Note: Descriptions are shown in the official language in which they were submitted.
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`
. BACKGROUND OF THE INVENTION
` Field of the Invention
.:
This application is directed to a process for the
removal of alkyl lead impurities Erom liquid hydrocarbons
Description of the Prior Art
Lead and its compounds, especially alkyl lead, R4
Pb, are not recognized as naturally occuring in crude oil.
However, lead is found in crude oils and their distillate
fractions and is usually traced to the lead contamination
in gasoline.
It is known to use cupric chloride impregnated on
nongraphitic carbon or on silica gel for removing lead contam-
ination from unleaded gasoline; A.A. Zimmerman, G.S. Musser
et al., SAE Fuels and Lubricants Meeting. (Houston 6/3-5/75)
-~ Technical Paper; Chemical Abstracts vol. 85-1976, 49026 G.
; It is also known to remove lead from motor fuels for internal
combustion engines by contacting the fuel with a strongly
acidic cation exchanger (German Patent ~T 2,361,025); and
to remove dissolved organic lead compounds from various
20 liquid hydrocarbons by pretreatment with SiC14, CuC12, CuBr2,
I2 or I2 combined with an acid followed by contacting the pre-
treated hydrocarbon with activated carbon and an acid treated
clay or silica gel (U.S. 3,893,912). However, significant
amounts of lead impurities remain after such treatments.
Additional lead contamination may be acquired in shipping,
for example, when a naphtha reformer feed is purchased in one
location and shipped to another for reforming.
SUMMARY OF THE INVENTION
Therefore, this application is directed to a novel
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process wherein substantially all of the lead contaminants
contained in a given liquid hydrocarbon solution are removed.
For example, feedstocks to reformer units in refineries should
be substantially free of lead impurit;ies to guarantee reasonable
economics of operation. Contamination of reformer feedstock by
lead impurities put the reformer facilities out of balance and
cause unnecessary reformer catalyst poisoning. By means of the
- process disclosed herein lead contamination in for example
naptha reformer feedstocks of 75 parts per million (ppm) is re-
duced to less than 5 parts per billion (ppb).
Accordingly, this application ls more particularly
directed to a process for effecting the removal of alkyl lead
contaminant from liquid hydrocarbon media containing said con-
taminant which comprlses contacting said hydrocarbon at a
temperature below the boiling point thereof with a solid sorbent
having an amount of anhydrous HCl gas adsorbed therein sufficient
to effect substantial reduction in the concentration of said
contaminant and maintaining said contact until substantially
all of said contaminants are removed therefrom.
DESCRIPTION OF SPECIFIC EMPODI~iTS
. .
The novel process in accordance with the invention
disclosed herein is generally useful for removing alkyl lead
impurities from any liquid hydrocarbon media. It is suitable
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; for treating petroleum oils of lubricating viscosity, distil- late fuel oils, gasoline and slmilar light liquid hydrocarbon
products lncluding both mineral oil and synthetic hydrocarbon
products. The preferred embodiment is the removal of lead
contamination from reformer feeds.
A wide variety of solid sorbents may be advantageously
used. These sorbents (supports) can be crystalline or amorphous.
Amorphous sorbents, however, have proven to be more advantageous.
In any event, the sorbents must have sufficlent surface area and
0 porosity to adsorb an effective amount of the anhydrous HCl. The
surface area of the sorbents useful herein is from about 5 m2/g
to about 1000 m2/g; the surface area of zeolite crystalline sor-
bents is usually from about 100 to about 1000 m2/g and preferential-
ly from 100 to about 750 m2/g; the surface area of the amorphous
sorbents is usually from about 5 to about 750 m2/g and pre-
ferably from about 150 - 600 m2/g. The average pore diameter
of the sorbent should be from about 3 to about 200A; the average
pore diameter of zeolite crystalline sorbents used herein is
usually less than about lOA~ i.e., from about 3-9~; of amorphous
~0 sorbents it is usually from about 10-20 to about 200A and pre-
ferentially from about 20-lOOA.
Suitable sorbents include synthetic or naturally oc-
curring materials such as fau~asite (zeolite X, zeolite Y),
mordenite, and various other zeolites as may be suitable, e.g.,
zeollte ZK-4, zeolite ZSM-5~ as well as such inorganic materials
as bauxite, clay, silica and/or metal oxides and natural~y oc-
curring clays which can be composited with the zeolites, these
include the montmorillonlte and kaolin families, which include
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the sub-bentonites and the kaollns commonly known as Dixie,
McNamme-Georgla and Florida clays or others ln which the main
mineral constituent is halloyxite, kaollnite, dickite, nacrite
or anauxite and activated carbons. Such clays can be used in
the raw state as originally mined or lnitially sub~ect to
calcination, acid treatment or chemical modification.
ln addition to the foregoing materials, zeolites em-
ployed herein may also be composited with materlal such as
bauxite, alumina, silica-alumina, silica-magnesia, sillca-
zirconia, silica-thoria, silica, berylia, silica-titania as well
as ternary compositions, such as sllica-alumlna-thorla, silica-
alumina, zirconia, silica,-alumina-magnesia and silica-magnesia-
zirconia. Preferred are sorbents selected from the group
consisting of various forms of silica, bauxite, mordenite,
natural and synthetic clays, amorphous and crystalline alumino-
silicates, alumina and silica-alumina mixtures; silica-alumina
mixtures may contain about 5 to 95% silica or preferably about
5-25 wt. % or about 75-95 wt. ~ silica to alumina. Thermofor
cracking catalysts (TCC) such as fresh, spent or regenerated
bead type TCC catalysts may be used herein as sorbents.
The effective amount of adsorbed anhydrous HCl gas
will vary dependent upon type of sorbent, adsorption conditions
of temperature and pressure as well as reaction parameters.
Usually the sorbent disclosed herein will contain from about
0.001 to about 20 wt. % of adsorbed HCl and preferably from
about 0.1 to about 17.5 wt. % based on the total weight of the
sorbent.
The process of removing lead contaminants, e.g.,
tetraethyl or tetramethyl lead, from liquld hydrocarbons is
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conveniently carried out in a simple flow or batch process.
A solution of the lead contaminated hydrocarbon is passed
over the sorbent, e.g., NaX-zeolite, amorphous silica, etc.,
lead compounds in the solution undergo a displacement reaction
giving an lnsoluble alkyl salt, i.e.~ R3PbCl and a gaseous pro-
duct, i.e., RH. The gas escapes through the solution and the
insoluble salt remains on the sorbent. The process is carrled
- out at room temperature or at any temperature below the boiling
point of the liquid hydrocarbons. Preferred operatlng condi-
tions are a temperature of from about 25-60C, LHSV of from
about 5-20 and atmospheric or slightly higher pressure. A
suitable sorbent, i.e., silica, alumina, mixtures thereof and
calcined X and Y zeolites such as calcined NaX, may be included
after the lead removal step to remove (i.e., adsorb) any HCl
desorbed durlng the lead removal stage of the process. For a
"wet" (having more than about 100 ppm water~ hydrocarbon feed,
a drying step utilizing the above operating conditions and also
utllizing calcined NaX or other suitable dessicant can precede
the lead removal step e.g., commercial drying agents comprised
of silica, alumina, mixtures thereof, and X and Y zeolites are
suitable.
EXAMPLE 1
100 grams NaX 1/16" extrudate were calcined in a
glass reactor at 350C in argon for about 16 hours and cooled
~5 at room temperature. A stream of anhydrous hydrogen chloride
gas was allowed to contact the zeolite (pore diameter about
7-9A; surface area about 750 m2/g~, downflow until the loading
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was complete, i.e., about 15.6~17.5 wt. % of HCl at
equllibrium at room temperature. When anhydrous HCl con-
tacts the sorbent, an exothermic reaction zone develops at
the top of the reactor. This zone moves down the bed. After
j the bottom section of the reactor cooled down, in an atmosphere
of HCl gas, the reactor was purged with dry argon for about 1
minute to remove any easily-desorbed HCl.
EXA~PLE 2
80 grams of a NaX molecular sleve, 1/16" extrudate,
were placed in a glass reactor, calcined at 400C. in argon
for about 16 hours and cooled to room temperature. Anhydrous
HCl gas was then passed downflow (as in Example 1~ over the
calcined sorbent until HCl loading was complete; the NaX ex-
trudate adsorbed about 12.5 g HCl, or about 15.6 wt. ~ and
was otherwise prepared in the manner of Example 1.
EXAMPLE 3
._
32.1 grams of a commercially obtained amorphous
silica-alumina sorbent (Durabead-l~ having the following
general properties: pore diameter about 80A; surface area
about 200 m2/g. and a silica to alumina ratio of about 9:1,
were calcined in argon at 350C for about 16 hours and cooled
to room temperature. Dry HCl gas was then passed downflow over
the catalyst until equilibrium at room temperature was reached.
0.345 grams of HCl ( ~ 1% wt.) were adsorbed by the sorbent.
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EXAMPLE 4
A regular gasoline containing 1.8 g/gal Pb was used
as a 10% contaminant ln a Pb-free naphtha reformer feed. A
suitable reactor containing the NaX sorbent with adsorbed an-
hydrous HCl as described in Example 1 was connected to a feed
pump. Naphtha was introduced at the bottom of the reactor at
o.6 LHSV and at a temperature of about 5C below the boiling
polnt of the naphtha by means of a metering pump and moves up-
flow through the bed until it reaches the exit at the top of
the reactor. The naptha is then collected as product. Reformer
naphtha properties are as shown in Table 1, C5 ppb lead before
contamination and 75,000 ppb after contamination. Product
naphtha properties are shown in Table 2, after treatment with
the sorbent of Example 2 lead contamination was reduced to
L5 < 5.
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TABLE 1
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PROPERTIES OF _ PHTH.A FEED
FreshContaminated ~ith
Na~htha10;r, Regular Ga~oline
Gravity, API 63.o 62.2
Vapor Pressure 2.3 3.3
I~later, ppm. 44
Lead, ppb. ~5 75,000 (75 ppm)
Chloride, Cl- absent absent
Distillation, F
5% 188
10% 198
30% 215
50% 237
70% 264
90~ 296
EP 335
TABLE 2
Properties of Naphtha Treated
20 With HCl/NaX, 0.6 LHSV, 10 vol~vol of Contact
Mass
25C 90C
Gravity, API 62.2
- - Lead, ppb. ~5 ~5
Chloride, Cl absent absent
EXAMPLE 5
One gallon of a hexane/toluene mixture (70/30 vol.)
containing 174 ppm Pb was pumped upflow, 0.5 LHSV and at
room temperature, through a sorben system as described in
Example 3 followed by another gallon containing 340 ppm lead.
Finally, 1500 ml containing 450 ppm lead were used. 10 ml
samples of product were taken for diagnostic Pb analyses by
Test Method A (described below) at 24 hour intervals. In
addition, 500 ml samples were taken at about 25%, 65%, and
75% HCl depletion points for ppb Pb analyses by Test Method
B (described below). Table 3 summarizes data obtained on
samples of Pb-contaminated light hydrocarbon mixtures treated
with the silica-alumina/HCl sorbent system of Example 3 at
room temperature.
Data in Table 3 show that the stoichiometry of the
reaction is one mole of HCl to one mole of R4Pb. Thus, for
the amount of HCl adsorbed, 0.345 gm. (9.45 mmols), a maximum
of 1.958 gm. of Pb would be expected to react,
R4Pb + HCl ~ RH + R3PbCl
where R4Pb is a commercial mixture of tetraalkyl lead; i.e.,
tetraethyl, tetramethyl, trimethylethyl, diethyl-dimethyl
etc.
Table 3 further shows that at 99.2% of HCl used, the
contact mass reduces 450 ppm Pb in the feed to 38 ppm and at
a point ~ 100% to ~ 300 ppm and that alkyl lead compounds
react with available HCl in the catalysts until all the HCl
is depleted.
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Test Method A is used to determine lead in reformer
naphthas and similar light hydrocarbon stocks at concentra-
tions below 100 ppb/ i.e., trace amounts of lead. Lead pre-
sent as alkyllead contamination and as naphthenates and other
compounds decomposed by bromine are determined. Other metals
do not interfere.
OUTLINE OF METHOD A
A 500-ml sample is reacted in an appropriate sample
bottle with 454g (5N) bromine diluted in carbon
tetrachloride to 1 liter, for 2 minutes at room
temperature, and then extracted with water. The
extract is transferred to a test tube and aspirated
into the burner of an atom~c absorption spectrometer.
The absorbance of the 2170A line is measured and con-
verted to lead content by means of a calibration
curve.
Test Method B (ASTM D3237) is used to analyze
unleaded materials such as fuels containing 0.5 ppm or more
of lead.
OUTLINE OF METHOD B
The atomic absorption spectrophotometer is adjusted
with the aid of commercially obtained standardization
solutions. The sample material is then aspirated
directly into the instrument and the absorption is
measured.
` As is readily apparent from the data in the foregoing Tables,
the sorbent system and method of use thereof is a significant
improvement in the art.
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EXAMPLE 6
Samples of naphtha (see Table 1) were contaminated
by the addition of about 0.2 ml oE a 5 g Pb/gal. gasoline
to 1 gallon of Kuwait naphtha to give 88 ppb of lead contamin-
ation; and processed as described above using the sorbent
of Example 3; see Tables 4 and 5.
The data in Tables 4 and 5 illustrate that reformer
feeds containing as little as 88 ppb contamination can be
even further reduced to safe reformer levels, i.e., <5 ppb
by the process of this invention.
Although preferred embodiments have been exemplified,
variations can be resorted to and are within the scope of
this invention as one of ordinary skill in the art will
readily understand.
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