Note: Descriptions are shown in the official language in which they were submitted.
4~
.,
BAC~GROUND OF THE I~IVENTION
The present invention relates to a process for the production
'of a svnthetic natural gas, more particularl~, to the production
of synthetic natural gas from a secondarv synthesis gas, by which
,term is meant a synthesis gas produced from the coal derivedliquid
hydrocarbon by-product resulting from the g~sification of coal to
produce gasifier synthetic natural gas. The secondary synthesis
,gas is methanated to provide additional synthetic natural gas which
may be blended with the gasifier synthetic natural gas.
Coal gasification technology is well known and has been in
,commercial use in South Africa since about 1954 and was commonly
used in the United.States prior to 1950 to make town gas. The
;most commonly employed gasifier process is that developed by
Lurgi ~ohle und Mineraloeltechni~ GmbH, Frankfurt (~lain), Federal
~epublic of Germany. The Lurgi process utili~es a fixed bed
gasifier in which coal of a selected particle size is fed into
the top of the gasifier countercurrently to a stream of steam and
, oxygen fed from the bottom of the gasifier. A synthesis gas
(herein and in the claims called gasifier synthesis gas) and a
' hydrocarbon liquid by-product are produced from the coal and with-
, drawn from,thetop of the gasifier. Solid ash residue is withdrawn
thro~gh a rotating grate at the bottom of the gasifier. Up to
~ about one fourth of the coal fed to the process will emerge as thc
! liquid hydrocarbon by-product, rather than as the desired gasifier
, synthesis gas. Thus, a gasification plant using 8 million tons
l of coal per year may produce as much as about 2 million tons of
' llquid hydrocarbon by-product.
Such liquid hydrocarbon by-product essentially comprise three
, major fractions classified as oil, tar and phenolics. The oil
~Zl(~2
fraction has ~ boiling range ofabout 200-600~ (93-316C) and
requires treatmcnt if it is to be cmployed as a petroleum product
substitute. The tar contains substantial quantities of oxyger.
and nitrogen and about .01 percent ash. The phenolics are some-
~hat similar to cresols and have a boiling range of about 29~-~noo.-
(1~3-~05C). Generally these by-products are not particularly
valuable and do not command a high price even in those areas where
a market exists for them. The liquid hydrocarbon by-product is
also carcinogenic and toxic. Disposition of the by-product l~hen
no market exists for it presents significant environmental and
economic problems.
The present invention enables the conversion of such liquid
hydrocarbon by-product into additional synthesis gas (herein and
in the claims called secondary synthesis gas). This "secondary
synthesis gas" (sometimes herein abbreviated to "secondary SG") is
to be distinguished from the "gasifier synthesis gas" (someLimss
herein abbreviated to "gasifier SG") which is obtained in the coal
gasification step. Methanation of the gasifier SG and secondary
SG is carried out to provide product synthetic natural gas (some-
2v times herein abbreviated to "SNG"). As explained below the con-
version of the liquid hydrocarbon by-product to secondary SG is
carried out by a catalytic partial oxidation process in which
steam reforming and hydrocrac~ing reactions are believed to also
take place and to provide an efficient and economical means of
2i converting the liquid hydrocarbon by-product.
Steam reforming is a well known method for treating hydro-
carbons to generate hydrogen therefrom. It is usually carried
out by supplying hea~ to a mixture of steam and a hydrocarbon feed
while contacting the mixture with a suitable catalyst usually
z
nic~el. Steam reforming is gcnerally limitcd to paraffinic
naphtha and lightcr fceds which have been de-sulfurizcd and .reatDd
to remove ~iLro~cn compo~lnds, because of difficulties in attempting
to steam reform heavier hydrocarbons and the poisoning of steam
reforming catalysts by sulfur and nitro~en compounds.
Another known method of obtaining hydrogen from a hydrocarbon
feed is partial oxidation, in which the hydrocarbon feed is intro-
duced into an oxidation zone maintained in a fuel rich mode so that
only a portion of the feed is oxidized.
It is known that steam may also be injected into the partial
o~idation reactor ~ressel to react with the feed and with products
of the partial oxidation reaction. The process is not catalytic
and requires high ~emperatures to carry the reactions to comple-
tion, resulting in a relatively high oxygen consumption. On the
other hand; the partial oxidation process has the advantage that
it is able to readily handle hydrocarbon liquids heavier than
paraffinic naphthas and can even utilize coal as the source of the
hydrocarbon feed.
Catalytic autothermal reforming of hydrocarbon liquids is
2~ also known in the art, as evidenced by a paper Catalytic
Autothermal Reforming of Hydrocarbon Liquids by ~laria Flytzani-
Stephanopoulos and Gerald E. Voecks, presented at the American
; Institute of ChemicalEngineers' 90th National Meeting, Hous-or,
Texas, April 5-9, 1981. Autothermal reforming is defined thcre-
in as the utilization of catalytic parital oxidation in the
presence of added steam, which is said to increase the hydrogen
yield becaus^ of simultaneous (with the catalytic partial
-3-
~2~2~
oxidation) stcam reforming being attained. The paper discloses
,utilization of a particulate bed of three different nicXel
catalysts into ~hic:~ steam, air and a hydrocarbon fuel supply
comprising a ~lo. 2 fuel oil are iniected. The resulting product
,gases contain hydrogen and carbon o~ides.
In Brennstoff-Chemie 46, ~'o. 4, p. 23 (1965), a German
publication, Von P. Schmulder describes a Badische Anilin and Soda
~Fabrik (B~SF) process for autothermal reforming of gasoline. The
'process utilizes a first, pelletized, i.e., particulate, platinum
catalyst zone followed by a second, pelletized nickel catalyst
zone. A portion of the product gas is recycled to the process.
Disclosure of the utilization ofa noble metal catalyzed mono-
lith to carry out catalytic partial oxidation to convert more
than half of the hydrocarbon feed stock upstream of a steam re-
l~ forming zone is disclosed in an abstract entitled Evaluation of
¦' Steam Reformin~ Catalvst for use in the_Auto-Thermal Reforming
li of Hydrocarbon Feed Stocks by R. M. Yarrington, I. R. Feins, and
~ S. ~Iwang (~ational Fuel Cell Seminar, July 14-16, 19~0, San
¦I Diego). The abs-~ract noted the unique ability of rhodium to
I steam reform light olefins with little coke formation and noted
I that results were obtained for a series of platinum-rhodium
¦ catalysts with various ratios of platinum to total metal in which
¦¦ the total metal content was held constant.
¦1 U. S. Patent 4,054,407, assigned to the assignee of this
¦¦ application, discloses two-stage catalytic o~idation using
platinum group metal catalytic components dispersed on a mono-
lithic body. At least the stoichiometric amount of air is
¦ supplied over the two stages and steam is not employed.
-4-
U.S. Patent 3,481,722, assigned to the assignee of
this application, discloses a two stage process for steam
reforming normally liquid hydrocarbons using a platinum
group metal catalyst in the first stage. Steam and hydro-
gen, the latter of which may be obtained by partially
cracking the hydrocarbon feed, are combined with the feed
to the process.
SUMMARY OF THE INVENTION
.
In accordance with the present invention there is
provided in a coal gasification process in which coal is
reacted with steam and oxygen to produce (i) a gasifier
synthesis gas which is methanated to produce a synthetic
natural gas, and (ii) a liquid hydrocarbon by-product,
the improvement of preparing a secondary synthesis gas
from the liquid hydrocarbon by-product, which secondary
; synthesis gas may be methanated to form additional synthetic
i! natural gas, by the following steps: preheating an inlet
stream comprising the liquid hydrocarbon by-product, H2O
and oxygen to a preheat temperature which is preferably
at least 800F (427C) but in any case sufficiently high
to initiate catalytic oxidation of the hydrocarbon by-product
as defined below, but less than about 1200F (649C)~
introducing the preheated inlet stream into a first catalyst
zone comprising a monolithic body having a plurality of
gas flow passages extending therethrough and comprising
palladium and platinum catalytic components and op-tionally
rhodium catalytic component dispersed therein, the amounts
of hydrocarbon by-product, H2O and oxygen introduced into
-- 5
~2~ 2
the first catalyst zone being controlled to maintain
an H2O to C ratio of from about 0.5 to 5 and an 2 to
C ratio from about 0.15 to 0.4 in the inlet stream;
contacting the preheated inlet stream within the first
catalyst zone with the aforesaid catalytic component to
initiate and sustain therein catalytic oxidation of a
quantity, substantially less than all, of the hydrocarbon
by-product sufficient to attain a temperature within the
`' first catalyst zone at least high enough to crac~ substan-
tially all unoxidized C4 or heavier hydrocarbons in the
by-product tD Cl to C4 hydrocarbons, the temperature of
at least a portion of said monolithic body being at least
250F (139C~ higher than the ignition temperature of said
inlet stream, but not more than about 2000F (1093C),
whereby to produce a first catalyst zone effluent comprising
~A methane, hydrogen, carbon monoxide, carbon dioxide and
. .
H2O; passing the effluent to a treatment zone for the
removal of carbon dioxide and water therefrom and with-
drawing the treated first catalyst zone effluent as second-
ary synthesis gas product; and methanating the gasifier
synthesis gas and the secondary synthesis gas to provide
synthetic natural gas therefrom.
In one aspect of the present invention, there is
included the step of passing the first catalyst zone eff-
-.;i luent, while still at an elevated temperature, from the
first catalyst zone to a second catalyst zone containing
a steam reforming catalyst, preferably comprising platinum
and rhodium catalytic components, and contacting the first
"
~2~ 2
zone effluent in the second catalyst zone with the steam
reforming catalyst to react hydrocarbons therein ~,Jith
H2O to produce hydrogen and carbon oxides therefrom, and
then passing the effluent of the second catalys'c zone as
the effluent to the aforesaid treatment zone for the re-
moval of carbon dioxide and water therefrom.
In preferred aspects of the inven~ion, at least
about 50% by weight of the hydrcarbon by-product is con-
verted to Cl hydrocarbons in the first catalyst zone and/
or a total of at least about 98% by weight of hydrocarbon
by-product is converted to Cl hydrocarbons in the first and
second catalyst zones.
In another aspect of the invention, the effluent
of the first catalyst zone may be substantially entirely
depleted of oxygen and the secondary synthesis gas may be
combined with the gasifier synthesis gas to provide a combined
product synthesis gas.
In another aspect of the invention, the first catalyst
zone is maintained at a temperature of from about 1400F
to 2000F (760C to 1093C) and the first zone effluent is
introduced into the second catalyst zone at substantially
the same temperature. A volumetric hourly rate of at least
100,000 volumes of throughput per volume of catalyst may
be maintained in the first catalyst zone and a volumetric
hourly rate of from about 2,000 to 20,000 volumes of
throughput per volume of catalyst may be maintained in the
second catalyst zone, and the process of making the second-
ary SG may be carried out at a pressure of from about 50 psig
to 1500 psig.
-- 7 --
~z~
In one aspect of the invention, the liquid h~dro-
carbon by-product is treated to remove ash and metals,
if any, and the heaviest portion of the tars therein,
prior to being passed to the first catalyst zone.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic elevation view in cross
section of a laboratory or p:ilot plant size embodiment
of an autothermal reformer apparatus utilizable in accordance
with the present invention; and
Figure 2 is a schematic flow sheet diagram of a
coal gasification plant, including an autothermal reforming
section for conve~ting liquid hydrocarbon by-product from
the coal gasifier to secondary synthetic natural gas.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In a preferred embodiment of the present invention,
a coal gasifier plant includes a section for making a
secondary SG~ which section includes an autothermal reformer.
By incorporating the secondary SG section into the coal
gasificatlon plant, a greater quantity of product SG can
be obtained with the same size coal gasifier plant or a
smaller plant can be utilized to produce a given total product
synthetic natural gas (SNG) while consuming an environmentally
damaging substance.
In a preferred embodiment of the present invention,
at least a first catalst zone is provided for carrying out
catalytic partial oxidation, an exothermic reaction, and a
second, catalytic zone is optionally provided for carrying
..~
-- 8
out steam reforming, an endothermic reaction. Steam
reforming, as well as hydrocracking ofheavier hydrocarbons,
, also appears to take place in the first catalyst zone
so that under certain conditions a second catalyst zone
specifically for steam reforming is not require. Such
steam reforming as takes place in the the first catalyst
zone absorbs some of the heat generated by the partial
oxidation step and tends to moderate the operating
temperature attained. The net reaction in the first catalyst
zone is however exothermic. The exothermic, first catalyst
zone comprises a monolithic catalyst carrier on which a
platinum group metal catalyst is dispersed. Such catalyst
can effectively catalyze the partial oxidation and steam
reforming of the liquid hydrocarbon by-product, resulting
in hydrogen being formed. As compared to a non-catalytic
combustion process, such as conventional non-catalytic
i partial oxidation, catalytic partial oxidation enables the
utilization of lesser amounts of oxygen and lower temper-
ature levels to both oxidize andhydrocrack the liquid
hydrocarbon by-product to lighter hydrocarbon fractions.
Nonetheless, the temperature of the reactant mass is
sufficiently elevated for the optional subsequent steam
reforming step, in those cases where steam reforming is
required. At the temperatures maintained in the catalytic
oxidation zone, and in the presence of the product hydrogen
and catalyst utilized in the first zone, hydrocracking of
the unoxidized C2 and heavier hydrocarbons takes place to
.~
~Z~L~Z~
form primarily Cl hydrocarbons, with minor amounts of C2
and C3 compounds. The effluent gas from the first catalyst
. .
zone contains primarily H2, H2O, CH4, CO and CO2 and,
, depending upon the sulfur content of the liquid hydrocarbon
by-product, H2S and COS.
The endothermic, second catalyst zone may contain any
suitable steam reforming platinum group metal catalyst.
Usually, the steam reforming catalyst will be utilized in
the form of a particulate bed comprised of spheres, extrud-
~ 10 ates, granules, configured packing material, e.g., rings,
saddles or the like, ox any suitable shape. Obviously, a
combination of different types of particulate materials may
be utilized as the steam reforming catalyst. Further, a
monolithic catalyst carrier may also be used in the second
catalyst zone, as is used in the first catalyst zone.
The process of the present invention provides a simpler
and less expensive means of converting the liquid hydrocarbon
by-product of a coal gasification process, e.g., the Lurgi
coal gasification process than the conventional partial
oxidation or steam reforming processes. The combination
of features provided by the present invention provides a
highly efficient and flexible method of effectuating the
conversion. The low pressure drop and high volumetric rate
throughput of a monolithic body platinum group metal catalyst
i provides a reduced size and volume of catalyst. The use
of platinum group metals as the catalyst metal re~uires
a very low catalytic metal loading as compared to use of
base metal catalyst. This provides good overall economies
~, -- 1 0
in reduced equipment size and enhanced throughput rates
despite the much higher unit weight cost of platinum group
metals as compared to base metals. The combination of the
monolithic platinum group metal partial oxidation catalyst
¦ with a platinum group metal steam reforming catalyst enables
operations at relatively very low 2 to C ratios without
carbon deposition fouling the catalyst, which is important
in attaining enhanced CH4 production in the process. Use
of platinum group metal catalysts also enhances resistance
of the catalyst to poisoning by sulfur compounds and enhances
the ability of the catalyst to treat the aromatics in the
liquid hydrocarbon by-product.
The Monolithic Partlal Oxidation Catalyst
The partial oxidation catalyst is provided on monolithic
carrier, that is, a carrier of the type comprising one or
more monolithic bodies having a plurality of finely divided
gas flow passages extending therethough. Such monolithic
carrier members are often referred to as "honeycomb" type
carriers and are well known in the art. A preferred from
of such carrier is made of a refractory, substantially inert
rigid material which is capable of maintaining its shape and
a sufficient degree of mechanical strength at high temperatures,
for example, up to about 3,272F (1,800C). Typically, a
material is selected for the support which exhibits a low
thermal coefficient of expansion, good thermal shock resistance
i and, though not always, low thermal conductivity. Two general
types of material of construction for such carriers are known.
-- 11 --
z~
One is a ceramic-like porous material comprised of one
or more metal oxides, for example, alumina, alumina-silica,
alumina-silica-titania, mullite~ cordierite, zirconia,
zirconia-spinel, zirconia-mullite, silicon carbide, etc.
A particularly preferred and commercially available
material of construction is cordierite, which is an alumina-
magnesia-silica material and well suited for operations
- below about 2,000F (1,093C). Honeycomb monolithic
supports are commercially available in various sizes and
configurations. Typically, the monolithic carrier would
comprise, e.g., a cordierite member of generally cylindrical
configuration (either round or oval in cross section) and
having a plurality of parallel gas flow passages of regular
polygonal cross sectional extending therethrough. The gas
flow passages are typically sized to provide from about
50 to 1,200, preferrably, 200-600 gas flow channels per
square inch of face area.
The second major type of preferred material of
construction for the carrier is a heat- and oxidation-
resistant metal, such as a stainless steel or the like.
Monolithic supports are typically made from such materials
by placing a flat and a corrugated metal sheet one over the
other and rolling the stacked sheets into a tubular
configuration about an axis parallel to the corrugations,
:d to provide a cylindrical-shaped body having a plurality of
fine, parallel gas flow passages extending therethrough.
The sheets and corrugations are sized to provide the desired
number of gas flow passages, which may range, typically,
- 12 -
~2~ Z
from about 200 to 1,200 per square inch of end face area
of the tubular roll.
Although the ceramic-like metal oxide materials such
as cordierite are somewhat porous and rough-textured, they
nonetheless have a relatively low surface area with respect
to catalyst support re~uirements and, of course, a stainless
steel or other metal support is essentially smooth. Accord-
ingly, a suitable high surface area refractory metal oxide
support layer is deposited on the carrier to serve as a
support upon which finely dispersed catalytic metal may be
distended. As is known in the art, generally, oxides of one
or more of the metals of Groups II, III and IV of the Periodic
Table of Elements having atomic numbers not greater than 40
are satisfactory as the support layer. Preferred high surface
area support coatings are alumina, berylia, zirconia, baria-
alumina, magnesia, silica and combinations of two or more of
the foregoing.
The most preferred support coating is alumina, most
preferably a stabilized, high-surface area transition alumina.
As used herein and in the claims, "transition alumina" includes
gamma, chi, eta, kappa, theta and delta froms and mixtures
thereof. An alumina comprising or predominating in gamma
alumina is the most preferred support layer. It is known
that certain additives such as, e.g., one or more rare earth
metal oxides and/or alkaline earth metal oxides may be included
in the transition alumina (usually in amounts comprising from
2 to 10 weight percent of the stabilized coating) to stabilize
it against the generally undesirable high temperature phase
transition to alpha alumina, which is of a relatively low
~,~
- 13 -
z~
surface area. For example, oxides of one or more of
lanthanum, cerium, praseodymium, calcium, barium, strontium
and magnesium may be used as a stabilizer. The specific
combination of oxides of lanthanum and barium is a preferred
stabilizer for transition alumina.
As used herein and in the claims, the term "platinum
group metal" means platinum, palladium, rhodium, iridium,
osmium and ruthenium. The platinum group metal used may
optionally be supplemented with one or more base metals,
; 10 particularly base metals of Group VII and metals of Groups
VB, VIB and VIIB of the Periodic Table of Elements. Preferably,
one or more of chronium, copper, vanadium, cobalt, nickel
and iron may be employed.
Desirable catalysts for partial oxidation should have
the following properties: They shouId be able to operate
effectively under conditions varying from oxidizing at the
inlet to reducing at the exit; they should operate effect-
ively and without significant temperature degradation over a
temperature range of about 800F to about 2400F (427C to
1315C); they should operate effectively in the presence of
carbon monoxide, olefins and sulfur compounds; they should
provide for low levels of coking such as by preferentially
catalyzing the reaction of carbon with H2O to form carbon
monoxide and hydrogen thereby permittlng only a low level
of carbon on the catalyst surface; they must be able to
resist poisoning from such common poisons as sulfur and
halogen compounds; further, all of these requirements must
be satisfied simultaneously. For example, in some otherwise
~ 14 -
~Z~24Z
suitable catalysts, carbon monoxide may be retained by the
catalyst metal at low temperatures thereby decreasing or
modifying its activity. The combined platinum and palladium
is a highly efficient oxidation catalyst for the purposes
j of the present invention. Generally, the catalyst activity
of platinum-palladium combination catalysts is not simply
an arithmetic combination of their respective catalytic
activities; the disclosed range of proportions of platinum
and palladium have been found to posses the previously
described desirable properties and, in particular, provide
efficient and effective catalytic activity in treating a
rather wide range of hydrocarbonaceous, particularly hydro-
carbon, feeds with good resistance to high -temperature
operation and catalyst poisons.
` The following data compare the effectiveness of pall-adium, rhodium and platinum, respectively, for the oxidation
of methane and further compares the efficacy of, respectively,
palladium-platinum, palladium-rhodium and platinum-rhodium
combined catalyst for oxidation of methane.
The catalyst of Table I-A comprise a lanthia-chromia-
alumina frit impregnated with the platinum group metals by
techniques as described aboveO The frit has the following
composition:
Component Weight Percent
23 3.8
Cr203 1.8
A123 94-4
The lanthia-chromia stabilized alumina is then impreg-
nated with the platinum group metal and calcined in air for
-~ -r 1 5
four hours at 230F and for an additional four hours at
1600F. Three catalysts of different platinum metal
loadings were prepared as follows:
Weight Percent
Sample No.PdPt Rh Total PGM
~063U-1 3.425.95 - 9.37
4063R-1 4.58- 4.52 9.10
4063V-1 -5.62 3.14 8.76
The resultant platinum group metal (PGM) impregnated
alumina frit was deposited on alumina beads and the thus-
coated beads were placed in a shallow bed and tested by
passing a 1% (volume) methane 99% (volume) air feed at about
atmospheric pressure through the catalyst. An electric
heater was used to cyclically heat the test gas stream fed
to the catalyst, and conversion results at the indicated
temperatures were obtained on both the heating and cooling
phases of each heat cycle.
The results are shown in the following Table I-A.
TABLE I-A
PGM Weight Percent of Original
Sample (Mole Ignition Content Converted at Indicated
No. Ratio) Temp. F Temperature (F)
600 700 800 900 1000 1100
4063U-1Pd,Pt(l.l) 610 - 3 10 26 60 80
4063R-1Pd,Rh(l-l) 710 - - 2 5 9 12
4063V-1Pt,Rh(l:l) 730 - - 1 1 3 5
:' .
These data demonstrate the ability of platinum-palladium
to promote catalytic oxidation over a wide range of temperatures.
Rhodium may optionally be included with the platinum
and palladium. Under certain conditions, rhodium is an
- 16 -
~` ~2~
effective oxidation as well as a steam re~orming catalyst,
particularly for light olefins. The combined platinum
group metal catalysts of the invention also have a signif-
icant advantage in the ability to catalyze the autothermal
reactions at quite low ratios of H2O to carbon (atoms of
carbon in the ~eed) and oxygen to carbon, without signif-
icant carbon deposition on the catalyst. This important
feature provides flexibility in selecting H2O to C and 2
- to C ratios in the inlet streams to be processed.
The platinum group metals employed in the catalysts
,of the present invention may be present in the catalyst
;.~ composition in any suitable form, such as the elemental
metals, as alloys or intermetallic compounds with the other
- platinum group metal or metals present, or as compounds
such as an oxide of the platinum group metal. As used in the
. claims, the terms palladium, platinum and/or rhodium
"catalytic component" or "catalytic components" is intended
to embrace the specified platinum group metal or metals
present in any suitable form. Generally, reference in the
claims or herein to platinum group metal or metals catalytic
component or compounds embraces one or more platinum group
metals in any suitable catalytic form. Table I-A demonstrates
that the palladium-rhodium and platinum-rhodium combinations
are rather ineffective for methane oxidation. The effect-
iveness of rhodium as a methane oxidation catalyst is
attenuated by the relatively high calcination temperature
of 1600F. At a lower calcination temperature used in
preparation of the catalyst, say 1100F, rhodium retains
- 17 -
good methane oxidation characteristics. Howe~er, the
catalytic partial oxidation catalyst of the present inven-
tion may operate at ranges well above 1100F, which wculd probabl~
also reduce the effectiveness of rhodium for methane oxid-
ation.
The tests in which the results of Table I-A were
developed used a bed of the pla-tinum group metal-impregnated
frit dispersed on alumina beads, rather than a monolithic
body on which the frit is dispersed. The bed of frit-coated
beads was of shallow depth to avoid excessive pressure drop.
The geometric confirguration of a 400 cell/in2 monolithic body
provides more geometric surface area exposed to the reactant
gas than does a bed of coated beads. Since the catalytic
partial oxidation reactions of this invention are extremely
rapid at the temperatures involved, the catalytic metals
which reside on or near the surface of ~he catalyst body
are predominatly involved in the reactions. The results of
the tests wlth coated beads are indicative of results with
monolithic bodies, but lower catalytic metal loading can be
used with the latter as compared to metal loadings on beads,
to attain equivalent results.
Table I-B shows the results of testing a monolithic
body-supported catalyst on which a ceria-stabilized alumina
frit impregnated with the indicated platinum group metals
was dispersed upon a monolithic support. The alumina frit
comprised 5~ by weight CeO2, balance A12O3, impregnated
with one or two platinum group metals to provide the PGM
loadings indicated in Table I-B. The catalyst was calcined
r
" -- 18 ~
in air at 500C for two hours and then was aged 24 hou~s
at 1800F in air.
Two different test gases, A and B, having the following
composition were passed through the catalyst:
PARTS PER MILLION (VOL) OR
COMPOSITION VOLUME PER CENT
B
2 3~ 3%
CO lg6 1%
C2 10% 10%
H O 10% 10%
NO 50Oppm 50Oppm
C2H4 300ppm
C3H8 - 300ppm
N2 balance balance
Table I-B indicates the temperature in degrees
centigrade for conversion of 50% by weight of the original
amount of the component present, indicated under the column
heading T50, and the temperature required for 75~ by weight
- conversion, under the heading T75. A lower temperature
accordingly indicates a more active catalyst. The results
obtained are as follows; the platinum group metal (PGM)
loading on the monlithic support is shown as grams of platinum
group metal per cubic inch of monlithic catalyst.
TABLE I-B
PGM
Catalyst Weight Ratio PGM Loading Total PGM
Sample No. Pt:Pd (Pt/Pd (g/in3) Loading (g/in3)
1 100:0 .051/- .051
2 82:18 .044/.010 .054
3 58:42 .027/.019 .046
4 25:75 .011/.031 .042
0:100 - /.039 .039
3p 6 11:89 .003/.025 .028
`~ 7 100:0 .035/- .035
8 70:30 .034/.014 .048
~ Iq_
Test Gas A Test Gas B
_
Component CO C2H4 CO C3H8
;. Percent Conversion T50 T7s T50 75 T50 T7s T50 75
~ Catalyst Sample No. C C C C
.
1. 325 335325 335265 275470 565
2. 270 275280 290280 285545 615
3. 235 250260 305260 265495 640
4. 235 245260 320260 270465 585
5. 230 235245 270245 255440 510
; 6. 270 275275 315245 255430 555
7. 345 355350 365320 330495 550
8. 255 265265 290245 250485 585
The data of Table I-B demonstrate the lower temperatures
at which a palladium containing catalyst will attain,
respectively, 50% to 75% conversion of ethylene as compared
to a platinum only catalyst. As mentioned above, the presence
of platinum in addition to palladium provides effective
catalyization of other species as well as providing enhanced
poison resistance.
An exemplary mode of preparation of partial oxidation
catalyst compositions utilizable in accordance with the
present invention is set forth in the following Example 1.
Example 1
(a) To 229g of 2.5 wt % lanthia, 2.5 wt % baria -
95 wt % A12O3 powder (a predominantly gamma alumina which
has been stabilized by incorporation of lanthia and baria
therein) is added a solution containing 20g Pt as H2Pt(OH)6
solubilized in monoethanolamine so as to give total volume
of 229 ml. After mixing for 5 minutes, 25 ml of glacial
,~
acetic acid is added and the material is mixed a~ additio-nal
5 mintues before being dried and then calcined for one and
one-half hours at 350C in air -to form a free flowing powder.
! (b) Similarly, to 229g of 2.5 wt % lanthia, 2.5 wt %
! baria 95 wt % A12O3 powder there is added 21 g Pd as Pd(NO3)3.
The material is mixed and reduced with 16 ml of N2H4H2O
so-lution with constant mixing. The impregnated powder is dried
and then calcined for one and one-half hours at 375C in air.
(c) Two hundred gram of each of powder (a) and (b)
is added to a 1/2 gallon size ball mill with appropriate
amount of grinding media. To the powder is added 20 ml of
glacial acetic acid and 550 ml of H2O. The sample is ball
milled for 16 hours. The resulting slurry has a solids
content of 43%, a pH of 4.0 and a viscosity of 337 cps and
is used to coat a Corning cordierite monolith having a
I diameter of 3.66", a length of 3" and 400 gas flow passages
(of square cross section) per square inch of end face area.
The coating is accomplished by dipping the monolith in the
slurry for 2 minutes, draining excess slurry and blowing
the excess slurry from the gas flow passages with high
pressure air. The resultant slurry-coated monolith is
dried at 110C and calcined at 500C in air for 30 minutes.
The finished catalyst body contains 238g of platinum group
metal per cubic foot of catalyst body volume at a weight
`j ratio of paltinum to palladium of 1:1, with the platinum
group metal dispersed on a ceria-stabilized alumina
"washcoat" support layer. The catalyst body contains 1.64
grams per cubic inch of catalyst body of s~abilized alumina
washcoat.
- 21 -
z~%
A series of partial oxidation catalyst
compositions utilizeable in accordance with the present
invention were prepared by substantially the procedure
described in Example 1, with appropriate modifications to
obtain the reported loadings of different catalyst metals.
Each of the below described materials is a monolithic
catalyst compositionO Except for the catalyst identified
as CPO-5, in each case the honeycomb carrier is a C-400
cordierite carrier (400 gas flow passages per square inch
of end face area) manufactured by Corning. The CPO-5
catalyst is on an alpha alumina monolith body, sold under
the trademark TORVEX by DuPont~ and having 64 gas flow
channels per square inch of end face area. The Corning
cordierite monoliths have gas flow channels which are
~' square in cross section; those of the ~ORVEX monolith are
hexagonal in cross section. The amount of platinum group
metal on the catalyst is given in grams of elemental
platinum group metal per cubic foot of monolith catalyst
and the amount of refractory metal oxide coating is given
in grams per cubit inch of monolith-catalyst~ The weight
ratio of the platinum group metals in the order listed
is given in parentheses~ Thus~ catalyst CPO-l in Table I,
-~ for example, contains platinum and palladium in a weight
-~ ratio of one part platinum to one part palladium. In eachcase, the refractory metal oxide coating is alumina,
predominantly comprising gamma alumina stabilized as
indicated, the respective weight percents of stabilizer
- 22 -
4~
being indicated, the balance comprising substantially
alumina.
- TABLE I
Weight % and Alumina Supp~rt
PG Metal PG Metal Stabilizer in Coating g/in
Catalyst - ~omponent~ g/ft3 `Support Coating (%Stabilizer)
CPO-l Pt, Pd (1:1) 219 5~ ceria 1.27
CPO-2 Pt, Pd (1~6 5~ ceria 1.64
CPO-3 Pt, Pd (1:4) 275 5% ceria 1.79
CPO-4 Pt, Pd (1:1) 310 5% ceria 2.32
CPO-5(*) Pt, Pd (1:1) 200 5% ceria 1 26
CPO-6 Pt, Pd Rh
(9.5:(.51) 230 5% ceria 1.47
CPO-7 Pt, Pd (1:1) 186 2.5~ lanthia
2.5% baria 1.64
_
(*) TORVEX alpha alumina monolith; all others are cordierite
~ monoliths.
9 Genexally, the most preferred catalysts comprise
platinum and palladium catalyst components and combinations
thereof, with other platinum group metal catalytic components,
preferably, combinations comprising 10-90% by weight
palladium, preferably 25-75%, more preferably 40 to 60%, by
weight palladium, and 90 to 10% by weight platinum, prefer-
ably 75 to 25%, more preferably 60 to 40%, by weight platinum.
Generally, as the sulfur content of the hydrocarbon feed
being treated in the first catalyst zone increases, a higher
proporation of platinum to palladium is preferred. On the
other hand, for feeds which have a relatively high methane
content, an increasing proporation of palladium is preferred.
- 23 -
The monolithic configuration of the catalytic
partial oxidation catlyst of the first catalyst zone
affords a relatively low pressure drop across it as
compared to the packed bed of a particulate support
catalyst. This is particularly important in view of
the increase in gas volume occasioned by the reactions
taking place in the first catalyst zonel The total moles
of product produced in the first catalyst zone is higher
than the total moles of the inlet stream introduced therein.
The individual gas flow passages of the monolith also
serve, in effect, as individual adiabatic chambersr thus
helping to reduce heat loss and promote hydrocracking.
This is particularly so when the monolithic carrier
comprises a ceramic-like material such as cordierite
which has generally better heat insulating properties than
do the metal substrates and, to this extent, the ceramic-
type monolithic carriers are preferred over the metal
substrate monolithic carriers~ Further~ as the monolith
body becomes heated during operation, the gas in the up-
stream portion of the monolith is preheated by the heat
whlch is transferred back from the down-stream catalytic
partial oxidation to the inlet thus facilitating desired
hydrocracking and oxidation reactions~
i Steam Reforming Catalyst
The steam reforming catalyst utilized in the
second catalyst zone in accordance with the present
invention may utilize a monolithic carrier as described
_ ~4 -
~L21~Z
above in connection with the partial oxidation catalyst
or it may comprise a particulate support such as spheres,
extrudates, granules, shaped members (such as rings or
saddles) or the like. As used herein and in the claims,
the term "particulate catalyst" or the like means catalysts
of regularly or irregularly shaped particles or shaped
members or combinations thereof. A preferred particulate
support is alumina pellets or extrudate having a BET
(Brunnauer-Emmett-Teller) surface area of from about 10 to
200 square meters per gram. Alumina or alumiina stabilized
with rare earth metal and/or alkaline earth metal oxides
as described above, may be utilized as the pellets or
extrudate. An alumina particulate support stabilized with
lanthanum and barium oxides as described above is preferred.
The catalytically active metals for the optional
s~eam reforming catalyst comprise the well known base
metals (e.g., nickel) as well as platinum group metals,
as stated above. A preferred platinum group metal steam
reforming catalyst is a combination of platinum plus
rhodium catalytic components with the rhodium comprising,
on an elemental metal basis, from about 10 to 90% by
weight, preferably 20 to 40% by weight, and the platinum
comprising 90 to 10% by weight, preferably 80 to 60% by
weight. The proportion of platinum and rhodium utilized
will depend on the type of hydrocarbon feed to be treated
in the processO Other platinum group metals may be utilized.
,~
~2~Z9LZ
Example 2
~ a) A barium nitrate solution is prepared by
dissolving 15909g Ba(NO ~2 in 1,650 ml of H2O. ~anthanum
nitrate, in the amount of 264~9g La~NO312.6H2O is dissolved
in the barium nitrate solution by mixing vigorously to yield
a barium-lanthanum solution, to which is added to 3,000g of
high surface area gamma alumina powder. The solution and
powder are throughly mixed in a sigma blade mixer for 30
minutes~
~b~ The impregnated alumina resulting from step
Ca~ was extruded through 1/16" diameter dies so as to give
1/16" diameter extrudate in lengths from 1/4" to 3/8".
rc) The extrudates from step (b) were dried
at lloQC for 16 hours and then calcined 2 hours at 1,050QC
in air.
(d) ~ platinum-rhodium solution was prepared by
dissol~ing 42.6g as H2Pt(OH)6 in monoethanolamine and
18g Rh as Rh(NO3)3.2H2) and combining the materials in H2O
to provide a solution having a volume of 1,186 ml and a
pH of 0.7 after adjustment with concentrated HNO3.
(e) The platinum-rhodium solution of step (d)
is added to the extrudate obtained in step (c) in a tumbling
coater and mixed for 30 minutes. The impregnated extrudate
is dried at 120~C for 4 hours and then-calcined for 30 minutes
at 500QC ln air.
The resultant particulate steam reforming catalyst,
designated SR-l, comprises 1.4 wt % platinum and 0.6 wt %
rhodium on La2O3-BaO stabilized gamma alumina extrudate.
- 26 -
Z
The catalysts of Examples 1 and 2 were utilized
in test runs. Before describing these test runs, however,
preferred embodiments of the apparatus of the present
invention are descri~ed in some detail below.
;~
The ~eactor Vessel
Preferably, the reactor utilized in the auto-
thermal reforming process of the invention comprises a
fixed ~ed, adiabatic reactor. Figure 1 shows a somewhat
schematïc rendition of a preferred laboratory or pilot plant
size reactor comprising a unitary vessel 1 within which a
monolithic carrier paxtial oxidation catalyst 2 is disposed
in flow communication via a passageway 3 with a bed of steam
reforming catalyst 4. The vessel is suitably insulated by
thermal insulating material 5 to reduce heat losses and to
provide essentially a fixed bed, adiabatic reactor. Inlet
lines 6, 7 and 8 feed a mixer 9 with, respectively, a
hydrocarbon feed, steam and oxygen. The admixed reactants
are introducted through an inlet line A into partial
oxidation catalyst 2, thence via passage 3 into steam
reforming bed 4 from which the contacted material is with-
drawn through outlet line B. Valves, flow meters and heat
exchange units, utilized in a manner known to those skilled
in the art, are not shown in the schematic illustration of
Figure 1.
Typically, in the apparatus of Figure 1, the
monolithic carrier catalyst 2 is of cylindrical configuration,
three quarters of an inch (1.9 cm) in diameter and nine inches
- 27 -
(22.9 cm) long. The steam reforming bed is a cylindrical
bed of particulate catalyst three inches (7.62 cm~ in
diameter by nine and a quarter inches 123.5 cm) long. In
operation, reactants are preheated with the oxidant stream
being preheated separately from the hydrocarbon feed as a
safety measure. After preheating, the streams were
intimately mixed and immediately fed into the partial
oxidation catalyst 2 of vessel l. Generally, all the
oxygen present in the feed reacts within monolithic catalyst
bed 2 to oxidize a portion, but not all, of the hydrocarbon
feed, resulting in an increase in temperature due to the
exothermic oxldation reaction. The heavier hydrocarbons
are hydrocrakced in catalyst bed 2 to lighter, predominantly
Cl hydrocarbons. The heated , partially oxidized and
hydrocracked effluent from catalyst bed 2 is then passed
through steam reforming catalyst bed 4 wherein the steam
reforming reaction takes place. The product gases with-
drawn via outlet B are cooled and unreacted water as well
as any unreacted hydrocarbon feed, if any, is condensed
and removed therefrom. The dry gas composition may be
monitored by gas chromatography. The same principles of
operation are followed in commercial embodiments of the
apparatus.
Referring now to Figure 2, there is shown a
schematic flow sheet illustration of a coal gasifier plant
including an autothermal reforming section utilized to convert
the liquid hydrocarbon by-product to secondary SG. A typical
- 28 -
coal gasification plant, such as one according to the
Lurgi design, includes a coal crushing and screening zone
10 to which coal is conveyed by suitable means for crushing
and screening to segregate the coal particies by size, and
any other treatments such as washing, etc., which may be
required. Finely crushed coal is transmitted by means 12
to a power plant 14 to which water and air is supplied and
in which the coal is burned to generate steam and electric
power required in operation of the plant.
A coarse coal stream is fed via means 16 to a
coal gasifier 18. Coal gasifier 18 may be of any suitable
design, such as a Lurgi fixed bed reactor with rotating
bottom grate, as briefly described a~ove. Steam is
transmitted via lines 20, 22 from power plant 14 to coal
gasifier 18.
An air separation plant 24 is supplied with air
and, by any suitable technique, separates an oxygen stream
from the air. Nitrogen is removed via line 26 and oxygen
transmitted via lines 28, 30 to coal gasifier 18. It will
be understood that in the case of the Lurgi coal gasifier
design, as mentioned above, the steam and oxygen are trans-
mitted through the gasifier counter-currently to descending
stream of coarse coal particles. Under the conditions of
temperature and pressure maintained in coal gasifier 18,
gasifier SG is generated in coal gasifier 18, together with
a liqued hydrocarbon by-product, both of which are removed
- 29 -
42
from coal gasifier 18 via line 32. Ash is removed fro~
coal gasifier 18 via line 34. The gasifier SG and liquid
hydrocarbon by-product are quenched in quench zone 36 from
which the liquid hydrocarbon by-product is removed via line
38. The gasifier SG is transmitted via line 40 to a gas
purification zone 42 in which carbon dioxide and hydrogen
sulfide are removed therefrom by any suitable, known
treatment.
The liquid hydrocarbon by-product is transmitted
via line 38 to a gas-liquor separation zone 46 in which a
gaseous fraction largely comprising ammonia and gasified
phenolics is separated and removed via line 48 to a phenols
separation zone 50, wherein off-gases including ammonia
are separated and removed via line 52. The phenolics are
- transmitted via line 54 to a blending zone 56 wherein the
recovered phenolics are combined with the liquor separated
from gas-liquor separation zone 46 via line 58.
A typical composition for the liquid hydrocarbon
by-product, comprising the re-combined phenolics and liquor
- 20 in line 60, is given in Table II.
TABLE II
Composition of Typical Hydrocarbon Liquid By-Product.
Component Average Formula Average Molecular Weight
1) Oil 13.5 18 180
2) Tar CllHloO 158
3) Phenolics C7H8O 108
4) Blend of
1), 2) and 3) 11 14.3 162
- 30 -
4~
The hydrocarbon by-product is transmitted via line 60 to a
solids removal zone 62 wherein ash and heavy tar components
are separated and removed via line 64. The hydrocarbons by-
product may be treated by any suitable technique such as
filtration and/or distillation for solids removal in zone 62.
In such process, metals and residual ash in the hydrocarbon
; by-products together with the heaviest tar fractions thereof
are removed.
While any suitable method or combination of methods
for removing solids and metals and the heavy tar fraction
j may be utilized, a particularly useful and efficient method
is the ARTSM treatment developed by Engelhard Corporation,
the assignee of this application. This process utilizes
; an ARTCATTM material to carry out an asphalt residual treat-
ment process which is highly effective and efficient in
treating heavy petroleum or o-ther hydrocarbon containing
: fractions to render them suitable for processing to more
valuable materials.
The ash and heavy tar removed via line 64 may be
cycled to power plant 14 for combustion of the combustible
values therein to supplement the coal supplied as fuel thereto.
The thus-treated liquid hydrocarbon by-product is passed via
line 66 through a heat exchanger 68 in which it is heated by
indirect heat exchange as described below, and thence into a
mixer 70.
- 31 -
~,
!~
2~Z
An oxygen stream is transmitted from air
separation zone 24 via lines 28, 72 and steam is trans-
. mitted from power plant 14 via lines 20, 74 through a heat
exchanger 7~ for indirect heat exchange as explained below,
thence to mixer 70 wherein the oxygen, steam and treated
liquid hydrocarbon by-product are admixed for transmission
; via line 78 as the inlet stream to an autothermal reformer
80.
In reformer 80 the mixture of hydrocarbon by-product,
steam and oxygen is passed through a catalytic partial
oxidation catalyst supported on a monolithic honeycomb carrier
disposed within neck portion 80a of reformer 80. Some, but
not all of the hydrocarbon is catalytically oxidized within
the first catalyst zone contained within neck portion 80a
and the heavier unoxidized hydrocarbons are hydrocracKed
to lighter constituents, mostly Cl hydrocarbons, with a very
minor amount o~ C2 and C3 hydrocarbons. Methane is the pre-
. dominant hydrocarbon product attained by the hydrocracking.
Depending on the specific nature of the hydrocarbon by-
product fed to autothermal reformer 80 and the specific
operating conditions utilized therin, the hydrocarbon by-
product may be substantially entirely converted to a gaseous
product containing H2, H2O, CH4, CO and CO2. However, under
conditions in which a significant amount of heavier hydro-
carbons would remain in the effluent from the first catalyst
zone, a second catalyst zone may be disposed within main body
32,
3Z4;~
portion 80b of reformer 80. In the second catalyst zone a
steam reforming reaction is catalyzed to convert hydrocarbons
to hydrogen and carbon oxides.
It is of course desired to provide a high methane
content in the secondary S~. Therefore, the exit temperature
of the gases exiting via line 82 is preferably controlled to
reduce the amount of C2 and C3 compounds formed within
reformer 800 For example, an outlet temperature at line 82
of about 1,400F (760DC) has been found to be satisfactory to
hydrocrack the material within the first catalyst zone to
mostly Cl hydrocarbons, i.e., CO, CO2 and CH4. A methanation
step as described below, for reacting carbon monoxide and
hydrogen to methane, is conveniently utilized in the process.
It is therefore desirable to also control the conditions with-
in reformer 80 to provide ln the gas obtained therein a molar
ratio of hydrogen to carbon monoxide of slightly more than
3:1, the molar ratio in which the two gases react to form
methane and H2O.
The effluent gas from reformer 80 is passed via
line 82 through heat exchanger 76 to heat therein the oxygen
and steam being transmitted via, respectively, lines 72 and
74 to mixer 70. The reformer effluent is then passed through
heat exchanger 68 to heat the incoming liquid hydrocarbon
by-product in line 66. The cooled reformer effluent gas is
passed via line 82 to a quench zone 84 wherein the gas is
cooled and water is separated therefrom via line 86. The
- 33 -
z~
cooled secondary SG is passed via line 88 to be introduced
into llne 40 to be admixed with the gasifier SG and the
combined gases are then passed to gas purification zone 42
wherein acid gases, e.g., CO2 and H2S, are removed by known
techniques and withdrawn via line 45. The purified combined
gases are then passed to methanation zone 90 in which carbon
monoxide contained therein is reacted with hydrogen to methane
and H20, thereby increasing the overall methane content of
the product synethesis gas which is withdrawn therefrom via
line 92. It is this product, after drying to remove water,
! which is usually called "synthetic natural gas" or "SNG".
The following example exemplifies operating conditions
and results obtained in treatlng a liquid hydrocarbon by-
product which has been treated, as described above, for the
removal of ash and heavy tars therefrom.
Example 3
Inlet Streamlb.-moles 2 -to C H20 to C
(78 in FIG. 2 Composition) per hour Ratio ~atio
1) Feed-item (4) of Table II 828 0.176 2.00
2) Steam 18,216 --
3) Oxygen 1,602
_________________________ _______________
Temperature of Inlet Stream (78 in FI5. 2) = 800F ( a 27C)
Pressure - 31 atmospheres.
h
- 34 -
242
Effluent Gas
(82 in FIG. 2) lb.-moles
Composition per hour
H2 8,325
11,212
CH4 2,300
CO 2,679
C2 ~,229
3 10 Temperature o Effluent Gas (82 in FIG. 2) - 1,400F (7~0C)
Pressure of Effluent Gas = 30 atmospheres
It will be seen that upon removal of H2O and CO2,
and conversion of CO and H2 to CH4 by methanation~ a pre-
dominantly hydroyen and methane containing synthetic natural
gas is obtained from the secondary SG to supplement the
synthesis natural gas obtained from the gasifier SNG.
While the invention has been described in detail
with respect to specific preferred embodiments thereof, it
will be appreciated that those skilled in the art, upon
20 reading and understanding of the foregoing will readily
envision modifications and variations to the preferred embodi-
3 ments which are nonetheless within the spirit and scope of
the invention and of the claims.
~' .3.
