阅读说明：本技术 用于通过高压过滤天然橡胶的湿凝结物来净化天然橡胶的方法 (Process for purifying natural rubber by high pressure filtration of wet coagulum of natural rubber ) 是由 J·杜斯罗尔斯 于 2018-06-06 设计创作，主要内容包括：本发明涉及用于通过过滤天然橡胶的湿凝结物来净化天然橡胶的方法。所述方法包括使水含量大于10％的天然橡胶凝结物穿过过滤器,在所述过滤器的入口处的压力大于100巴。(The present invention relates to a process for purifying natural rubber by filtering wet coagulum of natural rubber. The method comprises passing natural rubber coagulum having a water content greater than 10% through a filter at a pressure greater than 100 bar at an inlet of the filter.)

1.A process for purifying natural rubber, the process comprising passing natural rubber coagulum having a water content of greater than 10% through a filter at a pressure of greater than 100 bar at an inlet of the filter.

2. The method of claim 1, wherein the pressure at the inlet of the filter is between 100 bar and 700 bar.

3. The method according to any one of claims 1 and 2, wherein the pressure at the inlet of the filter is in the range of 150 bar to 500 bar.

4. A method according to any one of claims 1 to 3, wherein the temperature at the inlet of the filter is less than 210 ℃.

5. The method according to any one of claims 1 to 4, wherein the temperature at the inlet of the filter is between 50 ℃ and 150 ℃.

6. The method of any one of claims 1 to 5, wherein the temperature at the inlet of the filter is in the range of 80 ℃ to 120 ℃.

7. The method of any of claims 1-6, wherein the natural rubber coagulum has a water content of greater than 15%.

8. The method of any one of claims 1 to 7, wherein the natural rubber coagulum has a water content of at most 40%.

9. The method according to any one of claims 1 to 8, which is carried out in an apparatus comprising an extruder and a filter mounted at the outlet of the extruder, the extruder comprising a barrel and a screw disposed in the barrel, the barrel comprising a groove on its inner surface, the groove extending from the end of the barrel closest to the feed zone of the extruder.

10. The method of claim 9, wherein the apparatus further comprises a gear pump disposed at an end of the screw and in front of the filter.

11. The method of claim 10, wherein the cartridge has two consecutive portions along its length: a first portion in which the inner surface of the barrel is grooved; a second portion wherein the inner surface of the barrel is free of grooves; the first portion extends from the end of the barrel closest to the feed zone to the second portion, which extends to the end of the barrel closest to the outlet of the extruder.

12. The method of claim 11, wherein the second portion extends along at least a last third of an overall length of the cartridge.

13. The method of claim 11 or 12, wherein the second portion extends at least along the last third of the total length of the barrel and at most from the end of the feed zone to the end of the barrel closest to the outlet of the extruder.

14. The method of any one of claims 9 to 13, wherein the extruder is a single screw extruder.

Technical Field

The present invention relates to a process for purifying natural rubber by filtering the wet coagulum of natural rubber, which enables the elimination of the contaminants present in the natural rubber.

Background

Natural rubber, which contains a high cis content polyisoprene matrix, is a very widely used elastomer in the tire field due to its excellent properties. For example, they are used in rubber compositions intended for the manufacture of semi-finished products for the transport of heavy-duty vehicles, since they can contribute to the compromise of the properties of the tires. In fact, the introduction of natural rubber into rubber compositions reinforced with reinforcing fillers such as carbon black makes the rubber compositions have a very beneficial compromise in terms of hysteresis and wear, which in terms of tire performance represents a good compromise between the durability and wear of the tire.

Natural rubber originates from the dried rubber material of natural rubber latex, generally extracted from hevea (I' resorva) after extraction: the latex is typically collected in a container called a cup. According to a first coagulation process, known as spontaneous, the latex coagulates directly in the cups to form "cup clumps" coagulum, a term well known to those skilled in the art of producing natural rubber. According to a second coagulation process, known as induced, the latex still liquid in the cups is poured out, optionally stabilized, and then coagulated, for example by means of a chemical agent.

The spontaneous or induced coagulation product of natural rubber latex, hereinafter referred to as coagulation product, comprises a polyisoprene matrix immersed in a slurry. Typically, it also contains leaves, branches, sand and other debris that can contaminate the coagulum as it is collected. In conventional processes for manufacturing natural rubber, the coagulum is typically cut and washed to eliminate the largest contaminants (primary cleaning). To eliminate finer contaminants (secondary cleaning), the coagulum is also chopped into a rubber powder, then washed with water in a water basin before being conveyed to a crumpling machine. It is also known from patent application WO 2016162645 to eliminate the finest contaminants from natural rubber by passing wet coagulum through equipment comprising extruders, gear pumps and filters.

Since natural rubber is a viscoelastic product of high viscosity, its passage through the filter causes shear stresses, all of which are all the greater the higher the pressure applied. However, one of the properties of natural rubber is its shear sensitivity, which causes the polyisoprene chains to break and causes its viscosity to decrease. This property, which is utilized in operations such as plasticizing natural rubber (to make it easier to mix natural rubber with, for example, reinforcing fillers), can lead to a deterioration in the fracture properties and hysteresis properties of natural rubber-based rubber compositions.

Disclosure of Invention

In the research of the present applicant company, which is directed to further increasing the efficiency of the method for purifying natural rubber by filtering wet coagulation of natural rubber, a method for purifying natural rubber by filtering wet coagulation of natural rubber under high pressure has been found. This method enables the production of purified natural rubber while maintaining the properties of the natural rubber, in particular its viscosity, despite the very high pressure applied at the inlet of the filter. This process, which is usually carried out after a primary cleaning of the wet coagulum, thus enables a secondary cleaning of the natural rubber. The method also has the following advantages: purified natural rubber is produced with a much lower water content, which enables energy savings to be expected in subsequent operations for drying the natural rubber.

The subject of the invention is a process for purifying natural rubber, which comprises passing a natural rubber coagulum having a water content of greater than 10% through a filter, the pressure at the inlet of said filter being greater than 100 bar.

Drawings

I. Description of the drawings

Figure 1 shows very schematically the required apparatus that can be used in the present invention. The apparatus comprises an extruder (11) and a filter holder (12) (the filter is not shown in the figure). The extruder (11) comprises a feed hopper (111), a barrel (112) and a single screw (113), the single screw (113) having a hub and a flight extending radially outwardly relative to the hub. The inner surface (1121) of the barrel is also shown in fig. 1. At the outlet of the extruder, the system comprises one or more filters mounted on a filter holder (12). The system comprises measuring means, in particular means for measuring pressure and temperature (P, T).

Figure 2 shows very schematically another device that can be used for the requirements of the invention. The apparatus comprises an extruder (21) and a filter holder (22) (filter not shown in the figure) and an external gear pump (23). The extruder (21) comprises a feed hopper (211), a barrel (212), and a single screw (213), the single screw (213) having a hub and a flight extending radially outward relative to the hub. The inside surface (2121) of the barrel is also shown in fig. 2. At the outlet of the extruder, the system comprises one or more filters mounted on a filter holder (22). The system also comprises measuring means, in particular means for measuring pressure and temperature (P, T).

Fig. 3 shows a cross-sectional view of a cartridge with a groove.

In the right semicircular part (marked a in the figure), the groove (311) has a dovetail shape. In the left semicircular portion (marked B in the figure), the groove (312) has a saw-tooth shape.

The grooves (311, 312) define ribs (321, 322).

Fig. 4 schematically shows a three-dimensional view of two successive grooves separated by a rib. The groove comprises

A bottom surface (44) delimited by two bottom corners (432, 433),

-two side surfaces (422, 423) extending from the bottom surface (44) towards the inside, each side surface being delimited by a bottom corner (432, 433) and a corner (412, 413) intersecting the inner surface of the barrel.

The groove defines a rib whose upper surface (41) is bounded by two intersecting corners (411, 412) constituting the inner surface of the cartridge.

In fig. 4, the distance between two consecutive ribs is the distance between two intersecting corners (412) and (413), which distance is indicated by a double arrow. The distance between the two trenches is the distance between the two intersecting corners (411) and (412).

In fig. 4, the minimum distance between the bottom surface (44) and the plane passing through the intersecting corners (412) and (413) is indicated by the highlighted double arrow.

Detailed Description

Detailed description of the invention

Any numerical range denoted by the expression "between a and b" represents a numerical range from greater than a to less than b (i.e. excluding the extremes a and b), while any numerical range denoted by the expression "from a to b" means a numerical range from a to b (i.e. including the strict extremes a and b).

In the present specification, all percentages (%) given are% by weight unless explicitly stated otherwise.

In the present application, natural rubber latex is understood to mean the latex obtained by tapping of the hevea rubber tree.

The natural rubber coagulum intended to be filtered according to the process of the invention is a coagulum of natural rubber latex, whether obtained by spontaneous or induced coagulation. The coagulum is preferably a gel-cup block coagulum.

The condensate is said to be wet because it is saturated with slurry and is typically saturated with water, such as wash water resulting from the operation of washing the condensate, which is typically performed under water in a basin, particularly the wash water used in the primary cleaning operation. It should be remembered that the primary cleaning operation is intended to eliminate coarse objects. The coagulum has a water content of greater than 10%, preferably greater than 15%. The percentages are expressed by weight of the total weight of the coagulum. Advantageously, the water content in the coagulum is at most 40%.

The desired coagulum that can be used in the present invention can be in any form, provided that high pressure is applied to the coagulum at the inlet of the filter, the form of the coagulum being independent of the efficiency of the process. Thus, it may be in the form of a blade or a glue powder.

The method according to the invention has the feature that the wet coagulum is passed through a filter to eliminate the finest contaminants from the natural rubber by trapping the contaminants in the filter. The filter advantageously allows contaminants having a size greater than 1mm, advantageously greater than 500 μm, more advantageously greater than 100 μm, to be filtered.

Another essential feature of the method according to the invention is that a pressure of more than 100 bar is applied to the wet condensate at the inlet of the filter. The pressure is typically measured by a pressure sensor mounted upstream of the filter. The pressure may be measured as close as possible to the filter, for example at a distance of less than 1cm from the surface formed by the mesh of the filter or the mesh of the filter through which the wet condensate first passes when several filters are used. Alternatively, the pressure sensor may be provided at the outlet of the gear pump upstream of the filter, for example 10cm or 20cm from the filter surface. In order to take into account the pressure drop between the outlet of the gear pump and the filter, the pressure value at the outlet of the gear pump is the pressure value at the inlet of the filter plus the value of the pressure drop.

Preferably, the pressure at the inlet of the filter is between 100 bar and 700 bar. More preferably, it is in the range of 150 to 500 bar. The high pressure also promotes better dewatering of the wet coagulum, which results in a filtered coagulum with even lower residual water content. Conveying the relatively dry coagulum at the end of the secondary cleaning operation is advantageous in the overall process for manufacturing natural rubber, since less energy will be required for the subsequent operations of drying the natural rubber.

The temperature of the wet condensate at the inlet of the filter is preferably less than 210 ℃, more preferably between 50 and 150 ℃, even more preferably in the range of 80 to 120 ℃. The temperature may be measured by a sensor installed at the inlet of the filter, as close as possible to the filter, for example less than 1cm from the surface formed by the mesh of the filter or the mesh of the filter through which the wet condensate first passes when several filters are used.

The method can be carried out in any apparatus equipped with a filter and with a device capable of applying a pressure of greater than 100 bar at the inlet of the filter. The apparatus may also comprise heating or cooling means, such as a double jacket along the apparatus, which serve in particular to keep the condensate at a temperature selected according to the desired set value during the process.

The filter is any suitable filtering device. In particular, it may be one or more mesh filters mounted on a filter holder, the size of which is selected depending on the filter mesh. The mesh size is advantageously from 100 μm to 1 mm. If necessary, several filters may be provided in series. The filter can then be easily changed continuously or discontinuously during the process by using a suitable system.

According to a first variant, the device comprises a filter, a plunger and a cylindrical tank in which the plunger is movable. The canister has two openings, one for supplying condensate and the other for discharging condensate at a pressure exerted by the movement of the plunger as described below. The filter is disposed at the opening for discharging the condensate. This apparatus has the disadvantage that the process is carried out discontinuously.

According to a second variant, the device comprises a worm machine and a filter mounted at the outlet of the worm machine.

According to a third variant form, the device comprises a worm machine, a gear pump arranged at the end of the screw and in front of the filter, and a filter mounted at the outlet of the worm machine.

The apparatuses adopted according to the second and third variants have the advantage of being able to operate continuously and thus ensure a continuous process.

Whether the variant is the second variant or the third variant, the worm machine is generally an extruder comprising a barrel and a screw arranged in the barrel, in particular a single-screw extruder. According to a third variant, the gear pump is arranged at the end of the screw and in front of the filter.

The cartridge may be cylindrical or conical, preferably cylindrical. The screw includes a hub and a thread extending radially outward relative to the hub. The barrel has an opening connected to a hopper with which the extruder is normally equipped, said hopper allowing the introduction of wet coagulum. The cartridge further comprises one or more openings in the feed zone intended to drain water from the cartridge that can be drained from the condensate during the increase in pressure in the cartridge. The feed zone is the area below the hopper opening. The openings intended to discharge the water may be in the form of slits or circular holes.

The barrel includes a groove on its inner surface extending from the end of the barrel closest to the feed zone in the extruder. The presence of the grooves on the inner surface of the barrel promotes the movement of wet condensate in the barrel.

According to a preferred embodiment of the second variant form, the groove of the barrel extends from the end of the barrel closest to the feeding zone to the end of the barrel closest to the extruder outlet, the diameter of the hub in the screw is constant and the pitch of the flights in the screw is uniform. According to this preferred embodiment, the groove extends along the entire length of the cartridge.

According to a more preferred embodiment of the third variant form, the cartridge has two consecutive portions along its length: a first portion in which the inner surface of the barrel is grooved; the second part, where the inner surface of the barrel is free of grooves and is considered smooth. According to this preferred embodiment, the first portion of the barrel extends from the end of the barrel closest to the feed zone to the second portion, and the second portion extends to the end of the barrel closest to the extruder outlet. The second portion preferably extends along at least the last third of the total length of the cartridge. More preferably, the second portion extends at least along the last third of the total length of the barrel and at most from the end of the feed zone to the end of the barrel closest to the extruder outlet. The presence of the grooves on the inner surface of the first portion in the cartridge promotes movement of wet condensate in the cartridge. The absence of grooves on the internal surface of the barrel in the second portion of the barrel promotes a pressure rise at the suction inlet of the gear pump to feed the gear pump, ensuring its normal operation and nominal efficiency. Thus, the presence of a smooth surface in the second section of the barrel ensures a much better flow rate of the purified natural rubber than the flow rate of the purified natural rubber produced by the presence of a grooved surface in the second section of the barrel which does not prevent backflow of the natural rubber in the direction of the end of the barrel closest to the feed zone, this backflow being caused by the pressure rise at the end of the screw, with the result that the flow rate of the purified natural rubber is reduced.

In the first section of the barrel, the diameter of the hub in the screw is preferably held constant at a consistent pitch of the threads in the screw. In the second section of the barrel, the hub may be of constant diameter in the screw or may vary, with its diameter then increasing towards the end of the screw. This increase in diameter may also be accompanied by a decrease in the pitch of the thread. The latter feature allows the pressure of the condensate near the gear pump to be increased.

Since the cartridge is of axially symmetrical construction, the grooved cartridge includes a groove in its thickness that opens onto the inner surface of the grooved cartridge. In the remainder of the present description, the term "grooved cartridge" denotes both a cartridge along its entire length when the cartridge is grooved along its entire length and a grooved portion of the cartridge when the cartridge is grooved along part of its length.

Each groove is defined by a bottom surface bounded by two bottom corners from which two side surfaces extend inwardly, each of the two surfaces being bounded by a bottom corner and a corner that intersects the interior surface of the barrel with the groove. Preferably, in any plane perpendicular to the axis of the cartridge (where R, expressed in mm, is the distance between the centre of the cartridge and the inner surface of the cartridge with the groove), the cartridge with the groove satisfies:

a. the ratio (total length of the trench openings in mm)/(2 π R) represented by A is at least equal to 0.25 and at most equal to 0.9;

b. a ratio (number of grooves/2R) represented by B is greater than or equal to 0.1;

c. a ratio (depth of groove in mm)/(2R) represented by C is greater than 0.02, an

d. A plane passing through the two base corners forms with each plane passing through the base corners and the intersecting corners (delimited by the side surfaces) an angle δ at least equal to 60 ° and at most equal to 90 °.

Within the meaning of the invention, the groove defines a rib, the upper surface of which is delimited by two intersecting corners, constituting the inner surface of the cartridge.

Within the meaning of the present invention, an "intersecting corner" or "corner intersecting the inner surface of the barrel" (311, 312, 313) is a corner between the side surface and the inner surface of the barrel.

Within the meaning of the present invention, the "total length of the groove opening" is the sum of the distances (in mm) between two intersecting corners between two ribs.

Within the meaning of the present invention, "groove depth" is defined as the minimum distance, in mm, between the bottom surface and a plane passing through the intersecting corners.

Within the meaning of the present invention, the "minimum distance" is the smallest radial distance with respect to the axis of the barrel.

The cartridge with the groove advantageously satisfies a at least equal to 0.3 and at most equal to 0.7. More particularly, a is at least equal to 0.45 and at most equal to 0.55.

The distance between the two intersecting corners between two ribs is advantageously 8 to 15mm for an internal diameter 2R of the barrel with grooves of 60 to 230mm in any plane perpendicular to the axis of the cylinder.

The depth of the groove is advantageously 2 to 10mm for an internal diameter 2R of the cartridge with the groove of 60 to 230mm in any plane perpendicular to the axis of the cylinder.

The grooves may be in the form of serrations or dovetails. Thus, each groove is advantageously trapezoidal, the larger base of the trapezoid forming the bottom of the groove, the sides of the trapezoid adjoining the larger base forming the side surfaces of the groove, and the height of the trapezoid being the depth of the groove.

In particular, the bottom of the groove is a circular arc C_RAnd the ratio C is calculated by formula (I).

D_intFIs the diameter of the inner surface in the barrel with grooves, or 2R

D_extRIs a circle C_RThe center of the circle being the axis of the hub.

The groove may be parallel to the axis of the barrel or helical, preferably helical.

Gear pumps are typically simple gear pumps comprising two gears that are side-by-side and meshed (and thus rotate in opposite directions). A stable filtration flow rate can be ensured although a pressure variation can be generated at the inlet of the filter. The gear pump is designed to pump wet condensate to raise the pressure of the wet condensate to be filtered through the filter and to apply the required pressure at the inlet of the filter that can be used in the present invention.

The implementation of the method using the apparatus described in the third variant is very advantageous for the following reasons:

it is possible to ensure that the filtration is carried out continuously without interrupting the process,

a pressure of more than 100 bar can be applied without negatively affecting the filtration flow rate,

the variation of the filtration pressure does not have a significant negative effect on the filtration flow rate,

high filtration flow rates, for example greater than 1 ton/hour,

it is possible to ensure that the filtration and dehydration functions are performed simultaneously, thus making it possible to save energy for the subsequent drying step.

These advantages are observed and no reduction in the viscosity of the natural rubber is observed.

Whether the variant is the second variant or the third variant, the filter installed at the extruder outlet is generally carried by a filter support.

The apparatus employed according to the second or third variant may also comprise one or more feed rollers located in the feed zone, typically in the feed hopper, as close as possible to the screw. The rollers may rotate at the same speed as the screw or at a different speed independent of the screw speed.

At the outlet of the device, i.e. after the filter, any device for obtaining the filtered natural rubber in the desired form (e.g. strips, flakes, sausage-like, rubber powder, etc.) can be provided.

Exemplary embodiments of the invention

III.1. a-Water content in the coagulum:

the water content was determined using a Mettler Toledo HB43-S halogen dryer. The dryer is an automated device comprising a crucible, a balance and a cover intended to close the crucible. The crucible is located on a balance. The lid comprises means for heating by means of a halogen lamp, which heating means are activated when the lid is lowered onto the crucible. In a crucible, a 10-gram sample of natural rubber was accurately weighed: the device records the corresponding weight "a". The lid was lowered to close the crucible, thus triggering a temperature rise until the set value of 160 ℃ was reached. When the device detects a weight reduction of less than 0.001g per minute, the device will read the weight "b". The water content in the sample is given in weight percent by the following equation:

water content (%) ═ 100 [ ((a-b)/a)

III.1.b viscosity of Natural rubber:

the viscosity of natural rubber is measured by measuring its mooney plasticity. The oscillating consistometer described in French Standard NF T43-005 (11 months 1980) was used. The Mooney plasticity measurement is carried out according to the following principle: the natural rubber was molded in a cylindrical chamber heated to 100 ℃. After 1 minute of preheating, the rotor was rotated at 2 revolutions per minute within the test specimen and the working torque for maintaining this movement was measured after 4 minutes and 8 revolutions. Mooney plasticity (ML 1+4) is expressed in "mooney units" (MU, 1MU ═ 0.83 newton. m).

III.2-the method is carried out in a device according to the third variant described above, i.e.such a device The device comprises a worm machine, a gear pump and a filter arranged at the outlet of the worm machine, wherein the gear pump is arranged at the end of a screw rod At the front of the filter:

single screw extruder:

-diameter of the screw (D): 60mm, constant hub diameter and constant pitch

-the length of the screw: 14D

The length of the smooth portion extends from the end of the feeding zone to the end of the barrel closest to the extruder outlet. The feed zone is grooved.

Gear pump:

176cm of discharge³Gear pump

A filter:

diameter of the filter: 168mm

-the mesh of the filter: 1 500 μm filter +2 filters of 2.5mm mesh

The extruder was supplied with wet coagulum subjected to a primary cleaning treatment (rubber crusher, wet pre-crusher), the moisture content of which is given in table 1. The pressure and temperature conditions at the inlet of the filter, and the flow rate and properties of the natural rubber measured at the outlet of the filter are shown in table 1. The speed of the extrusion screw was adjusted to properly feed the gear pump. The speed of the gear pump is adjusted to obtain the flow rate of the filtered natural rubber.

The viscosity of the filtered natural rubber was measured after drying with air at 120 ℃ for 4 hours in a dryer. To investigate the effect of filtration on the viscosity of the natural rubber, the viscosity of the filtered natural rubber was compared to the viscosity of the control. The control was unfiltered natural rubber, which had been dried under the same conditions. The mooney plasticity of the control was 82.

It can be noted that the filtration process according to the invention is not accompanied by a reduction in the viscosity of the natural rubber.

TABLE 1

It can be noted that the contaminants are well retained by the filter, the mesh of the filter is not damaged after filtration, and therefore the condensate obtained after filtration is properly purified. It is necessary to periodically change the filters of the device. This change can be done in a few seconds, i.e. without any significant interruption of the method.