydroxide is added to the retentate at intervals of 10 to 30 minutes until about 40% to 50% by weight of the second permeate is obtained.
  • the solution containing ammonium laurate and potassium hydroxide comprises ammonium laurate and potassium hydroxide in a ratio of 1 :1.
  • the method further comprises cleaning the membrane module by soaking the membrane module in about 2% to 5% of hydrogen peroxide; backwashing or normal flushing the membrane module with 1 % to 2% of sodium hydroxide; and backwashing or normal flushing the membrane module with 1 % to 2% of nitric acid.
  • Figure 1 is a flow chart illustrating the single stage concentration method in accordance with the present invention.
  • FIG. 2 is a flow chart illustrating the two stage concentration method in accordance with the present invention. Description of the Invention
  • the skim latex generally contains about 5% of dry rubber.
  • the method in accordance with an embodiment of the invention comprises the step of pre-treating the skim latex.
  • the skim latex is pre-treated with ammonia and potassium hydroxide. In another embodiment, the skim latex is pre-treated with ammonia and a solution comprising ammonium laurate and potassium hydroxide. In a preferred embodiment, the skim latex is pre-treated with about 0.35% to 0.65% of ammonia and about 0.025% to 0.10% of potassium hydroxide. In another preferred embodiment, the skim latex is pre-treated with about 0.35% to 0.65% of ammonia and about 0.025% to 0.10% of the solution containing ammonium laurate and potassium hydroxide. Preferably, the solution contains ammonium laurate and potassium hydroxide in a ratio of 1 :1 .
  • the skim latex is pre-treated by simply adding ammonia and potassium hydroxide or ammonia and the solution containing ammonium laurate and potassium hydroxide to the skim latex.
  • the mixture is then homogenized by, for example, stirring.
  • the pretreated skim latex then undergoes a first stage concentration process.
  • the skim latex is concentrated to ca. 11% to 13% of dry rubber content.
  • the first stage concentration process is carried out by passing the skim latex through a multi-tubular membrane module repeatedly.
  • the skim latex passes through the multi-tubular membrane module by means of a pump.
  • pumps that can be used in the present invention include, but are not limited to, a diaphragm type of pump or a centrifugal type of pump.
  • a centrifugal type of pump is preferable.
  • the multitubular membrane module can be made of any suitable material. In a preferred embodiment, it is made of ceramic, and preferably with a pore size of about 0.05 ⁇ .
  • Potassium hydroxide or solution containing ammonium laurate and potassium hydroxide is added to the skim latex at intervals as the skim latex passes through the multi-tubular membrane module repeatedly.
  • the potassium hydroxide or the solution containing ammonium laurate and potassium hydroxide is added to the skim latex at intervals of 10 to 30 minutes.
  • about 0.025% to 0.10%) of potassium hydroxide or about 0.025% to 0.10% of the solution containing ammonium laurate and potassium hydroxide is added to the skim latex at each interval.
  • the inlet pressure of the multi-tubular membrane module is set at about 2.5 to 4.5 bar (2.5 x 10 5 to 4.5 x 10 5 Pa).
  • the trans-membrane pressure is set at about 1.5 to 3.0 bar (1.5 x 10 5 to 3.0 x 10 5 Pa).
  • the solution used in this step can either be potassium hydroxide or a solution containing ammonium laurate and potassium hydroxide, without limiting it to be of the same solution as that used in the step of pre-treating the skim latex,
  • the first stage concentration process continues until about 60% to 70% by weight of a clear serum is obtained.
  • the clear serum is removed as permeate, leaving behind a retentate which is the concentrated skim latex.
  • the retentate or the concentrated skim latex may be treated with further potassium hydroxide or solution containing ammonium laurate and potassium hydroxide before the concentrated skim latex undergoes a second stage concentration process.
  • the solution used in this step can either be potassium hydroxide or a solution containing ammonium laurate and potassium hydroxide, without limiting it to be of the same solution as that used in the step of pre-treating the skim latex.
  • about 0.025% to 0.10% of potassium hydroxide or about 0.025% to 0.10% of the solution containing ammonium laurate and potassium hydroxide is added to the concentrated skim latex to treat the skim latex.
  • the concentrated skim latex is further concentrated to ca. more than 20% of dry rubber content.
  • the second stage concentration process is carried out by passing the concentrated skim latex through a second multi-tubular membrane module repeatedly.
  • the second multitubular membrane module can be of the same type of membrane used in the first stage concentration process or it can be of any type suitable for use in the process.
  • the concentrated skim latex passes through the second multi-tubular membrane module by means of a pump. Examples of pumps that can be used in the method include, but are not limited to, a diaphragm type of pump or a centrifugal type of pump. For a large scale membrane unit, a centrifugal type of pump is preferable.
  • the multi-tubular membrane module can be made of any suitable material. In a preferred embodiment of the invention, the multi-tubular membrane module is made of ceramic and has a pore size of about 0.05 ⁇ . It has a channel internal diameter of about 3.0 to 4.0 mm and an overall length of about 1.0 to 1.2m.
  • the concentrated skim latex passes through the second multi-tubular membrane module at an inlet pressure of about 2.5 to 4.5 bar (2.5 x 10 5 to 4.5 x 10 5 Pa).
  • potassium hydroxide or solution containing ammonium laurate and potassium hydroxide is added to the concentrated skim latex at intervals to further concentrate the skim latex as the skim latex passes through the second multi-tubular membrane module repeatedly.
  • the potassium hydroxide or the solution containing ammonium laurate and potassium hydroxide is added to the concentrated skim latex at intervals of 10 to 30 minutes.
  • potassium hydroxide Preferably, about 0.025% to 0.10% of potassium hydroxide or about 0.025% to 0.10% of the solution containing ammonium laurate and potassium hydroxide is added to the skim latex at each interval.
  • Either potassium hydroxide or a solution containing ammonium laurate and potassium hydroxide can be used in this step without limiting it to be of the same solution as that used in the step of pre-treating the skim latex.
  • the second stage concentration process continues until about 40% to 50% by weight of a second clear serum is obtained.
  • the second clear serum is removed as a second permeate, leaving behind a second retentate which is the further concentrated skim latex.
  • the further concentrated skim latex may optionally be treated with tetramethylthiuramdisulphide (TMTD) and zinc oxide (ZnO) dispersion in a 1 :1 ratio with 30% concentration before the further concentrated skim latex is blended with a fresh field latex.
  • TMTD tetramethylthiuramdisulphide
  • ZnO zinc oxide
  • the further concentrated skim latex is treated with about 0.05% to 0.10 % by weight of the TMTD/ZnO dispersion.
  • This step is carried out depending on the quality of the further concentrated skim latex obtained after the concentration process, for example, the amount of volatile fatty acids present in the further concentrated skim latex.
  • this step is carried out when the volatile fatty acids number in the further concentrated skim latex exceeds 0.10.
  • the treated concentrated skim latex is blended with the fresh field latex in a ratio of 1 :9 parts.
  • the blended concentrated skim latex containing the fresh field latex is then centrifuged to obtain a latex concentrate.
  • the latex concentrate is blended with a fresh latex concentrate in a ratio of 1 :9 parts.
  • Ammonia is then added to the blended latex concentrate to more than 0.60% m/m to obtain the final latex concentrate.
  • the final latex concentrate thus obtained contains more than 60% of dry rubber.
  • the first stage concentration process and the second stage concentration process may be carried out in a single step.
  • the skim latex is similarly pre-treated with ammonia and potassium hydroxide or with ammonia and a solution containing ammonium laurate and potassium hydroxide.
  • the skim latex is pre-treated with about 0.35% to 0.65% of ammonia and about 0.025% to 0.10% of potassium hydroxide.
  • the skim latex is pre-treated with about 0.35% to 0.65% of ammonia and about 0.025% to 0.10% of the solution containing ammonium laurate and potassium hydroxide.
  • the solution containing ammonium laurate and potassium hydroxide is in a ratio of 1 :1.
  • the skim latex is pre-treated by simply adding ammonia and potassium hydroxide or ammonia and the solution containing ammonium laurate and potassium hydroxide to the skim latex. The mixture is then homogenized by, for example, stirring. The pretreated skim latex then undergoes a single stage concentration process.
  • the single stage concentration process is carried out by passing the skim latex through a multitubular membrane module repeatedly.
  • the skim latex passes through the multitubular membrane module by means of a pump.
  • pumps that can be used in the method include, but are not limited to, a diaphragm type of pump or a centrifugal type of pump.
  • a centrifugal type of pump is preferable.
  • the multi-tubular membrane module can be made of any suitable material.
  • the multi-tubular membrane module is made of ceramic and has a pore size of about 0.05 ⁇ . It has a channel intemal diameter of about 3.0 to 4.0 mm and an overall length of about 1.0 to 1.2m.
  • Potassium hydroxide or the solution containing ammonium laurate and potassium hydroxide is added to the skim latex as the skim latex passes through the multitubular membrane module repeatedly.
  • the potassium hydroxide or the solution containing ammonium laurate and potassium hydroxide is added to the skim latex at intervals.
  • the potassium hydroxide or the solution containing ammonium laurate and potassium hydroxide is added to the skim latex at intervals of 10 to 30 minutes.
  • about 0.025% to 0.10% of potassium hydroxide or about 0.025% to 0.10% of the solution containing ammonium laurate and potassium hydroxide is added to the skim latex at each interval.
  • the inlet pressure of the membrane is preferably set at about 2.5 bar to 4.5 bar (2.5 x 10 5 to 4.5 x 10 5 Pa). In a preferred embodiment, for optimum permeate flux, the trans-membrane pressure is set at about 1.5 to 3.0 bar (1.5 x 10 5 to 3.0 x 10 5 Pa).
  • the single stage concentration process continues until about 80% to 90% by weight of a clear serum is obtained.
  • the clear serum is removed as permeate, leaving behind a retentate which is the concentrated skim latex.
  • the concentrated skim latex may optionally be treated with TMTD/ZnO dispersion in a 1 :1 ratio with 30% concentration.
  • the concentrated skim latex is treated with about 0.05% to 0.10% by weight of the TMTD/ZnO dispersion.
  • This step is carried out depending on the quality of the concentrated skim latex obtained after the concentration process, for example, the amount of volatile fatty acids present in the concentrated skim latex.
  • this step is carried out when the volatile fatty acids number in the concentrated skim latex exceeds 0.10.
  • the treated concentrated skim latex is then blended with fresh field latex, preferably in a ratio of 1 :9 parts.
  • the blended concentrated skim latex containing the fresh field latex is centrifuged to obtain a latex concentrate.
  • the latex concentrate is then blended with a fresh latex concentrate in a ratio of 1 :9 parts.
  • Ammonia is then added to more than 0.60% m/m to obtain the final latex concentrate.
  • the final latex concentrate thus obtained contains more than 60% of dry rubber.
  • the solution of ammonium laurate and potassium hydroxide refers hereinabove may contain ammonium laurate and potassium hydroxide in any suitable amount. In a preferred embodiment, the solution contain ammonium laurate and potassium hydroxide in a ratio of 1 :1.
  • the clear serums produced from the skim latex concentration processes can be used to recover valuable bio-chemicals contain therein using suitable methods known in the art.
  • the membrane may become fouled after use.
  • the fouled membrane may be cleaned by soaking it in about 2% to 5% of hydrogen peroxide and backwashed or normal flushed with about 1 % to 2% of sodium hydroxide.
  • the fouled membrane may also be backwashed or normal flushed with nitric acid to remove inorganic foulants and to re-generate the membrane for further use.
  • the fouled membrane is backwashed or normal flushed with about 1 % to 2% of nitric acid
  • the skim latex is concentrated by the membrane system before the skim latex is blended with fresh field latex and re-centrifuged back as a latex concentrate.
  • the use of membrane as means to concentrate the skim latex eliminates the need for acid coagulation for recovery of rubber from skim latex. It also helps to improve the quality of the effluent produced by the method.
  • the fouled membrane may be cleaned using a combination of chemicals to regenerate it for subsequent concentration. The recovery of rubber and converting it into a latex concentrate is a value added process to the rubber industry.
  • potassium hydroxide acts as a latex stabilizer and latex preservative. It also gives a better shear resistance to agitation by any suitable mechanical means.
  • Example 1 Two-stage concentration process
  • Skim latex with 5% dry rubber content is sieved through a 60 mesh wire gauze and pre-treated with 0.65% of ammonia and 0.1 % of potassium hydroxide.
  • the treated skim latex then passes through a multi-tubular membrane module repeatedly.
  • the multi-tubular membrane module used in this example has a pore size of about 0.05 ⁇ , with a channel internal diameter of about 3.0 to 4.0 mm, with an overall length of 1.0 to 1.2m.
  • the inlet pressure of the membrane module is set at about 3 bar (3 x 10 5 Pa).
  • About 0.05 % of potassium hydroxide is added to the skim latex at 30 minute intervals to concentrate the skim latex.
  • This concentration step continues until about 60% to 70% by weight of a clear serum is obtained and removed as a first permeate, leaving behind a first retentate containing about 11 % of dry rubber.
  • the first retentate is then treated with another 0.1% of potassium hydroxide.
  • the treated first retentate then passes through a second multi-tubular membrane module repeatedly at an inlet pressure of about 3 bar (3 x 10 5 Pa).
  • About 00.05% of potassium hydroxide is added at 30 minute intervals to the first retentate to further concentrate the skim latex. This further concentration step is performed until about 40% to 50% by weight of a second clear serum is obtained and removed as a second permeate.
  • a second retentate containing more than 20% of dry rubber is also obtained after the second concentration step.
  • the second retentate is then treated with about 0.05% of TMTD/ZnO (in a 1 :1 ratio) dispersion (30% concentration) before the second retentate is blended with a fresh field latex in a ratio of 1 :9 parts.
  • the blended retentate containing the fresh field latex is then centrifuged using a selected skim screw (no. 12 or 12.5 mm in length) to obtain a latex concentrate.
  • the treated latex concentrate is then further blended with a fresh latex concentrate in a ratio of 1 :9 parts and ammoniated to more than 0.60% m/m ammonia to obtain the final latex concentrate.
  • the final latex concentrate obtained by this process has a quality comparable to a normal fresh latex concentrate. This is a value added process in rubber industry as recovering rubber from skim latex and converting it into a latex concentrate fetches a better price as compared to recovering and converting the skim latex into a skim crepe rubber.
  • Example 2 Two-stage concentration process
  • Skim latex with 5% dry rubber content is sieved through a 60 mesh wire gauze and pre-treated with 0.65% of ammonia and 0.1 % of solution containing ammonium laurate and potassium hydroxide in a ratio of 1 :1.
  • the treated skim latex then passes through a multi-tubular membrane module repeatedly.
  • the multi-tubular membrane module used in this example has a pore size of about 0.05 ⁇ , with a channel internal diameter of about 3.0 to 4.0 mm, with an overall length of 1.0 to 1.2m.
  • the inlet pressure of the membrane module is set at about 3 bar (3 x 10 5 Pa).
  • About 0.05% of ammonium laurate and potassium hydroxide is added to the skim latex at 30 minute intervals to concentrate the skim latex.
  • This concentration step continues until about 60% to 70% by weight of a clear serum is obtained.
  • the clear serum is removed as a first permeate, leaving behind a first retentate containing about 1 1 % of dry rubber.
  • the first retentate is then treated with another 0.1 % of solution containing ammonium laurate and potassium hydroxide.
  • the treated first retentate then passes through a second multi-tubular membrane module repeatedly at an inlet pressure of about 3 bar (3 x 10 5 Pa).
  • About 0.05% of ammonium laurate and potassium hydroxide is added at 30 minute intervals to the first retentate to further concentrate the skim latex. This further concentration step is performed until about 40% to 50% by weight of a second clear serum is obtained.
  • the second clear serum is then removed as a second permeate.
  • a second retentate containing more than 20% of dry rubber is obtained after the second concentration step.
  • the second retentate is then treated with about 0.05% of TMTD/ZnO (in a 1 :1 ratio) dispersion (30% concentration) before the second retentate is blended with a fresh field latex in a ratio of 1 :9 parts.
  • the blended retentate containing the fresh field latex is then centrifuged using a selected skim screw (no. 12 or 12.5 mm in length) to obtain a latex concentrate.
  • the treated latex concentrate is then further blended with a fresh latex concentrate in a ratio of 1 :9 parts and ammoniated to more than 0.60% m/m ammonia to obtain the final latex concentrate.
  • the final latex concentrate obtained by this process has a quality comparable to a normal fresh latex concentrate.
  • Example 3 Single-stage concentration process
  • the single-stage process only one concentration step is performed on the skim latex.
  • the pre-treatment step and the operating conditions in this process are similar to the two-stage process described in Examples 1 and 2 except that the single concentration step in the single-stage process continues until about 80% to 90% by weight of clear serum is obtained and removed as permeate.
  • the retentate obtained in this single-stage process contains more than 20% of dry rubber.
  • the retentate obtained from the concentration step is treated with about 0.05% of TMTD/ZnO (in a 1 :1 ratio) dispersion (30% concentration) before the retentate is blended with a fresh field latex in a ratio of 1 :9 parts.
  • the blended retentate containing the fresh field latex is then centrifuged using a selected skim screw (no. 12 or 12.5 mm in length) to obtain a latex concentrate.
  • the treated latex concentrate is then further blended with a fresh latex concentrate in a ratio of 1 :9 parts and ammoniated to more than 0.60% m/m ammonia to obtain the final latex concentrate.
  • the final latex concentrate obtained by this single-stage process has a quality comparable to that of a normal fresh latex concentrate and to a latex concentrate obtainable by the two-stage process as described above.

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Abstract

The present invention relates to an improved method of recovering rubber from skim natural rubber latex. The method comprises pre-treating the skim latex, concentrating the skim latex using one membrane module or two membrane modules in series with addition of potassium hydroxide or a solution containing ammonium laurate and potassium hydroxide, optionally treating the concentrated skim latex with a tetramethylthiuramdisulphide (TMTD) and zinc oxide (ZnO) dispersion, blending the concentrated latex with fresh field latex, centrifuging the blend to obtain a latex concentrate. The latex concentrate is further blended with a fresh latex concentrate and treated with ammonia to obtain the final latex concentrate.

Description

AN IMPROVED METHOD OF RECOVERING RUBBER FROM
SKIM NATURAL RUBBER LATEX
Field of the Invention
The present invention relates to an improved method of recovering rubber from skim natural rubber latex. More particularly, the present invention relates to an improved method of recovering rubber from skim natural rubber latex and converting the rubber into latex concentrate using a combination of membrane filtration and centrifugal separation techniques.
Background of the Invention
Skim natural rubber latex or skim latex is produced as a by-product in the process of concentrating natural rubber latex involving separation of the rubber latex into a concentrate and skim latex by centrifugation. Skim latex generally contains only about 5% of dry rubber and it is usually recovered as skim crepe rubber.
It is well known in the art that rubber can be recovered from skim latex by coagulation using sulphuric acid. The recovered rubber is then dried in the open before the rubber is sold as skim rubber. However, the skim rubber obtained from this coagulation method is of an inferior quality as it contains a high proportion of entrained non-rubber constituents and acid content. The skim rubber also possesses undesirable physical properties, including the generation of obnoxious odor, leading to low economic value in skim rubber. Furthermore, the method also produces highly acidic effluent which may cause pollution to the environment if the effluent is not treated in a proper manner before being discharged to the environment.
Coagulation of skim latex can also be performed by using proteolytic enzymes where enzymatic deproteinization of skim latex is achieved. This process however is not economical as it requires the use of large quantity of enzymes and involves deammoniation and acid coagulation steps in the process. Consequently, there is a need in the art to provide a method for recovering rubber from skim natural rubber latex that addresses at least one of the problems described above, or at least to provide an alternative.
Summary of the Invention The above and other problems are solved and an advance in the art is made by an improved method of recovering rubber from skim natural rubber latex in accordance with this invention. It is an advantage of a method in accordance with this invention that the recovery of rubber from skim natural rubber latex and converting the rubber into latex concentrate is carried out by using a combination of membrane filtration and centrifugal separation techniques, and thereby eliminates the need for acid coagulation for recovery of rubber from the skim natural rubber latex. A second advantage of this invention is that the method produces effluent with improved quality which in turn leads to less pollution to the environment.
In accordance with an embodiment of the invention, the method is performed in the following manner. The method begins by pre-treating the skim latex. The pre- treated skim latex then passes through a membrane module repeatedly with addition of potassium hydroxide or a solution containing ammonium laurate and potassium hydroxide at intervals to obtain a retentate and a permeate. The retentate is blended with a fresh field latex and centrifuged to obtain a latex concentrate. The latex concentrate is further blended with a fresh latex concentrate and treated with ammonia to obtain the final latex concentrate.
In accordance with some embodiments of the invention, the method further comprises treating the retentate with a tetramethylthiuramdisulphide (TMTD) and zinc oxide (ZnO) dispersion prior to the step of blending the retentate with a fresh field latex.
In accordance with another embodiment of the invention, the method further comprises subjecting the retentate to a second stage concentration prior to blending the retentate with the fresh field latex. The second stage concentration is carried out by passing the retentate through a second membrane module repeatedly with addition of further potassium hydroxide or solution containing ammonium laurate and potassium hydroxide to obtain a second retentate and a second permeate. The second retentate is optionally chemically treated and controllably blended with fresh field latex. The blended second retentate is centrifuged to obtain a latex concentrate. The latex concentrate then undergoes further control blending with fresh latex concentrate to obtain the final latex concentrate.
In accordance with some embodiments of this invention, the method further comprises pre-treating the retentate with potassium hydroxide or a solution containing ammonium laurate and potassium hydroxide prior to passing the retentate through the second membrane module.
In accordance with an embodiment of this invention, the potassium hydroxide or the solution containing ammonium laurate and potassium hydroxide is added to the pretreated skim latex at intervals of 10 to 30 minutes until about 80% to 90 % by weight of the permeate is obtained.
In accordance with some embodiments of this invention, the potassium hydroxide or the solution containing ammonium laurate and potassium hydroxide is added to the pretreated skim latex at intervals of 10 to 30 minutes until about 60% to 70% by weight of the permeate is obtained. Further potassium hydroxide or the solution containing ammonium laurate and potassium hydroxide is added to the retentate at intervals of 10 to 30 minutes until about 40% to 50% by weight of the second permeate is obtained.
In accordance with some embodiments of this invention, the solution containing ammonium laurate and potassium hydroxide comprises ammonium laurate and potassium hydroxide in a ratio of 1 :1.
In accordance with an embodiment of this invention, the method further comprises cleaning the membrane module by soaking the membrane module in about 2% to 5% of hydrogen peroxide; backwashing or normal flushing the membrane module with 1 % to 2% of sodium hydroxide; and backwashing or normal flushing the membrane module with 1 % to 2% of nitric acid.
Brief Description of the Drawings
The above and other advantages and features of this invention are described in the following detailed description and are shown in the following drawings:
Figure 1 is a flow chart illustrating the single stage concentration method in accordance with the present invention.
Figure 2 is a flow chart illustrating the two stage concentration method in accordance with the present invention. Description of the Invention
According to the present invention there is provided an improved method of recovering rubber from skim natural rubber latex or skim latex resulting from concentrating natural rubber latex by separating the natural rubber latex into a rubber-rich cream portion and a skim portion. The skim latex generally contains about 5% of dry rubber.
The method in accordance with an embodiment of the invention comprises the step of pre-treating the skim latex.
In one embodiment of the invention, the skim latex is pre-treated with ammonia and potassium hydroxide. In another embodiment, the skim latex is pre-treated with ammonia and a solution comprising ammonium laurate and potassium hydroxide. In a preferred embodiment, the skim latex is pre-treated with about 0.35% to 0.65% of ammonia and about 0.025% to 0.10% of potassium hydroxide. In another preferred embodiment, the skim latex is pre-treated with about 0.35% to 0.65% of ammonia and about 0.025% to 0.10% of the solution containing ammonium laurate and potassium hydroxide. Preferably, the solution contains ammonium laurate and potassium hydroxide in a ratio of 1 :1 . The skim latex is pre-treated by simply adding ammonia and potassium hydroxide or ammonia and the solution containing ammonium laurate and potassium hydroxide to the skim latex. The mixture is then homogenized by, for example, stirring. The pretreated skim latex then undergoes a first stage concentration process.
In the first stage concentration process, the skim latex is concentrated to ca. 11% to 13% of dry rubber content. The first stage concentration process is carried out by passing the skim latex through a multi-tubular membrane module repeatedly. The skim latex passes through the multi-tubular membrane module by means of a pump. Examples of pumps that can be used in the present invention include, but are not limited to, a diaphragm type of pump or a centrifugal type of pump. For a large scale membrane unit, a centrifugal type of pump is preferable. The multitubular membrane module can be made of any suitable material. In a preferred embodiment, it is made of ceramic, and preferably with a pore size of about 0.05μ. Potassium hydroxide or solution containing ammonium laurate and potassium hydroxide is added to the skim latex at intervals as the skim latex passes through the multi-tubular membrane module repeatedly. Preferably, the potassium hydroxide or the solution containing ammonium laurate and potassium hydroxide is added to the skim latex at intervals of 10 to 30 minutes. In a preferred embodiment, about 0.025% to 0.10%) of potassium hydroxide or about 0.025% to 0.10% of the solution containing ammonium laurate and potassium hydroxide is added to the skim latex at each interval. The inlet pressure of the multi-tubular membrane module is set at about 2.5 to 4.5 bar (2.5 x 105 to 4.5 x 105 Pa). Preferably, the trans-membrane pressure is set at about 1.5 to 3.0 bar (1.5 x 105 to 3.0 x 105 Pa). The solution used in this step can either be potassium hydroxide or a solution containing ammonium laurate and potassium hydroxide, without limiting it to be of the same solution as that used in the step of pre-treating the skim latex,
The first stage concentration process continues until about 60% to 70% by weight of a clear serum is obtained. The clear serum is removed as permeate, leaving behind a retentate which is the concentrated skim latex. The retentate or the concentrated skim latex may be treated with further potassium hydroxide or solution containing ammonium laurate and potassium hydroxide before the concentrated skim latex undergoes a second stage concentration process. The solution used in this step can either be potassium hydroxide or a solution containing ammonium laurate and potassium hydroxide, without limiting it to be of the same solution as that used in the step of pre-treating the skim latex. Preferably, about 0.025% to 0.10% of potassium hydroxide or about 0.025% to 0.10% of the solution containing ammonium laurate and potassium hydroxide is added to the concentrated skim latex to treat the skim latex.
In the second stage concentration process, the concentrated skim latex is further concentrated to ca. more than 20% of dry rubber content. The second stage concentration process is carried out by passing the concentrated skim latex through a second multi-tubular membrane module repeatedly. The second multitubular membrane module can be of the same type of membrane used in the first stage concentration process or it can be of any type suitable for use in the process. The concentrated skim latex passes through the second multi-tubular membrane module by means of a pump. Examples of pumps that can be used in the method include, but are not limited to, a diaphragm type of pump or a centrifugal type of pump. For a large scale membrane unit, a centrifugal type of pump is preferable. The multi-tubular membrane module can be made of any suitable material. In a preferred embodiment of the invention, the multi-tubular membrane module is made of ceramic and has a pore size of about 0.05μ. It has a channel internal diameter of about 3.0 to 4.0 mm and an overall length of about 1.0 to 1.2m.
Preferably, the concentrated skim latex passes through the second multi-tubular membrane module at an inlet pressure of about 2.5 to 4.5 bar (2.5 x 105 to 4.5 x 105 Pa). Further potassium hydroxide or solution containing ammonium laurate and potassium hydroxide is added to the concentrated skim latex at intervals to further concentrate the skim latex as the skim latex passes through the second multi-tubular membrane module repeatedly. In a preferred embodiment, the potassium hydroxide or the solution containing ammonium laurate and potassium hydroxide is added to the concentrated skim latex at intervals of 10 to 30 minutes. Preferably, about 0.025% to 0.10% of potassium hydroxide or about 0.025% to 0.10% of the solution containing ammonium laurate and potassium hydroxide is added to the skim latex at each interval. Either potassium hydroxide or a solution containing ammonium laurate and potassium hydroxide can be used in this step without limiting it to be of the same solution as that used in the step of pre-treating the skim latex.
The second stage concentration process continues until about 40% to 50% by weight of a second clear serum is obtained. The second clear serum is removed as a second permeate, leaving behind a second retentate which is the further concentrated skim latex.
The further concentrated skim latex may optionally be treated with tetramethylthiuramdisulphide (TMTD) and zinc oxide (ZnO) dispersion in a 1 :1 ratio with 30% concentration before the further concentrated skim latex is blended with a fresh field latex. Preferably, the further concentrated skim latex is treated with about 0.05% to 0.10 % by weight of the TMTD/ZnO dispersion. This step is carried out depending on the quality of the further concentrated skim latex obtained after the concentration process, for example, the amount of volatile fatty acids present in the further concentrated skim latex. Preferably, this step is carried out when the volatile fatty acids number in the further concentrated skim latex exceeds 0.10. Preferably, the treated concentrated skim latex is blended with the fresh field latex in a ratio of 1 :9 parts.
The blended concentrated skim latex containing the fresh field latex is then centrifuged to obtain a latex concentrate. The latex concentrate is blended with a fresh latex concentrate in a ratio of 1 :9 parts. Ammonia is then added to the blended latex concentrate to more than 0.60% m/m to obtain the final latex concentrate. The final latex concentrate thus obtained contains more than 60% of dry rubber.
In another embodiment of the present invention, depending on the feed quality used in the method, the first stage concentration process and the second stage concentration process may be carried out in a single step. In a single stage process, the skim latex is similarly pre-treated with ammonia and potassium hydroxide or with ammonia and a solution containing ammonium laurate and potassium hydroxide. In a preferred embodiment, the skim latex is pre-treated with about 0.35% to 0.65% of ammonia and about 0.025% to 0.10% of potassium hydroxide. In another preferred embodiment, the skim latex is pre-treated with about 0.35% to 0.65% of ammonia and about 0.025% to 0.10% of the solution containing ammonium laurate and potassium hydroxide. Preferably, the solution containing ammonium laurate and potassium hydroxide is in a ratio of 1 :1.
The skim latex is pre-treated by simply adding ammonia and potassium hydroxide or ammonia and the solution containing ammonium laurate and potassium hydroxide to the skim latex. The mixture is then homogenized by, for example, stirring. The pretreated skim latex then undergoes a single stage concentration process.
In accordance with this embodiment of the invention, the single stage concentration process is carried out by passing the skim latex through a multitubular membrane module repeatedly. The skim latex passes through the multitubular membrane module by means of a pump. Examples of pumps that can be used in the method include, but are not limited to, a diaphragm type of pump or a centrifugal type of pump. For a large scale membrane unit, a centrifugal type of pump is preferable. The multi-tubular membrane module can be made of any suitable material. In a preferred embodiment of the invention, the multi-tubular membrane module is made of ceramic and has a pore size of about 0.05μ. It has a channel intemal diameter of about 3.0 to 4.0 mm and an overall length of about 1.0 to 1.2m.
Potassium hydroxide or the solution containing ammonium laurate and potassium hydroxide is added to the skim latex as the skim latex passes through the multitubular membrane module repeatedly. The potassium hydroxide or the solution containing ammonium laurate and potassium hydroxide is added to the skim latex at intervals. Preferably, the potassium hydroxide or the solution containing ammonium laurate and potassium hydroxide is added to the skim latex at intervals of 10 to 30 minutes. In a preferred embodiment, about 0.025% to 0.10% of potassium hydroxide or about 0.025% to 0.10% of the solution containing ammonium laurate and potassium hydroxide is added to the skim latex at each interval. The inlet pressure of the membrane is preferably set at about 2.5 bar to 4.5 bar (2.5 x 105 to 4.5 x 105 Pa). In a preferred embodiment, for optimum permeate flux, the trans-membrane pressure is set at about 1.5 to 3.0 bar (1.5 x 105 to 3.0 x 105 Pa).
The single stage concentration process continues until about 80% to 90% by weight of a clear serum is obtained. The clear serum is removed as permeate, leaving behind a retentate which is the concentrated skim latex. The concentrated skim latex may optionally be treated with TMTD/ZnO dispersion in a 1 :1 ratio with 30% concentration. Preferably, the concentrated skim latex is treated with about 0.05% to 0.10% by weight of the TMTD/ZnO dispersion. This step is carried out depending on the quality of the concentrated skim latex obtained after the concentration process, for example, the amount of volatile fatty acids present in the concentrated skim latex. Preferably, this step is carried out when the volatile fatty acids number in the concentrated skim latex exceeds 0.10. The treated concentrated skim latex is then blended with fresh field latex, preferably in a ratio of 1 :9 parts.
The blended concentrated skim latex containing the fresh field latex is centrifuged to obtain a latex concentrate. The latex concentrate is then blended with a fresh latex concentrate in a ratio of 1 :9 parts. Ammonia is then added to more than 0.60% m/m to obtain the final latex concentrate. The final latex concentrate thus obtained contains more than 60% of dry rubber.
The solution of ammonium laurate and potassium hydroxide refers hereinabove may contain ammonium laurate and potassium hydroxide in any suitable amount. In a preferred embodiment, the solution contain ammonium laurate and potassium hydroxide in a ratio of 1 :1.
In the present invention, the clear serums produced from the skim latex concentration processes can be used to recover valuable bio-chemicals contain therein using suitable methods known in the art. The membrane may become fouled after use. The fouled membrane may be cleaned by soaking it in about 2% to 5% of hydrogen peroxide and backwashed or normal flushed with about 1 % to 2% of sodium hydroxide. The fouled membrane may also be backwashed or normal flushed with nitric acid to remove inorganic foulants and to re-generate the membrane for further use. Preferably, the fouled membrane is backwashed or normal flushed with about 1 % to 2% of nitric acid
In the method in accordance with the embodiment of the present invention, the skim latex is concentrated by the membrane system before the skim latex is blended with fresh field latex and re-centrifuged back as a latex concentrate. The use of membrane as means to concentrate the skim latex eliminates the need for acid coagulation for recovery of rubber from skim latex. It also helps to improve the quality of the effluent produced by the method. The fouled membrane may be cleaned using a combination of chemicals to regenerate it for subsequent concentration. The recovery of rubber and converting it into a latex concentrate is a value added process to the rubber industry.
It is advantageous to use potassium hydroxide in the method of the present invention as potassium hydroxide acts as a latex stabilizer and latex preservative. It also gives a better shear resistance to agitation by any suitable mechanical means.
The following examples are provided to further illustrate and describe particular specific embodiments of the present invention, and are in no way to be construed to limit the invention to the specific procedures, conditions or compositions described therein. EXAMPLES
Example 1 : Two-stage concentration process
Skim latex with 5% dry rubber content is sieved through a 60 mesh wire gauze and pre-treated with 0.65% of ammonia and 0.1 % of potassium hydroxide. The treated skim latex then passes through a multi-tubular membrane module repeatedly. The multi-tubular membrane module used in this example has a pore size of about 0.05μ, with a channel internal diameter of about 3.0 to 4.0 mm, with an overall length of 1.0 to 1.2m. The inlet pressure of the membrane module is set at about 3 bar (3 x 105 Pa). About 0.05 % of potassium hydroxide is added to the skim latex at 30 minute intervals to concentrate the skim latex.
This concentration step continues until about 60% to 70% by weight of a clear serum is obtained and removed as a first permeate, leaving behind a first retentate containing about 11 % of dry rubber.
The first retentate is then treated with another 0.1% of potassium hydroxide. The treated first retentate then passes through a second multi-tubular membrane module repeatedly at an inlet pressure of about 3 bar (3 x 105 Pa). About 00.05% of potassium hydroxide is added at 30 minute intervals to the first retentate to further concentrate the skim latex. This further concentration step is performed until about 40% to 50% by weight of a second clear serum is obtained and removed as a second permeate. A second retentate containing more than 20% of dry rubber is also obtained after the second concentration step.
The second retentate is then treated with about 0.05% of TMTD/ZnO (in a 1 :1 ratio) dispersion (30% concentration) before the second retentate is blended with a fresh field latex in a ratio of 1 :9 parts. The blended retentate containing the fresh field latex is then centrifuged using a selected skim screw (no. 12 or 12.5 mm in length) to obtain a latex concentrate. The treated latex concentrate is then further blended with a fresh latex concentrate in a ratio of 1 :9 parts and ammoniated to more than 0.60% m/m ammonia to obtain the final latex concentrate.
The final latex concentrate obtained by this process has a quality comparable to a normal fresh latex concentrate. This is a value added process in rubber industry as recovering rubber from skim latex and converting it into a latex concentrate fetches a better price as compared to recovering and converting the skim latex into a skim crepe rubber. Example 2: Two-stage concentration process
Skim latex with 5% dry rubber content is sieved through a 60 mesh wire gauze and pre-treated with 0.65% of ammonia and 0.1 % of solution containing ammonium laurate and potassium hydroxide in a ratio of 1 :1. The treated skim latex then passes through a multi-tubular membrane module repeatedly. The multi-tubular membrane module used in this example has a pore size of about 0.05μ, with a channel internal diameter of about 3.0 to 4.0 mm, with an overall length of 1.0 to 1.2m. The inlet pressure of the membrane module is set at about 3 bar (3 x 105 Pa). About 0.05% of ammonium laurate and potassium hydroxide is added to the skim latex at 30 minute intervals to concentrate the skim latex.
This concentration step continues until about 60% to 70% by weight of a clear serum is obtained. The clear serum is removed as a first permeate, leaving behind a first retentate containing about 1 1 % of dry rubber.
The first retentate is then treated with another 0.1 % of solution containing ammonium laurate and potassium hydroxide. The treated first retentate then passes through a second multi-tubular membrane module repeatedly at an inlet pressure of about 3 bar (3 x 105 Pa). About 0.05% of ammonium laurate and potassium hydroxide is added at 30 minute intervals to the first retentate to further concentrate the skim latex. This further concentration step is performed until about 40% to 50% by weight of a second clear serum is obtained. The second clear serum is then removed as a second permeate. A second retentate containing more than 20% of dry rubber is obtained after the second concentration step.
The second retentate is then treated with about 0.05% of TMTD/ZnO (in a 1 :1 ratio) dispersion (30% concentration) before the second retentate is blended with a fresh field latex in a ratio of 1 :9 parts. The blended retentate containing the fresh field latex is then centrifuged using a selected skim screw (no. 12 or 12.5 mm in length) to obtain a latex concentrate. The treated latex concentrate is then further blended with a fresh latex concentrate in a ratio of 1 :9 parts and ammoniated to more than 0.60% m/m ammonia to obtain the final latex concentrate. The final latex concentrate obtained by this process has a quality comparable to a normal fresh latex concentrate.
Example 3 : Single-stage concentration process
In the single-stage process, only one concentration step is performed on the skim latex. The pre-treatment step and the operating conditions in this process are similar to the two-stage process described in Examples 1 and 2 except that the single concentration step in the single-stage process continues until about 80% to 90% by weight of clear serum is obtained and removed as permeate. The retentate obtained in this single-stage process contains more than 20% of dry rubber.
After the concentration step, the retentate obtained from the concentration step is treated with about 0.05% of TMTD/ZnO (in a 1 :1 ratio) dispersion (30% concentration) before the retentate is blended with a fresh field latex in a ratio of 1 :9 parts. The blended retentate containing the fresh field latex is then centrifuged using a selected skim screw (no. 12 or 12.5 mm in length) to obtain a latex concentrate. The treated latex concentrate is then further blended with a fresh latex concentrate in a ratio of 1 :9 parts and ammoniated to more than 0.60% m/m ammonia to obtain the final latex concentrate.
The final latex concentrate obtained by this single-stage process has a quality comparable to that of a normal fresh latex concentrate and to a latex concentrate obtainable by the two-stage process as described above.
The above is a description of the subject matter the inventor regards as the invention and is believed that others can and will design alternative systems that include this invention based on the above disclosure.

Claims

1. A method for recovering rubber from skim latex resulting from concentrating a natural rubber latex by separating the natural rubber latex into rubber latex and skim latex, the method comprising:
pre-treating the skim latex;
passing the pretreated skim latex through a membrane module repeatedly with addition of potassium hydroxide or a solution containing ammonium laurate and potassium hydroxide at intervals to obtain a retentate and a permeate;
blending the retentate with a fresh field latex;
centrifuging the blended retentate to obtain a latex concentrate;
blending the latex concentrate with a fresh latex concentrate; and
treating the blended latex concentrate with ammonia to obtain the final latex concentrate.
2. The method according to claim 1 , further comprising:
treating the retentate with a tetramethylthiuramdisulphide (TMTD) and zinc oxide (ZnO) dispersion prior to the step of blending the retentate with a fresh field latex.
3. The method according to claim 1 , further comprising:
passing the retentate through a second membrane module repeatedly with addition of further potassium hydroxide or solution containing ammonium laurate and potassium hydroxide at intervals to obtain a second retentate and a second permeate prior to the step of blending the retentate with the fresh field latex.
4. The method according to claim 3, further comprising:
treating the second retentate with a tetramethylthiuramdisulphide (TMTD) and zinc oxide (ZnO) dispersion.
5. The method according to claim 3, further comprising:
pre-treating the retentate with potassium hydroxide or solution containing ammonium laurate and potassium hydroxide prior to passing the retentate through the second membrane module.
6. The method according to claim 1 , wherein the potassium hydroxide or the solution containing ammonium laurate and potassium hydroxide is added to the pretreated skim latex at intervals of 10 to 30 minutes until about 80% to 90% by weight of the permeate is obtained.
7. The method according to claim 3, wherein the potassium hydroxide or the solution containing ammonium laurate and potassium hydroxide is added to the pretreated skim latex at intervals of 10 to 30 minutes until about 60% to 70 % by weight of the permeate is obtained.
8. The method according to claim 7, wherein the further potassium hydroxide or the solution containing ammonium laurate and potassium hydroxide is added to the retentate at intervals of 10 to 30 minutes until about 40% to 50% by weight of the second permeate is obtained.
9. The method according to claim 1 or 3, wherein the skim latex is pre-treated with ammonia and potassium hydroxide or ammonia and solution containing ammonium laurate and potassium hydroxide.
10. The method according to claim 9, wherein the skim latex is pre-treated with 0.35% to 0.65% by weight of ammonia and 0.025% to 0.1 % by weight of potassium hydroxide.
1 1. The method according to claim 9, wherein the skim latex is pre-treated with 0.35% to 0.65% by weight of ammonia and 0.025% to 0.1% by weight of the solution containing ammonium laurate and potassium hydroxide.
12. The method according to claim 1 , 3, 5 or 1 1 , wherein the solution containing ammonium laurate and potassium hydroxide comprises ammonium laurate and potassium hydroxide in a ratio of 1 :1.
13. The method according to claim 1 , wherein the membrane module is a multitubular membrane.
14. The method according to claim 13, wherein the membrane module has an inlet pressure in the range of 2.5 x 105 to 4.5 x 105 Pa.
15. The method according to claim 3, wherein the second membrane module is a multi-tubular membrane.
16. The method according to claim 15, wherein the second membrane module has an inlet pressure in the range of 2.5 x 105 to 4.5 x 105 Pa.
17. The method according to claim 3, wherein the amounts of the second retentate and the fresh field latex is in a ratio of 1 :9.
18. The method according to claim 13, wherein the multi-tubular membrane module includes a diaphragm or a centrifugal type of pump.
19. The method according to claim 15, wherein the second multi-tubular membrane module includes a diaphragm or a centrifugal type of pump.
20. The method according to claim 1 , further comprising:
cleaning the membrane module by:
soaking the membrane module in 2% to 5% of hydrogen peroxide; backwashing or normal flushing the membrane module with 1 % to 2 % of sodium hydroxide; and
backwashing or normal flushing the membrane module with 1% to 2% of nitric acid, to re-generate the membrane module for further use.
21. The method according to claim 3, further comprising:
cleaning the second membrane module by:
soaking the second membrane module in 2% to 5% of hydrogen peroxide; and
backwashing or normal flushing the membrane module with 1 % to 2 % of sodium hydroxide; and backwashing or normal flushing the membrane module with 1 % to 2% of nitric acid, to re-generate the second membrane module for further use.
PCT/MY2013/000070 2012-10-29 2013-04-01 An improved method of recovering rubber from skim natural rubber latex WO2014069979A1 (en)

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