JPS5855965B2 - Polypropylene resin - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel method for recovering pure soluble polypropylene from a dilute solution in a spent polymerization medium, and more particularly to a novel method for recovering pure soluble polypropylene in a flowable form comprising the following steps: (1) partial steam stripping of the volatile components of the spent organic polymerization medium to produce an aqueous phase from the condensed steam and a concentrated water-insoluble organic phase containing soluble polypropylene; (2) separating the water-insoluble test phase from the aqueous phase and introducing the phase to an evaporator; and (3) evaporating volatile components from the separated water-insoluble test phase, A process that leaves behind a fluidized polypropylene that is later removed and converted into a solidified and commercially useful form.

In accordance with the present invention, soluble polypropylene is continuously recovered from a dilute solution of spent organic polymerization medium containing a polymerization diluent, soluble polypropylene, a small amount of a kill substance such as methanol, and entrained crystalline polypropylene. A method is disclosed.

Thereby, the relatively low concentration of soluble polypropylene in the spent polymerization medium is concentrated by partial steam stripping, and an aqueous phase from the condensed steam and a water-insoluble test phase (this phase consists of the remaining spent polymerization medium) are concentrated by partial steam stripping. A concentrated polypropylene solution is formed.

The amorphous concentrate is then transferred to a melt evaporator to remove residual volatile components, leaving a fluidized polypropylene that is removed and solidified.

Conventional processes for producing polypropylene typically involve stereospecific polymerization of propylene monomers in the presence of coordination complexes of transition metal olides and aluminum alkyl compounds or similar organometallic compounds.

The product obtained from this reaction is a slurry containing polypropylene and catalyst in a hydrocarbon diluent.

A low molecular weight alcohol is usually added to the slurry to quench the reaction and solubilize the catalyst in a process often referred to as the kill step.

The amorphous low molecular weight polypropylene remains in solution in the diluent as a by-product.

Subsequent steps of the process typically include recovery of the crystalline polypropylene, neutralization of the active catalyst, and recovery of a solution (spent polymerization medium) containing some alcohol and hydrocarbon diluent.

The crystalline polypropylene is usually recovered as a high purity polymer suitable for a wide range of applications such as coating, casting, and molding.

The soluble polypropylene can be recovered from the spent polymerization medium as an odorless, off-white, viscous thermoplastic after undergoing some purification treatment.

This material, which once had no commercial value, is now used as a formulation agent in hot melt adhesives.

Existing methods for separating soluble polypropylene, such as U.S. Pat. Nos. 3,296,240 and 3,437
The process described in No. 645 includes partial steam stripping of the spent polymerization medium at elevated temperatures.

Surfactants are often used to aid in the production of insoluble clamps.

This solid clamp can then be removed from the top of the liquid and discarded, or it can be further purified to be of commercial value.

However, this clamp entrains 5 to 10% polymerization medium and often large amounts of water, making it unsuitable for applications requiring medium-free polymer.

Additionally, this method wastes polymerization media and the large amount of water used is contaminated with relatively high levels of suspended solids, surfactants, polymerization media, and other organic components that can be treated with conventional wastewater reclamation methods. difficult to do.

In short, existing methods are difficult and wasteful, and generate unacceptably large amounts of contaminated wastewater in recovering amorphous polypropylene of low purity.

U.S. Pat.
No. 755484.

The process includes the steps of substantially completely stripping the light ends from the wax to form a wax layer above the aqueous layer, transferring the wax layer to another container, and gas drying the transferred product. .

In accordance with the present invention, a process has now been found in which relatively pure soluble polypropylene can be recycled in an economical manner.

This method greatly reduces problems with contaminated wastewater and loss of polymerization diluent.

FIG. 1 shows one embodiment of the method of the invention.

In this process, partial steam stripping is carried out in the first step using two steam strippers, each with a stirring device; separation, settling and decantation are carried out in a second vessel (decanter). .

Soluble polypropylene (amorphous concentrate) in second container
Aqueous and organic phases containing are pumped from the first step.

The amorphous concentrate is pumped into the third vessel (melt evaporator) and then evaporated at a temperature high enough to produce a fluidized polypropylene that can be easily transported.

The first step of the process, the feed to the steam stripper, is a dilute solution of polypropylene, ie, the spent polymerization medium resulting from the commercial production of polypropylene.

It consists primarily of used polymeric diluent, such as hexane.

However, other polymeric diluents such as alkanes, cycloalkanes, etc. other than those mentioned above can also be treated with the method of the present invention.

Generally, the feed to this step may contain small amounts of materials such as methanol, water and entrained crystalline polypropylene in addition to the polymerization diluent and soluble polypropylene.

The amount of soluble polypropylene included in the feedstock is generally less than about 10% by weight, and usually less than about 5% by weight.

Typically about 1 to about 3% by weight polypropylene is included.

The soluble polypropylene has an Mn greater than 5000.

For steam strippers, steam is supplied at a convenient temperature and at a rate set to bring the stripper temperature to the desired temperature.

As long as some water is present in the stripper, the pressure of the steam can be any value convenient for the temperature of the steam used.

The amount of steam used will vary depending on the rate of formation of the amorphous concentrate sent to the decantation step and the feed rate of the feedstock, as will be readily understood by those skilled in the art.

Agitation is generally achieved by agitation, which is desirable in carrying out the partial steam stripping process because it allows for better contact between the feedstock and the steam and keeps the two phases well mixed. That's true.

The concentration of polypropylene dissolved in the organic phase (amorphous concentrate) will vary depending on the temperature and pressure used in the steam stripper.

Generally, the concentration is determined by the ease with which the amorphous concentrate can be transferred between the decantation step and the melt concentrator step, and by the efficiency and size of the equipment used in the concentrator step. The minimum value is determined by

This temperature is preferably at a concentration of about 10 to about 70% by weight polypropylene in the organic phase.

More preferred concentrations are from about 30% to about 60% by weight, and most preferred concentrations from about 40 to about 55% by weight.

When hexane is used as a polymerization diluent, for example under 18.5 p, s, i, g, and 220, 6
A 5% by weight amorphous concentrate is formed.

A 20% by weight concentrate is formed at 195'F using the same pressure.

5.5 p, s, i, g, and 7 under 190
A 2% by weight concentrate is formed and at the same pressure under 165 a 30% by weight concentrate is formed.

5.5 p, s, i, g, in stripper about 5
To obtain 0% by weight hexane amorphous concentrate, 17
12. A temperature of 0T is required; Op, s, i,
g.

At 190'F a 50% by weight concentrate is formed;
5, Op, s, i, g, 50% by weight under 195
A concentrate of 18.5 p, s, iog, is formed;
At 205'F a 50% by weight concentrate is formed.

If too low a temperature is used, the weight percent of polypropylene will be too small to reach the optimum concentration.

If the temperature is raised too high, the pressure required to maintain the desired weight percent of amorphous concentrate may be undesirably high.

In a preferred example, the stripper temperature varies from about 160 below to about 250 below, and the stripper pressure varies from about 4 to about 2
It can vary between 5p, s, i, g.

In a more preferred example, the stripper temperature is about 170 below
The pressure varies between about 210 and below, and the pressure is about 5 to about 20 p, s,
In the most preferred example, the stripper temperature range is from about 175'P to about 195 P, and the pressure range is from about 7 to about 15 P,S,I,G.

As an illustration of how the viscosity of amorphous concentrates is affected by temperature and polypropylene concentration, the experimental results shown in the table below may be helpful.

In choosing the concentration of the amorphous concentrate, it is important that the viscosity is not too high.

This is because the transfer between processes, which is normally done by a pump,
This is because it becomes increasingly difficult as the viscosity increases.

For the particular Mn value of the soluble polypropylene treated by the method of the present invention, concentrations above about 70% by weight in the amorphous concentrate are not useful.

As those skilled in the art will appreciate, the number of strippers used will vary depending on the requirements of the process.

A stirred mixture consisting of an aqueous phase and an amorphous concentrate is
It is then separated to remove the amorphous concentrate, which is further processed.

The two layers can be separated by centrifugation, decantation, etc., but decantation is preferred.

In one preferred decantation embodiment, the amorphous concentrate is decanted at a rate that varies depending on the process requirements and equipment size as can be understood by those skilled in the art.
will be transferred to.

In the decanter, the amorphous concentrate forms a top layer on top of the denser aqueous phase.

This aqueous layer is removed and either discarded or cleaned and returned to the steam stripper.

In a decanter, the layer of amorphous concentrate is agitated just above the interface, generally by gentle agitation, to form a slurry of entrained crystalline polypropylene, which is always present in small amounts. A continuous dispersion is obtained.

Without agitation, this small amount of crystalline polypropylene tends to settle and collect at the interface and can cause fouling problems.

By comparing suspended solids and methanol to C0D (Chemical Oxygen Demand), the aqueous phase recovered from the decanter was found to be purer than the water removed by a typical lamping operation.

This may confer substantial economic and environmental benefits to the process of the invention.

The temperature of the decanter is preferably maintained at about the average temperature of the stripper to prevent the concentration of the amorphous concentrate from increasing further.

The pressure in the decanter is preferably the same as or slightly higher than that in the stripper.

The average temperature of the decanter is preferably no more than 2 below the average temperature at which the stripper operates, the average decanter pressure is at least as high as the pressure employed in the stripper, and the average decanter pressure is at least as high as the pressure employed in the stripper. Advantageously, the pressure does not exceed about twice the pressure.

The pressure within the decanter can be set by a pressure controller attached to the pressure tank to smooth pressure fluctuations by adding a relatively inert gas such as nitrogen.

It is also possible to use compressed air for this purpose, but the results are inferior to those described above.

The temperature of the decanter is maintained by supplying heat, for example using a steam coil.

The amorphous concentrate, which generally contains small amounts of entrained crystalline polypropylene, is transferred from the top layer of the decanter to the melt evaporator.

This melt evaporator is an evaporator whose surface is covered with a thin film.

The LUWA thin layer surface-coated evaporator manufactured by LUWA (Charlotte, N.C.) is preferred.

Other types of evaporators can also be used.

The remaining volatile components are removed as overhead in a melt evaporator, and the resulting relatively pure polypropylene is fluidized.

The temperature of the melt evaporator is such that the fluidized polypropylene is preferably about 300 T to about 475 T, more preferably about 325 T to about 425 T, most preferably about 3
It is adjusted to have a temperature ranging from 25T to below about 375T.

Melt evaporators are generally operated at pressures substantially above atmospheric pressure.

The fluidized polypropylene goes to the bottom of the evaporator, where it is conveniently collected by a tart pump, sent to storage, solidified, and converted into a commercially available form.

The temperature at which the melt evaporator is operated depends in part on the melt flow rate of the crystalline polypropylene produced in the process from which the feed originates.

This is because the viscosity range of the soluble polymer within the melt evaporator is influenced thereby.

For example, if the melt flow rate of the crystalline product produced is 1
If it is 0 to 15, the temperature of the melt evaporator can be set to the lower limit of the above range, and if the melt flow rate of the crystalline polypropylene to be produced is 1 to 2,
The temperature of the melt evaporator must be very high so that the liquefied polypropylene can be easily removed.

The melt evaporator temperature also varies somewhat depending on the amount of crystalline polypropylene entrained into the amorphous concentrate, since the presence of crystalline polymer increases the viscosity of the fluidized polypropylene.

The operating temperature of a melt evaporator for a given stripper feed will be apparent to those skilled in the art.

It is advantageous for the dispersion of the polypropylene product to add stabilizers and other additives to either the decanter or the melt evaporator, preferably the evaporator.

The amounts and types of such materials are well known to those skilled in the art.

One of the advantages of the method disclosed herein is that it is easily interconvertible to standard clamping operations.

In such a manner, decanters and melt evaporators are not employed, and the stripper is operated at the same temperatures, but at lower pressures, as commonly used in the processes described herein.

A further modification required when conducting normal crumbling operations is to use surfactants of the type commonly used in stripper crumbling processes and operations in a manner that facilitates removal of the clamps from the water. That's true.

As illustrated in the accompanying drawings, the method of the invention is carried out as follows.

The spent polymerization medium enters via path 1 and is split here into two streams, one being fed via path 3 to the first stripper 7 and the other being fed via path 5 to the stripper 27.

The steam passes through paths 4 and 28, respectively, to the stripper 7.
and enter 27.

Overhead from strippers 7 and 27 exits the stripper via paths 15 and 35 to heat exchanger 17.
and 37, which it then passes through via paths 19 and 39, respectively, to condenser drums 21 and 41.

Uncondensed material is removed from the condenser drums 21 and 41 via paths 23 and 43, and can be returned to the strippers 7 and 27 or disposed of.

The organic portion of the condensate is discharged via paths 25 and 45, and is preferably subjected to cleanup and recovery of polymeric diluent.

Strippers 7 and 27 are stirred by star twos 8 and 28.

The mixture of aqueous phase and amorphous concentrate leaves the strippers 7 and 27 via paths 9 and 29 and is passed by pumps 11 and 31 via paths 13 and 33 to the decanter 47.
sent to.

Separation of the two layers takes place in a decanter 47, the lower aqueous phase being removed to the outside via line 49 and either disposed of or returned to the strippers 7 and 27 after purification.

The decanter 47 is gently stirred by the star two 48.

This star two wing is positioned just above the interface between the aqueous layer and the amorphous concentrate.

Supplemental heating of the decanter 47 is provided through path 46 and is provided through path 5.
This is done by a heat transfer liquid that exits from 0.

The decanter pressure is in line 4 connected to the nitrogen source.
Controlled by a pressure setting valve in 4.

The amorphous concentrate is transferred from the top of decanter 47 through line 51 to melt evaporator 53 by pump 52.

Additives in molten form or dissolved in a small amount of diluent can be passed from path 57 into the feed to melt evaporator 53 or via path 55 directly into evaporator 53 or via both paths into the evaporator. can.

The overhead is removed from the melt evaporator 53 via path 59 and connected to an overhead condenser 61.
sent to.

The condensate from the overhead condenser 61 is sent to a condensation drum 67 where, after settling, the organic portion is discharged via a path 71, talinned and returned to the polymerization process.

The water collected in condensation drum 67 is drained through path 69 and either disposed of or sent to strippers 7 and 27.
be returned to.

The molten polypropylene falls to the bottom of melt evaporator 53 and is discharged via line 73 into surge pot 75 and then via line 77 to melt pump 79 for subsequent solidification and storage.

Although the invention will be described in connection with specific embodiments below,
It will be understood that it is for illustrative purposes only.

It will be readily apparent that many substitutions, modifications, and changes can be made to the following embodiments, and methods with such substitutions, changes, and modifications also fall within the technical scope of the present invention. It is.

Example 2.0-2.8% by weight soluble polypropylene, 0.0
A spent hexane-polymerization medium containing less than 6% by weight crystalline polypropylene, about 50 PPm water and 0.28-0.074% methanol was used as feedstock.

The working pressure of the steam stripper is 11.5 p, s,
i, g, and the operating temperature was set to 185'F.

Pressure was controlled via a backpressure controller regulating an air-to-open research control valve.

Due to the on/off operation of the steam sparge, the pressure is approximately 11.
It varied within the range of 0 to 12.5 p, s, i, g.

Vigorous agitation within the stripper was provided by an air motor and two four-blade turbines mounted on the shaft.

The temperature within the stopper was regulated through a temperature controller that activated an off-on solenoid in the steam introduction path.

During normal operation, temperature fluctuations are approximately ±
It was 2 below.

Spent media was continuously fed to the stripper.

Stripper concentrates, hexane, methanol and water, were removed continuously overhead.

When condensed, it contained approximately 6% by volume of water and 94% by volume of hexane.

The liquid contents of the stripper were removed and sent to a decanter.

The decanter was operated at the same temperature as the stripper.

A minimum pressure equal to that required in the stripper was provided by the pressure regulated nitrogen path to prevent additional losses.

A temperature regulated on-on solenoid regulated the heat input of the steam coil contained within the decanter.

Slight stirring of the amorphous concentrate (top layer) at the phase interface resulted in a continuous dispersion in which a small amount of crystalline polypropylene was always present.

Without stirring, this crystalline material tends to stagnate and collect at the interface.

The amorphous concentrate in the top layer varied in polypropylene concentration from about 39.5 to 55.6% by weight, with less than 1% entrained.

The remaining material was primarily hexane and a small amount of methanol.

Analysis of the aqueous phase discharged from the decanter, ie, the bottom layer, was found to contain 20-193 PPm of suspended solids, about 220-1900 PPm methanol, and a COD of about 630-2400.

The amorphous concentrate, the top layer, is transferred to the melt evaporator through four suction ports operated at ambient pressure.

These inlets are two-stage conical inlets through which heated Therminol (heat transfer fluid) is pumped.
It is located just above the flushing coil.

The surface temperature of the lower coil was maintained at approximately 420'F'' and the upper coil directly below the inlet was maintained at approximately 360'F''.

Additional heat was added to the bottom of the melt evaporator to keep the polypropylene pool below about 425°C.

The overhead from the evaporator was hexane and water with a small amount of methanol.

When condensed, it typically consisted of about 96-98% by volume hexane and 2-4% by volume water.

In most cases, the solidified polypropylene analyzed less than 1% by weight hexane, less than 0.03% by weight water, and did not contain appreciable amounts of methanol.

The table on the next page shows the viscosity range at 375'F of recovered polypropylene made by the process of this example as a function of the MFH of the crystalline product made in the step from which the feedstock was withdrawn. .

[Brief explanation of the drawing]

FIG. 1 shows a process diagram of a preferred embodiment of the continuous recovery of soluble polypropylene from spent polymerization medium according to the method of the present invention. Explanations of symbols are provided in the text of the specification.

Claims (1)

[Scope of Claims] 1. (a) Steam stripping of the spent polymerization medium, (a) an aqueous phase obtained from the condensed steam, and (b) about 10 to about 70% by weight of soluble polypropylene being polymerized. (b) separating the amorphous concentrate from the aqueous phase; (c) removing volatile materials remaining from the amorphous concentrate; A process for the continuous recovery of soluble polypropylene from spent polymerization media, comprising the steps of: removing substantially all of the soluble polypropylene from the spent polymerization medium, leaving a readily transportable fluid polypropylene.