U.S. patent application number 14/472239 was filed with the patent office on 2015-05-21 for method for treating coal tar using reactive distillation.
The applicant listed for this patent is UOP LLC. Invention is credited to Robert L. Bedard, John Q. Chen, Peter K. Coughlin, Stanley J. Frey, Jayant K. Gorawara, Deng-Yang Jan, James A. Johnson, Gregory F. Maher, Dean E. Rende, Vasant P. Thakkar.
Application Number | 20150136648 14/472239 |
Document ID | / |
Family ID | 53172207 |
Filed Date | 2015-05-21 |
United States Patent
Application |
20150136648 |
Kind Code |
A1 |
Maher; Gregory F. ; et
al. |
May 21, 2015 |
METHOD FOR TREATING COAL TAR USING REACTIVE DISTILLATION
Abstract
Methods of treating coal tar using reactive distillation are
described. The methods include introducing a coal tar stream into a
reactive distillation zone which has a reaction zone and a
separation zone. The reaction zone contains a hydrotreating
catalyst and an absorbent. The coal tar stream is contacted with a
hydrogen stream in the reaction zone to remove contaminants from
the coal tar stream, and the treated coal tar stream is separated
into at least two fractions.
Inventors: |
Maher; Gregory F.; (Aurora,
IL) ; Bedard; Robert L.; (McHenry, IL) ; Chen;
John Q.; (Glenview, IL) ; Coughlin; Peter K.;
(Mundelein, IL) ; Frey; Stanley J.; (Palatine,
IL) ; Gorawara; Jayant K.; (Buffalo Grove, IL)
; Jan; Deng-Yang; (Elk Grove Village, IL) ;
Johnson; James A.; (Burr Ridge, IL) ; Rende; Dean
E.; (Arlington Heights, IL) ; Thakkar; Vasant P.;
(Elk Grove Village, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
UOP LLC |
Des Plaines |
IL |
US |
|
|
Family ID: |
53172207 |
Appl. No.: |
14/472239 |
Filed: |
August 28, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61905912 |
Nov 19, 2013 |
|
|
|
Current U.S.
Class: |
208/89 ; 208/187;
208/210; 208/211; 208/212 |
Current CPC
Class: |
C10G 67/04 20130101;
C10G 65/12 20130101; C10G 2300/4087 20130101; C10G 2400/02
20130101; C10G 45/02 20130101; C10G 65/00 20130101 |
Class at
Publication: |
208/89 ; 208/212;
208/210; 208/187; 208/211 |
International
Class: |
C10G 65/04 20060101
C10G065/04; C10G 65/12 20060101 C10G065/12; C10G 45/10 20060101
C10G045/10 |
Claims
1. A method of treating coal tar using reactive distillation
comprising: introducing a coal tar stream into a reactive
distillation zone, the reactive distillation zone comprising a
reaction zone and a separation zone, the reaction zone containing a
hydrotreating catalyst and an absorbent; contacting the coal tar
stream with a hydrogen stream in the reaction zone to remove sulfur
compounds, nitrogen compounds, oxygenates, and metals from the coal
tar stream; and separating the treated coal tar stream into at
least two fractions.
2. The method of claim 1 wherein the reactive distillation zone
comprises a first reactive distillation column comprising a first
reaction zone and a first separation zone, the first reaction zone
containing a first hydrotreating catalyst and a first absorbent,
and a second reactive distillation column comprising a second
reaction zone and a second separation zone, the second reaction
zone containing a second hydrotreating catalyst and a second
absorbent.
3. The method of claim 2 wherein an outlet in the first reactive
distillation column is in fluid communication with an inlet in the
second reactive distillation column, further comprising:
introducing a fraction from the first reactive distillation column
into the second reactive distillation column; contacting the
fraction from the first reactive distillation column with a
hydrogen stream in the second reaction zone to remove sulfur
compounds, nitrogen compounds, oxygenate, compounds, and metals
from the fraction from the first reactive distillation column; and
separating the second treated fraction into at least two
fractions.
4. The method of claim 3 wherein the second reaction zone further
comprises a hydrocracking catalyst and wherein one of the fractions
from the second fraction comprises naphtha.
5. The method of claim 2 further comprising; separating the coal
tar stream into at least two fractions; introducing a first
fraction into the first reactive distillation column; contacting
the first fraction with a hydrogen stream in the first reaction
zone to remove sulfur compounds, nitrogen compounds, oxygenate,
compounds, and metals from the first fraction; separating the first
treated fraction into at least two fractions; introducing a second
fraction into the second reactive distillation column; contacting
the second fraction with a hydrogen stream in the second reaction
zone to remove sulfur compounds, nitrogen compounds, oxygenate,
compounds, and metals from the second fraction; and separating the
second treated fraction into at least two fractions.
6. The method of claim 5 wherein the second reaction zone further
comprises a hydrocracking catalyst and wherein one of the fractions
from the second treated fraction comprises naphtha.
7. The method of claim 2 wherein the first and second reactive
distillation columns are operated at different pressures.
8. The method of claim 1 further comprising recovering at least one
of the fractions.
9. The method of claim 1 wherein there are at least three
separation zones alternating with at least two reaction zones.
10. The method of claim 1 wherein there are at least two reaction
zones and wherein the hydrotreating catalyst in the first reaction
zone is different from the hydrotreating catalyst in the second
reaction zone.
11. The method of claim 1 further comprising removing at least one
product from the coal tar stream before introducing the coal tar
stream into the reactive distillation zone.
12. The method of claim 1 further comprising removing a pitch
fraction from the coal tar stream before introducing the coal tar
stream into the reactive distillation zone.
13. The method of claim 1 further comprising removing water from
the coal tar stream before introducing the coal tar stream into the
reactive distillation zone.
14. The method of claim 1 wherein the coal tar stream includes
components having a boiling point from about C5 to 350.degree.
C.
15. The method of claim 1 wherein the absorbent has a surface area
of at least about 200 m.sup.2/g.
16. A method of treating coal tar using reactive distillation
comprising: introducing a coal tar stream into a reactive
distillation zone, the reactive distillation zone comprising a
first reactive distillation column having a first reaction zone and
a first separation zone, the first reaction zone containing a first
hydrotreating catalyst and a first absorbent, and a second reactive
distillation column comprising a second reaction zone and a second
separation zone, the second reaction zone containing a second
hydrotreating catalyst and a second absorbent; contacting the coal
tar stream with a hydrogen stream in the reaction zone to remove
sulfur compounds, nitrogen compounds, oxygenates, and metals from
the coal tar stream; and separating the treated coal tar stream
into at least two fractions.
17. The method of claim 16 wherein an outlet in the first reactive
distillation column is in fluid communication with an inlet in the
second reactive distillation column, further comprising:
introducing a fraction from the first reactive distillation column
into the second reactive distillation column; contacting the
fraction from the first reactive distillation column with a
hydrogen stream in the second reaction zone to remove sulfur
compounds, nitrogen compounds, oxygenate, compounds, and metals
from the fraction from the first reactive distillation column; and
separating the second treated fraction into at least two
fractions.
18. The method of claim 17 wherein the second reaction zone further
comprises a hydrocracking catalyst and wherein one of the fractions
from the second fraction comprises naphtha.
19. The method of claim 16 further comprising; separating the coal
tar stream into at least two fractions; introducing a first
fraction into the first reactive distillation column; contacting
the first fraction with a hydrogen stream in the first reaction
zone to remove sulfur compounds, nitrogen compounds, oxygenate,
compounds, and metals from the first fraction; separating the first
treated fraction into at least two fractions; introducing a second
fraction into the second reactive distillation column; contacting
the second fraction with a hydrogen stream in the second reaction
zone to remove sulfur compounds, nitrogen compounds, oxygenate,
compounds, and metals from the second fraction; and separating the
second treated fraction into at least two fractions.
20. The method of claim 19 wherein the second reaction zone further
comprises a hydrocracking catalyst and wherein one of the fractions
from the second treated fraction comprises naphtha.
Description
[0001] This application claims the benefit of Provisional
Application Ser. No. 61/905,912 filed Nov. 19, 2013, entitled
Method for Treating Coal Tar Using Reactive Distillation.
BACKGROUND OF THE INVENTION
[0002] Many different types of chemicals are produced from the
processing of petroleum. However, petroleum is becoming more
expensive because of increased demand in recent decades.
[0003] Therefore, attempts have been made to provide alternative
sources for the starting materials for manufacturing chemicals.
Attention is now being focused on producing liquid hydrocarbons
from solid carbonaceous materials, such as coal, which is available
in large quantities in countries such as the United States and
China.
[0004] Pyrolysis of coal produces coke and coal tar. The
coke-making or "coking" process consists of heating the material in
closed vessels in the absence of oxygen to very high temperatures.
Coke is a porous but hard residue that is mostly carbon and
inorganic ash, which is used in making steel.
[0005] Coal tar is the volatile material that is driven off during
heating, and it comprises a mixture of a number of hydrocarbon
compounds. It can be separated to yield a variety of organic
compounds, such as benzene, toluene, xylene, naphthalene,
anthracene, and phenanthrene. These organic compounds can be used
to make numerous products, for example, dyes, drugs, explosives,
flavorings, perfumes, preservatives, synthetic resins, and paints
and stains but may also be processed into fuels and petrochemical
intermediates. The residual pitch left from the separation is used
for paving, roofing, waterproofing, and insulation.
[0006] Coal tar has a number of contaminants that need to be
removed, such as nitrogen, oxygen, or sulfur-containing compounds,
and metals.
[0007] There is a need for additional processes for removing
contaminants from coal tar.
SUMMARY OF THE INVENTION
[0008] One aspect of the invention is a method of treating coal tar
using reactive distillation. In one embodiment, the method includes
introducing a coal tar stream into a reactive distillation zone,
the reactive distillation zone having a reaction zone and a
separation zone, the reaction zone containing a hydrotreating
catalyst and an absorbent. The coal tar stream is contacted with a
hydrogen stream in the reaction zone to remove sulfur compounds,
nitrogen compounds, oxygenates and metals from the coal tar stream,
and the treated coal tar stream is separated into at least two
fractions.
BRIEF DESCRIPTION OF THE DRAWING
[0009] FIG. 1 is an illustration of one embodiment of a
pre-treatment process for the reactive distillation process of the
present invention.
[0010] FIG. 2 is an illustration of one embodiment of a reactive
distillation process of the present invention.
[0011] FIG. 3 is an illustration of another embodiment of a
reactive distillation process of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0012] Coal can be pyrolized by heating at high temperature, e.g.,
up to about 2,000.degree. C. (3600.degree. F.), in the absence of
oxygen to drive off the volatile components. Pyrolysis produces
coke and coal tar. The coke can be used in other processes, such as
the manufacture of steel. The coal tar stream comprises the
volatile components from the coking process.
[0013] FIG. 1 shows one embodiment of a pre-treatment process 5 for
the reactive distillation process of the present invention. The
coal tar stream 10 is introduced into an optional separation zone
15. Separation zone 15 is designed to recover valuable products
that would not survive hydrotreating and/or hydrocracking in the
reactive distillation zone (described below). In particular,
valuable oxygenated products, such as phenol, cresols or xylenols,
would be converted to products such as CO.sub.2 and a hydrocarbon
skeleton in the reactive distillation zone. These products 20 can
be recovered from the coal tar stream 10 before it is sent to the
reactive distillation zone by any suitable separation process.
Suitable separation processes include, but are not limited to,
fractionation, extraction, or other bulk separation processes. The
products 20 can be further purified (not shown) using additional
separation processes such as additional fractionation or
extraction, adsorption or treatment with molecular sieves or resins
for removal of trace contaminants, if desired. The residue
remaining after removal of the valuable product or products could
be further processed separately or sent forward into the reactive
distillation zone.
[0014] The treated coal tar stream 25 from the separation zone 15
can be sent to a dehydration zone 30 where water is removed from
the treated coal tar stream 25. The treated coal tar stream is
heated to approximately 150.degree. C. with a heater (not shown).
The overhead 35 from the dehydration zone 30 contains water and
some light oil. The water and light oil are separated in a decanter
40, for example. The water 45 is sent for processing. The light oil
50 can be divided, and a portion 55 is sent forward to the reactive
distillation zone, and a portion 60 may be used as reflux for
dehydration zone 30.
[0015] Bottoms stream 65 is pumped to an appropriate pressure,
heated to approximately 350.degree. C. and flashed in pitch flash
zone 70. The purpose of pitch flash zone 70 is to recover material
in bottoms stream 65 that boils below about 350.degree. C. The
overhead stream 75 from pitch flash zone 70 is condensed, pumped to
the needed pressure, and combined with the light oil portion 55 to
form feed 80 for the reactive distillation zone. Recovery of
material from the coal tar having a boiling point below about
350.degree. C. is maximized by combining pitch 85 from the bottom
of pitch flash zone 70 with bottoms stream 65 from the dehydration
zone 30 to form the feed for pitch flash zone 70. A constant level
of pitch is maintained in pitch flash zone 70 with overflow
recovered in stream 90. This arrangement maximizes recovery of
material having a boiling point below about 350.degree. C. for the
reactive distillation zone, while keeping the viscous, high
molecular weight pitch from entering the reactive distillation zone
and driving up the bottoms temperature of the pressurized columns.
The pitch could also potentially contribute to fouling of the
catalyst beds in the reactive distillation zone.
[0016] The feed 80 contains a number of contaminants. Examples of
contaminants to be removed include, but are not limited to, metals
such as antimony, arsenic, beryllium, cadmium, chromium, copper,
lead, mercury, nickel, selenium, silver, thallium or zinc; nitrogen
containing species, such as pyridines or quinoline; sulfur
containing species, such as thiophenes or mercaptans; and oxygen
containing species, such as phenols or carbazoles. Sulfur,
nitrogen, oxygen and metal containing contaminants are present
throughout the boiling ranges and must be removed before specific
products can be produced, or the coal tar can be used as fuel.
[0017] FIG. 2 illustrates one embodiment of a reactive distillation
zone 100. In this embodiment, the reactive distillation zone 100
includes first reactive distillation column 105 and a second
reactive distillation column 110. In general, hydrotreating of coal
tar requires higher pressure as the molecular weight of the
fraction increases. Because of the molecular weight range of
components in coal tar feed to be hydrotreated, as indicated by
atmospheric boiling points up to 350.degree. C., hydrotreating at
two different pressures is desirable. For the catalytic
distillation application, it would be desirable to have two columns
operating at different pressures. However, in some situations,
particularly if a limited number of products are to be produced,
the reactive distillation zone could utilize a single column at
conditions sufficient to hydrotreat the highest molecular weight
fractions.
[0018] The first reactive distillation column 105 includes at least
one reaction zone and at least one separation zone. As shown, there
are four separation zones 115, 120, 125, 130 alternating with three
reaction zones 135, 140, 145. The number of separation zones
corresponds to the number of products that the operator wants to
produce plus one for the feed inlet.
[0019] Separation zones 115, 120, 125, 130 contain one or more
trays. Typically, all of the inlets and outlets from the column are
located in the trayed separation zones for ease of introduction of
feeds and withdrawal of products. The trayed sections may include
equipment that will distribute and mix incoming feeds with column
internal streams or will collect products for removal from the
column. Potential mixers, distributors and collectors are well
known in distillation tower design.
[0020] The reaction zones 135, 140, and 145 are beds containing a
hydrotreating catalyst. In some embodiments, the reaction zones
will also include an absorbent. All of the beds can be the same
catalyst and/or absorbent, or one or more beds can have different
catalysts and/or absorbents depending on the specific processing
requirements. The purpose of the reaction zones 135, 140, and 145
is the simultaneous removal of contaminants such as metals,
nitrogen, sulfur or oxygen containing species, and the separation
of the feed into one or more specific cuts defined as useful by the
operator. The cuts may correspond to specific products or specific
boiling point regions convenient for further processing. The cuts
in the drawings (which are referenced to atmospheric boiling points
of coal tar components) are for illustration only and can vary
depending on operating objectives.
[0021] The catalysts generally used for hydrotreating contain at
least one Group VIII metal, such as iron, cobalt and nickel, and at
least one Group VI metal, such as molybdenum and tungsten, on a
high surface area support, such as alumina. The preferred
embodiment is a catalyst containing nickel and molybdenum.
[0022] Placement of the catalyst into the reactive distillation
zone requires promotion of intimate contact between the reactants
and the catalyst along with appropriate consideration of hydraulics
and the potential to flood the column should the catalyst bed
provide insufficient passage of vapor rising in the column.
Catalyst particles are sometimes larger than those in a
conventional fixed bed reactor, and the catalyst within a reactive
distillation unit is sometimes supported by contact structures
consisting of wire mesh tubes that also provide a mass transfer
surface for the distillation as in U.S. Pat. No. 5,730,843.
Consideration needs to be given to vapor passage rates as in U.S.
Pat. No. 5,449,501, and ease of catalyst replacement within the
column as in U.S. Pat. No. 6,299,845.
[0023] The absorbents are typically large surface area materials
used to specifically remove metal contaminants from the coal tar.
An alumina with a surface area greater than approximately 200
m.sup.2/g may be used, for example. The large surface area provides
space for metals to deposit. These absorbents are frequently
impregnated with metals that promote hydrotreating reactions, such
as nickel and molybdenum, to facilitate the absorption of the metal
contaminants.
[0024] Typical operating conditions for the reactive distillation
zone include a temperature between 300.degree. C. and 450.degree.
C., at a LHSV between 0.5 and 5/hr and H.sub.2 content between 1000
and 3000 scf/bbl coal tar. Pressure is a function of the
hydrocarbon molecular weight processed, with an expected range
between about 2.07 MPa (g) (300 psig) and 3.45 MPa (g) (500 psig)
for treatment of components with an atmospheric boiling point below
250.degree. C., and an operating range between 3.45 MPa (g) (500
psig) and 6.89 MPa (g) (1000 psig) for components with an
atmospheric boiling point between 250.degree. C. and 350.degree.
C.
[0025] As shown, the feed 80 is introduced into the first
distillation column 105 in separation zone 125. The feed 80 is
introduced at a point where there is at least one reaction zone
above the inlet and at least one reaction zone below it in order to
treat as much of the feed as required.
[0026] Hydrogen may be introduced into any or all of the separation
zones of the first reactive distillation column 105 for
hydrotreating. As shown, hydrogen streams 150, 155, and 160 are
introduced into separation zones 120, 125, and 130
respectively.
[0027] The first reactive distillation column 105 can be operated
at a pressure consistent with processing material with an
atmospheric boiling point up to about 250.degree. C. Typical
operating conditions for this would be temperatures between about
300.degree. C. and about 450.degree. C., LHSV between about 0.5 and
about 5/hr, an H.sub.2 content between about 1000 and about 3000
scf/bbl coal tar, and a pressure operating range between about 2.07
MPa (g) (300 psig) and about 3.45 MPa (g) (500 psig).
[0028] The first reactive distillation column 105 as illustrated
contains three beds of catalyst (and optionally absorbent) 135,
140, and 145, and produces three specific distillation cuts
referenced to the atmospheric boiling points of the components. For
example, overhead 165 can have an atmospheric boiling point up to
about 175.degree. C.; cut 170 can have an atmospheric boiling point
in the range of about 175.degree. C. to about 205.degree. C., and
cut 175 can have an atmospheric boiling point in the range of about
205.degree. C. to about 250.degree. C. The number of separation
sections and the number of catalyst beds may vary depending on the
processing objectives. For example, an operator may chose to
recover cut 170 with overhead 165 and eliminate tray section
120.
[0029] The overhead stream 165 containing hydrocarbon materials and
light components including H.sub.2S, CO.sub.2, NH.sub.3, and
H.sub.2 is condensed to separate the light components from the
hydrocarbons in overhead receiver 180. If desired, a portion or the
entire light stream 185 may be recompressed and recycled as H.sub.2
feed to either the first or second reactive distillation columns
105, 110. Water stream 187 can be removed and sent for treatment.
The hydrocarbon stream 190 now free of sulfur, nitrogen, oxygen and
metals is recovered as the liquid overhead product 195 and a
portion 200 can be used as reflux into the first reactive
distillation column 105.
[0030] Hydrogenation reactions through which a portion of the
contaminants are removed are exothermic. As material moves through
the catalyst beds, heat will be released. In addition to
potentially reduced capital requirements, a major advantage of
reactive distillation is the ability to consume the heat of
reaction as heat of vaporization. Better control of the reaction
heat rise leads to better selectivity, more stable catalyst, and
lower processing requirements. Heat within the column may also be
controlled by the placement and amount of H.sub.2 streams entering
the column, as well as the potential for multiple feed streams (not
shown), both of which can help regulate heat through their use as
quench. Finally, the amount of reflux returned to the column
represents another opportunity for control of reaction heat as
reflux can serve as a heat sink within the catalyst bed.
[0031] Another advantage of reactive distillation is the
counter-current contact of liquid and vapor, and the subsequent
promotion of intimate contact between the catalyst and the
contaminants to be removed. Organic sulfur and nitrogen species,
for example, tend to concentrate in the liquid, while the products
(H.sub.2S and nitrogen) are gas phase. Intimate liquid phase
contact between the organic species and the catalyst with immediate
removal of the products into the gas phase results in lower
processing requirements.
[0032] The bottoms 205 of the first reactive distillation column
105 is sent as feed to the second reactive distillation column 110.
In this example, second reactive distillation column 110 is
processing material with an atmospheric boiling point between about
250.degree. C. and 350.degree. C. The second reactive distillation
column 110 therefore operates at a higher pressure than the first
reactive distillation column 105. Typical expected second reactive
distillation column 110 operating ranges are a pressure between
about 3.45 MPa (g) (500 psig) and about 6.89 MPa (g) (1000 psig),
temperatures between about 300.degree. C. and about 450.degree. C.,
LHSV 1-5/hr, and an H.sub.2 content between 1000 and 3000 scf/bbl
coal tar.
[0033] As illustrated, the second reactive distillation column 110
can be divided into three separation zones 210, 215, and 220 and
two reaction zones 225 and 230. It produces two specific
distillation cuts referenced to the atmospheric boiling points of
the components. As with the first reactive distillation column 105,
all feeds and products are introduced or withdrawn in trayed
separation zones of the column. Hydrogen 235 and 240 can be
introduced into any or all of the separation zones. The excellent
heat control possible in reactive distillation can be enhanced by
the number and position of feed streams into the column and the
control of reflux.
[0034] The overhead stream 245 containing hydrocarbon materials and
light components including H.sub.2S, CO.sub.2, NH.sub.3 and H.sub.2
is condensed to separate the light components from the hydrocarbons
in overhead receiver 250. If desired, a portion or the entire
stream 255 may be recompressed and recycled as H.sub.2 feed to
either the first or second reactive distillation unit. Water stream
257 can be removed and sent for treatment. The hydrocarbon stream
260 now free of sulfur, nitrogen, oxygen and metals is recovered as
the liquid overhead product 265 and a portion 270 used as reflux
into the second reactive distillation column 110. The overhead
product stream 265 has an atmospheric boiling point in the range of
about 250.degree. C. to 280.degree. C.
[0035] The bottoms 275 of the second reactive distillation column
110 has an atmospheric boiling range over about 280.degree. C.
[0036] As an example of the usefulness of simultaneous contaminant
removal and separation, consider the topmost and bottom cuts in the
illustration of the first reactive distillation column 105. The
topmost cut 165 (up to 175.degree. C.) is high in C6-C8 aromatics
such as benzene, toluene and xylene. After removal of metal,
sulfur, nitrogen and oxygenate components in column 105, the
operator may wish to further process this material through a bulk
aromatic from non-aromatics separation process, such as the
Sulfolane process. The valuable aromatics can then be sent to an
aromatics complex for recovery while the non-aromatics can be sent
to a catalytic reformer. Valuable products such as naphthalene and
methyl-naphthalenes, now free of metal, sulfur, nitrogen and
oxygenate contaminants may be recovered from the bottommost cut 175
(205-250.degree. C.) via crystallization or adsorption. The
fraction remaining after naphthalene recovery may be sent to fuel.
Reactive distillation permits a low piece count, efficient
processing scheme for maximizing the value of coal tar.
[0037] The cuts from the second reactive distillation column 110
can be used for the production of diesel fuel. Given the
composition of some coal tars, the cetane number would be expected
to be low. As an alternative to diesel, rather than simply
hydrotreating the 250.degree. C.+ fraction, a portion of the
hydrotreating catalyst in the second reactive distillation column
can be replaced with a hydrocracking catalyst, and the 250.degree.
C.+ fraction can be cracked to produce additional naphtha. Naphtha
product offers additional processing outlets; for example, naphtha
can go to gasoline or aromatics via reforming or to light olefins
via steam cracking.
[0038] FIG. 3 illustrates an alternative second reactive
distillation column 305 which provides increased naphtha
production. The reactive distillation column 305 has two separation
zones 310 and 315 and a reaction zone 320. The feed 325 from the
first reactive distillation column (not shown) is introduced into
the separation zone 310, and hydrogen is introduced into the
separation zone 315. The separation zone 310 is used to fractionate
out the naphtha, while the separation zone 315 would remove heavier
product. Additional cuts may be withdrawn from 305, depending on
the processing objectives of the refiner.
[0039] In addition to the nickel-molybdenum hydrotreating catalyst
and the high surface area absorbent, a hydrocracking catalyst, such
as a zeolite, would be added for the cracking function. Processing
conditions would be about 8.27 MPa (g) (1200 psig) to about 11.03
MPa (g) (1600 psig), 300.degree. C. to 450.degree. C., 1000-3000
scf H.sub.2/bbl coal tar, and 0.5 to 3 LHSV. The primary advantage
of reactive distillation for hydrocracking, which is exothermic, is
control of heat effects via the heat of vaporization. Heat control
can be supplemented through the use of feed streams as quenches and
control of reflux.
[0040] The overhead stream 335 containing naphtha and light
components including H.sub.2S, CO.sub.2, NH.sub.3, and H.sub.2 is
condensed to separate the light components from the naphtha in
overhead receiver 340. If desired, a portion or the entire light
stream 345 may be recompressed and recycled as H.sub.2 feed to
either the first or second reactive distillation columns 105, 305.
Water stream 350 can be removed and sent for treatment. The naphtha
stream 355 now free of sulfur, nitrogen, oxygen, and metals can be
recovered as the liquid naphtha overhead product 360 and a portion
365 used as reflux into the reactive distillation column 305.
[0041] The bottoms 370 of the reactive distillation column 305 is
the high boiling product that may be used directly as a fuel or
fuel blending component or further processed.
[0042] The first and second reactive distillation columns 105 and
110 may be operated in series, as shown in FIG. 2. Alternatively,
the first and second reactive distillation columns may be preceded
by a splitter (not shown) which will separate the coal tar into a
light and heavy fraction. In this case, the two reactive
distillation columns are operated in parallel. The light fraction
is sent to the first column, and the heavy fraction is sent to the
second.
[0043] In another embodiment, either the first or second reactive
distillation unit can be converted into a hydroprocessing
reactor.
[0044] Previous reactive distillation processes have covered only a
gasoline fraction (with a boiling point range of about C5 to
232.degree. C.). Using the present invention, it was surprisingly
found that reactive distillation could be used to process a coal
tar stream over the entire useful range of composition. The range
of boiling points for the coal tar stream is from about C5 to about
350.degree. C. (compounds having boiling points above 350.degree.
C. desirably being removed prior to the reactive distillation).
[0045] While at least one exemplary embodiment has been presented
in the foregoing detailed description of the invention, it should
be appreciated that a vast number of variations exist. It should
also be appreciated that the exemplary embodiment or exemplary
embodiments are only examples, and are not intended to limit the
scope, applicability, or configuration of the invention in any way.
Rather, the foregoing detailed description will provide those
skilled in the art with a convenient road map for implementing an
exemplary embodiment of the invention. It being understood that
various changes may be made in the function and arrangement of
elements described in an exemplary embodiment without departing
from the scope of the invention as set forth in the appended
claims.
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