Process to produce sorbents

A process to produce a sorbent is provided. This process comprises: mixing a composition that comprises silica, a composition that comprises metal oxide, and a composition that comprises zinc oxide, to form a first mixture; and sphering said first mixture to form particles having a diameter from about 10 micrometers to about 1000 micrometers.

This invention relates to the field of processes that produce sorbents. In 
particular, this invention relates to an improved process for producing a 
sorbent, which can be used in a fluidized bed, and which can be used to 
remove sulfur from a fluid stream. 
The removal of sulfur from a fluid stream is desirable for a variety of 
reasons. If the fluid stream is to be released as a waste stream, removal 
of sulfur from the fluid stream can be necessary to meet the sulfur 
emission requirements. If the fluid stream is to be burned as a fuel, 
removal of sulfur from the fluid stream can be necessary to prevent 
environmental pollution. If the fluid stream is to be processed, removal 
of the sulfur is often necessary to prevent the poisoning of 
sulfur-sensitive catalysts. 
Various sorbents have been used to remove sulfur from a fluid stream when 
the sulfur is present as hydrogen sulfide. These sorbents can be 
manufactured by a variety of methods, such as, extrusion. A problem that 
is often encountered in the production of these sorbents is equipment wear 
caused by the abrasive nature of the sorbents being manufactured. In 
certain attempts to produce commercial quantities of sorbents, excessive 
equipment wear and downtime, which is caused by the abrasive 
characteristics of the sorbent components, have rendered the production 
commercially of such sorbents less viable. 
The use of fluidized beds have both advantages and disadvantages. Some 
advantages of fluidized beds are: continuous controlled operations; ease 
of handling; simple control; reliable operations; excellent heat transfer 
rates; and excellent mass transfer rates. Some disadvantages of fluidized 
beds are inefficient contacting of components and nonuniform residence 
times for components. However, despite these and other drawbacks, the 
economic advantages are compelling. 
In order to use a sorbent in a fluidized bed, the sorbent needs to be 
highly resistant to attrition. That is, the sorbent needs to be resistant 
to degradation of its physical size and properties. Additionally, such 
sorbents need to be made in a relatively simple and economical process, so 
that its use is more viable. 
Solutions to these problems are greatly needed. In particular, a simple, 
relativity inexpensive process, for the production of sorbents is greatly 
needed, so that commercial operations with such sorbents becomes more 
viable. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide a process to produce a 
sorbent. 
It is also another object of this invention to provide a process to produce 
a sorbent that can be used in a fluidized bed. 
In accordance with this invention a process to produce a sorbent is 
provided. This process comprises (or optionally: consists essentially of, 
or consists of): mixing a composition that comprises silica, a composition 
that comprises metal oxide, and a composition that comprises zinc oxide, 
to form a first mixture; and sphering said first mixture to form particles 
having a diameter from about 10 micrometers to about 1000 micrometers. 
These and other objects of this invention will be apparent to those skilled 
in the art from the following detailed description of the invention and 
claims. 
DETAILED DESCRIPTION OF THE INVENTION 
The sorbent produced by this invention can be used to remove hydrogen 
sulfide from a fluid stream. The hydrogen sulfide can be produced by the 
hydrodesulfurization of organic sulfur compounds, or it can be originally 
present in the fluid stream as hydrogen sulfide. Examples of such fluid 
streams include: light hydrocarbons such as methane, ethane and natural 
gas; gases derived from petroleum products and products from extraction, 
gasification, and/or liquefaction of coal and lignite; gases derived from 
tar sands and shale oil; coal-derived synthesis gas; gases such as 
hydrogen and nitrogen; gaseous oxides of carbon; steam and the inert gases 
such as helium and argon. Additional information concerning the types of 
processes can be found in U.S. Pat. No. 5,281,445 (the entire disclosure 
of which is hereby incorporated by reference). 
The sorbent produced by this invention comprises, in general, silica, metal 
oxide, and zinc oxide. The process to produce such sorbent comprises, in 
general, mixing silica, a metal oxide, and zinc oxide (ZnO) together to 
form a first mixture. These components (silica, metal oxide, and zinc 
oxide) can be mixed together simultaneously or sequentially. However, it 
is currently preferred to mix together the silica and the metal oxide to 
form an intermediate mixture followed by mixing this intermediate mixture 
with zinc oxide to form said first mixture. 
The first mixture is then sphered to form particles having a diameter from 
about 10 micrometers to about 1000 micrometers. The first mixture can be 
sphered without it being extruded. This saves on the wear and tear of 
extrusion equipment because none need be used on the first mixture, nor 
should any be used on the first mixture. This sphering can be accomplished 
by adding the first mixture to a cylindrical container that has a rotating 
plate at the bottom (hereafter "bottom plate"). This bottom plate can be 
either flat or grooved, however, grooved is currently preferred. The 
rotation of the bottom plate converts the first mixture into spherical 
particles. 
Equipment that can perform this sphering operation is available from 
various sources. Currently it is preferred to use a Marumerizer.TM. from 
the Luwa Corporation. Additional information concerning equipment of this 
nature can be found in U.S. Pat. Nos. 3,579,719; 4,316,822; 4,367,166; and 
5,387,740. 
After sphering the first mixture to obtain the spherical particles, these 
particles can be further processed by drying them to obtain dried 
particles. After drying, the dried particles can be further processed by 
calcining to obtain calcined particles. After calcining, the calcined 
particles can be contacted with a metal promoter to obtain promoted 
particles. After contacting, the promoted particles, can be further 
processed by drying to obtain dried, promoted particles. After drying, the 
dried, promoted particles can be further processed by calcining to obtain 
calcined, promoted particles. 
Drying is conducted at a temperature from about 75.degree. C. to about 
300.degree. C., more preferably, from 90.degree. C. to 250.degree. C., for 
a time period from about 0.5 hour to about 4 hours, more preferably, from 
1 hour to 3 hours. Calcining is conducted, in the presence of oxygen, at a 
temperature from about 375.degree. C. to about 750.degree. C., more 
preferably, from 500.degree. C. to 700.degree. C., for a time period from 
about 0.5 hour to about 4 hours, more preferably, from 1 hour to 3 hours. 
The silica used in this invention can be any suitable form of silicon 
dioxide (SiO.sub.2). Silica, for the purposes of this invention includes 
both naturally occurring silica and synthetic silica. Currently, however, 
natural silica is preferred. Suitable examples of natural silicas are 
diatomaceous earth (which is also called kieselguhr, diatomite, infusorial 
earth, or celite) and clay. Suitable examples of clay include aluminum 
silicates, magnesium silicates, and aluminum-magnesium silicates. Suitable 
examples of aluminum silicates include bentonite, halloysite, kaolinitc, 
montmorillonite, and pyrophylite. Suitable examples of magnesium silicates 
include hectorite, sepiolite, and talc. Suitable examples of 
aluminum-magnesium silicates include attapulgite and vermiculite. Suitable 
examples of synthetic silicas include zeolites, precipitated silicas, 
spray-dried silicas, and plasma-treated silicas. Mixtures of these silicas 
can also be used. Any commercially available silica can be used in this 
invention, however, diatomaceous earth is currently preferred. 
The amount of silica present in the sorbent should be from about 10 weight 
percent to about 90 weight percent. Preferably, the amount of silica 
should be in the range of about 25 weight percent to 75 weight percent, 
and most preferably, the amount should be in the range of 35 weight 
percent to 55 weight percent, where these weight percents are based on the 
total weight of the sorbent. 
Any suitable metal oxide can be used in this invention provided that it can 
be formed into colloidal-size particles and dispersed in an aqueous 
medium. This aqueous dispersion of the metal oxide can be referred to as a 
sol or a colloidal oxide solution. The colloid-size particles can range in 
size from less than one nanometer to greater than two micrometers. 
Colloid-size particles can be dispersed in an aqueous system by the 
addition of small quantities of acids such as hydrochloric acid, nitric 
acid, formic acid, or acetic acid. Typical solid concentrations of the 
colloidal oxide solutions can range from about 1 weight percent to about 
30 weight percent solids where the weight percent of solids is based on 
the total weight of the colloidal oxide solution. The solution pH can 
range from about 2 to about 11 depending upon the method of preparation of 
the colloidal oxide solution. The colloidal oxide solution should comprise 
a metal oxide selected from the group consisting of aluminum oxide, 
silicon oxide, scandium oxide, titanium oxide, vanadium oxide, chromium 
oxide, manganese oxide, iron oxide, cobalt oxide, nickel oxide, copper 
oxide, gallium oxide, germanium oxide, yttrium oxide, zirconium oxide, 
niobium oxide, molybdenum oxide, technetium oxide, ruthenium oxide, 
rhodium oxide, palladium oxide, silver oxide, cadmium oxide, indium oxide, 
tin oxide, antimony oxide, lanthanum oxide, hafnium oxide, tantalum oxide, 
tungsten oxide, rhenium oxide, osmium oxide, iridium oxide, platinum 
oxide, gold oxide, mercury oxide, thallium oxide, lead oxide, bismuth 
oxide, and cerium oxide. Currently, preferred are aluminum oxide, silicon 
oxide, zirconium oxide, tin oxide, antimony oxide, cerium oxide, yttrium 
oxide, copper oxide, iron oxide, manganese oxide, molybdenum oxide, 
tungsten oxide, chromium oxide and mixtures of any two or more thereof. It 
is presently even more preferred that the colloidal oxide solution be 
either a colloidal aluminum oxide solution or a colloidal silicon oxide 
solution. 
Generally, any suitable quantity of colloidal oxide solution can be mixed 
with the silica. It is preferred, however, to use an amount of colloidal 
oxide solution that will give a metal oxide concentration in the sorbent 
in the range of from about 1 weight percent to about 15 weight percent 
where the weight percents are based on the total weight of the sorbent. 
The zinc oxide used in the preparation of the sorbent can be either in the 
form of zinc oxide, or in the form of zinc compounds that are convertible 
to zinc oxide under the conditions of preparation described herein. 
Examples of such zinc compounds include zinc sulfide, zinc sulfate, zinc 
hydroxide, zinc carbonate, zinc acetate, zinc nitrate and mixtures of any 
two or more thereof. Preferably, the zinc oxide is in the form of powdered 
zinc oxide. The zinc oxide will generally be present in the sorbent in an 
amount in the range of from about 10 weight percent to about 90 weight 
percent, and will more preferably be in the range of from 20 weight 
percent to 80 weight percent, and will most preferably be in the range of 
from 40 weight percent to 70 weight percent based on the weight of the 
sorbent. 
It is preferred to mix the silica with a metal oxide prior to it being 
mixed with zinc oxide. The mixing can be performed by any suitable method 
known in the art. Suitable examples of such methods include, but are not 
limited to, standard incipient wetness impregnation, wet impregnation, 
spray drying, chemical vapor deposition, and plasma spray deposition. It 
is preferred, however, to use a spray impregnation technique whereby the 
silica material is contacted with a spray of a colloidal oxide solution, 
wherein the solution has the desired amount of colloidal oxide material 
dissolved in a sufficient volume of water to fill the total pore volume of 
the silica or, in other words, to effect an incipient wetness impregnation 
of the silica. 
Once the silica and the colloidal oxide solution are mixed to form the 
intermediate mixture, this intermediate mixture is then mixed with zinc 
oxide powder to form the first mixture. The mixing of these materials can 
be performed by any suitable method. Suitable examples of the types of 
mixing devices include, but are not limited to, tumblers, stationary 
shells, muller mixers, and impact mixers. It is currently preferred to use 
a muller mixer in the mixing of the silica, metal oxide, and zinc oxide. 
The sorbent can further comprise metal promoters selected from groups 6 
through 11 of the periodic table (see Hawley's Condensed Chemical 
Dictionary, 11th edition, inside front cover IU nomenclature). Examples 
of these metal promoters are chromium, molybdenum, tungsten, manganese, 
technetium, rhenium, iron, ruthenium, osmium, cobalt, rhodium, iridium, 
nickel, palladium, platinum, copper, silver, and gold. Currently, a 
preferred metal promoter is nickel. Mixtures of these metal promoters can 
also be used. 
The metal promoter can be added to the sorbent in the form of an elemental 
metal and/or a metal-containing compound, which is convertible to a metal 
oxide under the calcining conditions described herein. Some examples of 
such metal-containing compounds include metal acetates, metal carbonates, 
metal nitrates, metal sulfates, metal thiocyanates, and mixtures of any 
two or more thereof. 
The elemental metal and/or metal-containing compound can be contacted with 
the sorbent by any method known in the art. One such method is the 
impregnation of the sorbent with a solution, either aqueous or organic, 
that contains the elemental metal and/or metal-containing compound. After 
the elemental metal and/or metal-containing compound have been contacted 
with the sorbent, the promoted sorbent is dried and calcined, as herein 
described. 
It should be noted that the elemental metal and/or metal-containing 
compound can also be mixed with the silica, metal oxide, and zinc oxide to 
form the first mixture, thereby simplifying the production process. 
The metal promoter will generally be present in the sorbent in an amount in 
the range of from about 0.1 weight percent to about 30 weight percent, and 
will more preferably be in the range of from 2.0 weight percent to about 
15 weight percent based on the weight of the sorbent. 
The following examples are presented in further illustration of the 
invention.

COMATIVE EXAMPLES 
These comparative examples demonstrate that the compositions described in 
U.S. Pat. No. 4,367,166, col. 3, lines 49-59 will not make spherical 
particles in a Marumerizer.TM. in the absence of prior extrusion. 
Mixed in a Sigma mixer for 10 minutes were 560 grams of alumina 
(DIS.RTM. 180, average particle size of 40 micrometers (400,000 
angstroms) available from the Vista Chemical Company), 200 grams of 
magnesium oxide (MAGOX.RTM. 98 Premium calcined magnesite, available from 
Premier Services Corporation) and 7.6 grams of dextrin (available from 
Sigma Chemical Company). The mixture was then added to a Marumerizer.TM. 
using a 5 mm groove plate at 300 rpm. All material either dusted out the 
top or passed by the groove plate into the dust collector. No spheres were 
formed. The material stayed the same mesh size as originally fed to the 
Marumerizer.TM.. 
Likewise, 70 grams of alumina (Aluminum Oxide C, average primary particle 
size of 0.02 micrometers (200 angstroms) available from Degussa), 25 grams 
of magnesium oxide (MAGOX.RTM. 98 Premium calcined magnesite, available 
from Premier Services Corporation) and 0.95 gram of dextrin (available 
from Sigma Chemical Company) were mixed in a Sigma mixer for 10 minutes. 
This mixture was then added to a Marumerizer.TM. using a 5 mm groove plate 
at 300 rpm. All material either dusted out the top or passed by the groove 
plate into the dust collector. No spheres were formed. The material stayed 
the same mesh size as originally fed to the Marumerizer.TM.. 
INVENTIVE EXAMPLE 
This example demonstrates a composition that can be converted into 
spherical particles using a Marumerizer.TM. without having to first 
extrude said composition. This example further demonstrates that such 
spherical particles exhibit sufficient attrition resistance and sulfur 
removing capacity to function effectively in a fluidized bed to remove 
hydrogen sulfide from a fluid stream containing such hydrogen sulfide. 
Diatomite powder (Celite Filter Cel, available from Celite Corporation, 2.5 
micrometer median particle size) was mixed in a mixing bowl to incipient 
wetness using Nyacol Al-20 colloidal alumina solution (available from PQ 
Corporation, 500 Angstrom particle size) in an amount sufficient that the 
final formulation contained 12 weight percent alumina. This composition 
was then mixed with a calculated amount of dry zinc oxide powder to yield 
approximately 50 weight percent zinc oxide in the resulting product. The 
product was then added slowly to a Marumerizer.TM. using a 5 mm groove 
plate at 600-1200 rpm. A residence time of about one minute was required 
to form spherical particles having a particle diameter from 50 to 500 
micrometers (500,000 to 5,000,000 Angstroms). These spherical particles 
were then dried, in air, at 150.degree. C. for 3 hours, and then calcined, 
in air, at 635.degree. C. for 1 hour. Screen analysis indicated that about 
90 weight percent of the spherical particles were in the 50 to 500 
micrometer size range (about 6 percent were less than 50 micrometers and 
about 4 percent were greater than 500 micrometers). The bulk density of 
the particles was 1.19 grams per cubic centimeter. 
One hundred grams of this material was spray impregnated with a solution of 
29.71 grams of nickel(II) nitrate hexahydrate dissolved in 31.2 grams of 
deionized water. The impregnated material was dried, in air, at 
150.degree. C. for 1 hour and then calcined, in air, at 635.degree. C. for 
1 hour, ramping from ambient at 5.degree. C. per minute during the 
calcination. The resulting sorbent was tested for attrition resistance, 
for 5 hours, using the procedure disclosed in U.S. Pat. No. 4,010,116 (the 
entire disclosure of which is hereby incorporated by reference). The 
sorbent exhibited an attrition of 5.08 percent while that of the control 
(Davison GXP-5 fluidized catalytic cracking catalyst) was 4.59 percent. 
This indicates the sorbent has sufficient attrition resistance to function 
acceptably in a fluidized system. 
This sorbent was subjected to a standard sorption test in which the sorbent 
was alternately contacted with gaseous streams containing either hydrogen 
sulfide mixed with inert gases such as carbon dioxide and nitrogen, or air 
to regenerate the sulfur-laden sorbent. The reactor temperatures for the 
two steps were 426.7.degree. C. and 593.3.degree. C., respectively. The 
sulfur loading on the sorbent was determined to be complete when hydrogen 
sulfide was detected at 100 ppm in the effluent stream. At that point, the 
sulfided material was regenerated in air. A more detailed description of 
the testing procedure is disclosed in U.S. Pat. No. 5,306,685 (the 
disclosure of which is hereby incorporated by reference). The data for 
twenty cycles of testing, shown in Table 1, clearly show the sorbent, 
quite unexpectedly to be highly effective in sulfur removal. 
TABLE 1 
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SULFUR REMOVAL TEST RESULTS 
% SULFUR 
CYCLE PICKUP 
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1 14.6 
5 14.4 
10 14.3 
15 13.6 
20 13.1 
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Reasonable variations and modifications are possible within the scope of 
this disclosure without departing from the scope and spirit thereof.