U.S. patent application number 15/945155 was filed with the patent office on 2018-09-06 for liquid-phase decomposition of particulate mercury from hydrocarbon streams.
The applicant listed for this patent is Chevron U.S.A. Inc.. Invention is credited to Daniel Chinn, Russell Evan Cooper, Tapan K. Das, Dennis John O'Rear.
Application Number | 20180251688 15/945155 |
Document ID | / |
Family ID | 63357267 |
Filed Date | 2018-09-06 |
United States Patent
Application |
20180251688 |
Kind Code |
A1 |
O'Rear; Dennis John ; et
al. |
September 6, 2018 |
LIQUID-PHASE DECOMPOSITION OF PARTICULATE MERCURY FROM HYDROCARBON
STREAMS
Abstract
Particulate mercury is removed from crude oil by thermally
treating the crude oil or condensate at temperatures in a range
from 150.degree. C. to 350.degree. C. and at a sufficient pressure
with subsequent cooling under maintenance of pressure to provide
irreversible conversion to elemental mercury, which may be
preferentially removed in a mercury removal unit.
Inventors: |
O'Rear; Dennis John;
(Petaluma, CA) ; Cooper; Russell Evan; (Martinez,
CA) ; Chinn; Daniel; (Danville, CA) ; Das;
Tapan K.; (Albany, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Chevron U.S.A. Inc. |
San Ramon |
CA |
US |
|
|
Family ID: |
63357267 |
Appl. No.: |
15/945155 |
Filed: |
April 4, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14922383 |
Oct 26, 2015 |
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|
15945155 |
|
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|
62149751 |
Apr 20, 2015 |
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62073445 |
Oct 31, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C10G 31/06 20130101;
C10G 2300/205 20130101 |
International
Class: |
C10G 31/06 20060101
C10G031/06 |
Claims
1. A method for the removal of mercury from a crude oil comprising:
increasing the pressure on the crude so that it remains essentially
in the liquid state for a subsequent heating step; heating the
pressurized crude to temperature in a range from 150.degree. C. to
350.degree. C.; processing the crude in a thermal decomposition
reactor operating in a liquid phase at LHSV of greater than or
equal to 0.1 hr.sup.-1 and less than or equal to 10 hr.sup.-1 to
convert at least a portion of the particulate mercury to elemental
mercury)(Hg.sup.0); maintaining the pressure while concurrently
cooling the product from the thermal decomposition reactor to
greater than or equal to 40.degree. C. and less than or equal to
150.degree. C., feeding the cooled reaction product from the
thermal decomposition reactor to a unit for the preferential
removal of elemental mercury.
2. The method of claim 1, wherein the first temperature is in a
range from 200.degree. C. to 275.degree. C.
3. The method of claim 1, wherein the first pressure is in a range
from 250 psig to 1500 psig.
4. The method of claim 1, wherein the product is cooled from the
thermal decomposition reactor to a temperature range of 70.degree.
C. or less.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation in part of U.S.
application Ser. No. 14/922,383, filed on Oct. 26, 2015, which
claims priority from application Ser. No. 62/149,751, filed on Apr.
20, 2015 and application Ser. No. 62/073,445, filed on Oct. 31,
2014, the entire contents of all of these applications are hereby
incorporated by reference herein.
TECHNICAL FIELD
[0002] The invention relates generally to a process, method,
system, and management plan for removal and control of heavy metals
such as mercury from fluids.
BACKGROUND
[0003] Heavy metals such as mercury can be present in trace amounts
in hydrocarbon gases, crude oils, and produced water. The amount
can range from below the analytical detection limit to several
thousand ppbw (parts per billion by weight) depending on the
source. Crudes containing 50 ppbw total mercury or more are
referred here as high mercury crudes. When processed in a refinery,
the mercury in high mercury crudes accumulates in the distillation
products. In addition, liquid elemental mercury may accumulate in
some equipment. If mercury is removed from crude oil, a
mercury-containing waste product is generated, or the mercury is
recovered as a valuable byproduct. In order to minimize the volume
and cost of disposal of this waste mercury, it is desired that the
waste have as high a mercury content as possible. In addition the
mercury in the waste should be essentially non-leachable and pass
TCLP (Toxicity characteristic leaching procedure) requirements.
[0004] There are processes in the prior art to remove mercury in
crude oils. But these generate either a gaseous mercury-containing
waste product, an aqueous mercury-containing waste product, or a
dilute solid waste product that contains less than about 100 ppmw
Hg and is therefore produced in large volumes. Various methods to
remove trace metal contaminants in liquid hydrocarbon feed such as
mercury have been disclosed, including the removal of mercury from
water by iodide impregnated granular activated carbons. U.S. Pat.
No. 5,336,835 discloses the removal of mercury from liquid
hydrocarbon using an adsorbent comprising an activated carbon
impregnated with a reactant metal halide, with the halide being
selected from the group consisting of I, Br and Cl. U.S. Pat. No.
5,202,301 discloses removing mercury from liquid hydrocarbon with
an activated carbon adsorbent impregnated with a composition
containing metal halide or other reducing halide. US Patent
Publication No. 2010/0051553 discloses the removal of mercury from
liquid streams such as non-aqueous liquid hydrocarbonaceous streams
upon contact with a Hg-complexing agent for mercury to form
insoluble complexes for subsequent removal. U.S. Pat. No. 8,728,304
describes the removal of trace element levels of heavy metals such
as mercury in crude oil by contacting the crude oil with an iodine
source, generating a water soluble heavy metal complex for
subsequent removal from the crude oil.
[0005] Particulate mercury in crudes presents a challenge to the
removal of mercury from crude oil as particulate is more difficult
to remove than elemental mercury. While some particulate can be
removed by filtration, filtration may not be effective in removing
particulate mercury when substantial amounts are present in
particles below 0.45 .mu.m (microns).
[0006] Adsorption technology does not work well for crude oils and
condensates with low levels of mercury, and particularly crude oils
containing the non-volatile form of mercury, which has not been
well addressed in the prior art. There is a need for improved
methods for the removal of mercury from liquid hydrocarbon streams,
especially the non-volatile particulate form of mercury.
[0007] What is needed is a process to remove mercury from crudes
and condensates that does not generate gaseous or liquid
mercury-containing waste products; which removes particulate
mercury, especially fine particulate mercury present in particles
below 0.45 .mu.m; which produces a concentrated solid waste product
containing more than 100 ppmw Hg; and which also removes elemental
mercury in the crude oil or in a gas that is in contact with the
crude oil.
[0008] There is a need for an improved method to manage, control,
and remove mercury in produced fluids from a reservoir, e.g., gas,
crude, condensate, and produced water.
SUMMARY
[0009] In one aspect, the invention relates to a method for
converting particulate mercury in a crude oil by thermal
decomposition. The crude oil may contain 0.1 wt. % or more of C4-
hydrocarbons. Further, at least 10 wt. % of the mercury containing
in the crude oil is present in particulate form. The invention
further relates, in one aspect, to a method for stabilizing a crude
oil feed. The stabilization method may involve a step of removing
mercury from an unstable crude oil. Thus, the invention relates to
a method for removing mercury from a mercury-containing crude oil
feed in which greater than 10 wt. % of the mercury contained
therein is particulate mercury, the crude oil feed containing C4-
hydrocarbons, the method comprising: heating the crude oil feed to
a first temperature in a range from 150.degree. C. to 350.degree.
C. and at a first pressure to retain at least 90 vol. % of the C4-
hydrocarbons in the liquid phase crude oil; maintaining the heated
crude oil at the first temperature and at the first pressure for
0.1 hours to 10 hours, to convert particulate mercury in the crude
oil to elemental mercury (Hg0); cooling the heated crude oil to a
second temperature in a range from 40.degree. C. to 150.degree. C.;
reducing the pressure of the cooled crude oil to a second pressure
lower than the first pressure, and maintaining the cooled crude oil
at the second temperature and at the second pressure for 0.1 hours
and 10 hours to vaporize at least a portion of the C4- hydrocarbons
and at least a portion of the elemental mercury contained in the
crude oil; and recovering a stabilized crude oil containing a
reduced amount of C4- hydrocarbons and at least 10 wt. % less
mercury than is contained in the crude oil feed.
[0010] In one respect, the method includes a partially stabilizing
a crude oil prior to the mercury removal process. Thus, a method is
provided for removing mercury from a mercury-containing crude oil
feed in which greater than 10 wt. % of the mercury contained
therein is particulate mercury, the crude oil feed containing 0.1
wt. % or more of C4- hydrocarbons, the method comprising: degassing
the crude oil feed by removing C4- hydrocarbons contained therein,
to produce a partially stabilized crude oil having a true vapor
pressure in a range of between greater than 9 psig and less than or
equal 14 psig, and a first C4- hydrocarbon enriched gaseous stream;
heating the partially stabilized crude oil to a first temperature
in a range from 150.degree. C. to 350.degree. C. and at a first
pressure, to retain at least 90 vol. % of the C4- hydrocarbons in
the liquid phase crude oil; maintaining the heated partially
stabilized crude oil at the first temperature and at the first
pressure for 0.1 hours to 10 hours, to convert particulate mercury
in the crude oil to elemental mercury; cooling the heated partially
stabilized crude oil to a second temperature in a range from
40.degree. C. to 150.degree. C.; reducing the pressure of the
cooled partially stabilized crude oil to a second pressure lower
than the first pressure, and maintaining the cooled partially
stabilized crude oil at the second temperature and at the second
pressure for 0.1 hours and 10 hours to produce a second C4-
hydrocarbon enriched gaseous stream that contains at least a
portion of the elemental mercury from the crude oil; and recovering
a stabilized crude oil containing a reduced amount of C4-
hydrocarbons and at least 10% less mercury than is contained in the
crude oil feed.
[0011] In another aspect, the invention relates to removing mercury
from crude oil using a mercury reactive adsorbent. Thus, a method
is provided for removing mercury from a mercury-containing crude
oil feed in which greater than 10 wt. % of the mercury contained
therein is particulate mercury, the method comprising: heating the
crude oil feed at a first temperature to convert particulate
mercury in the crude oil to elemental mercury (Hg0) and at a first
pressure above a bubble point pressure of the crude oil for a time
sufficient to convert particulate mercury in the crude oil to
elemental mercury; cooling the crude oil and contacting the cooled
crude oil with a mercury removal adsorbent to adsorb elemental
mercury from the cooled crude oil; recovering a mercury-reduced
crude oil that contains an amount of mercury that is at least 10
vol. % lower than the mercury content of the crude oil feed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 illustrates an embodiment of the process, having a
thermal decomposition reactor for converting mercury in crude oil
to elemental mercury, and a treater degasser that produced a
stabilized crude oil.
[0013] FIG. 2 illustrates an embodiment of the process, having a
thermal decomposition reactor for converting mercury in crude oil
to elemental mercury, and an adsorption bed that produces a low
mercury crude oil.
[0014] FIG. 3 is a graphical representation of first order rate
constants for particulate mercury decomposition reactions.
[0015] FIGS. 4A. and 4B are graphs of mercury removal with a
decomposition test, under N2, 3-4 bar pressure with varying
adsorbents.
[0016] FIGS. 5A. and 5B are graphs of mercury removal with a
decomposition test, under N2, 3-4 bar pressure, 3 hr. residence
time with varying adsorbents.
[0017] FIGS. 6 & 7 are graphs of decomposition tests under 10
and 20 min. residence times.
[0018] FIG. 8 is a graph of first order rate constant measured in
continuous flow kinetics for stabilized condensate at 70 psig
pressure and atmospheric pressure.
[0019] FIG. 9-FIG. 12 are iterative schematic diagrams of the
liquid phase thermal decomposition process.
DETAILED DESCRIPTION
[0020] The following terms will be used throughout the
specification and will have the following meanings unless otherwise
indicated.
[0021] "Hydrocarbon" refers to a pure compound or mixtures of
compounds containing hydrogen and carbon and optionally sulfur,
nitrogen, oxygen, and other elements. The term "crude oil" refers
to a liquid hydrocarbon material produced from a subterranean
geological formation, which may optionally be dewatered and/or
degassed following production. "Crude", "crude oil", "crudes" and
"crude blends" are used interchangeably and each is intended to
include both a single crude and blends of crudes. As used herein,
the term crude oil may also refer to a light petroleum product
termed a "condensate" that is typically associated with natural gas
production for a subterranean formation. While condensate can leave
the reservoir either as a liquid or as a gas, it is processed as a
liquid. Other exemplary crude oils that may be treated in the
process include synthetic crude oils such as shale oils, biomass
pyrolysis products, etc.
[0022] "High mercury crude oil" refers to a crude oil or condensate
containing 50 ppbw or more of total mercury. Exemplary high mercury
crude oil contains 100 ppbw or more of total mercury; or 250 ppbw
or more of total mercury, or 1000 ppbw or more of total
mercury.
[0023] "Total Mercury" is the sum of all mercury species and phases
present in a sample. It is measured by Lumex or other appropriate
alternative method for crudes having more than 50 ppbw mercury. If
an alternative method does not agree with a Lumex measurement, the
Lumex measurement is used. For crudes having less than 50 ppbw
mercury, the total mercury is measured by CEBAM analysis or other
appropriate alternative method. If an alternative method does not
agree with a CEBAM measurement, the CEBAM measurement is used.
[0024] "Particulate Mercury" refers to mercury that can be removed
by filtration or centrifugation. Solid metacinnabar and cinnabar
are examples of species which contribute to particulate mercury.
For purposes of this disclosure, elemental mercury is not included
in "particulate mercury".
[0025] "Percent Particulate Mercury" refers to the portion of
mercury that can be removed from the crude oil by centrifugation or
filtration. After the centrifugation the sample for mercury
analysis is obtained from the middle of the hydrocarbon layer. The
sample is not taken from sediment, water or rag layers. The sample
is not shaken or stirred after centrifugation. In one embodiment,
percent particulate mercury is measured by filtration using a 0.45
micron filter or by using a modified sediment and water (BS&W)
technique described in ASTM D4007-11. The sample is heated in
accordance with the procedure. If the two methods are in
disagreement, the modified basic BS&W test is used. The
modifications to the BS&W test includes: omission of dilution
with toluene; demulsifier is not added; and the sample is
centrifuged two times with the water and sediments values measured
after each time. If the amount of sample is small, the ASTM
D4007-11 procedure can be used with smaller centrifuge tubes, but
if there is disagreement in any of these methods, the modified
basic BS&W test is used with the centrifuge tubes specified in
ASTM D4007-11.
[0026] "Percent fine particulate mercury" is limited to crude or
condensates in which the mercury is predominantly non-volatile. It
refers to the portion of mercury that cannot be removed from crude
oil by vacuum filtration using a 0.45 micron filter at room
temperature for crude oils that are fluid at room temperature, or
at 10.degree. C. above the pour point for crudes that are not fluid
at room temperature. The filtration uses 25 mL samples of crude in
47 mm filters in glass vacuum filtration apparatus. If the crude is
fluid at room temperature, the filtration is done at room
temperature. If the crude is not fluid at room temperature, it is
heated to approximately 10.degree. C. above its pour point.
[0027] "Volatile Mercury" refers to mercury that can be removed by
stripping with nitrogen. Elemental mercury is an example of a
species which contributes to volatile mercury. Cinnabar and
metacinnabar are examples of species which do not contribute to
volatile mercury. Cinnabar and metacinnabar are examples of
non-volatile mercury species.
[0028] "Percent volatile mercury" is measured by stripping 15 ml of
crude or condensate with 300 ml/min of nitrogen (N2) for one hour.
For samples which are fluid at room temperature, the stripping is
carried out at room temperature. For samples which have a pour
point above room temperature, but below 60.degree. C., the
stripping is done at 60.degree. C. For samples which have a pour
point above 60.degree. C., the stripping is at 10.degree. C. above
the pour point. Mercury is measured on the original and stripped
crude by the methods described under "Total Mercury". During
stripping some oil may be evaporated along with the volatile
mercury. This evaporation will concentrate the non-volatile mercury
in the stripped crude. To correct for this concentration by
evaporation, the loss in crude by evaporation is determined by
weighing the initial crude and stripped crude. The percent loss in
crude by evaporation is used to correct the total mercury
determined in the stripped crude. This corrected value is then used
to determine the percent volatile mercury.
[0029] "Predominantly non-volatile (mercury)" in the context of
crude oil means that the percentage of total mercury in the crude
oil that is volatile mercury is less than 50%. In another
embodiment, the percentage that is volatile mercury is less than
25%. In yet another embodiment, the percentage that is volatile
mercury is less than 15%.
[0030] "Non-leachable" refers to a mercury adsorbent that will not
leach adsorbed mercury in a simulation of landfill disposal. To be
non-leachable, the mercury in the adsorbent must meet TCLP
standards established for the mercury listed in EPA's Land Disposal
Restrictions: Summary of Requirements. Revised August 2001.
[0031] "Mercury sulfide" may be used interchangeably with HgS,
referring to mercurous sulfide, mercuric sulfide, or mixtures
thereof. Normally, mercury sulfide is present as mercuric sulfide
with a stoichiometric equivalent of approximately one mole of
sulfide ion per mole of mercury ion. Mercury sulfide can be in any
form of cinnabar, metacinnabar, hyper-cinnabar and combinations
thereof.
[0032] "Ebullated" or "expanded" bed reaction system refers to a
reactor system having an upflow type single reaction zone reactor
containing adsorbent in random motion in an expanded catalytic bed
state, typically expanded from 10% by volume to about 35% or more
by volume above a "slumped" adsorbent bed condition (e.g. a
non-expanded or non-ebullated state).
[0033] "Trace amount" refers to the amount of mercury in the crude
oil. The amount varies depending on the crude oil source and the
type of heavy metal, for example, ranging from a few ppbw to up to
100,000 ppbw for mercury and arsenic.
[0034] "Carbon number" represents a hydrocarbon molecule, and gives
the total number of carbon atoms in the molecule. Thus, the term C4
represents hydrocarbon molecules having 4 carbon atoms per
molecule.
[0035] "C4- hydrocarbons" or "C1-C4 hydrocarbons" represent a
hydrocarbonaceous material having from 1 to 4 carbon atoms per
molecule. Methane, ethane, propane, butane, their branched, cyclic,
and olefinic analogs, and mixtures thereof are examples of C4-
hydrocarbons. Unless otherwise specified, volatilization of C4-
hydrocarbons may be accompanied by volatilization of other low
boiling components of crude oil, including one or more of C5, C6,
C7 and C8 hydrocarbons.
[0036] "True vapor pressure" refers to the equilibrium partial
pressure exerted by a volatile organic liquid as a function of
temperature as determined by the test method ASTM D 2879-97
(2007).
[0037] "Bubble point pressure" refers to the pressure at which a
first bubble of gas evolves from a liquid as the pressure on the
liquid is decreased. The bubble point pressure of a crude oil may
be determined from a PVT analysis of a crude oil sample or
calculated by a flash calculation procedure if the composition of
the crude oil is known. Empirical correlations for estimating
bubble point pressure from limited data are also known (see, for
example, Petroleum Engineering Handbook, 2nd printing (June 1989),
Society of Petroleum Engineers, Richardson, Tex., USA, p.
22-5.)
[0038] In one aspect, particulate mercury in crude oil is converted
to elemental mercury by thermal decomposition. The product
elemental mercury is removed from the crude oil by either
vaporizing the elemental mercury or by adsorption of the elemental
mercury from the crude oil onto a solid adsorbent. The process
works at temperatures from 150 to 350.degree. C. and at a pressure
sufficient to limit the amount of crude vaporizing to be less than
or equal to 10 wt. %. By limiting the crude vaporization, the
energy usage required in this thermal process is minimized. Energy
is needed only to heat the crude, not to vaporize a large portion
of it. The residence time of crude oil in a thermal treater is
greater than or equal to 0.01 hours and less than or equal to 10
hours. If elemental mercury is present in the crude along with the
particulate mercury, it too is removed in the process.
[0039] In an embodiment of the invention, the product elemental
mercury is removed from crude oil or condensate in a liquid phase
without employing a stripping or vaporization step by: (1)
pressurization of crude oil or condensate while still in a liquid
phase above the bubble point pressure; (2) employing the thermal
decomposition step described herein where the chosen decomposition
temperature, ranges from 150 to 350.degree. C., preferably
240.degree. C.; (3) cooling the liquid of the decomposition
reaction, equal to 40.degree. C. and less than or equal to
150.degree. C., preferably 65.degree. C. to 70.degree. C., while
maintaining or not reducing the pressure; feeding the cooled
reactor effluent containing the elemental mercury to a mercury
removal unit that preferentially removes the elemental mercury,
wherein the pressure prior to the MRU feed is maintained. This
embodiment additionally minimizes the size of the decomposition
reactor as the process operates 100% in the liquid phase at a given
residence time, minimizes the overall heating duty needed for the
heater employed in the decomposition reaction since there is no
phase-change vaporization and is irreversible with regards to the
formation of mercury sulfide species post thermal
decomposition.
[0040] A crude oil feed that is treated in the process may contain
dissolved gaseous hydrocarbons, including C4- hydrocarbons.
Transportation requirements of crude oil feed, relating to vapor
pressure and/or flash point specifications of the feed, may require
that the crude oil feed be stabilized prior to shipping. In this
regard, stability involves reducing the true vapor pressure of the
crude oil to 9 psig or less. In one embodiment, the process
includes converting particulate mercury in the crude oil feed to
elemental mercury, and removing the elemental mercury, along with
C4- hydrocarbons, during crude oil feed stabilization.
[0041] In order to eliminate the need for a separate gas stream to
strip the elemental mercury from the crude oil, the crude oil can
be thermally treated prior to stabilization--a process which
removes C4- hydrocarbons. In one embodiment, the crude oil that is
treated thermally can contain more than 0.1 wt. % of C4-
hydrocarbons After thermal treatment, the crude is cooled, for
example, to from 40 to 150.degree. C. and the pressure is reduced
to, for example, within a range from atmospheric pressure (0 psig)
to 250 psig. The C4- hydrocarbons then vaporize from the crude and
carry the elemental mercury with them. The elemental mercury in
this hydrocarbon gas stream can then be removed by a solid
adsorbent--a mercury removal adsorbent.
[0042] The process removes 10% or more of the mercury from a crude
oil or condensate; in another embodiment, 50% or more; in another
embodiment 75% or more; in another embodiment 90% or more.
[0043] The process produces a stable crude oil containing less than
or equal to 500 ppbw mercury. In another embodiment, the process
produces a stable crude oil containing less than or equal to 100
ppbw mercury. In another embodiment, the process produces a stable
crude oil containing less than or equal to 50 ppbw mercury.
[0044] The process works for crude oil feeds that contain
particulate mercury. In one embodiment, at least 10 wt. % of the
total mercury contained in the crude oil feed is percent
particulate. In another embodiment, at least 50 wt. % of the total
mercury contained in the crude oil feed is particulate mercury. In
another embodiment, at least 75 wt. % of the total mercury
contained in the crude oil feed is particulate mercury.
[0045] The process is a method for removing mercury from a
mercury-containing crude oil feed. The crude oil feed may be
treated in the process as produced from a production wellbore, or
following a vapor pressure reduction procedure to remove some
highly volatile hydrocarbons, including C4- hydrocarbons, from the
crude oil feed. In one embodiment, the crude oil feed is an
unstabilized crude oil, containing volatile hydrocarbons. A crude
oil feed that can be treated in the process contains 0.1 wt. % or
more C4- hydrocarbons. An exemplary crude oil feed contains in a
range from 0.1 to 10 wt. % C4- hydrocarbons. Another exemplary
crude oil feed contains from 0.1 to 5 wt. % C4- hydrocarbons. Such
a crude oil feed has a true vapor pressure of greater than 9 psig.
An exemplary crude oil feed for the process has a true vapor
pressure in a range of between greater than 9 psig and less than or
equal 14 psig.
[0046] The process may be employed with crude oils containing
mercury over a wide range may be treated as disclosed herein. Use
of the method is preferred for higher amounts of mercury, since the
benefits of removing mercury from highly contaminated crude oil and
condensates are great. In practice, the method is applied over any
range of amounts of mercury that are detrimental to the value of
crude oil containing the mercury, or detrimental to processes and
personnel involved in processing the crude oil, and can range from
a few ppbw to up to 100,000 ppbw. Practically, the method may be
applied to crude oil or condensates containing 10 ppbw or more of
total mercury. In embodiments, the method may be usefully used to
treat crude oil containing 50 ppbw or more of total mercury.
Exemplary high mercury crude oil contains 100 ppbw or more of total
mercury; or 250 ppbw or more of total mercury, or 1000 ppbw or more
of total mercury.
[0047] The crude oil feed may contain mercury in one or more of a
number of different forms, including elemental mercury (e.g., Hg0),
particulate mercury (e.g. mercury sulfide, mercury oxide, and
mercury sulfate), mercury alky complexes (e.g. dimethyl mercury)
and cationic mercury. An exemplary particulate mercury is mercury
sulfide (e.g. HgS). In an exemplary crude oil feed, at least 10 wt.
% of the total mercury in the crude oil feed is particulate
mercury. In one embodiment, at least 25 wt. % of the total mercury
is particulate mercury. In one embodiment, at least 50 wt. % of the
total mercury is particulate mercury.
[0048] In one embodiment, a stabilized crude oil is prepared in the
process. Stabilizing the crude oil involves removing a portion of
the C4- hydrocarbons from an unstabilized crude oil; removal of the
C4- hydrocarbons may be done in a single step or in multiple steps.
In a multiple step process, the first step removes some of the C4-
components from the crude oil feed to make a partially stabilized
crude oil, and a second step removes additional C4- components
while concurrently removing elemental mercury from the partially
stabilized crude oil, forming a stabilized crude oil having a
reduced content of mercury.
[0049] Stabilized crude oil recovered from the separation unit
contains less than 500 ppbw total mercury. In embodiments, the
stabilized crude oil contains in a range from 10 to 500 ppmw total
mercury; or from 20 to 200 ppmw total mercury. An exemplary
stabilized crude oil contains less than 100 ppbw total mercury.
[0050] The stabilized crude oil has a total mercury content that is
less than that of the crude oil feed. An illustrative stabilized
crude oil prepared in the process contains at least 10 wt. % less
total mercury than is contained in the crude oil feed. Another
illustrative stabilized crude oil prepared in the process contains
at least 50 wt. % less total mercury than is contained in the crude
oil feed. Another illustrative stabilized crude oil contains at
least 75 wt. % less total mercury than is contained in the crude
oil feed.
[0051] The stabilized crude oil further has a vapor pressure less
than or equal to 9 psia. In one embodiment, the stabilized crude
oil contains less than 0.1 wt. % of C4- hydrocarbons.
[0052] The crude oil feed may be prepared for the mercury removal
method by a preliminary dewatering step. Methods to separate water
and brine solutions from crude oil are well known and practiced
worldwide. Exemplary methods include liquid-liquid separations, and
separations using a demulsifier. Such methods are generally
practiced at a temperature approximately equal to the temperature
of the crude entering the dewatering process, and are generally
conducted at a temperature in a range from 25 to 200.degree. C. and
at pressure in a range of 1 atmosphere to 10 atmospheres.
[0053] In one embodiment, the crude oil feed may be prepared for
mercury removal by a preliminary stabilization step, for removing
amounts of high volatility components from the crude oil above what
is required for mercury removal. A preliminary stabilization step
requires little or no added heat, to avoid conversion of mercury in
the crude oil to elemental mercury at this point. In one
embodiment, a preliminary stabilization step involves passing the
crude oil through a preliminary separation unit, optionally
supplied with internal features and optionally with a gas purge to
facilitate removal of excessive high volatility components from the
crude oil. In one embodiment, the high volatility components
include C4- hydrocarbons. In one embodiment, the preliminary
stabilization step produces a partially stabilized crude oil
containing in a range from 0.1 to 5 vol. % C4- hydrocarbons. In one
embodiment, the partially stabilized crude oil has a true vapor
pressure in a range of between greater than 9 psig and less than or
equal 14 psig.
[0054] In the process, the crude oil feed is heated in a thermal
decomposition step at a temperature to convert mercury in the crude
oil feed, including particulate mercury, to elemental mercury. An
exemplary temperature of the thermal decomposition step is in a
range from 150.degree. C. to 350.degree. C. In an embodiment, the
temperature is in a range from 175.degree. C. to 300.degree. C. The
pressure of the crude oil feed during thermal decomposition is
sufficiently high to retain the elemental mercury in the crude oil,
and to minimize elemental mercury vaporization at this point. An
exemplary pressure of the thermal decomposition step is in a range
from 100 psig to 5000 psig. In one embodiment, the pressure during
thermal decomposition is in a range from 250 psig to 1500 psig.
[0055] The thermal decomposition step may be conducted in a thermal
decomposition reactor. The thermal decomposition reactor may be a
static batch reactor, a continuous stirred tank reactor or a flow
reactor, through which the crude oil continuously flows as the
decomposition reactions take place in the heated crude oil. Flow
through a flow reactor may be in an upward, downward, or horizontal
direction. The thermal decomposition reactor may include internal
elements to improve heat flow through the crude oil and to improve
mixing of the crude oil. The thermal decomposition reactor may also
contain solid particles to improve heat transfer and promote the
mercury decomposition reactions.
[0056] Crude oil is treated in the thermal decomposition step for
at least 1 minute. Exemplary treatment options include treating for
a period of from 1 to 30 minutes, or for a period from 10 to 30
minutes. Residence time of the crude oil in a thermal decomposition
reactor is, in embodiments, in a range from 0.1 hr-1 to 10 hr-1, or
in a range from 0.5 hr-1 to 5 hr-1. In one embodiment, no catalyst
is included in the reactor during thermal decomposition. In one
embodiment, a stripping gas is not provided for the reactor during
thermal decomposition.
[0057] The crude oil feed to a thermal decomposition step is an
unstable crude oil, containing C4- hydrocarbons and having a true
vapor pressure above 9 psig. Depending on the crude oil used, the
crude oil feed may optionally have been partially stabilized in a
preliminary stabilization step. During the thermal decomposition
step, particulate mercury in the crude oil converts (i.e.,
decomposes) to elemental mercury, Hg0. In one embodiment, at least
25 wt. %, in one embodiment at least 50 wt. %, and in one
embodiment at least 75 wt. % of the particulate mercury in the
crude oil feed is converted to elemental mercury during thermal
decomposition.
[0058] In one embodiment, process conditions during the thermal
decomposition step are selected to retain C4- hydrocarbon gases in
the liquid phase crude oil feed. This may be achieved, for example,
by maintaining the pressure during the thermal decomposition step
of above the bubble point of the crude oil, while maintaining a
temperature at least equal to the decomposition temperature of the
mercury in the crude oil feed at the decomposition pressure. In
another aspect, the pressure is maintained such that, in
embodiments, no more than 10 wt. %; or no more than 5 wt. %; or no
more than 1 wt. % of the crude oil is vaporized during heating.
While some of the volatile components present in the crude oil feed
are vaporized during heating, the pressure is maintained such that
the amount of C4- vaporization is controlled. The pressure during
thermal decomposition is controlled to retain, in embodiments, at
least 80 vol. %, or at least 90 vol. % of the C4- hydrocarbons in
the liquid phase crude oil during the thermal decomposition
step.
[0059] The elemental mercury which is formed in the crude oil feed
during thermal decomposition is removed from the crude oil in a
following separation step. In one embodiment, elemental mercury is
vaporized during the separation. The vaporization is facilitated in
the process by the use of C4- hydrocarbons remaining in the crude
oil feed at the end of the decomposition step. The temperature and
the pressure of the crude oil during separation are selected to
enhance vaporization of C4- hydrocarbons in the crude oil, thereby
stripping elemental mercury from the crude oil. In effect, the
temperature and pressure of the separation step are selected to
stabilize the crude oil by removing dissolved C4- hydrocarbon gases
from the crude oil. Separation of C4- gases from the crude oil has
the additional effect of sweeping elemental mercury from the crude
oil into the gas phase, in combination with the vaporizing C4-
gases.
[0060] Process conditions employed during separation are selected
to cause vaporization of the C4- from the crude oil to reduce the
C4- content of the liquid hydrocarbon, in embodiments, to less than
2 wt. %; or to less than 1.5 wt. %; or to less than 1 wt. %. The
separation is conducted at a temperature, in embodiments, of less
than 200.degree. C.; or in a range from 25.degree. C. to
200.degree. C.; or in a range from 40.degree. C. to 150.degree. C.;
or in a range from 60.degree. C. to 100.degree. C. The separation
is conducted at a pressure that is less than the first pressure. In
embodiments, a separation pressure may be less than 1000 psig; or
less than 250 psig; or in a range from atmospheric pressure (0
psig) to 250 psig; or in a range from 10 to 200 psig.
[0061] Vaporization may be enhanced by conducting the separation in
a separation zone that is configured to enhance removal of volatile
compounds. Vaporization may be further enhanced to introduction of
a stripping gas, such as nitrogen, for stripping volatile compounds
from the crude oil.
[0062] The separation step may be conducted for a period of a few
minutes, up to a period of hours. When the sole stripping medium is
vaporization of C4- hydrocarbons from the crude, the separation
step may have a residence time of greater than 0.01 hours. In
embodiments, the residence time is in a range from 0.01 hours to 10
hours; or from 0.1 hours to 2 hours; or from 0.5 hours to 1.5
hours.
[0063] A separator zone that may be used in the separation step may
include, for example: a packed column, a plate column, or a bubble
column, each being filled with a filler such as a Raschig ring, a
Pall ring, an Intalox (registered trademark) saddle, a Berl saddle,
and a Goodloe (registered trademark) packing. The separator may be
a device which distributes the liquid hydrocarbon from the liquid
injection point near the top of the column and facilitates the
vaporization of dissolved C4- hydrocarbons from the crude oil
through the column. The separator may include an electrostatic grid
to assist in the removal of traces of water droplets. The separator
further facilitates contact between liquid and gaseous hydrocarbons
in the column, thereby transferring the elemental mercury in the
liquid hydrocarbon to the vaporized C4- stripping gas, and then
withdraws the first gaseous hydrocarbon containing elemental
mercury and the Hg-depleted liquid hydrocarbon from the bottom of
the column.
[0064] In one embodiment, the separation step includes contacting
the crude oil from the decomposition step with an adsorbent, for
reacting with the elemental mercury and removing the mercury from
the crude oil.
[0065] When the adsorbent is employed after the thermal
decomposition stage, the crude oil is generally cooled to a
temperature below the thermal decomposition temperature and to a
pressure below the thermal decomposition pressure, and contacted
with an adsorption bed containing particulate adsorbent, for
adsorbing elemental mercury from the crude oil. Various processes
well-known in the industry are available for adsorption. The
adsorption can be performed using extrudates, granules or tablets
in a fixed bed where the crude oil flows either downflow or upflow.
Fixed beds may encounter plugging problems due to the fines in the
crude. One way to prevent this is to use a guard bed of high pore
volume material to capture the fines and prevent formation of a
non-porous crust. The adsorption process can also be performed in a
fluidized bed or ebullated bed or continuously stirred tank reactor
(CSTR) reactors. These options are suitable for use when the total
particulate content of the crude is high enough to cause plugging
in a fixed bed even with use of a guard bed. Alternatively, the
formation of plugs can be prevented by use of sonication or pulsed
flow. Both gently agitate the particles and prevent the formation
of a crust. The adsorption can also be performed in processes known
as mixer-settlers using fine particulate adsorbents which are mixed
with the crude and then removed by settling, filtration,
centrifugation, hydrocyclones and combinations. Multiple adsorbent
units of any type can be used in series. Typically this is a
lead-lag operation where the first adsorber (lead) is removing the
majority of the mercury and the second adsorber (lag) removes the
final traces. When the first adsorber is spent and mercury
concentrations in the outlet of the first adsorber increase, the
inlet flow is reversed to the second adsorber and the first
adsorber it taken off-line to replace the adsorbent. It is then
brought back on-line and operates in the lag position. When an
adsorbent is used in a fixed bed, fluidized bed, ebullated bed or
expanded bed, the space velocity may, in embodiments, be greater
than or equal to 0.01 hr-1; or in a range from 0.1 to 25 hr-1; or
in a range from 1 to 5 hr-1. For ebullated or expanded beds, the
space velocity may be based on the bed volume before ebullition or
expansion. The particulate adsorbent may be added to the crude oil
during or after the thermal decomposition step, or may be supplied
to the crude oil in a separate vessel downstream of a thermal
decomposition reactor. Elemental mercury may be vaporized from the
crude oil during the adsorbent separation step, either by reason of
the temperature of the crude oil or on account of the use of a
stripping gas, either generated in situ in the crude oil or
supplied externally. However, in one embodiment, the separation
process using the adsorbent is controlled to prevent, or at least
minimize, elemental mercury vaporization.
[0066] A portion of the particulate mercury, and solids of all
types, can be removed in advance of this process by use of
filtration, centrifugation, hydrocyclones and settling.
[0067] The temperature of the crude oil in contact with an
adsorbent during the separation step is generally within a range
below 200.degree. C., or, in embodiments, within a range of
20.degree. C. to 200.degree. C., or within a range of 40.degree. C.
to 150.degree. C. The pressure of the crude oil in contact with an
adsorbent during the separation step is generally less than 1500
psig; or, in embodiments, less than 1000 psig; or in a range from
50 psig to 1000 psig; or in a range from 100 to 750 psig.
[0068] When a particulate adsorbent is mixed with the treated
crude, the amount of adsorbent added, in embodiments, is greater
than 0.001 wt. %; or in a range from 0.01 to 10 wt. %; or in a
range from 0.1 to 2 wt. %.
[0069] An effective particulate adsorbent may have an average
particle diameter in a range from 0.1 mm to 10 mm; in embodiments,
in a range from 0.5 mm to 5 mm; or from 1 mm to 10 mm.
[0070] Adsorbents useful for removing mercury from liquid
hydrocarbons are those which comprise constituents chemically
reactive with mercury or mercury compounds. Examples include
carbons, sulfided carbons, halogen-treated carbons, clays, zeolites
and molecular sieves, and supported or unsupported metal sulfides.
Cupric sulfide is an example of a metal sulfide. Various cationic
forms of several zeolite species, including both naturally
occurring and synthesized compositions, exhibit appreciable
capacities for mercury adsorption due to the chemisorption of
metallic mercury at the cation sites. Some of these zeolitic
adsorbents reversibly adsorb mercury and others exhibit less than
full, but nevertheless significant, reversibility. An especially
effective adsorbent is one of the zeolite-based compositions
containing cationic or finely dispersed elemental forms of silver,
gold, platinum or palladium. Zeolites X and A are effective for
this purpose. These adsorbents, as well as the other zeolite-based
adsorbents containing ionic or elemental gold, silver, platinum, or
palladium, are capable of selectively adsorbing and sequestering
organic mercury compounds as well as elemental mercury. Activated
carbon may also be used as an effective mercury adsorbent. The
specific mention of these materials is not intended to be limiting,
the composition actually selected being a matter deemed most
advantageous by the practitioner give the particular circumstances
to which the process in applied.
[0071] The crude oil following the separation step has a total
mercury content that is less than that of the crude oil feed. An
illustrative crude oil prepared in the process contains at least 10
wt. % less total mercury than is contained in the crude oil feed.
Another illustrative crude oil prepared in the process contains at
least 50 wt. % less total mercury than is contained in the crude
oil feed. Another illustrative crude oil contains at least 75 wt. %
less total mercury than is contained in the crude oil feed.
[0072] In an embodiment, the C4- hydrocarbons, containing elemental
mercury from the separation step, may be treated to separate the
mercury from the hydrocarbons, using a mercury adsorber or a
scrubber to treat the stripping gas after it exits the stripper.
Adsorbents useful for removing mercury from gaseous hydrocarbons
are those which comprise constituents chemically reactive with
mercury or mercury compounds. Examples include carbons, sulfided
carbons, halogen-treated carbons, clays, zeolites and molecular
sieves, and supported or unsupported metal sulfides. Cupric sulfide
is an example of a possible metal sulfide. Activated carbon may
also be used as an effective mercury adsorbent. Active metal
compounds may be supported on solid materials, such as carbon and
alumina. The adsorber is sufficiently large to remove at least
ninety percent of the mercury from the stripping gas. Typical
superficial gas velocity through the bed is generally in a range
from 0.1 to 50 ft/s, with one embodiment in a range from 0.5 to 10
ft/s. Depending upon the nature and activity of the adsorbent, the
temperature is generally maintained in a range from 10.degree. C.
to 200.degree. C., with an embodiment in a range from 20.degree. C.
to 100.degree. C. If the adsorption bed is to be regenerated the
purge medium is heated to at least 100.degree. C., and preferably
at least 200.degree. C., higher than the temperature of the
feedstock being purified. Pressure conditions can range from about
0 to 250 psig.
[0073] FIG. 1 illustrates an embodiment of the invention. In FIG.
1, particulate mercury is removed from a mercury-containing
unstabilized crude oil that contains in a range from 0.1 wt. % to 5
wt. % C4- hydrocarbons. The crude oil (11) is obtained from a
subsurface reservoir (10), where the surface is illustrated at (12)
and sent to initial separators (20). These separators produce a
first gas stream (21), an unstabilized crude oil (22) and produced
water (23). The unstabilized crude contains in a range from 0.1 wt.
% to 5 wt. % (e.g. 1 wt. %) C4- hydrocarbons. The unstabilized
crude also contains greater than 100 ppbw (e.g. 1000 ppbw) total
mercury, with greater than 50 wt. % (e.g. 75 wt. %) of the total
mercury being in the form of particulate mercury. The unstabilized
crude oil is pressured within a range from 100 psig to 5000 psig
(e.g. 1000 psig) by a pump (30) and heated at a temperature within
a range of 100.degree. C. to 300.degree. C. (e.g. 250.degree. C.)
by equipment not shown. The selected pressure is above the bubble
point pressure of the unstabilized crude. The heated unstabilized
crude oil enters a thermal decomposition reactor (40) where it
flows upward and has a residence time of greater than 1 minute
(e.g. 30 minute). The thermal decomposition reactor converts the
particulate mercury to elemental mercury. After the thermal
decomposition reactor, the treated unstabilized crude oil (41) is
cooled to less than 200.degree. C. (e.g. 90.degree. C.) by
equipment not shown and the pressure is reduced to from 0 to 250
psig (e.g. 10 psig) by equipment not shown. The depressurized crude
is sent to a treater degasser (60) to recover C4- hydrocarbons as a
second gas (61). The temperature of the treater degasser is less
than 200.degree. C. (e.g. 90.degree. C.) and the crude has a
residence time of from 10 minutes to 12 hours (e.g. one hour). The
treater degasser produces a stabilized crude (62) that contains
less than 500 ppbw (e.g. 50 ppbw) total mercury. The first gas
stream (21) and the second gas stream (61) are blended and sent to
a gas-phase mercury removal unit using a cupric sulfide adsorbent
(70). This mercury removal unit produces a treated gas (71) having
a mercury content of less than 1 .mu.g Hg per normal m3.
[0074] FIG. 2 illustrates another embodiment of the Invention. In
FIG. 2, the particulate mercury in a high mercury crude is
thermally decomposed to form elemental mercury. The elemental
mercury is removed by use of a mercury adsorber that directly
processes the liquid crude. This embodiment utilizes existing
equipment that is common in oil production operations: the initial
separators, the treater-degasser that is used to prepare the
stabilized crude, and the mercury removal unit that is used to
treat the gas. This embodiment avoids the use of a separate
stripping gas.
[0075] A high mercury crude that contains 1000 ppbw total mercury
with a percent particulate mercury of 75%, (31) is heated to
250.degree. C. by equipment not shown and pressured to 500 psig by
a pump (30), a pressure that is above the bubble pressure of the
crude. The heated crude enters a thermal decomposition reactor (40)
where it flows upward and has a 30 minute residence time. The
thermal decomposition reactor converts the particulate mercury to
elemental mercury. After the thermal decomposition reactor, the
treated crude (41) is cooled to 90.degree. C. by equipment not
shown. The pressure is maintained at near 500 psig and the crude
enters an ebullated bed adsorber that contains a cupric sulfide
adsorbent (50) and which produces a low mercury crude containing
less than 50 ppbw mercury (51). The adsorber operates at 90.degree.
C. and has a residence time of 0.25 hours. The average diameter of
the adsorbent is 2 mm, and the ratio of the diameter of the vessel
to the diameter of the particles is >14. The pressure of the low
mercury crude is reduced to atmospheric and the crude is stored in
a tank (not shown).
EXAMPLES
[0076] The illustrative examples are intended to be
non-limiting.
Example 1
[0077] In this example, a sample of volatile Hg0 in simulated crude
was prepared. First, five grams of elemental mercury Hg0 was placed
in an impinger at 100.degree. C. and 0.625 SCF/min of nitrogen gas
was passed over through the impinger to form an Hg-saturated
nitrogen gas stream. This gas stream was then bubbled through 3123
pounds of Superla.RTM. white oil held at 60-70.degree. C. in an
agitated vessel. The operation continued for 55 hours until the
mercury level in the white oil reached 500 ppbw by a Lumex.TM.
analyzer. The simulated material was drummed and stored.
Example 2
[0078] The example illustrates the stripping of volatile Hg0 from a
crude oil. First, 75 ml of the simulated crude from Example 1 was
placed in a 100 ml graduated cylinder and sparged with 300 ml/min
of nitrogen at room temperature. The simulated crude had been
stored for an extended period of time, and its initial value of
mercury had decreased to about 369 ppbw due to vaporization (time
at 0 min in Table 1). The mercury in this simulated crude was
rapidly stripped consistent with the known behavior of Hg0, as
shown in Table 1. The detection limit of the Lumex.TM. analyzer is
about 50 ppbw; the effective level of mercury beyond about 60
minutes was below the detection limit.
TABLE-US-00001 TABLE 1 Time, min Mercury, ppbw 0 369 10 274 20 216
30 163 40 99 50 56 60 73 80 44 100 38 120 11 140 25 % Volatile Hg
80
[0079] Superla.RTM. white oil is not volatile and there were no
significant losses in the mass of the crude by evaporation. Thus
the mercury analyses of the stripped product did not need to be
corrected for evaporation losses.
[0080] The mercury in this crude is volatile. Filtering this
simulated crude through a 0.45 micron syringe filter to avoid
losses of volatile mercury resulted in no change in the mercury
content. This in an example of a volatile mercury crude and a
non-particulate mercury crude.
Examples 3-6: Determination of the Percent Volatile Mercury in
Crudes by Stripping
[0081] The mercury content in the vapor space of these six samples
was measured by a Jerome analyzer and found to be below the limit
of detection. Thus this indirect qualitative method indicates that
there is no volatile mercury in these samples.
[0082] The initial total mercury content of the six samples was
determined and then the samples were stripped as indicated. The
loss of weight of crude by evaporation was determined, and the
total mercury in the stripped crude was measured. The percent
volatile mercury was determined from these values based on a
corrected value for the stripped total mercury to account for
losses in the crude by evaporation using the following formula.
Percent volatile Hg=100*X1-[(100-X2)*(X3)/100]/X1
[0083] where: X1=(Total Hg in the original sample); X2=(% Oil
Loss); X3=(Hg in stripped sample)
[0084] All samples contained predominantly non-volatile mercury.
Results are summarized in Table 2.
TABLE-US-00002 TABLE 2 Example Condensate 3 Condensate 4 Condensate
5 Crude 6 Volatile Hg by Jerome, .mu.g/m3 0.00 0.00 0.00 0.00 Total
Hg by Lumex (or CEBAM), ppbw 2,102 1,388 1,992 9,050 Hg after 1 hr
RT stripping, ppbw 2,357 1,697 2,787 8,951 Oil loss after 1 hr RT
stripping, wt. % 14.00 10.83 30.01 16.01 Percent Volatile Hg 4 -9 2
17
[0085] All these crudes and condensates are examples of
predominantly non-volatile mercury-containing crudes and
condensates.
[0086] Volatile mercury compounds, such as elemental mercury, can
be found in crudes and condensates sampled near the well-head.
These have not been stabilized to remove light hydrocarbon gases
(methane, ethane, propane, and butanes). The stabilization process
typically removes most if not all of the elemental mercury from
crudes and condensates.
Examples 7 to 16
[0087] Size Distribution of Particulate Mercury in Crudes and
Condensates. Ten crude and condensate sample were vacuum filtered
through 47 mm filters with pore sizes of 20, 10, 5, 1, 0.45 and 0.2
.mu.m. The temperature of the filtration was set above the crude
pour point. The total mercury in the crudes, condensates and their
filtrates was determined by Lumex. The amount of mercury in each
size fraction was determined by comparing the amount removed in
successive filter sizes. On occasion, this resulted in negative
numbers, which should be interpreted as meaning that there was
little or no particulate mercury in this size range. Results are
summarized in Table 3.
TABLE-US-00003 TABLE 3 Percent Hg removed in each size Filtering
fraction % Part. % Part. Ex. Sample Temp. Hg, >20 .mu.m 10-20
.mu.m 5-10 .mu.m 1-5 .mu.m 0.45-1 .mu.m 0.2-0.45 .mu.m <0.2
.mu.m Hg > 0.45 Hg By No ID .degree. C. ppbw % % % % % % % .mu.m
Centrifuge 7 Crude-1 65 1,947 42 10 1 -4 34 1 16 83 8 Crude-1 70
1,256 35 18 21 7 4 0 16 84 NA 9 Condensate- 25 2,102 89 5 -3 3 6 1
0 99 92 1 10 Condensate- 48 1,510 3 0 8 12 3 -2 76 26 22 2 11
Crude-2 70 230 19 10 19 -2 25 1 28 71 12 Crude-3 70 360 16 8 9 -1
24 2 43 55 13 Crude-4 70 429 9 -8 19 -2 32 2 48 50 14 Crude-5 70
940 14 59 14 0 5 0 8 92 15 Condensate- 40 2,021 11 3 15 -14 29 -1
57 45 31 3 16 Crude-2 25 9,050 16 16 11 32 20 1 4 95 693
[0088] The data show that the size distribution of
mercury-containing particles in crudes and condensates varies
significantly. The presence of fine particles, those with sizes of
0.45 .mu.m and below, will present a problem for processes which
remove mercury particles by filtration, centrifugation or
settling.
[0089] All of these are examples of high mercury crudes and high
mercury condensates. All of these have a percent particulate
mercury concentration of 10% or more. All these except number 9 are
examples of fine-particulate high-mercury crudes and
condensates.
[0090] Mercury which passes through the smallest filter tested, 0.2
.mu.m, is believed to be fine metacinnabar particles. EXAFS
analysis of a series of solids removed from crudes detects only
metacinnabar, and on occasion, a small amount of related solid
mercury dithiol species with EXAFS structures matching the
mercury-cysteine complex.
[0091] The percent particulate Hg is measured by filtration using a
0.45 micron filter and by centrifugation (data from Table 5). For
most examples, the two methods agree. When they differ, the method
described in the definition should be used.
Examples 17 to 21
[0092] In these examples, metacinnabar are determined as the Hg
species in stabilized crude. The examples show that the predominant
form of mercury in solid residues from various stabilized crudes is
metacinnabar. The metacinnabar particles are either very small
(nanometer scale), highly disordered, or both.
[0093] Solid residues from several crudes were analyzed by EXAFS to
determine the composition of the solids components. The mercury
coordination number (CN) was also measured. Efforts were made to
look for other species, but they could not be detected and must be
present at levels much less than 10%. The searched-for species
include: elemental mercury (on frozen samples), mercuric oxide,
mercuric chloride, mercuric sulfate, and Hg3S2C12. Also the
following mineral phases were sought and not found: Cinnabar,
Eglestonite, Schuetite, Kleinite, Mosesite, Terlinguite. Results
are shown in Table 4, showing a summary of Hg species identified in
the samples and the calculated first shell coordination number for
each Hg species.
TABLE-US-00004 TABLE 4 Coordination Example Source Species (%)
number 17 Crude-1 (toluene washed) B-HgS (101) 2.61 .+-. 0.26 HgSe
(10) 18 Crude-3 (as is) B-HgS (91) 2.40 .+-. 0.98 Hg-(SR).sub.2
(24) 1.22 .+-. 0.85 19 Crude 1 B-HgS (104) 2.61 .+-. 0.17 20
Crude-5 B-HgS (139) 3.46 .+-. 0.21 21 Crude 1 SA B-HgS (129)
[0094] The percentages of mercury in the samples were calculated by
comparison to standards and with measurement of the mercury content
of the sample. Metacinnabar (B--HgS) is the predominant species for
all stabilized crudes obtained from around the world. On occasion
traces of mercury selenide are seen. Higher amounts of related
mercury dithiol (Hg--(SR)2) can be seen in samples that are not
washed with toluene solvent. The dithiol is believed to be an
intermediate product from the reaction between elemental mercury
and mercaptans. It eventually condenses to form metacinnabar which
adsorbs on the surface of the formation material. The standard used
for analysis of the dithiol was HgCysteine. The coordination
numbers below 4 indicate that the metacinnabar crystallites are
either very small (nanometer scale), or are very poorly
crystalized, or both.
[0095] SEM and TEM studies show that the metacinnabar can be
present as either micron-sized aggregates of nanometer sized
metacinnabar crystallites, or as nanometer sized metacinnabar
crystallites coating the outside of other micron-sized solids,
typically formation material--quartz, clay and the like. Because
the metacinnabar crystallites are in the nanometer size range, they
are difficult or impossible to detect by conventional XRD because
of line broadening. The metacinnabar nanoparticles can also be
converted to diethyl mercury using ethyl chloride. Reagent
metacinnabar powders show little or no reactivity presumably due to
their lower surface area and larger crystal size.
Examples 22 to 26
[0096] Determination of Percent Particulate Hg by Centrifugation.
Ten ml of the following seven crudes were placed in a small
centrifuge tube. Samples that were fluid at room temperature were
centrifuged at room temperature. Samples that were waxy at room
temperature were heated to 40.degree. C. The samples were spun at
1800 RPM for 10 minutes. The mercury content of the supernatant was
measured by Lumex.RTM. and compared to the mercury content of the
original sample, and the ratio was used to calculate the percent
particulate mercury. Results are summarized in Table 5.
TABLE-US-00005 TABLE 5 Percent Particulate Hg by Example Sample ID
Centrifuge 22 Condensate-1 92 23 Condensate-6 80 24 Condensate-2 22
25 Condensate-3 31 26 Crude-2 69 Percent Particulate Mercury = 100
* (Original Hg - Centrifuged Hg)/(Original Hg)
Comparative Examples 27 and 28
[0097] These examples show that commercial adsorbents designed to
remove elemental mercury from liquids and gases are highly
effective in removing volatile elemental mercury from this
simulated crude.
[0098] PURASEC.RTM. 5158, and JM Catalyst CP662 are commercial
adsorbents from Johnson Matthey designed to remove elemental
mercury from hydrocarbon liquids, such as refinery naphthas.
PURASEC.RTM. 5158 contains cupric sulfide and alumina. It has been
passivated to prevent rapid oxidation in air. JM Catalyst CP662 is
a clay that does not contain a metal sulfide.
[0099] 0.1 grams of each material were placed in 40 ml VOA vials.
10 ml of the volatile Hg0 in simulated crude from example 1 was
added. These were then mixed overnight on a rotating disc and
allowed to settle. The final mercury content of the supernatant was
compared to the initial Hg, and used to calculate the percent
removed by adsorption and settling. The results are shown in Table
6 below.
TABLE-US-00006 TABLE 6 Initial Final Hg, Percent Example Adsorbent
Hg, ppbw ppbw Removed 27 PURASEC .RTM. 5158 380 18 95.25 28 JM
Catalyst CP662 380 26 93.16
[0100] Both materials are highly effective in removing volatile
elemental mercury from this simulated crude.
Comparative Examples 29 to 34
[0101] These examples show that commercial adsorbents designed to
remove elemental mercury from liquids and gases are ineffective in
removing non-volatile particulate mercury from crude oil.
[0102] The Johnson Matthey adsorbents of examples 27 and 28 were
tested as described in Examples 17 and 18 but with a crude and a
condensate. The crude had an average particle size determined by
filtration of 11 microns. The condensate had a smaller average
particle size of 6 microns. Since the mercury in these samples is
particulate, some amount will settle in the absence of an
adsorbent. The effectiveness of an adsorbent must be judged by the
increase in removal compared to settling without an adsorbent.
Results are shown below in Table 7.
TABLE-US-00007 TABLE 7 Example Adsorbent Crude Percent Removed 29
None-Control NA. Crude 32 30 PURASEC .RTM. 5158 NA. Crude 39 31 JM
Catalyst CP662 NA. Crude 17 32 None-Control SEA Cond. 37 33 JM
Catalyst CP662 SEA Cond. 0 34 JM Catalyst CP662 SEA Cond. 25
[0103] These results show that the commercial adsorbents which work
well to remove elemental mercury are ineffective in removing
non-volatile particulate mercury. The amount removed was much less
than 100%, and about the same as was removed by settling alone in
the absence of an adsorbent.
Comparative Examples 35 and 36
[0104] These examples show that commercial adsorbents designed to
remove elemental mercury from liquids and gases are highly
effective in removing volatile elemental mercury from this
simulated crude.
[0105] Adsorbents used commercially to remove elemental mercury
from hydrocarbon liquids include copper-alumina and clay-containing
materials. Adsorbents of both classes were evaluated. The
clay-adsorbent contained Attapulgite.
[0106] 0.1 grams of each material were placed in 40 ml VOA vials.
10 ml of the volatile Hg0 in simulated crude from example 1 was
added. These were then mixed overnight on a rotating disc and
allowed to settle. The final mercury content of the supernatant was
compared to the initial Hg, and used to calculate the percent
removed by adsorption and settling. The results are shown in Table
8 below.
TABLE-US-00008 TABLE 8 Initial Final Example Adsorbent Hg, ppbw Hg,
ppbw Percent Removed 35 Copper-Alumina 380 18 95.25 36 Attapulgite
380 26 93.16
[0107] Both materials are highly effective in removing volatile
elemental mercury from this simulated crude.
Comparative Examples 37 to 42
[0108] These examples show that commercial adsorbents designed to
remove elemental mercury from liquids and gases are ineffective in
removing non-volatile particulate mercury from crude oil.
[0109] The adsorbents of examples 35 and 36 were tested as
described in Examples 17 and 18 but with a crude and a condensate.
The crude had an average particle size determined by filtration of
11 microns. The condensate had a smaller average particle size of 6
microns. Since the mercury in these samples is particulate, some
amount will settle in the absence of an adsorbent. The
effectiveness of an adsorbent must be judged by the increase in
removal compared to settling without an adsorbent. Results are
shown below in Table 9.
TABLE-US-00009 TABLE 9 Example Adsorbent Crude Percent Removed 37
None-Control Crude 1 32 38 Copper-alumina Crude 1 39 39 Attapulgite
Crude 1 17 40 None-Control Cond. 1 37 41 Copper-alumina Cond. 1 0
42 Attapulgite Cond. 1 25
[0110] These results show that the adsorbents which work well to
remove elemental mercury are ineffective in removing non-volatile
particulate mercury. The amount removed was much less than 100%,
and about the same as was removed by settling alone in the absence
of an adsorbent.
Example 43
[0111] This procedure was used to study the thermal decomposition
of particulate mercury in crudes at atmospheric pressure. As
elemental mercury was formed, it was continually stripped by a
stream of nitrogen gas.
[0112] One hundred ml of crude was placed in a 250 ml round bottom
flask. The flask also contained a magnetic stir bar and a glass
tube which supplied 300 ml/min of nitrogen gas below the level of
crude in the flask. The flask was wrapped with a heating mantle,
and placed on a magnetic stirrer. The nitrogen gas that exited the
flask went first to a condenser which collected naphtha formed from
heating the crude. Then the gas went to a second impinger filled
with 200 ml of 3 wt. % sodium polysulfide solution. The sodium
polysulfide adsorbed the elemental mercury and converted it into a
non-volatile compound, presumably HgS2H--.
[0113] At the start of the experiment, the vessels were sealed, the
stirrer was started, and the nitrogen flow was started. Then the
flask was heated rapidly to the desired temperature. The heating
was typically complete in 15 minutes. The temperature was
maintained for the duration of the experiment--from one hour to six
hours. The mercury contents of the crude, polysulfide, and gases
leaving the flask and polysulfide scrubber were measured by
Lumex.RTM.. The mercury content of the crude declined with time and
the mercury content of the polysulfide increased. Mercury was never
detected in any significant amount in the naphtha or in the gas
leaving the polysulfide scrubber. The mass balance for mercury
varied from 52 to 115%. Missing mercury was assumed to be adsorbed
on the glass tubing walls which were also wet with small amounts of
liquid hydrocarbon distilled from the crude.
[0114] The mercury measurements of the crude during the run were
used to determine the kinetics of the reaction. Corrections were
made for the amount of naphtha distilled from the crude. The
natural log of the ratio of the initial mercury content to the
mercury content at the time (corrected for naphtha vaporization)
was plotted versus time in a first order rate analysis. Results
fell on a straight line for all cases, and the slope gave the first
order rate constant. The reaction was found to follow first order
kinetics, but on occasion two kinetic species were apparent in the
kinetic plots. The majority species (typically about 88%) was a
rapidly-reacting species referred to as reactive mercury. A minor
species (typically about 12%) was less active and referred to as
refractory mercury.
Examples 44 to 68
[0115] A series of crudes, condensates and slurries of mercury
sulfide reagents were tested according to the procedure in Example
43. Results are shown in Table 10.
[0116] In examples 59 and 60 reagent metacinnabar (.beta.HgS) was
dispersed in Superla.TM. white oil. In examples 61 and 64 reagent
cinnabar (.alpha.HgS) was dispersed in Superla.TM. white oil. In
examples 67 and 68 the solid residue from the crude was dispersed
in Superla.TM..
TABLE-US-00010 TABLE 10 Re- Re- % active fractive Re- Feed Hg Hg
Rate Hg Rate frac- T Hg Closure Constant Constant tory Ex. Crude ID
.degree. C. pppw % Min-1 Min-1 Hg 44 Crude-1 150 659 95.15 0.001379
45 Crude-1 175 1,870 84.68 0.011281 46 Crude-1 175 1,106 89.67
0.017117 47 Crude-1 200 1,633 94.96 0.026871 0.004348 3.5 48
Crude-1 225 2,061 82.86 0.046989 0.020548 7.4 49 Crude-1 165 1,921
82.97 0.006739 50 Crude-1 196 1,825 77.02 0.037879 0.004980 5.6 51
Crude-1 150 1,741 108.51 0.003213 52 Crude-1 175 3,233 94.50
0.005363 53 Crude-1 200 3,276 92.73 0.022106 0.008391 19.6 54
Crude-1 225 3,203 97.87 0.055720 55 Crude-3 150 496 115.84 0.002496
56 Crude-3 175 604 66.26 0.020805 0.005798 11.7 57 Crude-3 200 627
91.58 0.065734 0.018915 8.4 58 Crude-3 225 618 93.65 0.087902
0.083873 44.6 59 .beta. HgS in 175 3,347 52.37 0.002269 0.003303
Superla 60 .beta. HgSin 200 2,757 90.54 0.013611 Superla 61 .alpha.
HgS in 250 939 92.14 0.015320 Superla 62 Condensate- 225 1,941
95.96 0.010612 0.010241 13.3 2 63 Condensate- 175 1,771 82.76
0.055231 0.003476 5.7 2 64 .alpha. HgS in 275 6,454 106.87 0.033585
0.011495 45.2 Superla 65 Condensate- 175 2,664 62.79 0.008675 7.1 1
66 Crude-2 200 8,793 100.06 0.027597 0.002535 9.2 67 Example 225
2,556 85.32 0.040714 0.008015 3.6 26 in Superla 68 Example 225
2,696 101.06 0.015167 0.002442 11.8 26 in Superla
[0117] The rate constants from all the crudes were analyzed on an
Arrhenius plot and the activation energy for the reactive mercury
species in thermal decomposition was found to be 13 kcal/mol. There
was no significant variation between the crudes. The examples using
crude where the refractory mercury species were observed were
analyzed and found to have a first order activation energy of 31
kcal/mol.
[0118] The mercury in the solid recovered from the crude of Example
21 and tested in examples 67 and 68 showed a rate of decomposition
comparable to the rates measured by the crudes. In contrast the two
reagent mercury sulfides, .alpha.HgS and .beta.HgS, had rates
significantly lower than the values found for crudes. Apparently
the nanometer scale metacinnabar particles in crude oil, or in
solid residues recovered from crude oils, decomposes at a faster
rate than the micron-scale reagent mercury sulfides. In comparing
the two reagent mercury sulfides, .alpha. HgS decomposed at a
slower rate than .beta.HgS. This is to be expected since .alpha.HgS
is more j
[0119] The nature of the refractory mercury compound could not be
identified. It may have been an artifact of the experiment.
Metacinnabar (.beta.HgS) is known to convert to the more stable
cinnabar (.alpha.HgS) during heating. This could have led to the
appearance of a more stable species which was termed
refractory.
Example 69
[0120] In this experiment the thermal decomposition of particulate
metacinnabar in crudes was studied in a flow reactor and at 1000
psig to prevent vaporization of the crudes. The crude was passed
upflow using an ISCO pump through a three zone furnace in 3/8'
tubing. The top and bottom zones had metal rods filling the center
and leaving narrow annuli to heat the crude rapidly and to minimize
the time spent in this transition. The middle zone had a 8.67 cc
wide spot to allow the thermal decomposition to proceed at a
uniform temperature. There was no gas fed to the unit, only crude.
Once the crude left the top of the reactor, it was cooled and the
pressure reduced to atmospheric. Then the crude was passed to a
nitrogen stripper which removed the volatile elemental mercury
reaction product. The mercury content of the stripped product was
measured by Lumex.
[0121] The rate constant was calculated from the mercury content of
the crude, the mercury content of the product and the LHSV by the
following equation.
Rate Constant, min-1=LHSV ln (Crude Hg/Product Hg)/60
[0122] where ln means the natural logarithm of the ratio of mercury
contents.
Examples 70 to 96
[0123] The procedure in example 69 was used on a series of crudes
and condensates at various temperatures and pressures. Results are
summarized in Table 11.
TABLE-US-00011 TABLE 11 Crude Stripper 1 s Order Example Hg, Temp,
Hg, Rate k, No Crude ID ppbw LHSV C. ppbw min.sup.-1 70
Condensate-2 2248 5 175 1688 0.0239 71 Condensate-2 2248 5 225 396
0.1447 72 Condensate-2 2248 0.5 250 231 0.0190 73 Condensate-2 2248
0.5 250 164 0.0218 74 Condensate-2 2248 1 250 284 0.0345 75
Condensate-2 2248 0.5 250 175 0.2128 76 Condensate-2 2248 1 175 980
0.0138 77 Condensate-2 2248 0.5 175 725 0.0094 78 Condensate-2 2248
5 175 1743 0.0212 79 Crude-1 3077 1 250 396 0.0342 80 Crude-1 3077
5 250 481 0.1547 81 Crude-1 3077 5 175 2437 0.0194 82 Crude-1 3077
1 175 1353 0.0137 83 Crude-1 3077 5 225 1163 0.0811 84 Crude-1 3077
1 225 333 0.0371 85 Crude-1 3077 0.5 225 199 0.0228 86 Crude-1 3077
0.5 250 109 0.0278 87 Crude-2 1601 5 250 232 0.1608 88 Crude-2 1601
0.5 250 77 0.0253 89 Crude-2 1601 1 250 109 0.0448 90 Crude-2 1601
5 225 327 0.1324 91 Crude-2 1601 1 225 81 0.0497 92 Crude-2 1601
0.5 225 84 0.0246 93 Crude-2 1601 1 175 415 0.0225 94 Crude-2 1601
0.05 175 250 0.0015 95 Crude-2 1601 0.5 175 447 0.0106 96 Crude-2
1601 5 175 2207 <0
[0124] As shown in FIG. 3 the first order rate constants measured
at atmospheric pressure in a glass flask were indistinguishable
from the rate constants measured at 1000 psig in a metal reactor.
All data was spaced uniformly around the common line found for all
crudes.
Example 97
[0125] The experimental procedure used in example 61 was modified
to study adsorption of the product elemental mercury following the
thermal decomposition. A second upflow reactor in a 3 zone furnace
was placed after the thermal decomposition reactor. Five cc of
24/42 mesh PURASEC 5158 was place in the reactor with 24/42 mesh
Alundum above and below the adsorbent. Operation was at 500
psig.
[0126] The tests began with pumping the crude through only the
thermal treater. The adsorber was by-passed. Then the flow was
directed to the adsorber. The product mercury content was
determined by either LUMEX.RTM. or CEBAM. The latter was used when
the LUMEX.RTM. were below 50 ppbw.
TABLE-US-00012 Total Total Heat Air- Exchanger Total Cooling
Economizer Product % Hg Heating Duty UA Values Process (bpd)
Removal Duty (kW) (kW) (kJ/C-hr) Thermal-4: 20,000 85.2 1469 12,860
181,900 Liquid-Phase, No Stripping Thermal-5: Full 19.650 84.8
12,488 11,216 252,400 Reflux Column Thermal-6: No 20,000 85.1 3423
14,843 195,800 Reflux Column Thermal-7: 20,000 82.5 2331 13,753 0
Flash
Examples 98 to 95
[0127] The procedure described in example 97 was used on a crude
containing about 9,000 ppbw Hg. Results are summarized in Table
12.
TABLE-US-00013 TABLE 12 Ex- Rx 1 Rx 2 Hours Delta ample T, T, on P,
Hg, No Flow LHSV .degree. C. .degree. F. Stream psig ppbw Method 98
1st Rx 10 150 3 400 99 1st Rx 1 150 19 100 1st Rx 1 150 20 5470
Lumex 101 1st Rx 1 150 40 1158 Lumex 102 1st Rx 1 250 59 271 Lumex
103 Both 1 250 150 82 45 Lumex RX
[0128] This example showed that the mercury content of the crude
was reduced from its initial very high value of over 9,000 ppbw to
less than 50 ppbw. Unfortunately the fixed bed reactor plugged
shortly after flow was routed to the adsorber.
Examples 104 to 113
[0129] The procedure described in example 97 was used on a sample
of a crude containing about 9,000 ppbw Hg except the adsorber was
used as 16/24 mesh to reduce the tendency to plug. Results are
summarized in Table 13.
TABLE-US-00014 TABLE 13 Ex- Rx 1 Rx 2 Hours Delta ample T, T, on P,
Hg, No Flow LHSV .degree. C. .degree. F. Stream psig ppbw Method
104 1st Rx 10 150 6 0 3416 Lumex 105 1st Rx 1 250 46 0 287 Lumex
106 Both Rx 1 250 150 69 150 835 Lumex 107 Both Rx 1 250 150 90 260
24 CEBAM 108 Both Rx 1 250 150 178 250 20 CEBAM 109 Both Rx 1 250
150 225 630 57 CEBAM 110 Both Rx 1 250 150 241 520 68 CEBAM 111
Both Rx 1 250 150 269 720 12 CEBAM 112 Both Rx 1 250 150 289 764 37
CEBAM 113 Both Rx 1 250 150 380 764 82 CEBAM
[0130] These results show that very low values of mercury could be
obtained. But as with the previous set of examples, the reactor
plugged. Plugging can be avoided by use of many techniques
well-known in the industry: guard beds, graded beds, expanded bed,
ebullated beds, CSTR reactors etc.
[0131] For the purposes of this specification and appended claims,
unless otherwise indicated, all numbers expressing quantities,
percentages or proportions, and other numerical values used in the
specification and claims are to be understood as being modified in
all instances by the term "about." Accordingly, unless indicated to
the contrary, the numerical parameters set forth in the following
specification and attached claims are approximations that can vary
depending upon the desired properties sought to be obtained by the
present invention. It is noted that, as used in this specification
and the appended claims, the singular forms "a," "an," and "the,"
include plural references unless expressly and unequivocally
limited to one referent.
[0132] As used herein, the term "include" and its grammatical
variants are intended to be non-limiting, such that recitation of
items in a list is not to the exclusion of other like items that
can be substituted or added to the listed items. The terms
"comprises" and/or "comprising," when used in this specification,
specify the presence of stated features, integers, steps,
operations, elements, and/or components, but do not preclude the
presence or addition of one or more other features, integers,
steps, operations, elements, components, and/or groups thereof.
Unless otherwise defined, all terms, including technical and
scientific terms used in the description, have the same meaning as
commonly understood by one of ordinary skill in the art to which
this invention belongs.
[0133] This written description uses examples to disclose the
invention, including the best mode, and also to enable any person
skilled in the art to make and use the invention. The patentable
scope is defined by the claims, and can include other examples that
occur to those skilled in the art. Such other examples are intended
to be within the scope of the claims if they have structural
elements that do not differ from the literal language of the
claims, or if they include equivalent structural elements with
insubstantial differences from the literal languages of the claims.
All citations referred herein are expressly incorporated herein by
reference.
* * * * *