Irwin, Charles Lewis, Strongville, Ohio 44136, US; Chang, Ching-Feng, Ohio 44136, US; Keller, George Ernest, II, SO. Charleston, W. Virginia 25303, US; Gillespie, Gary Louis, Dunbar, W. Virginia 25064, US; Shao, Richard Liichang, North Royalton, Ohio 44133, US
The present invention relates to a continuous method for treating
a liquid tar containing Q.I. solids to provide a liquid tar product having increased
Q.I. concentration and, concurrently, a Q.I. free liquid tar product.
More particularly the present invention provides a method which utilizes
cross-flow filter membranes.
In the preparation of carbon artifacts such as graphite electrodes,
a carbonaceous filler such as petroleum coke is admixed with a coal tar pitch binder
and then formed, carbonized, and graphitized to produce a graphite product. For
maximum product strength, it is important that the coal tar pitch binder give
a good yield of carbon after carbonization. The presence of relatively high amounts
of infusible carbon solids i.e. fine particles, generally called Q.I. (Quinoline
Insoluble), is desirable for an effective binder in order to increase coking yield
and to provide a source of fine carbon particles which also improve graphite artifact
strength. Commercial coal tar binder pitches usually contain about 8-20% by weight
Q.I. mainly in the form of small (micron) size spherulitic carbon particles. These
particles, which are called natural Q.I., are generated during the preparation
of the tar precursors used to produce the binder pitch. The Q.I. in pitches can
also contain larger carbonaceous particles called cenospheres, carbonized coal
particles, and inorganic ash. These components also originate in the preparation
of the tar precursor and are generally not beneficial for use of the pitch as a
binder. An additional form of Q.I. called secondary Q.I. or mesophase can be formed
by heat treatment during the conversion of tar to pitch.
Very often, in order to increase strength, the carbon artifact is
impregnated with molten pitch after baking, but before graphitization. The molten
pitch impregnant fills the pores generated during the initial baking of the carbon
article and increases final strength and density. In contrast to the requirements
for binder pitch, an impregnant pitch should have very low or preferably zero amounts
of solids (Q.I.). The presence of solid particles which are not miscible with the
molten pitch would block the pores of the carbon article and prevent full impregnation
of the pitch into the artifact.
It is presently difficult to produce impregnating pitches which are
solids-free, i.e. Q.I. free. Conventional filtration or centrifugation of precursor
coal tars can be used to remove the Q.I. particles prior to conversion to pitch.
However, these operations are costly since they are batch operations and must be
done at high temperatures. Additionally, the Q.I. particles must be separated
from the solids-free tar and then disposed of. There is currently no domestic,
i.e. United States source of a solids-free coal tar impregnating pitch. Batch processes
have been developed in Japan for removal of Q.I. from coal tars to produce solids-free
impregnating pitches (U.S. Patent 4,127,472) which involve treatment of the tar
with an anti-solvent to settle the Q.I., followed by separation of the Q.I. by
filtration or centrifugation. The separated Q.I. must then be disposed of. Japan
published patent application 1(1989)-305,640 discloses the use of membrane filters
to remove Q.I. solids from coal tar and coal tar pitch in a batch type procedure.
There is also difficulty obtaining high Q.I. content tars which are
suitable for binder pitches. With increasing environmental controls, the coking
operations used to produce the tars have been reduced in severity with a resulting
reduction in the Q.I. levels in the tars. The derived pitches are, therefore,
low in Q.I. and lead to reduced strength in graphite products when used as binder
pitch. In Europe, Q.I. levels of binder pitch are generally below the minimum desired
level of 8%. In order to increase the Q.I. content, processes have been developed
in which artificial carbon fines are added back to the tar or pitch (U.S. Patent
For these reasons, it would be very advantageous to have a continuous
process which could produce, at the same time, 0% Q.I. tars for impregnating pitches,
and high Q.I. tars for binder pitches.
Over the last decade or so, an advanced form of ceramic membrane
technology has become commercialized. This technology involves the use of ceramic
monoliths, known as cross-flow filters, whose channel walls contain carefully controlled
pore sizes. Pore sizes can be varied from somewhat above one micron down to 50
These membranes operate in a fundamentally different manner from
conventional dead-end filters. Instead of depositing the solids on a filter medium
as occurs with dead-end filters, the feed stream flows across the surface of the
membrane and the solids stay suspended in the liquid. The permeate or filtrate
passes through the membrane and is collected.
According to the present invention there is provided a continuous
method is provided for increasing the concentration of infusible solids (Q.I.)
in a liquid Q.I. containing tar to a desired level to provide a Q.I. containing
concentrate having an increased Q.I. level while providing a Q.I. free tar which
method comprises: continuously introducing Q.I. containing liquid tar feed having
a known Q.I. concentration into a circulation loop which includes, in series, a
tar feed input, a cross-flow filtration membrane filter, an outlet for Q.I. containing
concentrate which can be recirculated or collected, a pump and a flow controller
to continuously circulate said feed in said circulation loop and obtain a Q.I.
free permeate liquid tar exiting the circulation loop via said cross-flow filter
at a desired permeate flow rate and a Q.I. containing liquid concentrate of a
desired increased Q.I. concentration which passes through said cross-flow filter
and circulates in the circulation loop; thereafter continuously, and concurrently
with the introduction of additional tar feed into the circulation loop, withdrawing
a portion of said Q.I. containing liquid concentrate from the circulation loop
by way of said outlet for Q.I. containing concentrate.
The present invention will now be further described, by way of example,
with reference to the accompanying drawings, in which:-
Figure 1 is a schematic representation of a cross-flow ceramic membrane filter.
Figure 2 shows an experimental system using a cross-flow ceramic membrane.
Figures 3-6 show graphs of results obtained using the experimental system of
Figure 2, and
Figure 7 shows a system in accordance with the present invention for the continuous
concentration of Q.I. containing tar with the concurrent production of Q.I. free
Filtration trials of tars were carried out using commercial tubular
U.S. Filter ceramic membranes operating in a cross-flow configuration shown schematically
at 1 in Figure 1. A porous membrane indicated at 3 typically consists of selective
layers of alpha alumina, zirconia, or gamma alumina deposited on an alpha alumina
support. The substantial chemical stability offered by these materials makes ceramic
membranes resistant to a wide range of organics, including the aromatics present
in coal tar. In addition, ceramic membranes are stable at relatively high temperatures.
When using undiluted tar, high temperature operation (i.e., >80°C) is required
to reduce the viscosity of a tar so that a practical filtration rate (i.e., permeation
flux) may be attained.
In cross-flow filtration, illustrated schematically in Figure 1,
feed 5 flows parallel (rather than perpendicular) to the surface of membrane 3.
The feed stream 5 is kept at a higher pressure than the permeate (i.e. filtrate)
7 so that a cross-flow of permeate passes through the pores of membrane 3. Particles
larger than the membrane pores do not pass through the membrane and, hence, are
rejected. The rejected particles, indicated at 8, form a thin layer at the membrane
surface which increases the resistance to permeate flow. However, the parallel
flow through the tube creates shear forces which keep this layer thin. Thus, a
filter cake does not continuously accumulate with time as with dead-end filtration
and the permeation flux reaches a substantially constant value. In practice, the
flux may further decline after long-term, but at a much slower rate than the initial
rate of flux decline due to cake formation and pore blockage.
In addition to chemical and thermal stability, ceramic membranes
posses high strength and relatively strong bonds between the layers that make up
the membrane. These properties allow ceramic membranes to be backflushed periodically
in order to restore the permeation flux. Backflushing involves reversing the flow
of permeate through the membrane pores to essentially eliminate the layer of particles
that has accumulated at the membrane surface.
A schematic of the experimental apparatus used to investigate removal
of Q.I. particles from coal tar is shown in Figure 2. A rotary lobe positive displacement
pump (Jabsco Pureflo Model A1) 10 was used to deliver liquid coal tar or a coal
tar/toluene mixture 35, containing Q.I. particles, to a ceramic membrane filter
20. A bypass line, 83, containing a valve, 85, was used to regulate the flow rate
to the membrane. Feed pressures between 40 and 60 psig, and feed flow rates between
three and seven gpm (gallons per minute) were used in the investigation. The feed
delivered to membrane 20 is divided into two streams by the membrane: a concentrate
40 having increased Q.I. content, and a permeate 30 which is Q.I. free. The concentrate
stream 40 is returned to the feed tank 50 as indicated or can be withdrawn through
valve 65. Due to axial pressure drop in the tubular membrane 20, the pressure of
the concentrate stream at the exit of the membrane 20 is typically 10-30 psi less
than the feed pressure at the inlet to membrane 20. The pressure of permeate stream
30, is maintained at 0 psig, and can be returned to the feed tank 50, or removed
from the system as indicated at 55. By recycling both the concentrate 40 and permeate
30, a constant particle concentration in the feed could be maintained during the
trials and removal of a portion of permeate 30 results in an increase of the concentration
of Q.I. particles in the concentrate.
To provide heat to the system, the feed tank 50, the tubing 53 between
the feed tank and the membrane 20, the pump 10, the concentrate line 43 and the
permeate line 33 were conventionally traced with electrical tape (not shown) and
insulated. The temperature in the tank was controlled with an Athena temperature
controller (not shown). The heat input to the pump 10 and the process lines was
controlled by varying the voltage input to the heat tape with a Variac (not shown).
Temperatures were monitored with thermocouples in the feed tank, the concentrate
stream, and the permeate line. Back flushing to remove accumulated solids on membrane
20 was accomplished by two procedures. In one procedure, valve 45 is closed, valve
95 is opened and a 15 second pulse of nitrogen from line 70 is applied at a pressure
which is 20 psi greater than the feed pressure which causes pure toluene to flow
from tank 90 to fill the interior 23 of membrane housing 25 and to flow across
membrane 20 to remove particles accumulated on its inner surface 27. In another
procedure, valve 45 is closed, valve 105 is opened and a 15 second pulse of nitrogen
from line 70 is applied at a pressure which is 20 psi higher than the feed pressure
causing permeate to flow across membrane 20 to remove particles accumulated on
its inner surface 27.
In each trial using the system of Figure 2, three to five gallons
of feed 35 were charged to the system. Four different feeds were used in the trials:
a commercial coal tar (A) containing 2.4 wt.% Q.I., a commercial coal tar (B) containing
5.0 wt.% Q.I., a 1 to 1 blend by weight of coal tar (A) in toluene and a 1 to
1 blend by weight of coal tar (B) in toluene.
In addition to Q.I. content, tar (A) and tar (B) also differ in viscosity.
The following examples 1-4 show results of the investigation:
EXAMPLE 1 - TEST MATERIALS (TARS)
a) Coal Tar A - A commercial tar derived from coal coking processes
with the following properties:
Coking Yield =
Viscosities at different temperatures are:
746 cps at 55°C
101 cps at 80°C
27 cps at 105°C
The average molecular weight measured by gel permeation chromatography
(GPC) was 316.
The Q.I. size as observed by SEM and measured by light scattering
ranged from about 0.3 to 10 microns with an average size of 2.7 microns.
b) Coal Tar B
Coking Yield =
Viscosity at different temperatures are:
Average Molecular Weight = 345
Q.I. Size Range = 0.1 - 3 Microns
Average Size of Q.I. = 0.8 Micron
EXAMPLE 2FILTRATION OF A DILUTED COAL TAR USING A 0.2 MICRON MEMBRANE
Commercial coal tar B containing 5.0 wt% Q.I. was blended with toluene
to produce a 50/50 weight % mixture of coal tar/toluene. About 12,000 grams of
this blend was charged to the system of Figure 2 operating at 68°C. The Q.I. content
of the blend was 2.5 wt%. A ceramic membrane with an average pore size of 500
Angstroms (0.05 micron) was used for the filtration. The coal tar was recycled
through the membrane and varying amounts of solids-free permeate were removed.
The Q.I. level of the tar toluene mixture was measured as a function of the amount
of permeate removed. The results are summarized in Figure 3 which shows that the
Q.I. was concentrated from 2.5 wt% to 3.1 wt% by removing 2100 ml of permeate (approximately
20 wt%). Analysis of the permeate showed it to contain 0.0 wt% Q.I.
The concentrated Q.I. level was as predicted from the amount of permeate
2.5 wt%/0.80 = 3.1 wt%
EXAMPLE 3FILTRATION OF TOLUENE DILUTED TARS (A) AND (B) USING 0.2 AND 0.1 MICRON
PORE SIZE MEMBRANES
Filtration tests were carried out using the system of Figure 2 and
ceramic membranes with average pore sizes of 0.2 and 0.1 micron. Although membranes
with pores 0.2 micron in size and larger can be used to produce a solids-free permeate,
these membranes could not be satisfactorily operated in a continuous flow/backflush
manner to concentrate the Q.I.
For this example, the coal tar "A" containing a 2.4 wt% Q.I. was
diluted 50/50 weight % with toluene and filtered through a 0.2 micron pore size
membrane operating at 80°C and using a flow rate of 3.9 gpm. The results are shown
in Figure 4 along with the other operating parameters. The initial permeate flux
was very high at 300 gfd, but after two hours, it had dropped to only 37 gfd (gallons/ft2/day)
(factor of eight).
The first data point shown in Figure 4 was taken immediately after
exposing the clean membrane to the feed. This figure shows a sharp decrease in
the permeate flux early in the run followed by a slower decrease (i.e., leveling
off) in the permeate flux as the run continued. The initially sharp decrease in
permeate flux is typical of cross-flow filtration processes and is usually attributed
to the buildup of particles at the surface of the membrane in contact with the
feed. The permeate flux levels off with time as the layer of retained solids reaches
a constant thickness. If particle accumulation at the membrane surface were responsible
for the decline in permeate flux, then backflushing should have temporarily increased
the permeate flux. However, as shown in Figure 4, backflushing with toluene had
a negligible effect on the measured permeate flux. There are two possible explanations
for the ineffectiveness of backflushing in this case: (i) the backflush pressure
was too small to remove a significant amount of retained solids; and (ii) irreversible
internal membrane fouling occurred. If internal fouling of the membrane were great
enough, the membrane could offer a significantly larger resistance to permeate
flow than the filter cake, and backflushing would have a negligible effect on the
flux values measured.
A similar run was performed with a 0.1 micron pore size column and
the results are shown in Figure 5. The initial permeation flux was a high 771 gfd.
After 100 minutes, the flux declined to about 54 gfd. When the membrane was backflushed
with toluene, the flux was increased to 419 gfd. After another 100 minutes of
operation, the flux decreased 45 gfd, but was restored to 428 gfd by backflushing.
These data show that unlike the 0.2 micron membrane, the 0.1 micron membrane was
not irreversibly clogged with solids and that the system could be practically
operated in a continuous manner with periodic backflushing. In each instance, the
permeate removed contained 0 wt% solids. Results of these tests show that pore
sizes of 0.1 micron or less are needed to prevent entrapment of the solids into
the pores and enable continuous operation employing backflushing.
EXAMPLE 4FILTRATION USING A 0.1 micron MEMBRANE AND BACKFLUSHING WITH PERMEATE
To avoid backflushing with a fluid whose composition was different
than that of the feed, several trials were performed using permeate as the backflush
fluid. A Plot showing the permeation flux versus time for this run is given in
Figure 6. The run was carried out with a 50/50 (by weight) mixture of tar (B)
and toluene and a 1000 (.1 micron) Angstrom membrane.
The results in Figure 6 show that early in the run, this mechanism
of backflushing produced large increases in the flux across the 1000 (.1 micron)
Angstrom membrane. However, as the run proceeded, backflushing had a diminishing
effect on the permeation rate, indicating that irreversible internal fouling may
have occurred during the course of the run.
EXAMPLE 5FILTRATION OF UNDILUTED COAL TAR USING 0.05 micron PORE SIZE MEMBRANE
Since it would be more economical to carry out the Q.I. concentration/removal
with pure undiluted tar, experiments were carried out with pure tar (B) using a
0.05 micron (500 Angstrom) ceramic filter. This size filter would have a reduced
chance of pore plugging with the Q.I. particles. Experiments were carried out
at temperatures of 80°-90°C where the tar would have a viscosity of 32 cps or lower.
The results are summarized in Table III.
The values listed for the permeation flux in Table III are values
averaged over the course of a run. Trends such as that shown in Example 3 in which
the flux was high at the beginning of the run and leveled off as the run proceeded
were not observed with the undiluted tars; that is, the flux remained approximately
constant throughout the run. Hence, the flux values reported in Table III should
be considered steady-state values.
The results shown in Table III indicate that the 500 Angstrom membrane
was able to produce a solids-free permeate during all runs, and that by removing
permeate from the system rather than returning it to the feed tank, it was possible
to concentrate Q.I. particles in the feed stream. This Table III also shows the
effect of various operating conditions on the permeation flux. For example, a comparison
between run 3-GLG-X-13 and 3-GLG-X-14 indicates that an increase in the feed flow
rate results in an increased permeation flux across the membrane. This result
is expected since high flow rates result in a thinner filter cake at the membrane
In addition to runs with undiluted tar (B), runs with undiluted tar
(A) were also performed. This tar has a higher viscosity. Table IV lists the results
from runs made with undiluted tar (A). Also shown in the table are results from
runs with undiluted tar (B) and a 50/50 (by weight) mixture of tar (A) and toluene.
The flux values measured for the tar (A) are smaller than those measured for either
the undiluted tar (B) or the 50/50 (by weight) mixture of tar (B) with toluene.
These data demonstrate the strong dependence of flux on viscosity. The flux measured
for the tar (A)/toluene mixture has a value of 25.5 gfd and since the tar constitutes
50 wt% of the mixture, the flux of tar (A) is about half of the total flux. Thus,
higher fluxes of coal tar are obtained when the feed is diluted.
The method of the invention is operable with tar having a viscosity
as high as 500 cps; a preferred tar viscosity for increased through put is 50 cps
or less. Such lower viscosities are obtainable by heating the tar to a suitable
temperature suitable for the particular tar; alternatively a solvent can be added
to the tar, as disclosed herein, in amounts of 20 to 80% by weight.
Operation of the method at temperatures as low as room temperature
is achievable by diluting the coal tar with a suitable solvent such as toluene,
benzene, pyridine chlorobenzene, trichlorobenzene, coal tar petroleum distillate
oils, anthracene oil and the like.
With reference to Figure 7, a schematic for a continuous-operation
Q.I. particle filtration and concentration unit for processing Q.I. containing
liquid tar is shown at 100. The unit 100 comprises a pre-heater 102 which contains
Q.I. containing tar feed material 104. The tar feed material 104 is heated to a
temperature in the range of 80-320°C in order to reduce the viscosity to a minimum
value without the occurrence of volatilization or chemical reaction in the tar
(see Example I for tar (A) and tar (B)). The particular temperature for minimum
viscosity for different tars will vary and is determined by routine measurement.
With valve 106 open, tar feed 104 is moved by pump 108 and mass flow controller
110 into circulation loop 112 through loop inlet 114. The fresh Q.I. containing
tar feed thus introduced into circulation loop 112 passes by way of conduit 111
into the inlet 129 of membrane filter 115 and a Q.I. free liquid tar permeate 116
exits filter 115 at 118, and the Q.I. containing concentrate exits the membrane
filter 115 at 125. A desired Q.I. free liquid tar permeate flow rate is established
by regulation of mass flow controller 120 while correspondingly adjusting the flow
of tar feed into circulation loop 112 at 114 so that the amount (quantity) of tar
being circulated in loop 112 remains substantially constant while being repeatedly
circulated as shown at 113 at a high rate of flow in loop 112, by high pressure
pump 122 in conjunction with mass flow controller 123. In the course of the repeated
circulation of liquid tar in loop 112, the concentration of Q.I. in this circulating
liquid tar is increased due to permeate removal from loop 112. With a desired Q.I.
free permeate flow rate established at 116 in conduit 119, valve 124 is opened
and liquid tar concentrate 128, i.e. tar of higher Q.I. concentration than feed
104, is withdrawn from circulation loop 112 at outlet 126. That is, the Q.I. concentration
in the liquid tar circulating in the portion of loop 112 between the exit 125 of
filter 115 and feed inlet 114, Cl, is the same as the Q.I. concentration,
Cc, in the liquid tar concentrate 128. The flow of liquid tar concentrate
(high "Q.I.") 128 is regulated at mass flow controller 130 and the amount of tar
feed introduced at 114 into circulation loop 112 before filter 115 is correspondingly
The Q.I. concentration and flow rate of the tar concentrate withdrawn
from the circulation loop at 126 is determined by the following relationship:
(I) Cc = Cf x Ff / (Ff
- Fp) (II) Ff - Fp = Fc
Q.I. concentration in weight percent in the tar concentrate (128)
Q.I. concentration in weight percent in the tar feed (104)
the flow rate of the tar feed (104)
the flow rate at which Q.I. free permeate (116) exits filter and circulation
the flow rate at which tar concentrate (128) is withdrawn from the circulation
Example 6 will serve to further illustrate the preferred embodiment
of Figure 7.
EXAMPLE 6 (Hypothetical)CONTINUOUS PROCESS FOR Q.I. CONCENTRATION
A continuous microfiltration plant for Q.I. concentration in liquid
tar and concurrent production of Q.I. free tar is shown in Figure 7 at 100. Ceramic
membrane filter 115 (U.S. Filter) is housed inside a stainless-steel case and has
a nominal pore diameter of 500 angstrom and a total surface area of 75 ft2.
The fresh feed of coal tar 104 is preheated to between 80 and 350°C to minimize
viscosity and pumped into the "circulation" process loop 112 which includes a large
WAUKESHA positive displacement pump 122, the U.S. Filter ceramic membrane module
115 and a MICRO MOTION mass flow controller 123. The temperature of the circulation
process loop is likewise maintained at the minimum viscosity temperature between
80 and 320°C using hot oil tracing.
The flow rates of fresh feed 104, permeate 116, concentrate 128,
and recirculation 113 are respectively regulated by MICRO MOTION mass flow controllers
110, 120, 130, and 123. The flow rates of fresh feed 104 and concentrate 128 are
controlled according to the initial Q.I. level in the fresh coal tar feed 104,
the desired Q.I. level of the concentrate 128, and the flow rate of permeate 116.
The flow rate of coal tar 111 inside the circulation loop 112 is maintained very
high, 102-104 times the flow rate of the fresh feed 104,
in order to create and maintain a turbulent flow inside the tubular ceramic membrane.
A material balance of the system with permeate from the membrane
filter being Q.I. free gives the following:
Ff = Fp + FcFf x Cf = Fp x Cp + Fc
x Cc = Fc x Cc (Cp = O)
where Ff, Fp, and Fc denote the respective flow
rates of the fresh feed, permeate, and concentrate and Cf, Cp
and Cc denote the solid wt.% correspondingly. As indicated in previous
examples, with cross-flow filters, Cp is equal to zero; i.e., the permeate
is Q.I. free.
From previously noted Table III, the filtration rate, i.e., the permeation
flux, is approximately 10 gallon/ft2/day (gfd) for filtering a undiluted
coal tar (B) with the use of a 500-Angstrom membrane. The steady-state permeation
flow rate, Fp, is determined as follows:
Fp = (permeate flux) x (filter surface area) Fp = 10 gallons/ft2/day x 75 ft2Fp = 750 gallons permeate/day = 31.3 gallons permeate/hr.
If the fresh feed has 1 wt.% solids (Q.I.) Cf, concentrating
the tar to contain 3, 4, and 5 wt.% Q.I. solids can be achieved by operating the
system according to the following sets of conditions:
In the foregoing exemplary situations with valve 124 closed, the
fresh feed rate Ff is adjusted until the permeate rate Fp
is equal to Ff) reaches 31.3 gallons per hour, and the circulation in
loop 112 is about 100,000-300,000 gallons per hour. There is no flow of concentrate
from circulation loop 112 since valve 124 is closed. Upon attaining a constant
permeate flow rate Fp of 31.3 gallons per minute, valve 124 is opened
and tar concentrate is withdrawn from circulation loop 112 at the rate Fc
corresponding to the desired Q.I. concentration Cc by operation of mass
flow controller 130; concurrently, the fresh feed flow rate Ff is increased
by amount of withdrawn tar concentrate, Fc.
Kontinuierliches Verfahren zur Erhöhung der Konzentration schwer schmelzbarer
Feststoffe (Q.I.) in einem schwer schmelzbare Feststoffe (Q.I.) enthaltenden flüssigen
Teer auf einen gewünschten Pegel, wobei im Zuge des Verfahrens ein Einsatz an schwer
schmelzbare Feststoffe (Q.I.) enthaltendem flüssigen Teer mit einer bekannten Konzentration
an schwer schmelzbaren Feststoffen (Q.I.) in eine Umwälzschleife eingebracht wird,
die einen Querstrom-Filtermembran-Filter, eine Pumpe und ein Durchflußsteuergerät,
welche in Reihe angeordnet sind, aufweist, um den Einsatz in der Umwälzschleife
kontinuierlich zirkulieren zu lassen, um (i) eine von schwer schmelzbaren Feststoffen
(Q.I.) freie Permeatflüssigkeit zu erhalten, welche die Umwälzschleife über den
Querstromfilter bei einer gewünschten Permeatdurchflußrate verläßt, sowie (ii)
ein schwer schmelzbare Feststoffe (Q.I.) enthaltendes flüssiges Konzentrat mit
erhöhter Konzentration an schwer schmelzbaren Feststoffen (Q.I.) zu erhalten, welches
durch den Querstromfilter gelangt und in der Umwälzschleife zirkuliert; und anschließend
im Gleichstrom mit der Einleitung von weiterem Teereinsatz in die Umwälzschleife
ein Teil des schwer schmelzbare Feststoffe (Q.I.) enthaltenden flüssigen Konzentrats
kontinuierlich von der Umwälzschleife abgezogen wird und die Beziehung zwischen
den Konzentrationen an schwer schmelzbaren Feststoffen (Q.I.) und den Durchflußraten
wie folgt gehalten wird:
Verfahren nach Anspruch 1, bei welchem der flüssige Teereinsatz, die Permeatflüssigkeit
und das Flüssigkeitskonzentrat in der Umwäzschleife auf einer Temperatur im Bereich
von 80 bis 320 °C gehalten werden.
Verfahren nach Anspruch 1, bei welchem das Flüssigkeitskonzentrat in der Umwäzschleife
bei einer Rate zirkuliert wird, die das 102- bis 104-fache
der Durchflußrate des flüssigen Teereinsatzes beträgt, um für eine turbulente Strömung
in der Umwälzschleife zu sorgen.
Verfahren nach Anspruch 1, bei welchem der Membranfilter ein keramischer Membranfilter
mit einer Porengröße von 0,1 µm oder weniger ist.
Verfahren nach Anspruch 1, bei welchem der Teereinsatz mit einem Lösungsmittel
verdünnt wird, um die Viskosität des Teereinsatzes zu senken und den Betrieb des
Verfahrens bei Raumtemperatur zu ermöglichen.
Continuous method for increasing the concentration of infusible solids (Q.I.)
in a Q.I. containing liquid tar to a desired level which comprises: continuously
introducing Q.I. containing liquid tar feed having a known Q.I. concentration into
a circulation loop which includes, in series, a cross-flow filtration membrane
filter, a pump and a flow controller to continuously circulate said feed in said
circulation loop to obtain (i) a Q.I. free permeate liquid exiting the circulation
loop via said cross-flow filter at a desired known permeate flow rate and (ii)
a Q.I. containing liquid concentrate of increased Q.I. concentration which passes
through said cross-flow filter and circulates in the circulation loop; thereafter
continuously, and concurrently with the introduction of additional tar feed into
the circulation loop, withdrawing a portion of said Q.I. containing liquid concentrate
from the circulation loop and maintaining the relationship between Q.I. concentrations
and flow rates as follows:
Method in accordance with claim 1 wherein the liquid tar feed, permeate liquid,
and liquid concentrate in the circulation loop are maintained in the temperature
range of 80 to 320°C.
Method in accordance with claim 1 wherein the liquid concentrate in the circulation
loop is circulated at a rate which is 102 - 104 times the
flow rate of the liquid tar feed in order to establish turbulent flow in the circulation
Method in accordance with claim 1 wherein said membrane filter is a ceramic
membrane filter having a pore size of 0.1 micron or less.
Method in accordance with claim 1 wherein said tar feed is diluted with a solvent
to reduce viscosity of the tar feed and enable operation of the method at room
Procédé continu pour augmenter la concentration des matières solides infusibles
(Q.I.) dans un goudron liquide contenant des Q.I. à un degré désiré, qui comprend
: le fait d'introduire en continu une charge de goudron liquide contenant des Q.I.
ayant une concentration connue en Q.I. dans une boucle de circulation qui comporte,
en série, un filtre à membrane de filtration à courant transversal, une pompe et
un régulateur de débit pour faire circuler en continu cette charge dans cette
boucle de circulation afin d'obtenir (i) un liquide de perméat exempt de Q.I. sortant
de la boucle de circulation par ce filtre à courant transversal avec un débit
en perméat connu désiré et (ii) un concentré liquide contenant des Q.I. présentant
une concentration accrue en Q.I. qui traverse ce filtre à courant transversal et
circule dans la boucle de circulation ; le fait de prélever ensuite en continu
et concurremment avec l'introduction d'une charge en goudron supplémentaire dans
la boucle de circulation, une partie de ce concentré liquide contenant des Q.I.
de la boucle de circulation et de maintenir comme suit la relation entre les concentrations
en Q.I. et les débits :
Procédé selon la revendication 1, dans lequel la charge en goudron liquide,
le liquide de perméat et le concentré liquide dans la boucle de circulation sont
maintenus dans l'intervalle de températures de 80 à 320 °C.
Procédé selon la revendication 1, dans lequel on fait circuler le concentré
liquide dans la boucle de circulation à une vitesse qui est 102 à 104
fois le débit de la charge en goudron liquide pour établir un écoulement turbulent
dans la boucle de circulation.
Procédé selon la revendication 1, dans lequel ce filtre à membrane est un filtre
à membrane céramique ayant une taille de pores de 0,1 micromètre ou moins.
Procédé selon la revendication 1, dans lequel cette charge en goudron est diluée
avec un solvant pour réduire la viscosité de la charge en goudron et permettre
le fonctionnement du procédé à la température ambiante.