GB2378184A

GB2378184A - Contactor for separating solvent from polymer crumb

Info

Publication number: GB2378184A
Application number: GB0217508A
Authority: GB
Inventors: Jean-Pierre Arzoumanian; Guy Andrew Cordonier; Philippe Ducos; Rombout Hartemink; Rong-Her Jean; Serge Latil; Chin-Yan George Ma
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 2001-07-31
Filing date: 2002-07-29
Publication date: 2003-02-05
Also published as: GB0217508D0

Abstract

A contactor 100 for separating solvent from a polymer crumb, comprises a first section 110 having concentrically disposed inner 118 and outer 116 nozzles, a second section 120 having between four and twenty injection ports 125, 127, and a third section 130 having a diverging cross-sectional area. The injections ports 125, 127 are preferably disposed at an angle between 20{ and 50{ from normal and may extend into the inner nozzle 118. The contactor is particularly suitable for separating multi-block conjugated diene copolymers from aromatic hydrocarbon solvents. There are independent claims for contactors having a specified number of injection ports at a specified angle to the normal.

Description

APPARATUS AND METHOD FOR FORMING POLYMER CRUMB BACKGROUND OF THE INVENTION This invention relates to an apparatus and method for removing a solvent from a polymer cement. More particularly, the invention relates to an efficient apparatus and method for devolatilizing polymer cement.

After solution polymerization of a monomer, the resulting polymer is often isolated from its solvent. A typical method for isolation of certain polymers, such as conjugated diene polymers and copolymers, utilizes a high shear mixer whereby the polymer solution or"cement"is combined with high-pressure steam in a mixing zone of a cylindrical tube. The temperature of the steam is above the maximum boiling point of the solvent and below the glass transition temperature of the polymer. The sheared mixture is then passed into a cyclone separation zone where the polymer is separated from the steam and the vaporized solvent.

One such process is described in U. S. Patent No. 3,804, 145. This patent teaches a high shear contactor having a central zone with an adjustable flow constrictor mounted therein. The cement is fed through an opening into a high shear, annular space formed by the constrictor within the central zone. The cement is contacted with steam in the annular space where the solvent begins to vaporize. The mixture of steam, vaporized solvent, and polymer then exit the open end of the contactor at near sonic speeds.

Another separation process is disclosed in U. S.

Patent No. 3,202, 647. This patent discloses a mixer

having a high shear portion whereby the steam and polymer cement are mixed together and injected into the bottom of a hot water vessel by a steam jet system. The steam jet system is generally in the configuration of a convergediverge shape such as the construction of a Penberthy steam ejector.

While the foregoing designs are adequate for separating polymer cements from solvent, the foregoing designs are not efficient in the use of steam. Steam consumption is a major expense in a commercial polymer finishing operation. To achieve sufficient solvent removal in a conventional contactor such as the foregoing designs, a steam to cement weight ratio of about 1.2 : 1.0 to 1.5 : 1.0 is required. In other words, for every pound of polymer cement treated in the prior art contactor, 1.2 to 1.5 Ibs of high pressure steam is consumed.

There is a need therefore, for an apparatus capable of separating a polymer from solvent while consuming less steam.

SUMMARY OF THE INVENTION The present invention provides an improved method and apparatus for separating polymer from solvent using high pressure steam. In one aspect, a contactor is provided comprising a first section having concentrically disposed inner and outer nozzles, a second section having between four and twenty equally disposed injection ports, and a third section having a diverging cross-sectional area.

The second section preferably comprises from twelve to twenty injection ports that extend into the inner nozzle and are angled from about 20 to about 50 degrees from normal. More preferably, the second section comprises about sixteen injection ports angled at about 30 to about 45 degrees from normal. The angled injection ports extend

into the inner nozzle so that the polymer cement and steam may intimately contact and mix. The preferred configurations provide significant and surprising improvements in efficiency by reducing steam to cement weight ratio below 1.0 : 1.0.

BRIEF DESCRIPTION OF THE DRAWINGS So that the manner in which the above recited features, advantages and objects of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings.

It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

Figure 1 is a section view of a contactor according to the present invention.

Figure 2 is a cross section view of the contactor of Figure 1 along lines 2-2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Figure 1 illustrates a contactor 100 according to a preferred embodiment of the present invention. The contactor 100 includes a first section 110, a second section 120, and a third section 130. The first section 110 includes an outer nozzle 116 concentrically disposed about an inner nozzle 118. The third section has a gradually increasing cross-sectional area that corresponds to an effective angle of divergence between about 4 degrees and about 70 degrees. In one aspect, a ratio of cross sectional areas of the third section to

the first section is between about 4: 1 to about 2: 1.

Preferably, the ratio of cross sectional areas of the third section to the first section is about 3: 1.

The second section 120 is an annular member and is disposed between the first 110 and third 130 sections.

The second section 120 includes between four to twenty injection ports 125 equally disposed about a diameter thereof. In one aspect, the second section 120 has twelve to twenty injection ports 125. Preferably, the second section 120 has about sixteen injection ports 125 equally disposed about the diameter of the second section, as is shown in Figure 2.

Referring to Figures 1 and 2, a first end 126 of the injection port 125 is substantially parallel with the first nozzle 116. A second end 127 of the injection port 125 is angled from normal, toward the flow direction of the second nozzle 118. In one aspect, the injection ports 125 are angled from about 20 to about 50 degrees from normal. More preferably, the injection ports 125 are angled'at about 30 to about 45 degrees from normal as shown in Figure 1.

The second section 120 further includes one or more recessed grooves 129 to house an elastomeric seal therein. The three sections 110,120, 130 are secured together using one or more fasteners (not shown), such as a bolt, for example, to provide a fluid tight connection there-between.

The contactor 100 is useable with any polymer/solvent cement system that can withstand the high temperature steam without decomposing or cross-linking. It is especially good with polyolefin/hydrocarbon cements, polyalkenyl aromatic polymers/inert solvent cements, polyconjugated diene polymer/hydrocarbon cements,

copolymers and block-polymers of conjugated diene and alkenyl aromatic hydrocarbons in inert solvents and the hydrogenated and partially hydrogentated derivatives of the above co-polymers and block polymers in inert solvents. The preferred cements are the two and multiblock alpha alkenyl aromatic hydrocarbon/conjugated diene polymers and selectively or totally hydrogenated derivatives of said block polymers preferably dissolved in hydrocarbon solvents having relatively low boiling points such as alkenes, alkanes, arenes, cycloalkenes, or cycloalkanes. These include for example, mixed pentenes, mixed pentanes, cyclohexane, toluene, and mixtures thereof, the only criterion being that the solvent employed in the apparatus and process of the invention have a maximum boiling point such that it is readily vaporized upon contact with steam of a given temperature.

The particularly preferred cements are the polystyrene/ polybutadiene, polystyrene/polyisoprene, polystyrene/ poly-butadiene/polystyrene, polystyrene/polyisoprene/ polystyrene block copolymers, or their hydrogenated or partially hydrogenated derivatives.

In operation, a polymer cement flows through the first nozzle 116, through the injection ports 125 into the contactor 100 where the polymer cement is contacted with steam flowing through the second nozzle 118. The temperature of the steam is between about 335 OF and about 550 F, preferably between about 365 OF and about 550 F, and more preferably between about 400 OF and 550 F. The pressure of the steam at the contactor is 45 psig to 450 psig, preferably 50 psig to 350 psig, and more preferably 50 psig to 200 psig.

The cement concentration may vary from about 5 percent polymer by weight to about 60 percent polymer

by weight. More preferred are cements which vary from about 5 percent polymer by weight to about 25 percent polymer by weight. Particularly preferred are cement concentrations from about 10 percent polymer by weight to about 20 percent polymer by weight. The pressure drop across the injection ports 125 is preferably designed to be in a range from about 10 psi to about 150 psi to control the ratio of steam and polymer cement.

Within the second section 120 of the contactor 100, the steam and cement are mixed and intimately contacted at the point of injection which occurs at the second end 127 of the injection ports 125. As the cement and steam are mixed, solvent droplets begin to form due to the shearing effect from the steam velocity. A near vacuum, or close to atmospheric pressure, is created by pressure differential due to the sudden enlargement of volume within the third section 130. This sudden pressure drop results in a rapid de-volatilization of the solvent, and a sufficient separation of the flashing solvent from the polymer crumb.

A cement to steam ratio passing through the contactor apparatus determines the size of the polymer particles.

The higher the steam to cement ratio, the smaller the particle size. However, the ratio is often limited by economics and the ability of the down-stream processing equipment to remove the solvent vapour and steam. Using the contactor 100 described above, acceptable particle sizes have unexpectedly and surprisingly been achieved at steam/cement ratios from about 0.8 : 1.0 to about 1.0 : 1.0.

This is a surprising improvement over conventional contactors which typically consume between about 1.2 to 1.5 pounds of steam for every pound of polymer. It is believed that the injection ports 125 being spaced about

the cross section of the steam nozzle 118 in addition to the angle of the injection ports 125 in the direction of the steam flow, provide better contact and mixing which significantly reduces the amount of steam consumption.

The following examples are used to illustrate the advantages of the present invention. The polymer cements included of cyclohexane and about 16.5 percent by weight of a polystyrene hydrogenated polybutadiene-polystyrene block copolymer having a number average molecular weight between about 100,000 and about 300,000 and a polystyrene content of about 30%. The steam had a pressure of 60 psig at a temperature of 515 F.

COMPARATIVE EXAMPLE 1 A polymer cement and steam were run through a contactor having eight injection ports angled 45 degrees from normal. A steam to cement ratio of 1.5 : 1 was used to produce a polymer crumb consisting of small particles having good smoothness and a low frequency of fines/ fisheyes. The polymer crumb had an oil adsorption rate of 58.7% and a bulk density of 0.2 g/cc.

EXAMPLE 1 A polymer cement and steam were run through a contactor having sixteen injection ports 125 angled 30 degrees from normal. A steam to cement ratio of 1: 1 was used to produce a polymer crumb consisting of small particles having good smoothness and a low frequency of fines/fisheyes. The polymer crumb had an oil adsorption rate of 56.7% and a bulk density of 0.185 g/cc.

EXAMPLE 2 A polymer cement and steam were run through a contactor having sixteen injection ports 125 angled 30 degrees from normal. A steam to cement ratio of 0.8 : 1 was used to produce a polymer crumb consisting of small

particles having good smoothness and a low frequency of L fines/fisheyes. The polymer crumb had an oil adsorption rate of 55.2% and a bulk density of 0.17 g/cc.

As shown, polymer crumbs produced by the contactor having sixteen injection ports 125 angled 30 degrees (examples 1 and 2) had similar particle size distributions, porosity, and oil adsorption rates compared with the polymer crumb produced using a contactor having eight injection ports angled 45 degrees (comparative example 1). However, the polymer crumb of examples 1 and 2 were produced using surprisingly and unexpectedly less steam. In fact, about 50% less steam was consumed to produce a substantially similar polymer crumb.

While foregoing is directed to the preferred embodiment of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

C L A I M S 1. A contactor for separating solvent from a polymer crumb, comprising: a first section having concentrically disposed inner and outer nozzles; a second section having between four and twenty injection ports; and a third section having a diverging cross-sectional area.
2. The contactor of claim 1, wherein the second section comprises between twelve and twenty injection ports.
3. The contactor of claim 1, wherein the injection ports are disposed at an angle between about 20 degrees and about 50 degrees from normal.
4. The contactor of claim 1, wherein the second section comprises about sixteen injection ports angled about 30 to about 45 degrees from normal.
5. The contactor of claim 1, wherein the injection ports extend into the inner nozzle.
6. The contactor of claim 5, wherein the polymer cement is a multi-block copolymer comprising an aromatic hydrocarbon and a conjugated diene.
7. The contactor of claim 1, wherein a ratio of crosssectional areas of the first section to the third section ranges from about 1: 2 to about 1: 5.
8. The contactor of claim 1, wherein the third section diverges from the horizontal at an angle of about 4 to about 70 degrees.

<Desc/Clms Page number 10>
9 The contactor of claim 1, wherein the second section comprises about sixteen injection ports angled about 30 degrees from normal.
10. A contactor for separating solvent from a polymer crumb, comprising: a first section having concentrically disposed inner and outer nozzles; a second section having between twelve and twenty injection ports angled about 20 to about 50 degrees from normal; and a third section having a diverging cross-sectional area.
11. The contactor of claim 10, wherein the second section comprises about sixteen injection ports angled about 30 to about 45 degrees from normal.
12. The contactor of claim 10, wherein the second section comprises about sixteen injection ports angled about 30 degrees from normal.
13. A contactor for separating solvent from a polymer crumb,'comprising : a first section having concentrically disposed inner and outer nozzles; a second section having a plurality of injection ports angled about 20 to about 50 degrees from normal; and a third section having a diverging cross-sectional area.
14. The contactor of claim 13, wherein the second section comprises about sixteen injection ports.
15. The contactor of claim 13, wherein the injection ports are disposed at an angle of about 30 to about 45 degrees from normal.

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16. The contactor of claim 11, wherein the second section comprises about sixteen injection ports angled about 30 degrees from normal.
17. A contactor for separating solvent from a polymer crumb, comprising: a first section having concentrically disposed inner and outer nozzles; a second section having about sixteen injection ports angled about 30 to about 45 degrees from normal, wherein the injection ports protrude into the inner nozzle; and a third section having a diverging cross-sectional area.
18. The contactor of claim 17, wherein the second section comprises about sixteen injection ports angled about 30 degrees from normal.