U.S. patent application number 10/458432 was filed with the patent office on 2004-04-08 for conversion of sodium bromide to anhydrous hydrobromic acid and sodium bisulfate.
This patent application is currently assigned to The Procter & Gamble Company. Invention is credited to Back, Deborah Jean, Bourgeois, Daniel Martin, Kenneally, Corey James.
Application Number | 20040067192 10/458432 |
Document ID | / |
Family ID | 32095661 |
Filed Date | 2004-04-08 |
United States Patent
Application |
20040067192 |
Kind Code |
A1 |
Kenneally, Corey James ; et
al. |
April 8, 2004 |
Conversion of sodium bromide to anhydrous hydrobromic acid and
sodium bisulfate
Abstract
Process for the conversion of sodium bromide to anhydrous
hydrobromic acid and sodium bisulfate, said process with the
following sequential steps: reaction of sodium bromide and sulfuric
acid in a solution of water to produce hydrobromic acid and sodium
bisulfate wherein the conversion of sodium bromide is greater than
about 99%; adsorption of iron bromide onto a solid adsorbent;
separation of hydrobromic acid and water from the sodium bisulfate;
separation and drying of hydrobromic acid; and solidification of
the sodium bisulfate into a flaked or granular form.
Inventors: |
Kenneally, Corey James;
(Mason, OH) ; Bourgeois, Daniel Martin; (Mason,
OH) ; Back, Deborah Jean; (Cleves, OH) |
Correspondence
Address: |
THE PROCTER & GAMBLE COMPANY
INTELLECTUAL PROPERTY DIVISION
WINTON HILL TECHNICAL CENTER - BOX 161
6110 CENTER HILL AVENUE
CINCINNATI
OH
45224
US
|
Assignee: |
The Procter & Gamble
Company
|
Family ID: |
32095661 |
Appl. No.: |
10/458432 |
Filed: |
June 10, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10458432 |
Jun 10, 2003 |
|
|
|
10265812 |
Oct 7, 2002 |
|
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Current U.S.
Class: |
423/482 |
Current CPC
Class: |
C01D 5/02 20130101; C01B
7/093 20130101 |
Class at
Publication: |
423/482 |
International
Class: |
C01B 007/01 |
Claims
What is claimed is:
1. A process for the conversion of sodium bromide to anhydrous
hydrobromic acid and sodium bisulfate, said process comprising the
following sequential steps: a) reaction of sodium bromide and
sulfuric acid in a solution of water to produce hydrobromic acid
and sodium bisulfate wherein the conversion of sodium bromide is
greater than about 99%; b) separation of hydrobromic acid and water
from the sodium bisulfate; and c) separation of hydrobromic acid
from water; followed by drying of hydrobromic acid.
2. A process according to claim 1 wherein the process further
includes the step of absorption of iron bromide onto a solid
adsorbent, before the separation of hydrobromic acid and water from
the sodium bisulfate.
3. A process according to claim 2 wherein a chemical additive is
included with the reaction of sodium bromide and sulfuric acid in a
solution of water.
4. A process according to claim 1 wherein the process further
includes the step of solidifying the sodium bisulfate into a
flaked, or granular form after the drying of hydrobromic acid.
5. A process according to claim 1 wherein the reaction step (a)
uses a reactor device selected from the group consisting of tanks,
columns, pipes, and mixtures thereof.
6. A process according to claim 5 wherein the reactor device is
selected from the group consisting of columns, pipes, and mixtures
thereof, and further comprises an internal blending device selected
from the group consisting of orifice plates, segmented baffles,
static mixers, and mixtures thereof.
7. A process according to claim 1 wherein the reactor device is a
pipe and wherein the blending is provided solely by a pump which
operates in a turbulent flow regime.
8. A process according to claim 4 wherein the temperature used for
solidification is from about 180.degree. C. to about 220.degree.
C.
9. A process according to claim 5 wherein the molar ratio of
sulfuric acid to sodium bromide is from about 0.95 to about 1.05
and the ratio of sodium bromide to water is less than about 0.9
parts by weight sodium bromide to 1 part water.
10. A process according to claim 9 wherein the sulfuric acid is
added slowly to the sodium bromide solution.
11. A process according to claim 9 wherein the temperature for the
reaction is from about 20.degree. C. to about 180.degree. C. at one
atmosphere pressure.
12. A process according to claim 5 wherein the separation of
hydrobromic acid and water from the sodium bisulfate step (b) uses
a separation device selected from the group consisting of
evaporators, dryers, crystallizers, centrifuges, filters, and
mixtures thereof.
13. A process according to claim 12 wherein the separation device
is selected from the group consisting of evaporators, dryers, and
mixtures thereof, wherein the evaporators are selected from the
group consisting of forced circulation, vertical and horizontal
tube, jacketed kettles, agitated thin film devices, and mixtures
thereof and wherein the dryers are selected from the group
consisting of pan dryers, indirect rotary dryers, fluidized beds,
spray dryers, drum dryers, and mixtures thereof.
14. A process according to claim 13 wherein the separation device
is a forced circulation evaporator.
15. A process according to claim 12 wherein the exposure time to
temperatures above 200.degree. C. during the separation step (b) is
less than 10 minutes.
16. A process according to claim 13 wherein the separation device
is an evaporator and the sodium bisulfate is in a molten state.
17. A process according to claim 1 wherein the separation of
hydrobromic acid from water step (c) uses an approach selected from
the group consisting of multi-stage distillation, liquid
extraction, membrane separation, and mixtures thereof.
18. A process according to claim 17 wherein the step (c) approach
is azeotropic distillation.
19. A process according to claim 18 wherein the step (c) approach
is pressure swing azeotropic distillation.
20. A process according to claim 1 wherein the drying of
hydrobromic acid step (d) results in a hydrobromic acid product
having a moisture content of less than about 0.4%.
21. A process according to claim 20 wherein the drying of
hydrobromic acid step (d) uses a drying approach selected from the
group consisting of distillation, stripping, solids adsorption, gas
separation membranes, gas absorption, or mixtures thereof.
22. A process according to claim 21 wherein the drying step (d)
uses distillation.
23. A process for the conversion of sodium bromide to anhydrous
hydrobromic acid and a sodium bisulfate coproduct, said process
comprising the following sequential steps: a) reaction of sodium
bromide and sulfuric acid in a solution of water to produce
hydrobromic acid and sodium bisulfate wherein the conversion of
sodium bromide is greater than about 99% by means of an adiabatic
loop reactor and wherein the molar ratio of sulfuric acid to sodium
bromide is from about 0.95 to about 1.05 and the ratio of sodium
bromide to water is less than about 0.9 parts by weight sodium
bromide to 1 part water; b) separation of hydrobromic acid and
water from the sodium bisulfate by means of a forced circulation
evaporator; c) separation of hydrobromic acid from water by means
of azeotropic distillation; and d) drying of hydrobromic acid.
22. An anhydrous hydrobromic acid product made according to the
process of claim 1
23. A sodium bisulfate product made according to the process of
claim 1.
24. An anhydrous hydrobromic acid product made according to the
process of claim 21.
25. A sodium bisulfate product made according to the process of
claim 21.
26. A process for the conversion of sodium bromide to anhydrous
hydrobromic acid and a sodium bisulfate coproduct, said process
comprising the following sequential steps: a) reaction of sodium
bromide and sulfuric acid in a solution of water to produce
hydrobromic acid and sodium bisulfate wherein a chemical additive
is included with the reaction of sodium bromide and sulfuric acid
in the solution of water; wherein the conversion of sodium bromide
is greater than about 99%, by means of an adiabatic loop reactor
and wherein the molar ratio of sulfuric acid to sodium bromide is
from about 0.95 to about 1.05 and the ratio of sodium bromide to
water is less than about 0.9 parts by weight sodium bromide to 1
part water; b) absorption of iron bromide onto a solid adsorbent;
c) separation of hydrobromic acid and water from the sodium
bisulfate by means of a forced circulation evaporator; d)
separation of hydrobromic acid from water by means of azeotropic
distillation; e) drying of hydrobromic acid; and f) solidifying the
sodium bisulfate into a form selected from the group consisting of
flaked, granular, and mixtures thereof.
Description
CROSS-REFERENCE
[0001] This application is a continuation-in-part of prior
application Ser. No. 10/265,812, filed Oct. 7, 2002.
FIELD OF INVENTION
[0002] The present invention relates to the conversion of sodium
bromide to hydrobromic acid and sodium bisulfate with improved
product quality and improved process economics.
BACKGROUND OF THE INVENTION
[0003] Hydrobromic acid is widely used as an intermediate in the
chemical industry. It is utilized in the production of inorganic
bromides by reaction with metal hydroxides, oxides, or carbonates;
in the production of organic bromides by reaction with alkyl
alcohols or alkenes; and as a catalyst for oxidations, alkylations,
and condensations in organic chemistry.
[0004] Sodium bisulfate is an industrial and household acidulant
with many different uses, including toilet bowl cleaners, cleaning
compounds, swimming pool pH adjustment, pulp and paper processing,
metal finishing, and food and beverage additives.
[0005] In the past, halogenated acids such as hydrobromic acid have
been prepared in gaseous form by several laboratory methods such as
direct combination of hydrogen and bromide, using platinized silica
gel as a catalyst; bromination of organic compounds such as
benzene, naphthalene, or tetrahydro-napthalene; and reacting
bromine with red phosphorus and water. None of these processes are
practical for the industrial production of hydrobromic acid. The
first process is generally expensive and presents a considerable
explosion hazard. The second process is inefficient and costly in
that it typically utilizes only about half of the expensive bromine
employed. The last is apt to be violent, difficult to control, and
may present a serious explosion hazard.
[0006] Currently, there are two main approaches for the industrial
production of hydrobromic acid. The first approach is a two
conversion process whereby low purity, natural deposits of sodium
bromide are converted first into elemental bromine and second into
hydrobromic acid. The first conversion is done by oxidation with
chlorine, where the sodium bromide is converted into sodium
chloride and bromine by the reaction:
2NaBr+Cl.sub.2.fwdarw.2NaCl+Br.sub.2
[0007] According to Stanford Research Institute's Chemical
Economics Handbook, commercial bromine suppliers such as Great
Lakes Chemicals (located in El Dorado and Marysville, Ak.),
Albemarle (located in Magnolia, Ak.), and Dead Sea Bromine Co.
(located in Sdom, Israel), currently practice this step. A second
conversion involves either (a) burning bromine and hydrogen to form
hydrobromic acid, such as discussed in Ullman's Encyclopedia of
Industrial Chemistry, 5.sup.th edition, 1985, Volume A4, pg. 396,
according to the reaction:
Br.sub.2+H.sub.2.fwdarw.2HBr
[0008] or (b) by an electrolytic process whereby a solution of
bromine is converted into hydrobromic acid and oxygen (as disclosed
in U.S. Pat. No. 4,069,120 to United Technologies Corporation,
issued Jan. 17, 1978 and U.S. Pat. No. 4,203,813 to United
Technologies Corporation, issued May 20, 1980), according to the
reaction:
2Br.sub.2+2H.sub.2O.fwdarw.4HBr+O.sub.2
[0009] This two conversion process to produce hydrobromic acid has
a number of drawbacks. First, operating and capital costs are high
since a separate manufacturing plant is employed for each
conversion. In addition, if bromine burning is implemented, free
bromine is often present in the hydrobromic acid product, resulting
in a product with the characteristic yellow and/or orange color
associated with free bromine. This is generally unacceptable for
applications requiring a colorless hydrobromic acid product.
[0010] The second approach for chemical manufacture of hydrobromic
acid is a one conversion process whereby high purity sodium bromide
is reacted with sulfuric acid (U.S. Pat. No. 1,379,731 to
Lowenstein Radio Corporation, issued May 31, 1921 and U.S. Pat. No.
2,705,670 to American Cyanamid, issued Apr. 5, 1955) according to
the reaction:
NaBr+H.sub.2SO.sub.4.fwdarw.HBr+NaHSO.sub.4
[0011] This approach is well suited for industrial companies which
wish to convert high purity sodium bromide to hydrobromic acid and
sodium bisulfate products. However, this approach has a number of
drawbacks as well. First, if the hydrobromic acid is of low purity,
then product applications are limited and/or capital and operating
costs are high to purify the material. This can occur if (a)
significant levels of bromine are generated from hydrobromic acid
via the following reaction,
2HBr+H.sub.2SO.sub.4.fwdarw.Br.sub.2+SO.sub.2+2H.sub.2O
[0012] or, (b) the hydrobromic acid is not sufficiently free of
water. Second, if the sodium bisulfate salt is of low purity, then
product applications are limited and/or capital and operating costs
are high to purify this material as well. This can occur if (a)
iron bromide is present in the sodium bisulfate at levels
sufficient to impart an orange color to the product, (b)
significant quantities of sodium bromide or hydrogen bromide are
left in the sodium bisulfate, (c) a significant portion of sodium
bisulfate reacts with sodium bromide to produce sodium sulfate,
according to the reaction:
NaHSO.sub.4+NaBr.fwdarw.HBr+Na.sub.2SO.sub.4
[0013] or, (d) the sodium bisulfate undergoes decomposition to
sodium pyrosulfate via the following reaction,
2NaHSO.sub.4.fwdarw.Na.sub.2S.sub.2O.sub.7+H.sub.2O
[0014] Therefore, there is a continuing need for an improved
process approach for making anhydrous hydrobromic acid and sodium
bisulfate. Specific areas for improvement vs. current commercial
processes include improving product purity, reducing operating
cost, and reducing capital cost.
SUMMARY OF THE INVENTION
[0015] It has now surprisingly been discovered that sodium bromide
can be converted into anhydrous hydrobromic acid (also referred to
as hydrogen bromide) and sodium bisulfate with minimal levels of
by-products such as bromine, bromides, sulfuric acid, or sodium
pyrosulfate by using a one conversion process consisting of a
simple reactor and three simple separation processes.
[0016] The present invention therefore relates to a process for the
conversion of sodium bromide to hydrobromic acid and sodium
bisulfate with the following steps:
[0017] 1) Reaction of sodium bromide and sulfuric acid in a
solution of water to produce hydrobromic acid and sodium
bisulfate
[0018] 2) Optional adsorption of iron bromide onto a solid
adsorbent
[0019] 3) Separation of hydrobromic acid and water from the sodium
bisulfate
[0020] 4) Separation of hydrobromic acid from water; followed by
drying of the hydrobromic acid
[0021] 5) Optional solidification of the sodium bisulfate into a
flaked or granulated form
[0022] These and other features, aspects, and advantages of the
present invention will become evident to those skilled in the art
from a reading of the present disclosure.
[0023] All documents cited are, in relevant part, incorporated
herein by reference; the citation of any document is not to be
construed as an admission that it is prior art with respect to the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0024] While the specification concludes with the claims
particularly pointing and distinctly claiming the invention, it is
believed that the present invention will be better understood from
the following description.
[0025] All percentages and ratios used herein are by weight of the
total composition and all measurements made are at 25.degree. C.,
unless otherwise designated.
[0026] Without being limited by theory, it is believed that
economical, commercial production of anhydrous hydrobromic acid
from concentrated sodium bromide is best accomplished by: a one
conversion process (which avoids elemental bromine as an
intermediate) that (a) maximizes the yield and purity of both
hydrobromic acid and sodium bisulfate, and (b) minimizes the number
of unit operations in the overall process.
[0027] These objectives are accomplished by: (a) high conversion of
sodium bromide using a single, simple reactor, whereby the
conversion is greater than about 99%, preferably greater than about
99.9%, (b) selective production of hydrobromic acid with less than
about 200 ppm bromine and 100 ppm water and greater than about 99%
theoretical yield of hydrobromic acid, preferably with no
detectible level of bromine, 50 ppm or less water, and greater than
about 99.9% theoretical yield, (c) removal of iron bromide to a
level of less than 1 ppm in sodium bisulfate, which corresponds to
a pure white or cream color, (d) selective production and
separation of sodium bisulfate with purity between 91.5% and 95.5%,
the balance being primarily sodium sulfate with less than 0.5%
water, and (e) accomplishing all of the separations using
commercially available separation devices, preferably three or
fewer devices, more preferably all conducted in a liquid product
state.
[0028] The present invention has several advantages over the
current practice. High conversion of sodium bromide in a single,
simple reactor is advantageous over the two conversion process and
also the existing one conversion process for the case of
substantially lower sodium bromide conversion which requires
separation and recycle steps for the unreacted sodium bromide and
sulfuric acid. The selective production of hydrobromic acid with
minimal levels of bromine and water is advantageous over current
practice where higher levels of bromine and water are present from
both a process materials standpoint (bromine is more corrosive) and
from a product quality standpoint. The selective production of
sodium bisulfate with minimal bromide, sulfuric acid, or sodium
pyrosulfate contaminants is advantageous to maximize the value of
the salt for use in the broadest variety of applications, including
food and beverages. Finally, the use of preferably three or fewer
separation devices, more preferably in the liquid state, is
advantageous over the current practice of using one or more
liquid/solid separation devices, which are generally more expensive
and of lower reliability than the liquid separation devices.
[0029] The processes and methods herein may also include a wide
variety of other variations. The processes and methods of the
present invention, are described in detail hereinafter.
[0030] The present invention relates to a process for the
converting sodium bromide and sulfuric acid in a solution of water,
under specified conditions, in order to produce hydrobromic acid
and sodium bisulfate. The steps of such process are as follows:
[0031] I. Reaction of Sodium Bromide and Sulfuric Acid in a
Solution of Water to Produce Hydrobromic Acid and Sodium
Bisulfate.
[0032] All reactants and products according to the conversion of
sodium bromide and sulfuric acid to produce hydrobromic acid and
sodium bisulfate process outlined herein are soluble in water up to
about 0.9 parts by weight NaBr/1 part H2O, and about 1.0 parts by
weight sodium bisulfate/1 part H2O.
[0033] The reaction process consists of the blending of water,
sodium bromide, sulfuric acid, and optionally a chemical additive
to suppress formation of free bromine in a single miscible phase,
resulting in complete conversion of reactants to their respective
products.
[0034] Suitable chemical additives for suppression of free bromine
include additional water, sulfur dioxide (SO.sub.2), and various
derivatives of SO.sub.2 including sodium sulfite and sodium
bisulfite. The chemistry for free bromine suppression is as
follows:
Br.sub.2+SO.sub.2+2H.sub.2O.fwdarw.2HBr+H.sub.2SO.sub.4
[0035] Preferred chemical additives include sodium sulfite and
sodium bisulfite since they are typically non-hazardous, easy to
handle, low cost, and soluble in water. The use of additional water
to inhibit bromine is less preferred because it dilutes the
products of the reaction, resulting in higher capital cost to
remove the water in downstream separation steps. Suitable grades of
sulfuric acid include technical grade and reagent grade, with
technical grade preferred due to the typically lower cost. Suitable
specifications for the technical grade material are color less than
100 APHA; less than 10 ppm lead, less than 30 ppm heavy metals as
lead; and less than 40 ppm iron. Sulfuric acid may be of high
concentration (about 97%) or it may be of lower concentration. The
sulfuric acid may be added all at once to the sodium bromide
solution, or it may be added slowly over time. Preferably, the
sulfuric acid is added slowly over time (in a batch process) or
diluted in the product stream (in a continuous process) in order to
minimize the likelihood of degrading hydrobromic acid in the
presence of concentrated sulfuric acid to free bromine and sulfur
dioxide. Suitable grades of sodium bromide include industrial grade
and reagent grade, with industrial grade preferred due to the low
cost. Suitable specifications for the industrial grade material (on
a dry basis) are assay >90%, sodium hydroxide <5%, organic
substances <10 ppm, and no suspended solids.
[0036] Conversion of sodium bromide to its respective products is
preferably greater than about 99%, more preferably greater than
about 99.9%. In order to achieve this conversion, the molar ratio
of sulfuric acid to sodium bromide is preferably between about 0.95
and about 1.05. A ratio of about 1.0 to about 1.05 moles of
sulfuric acid per mole of sodium bromide is preferred to encourage
the complete conversion of the sodium bromide. The ratio of sodium
bromide to water is kept below the solubility limit of about 0.9
parts by weight sodium bromide/1 part H.sub.2O. Preferably, the
ratio is kept below about 0.8 parts by weight sodium bromide/1 part
H.sub.2O (or about 0.44 parts sodium bromide/1 part solution) in
order to keep the sodium bisulfate from precipitating out over a
range of reaction temperatures. Suitable levels of sodium sulfite
are 10 ppm to 1000 ppm on a total solution basis, with preferred
levels of 100-500 ppm on a total solution basis. Temperature for
the reaction is from about 20.degree. C. to about 180.degree. C.,
preferably from about 20.degree. C. to about 100.degree. C. at one
atmosphere pressure, more preferably from about 50.degree. C. to
about 90.degree. C. at one atmosphere pressure.
[0037] A variety of different reactor designs can be used,
including tanks, columns, and pipes, with a wide range of
length/diameter ratios. One example of a commercially available
device is the Buss Loop Reactor supplied by Davy Process Technology
(Switzerland) AG. Internal blending devices useful herein include
baffles, agitators and jets for tanks and columns; and orifice
plates, segmented baffles, or static mixers for columns and pipes.
Suitable agitators for tanks and columns include helical ribbons,
screws, or anchors for laminar mixing; and turbines, propellers, or
hydrofoils for turbulent mixing. Suitable static mixers for pipes
include the multi-element, helical design from Kenics. An industry
guideline is that blending of miscible solutions is generally
excellent after about 6-20 static mixer elements. Alternatively, a
pipe reactor can be used with no internals for blending but with
turbulence provided solely by high throughput velocity. The high
throughput velocity is preferably provided by a pump, such as those
commonly known in the art, including centrifugal and positive
displacement pumps.
[0038] The reactor can be backmixed or plug flow, but backmixing is
preferred, since it provides dilution of sodium bromide and
sulfuric acid, thereby minimizing the likelihood of degrading
hydrobromic acid in the presence of concentrated sulfuric acid to
produce free bromine and sulfur dioxide. Both batch and continuous
reactors can be used. The reactor can be designed for adiabatic or
isothermal operation, the latter with a jacket or heat exchanger to
remove the heat of reaction. The degree of blending required for
complete conversion is a complex function of the type of reactor
used, geometry factors, and fluid properties. For a
turbine-agitated baffled tank operating in the turbulent regime
(impeller Reynold's number >about 10.sup.4), about 30 seconds of
contact time is sufficient. By contrast if operating in the laminar
regime (impeller Reynold's number <about 10), or the transition
regime (impeller Reynold's number from about 10 to about 10.sup.4),
mixing time is generally about 2-20 times longer. Mixing guidelines
for miscible fluids using different agitators or liquid jets can be
found in the textbook, "Unit Operations of Chemical Engineering",
by McCabe and Smith, Third Edition, McGraw-Hill, 1976, pp.
248-249.
[0039] A preferred reactor is an adiabatic loop reactor, which is a
continuous, recirculating tubular reactor with backmixing. The feed
rate and outlet rate are balanced so that accumulation is kept
constant in the loop. The Reynolds number is greater than about
10.sup.3, preferably greater than about 10.sup.4, thereby providing
what is commonly referred to as a "turbulent flow regime." The
recirculation rate is about ten times the combined feed rate of the
sodium bromide, water, and sulfuric acid, preferably about twenty
times, more preferably about thirty times the combined feed rate.
The residence time in the loop is between about 0.2 and about 20
minutes, preferably between about 0.5 and about 10 minutes, most
preferably between about 1 and about 5 minutes.
[0040] II. Adsorption of Iron Bromide Onto a Solid
[0041] Iron bromide (FeBr.sub.3) forms as a by-product in the
reaction between sodium bromide and sulfuric acid. It is an orange
colored material of low volatility, which if not removed, carries
over to the products of the reaction (hydrobromic acid and sodium
bisulfate) and discolors the final product. When technical grade
sulfuric acid is used, iron is present at typically at levels of
5-50 ppm. Iron may also be introduced from the sodium bromide
material as well. When iron is present in sulfuric acid, the
reaction to produce iron bromide is as follows:
Fe.sub.2(SO.sub.4).sub.3+6HBr.fwdarw.2FeBr.sub.3+3H.sub.2SO.sub.4
[0042] There are three approaches that may optionally be used to
minimize the color impact of iron bromide in the aforementioned
products of the reaction. First, reagent grade sulfuric acid with
an iron content below 0.2 ppm can be used. This level of iron is
sufficiently low to eliminate any traces of color in the products
of the reaction. A second option is to use a chemical additive to
convert iron bromide to an alternate iron species, such as iron
sulfate or iron chloride, that imparts less color to the products
of the reaction. A third option, which is most preferred, is to
remove the iron by adsorption onto a porous solid. While not
wishing to be bound by theory, it is believed that the iron bromide
is chemisorbed onto the surface of certain porous solids.
Adsorption can be done at virtually any stage of the process for
making hydrobromic acid and sodium bisulfate but removal after the
reaction step and before the separation steps is preferred, since
the material at this stage is an aqueous acid stream with low
viscosity and moderate acid strength. Treatment of streams with
higher acid strength (i.e 97% sulfuric acid) or higher viscosity
(i.e. molten sodium bisulfate) is also optional, but less preferred
due to lower adsorption efficiencies and higher pressure drops.
[0043] Suitable adsorbents include activated carbon, silica gel,
and alumina in either a powdered or a granular form. A preferred
adsorbent is activated carbon sourced from coal, coconut, or wood
materials, washed with phosphoric acid to remove iron and ash, with
a surface area of 800-1800 m2/gr, an internal porosity of 60-80%,
an average pore diameter of 2-4 nanometers, and an iron content of
<1000 ppm. A suitable particle size is <100 mesh for slurry
operations and 12 to 40 mesh for packed beds. Mixtures of more than
one adsorbent may be used.
[0044] As used herein, a "slurry operation" generally refers to a
powdered carbon, added to a liquid stream containing hydrobromic
acid, sodium bisulfate, and iron bromide, mixed for a period of
time in a batch or a continuous flow vessel, and then filtered to
separate out the adsorbent from the purified liquid. Suitable
vessels for mixing include tanks, pipes, reactors, and the like,
with enough mixing or turbulence to keep the carbon suspended in
the slurry. Suitable temperatures include from about 20.degree. C.
to about 100.degree. C. at atmospheric pressure, preferred
temperatures include from about 50.degree. C. to about 80.degree.
C. Suitable mixing times include from about 20 minutes to about 48
hours, with from about 4 to about 8 hours preferred to achieve
equilibration between the aqueous solution and the carbon. Suitable
usage levels include from about 0.005% to about 2%, by weight,
carbon in the slurry. Preferred usage levels are from about 0.02%
to about 0.2%. Suitable equipment for filtering the carbon from the
aqueous stream is reviewed in Chapter 18 of "Perry's Chemical
Engineers Handbook", by Green (ed), McGraw-Hill, 7.sup.th edition.
These include batch cake filters such as a filter press, liquid bag
filter, or Nutsche filter, and continuous filters such as a rotary
drum or a horizontal vacuum filter. A combination of more than one
filter may be used.
[0045] As used herein, a "packed bed operation" refers to granular
carbon generally contained in a vertical column. The carbon can be
fixed in the column, or there can be continuous flow whereby spent
carbon is substantially continuously replaced with fresh carbon.
The most common operation is a fixed bed of carbon with continuous
flow of liquid, with periodic interruption for regeneration.
Suitable conditions include a column flux rate of from about 0.5 to
about 4 gpm/ft2, a liquid residence time of from about 10 minutes
to about 2 hours, and temperatures of from about 20.degree. C. to
about 100.degree. C. at atmospheric pressure, preferred
temperatures including from about 50.degree. C. to about 80.degree.
C. As used herein, "regeneration" refers to the steps of physically
removing the spent carbon from the column and replacing with fresh
carbon; or a clean-in-place system where soaking with water and
caustic streams serves to desorb the iron bromide from the bed,
after which fresh aqueous acid, rich in iron bromide, can be
adsorbed onto the solid again.
[0046] III. Separation of Hydrobromic Acid and Water from the
Sodium Bisulfate.
[0047] Coming out of the adsorption step, a miscible solution of
hydrobromic acid, sodium bisulfate, and water is present. The first
separation is conducted between sodium bisulfate and hydrobromic
acid/water. Suitable devices for the separation include evaporators
and dryers, where liquid/liquid or liquid/solid separation between
volatiles and non-volatiles is done using either single or multiple
equilibrium stages. Other liquid/solid separation devices such as
crystallizers, centrifuges, and filters may be used, but the
evaporators and dryers are preferred, as the crystallizers,
centrifuges and filters all require some removal of volatile
material before a solid precipitate can be removed.
[0048] Suitable types of evaporators are reviewed in Chapter 11 of
"Perry's Chemical Engineers Handbook", by Green (ed), McGraw-Hill,
7.sup.th edition. These include forced circulation, vertical and
horizontal tube (including rising film and falling film
evaporators), jacketed kettles, and agitated thin film devices
(i.e. wiped film evaporators from Pope Scientific and the
Rototherm.RTM. by Artisan Industries). Suitable types of dryers are
reviewed in Chapter 12 of Perry's and include pan dryers, indirect
rotary dryers, fluidized beds, spray dryers, and drum dryers. One
can select a single type of device for the separation or a
combination of two or more devices, i.e. a falling film evaporator
in combination with a spray dryer.
[0049] A preferred separation device is a forced circulation
evaporator, which is designed to handle corrosive solutions and
crystalline products. Non-circulating evaporators are better suited
for clear liquids with no crystalline product. The evaporator can
be either single effect or multiple effect, the latter having the
vapor from one effect as the heating medium for another effect in
which boiling takes place at a lower temperature and pressure.
[0050] Evaporation temperatures and pressures are dependent on the
residual moisture specification for the sodium bisulfate salt. For
monohydrate salt, temperatures and pressures are from about
20.degree. C. to about 183.degree. C. and from about 0.002 atm to
about 5 atm respectively. For anhydrous salt, temperatures and
pressures are from about 80.degree. C. to about 220.degree. C. and
from about 0.002 atm to about 5 atm respectively. Preferably, the
temperature is from about 60.degree. C. to about 120.degree. C. for
the monohydrate salt and from about 170.degree. C. to about
200.degree. C. for the anhydrous salt so that the salt is in a
generally molten form and very little or no crystallized solids are
present. Processing the salt in a molten state minimizes the
chances of fouling in a forced circulation evaporator and also
allows the opportunity to use non-circulating evaporators for the
separation. In addition, processing the salt in a molten state is
preferable for separating low levels of hydrobromic acid and water
from the salt. Residence times in the evaporator are from about 2
seconds to about 20 minutes, preferably from about 10 seconds to
about 1 minute. Residual moisture content for the anhydrous salt is
less than about 1%, preferably less than about 0.5%, more
preferably less than about 0.2%, most preferably less than
0.05%.
[0051] Care must be taken to avoid thermal decomposition of the
sodium bisulfate to form sodium pyrosulfate. According to Ullman's
Encyclopedia of Industrial Chemistry, 5.sup.th edition, 1985,
Volume A24, pg. 366, this transition takes place near the melt
point of anhydrous sodium bisulfate (about 183.degree. C.) and is
complete after heating for approximately four hours at from about
240.degree. C. to about 260.degree. C. Accordingly, exposure to
temperatures above about 200.degree. C. during the evaporation step
should be kept to less than about ten minutes, preferably less than
about five minutes, and more preferably less than about one
minute.
[0052] IV. Separation of Hydrobromic Acid from Water, Followed by
Drying of Hydrobromic Acid.
[0053] Separation of hydrobromic acid from water can be
accomplished using a number of different approaches, including
multi-stage distillation, liquid extraction, and membrane
separation. Hydrobromic acid forms an azeotrope with water at about
48% acid concentration at one atmosphere pressure. Thus for the
case of distillation, azeotropic distillation is required in order
to separate hydrobromic acid from water. Approaches for azeotropic
distillation include choosing an entraining agent to alter the
vapor liquid equilibrium (and optionally the liquid phase
miscibility) of hydrobromic acid and water to enable separation of
hydrobromic acid, exploiting changes in azeotropic composition with
total system pressure, and exploiting curvature in the vapor-liquid
equilibrium diagram. For further detail, see Chapter 13 of "Perry's
Chemical Engineers Handbook", by Green (ed), McGraw-Hill, 7.sup.th
edition. Examples of the first approach include ethanol in water
and pyridine in water (using benzene as an entrainer). Examples of
the second approach include THF in water and ethanol in water.
Examples of the third approach include hydrochloric acid in water
and nitric acid in water, with sulfuric acid as an entrainer.
[0054] Preferably, pressure swing azeotropic distillation is used
to separate hydrobromic acid from water. Liquid extraction or
membranes may also be used, but these are less preferred due to
introduction of additional chemical agents and/or due to high
capital and operating costs. Pressure swing azeotropic distillation
takes advantage of the fact that the azeotropic composition of
hydrobromic acid in water generally decreases upon an increase in
pressure. By operating two distillation columns in series at
different pressures (the second one at a higher pressure than the
first), the composition of hydrobromic acid from the first column
will generally be above the azeotropic composition for hydrobromic
acid in the second column. This allows one to obtain pure
hydrobromic acid out of the second column without running into any
barriers from the azeotrope.
[0055] Distillation operations are usually carried out in vertical,
cylindrical columns or towers in which devices such as plates or
packing elements are placed. The vapor and liquid streams normally
flow countercurrently and the devices serve to provide the
contacting and development of interfacial surface through which
mass transfer takes place. Sieve trays, bubble cap trays,
structured packing, and loose packing such as rings or saddles are
examples of column internals that may be used herein.
[0056] Preferred operating conditions for the first column are a
pressure of from about 0.01 to about 2 atmospheres and a bottoms
temperature of from about 50.degree. C. to about 140.degree. C. As
used herein, "tops" refers to the vapor or relatively more volatile
stream that is separated from the relatively less-volatile or
"bottom" stream in distillation columns. The "tops" is also
sometimes referred to as "overhead" in the art. With from about 2
to about 20, preferably from about 3 to about 10, most preferably
about 5 separation stages and a mass reflux ratio of from about 0.1
to about 10, preferably from about 0.5 to about 2, most preferably
about 1.0, the bottoms composition of hydrobromic acid in water is
increased to its azeotrope for the corresponding operating
pressure. The tops composition is nearly pure water. Preferred
operating conditions for the second column are a pressure of from
about 1 to about 20 atmospheres with a bottoms temperature
corresponding to the boiling point at a given pressure. With from
about 2 to about 20, preferably from about 3 to about 10, more
preferably about 5 separation stages and a mass reflux ratio of
from about 0.1 to about 10, preferably from about 0.5 to about 5,
more preferably about 2.5, the composition of the hydrobromic acid
in water is increased from about 48% to about 99% or greater and
taken overhead as a nearly anhydrous gas product. The bottoms from
the second column are at the azeotropic composition corresponding
to its operating pressure and are sent back to the first
distillation column as a feed stream.
[0057] After the separation of hydrobromic acid from water, there
may still be residual moisture in the hydrobromic acid product. In
order to produce an anhydrous hydrobromic acid (also referred to as
hydrogen bromide), a drying step is utilized. As referenced herein,
"anhydrous" hydrobromic acid according to the present invention has
a residual moisture content below about 0.4%, preferably below
about 0.2%, more preferably below about 0.1%. In order to produce
anhydrous hydrobromic acid, several different approaches can be
employed, including distillation, stripping, solids adsorption, gas
separation membranes, and gas absorption. Distillation can be used,
and is especially preferred if it is incorporated as part of the
design of the aforementioned distillation column used to remove the
bulk of the water from hydrobromic acid. Alternatively, stripping
with a supercritical gas at low temperatures and high pressures may
be used. Adsorption onto a solid adsorbent is another approach that
is commonly used for drying gases. Solid adsorbents, typically in
granular, bead, or pellet form, can be used in adsorbers with
either fixed inventory, intermittent solids flow, or with
continuous moving solids flow. The most common are fixed beds
operating as batch units or as beds through which the gas passes
with period intervention for regeneration. Regeneration is
accomplished using either temperature swing (higher temperature
during desorption) or pressure swing (lower pressure during
desorption). A commercial example of this approach is instrument
air dryers which use pressure swing adsorption with either
activated alumina or silica gel as the sorbent. A specific, low
cost device for adsorption (particularly for removal of VOCs) is
the adsorbent wheel. The gas to be treated flows through the wheel
parallel to the axis of rotation. Most of the wheel removes
adsorbates. The remaining part undergoes thermal regeneration,
usually countercurrent. Dehydration of air and other gases is a
rapidly growing membrane application. Gas membranes generally work
because individual gases differ in their solubility and diffusivity
through nonporous polymers. Water is extremely permeable in polymer
membranes. Finally, gas absorption, also known as scrubbing, can be
used by passing hydrobromic acid vapor through a packed bed or
tower in countercurrent flow to a liquid absorbate. As used herein,
"liquid absorbate" refers to a liquid stream which absorbs the
water vapor into the liquid phase. While a variety of non-volatile
liquid streams can be used to absorb moisture, sulfuric acid is a
preferred liquid absorbate for this application since it is already
used in the reaction process, and the liquid absorbate from the
scrubber column can then be used "as is" in the reaction step.
[0058] V. Solidification of the Sodium Bisulfate into a Flaked or
Granulated Form
[0059] Many applications of sodium bisulfate are for a powdered or
granular material which can be easily dispersed or dissolved in
water. Additional steps may be taken in order to ensure that the
finished product is in flaked and/or granulated form. As used
herein, "solidification" refers to the process whereby molten salt
from the evaporator is crystallized and shaped into a particle with
the proper shape, density, and particle size. A variety of
different processes can be used to solidify the molten material,
including flaker rolls, mechanical mills, pastillators, extruders,
and prilling towers. Other processes whereby water or steam is
added to the molten salt in order to generate evaporative cooling
during both crystallization and drying include spray dryers, spray
congealers, and fluidized bed granulators. Particle shape and
particle size will vary according to the type of process used.
Flakers will generate 1/4" to 1" diameter irregular particles with
thickness of about 0.5 to 3 mm. Mechanical mills will generate high
density, irregular shaped granules or powders, with a diameter
generally below 1 mm. Spray dryers will generate low density
powders. Pastillators will generate spheres or hemispheres with a
diameter of about 1 mm to 5 mm. Prilling towers, spray congealers,
and fluid bed granulators will generate high density, spherical
shaped particles with a diameter ranging from 300 microns to
several millimeters. For all of the solidification processes,
sieving may optionally be used to segregate the desirable from the
undesirable particle sizes if necessary. Oversize and undersize
particles can be recycled back as either molten salt or as "seed"
material for solidification processes where the particle diameter
is built up in layers, as in fluidized bed granulation.
[0060] Temperatures useful for solidification processes without
drying are from about 160.degree. C. to about 220.degree. C.
Preferably the temperature is about 200.degree. C. and the pressure
is atmospheric. For solidification processes involving drying, a
useful temperature range for the inlet air is from about 20.degree.
C. to about 225.degree. C., preferably from about 40.degree. C. to
about 90.degree. C. The air velocity required to fluidize the
particles ranges from about 1 to about 7 ft/sec, preferably about 3
ft/sec. Water or steam addition ranges from about 2% to about 50%,
by weight of the sodium bisulfate product exiting the dryer, more
preferably from about 5% to about 10%, by weight water or steam.
Operating pressure in the dryer ranges from about 0.01 atm to about
2 atm, preferably from about 0.9 atm to about 1.1 atm. Residence
time ranges from about 1 second to about 3 hours, preferably from
about 2 minutes to about 2 hours.
EXAMPLES
[0061] The following examples further describe and demonstrate
embodiments within the scope of the present invention. The examples
are given solely for the purpose of illustration and are not to be
construed as limitations of the present invention, as many
variations thereof are possible without departing from the spirit
and scope of the invention.
[0062] The following analytical methods are referenced in the
examples.
[0063] Bromine in aqueous hydrobromic acid. Weigh about 50 grams of
sample into a 250 ml. Erlenmeyer flask. Add 20 ml. of a 10%
potassium iodide solution in water and 15 ml. of glacial acetic
acid. Titrate the liberated iodine with 0.02 Normality sodium
thiosulfate until only a slight yellow color of free iodine
remains. % Bromine=(ml. of sodium
thiosulfate.times.Normality.times.79.92)/(10.times.grams
sample).
[0064] Hydrobromic acid solution: apparent yield. % yield=[(grams
hydrobromic acid solution recovered)/(gr. water added+gr. moles
sodium bromide added.times.80.9)].times.100
[0065] Sodium bisulfate: apparent purity. Weigh about 1.0 grams of
sample into a 250 ml. beaker. Add approximately 75 ml. of distilled
water and titrate to pH 7.0 with 0.1 Normality standard sodium
hydroxide solution using a pH meter. Calculation: % sodium
bisulfate=(ml. of sodium
hydroxide.times.Normality.times.120.1)/(10.times.grams sample).
[0066] Sodium bisulfate: apparent yield. % yield=(grams solid
residue recovered)/(gr. moles sodium bromide
added.times.120.1).times.(100-sodium bisulfate moisture)
[0067] Sodium bisulfate moisture. Weigh out 1-2 grams of finely
ground sample on a small pan. Place in an oven at 210.degree. C.
and atmospheric pressure for 30 minutes. Cool and weigh the sample
again. Record the difference in weight as a percentage of
total.
Example 1
[0068] This example is a batch reaction between sodium bromide and
sulfuric acid under conditions where the quality and yield of the
hydrobromic acid and sodium bisulfate are maximized. 63.5 grams
(0.62 gram moles) of sodium bromide from EM Science was dissolved
in 175 grams (9.72 gram moles) water in a 500 ml round bottom flask
with a heating mantle, agitator, overhead condenser, receiver
flask, and dry ice trap. The mixture was heated to 80.degree. C.
with agitation and then 62.1 grams (0.62 gram moles) of 97%
sulfuric acid (reagent grade) was added dropwise over a period of
20 minutes to the reaction flask. The product in the reactor was
colorless through the duration of sulfuric acid addition. After all
sulfuric acid was added, the mixture was heated to evaporate
hydrobromic acid and water. A steady stream of vapor was condensed
from the reactor over a temperature range of 115.degree. C. to
130.degree. C. (The hydrobromic acid/water azeotrope boils at
125.degree. C. at one atmosphere pressure.) The sodium bisulfate
salt was further dehydrated in the reactor over a temperature range
of 130.degree. C. to 175.degree. C. The melt point of the nearly
anhydrous salt was observed to be about 150.degree. C. The apparent
yield of the hydrobromic acid solution was 101% and the apparent
yield of the sodium bisulfate salt was 98%. The hydrobromic
acid/water azeotrope was not purified in the lab. However, an ASPEN
computer simulation indicated that hydrobromic acid can be
separated from water (up to 99.5% purity) using the following
design specs.
1 Column 1 Column 2 Bottoms pressure, atm 0.15 8.0 Bottoms
temperature, .degree. C. 79 188 Theoretical stages 5 5 Mass reflux
ratio 1.1 2.5 % HBr - tops 0.5 99.5 % HBr - bottoms 49.3 37.2
[0069] Product Analysis
[0070] The hydrobromic acid/water solution was titrated with 0.1 N
caustic and a strong acid content of 22.3% was measured (vs. a
theoretical concentration of 22.2%). Bromine levels were non
detectible. Elemental analysis by ICP indicated that the residual
sodium and sulfur levels were 10 ppm and 44 ppm, respectively. The
sodium bisulfate product was also subjected to elemental analysis
using ICP. The sodium and sulfur levels were 19.1% and 26.5% by
weight respectively. The apparent purity of the sodium bisulfate
was 95%.
Example 2
[0071] This example is similar to Example 1 except more
concentrated solutions of sodium bromide in water are used in the
reaction. As in Example 1, a reaction stoichiometry of 1 mole
sulfuric acid to 1 mole sodium bromide was used. Sulfuric acid was
added to the sodium bromide solution over a period of 20-40
minutes. Hydrobromic acid solution was evaporated from the sodium
bisulfate and the sodium bisulfate was dried to a moisture content
of 2% or less. Bromine content and apparent yield of the
hydrobromic acid solution was measured, along with apparent purity
and apparent yield of the sodium bisulfate.
2 Hydrobromic Acid Solution Sodium Bisulfate NaBr:H2O mass ratio
Br2 conc. % Yield % Purity % Yield 0.64:1.0 0 ppm 100 97.5 102
0.7:1.0 92 ppm 99 89.5 103 0.89:1.0 105 ppm 99 92.5 102 1.03:1.0
143 ppm 98 92.4 98 1.17:1.0 234 ppm 93 98.5 98
[0072] The results show that as the concentration of sodium bromide
is increased, the concentration of bromine in the hydrobromic
acid/water solution is increased proportionally. Also, the yield of
hydrobromic acid solution and sodium bisulfate is decreased.
Example 3
[0073] This example is similar to the first data point in Example 2
(0.64:1.0 mass ratio of sodium bromide:water) except that the
sulfuric acid is added all at once instead of slowly over a period
of 20-40 minutes. 27.6 grams (0.27 gram moles) of sodium bromide
was dissolved in 42.9 grams (2.38 gram moles) of water and then
26.3 grams (0.27 gram moles) of 97% sulfuric acid was immediately
added to the sodium bromide solution. The free bromine
concentration in the hydrobromic acid solution was 81 ppm. This
result indicates the rate of addition of sulfuric acid is an
important variable to control in the batch process in order to
ensure no detectible levels of free bromine.
Example 4
[0074] This example is similar to example 1 except that the
reaction and the evaporation steps are done in continuous flow
rather than in a batch process. 65.8 grams/min (0.64 gram
moles/min) of dry sodium bromide and 187.2 grams/min (10.4 gram
moles/min) of water were conveyed using a peristaltic pump (Cole
Parmer). 67 grams/min (0.66 gram moles/min) of 97% sulfuric acid
(reagent grade) was conveyed using a second peristaltic pump. The
output from the two pumps was combined and fed to a
non-recirculating plug flow reactor. The reactor consisted of 3.2
mm id.times.65 ft long Viton tubing with a residence time of 30
seconds and a Reynolds number of approximately 2100. The crude
product from the plug flow reactor was then fed at a rate of
approximately 2-5 ml/minute through a 2" wiped file evaporator
(Pope Scientific) with an internal condenser. Operating conditions
were a pressure of 200 mm Hg and a jacket temperature of
160.degree. C. 75.degree. F. cooling water was circulated through
the condenser. The hydrobromic acid and water were vaporized and
recondensed and the sodium bisulfate was collected as a powdery,
non-volatile residue.
[0075] Product Analysis
[0076] The crude reaction product was analyzed for bromine content
and the result was 112 ppm. The hydrobromic acid/water solution
that was flashed and recondensed in the evaporator was titrated
with 0.1 N caustic and a strong acid content of 21.3% was measured
(vs. a theoretical concentration of 21.7%). The sodium bisulfate
residue from the evaporator had an apparent purity of 95%. The
moisture level of the sodium bisulfate was 1%.
Example 5
[0077] This example demonstrates the removal of iron from a mixture
of hydrobromic acid, sodium bisulfate, and water using a continuous
flow loop reactor and a fixed bed of activated carbon. The
activated carbon was Calgon CPG granular 12.times.40 mesh. A glass
column jacketed with hot oil, with dimensions of 2" inside diameter
and 20" length, was filled with carbon. The carbon was soaked in
water, then soaked in 10% sulfuric acid for several hours prior to
use. The reactor was a continuous flow loop reactor, made of Kynar
tubing with dimensions 5/8" diameter and 10 ft. length. The reactor
had a centrifugal pump with a flow rate of 8 liters/hour. The
calculated residence time of fluid in the loop reactor was about 2
minutes. A premix containing 44% sodium bromide, 55.95% water, and
0.05% sodium sulfite was prepared in a 5 gallon bucket with
agitation. 210 gr/min of premix (92.4 gr/min sodium bromide, 117.5
gr/min water, and 0.1 gram/minute sodium sulfite) and 90 gr/min of
97% sulfuric acid (technical grade--9 ppm iron) were pumped into
the loop reactor so that the molar ratio between sodium bromide and
sulfuric acid was approximately 1:1.
[0078] The liquid coming out of the loop reactor was a mixture of
hydrobromic acid, water, and sodium bisulfate at a temperature of
approximately 72.degree. C. The liquid was surged in a 22 liter
flask at 75.degree. C. and then pumped into the top of the carbon
column at a flowrate of approximately 41 cc/min (66 gr/min). The
concentration of iron before the carbon column was approximately 5
ppm. The concentration of iron after the carbon column was
approximately less than 0.5 ppm for the first 35 hours, then
approximately 0.5 ppm from 35 to 45 hours, then 1.5 ppm after 48
hours when the flow through the column was terminated.
[0079] The color of the sodium bisulfate residue after evaporating
off the hydrobromic acid and water was white for the first 35
hours, cream colored from 35 to 45 hours, and orange at 48
hours.
Example 6
[0080] This example shows the impact of evaporation temperature on
residual moisture and bromide in solidified sodium bisulfate. 17.7
grams (0.17 gram moles) of sodium bromide, 42.3 grams (2.35 gram
moles) of water, and 0.02 grams (0.0002 gram moles) of sodium
sulfite were mixed together in a 200 ml. beaker with a stirring bar
at ambient temperature and pressure. 17.2 grams (0.17 gram moles)
of 97% sulfuric acid (reagent grade) was then added slowly to the
mix. When all of the sulfuric acid was added, the beaker was
transferred to a hot plate and the hydrobromic acid and water were
evaporated to a maximum temperature of 150.degree. C. at
atmospheric pressure. The sodium bisulfate residue was poured out
of the beaker into a ceramic dish and allowed to crystallize. After
cooling, the material was crushed with a mortar and pestle and
analyzed for moisture and total bromide (as either sodium or
hydrogen bromide). The experiment was repeated with evaporation
temperatures of 180.degree. C. and 200.degree. C. to gauge the
impact on product quality.
3 Evaporation % temp (.degree. C.) water in sodium bisulfate %
bromide in sodium bisulfate 150 2.25 1.96 180 0.5 0.38 200 0.35
0.03
[0081] The results indicate that at an evaporation temperature of
200.degree. C., sodium bisulfate is readily produced with very low
levels of moisture and bromide.
[0082] While particular embodiments of the present invention have
been illustrated and described, it would be obvious to those
skilled in the art that various other changes and modifications can
be made without departing from the spirit and scope of the
invention. It is therefore intended to cover in the appended claims
all such changes and modifications that are within the scope of
this invention.
* * * * *