U.S. patent application number 14/260421 was filed with the patent office on 2015-10-29 for middle distillate hydrocracking catalyst with a base extrudate having a high nanopore volume.
This patent application is currently assigned to CHEVRON U.S.A. INC.. The applicant listed for this patent is Theodorus Ludovicus Michael Maeson, Yihua Zhang. Invention is credited to Theodorus Ludovicus Michael Maeson, Yihua Zhang.
Application Number | 20150306583 14/260421 |
Document ID | / |
Family ID | 54333894 |
Filed Date | 2015-10-29 |
United States Patent
Application |
20150306583 |
Kind Code |
A1 |
Zhang; Yihua ; et
al. |
October 29, 2015 |
MIDDLE DISTILLATE HYDROCRACKING CATALYST WITH A BASE EXTRUDATE
HAVING A HIGH NANOPORE VOLUME
Abstract
The present invention is directed to an improved hydrocracking
catalyst containing a amorphous silica-alumina (ASA) base and
alumina support. The ASA base is characterized as having a high
nanopore volume and low particle density. The alumina support is
characterized as having a high nanopore volume. Hydrocracking
catalysts employing the combination high nanopore volume ASA base
and alumina support exhibit improved hydrogen efficiency, and
greater product yield and quality, as compared to hydrocracking
catalysts containing conventional ASA base and alumina
components.
Inventors: |
Zhang; Yihua; (Albany,
CA) ; Maeson; Theodorus Ludovicus Michael; (Moraga,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Zhang; Yihua
Maeson; Theodorus Ludovicus Michael |
Albany
Moraga |
CA
CA |
US
US |
|
|
Assignee: |
CHEVRON U.S.A. INC.
San Ramon
CA
|
Family ID: |
54333894 |
Appl. No.: |
14/260421 |
Filed: |
April 24, 2014 |
Current U.S.
Class: |
208/111.3 ;
502/66 |
Current CPC
Class: |
C10G 2300/1044 20130101;
B01J 29/166 20130101; B01J 35/1061 20130101; B01J 35/1047 20130101;
C10G 2300/70 20130101; B01J 35/1019 20130101; B01J 35/0026
20130101; B01J 35/108 20130101; B01J 21/12 20130101; B01J 35/1023
20130101; B01J 29/084 20130101; B01J 35/1042 20130101; B01J 35/002
20130101; C10G 47/20 20130101; B01J 29/064 20130101; B01J 35/023
20130101; B01J 37/0201 20130101; B01J 2229/42 20130101; B01J
37/0009 20130101; B01J 2229/20 20130101; B01J 23/888 20130101; B01J
29/076 20130101 |
International
Class: |
B01J 29/16 20060101
B01J029/16; C10G 47/20 20060101 C10G047/20 |
Claims
1. A hydrocracking catalyst, comprising: a base extrudate
comprising at least one molecular sieve, an alumina and an
amorphous silica alumina support, wherein the base extrudate has a
nanopore volume in the 6 nm to 11 nm range of 0.5 to 0.9 cc/g; and
at least one metal selected from the group consisting of elements
from Group 6 and Groups 8 through 10 of the Periodic Table.
2. The hydrocracking catalyst of claim 1, wherein the base
extrudate is formed using an alumina having a nanopore volume in
the 6 nm to 11 nm range of 0.1 to 0.3 cc/g.
3. The hydrocracking catalyst of claim 2, wherein the base
extrudate is formed using an amorphous silica alumina support
having a nanopore volume in the 6 nm to 11 nm range of 0.6 to 0.9
cc/g.
4. The hydrocracking catalyst of claim 1, wherein the base
extrudate is formed using an amorphous silica alumina support
having a nanopore volume in the 6 nm to 11 nm range of 0.6 to 0.9
cc/g.
5. The hydrocracking catalyst of claim 1, wherein the base
extrudate has a total nanopore volume in the 2 to 50 nm of 0.7 to
1.2 cc/g.
6. The hydrocracking catalyst of claim 1, wherein the base
extrudate has a particle density of 0.7 to 0.9 cc/g.
7. A method for making a hydrocracking catalyst, comprising the
steps of: forming a base extrudate comprising at least one
molecular sieve, an alumina and an amorphous silica alumina
support, wherein the base extrudate has a nanopore volume in the 6
nm to 11 nm range of 0.5 to 0.9 cc/g; and impregnating the base
extrude with at least one metal selected from the group consisting
of elements from Group 6 and Groups 8 through 10 of the Periodic
Table.
8. The method of claim 7, wherein the base extrudate is formed
using an alumina having a nanopore volume in the 6 nm to 11 nm
range of 0.1 to 0.3 cc/g.
9. The method of claim 8, wherein the base extrudate is formed
using an amorphous silica alumina support having a nanopore volume
in the 6 nm to 11 nm range of 0.6 to 0.9 cc/g.
10. The method of claim 7, wherein the base extrudate is formed
using an amorphous silica alumina support having a nanopore volume
in the 6 nm to 11 nm range of 0.6 to 0.9 cc/g.
11. The method of claim 7, wherein the base extrudate has a total
nanopore volume in the 2 to 50 nm of 0.7 to 1.2 cc/g.
12. The method of claim 7, wherein the base extrudate has a
particle density of 0.7 to 0.9 cc/g.
13. A process for hydrocracking a hydrocarbonaceous feedstock,
comprising contacting the feedstock with a hydrocracking catalyst
under hydrocracking conditions to produce a hydrocracked effluent;
the hydrocracking catalyst comprising a base extrudate comprising
at least one molecular sieve, an alumina and an amorphous silica
alumina support, wherein the base extrudate has a nanopore volume
in the 6 nm to 11 nm range of 0.5 to 0.9 cc/g; and at least one
metal selected from the group consisting of elements from Group 6
and Groups 8 through 10 of the Periodic Table.
14. The process of claim 13, wherein the base extrudate is formed
using an alumina having a nanopore volume in the 6 nm to 11 nm
range of 0.1 to 0.3 cc/g.
15. The process of claim 14, wherein the base extrudate is formed
using an amorphous silica alumina support having a nanopore volume
in the 6 nm to 11 nm range of 0.6 to 0.9 cc/g.
16. The process of claim 13, wherein the base extrudate is formed
using an amorphous silica alumina support having a nanopore volume
in the 6 nm to 11 nm range of 0.6 to 0.9 cc/g.
17. The process of claim 13, wherein the base extrudate has a total
nanopore volume in the 2 to 50 nm of 0.7 to 1.2 cc/g.
18. The process of claim 13, wherein the base extrudate has a
particle density of 0.7 to 0.9 cc/g.
Description
FIELD OF THE INVENTION
[0001] The present invention is directed to an improved
hydrocracking catalyst containing a high nanopore volume (HNPV)
amorphous silica-alumina (ASA) component in combination with a HNPV
alumina support. The HNPV ASA component is also characterized as
having a low particle density. The HNPV ASA component and HNPV
alumina support are combined to form a HNPV base extrudate suitable
for manufacturing the finished improved hydrocracking catalyst of
the present invention.
[0002] Finished hydrocracking catalysts employing the HNPV ASA
component in combination with a HNPV alumina support exhibit
improved hydrogen efficiency, and greater product yield and
quality, as compared to conventional hydrocracking catalysts.
BACKGROUND OF THE INVENTION
[0003] Catalytic hydroprocessing refers to petroleum refining
processes in which a carbonaceous feedstock is brought into contact
with hydrogen and a catalyst, at a higher temperature and pressure,
for the purpose of removing undesirable impurities and/or
converting the feedstock to an improved product.
[0004] Heavy hydrocarbon feedstocks can be liquid, semi-solid
and/or solid at atmospheric conditions. Such heavy
hydrocarbonaceous feedstocks can have an initial ASTM D86-12
boiling point of 600.degree. F. (316.degree. C.) or greater.
[0005] The feedstock properties that influence its
hydroprocessability include: organic nitrogen content, especially
basic nitrogen content; feed boiling range and end point;
polycyclic aromatics content and previous processing history (i.e.,
straight run versus thermally cracked).
[0006] Heavy hydrocarbonaceous oils boiling in the gas oil range
can be high in heteroatom content, especially nitrogen. Nitrogen
content can range from about 50 ppmw to greater than 5000 ppmw
elemental nitrogen, based on total weight of the heavy
hydrocarbonaceous oils. The nitrogen containing compounds can be
present as basic or non-basic nitrogen species. Examples of basic
nitrogen species include pyridines, alkyl substituted pyridines,
quinolones, alkyl substituted quinolones, acridines, alkyl
substituted acridines, phenyl and naphtha substituted acridines.
Examples of non-basic nitrogen species include pyrroles, alkyl
substituted pyrroles, indoles, alkyl substituted indoles,
carbazoles and alkyl substituted carbazoles.
[0007] Heavy hydrocarbonaceous oils boiling in the gas oil range
can have sulfur contents ranging from about 500 ppmw to about
100,000 ppmw elemental sulfur (based on total weight of the heavy
hydrocarbonaceous oils). The sulfur will usually be present as
organically bound sulfur. Examples of such sulfur compounds include
the class of heterocyclic sulfur compounds including but not
limited to thiophenes, tetrahydrothiophenes, benzothiophenes and
their higher homologues and analogues. Other orgranically bound
sulfur compounds include aliphatic, naphthenic and aromatic
mercaptans, sulfides, disulfides and polysulfides.
[0008] Gas oil range feeds contain polycyclic condensed
hydrocarbons having two or more fused rings. The rings can either
be saturated or unsaturated (aromatic). For the latter, these
polycyclic condensed hydrocarbons are also called polynuclear
aromatics (PNA) or polyaromatic hydrocarbons (PAH). The light PNAs,
with two to six rings, are present in virgin vacuum gas oil
streams. The heavy PNAs (HPNA) generally contain 7-10 rings, but
can contain higher amounts including 11 rings or at least 14 rings
or dicoronylene (15-rings) or coronylenovalene (17-rings) or
higher.
[0009] Hydrocracking is an important refining process used to
process manufacture middle distillate products boiling in the
250-700.degree. F. (121-371.degree. C.) range, such as, kerosene,
and diesel. Hydrocracking feedstocks contain significant amounts of
organic sulfur and nitrogen. The sulfur and nitrogen must be
removed to meet fuel specifications.
[0010] Generally, conventional hydrocracking catalysts are composed
of (1) at least one acidic component which can be crystallized
aluminosilicate and/or amorphous silica alumina; (2) a binding
material such as alumina, titania, silica, etc; and (3) one or more
metals selected from Groups 6 and 8-10 of the Periodic Table,
particularly nickel, cobalt, molybdenum and tungsten.
[0011] There are two broad classes of reactions that occur in the
hydrocracking process. The first class of reactions involves
hydrotreating, in which impurities such as nitrogen, sulfur,
oxygen, and metals are removed from the feedstock. The second class
of reactions involves hydrocracking, in which carbon-carbon bonds
are cleaved or hydrocracked, in the presence of hydrogen, to yield
lower boiling point products.
[0012] Hydrocracking catalysts are bifunctional: hydrotreating is
facilitated by the hydrogenation function provided by the metal
components, and the cracking reaction is facilitated by the solid
acid components. Both reactions need the presence of high pressure
hydrogen.
[0013] During hydrocracking, the heavy hydrocarbon feed molecules
form a liquid film and covers the active sites of the catalyst. Due
to the limitation of hydrogen solubility in hydrocarbons, the
hydrogen availability in the hydrocracking catalyst extrudates has
been an issue. In practice, the heavy hydrocarbon feed fills the
pores first, and reactant hydrogen must then access the active
sites in the pores via diffusion through the heavy hydrocarbon
feed. Conventional hydrocracking catalysts exhibit limited hydrogen
pore diffusivity with heavy, more refractive feedstocks. This has
inhibited the hydrogenation function of the hydrocracking
catalysts, which results in middle distillates and unconverted oil
(UCO) products with poor quality. This issue becomes more
significant when the hydrocracking feed become more disadvantaged,
as these feeds consume greater amounts of hydrogen during
hydroprocessing, making even less hydrogen available for diffusion
into the pores.
[0014] Accordingly, there is a current need for a hydrocracking
catalyst that exhibits a higher degree of hydrogen efficiency, and
greater product yield and quality, as compared to conventional
hydrocracking catalysts.
SUMMARY OF THE INVENTION
[0015] The present invention is directed to an improved finished
hydrocracking catalyst containing a HNPV ASA component in
combination with a HNPV alumina support. The ASA base is
characterized as having a low particle density. The HNPV ASA
component employed in the catalyst of the present invention is
characterized as having a narrower pore size distribution as
compared to a conventional ASA, and the alumina support is
characterized as having a broader pore size distribution as
compared to an alumina base used in conventional hydrocracking
catalysts.
[0016] It has been found that by employing ASA and alumina
materials having a higher nanopore volume in the 6 to 11 nm range,
the base extrudate exhibits a lower particle density. A lower base
extrudate particle density allows for increased metals loading
while maintaining a conventional particle density for the finished
hydrocracking catalyst. The finished hydrocracking catalysts
employing using the novel combination of the HNPV ASA component and
HNPV alumina support exhibit improved hydrogen efficiency, and
greater product yield and quality as compared to conventional
hydrocracking catalysts containing conventional ASA and alumina
components. This unique combination of the ASA and alumina support
provides for a finished hydrocracking catalyst that is particularly
suited for hydroprocessing disadvantaged feedstocks.
DETAILED DESCRIPTION OF THE INVENTION
Introduction
[0017] "Periodic Table" refers to the version of IUPAC Periodic
Table of the Elements dated Jun. 22, 2007, and the numbering scheme
for the Periodic Table Groups is as described in Chemical and
Engineering News, 63(5), 27 (1985).
[0018] "Hydroprocessing" or "hydroconversion" refers to a process
in which a carbonaceous feedstock is brought into contact with
hydrogen and a catalyst, at a higher temperature and pressure, for
the purpose of removing undesirable impurities and/or converting
the feedstock to a desired product. Such processes include, but not
limited to, methanation, water gas shift reactions, hydrogenation,
hydrotreating, hydrodesulphurization, hydrodenitrogenation,
hydrodemetallation, hydrodearomatization, hydroisomerization,
hydrodewaxing and hydrocracking including selective hydrocracking.
Depending on the type of hydroprocessing and the reaction
conditions, the products of hydroprocessing can show improved
physical properties such as improved viscosities, viscosity
indices, saturates content, low temperature properties,
volatilities and depolarization.
[0019] "Hydrocracking" refers to a process in which hydrogenation
and dehydrogenation accompanies the cracking/fragmentation of
hydrocarbons, e.g., converting heavier hydrocarbons into lighter
hydrocarbons, or converting aromatics and/or cycloparaffins
(naphthenes) into non-cyclic branched paraffins.
[0020] "Column" refers to a distillation column or columns for
separating a feedstock into one or more fractions having differing
cut points.
[0021] "Cut point" refers to the temperature on a True Boiling
Point ("TBP") curve (i.e., a batch process curve of percent of feed
removed in a heavily refluxed tower versus temperature reached to
achieve that removal) at which a predetermined degree of separation
is reached.
[0022] "True Boiling Point" (TBP) refers to the boiling point of a
feed which as determined by ASTM D2887-13.
[0023] "Bottoms fraction" means the heavier fraction, separated by
fractionation from a feedstock, as a non-vaporized (i.e. residuum)
fraction.
[0024] "Hydrocracked heavy fraction" means the heavy fraction after
having undergone hydrocracking.
[0025] "Hydrocarbonaceous" means a compound or substance that
contains hydrogen and carbon atoms, but which can include
heteroatoms such as oxygen, sulfur or nitrogen.
TABLE-US-00001 "Middle distillates" include jet fuel, diesel fuel,
and kerosene. Typical Cut Points, .degree. F. (.degree. C.)
Products For North American Market Light Naphtha C.sub.5-180
(C.sub.5-82) Heavy Naphtha 180-300 (82-149) Jet 300-380 (149--193)
Kerosene 380-530 (193-277) Diesel 530-700 (277-371)
[0026] "LHSV" means liquid hourly space velocity.
[0027] "SCF/BBL" (or scf/bbl, or scfb or SCFB) refers to a unit of
standard cubic foot of gas (N.sub.2, H.sub.2, etc.) per barrel of
hydrocarbon feed.
[0028] "Nanopore" means pores having a diameter between 2 nm and 50
nm, inclusive.
[0029] Where permitted, all publications, patents and patent
applications cited in this application are herein incorporated by
reference in their entirety; to the extent such disclosure is not
inconsistent with the present invention.
[0030] Unless otherwise specified, the recitation of a genus of
elements, materials or other components, from which an individual
component or mixture of components can be selected, is intended to
include all possible sub-generic combinations of the listed
components and mixtures thereof. Also, "include" and its 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 may also be
useful in the materials, compositions and methods of this
invention.
[0031] All numerical ranges stated herein are inclusive of the
lower and upper values stated for the range, unless stated
otherwise.
[0032] Properties for materials described herein are determined as
follows:
[0033] (a) Constrained index (CI): indicates the total cracking
conversion of a 50/50 mixture of n-hexane and 3-methyl-pentane by a
sample catalyst at 900.degree. F. (482.degree. C.), 0.68 WHSV.
Samples are prepared according to the method described in U.S. Pat.
No. 7,063,828 to Zones and Burton, issued Jun. 20, 2006.
[0034] (b) Bronsted acidity: determined by
isopropylamine-temperature-programmed desorption (IPam TPD) adapted
from the published descriptions by T. J. Gricus Kofke, R. K. Gorte,
W. E. Farneth, J. Catal. 114, 34-45, 1988; T. J. Gricus Kifke, R.
J. Gorte, G. T. Kokotailo, J. Catal. 115, 265-272, 1989; J. G.
Tittensor, R. J. Gorte and D. M. Chapman, J. Catal. 138, 714-720,
1992.
[0035] (c) SiO.sub.2/Al.sub.2O.sub.3 Ratio (SAR): determined by ICP
elemental analysis. A SAR of infinity (.infin.) represents the case
where there is no aluminum in the zeolite, i.e., the mole ratio of
silica to alumina is infinity. In that case the molecular sieve is
comprised of essentially all of silica.
[0036] (d) Surface area: determined by N.sub.2 adsorption at its
boiling temperature. BET surface area is calculated by the 5-point
method at P/P.sub.0=0.050, 0.088, 0.125, 0.163, and 0.200. Samples
are first pre-treated at 400.degree. C. for 6 hours in the presence
of flowing, dry N.sub.2 so as to eliminate any adsorbed volatiles
like water or organics.
[0037] (e) Nanopore and micropore volume: determined by N.sub.2
adsorption at its boiling temperature. Micropore volume is
calculated by the t-plot method at P/P.sub.0=0.050, 0.088, 0.125,
0.163, and 0.200. Samples are first pre-treated at 400.degree. C.
for 6 hours in the presence of flowing, dry N.sub.2 so as to
eliminate any adsorbed volatiles like water or organics.
[0038] (f) Nanopore diameter: determined by N.sub.2 adsorption at
its boiling temperature. Mesopore pore diameter is calculated from
N.sub.2 isotherms by the BJH method described in E. P. Barrett, L.
G. Joyner and P. P. Halenda, "The determination of pore volume and
area distributions in porous substances. I. Computations from
nitrogen isotherms." J. Am. Chem. Soc. 73, 373-380, 1951. Samples
are first pre-treated at 400.degree. C. for 6 hours in the presence
of flowing, dry N.sub.2 so as to eliminate any adsorbed volatiles
like water or organics.
[0039] (g) Total nanopore volume: determined by N.sub.2 adsorption
at its boiling temperature at P/P.sub.0=0.990. Samples are first
pre-treated at 400.degree. C. for 6 hours in the presence of
flowing, dry N.sub.2 so as to eliminate any adsorbed volatiles like
water or organics.
[0040] (h) Unit cell size: determined by X-ray powder
diffraction.
[0041] (i) Alpha value: determined by an Alpha test adapted from
the published descriptions of the Mobil Alpha test (P. B. Weisz and
J. N. Miale, J. Catal., 4, 527-529, 1965; J. N. Miale, N. Y. Chen,
and P. B. Weisz, J. Catal., 6, 278-87, 1966). The "Alpha Value" is
calculated as the cracking rate of the sample in question divided
by the cracking rate of a standard silica alumina sample. The
resulting "Alpha" is a measure of acid cracking activity which
generally correlates with number of acid sites.
[0042] (j) API gravity: the gravity of a petroleum
feedstock/product relative to water, as determined by ASTM
D4052-11.
[0043] (k) Polycyclic index (PCI): as measured by ASTM
D6397-11.
[0044] (l) Viscosity index (VI): an empirical, unit-less number
indicated the effect of temperature change on the kinematic
viscosity of the oil. The higher the VI of a base oil, the lower
its tendency to change viscosity with temperature. Determined by
ASTM 2270-04.
[0045] (m) Viscosity: a measure of fluid's resistance to flow as
determined by ASTM D445.
[0046] (n) Loose bulk density: weight per unit volume of powder or
extrudate in a loose condition as determined by ASTM D7481.
[0047] (o) Water pore volume: a test method to determine the amount
of water that a gram of catalyst can hold in its pores. Weigh out
5-10 grams of sample (or amount specified by the engineer) in a 150
ml. beaker (plastic). Add deionized water enough to cover the
sample. Allow to soak for 1 hour. After 1 hour, decant the liquid
until most of the water has been removed and get rid of excess
water by allowing a paper towel absorb the excess water. Change
paper towel until there is no visible droplets on the walls of the
plastic beaker. Weigh the beaker with sample. Calculate the Pore
volume as follows:
F-I=W* [0048] F=final weight of sample [0049] I=initial weight of
sample [0050] W*=weight or volume of water in the sample [0051]
PV=W*/I (unit is cc/gm)
[0052] (p) Acid site density: temperature-programmed desorption
(TPD) of isopropylamine (IPAm) to quantify the Bronsted acid site
distribution of a material is described by Maesen and Hertzenberg,
Journal of Catalysis 182, 270-273 (1999).
[0053] (q) Particle density: Particle density is obtained by
applying the formula D=M/V. M is the weight and V is the volume of
the catalyst sample. The volume is determined by measuring volume
displacement by submersing the sample into mercury under 28 mm Hg
vacuum.
Hydrocracking Catalyst Composition
[0054] Catalysts used in carrying out the hydrocracking process
includes an amorphous silica-alumina (ASA) component characterized
as having a high nanopore volume (HNPV) and low particle density, a
HNPV alumina support, one or more metals, one or more molecular
sieves, and optionally one or more promoters. The composition of
the finished catalyst, based on the bulk dry weight of the finished
hydrocracking catalyst, is described in Table 1 below.
TABLE-US-00002 TABLE 1 HNPV ASA component 15-85 wt. % HNPV alumina
support 5-55 wt. % total molecular sieve content 0.1-75 wt. % total
metal oxide content 15-55 wt. % total promoter content 0-15 wt.
%
[0055] For each embodiment described herein, the HNPV ASA component
is characterized as having a low particle density. In addition, the
HNPV ASA component employed in the catalyst of the present
invention is characterized as having a narrower pore size
distribution as compared to conventional ASA materials. The alumina
support is characterized as having a broader pore size distribution
as compared to an alumina base used in conventional hydrocracking
catalysts.
[0056] A HNPV ASA used in the manufacture the finished
hydrocracking catalyst of the present invention will have a NPV (6
nm-11 nm) of 0.6 to 0.9 cc/g.
[0057] A HNPV alumina extrudate used in the manufacture the
finished hydrocracking catalyst of the present invention will have
a NPV (6 nm-11 nm) of 0.1 to 0.3 cc/g.
[0058] The HNPV ASA component and HNPV alumina support are combined
to form a HNPV base extrudate suitable for increased metal loading
on the finished improved hydrocracking catalyst of the present
invention. As used herein, the term HNPV base extrudate means the
base extrudate has a total nanopore volume that is greater than a
conventional base containing conventional ASA and alumina
materials. A HNPV base extrudate used to manufacture the finished
hydrocracking catalyst of the present invention will have a NPV (6
nm-11 nm) of 0.1 to 1.0 cc/g.
[0059] It has been found that by employing ASA and alumina
materials having a higher nanopore volume in the 6 to 11 nm range,
the base extrudate exhibits a lower particle density. A lower base
extrudate particle density allows for increased metals loading
while maintaining a conventional particle density for the finished
hydrocracking catalyst.
[0060] Finished hydrocracking catalysts manufactured using the HNPV
base extrudate of the present invention exhibit improved hydrogen
efficiency, and greater product yield and quality as compared to
conventional hydrocracking catalysts containing conventional ASA
and alumina components.
[0061] The HNPV ASA and HNPV alumina support components useful in
the hydrocracking catalysts of the present invention, and base
extrudates formed from these components, are characterized as
having the properties described in Tables 2 and 3 below,
respectively.
TABLE-US-00003 TABLE 2 HNPV ASA HNPV alumina d10 (nm) 55-70 60-70
d50 (nm) 100-110 140-160 d90 (nm) 270-300 180-220 Peak Pore
Diameter (.ANG.) 80-100 160-200 NPV - 6 nm-11 nm (cc/g) 0.6-0.9
0.1-0.3 NPV - 11 nm-20 nm (cc/g) 0.4-0.7 0.4-0.7 NPV - 20 nm-50 nm
(cc/g) 0.2-0.4 .sup. 0-0.3 Total NPV (2-50 nm) (cc/g) 1.5-2.0
0.7-1.2 loose bulk density (g/mL) 0.15-0.35 0.4-0.6 BET surface
area (m.sup.2/g 450-600 180-350
TABLE-US-00004 TABLE 3 HNPV Base Extrudate d10 (nm) 40-60 d50 (nm)
70-90 d90 (nm) 90-120 Peak Pore Diameter (.ANG.) 70-100 NPV - 6
nm-11 nm (cc/g) 0.5-0.9 NPV - 11 nm-20 nm (cc/g) 0.05-0.25 NPV - 20
nm-50 nm (cc/g) .sup. 0-0.1 Total NPV (2-50 nm) (cc/g) 0.7-1.2 BET
surface area (m.sup.2/g) 400-600 WPV (water pore volume) (g/cc)
0.85-1.25 particle density (g/cc) 0.7-0.9
[0062] For each embodiment described herein, the amount of HNPV ASA
component in the finished hydrocracking catalyst is from 15 wt. %
to 85 wt. % based on the bulk dry weight of the hydrocracking
catalyst. In one subembodiment, the amount of HNPV ASA component in
the hydrocracking catalyst is from 25 wt. % to 75 wt. % based on
the bulk dry weight of the finished hydrocracking catalyst
[0063] For each embodiment described herein, the hydrocracking
catalyst contains one or more molecular sieves selected from the
group consisting of BEA-, ISV-, BEC-, IWR-, MTW-, *STO-, OFF-,
MAZ-, MOR-, MOZ-, AFI-, *NRE, SSY-, FAU-, EMT-, ITQ-21-, ERT-,
ITQ-33-, and ITQ-37-type molecular sieves, and mixtures
thereof.
[0064] In one subembodiment, the one or more molecular sieves
selected from the group consisting of molecular sieves having a FAU
framework topology, molecular sieves having a BEA framework
topology, and mixtures thereof.
[0065] The amount of molecular sieve material in the finished
hydrocracking catalyst is from 0.1 wt. % to 75 wt. % based on the
bulk dry weight of the hydrocracking catalyst. In one
subembodiment, the amount of molecular sieve material in the
finished hydrocracking catalyst is from 1 wt. % to 8 wt. %.
[0066] The finished catalyst may optionally contain a non-zeolitic
molecular sieves which can be used include, for example,
silicoaluminophosphates (SAPO), ferroaluminophosphate, titanium
aluminophosphate and the various ELAPO molecular sieves described
in U.S. Pat. No. 4,913,799 and the references cited therein.
Details regarding the preparation of various non-zeolite molecular
sieves can be found in U.S. Pat. No. 5,114,563 (SAPO); U.S. Pat.
No. 4,913,799 and the various references cited in U.S. Pat. No.
4,913,799. Mesoporous molecular sieves can also be used, for
example the M41S family of materials (J. Am. Chem. Soc., 114:10834
10843(1992)), MCM-41 (U.S. Pat. Nos. 5,246,689; 5,198,203;
5,334,368), and MCM-48 (Kresge et al., Nature 359:710 (1992)).
[0067] In one subembodiment, the molecular sieve is a Y zeolite
with a unit cell size of 24.15 .ANG.-24.45 .ANG.. In another
subembodiment, the molecular sieve is a Y zeolite with a unit cell
size of 24.15 .ANG.-24.35 .ANG.. In another subembodiment, the
molecular sieve is a low-acidity, highly dealuminated ultrastable Y
zeolite having an Alpha value of less than 5 and a Bronsted acidity
of from 1 to 40. In one subembodiment, the molecular sieve is a Y
zeolite having the properties described in Table 4 below.
TABLE-US-00005 TABLE 4 Alpha value 0.01-5.sup. Cl 0.05-5% Bronsted
acidity 1-80 .mu.mole/g acid site density 0.9-2 mmol/g SAR 15-150
surface area 600-900 m.sup.2/g micropore volume 0.25-0.30 mL/g
total pore volume 0.51-0.55 mL/g unit cell size 24.15-24.35
.ANG.
[0068] In another subembodiment, the molecular sieve is a Y zeolite
having the properties described in Table 5 below.
TABLE-US-00006 TABLE 5 SAR 10-.infin. micropore volume 0.15-0.27
mL/g BET surface area 700-825 m.sup.2/g unit cell size 24.15-24.45
.ANG.
[0069] As described herein above, the finished hydrocracking
catalyst of the present invention contains one or more metals. For
each embodiment described herein, each metal employed is selected
from the group consisting of elements from Group 6 and Groups 8
through 10 of the Periodic Table, and mixtures thereof. In one
subembodiment, each metal is selected from the group consisting of
nickel (Ni), cobalt (Co), iron (Fe), chromium (Cr), molybdenum
(Mo), tungsten (W), and mixtures thereof. In another subembodiment,
the hydrocracking catalyst contains at least one Group 6 metal and
at least one metal selected from Groups 8 through 10 of the
Periodic Table. Exemplary metal combinations include Ni/Mo/W,
Ni/Mo, Ni/W, Co/Mo, Co/W, Co/W/Mo and Ni/Co/W/Mo.
[0070] The total amount of metal oxide material in the finished
hydrocracking catalyst is from 15 wt. % to 55 wt. % based on the
bulk dry weight of the hydrocracking catalyst. In one
subembodiment, the hydrocracking catalyst contains from 30 wt. % to
50 wt. % of nickel oxide and from 15 wt. % to 25 wt. % of tungsten
oxide based on the bulk dry weight of the hydrocracking
catalyst.
[0071] The finished hydrocracking catalyst of the present invention
may contain one or more promoters selected from the group
consisting of phosphorous (P), boron (B), fluorine (F), silicon
(Si), aluminum (Al), zinc (Zn), manganese (Mn), and mixtures
thereof. The amount of promoter in the hydrocracking catalyst is
from 0 wt. % to 15 wt. % based on the bulk dry weight of the
hydrocracking catalyst. In one subembodiment, the amount of
promoter in the hydrocracking catalyst is from 1 wt. % to 5 wt. %
based on the bulk dry weight of the hydrocracking catalyst.
Hydrocracking Catalyst Preparation
[0072] In general, the hydrocracking catalyst of the present
invention is prepared by: [0073] (a) mixing and pepertizing the
HNPV ASA and HNPV alumina support with at least one molecular sieve
and a support to make an extrudate base; [0074] (b) impregnate the
base with a metal impregnation solution containing at least one
metal; and [0075] (c) post-treating the extrudates, including
subjecting the metal-loaded extrudates to drying and
calcination.
[0076] Prior to impregnation, the extrudate base is dried at
temperature between 90.degree. C. and 150.degree. C. (194.degree.
F.-302.degree. F.) for 1-12 hours, followed by calcination at one
or more temperatures between 350.degree. C. and 700.degree. C.
(662.degree. F.-1292.degree. F.).
[0077] The impregnation solution is made by dissolving metal
precursors in deionized water. The concentration of the solution
was determined by the pore volume of the support and metal loading.
During a typical impregnation, the support is exposed to the
impregnation solution for 0.1-10 hours. After soaking for another
0.1-10 hours, the catalyst is dried at one or more temperatures in
the range of 38.degree. C.-149.degree. C. (100.degree.
F.-300.degree. F.) for 0.1-10 hours. The catalyst is further
calcined at one or more temperatures in the range of 316.degree.
C.-649.degree. C. (600.degree. F.-1200.degree. F.), with the
presence of sufficient air flow, for 0.1-10 hours.
[0078] In one embodiment, the impregnation solution further
contains a modifying agent for promoting the deposition of the at
least one metal. Modifying agents, as well as methods of making
hydrocracking catalysts using such modifying agents, are disclosed
in U.S. Publication Nos. 20110000824 and 20110132807 to Zhan et
al., published Jan. 6, 2011 and Jun. 9, 2011, respectively.
Hydrocracking Overview
[0079] The hydrocracking catalyst of the present invention is
suitable for hydroprocessing a variety of hydrocarbonaceous
feedstocks, including disadvantaged feedstocks that are normally
not conducive to middle distillate production using a conventional
one- or two-stage hydrocracking process, such as visbroken gas
oils, heavy coker gas oils, gas oils derived from residue
hydrocracking or residue desulfurization, other thermally cracked
oils, de-asphalted oils, Fischer-Tropsch derived feedstocks, cycle
oils from an FCC unit, heavy coal-derived distillates, coal
gasification byproduct tars, and heavy shale-derived oils, organic
waste oils such as those from pulp/paper mills or waste biomass
pyrolysis units.
[0080] Table 6 below lists the typical physical properties for a
feedstock suitable for manufacturing middle distillates using the
catalyst of the present invention, and Table 7 illustrates the
typical hydrocracking process conditions.
TABLE-US-00007 TABLE 6 Properties Feedstock Gravity, .degree.API
13.5-22.0 N, ppm 0.5-2,000 S, wt % 0-3 Polycyclic index (PCI)
1500-3000 Distillation Boiling Point Range .degree. F. (.degree.
C.) 700-1200
TABLE-US-00008 TABLE 7 Hydrocracking Conditions Liquid hourly space
velocity (LHSV) 0.1-5 hr.sup.-1 H.sub.2 partial pressure 800-3,500
psig H.sub.2 consumption rate 200-20,000 SCF/Bbl H.sub.2
recirculation rate 50-5,000 SCF/Bbl Operating temperature
200-500.degree. C. (392-932.degree. F.) Conversion (%) 30-90
[0081] Prior to introduction of the hydroprocessing feed, the
catalyst is activated by contacting with petroleum liquid
containing sulfiding agent at a temperature of 200.degree. F. to
800.degree. F. (66.degree. C. to 482.degree. C.) from 1 hour to 7
days, and under a H.sub.2-containing gas pressure of 100 kPa to
25,000 kPa. Suitable sulfiding agents include elemental sulfur,
ammonium sulfide, ammonium polysulfide (RNH.sub.4).sub.2S.sub.x),
ammonium thiosulfate ((NH.sub.4).sub.25.sub.2O.sub.3), sodium
thiosulfate (Na.sub.2S.sub.2O.sub.3), thiourea CSN.sub.2H.sub.4,
carbon disulfide, dimethyl disulfide (DMDS), dimethyl sulfide
(DMS), dibutyl polysulfide (DBPS), mercaptanes, tertiarybutyl
polysulfide (PSTB), tertiarynonyl polysulfide (PSTN), aqueous
ammonium sulfide.
[0082] As noted above, the finished hydrocracking catalysts
employing using the novel combination of the HNPV ASA component and
HNPV alumina support exhibit improved hydrogen efficiency, and
greater product yield and quality as compared to conventional
hydrocracking catalysts containing conventional ASA and alumina
components. This unique combination of the ASA and alumina support
provides for a finished hydrocracking catalyst that is particularly
suited for hydroprocessing disadvantaged feedstocks.
[0083] Depending on the feedstock, target product slate and amount
of available hydrogen, the catalyst of the present invention can be
used alone or in combination with other conventional hydrocracking
catalysts.
[0084] In one embodiment, the catalyst is deployed in one or more
fixed beds in a single stage hydrocracking unit, with or without
recycle (once-through). Optionally, the single-stage hydrocracking
unit may employ multiple single-stage units operated in
parallel.
[0085] In another embodiment, the catalyst is deployed in one or
more beds and units in a two-stage hydrocracking unit, with and
without intermediate stage separation, and with or without recycle.
Two-stage hydrocracking units can be operated using a full
conversion configuration (meaning all of the hydrotreating and
hydrocracking is accomplished within the hydrocracking loop via
recycle). This embodiment may employ one or more distillation units
within the hydrocracking loop for the purpose of stripping off
product prior to the second stage hydrocracking step or prior to
recycle of the distillation bottoms back to the first and/or second
stage.
[0086] Two stage hydrocracking units can also be operated in a
partial conversion configuration (meaning one or more distillation
units are positioned within hydrocracking loop for the purpose of
stripping of one or more streams that are passed on for further
hydroprocessing). Operation of the hydrocracking unit in this
manner allows a refinery to hydroprocess highly disadvantaged
feedstocks by allowing undesirable feed components such as the
polynuclear aromatics, nitrogen and sulfur species (which
deactivate hydrocracking catalysts) to pass out of the
hydrocracking loop for processing by equipment better suited for
processing these components, e.g. an FCC unit.
[0087] In one embodiment, the catalyst is used in the first stage
and optionally the second stage of a partial conversion, two-stage
hydrocracking configuration which is well suited for making at
least one middle distillate and a heavy vacuum gas fluidized
catalytic cracking feedstock (HVGO FCC), by:
[0088] (a) hydrocracking a hydrocarbonaceous feedstock to produce a
first stage hydrocracked effluent;
[0089] (b) distilling the hydrocracked feedstock by atmospheric
distillation to form at least one middle distillate fraction and an
atmospheric bottoms fraction;
[0090] (c) further distilling the atmospheric bottoms fraction by
vacuum distillation to form a side-cut vacuum gas oil fraction and
a heavy vacuum gas oil FCC feedstock;
[0091] (d) hydrocracking the side-cut vacuum gas oil fraction to
form a second stage hydrocracked effluent; and
[0092] (e) combining the second stage hydrocracked effluent with
the first stage hydrocracked effluent.
[0093] The refinery configuration illustrated above has several
advantages over conventional two-stage hydrocracking schemes.
First, in this configuration, the catalyst and operating conditions
of the first stage are selected to yield a HVGO FCC stream having
only the minimum feed qualities necessary to produce FCC products
which meet the established commercial specifications. This is in
contrast to a conventional two-stage hydrocracking scheme where the
first stage hydrocracking unit is operated at a severity necessary
to maximize distillate yield which, in turn, requires the unit to
be operated at more severe conditions (which requires more hydrogen
and reduces the life of the catalyst).
[0094] Second, the side-cut VGO sent to the second stage
hydrocracker unit is cleaner and easier to hydrocrack than a
conventional second stage hydrocracker feed. Therefore, higher
quality middle distillate products can be achieved using a smaller
volume of second stage hydrocracking catalyst which, in turn,
allows for the construction of a smaller hydrocracker reactor and
consumption of less hydrogen. The second stage hydrocracking unit
configuration reduces construction cost, lowers catalyst fill cost
and operating cost.
Products
[0095] The process of this invention is especially useful in the
production of middle distillate fractions boiling in the range of
about 380-700.degree. F. (193-371.degree. C.). At least 75 vol %,
preferably at least 85 vol % of the components of the middle
distillate have a normal boiling point of greater than 380.degree.
F. (193.degree. C.). At least about 75 vol %, preferably 85 vol %
of the components of the middle distillate have a normal boiling
point of less than 700.degree. F. (371.degree. C.).
[0096] Gasoline or naphtha may also be produced in the process of
this invention. Gasoline or naphtha normally boils in the range
below 380.degree. F. (193.degree. C.) but boiling above the boiling
point of C.sub.5 hydrocarbons, and sometimes referred to as a
C.sub.5 to 400.degree. F. (204.degree. C.) boiling range. Boiling
ranges of various product fractions recovered in any particular
refinery will vary with such factors as the characteristics of the
crude oil source, local refinery markets and product prices.
[0097] The following examples will serve to illustrate, but not
limit this invention.
Example 1
Preparation of Catalysts A1 and A2 (6% USY)
[0098] Preparation of conventional Catalyst A1 containing
USY/ASA/alumina was prepared per following procedure. 9 wt-% USY
(Zeolyst), 75 wt-% ASA powder (Siral-40 from Sasol), and 16 wt-%
pseudo-boehmite alumina (CATAPAL B from Sasol) powder were mixed
well. To this mix, a diluted HNO.sub.3 acid aqueous solution (1 wt.
%) was added to form an extrudable paste. The paste was extruded in
1/16'' cylinder shape, and dried at 266.degree. F. (130.degree. C.)
overnight. The dried base extrudates were calcined at 1184.degree.
F. (640.degree. C.) for 1 hour with purging excess dry air, and
cooled down to room temperature.
[0099] Impregnation of Ni and W was performed using a solution
containing ammonium metatungstate and nickel nitrate in
concentrations equal to the target metal loadings of 3.8 wt. % NiO
and 25.3 wt. % WO.sub.3 based on the bulk dry weight of the
finished catalyst. Then the extrudates were dried at 250.degree. F.
(121.degree. C.) for 1 hour and 350.degree. F. (177.degree. C.) for
1 hour. The dried extrudates were then calcined at 950.degree. F.
(510.degree. C.) for 1 hour with purging excess dry air, and cooled
down to room temperature.
[0100] Catalyst A2 of the present invention was prepared by
following the same procedure as that used for Catalyst A1, except
that 75 wt-% HNPV ASA powder, 16 wt-% of HNPV support material and
9 wt-% USY (Zeolyst) were used to make the base extrudate, Ni and W
loading was adjusted to 4.8 wt. % NiO and 29.6 wt. % WO.sub.3.
Preparation of Catalysts B1 and B2 (4% USY)
[0101] Conventional Catalyst B1 was prepared by following the same
procedure as that used for Catalyst A1, except that the mixture was
prepared by using 5.7 wt. % USY, 71.3 wt. % silica-alumina (Siral
40 from Sasol) and 23 wt. % pseudo-boehmite alumina powder (CATAPAL
B from Sasol). The base extrudate was dried at 120.degree. C.
(248.degree. C.) for 1 hour and calcined at 1100.degree. F.
(593.degree. C.) for 1 hour. Impregnation of Ni and W was performed
using a solution containing ammonium metatungstate and nickel
nitrate in concentrations equal to the target metal loadings of 3.8
wt. % NiO and 25.3 wt. % WO.sub.3 based on the bulk dry weight of
the finished catalyst. After impregnation, the catalyst was dried
at 270.degree. F. (132.degree. C.) for 1/2 hour and calcined at
950.degree. F. (510.degree. C.) for 1 hour.
[0102] Catalyst B2 of the present invention was prepared by
following the same procedure as that used for Catalyst 2A, except
that 72.7 wt-% HNPV ASA powder, 21.5 wt-% of HNPV support material
and 5.8 wt-% USY (Zeolyst) were used to make the base extrudate, Ni
and W loading was adjusted to 4.8 wt. % NiO and 29.6 wt. %
WO.sub.3.
[0103] Table 7 below is a summary of the composition of A1 through
B2. Tables 8 and 9 below are a summary of the pore size
distributions and nanopore volumes for the base extrudates, and
Table 10 is a summary of the physical properties for the ASA and
binder materials used in each catalyst.
TABLE-US-00009 TABLE 7 Particle ASA Support USY Ni W Density
Catalyst (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (g/cc) A1 53.2
11.3 6.3 3.8 25.3 1.35 (conventional) A2 49.2 10.5 5.9 4.8 29.6
1.34 (HNPV) B1 50.6 16.3 4.0 5.1 25.3 1.41 (conventional) B2 47.7
14.1 3.8 4.8 29.6 1.31 (HNPV)
TABLE-US-00010 TABLE 8 Base Extrudate A1 A2 (conventional) (HNPV)
d10 (nm) 41 46 d50 (nm) 74 74 d90 (nm) 135 102 Peak Pore Diameter
(.ANG.) 69 75 NPV - 6 nm-11 nm (cc/g) 0.35 0.6 NPV - 11 nm-20 nm
(cc/g) 0.08 0.05 NPV - 20 nm-50 nm (cc/g) 0.03 0.01 Total NPV (2-50
nm) (cc/g) 0.67 0.88 BET surface area (m.sup.2/g) 379 434 WPV,
(g/cc) 0.81 0.87 particle density (g/cc) 0.93 0.87
TABLE-US-00011 TABLE 9 Base Extrudate B1 B2 (conventional) (HNPV)
d10 (nm) 37 46 d50 (nm) 68 75 d90 (nm) 121 107 Peak Pore Diameter
(.ANG.) 69 75 NPV - 6 nm-11 nm (cc/g) 0.33 0.6 NPV - 11 nm-20 nm
(cc/g) 0.07 0.07 NPV - 20 nm-50 nm (cc/g) 0.02 0.01 Total NPV (2-50
nm) (cc/g) 0.67 0.9 BET surface area (m.sup.2/g) 377 429 WPV,
(g/cc) 0.84 0.93 particle density (g/cc) 1.01 0.85
TABLE-US-00012 TABLE 10 HNPV CONV. HNPV CONV. ASA ASA alumina
Alumina d10 (nm) 60 35 69 34 d50 (nm) 109 73 147 51 d90 (nm) 286
161 201 72 Peak Pore Diameter (.ANG.) 89 57 167 51 NPV - 6 nm-11 nm
(cc/g) 0.7 0.41 0.18 0.012 NPV - 11 nm-20 nm (cc/g) 0.5 0.16 0.54
0.01 NPV - 20 nm-50 nm (cc/g) 0.34 0.06 0.09 0 Total NPV (2-50 nm)
(cc/g) 1.71 0.98 0.87 0.5 loose bulk density (g/mL) 0.2 0.25-0.35
0.4-0.6 0.6-0.8 BET surface area (m.sup.2/g) 528 540 226 297
Example 2
Hydrocracking Performance
[0104] Catalysts A1 through B2 were used to process a typical
Middle Eastern VGO. The feed properties are listed in Table 11. The
run was operated in pilot plant unit under 2300 psig total pressure
and 1.0-2.2 LHSV. The feed was passed a catalyst bed filled with
hydrotreating catalyst before flowing into the hydrocracking zone.
Prior to introduction of feed, the catalysts were activated either
with DMDS (gas phase sulphiding) or with a diesel feed spiked with
DMDS (liquid phase sulphiding).
[0105] The results of the tests are noted below in Tables 12 and
13. As Tables 12 and 13 indicate, Catalysts A2 and B2 achieved a
60% conversion at lower reaction temperatures (CAT) relative to
conventional catalysts A1 and B1. In other words, Catalysts A2 and
B2 were more catalytically active than their conventional
counterparts, Catalysts A1 and B1, respectively.
[0106] Further, Catalysts A2 and B2 produced less undesirable gas
and light ends (C.sub.4- and C.sub.5-180.degree. F.) compared to
conventional catalysts A1 and B1. Further, the desirable middle
distillate (380-700.degree. F.) yields for Catalysts A2 and B2 were
higher than conventional catalysts A1 and B1.
[0107] The unconverted oil (UCO) (700.degree. F.+) product for
Catalysts A2 and B2, which is used in refineries as a base oil
feedstock, exhibited higher waxy Viscosity Indexes (VI) and lower
viscosities as compared to the UCO products for conventional
catalysts A1 and B1.
TABLE-US-00013 TABLE 11 Feedstock Properties Gravity, .degree.API
21 N, ppm 1140 S, wt % 2.3 Polycyclic index (PCI) 2333 Distillation
Temperature (wt %), .degree. F. (.degree. C.) 5 708 (376) 10 742
(394) 30 810 (432) 50 861 (461) 70 913 (489) 90 981 (527) 95 1008
(542) Entire product 1069 (576)
TABLE-US-00014 TABLE 12 A1 CATALYST (conventional) A2 CAT, .degree.
F. (60% conv.) base -5 Yields - by cut point C.sub.4-, wt % 2.6 2.1
C.sub.5-180.degree. F., lv % 5.1 4.1 180-380.degree. F., lv % 23.6
24.2 380-530.degree. F., lv % 20.3 21.4 530-700.degree. F., lv %
20.5 21.1 middle distillates (380-700.degree. F.), lv % 40.7 42.5 %
yield increase base +1.8 UCO Properties (700.degree. F.+) UCO Waxy
VI 144 146 UCO viscosity at 100.degree. C. (cSt) 5.564 5.070
TABLE-US-00015 TABLE 13 B1 CATALYST (conventional) B2 CAT, .degree.
F. (60% conv.) base -10 yields - by cut point C.sub.4-, wt % 2.3
2.0 C.sub.5-180.degree. F., lv % 4.9 5.1 180-380.degree. F., lv %
25.9 25.3 380-530.degree. F., lv % 19.4 20.7 530-700.degree. F., lv
% 19.9 20.0 middle distillates (380-700.degree. F.), lv % 39.3 40.7
% yield increase base 1.4 UCO Properties (700.degree. F.+) UCO Waxy
VI 139 145 UCO viscosity at 100.degree. C. (cSt) 5.565 5.281
[0108] While the invention has been described in detail and with
reference to specific embodiments thereof, it will be apparent to
one skilled in the art that various changes and modifications can
be made without departing from the spirit and scope of the
invention.
* * * * *