Patent Description:
Industrially important hydrofluorocarbons, such as those used as refrigerants and blowing agents, are prepared from hydrochlorocarbon feedstocks. For example, <NUM>,<NUM>,<NUM>,<NUM>,<NUM>-pentafluoropropane (HFC-245fa) is a widely employed hydrofluorocarbon that, according to <CIT>, can be prepared from a <NUM>,<NUM>,<NUM>,<NUM>,<NUM>-pentachloropropane (HCC-240fa) feedstock.

According to <CIT>, the <NUM>,<NUM>,<NUM>,<NUM>,<NUM>-pentachloropropane can be synthesized by reacting carbon tetrachloride with vinyl chloride in the presence of an iron catalyst and tributylphosphate. Vinyl chloride is fed to the reactor as a liquid or vapor, and metallic iron, preferably in the form of a slurry within carbon tetrachloride, is added to the reactor. The reactor contents are continually drawn from the reactor, preferably through a sedimentation tube, in order to maintain the unconverted metallic iron within the reactor. This process is enhanced by drawing the reactor effluent from a still zone created within the reactor. The reactor effluent is distilled to recover catalyst and ultimately isolate the desired <NUM>,<NUM>,<NUM>,<NUM>,<NUM>-pentachloropropane product. <CIT> suggests that the formation of polyvinyl chloride within the reactor can be reduced by feeding the vinyl chloride as a vapor through a dip tube or sponge-type gas diffuser into a reactor precharged with carbon tetrachloride, tributylphosphate, and iron powder.

Hydrofluoroolefins have been targeted as replacements for hydrofluorocarbons. For example, <NUM>,<NUM>,<NUM>,<NUM>-tetrafluoropropene (HFO-1234yf) has been proposed as a replacement for <NUM>,<NUM>,<NUM>,<NUM>-tetrafluoroethane (R-134a) as a refrigerant in automobile air conditioners. As with the hydrofluorocarbons, chlorinated organics play an important role in the synthesis of hydrofluoroolefins. For example, <CIT>and <CIT>teach that <NUM>,<NUM>,<NUM>,<NUM>-tetrachloropropene (HCC-1230xa) is an advantageous starting molecule for the production of <NUM>,<NUM>,<NUM>,<NUM>-tetrafluoropropane (HFO-1234yf).

<CIT>teaches that <NUM>,<NUM>,<NUM>,<NUM>-tetrachloropropene (HCC-1230xa) can be prepared by dehydrochlorinating <NUM>,<NUM>,<NUM>,<NUM>,<NUM>-pentachloropropane, and that the <NUM>,<NUM>,<NUM>,<NUM>,<NUM>-pentachloropropane can be prepared within a single reactor by reacting <NUM>,<NUM>,<NUM>,<NUM>-tetrachloropropane (HCC-250fb) with chlorine in the presence of a Lewis acid. According to <CIT>, <NUM>,<NUM>,<NUM>,<NUM>-tetrachloropropane can be synthesized by reacting carbon tetrachloride with ethylene in the presence of metallic iron, dissolved iron (II), iron (III) compounds, and an organophosphate cocatalyst. <CIT> teaches that the reactor in which the carbon tetrachloride and ethylene are reacted is agitated to provide adequate contact of the liquid reactants with the surface of the metallic iron, to provide adequate contact of the liquid reactants with the vapor in the reactor headspace so that ethylene is readily dissolved in the liquid, and to provide adequate contact of the reaction mixture with heat-transfer surfaces to thereby enable adequate temperature control.

Because <NUM>,<NUM>,<NUM>,<NUM>-tetrachloropropane is an important halogenated propane, there remains a desire to improve synthetic techniques employed in its preparation.

The present invention provides a process for preparing chlorinated propanes according to claim <NUM> or claim <NUM>. A further embodiment is disclosed in the dependent claim.

Embodiments of the invention are based, at least in part, on the discovery of a method for producing chlorinated propanes. According to one embodiment, chlorinated propanes are prepared by reacting carbon tetrachloride with an olefin (e.g. ethylene) in the presence of an iron-based catalyst, and the chlorinated propanes are removed from the reaction zone through a conically-shaped effluent nozzle drawing from a still zone created within the reactor. In one or more embodiments, the still zone is configured to minimize liquid flow velocity and thereby maximize iron sedimentation while allowing gaseous reactants to rise to the reactor headspace. Thus, while the prior art suggests advantages associated with withdrawing reactor fluid from a still zone, it is now contemplated that specific reactor designs can give rise to process efficiencies.

As suggested above, the processes of the invention generally relate to the preparation of chlorinated hydrocarbons by reacting carbon tetrachloride with an olefin. These reactions are generally known in the art, and disclosed in <CIT> and <CIT> and <CIT>. Practice of embodiments of the invention are not necessarily limited by the olefin employed as a reactant, although common olefins for use in these reactions include ethylene and vinyl chloride. As the skilled person appreciates, ethylene is a gaseous olefin, and therefore embodiments of the invention may provide distinct advantages where ethylene is employed as a reactant. Other embodiments may be particularly beneficial where vinyl chloride is employed as a reactant. In any event, the following embodiments may be described with reference to a particular olefin (e.g. ethylene), although the skilled person will appreciate that other olefins can likewise be used. Also, the reaction between carbon tetrachloride and an olefin can be catalyzed by using a variety of catalytic species, many of which are or derive from species that are insoluble or only partially soluble in the reaction medium. A common catalyst or catalyst precursor is iron, and therefore embodiments of the invention may be described with reference to iron, but the skilled person will appreciate that embodiments of the invention can likewise be extended to other insoluble or partially soluble catalysts or catalyst precursors. Additionally, the skilled person appreciates that these insoluble or partially soluble catalysts may be used in conjunction with cocatalysts or ligands, which are believed to complement the catalyst; for example, tributylphosphate has been used in conjunction with an iron catalyst. Thus, while embodiments of the invention may be described with reference to tributylphosphate as a cocatalyst or ligand used in conjunction with iron, the skilled person will appreciate that the invention can be extended to the use of other cocatalysts or ligands.

One or more processes can be described with reference to <FIG>. As shown, system <NUM> includes iron slurry mix tank <NUM>, which is in fluid communication with reactor <NUM> (which may be referred to as addition reactor <NUM>) through a conduit loop <NUM>. Slurry tank <NUM> receives carbon tetrachloride <NUM> through inlet <NUM> and iron powder <NUM> through inlet <NUM>. Slurry tank <NUM> may also optionally receive other materials <NUM>, such as additional solvents, catalysts, catalyst ligands, or recycle streams captured downstream in the process, through inlet <NUM>. Carbon tetrachloride <NUM> may be fed continuously, or it may be periodically injected, into slurry tank <NUM> through inlet <NUM>. Likewise, iron powder <NUM> may be periodically added to slurry tank <NUM>, or, iron powder <NUM> may be continuously charged to slurry tank <NUM> by employing continuous feeding apparatus. For example, iron powder <NUM> can be charged to slurry tank <NUM> by employing a dustless bucket tipper.

A slurry <NUM> of carbon tetrachloride <NUM> and iron powder <NUM> is formed by agitating the mixture within slurry tank <NUM> via one or more mixing elements <NUM>, which may include agitation devices or baffles. Mixing elements <NUM> may be operated in a manner to substantially disperse the catalyst (e.g. iron) within the chlorinated hydrocarbon liquid (e.g. carbon tetrachloride); agitation is sufficient to achieve a substantially homogenous concentration of the catalyst within the carbon tetrachloride.

Slurry <NUM> is continuously circulated through a conduit loop <NUM> via one or more pumps <NUM> that are upstream of reactor <NUM>, which pumps may also advantageously maintain pressure within loop <NUM>. Adequate pressure may also be maintained within loop <NUM> through the assistance of a back-pressure valve <NUM>, which is downstream of where loop <NUM> delivers slurry <NUM> to reactor <NUM> (i.e. downstream of valve <NUM> within loop <NUM>). Slurry <NUM> moving through loop <NUM> may be heated or cooled by heating or cooling elements <NUM>. Other materials <NUM>, such as those described above, may also optionally be injected into loop <NUM>. Mixing of the various constituents within slurry <NUM> can be enhanced by one or more in-line mixers, which are not shown. Circulation loop <NUM> also includes valve <NUM> that, when in the open position, allows slurry <NUM> to feed reactor <NUM>. When valve <NUM> is in its closed position, slurry <NUM> circulates through loop <NUM> back to mix tank <NUM>. Valve <NUM> may include a control valve or solenoid valve that can be controlled by a signal flow sensor or similar device.

Reactor <NUM> receives slurry <NUM> from loop <NUM> via inlet <NUM>. Reactor <NUM> also receives olefin <NUM>, such as ethylene, via inlet <NUM>. Additionally, and as will be explained in greater detail below, reactor <NUM> may also optionally receive other material inputs <NUM>, such as those described above, via additional inlet <NUM>. Reactor effluent <NUM> exits reactor <NUM> at outlet <NUM>. Volatiles can be vented through outlet <NUM>.

The flow of slurry <NUM> into reactor <NUM>, which flow is at least partially regulated by valve <NUM>, can be proportional to the olefin <NUM> feed rate into reactor <NUM>.

Loop <NUM> can be maintained at a pressure that is greater than the pressure within reactor <NUM>;the pressure within loop <NUM> may be sufficient to create flow into reactor <NUM> (when valve <NUM> is open) while taking into account potential gravitational assistance. As the skilled person will appreciate, sufficient pressure can be maintained within loop <NUM> while valve <NUM> provides flow into reactor <NUM> by back-pressure valve <NUM>. Valve <NUM> may include a control valve or solenoid valve that can be controlled by a signal flow sensor or similar device. Temperature controls (e.g. element <NUM>) may provide cooling to maintain the temperature of slurry <NUM> below the boiling point of the chlorinated hydrocarbon (e.g. below <NUM> for carbon tetrachloride). The loop temperature may be maintained at from about <NUM> to about <NUM>, from about <NUM> to about <NUM>, and from about <NUM> to about <NUM>.

The concentration of iron powder <NUM> within slurry <NUM> may be represented as a percent solids within the weight of liquid. In one or more embodiments, the percent solids iron powder within slurry <NUM> may be from about <NUM> to about <NUM> wt %, from about <NUM> to about <NUM> wt %, and from about <NUM> to about <NUM> wt %.

As indicated above, carbon tetrachloride reacts with olefin, such as ethylene, in the presence of a catalytic species, such as iron powder or derivatives thereof, to produce a chlorinated propane within reactor <NUM>. In particular, carbon tetrachloride reacts with ethylene to produce <NUM>,<NUM>,<NUM>,<NUM>-tetrachloropropane. In this regard, <CIT> and <CIT>are mentioned.

Reactor <NUM> can be further described with reference to <FIG>, which shows slurry <NUM> entering reactor <NUM> at inlet <NUM>, as well as olefin <NUM> (e.g. ethylene) entering at inlet <NUM>, and other optional materials, such as tributylphosphate ligand <NUM> and catalyst recycle stream <NUM>, entering via inlet <NUM>. The contents of the reactor form a liquid level <NUM>, which is the liquid level upon aeration, and the skilled person will appreciate that the liquid level will be lower when still (i.e. not aerated). Reactor <NUM> may generally include a tank reactor of the type known in the art (e.g. a CSTR).

The charging of slurry <NUM>, olefin <NUM>, and other materials <NUM>, <NUM>, may take place by injecting the materials below the liquid level <NUM> within reactor <NUM>. As the skilled person will appreciate, this may take place by the use of dip tubes, as well as various nozzles or diffusion devices. Olefin <NUM> may be injected at a location proximate to the bottom end <NUM> of reactor <NUM>. Olefin <NUM> may be injected at or near mixing elements <NUM> of mixing device <NUM>. One or more of the reactants or catalysts may be injected above liquid level <NUM> (i.e. within the reactor head space); advantageously, the use of an aspirating agitator allows for the introduction of gaseous materials into the head space since the agitator will ultimately deliver the gaseous materials to the reaction zone. As indicated above, reactor effluent <NUM> exits reactor <NUM> via outlet <NUM>.

Agitation device <NUM> may include a conduit that provides gaseous communication between headspace <NUM> and liquid mixture (i.e. slurry <NUM>) below the liquid level <NUM>. As a result, volatile compounds, especially ethylene, within the headspace can be returned to liquid mixture <NUM> to facilitate the desired reaction. Agitation device <NUM> may be an aspirating agitator. As the skilled person appreciates, these agitators draw gaseous materials (e.g. ethylene) from the head space and reintroduce the gaseous materials into the reaction zone (i.e. into liquid mixture <NUM>). Agitation device <NUM> may be operated at a power to volume ratio of at least <NUM> kilowatts per cubic meter (kW/m<NUM>), at least <NUM> kW/m<NUM>, at least <NUM> kW/m<NUM>, and from about <NUM> to about <NUM> kW/m<NUM>.

As also shown in <FIG>, as well as <FIG>, reactor <NUM> includes one or more agitation baffles <NUM>, <NUM>, <NUM>, and <NUM>. Each of these respective agitation baffles (<NUM>, <NUM>, <NUM>, <NUM>) are attached to the wall of the reactor (or to the top or bottom of the reactor). The dimensions and geometry of agitation baffles are known in the art. As best shown in <FIG>, reactor <NUM> is equipped with a still-zone baffle <NUM>. Still-zone baffle <NUM> includes opposed walls <NUM>, <NUM>, which are each respectively attached to circumferential wall <NUM> of reactor <NUM>. Still-zone baffle <NUM> also includes interconnecting wall <NUM> connecting opposed walls <NUM>, <NUM> to thereby form still zone <NUM>. Still zone baffle <NUM> partially extends across the height <NUM> of wall <NUM> in order to provide a baffle gap <NUM> (best shown in <FIG>) proximate to bottom <NUM> of reactor <NUM>. Stated another way, still-zone baffle <NUM> has a height that extends above liquid level line <NUM> at its upper end <NUM>, and at its lower end <NUM> does not contact bottom <NUM> of reactor <NUM> so as to provide a gap <NUM> through which liquid can flow. Still-zone baffle <NUM> is positioned within reactor <NUM> to surround outlet <NUM>. As a result, reactor effluent <NUM> must enter still zone <NUM> formed by still-zone baffle <NUM> via baffle gap <NUM> in order to exit outlet <NUM>.

As a result of this configuration, still-zone baffle <NUM> shields outlet <NUM> from direct agitation caused by agitation device <NUM>. Gaseous bubbles, such as ethylene within liquid medium <NUM>, therefore have an unrestricted path to rise out of still-zone <NUM> into the reactor headspace <NUM>. Likewise, the configuration of still-zone baffle <NUM>, which impacts still-zone <NUM>, provides for a low liquid flow velocity as the reactor contents enter baffle gap <NUM> and exit outlet <NUM>. This low velocity promotes iron powder sedimentation. As the skilled person will appreciate, by inhibiting iron powder from exiting reactor <NUM>, the iron powder can be recirculated within the reactor so that it can be converted to soluble species by reaction or interaction with one or more constituents within the reactor. Thus, with the unrestricted path for gaseous materials to leave still-zone <NUM> and with the decreased flow velocity promoting iron powder sedimentation, the amount of gaseous reactants (e.g. ethylene) and iron powder exiting reactor <NUM> through outlet <NUM> is minimized. In these or other embodiments, outlet <NUM> is equipped with a conically shaped effluent nozzle <NUM>, wherein wide end <NUM> is attached to reactor wall <NUM>. This configuration further inhibits gas entrainment within effluent <NUM>. Also, the height of outlet <NUM>, relative to the height of the reactor, is designed to avoid substantial or appreciable turbulence that is present at the bottom of the reactor. The skilled person will appreciate that outlet <NUM> is nonetheless positioned relatively low within the reactor to provide for the ability to empty the contents of the reactor when desired.

In one or more embodiments, the velocity of liquid medium <NUM> traveling through baffle gap <NUM> is less than <NUM>, in other embodiments less than <NUM>, and in other embodiments less than <NUM>/s.

Reactor effluent <NUM> exiting reactor <NUM> includes the desired chlorinated propane product (e.g. <NUM>,<NUM>,<NUM>,<NUM>-tetrachloropropane) together with unreacted reactants (e.g. carbon tetrachloride and ethylene), reaction byproducts, and catalyst and catalyst residues. Reactor effluent <NUM> may therefore be referred to as crude chlorinated hydrocarbon stream (e.g. <NUM>,<NUM>,<NUM>,<NUM>-tetrachloropropane crude). This crude is then purified by employing one or more distillation techniques to obtain a purified chlorinated propane stream (e.g. purified <NUM>,<NUM>,<NUM>,<NUM>-tetrachloropropane).

The purification process can be described with reference to <FIG>, which shows purification system <NUM> including distillation column <NUM> and reboiler <NUM>. As generally known in the art, column <NUM> includes a bottom zone 103A, where column bottoms <NUM> in the form of liquid collect and form liquid level 106A, packing zone 103B, where packing materials and/or trays are located, and head space 103C through which vapor passes out of column <NUM>.

Reboiler <NUM>, which may also be referred to as a forced recirculation boiler <NUM>, may include a single or multi-pass reboiler. As will be described herein below, a heating fluid or media may travel shell side through reboiler <NUM>. Practice is not limited by the type of heating fluid employed and may include, for example, steam.

Distillation column <NUM> and reboiler <NUM> are in fluid communication via reboiler loop <NUM>. Crude <NUM> enters column <NUM> at bottom 103A at or near liquid level 106A, where crude <NUM> becomes included in column bottoms <NUM> at the bottom of distillation column <NUM>. Column bottoms <NUM> (which include the target chlorinated propanes) enter loop <NUM> from outlet <NUM>. The velocity of column bottoms <NUM> flowing through loop <NUM> is regulated by, for example, pump <NUM>. The velocity of the column bottoms flowing through loop <NUM> may be maintained at a rate sufficient to reduce tube wall temperatures within reboiler <NUM> and thereby inhibit reactions and/or the formation of deposits within reboiler <NUM>. Column bottoms <NUM> enter reboiler <NUM> at inlet <NUM> and circulate tube side within reboiler <NUM>. The velocity of column bottoms <NUM> through reboiler <NUM> may be at least <NUM>, at least <NUM>, and at least <NUM>/s. The velocity of column bottoms <NUM> through reboiler <NUM> may be from about <NUM> to about <NUM>, from about <NUM> to about <NUM>, and from about <NUM> to about <NUM>/s.

As suggested above, column bottoms <NUM> travel tube side through reboiler <NUM> where they are subjected to heat that is transferred from heating fluid steam <NUM> (e.g. steam) introduced through inlet <NUM> shell side of bottoms <NUM>. Heat flux across the tubes within reboiler <NUM> may beless than <NUM>, less than <NUM>, and less than <NUM> kW/m<NUM>. The heat flux across the tubes within reboiler <NUM> is from about <NUM> to about <NUM>, from about <NUM> to about <NUM>, and from about <NUM> to about <NUM> kW/m<NUM>.

Column bottoms <NUM> exit reboiler at exit <NUM>, as a heated liquid, and are injected into column <NUM> at inlet <NUM>, which is positioned below packing zone 103B; column bottoms <NUM> may enter at or near liquid level 106A. Column bottoms <NUM> leaving reboiler <NUM> through outlet <NUM> are heated to an extent that they will flash (i.e. boil) due to pressure differentials experienced upon entry into column <NUM>. Also, as suggested by <FIG>, reboiler <NUM> may be located at a lower elevation relative to the bottom of distillation column <NUM> to thereby provide sufficient hydrostatic pressure and thereby prevent premature boiling of the column bottoms within reboiler <NUM>. Accordingly, the combination of fluid velocity, heat reflux within reboiler <NUM>, and the pressure maintained within loop <NUM> serve to inhibit reactions and/or the formation of deposits onto the tube walls or within distillation column <NUM>.

Claim 1:
A process for preparing chlorinated propanes by reacting carbon tetrachloride with an olefin in the presence of an insoluble or partially soluble catalyst or catalyst precursor within a liquid reaction mixture being continuously stirred within a tank reactor, the process comprising removing the chlorinated propane product from the tank reactor from a still zone within said reactor, where said still zone is defined by three internal walls and the wall of the reactor, which provide a still-zone baffle, and where said still-zone baffle includes an opening proximate to the bottom of the reactor to thereby allow the reaction mixture to enter the still zone.