BACKGROUND OF THE INVENTION
The present invention relates to humidification of hydrocarbons,
such as butadiene, prior to polymerization and will be described with particular
reference thereto. The process is also applicable to other fluids in which water
is poorly soluble, however.
Polymerization of 1,3-butadiene to form cis-1,4-polybutadiene
with the aid of Ziegler-Natta type catalyst systems is known. The presence of controlled
amounts of water in certain such polymerizations has been found to have a beneficial
effect on the activation of the catalyst. In particular, small amounts of dissolved
water, of the order of 10 to 200 ppm, have been found to be beneficial to catalytic
Water may be introduced by a dispersion in the reactants
themselves or in the solvent(s). In one method, water is passed through a porous
frit material into a stream of the hydrocarbon mixture. In other methods, water
is introduced to the polymerization reactor. Another method of introducing water
employs a cyclone. However, the presence of free water in liquid form in the polymerization
reactor can inactivate the catalyst rather than assist in its activation. Prior
methods of incorporating water have often resulted in the presence of water droplets
in the hydrocarbon feed.
European patent application EP 0 970 939 A1
describes a humidification process for hydrocarbons wherein a hydrocarbon
gas heated to a temperature is introduced into an adiabatic humidifier and comes
in contact with the waste water from a distillation step. The adiabatic humidifier
is provided with a packed bed to increase the contact efficiency between the water
and the hydrocarbon. Moreover,
discloses a process for humidifying hydrocarbons by bringing a gaseous
stream of hydrocarbon into contact with water in a packed column so as to increase
contact efficiency. Similarly,
Japanese patent applications JP 63315502
describe humidification methods for hydrocarbon gases in which a stream
of that hydrocarbon gas is mixed with liquid water in a packed column. Furthermore,
discloses a process for humidifying a non-hydrocarbon gas stream with
a precise amount of moisture wherein the gas to be humidified and a controlled amount
of water are inserted at the top of a packed column and the humidified non-hydrocarbon
gas is removed at the bottom of the column.
The present invention provides a new and improved apparatus
and method for humidification of a hydrocarbon, which overcomes the above-referenced
problems and others.
SUMMARY OF THE INVENTION
The invention provides a method of humidifying a hydrocarbon
stream wherein the stream is passed through a bed including a packing material and
water, wherein said hydrocarbon stream passes upwardly through said bed. The result
is a humidified hydrocarbon stream having water dissolved therein. (Dissolved indicates
a lack of unassociated, entrained water in liquid form such as, e.g., droplets.)
In another aspect, an apparatus for humidifying a hydrocarbon
stream is provided. The apparatus includes a vessel which defines an interior cavity.
A bed of a packing material is disposed in the cavity. Water fills at least a portion
of the bed. An inlet adjacent, e.g., a lower end of the cavity receives a hydrocarbon
The hydrocarbon stream resulting from this process and
apparatus is humidified but is essentially free of liquid water. Additionally, the
level of water in (i.e., humidification of) the hydrocarbon stream may be controlled.
BRIEF DESCRIPTION OF THE FIGURES
DESCRIPTION OF PREFERRED EMBODIMENTS
- FIG. 1 is a schematic view of a system for humidifying hydrocarbons according
to the present invention.
- FIG. 2 is a side sectional view of the column of FIG. 1.
In FIGURE 1, a system A for humidifying a hydrocarbon stream
is shown. The system dissolves water in the hydrocarbon stream at or below its saturation
limit and ensures that little or no free (i.e., undissolved) water exists in the
final process stream as water droplets. The hydrocarbon stream can be a single hydrocarbon
in liquid or gaseous form or a mixture of hydrocarbons, such as a reactive monomer
in an inert solvent.
Exemplary hydrocarbon monomers include mono-unsaturated
alkenes such as ethene, propene, butene, etc.; conjugated dienes such as butadiene,
isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, and the like;
and styrene and its derivatives, and combinations thereof. The system is particularly
useful for hydrocarbon monomers in which water is poorly soluble, such as butadiene.
Suitable solvents include aliphatic, aromatic, or cycloaliphatic
hydrocarbons, examples of which are butane, pentane, hexane, toluene, benzene, cyclohexane,
and the like. In one embodiment, the hydrocarbon stream includes a mixture of butadiene
and hexane in a ratio of from 1:0 (i.e., pure butadiene) to 1:20.
In an alternative embodiment, one or more components of
a hydrocarbon stream is humidified and then mixed with other component(s) of the
stream downstream of the column 10. This is particularly preferred when one
of the components of the hydrocarbon stream has a lower water saturation level than
the others. When relatively high water concentrations are desired, the component
having a poor water solubility may be omitted from the hydrocarbon(s) to be humidified
and added to the humidified component(s) prior to processing. For example, in the
case of butadiene and hexane, butadiene has a saturation level of around 700 ppm
at room temperature while hexane has a saturation level of around 200 ppm. Butadiene
may be humidified alone to a water content of, for example, above 200 ppm prior
to hexane being added to the humidified butadiene. Preferably, the butadiene is
humidified to a level below that at which water drops out of the combined butadiene/hexane
mixture once the hexane is added.
The hydrocarbon stream leaves the system with dissolved
water up to the saturation limit of the hydrocarbon stream. For example, a hexane-butadiene
mixture may be saturated up to about 200 ppm water, depending on the composition
of the stream.
With reference also to FIGURE 2, dissolution of water in
the hydrocarbon stream may take place in a cylindrical column 10 packed with
a bed 12 of a dispersion material. Column 10 is formed from a structural
material, preferably a non-reactive metal such as steel, and has a cylindrical side
wall 14 closed at upper and lower ends by flanges 16, 18. Bed
12 partly fills an interior 20 of the column, preferably about the
lower half, leaving a head space 22 which is free of the dispersion material.
A water zone 26 fills the column interior approximately
up to the top of the dispersion material, i.e., approximately the lower half of
the column, and fills the voids in column packing bed 12. Preferably, the
water covers the packing material although the water level may drop during humidification
process such that the packing material becomes only partially covered by the water.
The water, which is preferably distilled or otherwise purified, can be introduced
to the column through an inlet line 30 adjacent the lower end of the column.
A liquid level gauge 32 can be used to adjust the height of the water to
the desired level. Once the desired water level is achieved, a valve 34 in
the inlet line is closed and the column is ready to receive the hydrocarbon stream.
The valve may be a non-return valve, or have a non-return valve 36 associated
therewith for inhibiting backflow from the column.
The bed 12 is preferably formed from small particles
or beads 38 (not shown to scale) formed of an inert material, such as porcelain.
Preferably, the beads are spherical in shape, although other configurations are
also contemplated. In a preferred embodiment, the beads range in diameter from smaller
at the bottom to slightly larger at the top of the bed. As shown in FIGURE 2, this
size configuration can be achieved using a lower layer 40, in which the beads
have a diameter of from about 0.2 to about 0.4 cm, an intermediate layer
42 in which the beads have a diameter of from about 0.5 to about 0.8 cm,
and upper layer 44 with about 1.0 to about 1.5 cm diameter beads. Alternatively,
the beads may be of the same size throughout the column. Bead size and arrangement
can depend on factors such as the height of the column and desired flow rate through
In this exemplary embodiment, the column is about one 1
m in height and 10-20 cm in diameter; beads occupy the lower 40-50 cm. The smaller
the beads and the higher the bed, the greater the reduction in flow rate. However,
smaller beads tend to break up the hydrocarbon stream into droplets more quickly.
Thus, a compromise between the size of the beads and the desired flow rate must
be made. An exemplary bead size ranges from about 0.2 to 1.5 cm expressed in average
The hydrocarbon stream is introduced to the column interior
through an inlet line 50 via an inlet port 52 in the lower flange
18. The hydrocarbon stream is preferably introduced as a dry blend. By "dry"
it is meant that the hydrocarbon or blend is essentially free of water. However,
the blend can contain water, as dissolved water and/or water droplets, because the
water droplets where present are advantageously removed by the system.
A pump 54, such as a gear pump in the inlet line,
pressurizes the dry blend to a pressure of about 10 kg/cm2. Excess pressure
may be relieved through a pressure relief valve 56 which is set at just below
the maximum pressure desired, e.g., about 13 kg/cm2. A valve
60 in the inlet line 50 may be closed or adjusted to reduce or stop
the flow of the hydrocarbon stream into the column. A non-return valve
62 prevents backflow of the stream to its source 64.
The entering hydrocarbon stream passes through the water
and packed bed 12. The dispersion material breaks the stream into numerous
narrow pathways and provides a high surface area of contact between the hydrocarbon
stream and the water. The hydrocarbon stream is rapidly broken into small droplets
that come into contact with the surrounding water, dissolving a portion of the water
into each droplet. The hydrocarbon, being lighter than the water, continues upwards
into a disengagement zone 70, above the water layer. In this zone, any undissolved,
entrained water falls back down into the bed, due to its higher density. The hydrocarbon
droplets coalesce in the upper region 72 of the disengagement zone
70 and exit the column through an outlet 74 as a single hydrocarbon
phase, which is substantially free of water droplets but contains the desired dissolved
water. The disengagement zone 70 is thus preferably of sufficient height
to allow the separation of entrained water and hydrocarbon to occur. Alternatively,
a separate chamber is used for separating the entrained water droplets from the
Optionally, a portion of the resulting wet hydrocarbon
stream may be recycled back to the bottom of the column via a recycle line
80 for another pass through the column (see FIGURE 1). The pump
54 can be used to control the proportion returning to the column. Recycling
the hydrocarbon stream in this way ensures that the wet hydrocarbon stream in the
column is saturated with water and tends to ensure that a more stable water content
value is achieved. The portion which is recycled can vary depending on the flow
rate of the hydrocarbon and the solubility of water in the hydrocarbon. At relatively
low flow rates, particularly where the desired water concentration is less than
the maximum achievable saturation limit, a single pass has been found to be adequate.
At higher flow rates, 50% or more of the hydrocarbon stream may be recycled through
the column. A non-return valve 82 in the return flow line 80 ensures
that the fluids maintain the direction of flow as shown in FIGURE 1.
The exiting wet hydrocarbon blend may be mixed with additional
dry blend to achieve a desired dissolved water content, although other methods of
combining the two streams are also contemplated. FIGURE 1 shows a static mixer
90 which combines wet and dry streams. For example, the water content may
be reduced to 50% or 20% of the saturation limit by appropriate mixing of wet and
dry blend streams. Specifically, a portion of the dry blend from the inlet line
is fed via a direct line 92 to the mixer where it is mixed with the wet blend
from the column. A valve 94 adjusts the portion of the dry blend which passes
directly to the static mixer. The dry blend passing to the static mixer is preferably
of the same hydrocarbon composition as that passing through the humidification column
10, although the dry blend can have a different hydrocarbon composition.
If a fully water-saturated hydrocarbon stream is required, the step of mixing with
a portion of the dry blend may, of course, be eliminated.
The mixed stream, i.e., a humidified blend, having a lower
water content than the wet blend from the column, exits the mixer via an outlet
line 96 which transports the humidified blend to a site 98 at which
it is to be utilized, such as a polymerization reactor. Such reactors are disclosed
in, for example,
U.S. Patent No. 4,472,559
to which the reader is referred for more detail.
A moisture probe 100, fluidly coupled with the outlet
line 96, detects the moisture content of the humidified blend and signals
a moisture analyzer 102. The moisture analyzer provides an indication of
the moisture level of the humidified blend. An operator may manually adjust the
control valve 94 to set the ratio of dry to wet fraction or the control valve
94 may be adjusted automatically using a process loop controller
106, integral with or separate from the moisture analyzer 102, whose
process variable input is the moisture level and whose output drives the control
valve position. In this way, a desired output moisture level may be maintained.
Moisture probe 100 may be positioned directly in
the outlet line 96 from the static mixer or, as shown in FIGURE 1, may be
positioned in a separate sampling chamber 110 into which a portion of the
humidified blend is directed periodically for evaluation. In the embodiment of FIGURE
1, a 3-way valve 112 in the outlet line is operated periodically to pass
a sample of the humidified blend into the sampling chamber 110 through a
sampling line 114. Optionally, a heater 118 in the sampling line heats
the sample to a sufficient temperature to lower the relative humidity of the analyzed
blend and thereby maintain the integrity of probe 100. Water, which falls
out of the humidified blend in the chamber, is carried out of the bottom of the
chamber via a drain line 120 by periodically opening a drain valve
The sampled humidified blend may be returned to the outlet
line 96 or passed out of the sampling chamber 110 to a waste line
120 via valve 122. Alternatively, the sample may be returned to the
column and mixed with the incoming dry blend.
After a sampling operation is complete, the sampling chamber
110 may be flushed with a dry fluid such as a dry hexane to remove traces
of moisture from the chamber. For this purpose a 3-way valve 136 in the sampling
line 114 is operated with the waste valve 122 open to carry the dry
hexane purge through the sampling line and through the chamber 110, carrying
any remaining wet hydrocarbon out of the chamber through the waste line
130. When another moisture determination is to be made, hexane is flushed
from the chamber by passing a portion of the wet blend through the chamber until
the moisture content is stabilized.
The system shown is designed for periodic sampling of the
wet blend and for the subsequent draining and flushing of the moisture probe in
an effort to maintain probe integrity, accuracy and longevity during process monitoring.
The composition and construction of the moisture probe make it typically sensitive
to high moisture levels and to process streams with high saturation levels. Using
the probe for intermittent monitoring and by flushing the probe with dry solvent
can maintain a long probe life and helps to maintain the probe within its current
The system may include additional valves and regulators
for regulating flow through the system, such as a pressure regulating valve
140 in the outlet line which maintains the humidified blend and column at
a positive pressure. This may be associated with a pressure transducer
142 for detecting the pressure in the outlet line. Other pressure transducers
may be provided, for example, at 144, 146, 148, and 150. Other valves
may be provided, such as a wet blend sampling valve 152, which allows a sample
of the wet blend to be withdrawn from chamber 110 through a line
156 for analysis. A valve 158 may also be provided for closing off
a line 160 between the chamber 70 and the liquid level gauge
32. A supplementary pressure relief valve 162 may be provided in a
portion 164 of the inlet line, which carries both dry blend and recycled
wet blend to the chamber. A valve 170 for closing off the line between the
humidification system and the polymerization reactor may also be provided.
For a column of the dimensions described above, flow rates
of the humidified blend of about 20 to about 50 Uhr or more are readily achieved.
Obviously, greater flow rates may be achieved with larger columns.
When the water level in the column drops below a selected
minimum level, typically just above the top of the dispersion material, the valve
34 is opened again to allow more water into the column. During water addition,
valve 60 may be closed. In this way, the system can be run relatively continuously
for long periods of time.
The humidified hydrocarbon stream may be used as a process
stream in a polymerization reaction which relies on the presence of small amounts
of dissolved water to activate a catalyst for the polymerization reaction, such
as the production of high cis-content polybutadiene with Ziegler Natta-type
catalysts, such as those incorporating aluminum alkyls, alkyl chlorides, or aluminum
alkoxides with a transition element, such as Co or Ni. Alternatively, or additionally
the humidified hydrocarbon stream may be used for in situ generation of catalyst
systems, for example, the preparation of alkyl aluminoxanes such as methyl aluminoxanes.
This avoids the need to prepare the catalyst system in advance and store it in a
hydrocarbon carrier liquid.
The following example demonstrates the effectiveness of
the humidification system.
Three layers of porcelain beads occupying the lower 40
cm of a 1 m-tall column (a lower layer 40 of a bead diameter of about 0.3
cm, an intermediate layer 42 of a diameter of about 0.6 cm, and an upper
layer 44 of a diameter of about 1.3 cm) was filled about 50% with water.
The pressure in the inlet line 50 was maintained at 10.5 kg/cm2.
A dry, 15% mixture of butadiene in hexane was fed to the column. The control valve
94 was opened at about 50% to mix about 50% dry blend with the wet blend
exiting from the column. A flow rate of 22-45 L/hr. of a humidified blend containing
a well-controlled 100 ppm moisture at an outlet pressure of 10 kg/cm2