CA1103888A - Production of sodium dithionite from sulfur dioxide, sodium formate and sodium carbonate with minimum solvent - Google Patents
Production of sodium dithionite from sulfur dioxide, sodium formate and sodium carbonate with minimum solventInfo
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- CA1103888A CA1103888A CA280,843A CA280843A CA1103888A CA 1103888 A CA1103888 A CA 1103888A CA 280843 A CA280843 A CA 280843A CA 1103888 A CA1103888 A CA 1103888A
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- Prior art keywords
- sodium
- methanol
- sulfur dioxide
- formate
- sodium carbonate
- Prior art date
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B17/00—Sulfur; Compounds thereof
- C01B17/64—Thiosulfates; Dithionites; Polythionates
- C01B17/66—Dithionites or hydrosulfites (S2O42-)
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- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
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Abstract
"PRODUCTION OF SODIUM DITHIONITE FROM SULFUR
DIOXIDE, SODIUM FORMATE, AND SODIUM CARBONATE
WITH MINIMUM SOLVENT"
ABSTRACT OF THE DISCLOSURE
A batch process having high sodium efficiency is described for producing anhydrous sodium dithionite by using minimum amounts of water and methanol while reacting sulfur dioxide with sodium formate and with sodium carbonate. Based on sodium, yields of pure sodium dithionite exceed 73%, and productivity in terms of pounds per hour per gallon of reactor volume is at least about 0.6.
An improved soda-ash batch process is also described for producing anhydrous sodium dithionite by using minimum amounts of water and methanol while pre-reacting sulfur dioxide with sodium carbonate in methanol and admixing the reaction product, as a methanol slurry, with aqueous sodium formate at up to maximum concentration. This externally reacted process results in at least 25% greater yield than the standard caustic soda process while consuming less SO2 and less equivalent NaOH.
A second improved process utilizes the reaction product of soda ash with a portion of the sulfur dioxide by adding sodium metabisulfite and about 30% of the sulfur dioxide to the methanol and adding the slurry to the same concentrated aqueous solution of sodium formate while adding the remaining 20% of the sulfur dioxide thereto. This MBS process produces sodium dithionite having excellent particle size and dust properties at about 20% greater yield than the standard caustic soda process while consuming less equivalent NaOH.
DIOXIDE, SODIUM FORMATE, AND SODIUM CARBONATE
WITH MINIMUM SOLVENT"
ABSTRACT OF THE DISCLOSURE
A batch process having high sodium efficiency is described for producing anhydrous sodium dithionite by using minimum amounts of water and methanol while reacting sulfur dioxide with sodium formate and with sodium carbonate. Based on sodium, yields of pure sodium dithionite exceed 73%, and productivity in terms of pounds per hour per gallon of reactor volume is at least about 0.6.
An improved soda-ash batch process is also described for producing anhydrous sodium dithionite by using minimum amounts of water and methanol while pre-reacting sulfur dioxide with sodium carbonate in methanol and admixing the reaction product, as a methanol slurry, with aqueous sodium formate at up to maximum concentration. This externally reacted process results in at least 25% greater yield than the standard caustic soda process while consuming less SO2 and less equivalent NaOH.
A second improved process utilizes the reaction product of soda ash with a portion of the sulfur dioxide by adding sodium metabisulfite and about 30% of the sulfur dioxide to the methanol and adding the slurry to the same concentrated aqueous solution of sodium formate while adding the remaining 20% of the sulfur dioxide thereto. This MBS process produces sodium dithionite having excellent particle size and dust properties at about 20% greater yield than the standard caustic soda process while consuming less equivalent NaOH.
Description
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"1 :
BACKGROUND OF THE INVENTION
F.Leld of__he Invent:ion 'rhis LllvelltLorl relates to the product:Lon oE anhydrous u.lkal~ e metal llyclrosulfltes or tli.thlonites .Erom :Eortnates and sul.Eur clioxLde. It spec:lically relates to production of sodium ! clLthion:Lte :Ln an aqueous methano:l.ic solution in which both ,I sodium formate and sulfur dioxide are dissolved.
I¦ Review of the Prior Art I¦ llydrosulfites, also termed dithionites, are in demand , as bl.eaching agents, such as for bleaching groundwood pulps. ~
Zinc dithionite is being replaced by sodiu~. dithionlte because of i the shortage and increasing cost of zinc dust to produce ~inc dithionite and because of ecological ob~jections to disposal of Il zinc-conta:in:ing wastes.
l; Sodium dithionite can be produced by electrolytic and ~ borohydride procedures, but the most economical procedures for 'l making a high-quality solid product increasingly use the formate radical as a means for reducing the valence of the sulfur atom.
I This development began in 1933 with U.S. Patent No. I
jl 2,010,615 which discloses a method for producing anhydrous alkali~
metal dithionites by introducing gaseous sulfur dioxide into an aqueous methanol solution, which contains sodium formate and sodium carbonate and is held at a temperature below 30C~ and then bringing the SO2-methanol solut.ion to th,ç temperature at which sodium dithionite formation beglns. ~In one Example, Na2CO3 is 19.0%
. . .
"1 :
BACKGROUND OF THE INVENTION
F.Leld of__he Invent:ion 'rhis LllvelltLorl relates to the product:Lon oE anhydrous u.lkal~ e metal llyclrosulfltes or tli.thlonites .Erom :Eortnates and sul.Eur clioxLde. It spec:lically relates to production of sodium ! clLthion:Lte :Ln an aqueous methano:l.ic solution in which both ,I sodium formate and sulfur dioxide are dissolved.
I¦ Review of the Prior Art I¦ llydrosulfites, also termed dithionites, are in demand , as bl.eaching agents, such as for bleaching groundwood pulps. ~
Zinc dithionite is being replaced by sodiu~. dithionlte because of i the shortage and increasing cost of zinc dust to produce ~inc dithionite and because of ecological ob~jections to disposal of Il zinc-conta:in:ing wastes.
l; Sodium dithionite can be produced by electrolytic and ~ borohydride procedures, but the most economical procedures for 'l making a high-quality solid product increasingly use the formate radical as a means for reducing the valence of the sulfur atom.
I This development began in 1933 with U.S. Patent No. I
jl 2,010,615 which discloses a method for producing anhydrous alkali~
metal dithionites by introducing gaseous sulfur dioxide into an aqueous methanol solution, which contains sodium formate and sodium carbonate and is held at a temperature below 30C~ and then bringing the SO2-methanol solut.ion to th,ç temperature at which sodium dithionite formation beglns. ~In one Example, Na2CO3 is 19.0%
. . .
- 2 -~ 3~
I,of the sodlum formate. This process requires a considerable ¦excess of sodium formate ~o buE~er -the acidity of the solution ¦and produces crystals of excessive Eineness and low s-tabili-ty.
~ lore than 30 years later, a succession of improvements, l¦based Oll sodlum hyclroxlde as the source oE al~ali, w~re dis-¦¦closed, particularly inclucling U S. Pat. Nos. 3,411,875,
I,of the sodlum formate. This process requires a considerable ¦excess of sodium formate ~o buE~er -the acidity of the solution ¦and produces crystals of excessive Eineness and low s-tabili-ty.
~ lore than 30 years later, a succession of improvements, l¦based Oll sodlum hyclroxlde as the source oE al~ali, w~re dis-¦¦closed, particularly inclucling U S. Pat. Nos. 3,411,875,
3,576,598, 3,714,340, 3,718,732, 3,872,221, 3,887,695, and 3,897,544; Jap. Pat. Nos. 1003/68 and 2,405/71; and Belgium jPat. No. 698,2~7.
¦, These improvements comprise -the addition of ¦~sulfur dioxide-containing methanol and an alkaline agent to an aqueous solution of an alkali metal formate, the resulting aqueous l¦me-thanol solu-tion being held at a reaction temperature above the jjdehydration point oE a hydrated alkali metal dithionite in order to prevent the formation of crystals having water of crystalli-l¦zation occluded therewi-thin. The rate of addi-tion must ¦Icorrespond to the ra-te of production of dithionite; if too rapid, the dithioni-te ion decomposes, thus reducing yieldO
The improvements comprise absorbing sulfur dioxide in a ~! water-miscible alcohol as a first feed solution, dissolving ¦sodium hydroxide and sodium formate outside of the reactor in very hot water as a second feed solution, and feeding these two i solutions into a reactor which is held at 50-9~C and contains a small amount of the alcohol under superatmospheric pressure.
l ll .
Il - 3 -I' i I
_ 3 ~
~ High reactor concentrations are used -to ob-tain high I¦ production per unit of reactor volume and per unit of alcohol volume, and methyl forma-te (which can be a by-product of a previous reaction) ls dissolved :in tl~e me-thyl alcohol used as recipient in the reactor for the adcled solutiolls, particularly as t~u~ht irl U.s~ Pa-t. No. 3,~7,695.
~ lthoucJh each oE -these new~r processes uses sodium hydroxide as the source o alkali ancl barely mentions sodium ¦ carbonate therefor, it is noteworthy -that Japanese Patent Number 7,003/68 teaches absorption of sulfur dioxide in methanol to a suitable concentration and then gradually adding an alkaline ¦ a~ueous solution includiny both sodium formate and sodium carbonate which is 33% by weight of -the sodium formate. The yield is about 56% based on sulfur dioxide and 54% based on ¦ sodium.
Tables I and II give comparative experimental data and results ~or the lS examples of the four most pertinent United States prior art patents. Data on dust characteristics of the ¦¦ products are not available.
From the examples showing experirnental results in the ¦ prior art, it appears that: (a) sodium hydroxide has been routinely selected as the alkali source; (b) sodium carbonate has seldom been used but is often mentioned; and ~) in the few available examples that have employed sodium carbonate as the alkali source, the yield is decidedly inferior to sodium hydroxide in the production of sodium dithionite. Nevertheless, simply because sodium carbonate is considerably cheaper than sodium hydroxide, its use is highly desirable. Moreover, production rate ¦ per uni of reactor volum~ i5 a critically im nrtant economic ,1.~.~ ' s ~ ~L~L4~3~
. . .
, TABLE I
.
t!. s . 3.4 L L ~ 875 x . 3 ~.x. ~ !
¦ NaOtl, l~arts 23 21 20 30 ~¦ N~2C~3, parts __ __ __ __ I
¦ }l2, partg 200 240 13fi loo IICOONa, parts 80 90 70 75 Il Cl130M, parts 470 soo 386 424 I! ~COOC~13, parts -- _~
¦¦ 52, parts 80 87 72 loo . Na2S204 (gross/100% basis) 84/76.0 90l78.3 72/64.1 104/94.2 i Assay~ % 90-5 91.2 89.0 90.6 ' Temp. Range, C. 60.70 70 70 70 Total Reactlon T:ime, Hrs. 4.8 5.3 5.0 5.3 1~ Productivlty (lbs/llr/gal) -- -- -- 0.191 Total Na equ:ivalents1.751 1.848 1.529 1.853 Total formate equivalents 1.176 1.3231.029 1.103 l¦ Total S02 equivalents 1.249 1.3581.124 1.561 ¦¦ Total CH30H equivalents 14.669 15.60512.047 13.233 i , i'' .....
., , .
consideration in view of the reaction being relatively slow and requiring repetitive batch pressure reactions. Also, as commented upon in German Patent Number 2,000,877 and in U.S. Paten-t Number 3,8~7,695, it is difE.icult to enhance the productivity of the reaction system, particularly by decreasing the volume of alcohol with which the sulfur dioxide is added to the system, partly because water both accompanies caustic soda (generally added as a concentrated solution) and is chemically bound therewith and because the ratio of alcohol to water cannot be lowered without promoting the solubility of dithionite (dissolved dithionite immediately decomposes at the reaction pH, thereby causing a reduction in both yield and efficiency of the process).
SUMMARY OF THE INVENTION
It is accordin~ly an object o this invention to provide a process for the production of anhydrous alkali metal dithionites from sulfur dioxide and formates in which a substantial amount of sodium ion is supplied by sodium carbonate or by the reaction product of sodium carbonate with sulfur dioxide.
It is also an object to provide a batch process for dithionite production having high production per unit of reactor volume..
In accordance with the spirit and objectives of this invention, there is provided in a process for the production of anhydrous Na2S204 by introducing a~ueous sodium formate, a sulfur dioxide-methanol solution and a sodium compound into a reactor wherein, (a) the mekhanol-to water weight ratio is 4.2 to about 5.2; and (b) the S02-to-water weight ratio is 1.7 to about 2.4;
the improvement which comprises using sodium carbona-te as said sodium compound in the proportion of at least 50% by weight of said sodium formate, allowing reagen~s to react, and recovering said anhydrous Na2S20~. The sodium formate is dissolved preferably in water at about 120C and the sodium carbonate is preerably added as a dry powder to the recipient methanol so:Lutlon to wh.ich the SO2-methanol and a~ueous ormate solutions are :Eed. 'rhe methanol and the water are thus at a selected weight - 7a -ratio, and the water is the minimum amount required for dissol- I
ving the sodium formate at max:imum concentration and at elevated tempera~lre. The quarltities of s~llfur dioxide, methanol, so(li~l Eormate, watcl, nnd socliulll carbollate are pre~erably aclJusted so that the flxed reactor volume ;s Eully utilized.
Eacll tnetllalloL soLution Lncludes about 4% methyl formate. An add:itional amount of methanol is added to the reflux condenser to minimi~e loss oE methyl formate and other by-products. This additional amount is about 15% of the total methanol used.
The ratio oE methanol to water by weight is about 4.2 to 5.2.
The sulfur dioxide-to-methanol ratio on an equivalence basis is about 0.20 to 0.25. On a weight basis, the ratio of sulfur dioxide to water is about 1.7 to about 2.4. On an equivalence basis, the ratio oE sulfur dioxide to formate ion is about 1.4. On a weight basis, the sodium carbonate is about 60% Of the sodium formate; on an equivalence basis, the Na2CO3/HCOONa ratio is about 0.8.
On a sulfur dioxide basis, the yield is about 74-82~.
On a formate basis, the yield is about 53-59~. On a sodium basis, the yield is about 65-75%. On a basis of reactor volume, this process produces about 2.3 pounds per gallon and about 0.6 pounds per hour per gallon.
It was found that soda ash is at least 7% more e;fficient than caustic soda with respect to usage of Na2O in the process of this invention which is an improvement on U.S. Patent Number 3,887,695. Although the reaso~s are not ent`irely understood, it is thought that perhaps the very strong alkalinity of NaOH, which is preseDt when an lncremenL of the NaOh s~lution cont~cts , ~
?, ~ f the reaction medium and dissolves, results in the Eormation of some by-product, such as Na2SO3, wh:ich -is insoluble and largely unreactive. Soda ash, on tlle other hancl,ls not imn~ecl:Lately dLssolved wllen aclded ~nd thereEore tends to reLease its alka-LnLty at a slower rate.
I llowever,a comparative calculation of prior art results ! for Na20, on the basis of alkaline Na versus total Na added, can be mis:leacling for those examples (such as Example 4 in ' United States Patent 3,897,544) wherein no caustic soda is added, all sodium being supplied by sodium Eormate. The reason thereEor is that the process cannot be continued with recycled alcohol. To explain, the desired reaction requires one ! mol of formic acid and two mols oE bisulELte:
i !
I` HCOO}I + 2NaHSO3 - ~ Na~S204 -~ CO2 + 2H2 l' l When one adds S2 to sodium Eormate as :in Example 4 of United States Patent Number 3,897,544, one produces two mols of formic acid -Eor two mols of NaHSO3:
2 ~ 2S2 ~ 2HCooNa ~ ~ 2HCOOH + 2NaHSO3 The extra formic acid must react with excess methanol I to produce methyl formate. Otherwise, the excess formic acid il would cause the hydrosulfite to decompose. The problem occurs ~ when the methanol is recovered for the next ba~ch. It will now il contain much methyl formate, and could resul~.in a run with j severe decomposition if used according to Example 4 of United States 3,897,544 because of an excess o~- formic acid produced, which cannot be converted to methyl formate due to the latter already being present.
g The formulations in the examples given hereinafter, in wh.ich sodium formate is balanced with either NaOH or Na2CO3, are I based on the assumpti.on that -the methallol, containing methyl formate~, wi:l.l be .recoverecl.Erom a previous run so that the methyl 11l Eormate whl.ch iS added is nei-the:r consumed no.r produced. The ¦~ examples thus simulate normal commercial production i.n which the me-thyl alcohol is recycled ove.r and over.
In virgin batches such as the demonstrative examples of the prior art, in which caustic soda is used, methyl formate is no-t fed. Formate ion must consequently be supplied entirely from HCOONa, and NaO~ must be correspondingly reduced. ¦.
~ s a result of this, the recycle formulations in the ' following examples cannot be literally compared with the virgin formulations of the prior art examples. For this reason, comparisons are hereinafter made on a basis of total sodium use j even though the consumption of less total Na i.s less apparent because the sodium formate tends to l'dilutell the effect.
This process may be summarized as comprising the following steps:
(A) dissolving sodium formate in wa-ter at elevated temperatures and up to maximum concentra-tion -to form an aqueous I formate solution;
¦ (B) dissolving sulfur dioxide in methanol l (C) providing a recipient or puddle methanol solution 'I within a fixed reactor and adding there-to: ~.
1 (1) sodium carbonate,~preferably as a dry powder, according to a first specific schedule to provide at least a substantial proportion :; I
~?3~
of the alkali needed for the reaction, this sodium carbonate being at least 50% by weight oE the sod:ium Eormate when used as 100~ of th~ neecled alka:Li;
(2) the a~ueous formate solution according -to a second specific schedule, and (3) the SO2-methanol solution according to a third specific schedule in which about 80~ is added as a "fast" ~2 feed, the remainder as a "slow" SO2 feed at progressively slower addition rates. ¦~
As an improved soda ash embodiment, even better results are obtained by pre-reacting the sulfur dioxide with the sodium carbonate suspended in the methanol and -then adding the resultant slurry of sodium bisulfite in methanol along with the concentrated sodium formate solution to -the main reactor at a controlled rate. This embodiment produces sodium dithionite having acc~ptable particle size and dust properties and an assay that is a-t least as good as the product of the standard caus-tic process as disclosed in United States Patent 3,887,695 at a yield which is 22-25% greater than the yield of the standard caustic process while consuming about 3.0% less sulfur dioxide and about 8.6% less equivalent NaOH.
An addi-tional soda ash embodiment comprises slurrying sodium metabisulfite (representing the stoichi~metric reaction product of all of the soda ash with about half of the sulfur dioxide) with most of the methanol, and dissolving 60% of the other half of the SO2 in the methanol, and then adding this ll metabisulEite slurry to the main reactor along with the concentrated aqueous solu-tion of sodium formate. This second improvement produces sodium dlthionite with excellent par-ticle size alld clust properties at about 20~ improved yield as compared to tile standard caust,ic p.rocess according to U.S. Patent 3,897,544 while consuming about 5.4~ less equivalen-t sodium hydroxlde.
In contrast to prior art experimentation with Na2CO3, these results demonstrate that an opt:imum ratio of reactants and an optimum experimental procedure have been discovered for using sodium carbonate as the source of a substan-tial amount 1, of added alkali in the incremental reduction of sulfur dioxide with formate ion in aqueous methanolic solution.
The novel process of this invention is effective whether the alkali is in the form of sodium carbonatet sodium bicarbonate, sodium sulfite, sodium metabisulfite, or sodium hydroxide. However, i-t is particularly preferred to use sodium carbonate for a wide varie-ty of reasons including its relatively low cost.
DESCRIPTION OF THE INVENTION
Investigation of the feasibillty of substituting sodium carbonate for sodium hydroxide in a standardized process,as disclosed in ~nited States Patent Number 3,887,695 proceeded by making a direct substitution of an amount of Na2CO3 equivalent to the NaOH while maintaining the same amount o~ water, including .. .
:, .j il .
8~
the chemically bound water in the NaOH. Undesirable amounts of dust were obtained and the product was of lower purity. Next, `~ the amount oE soda ash was reduced, all other variables being llStallt. Th:l9 llllprOVed the purity of assay o~ the product and lowered the dust.
~¦ In one set oE experiments, clust was reduced from 350 to j 307 by adding 45 g. less Na2CO3 and was Eurther reduced to 215 by a five-minute delay in feeding the Na2CO3, but the most effective variab:Le for decreasing dust was found to be the SO2 "split" as shown by the following results for another set of experiments:
!
Split Dust Number Il , 82/18 196 l'l 83/17 1~7 The dustiness of production batches of sodium dithionite !
is checked with a colorimetric analytical method that uses a i !
rubine solution tomeasure the sodium dithionite dust in a sample., In this method, 0.0256 grams Na2S2O4 react with and decolorize 25 milliliters of rubine solution for determining the dust ratingl i of each production batch.
A dustometer apparatus is assembled for carrying out this¦
dust rating procedure. A carefully cleaned and dried elutriator tube, one inch in internal diameter and 34 inches in length and havillg a ball joint at each end thereof,~is mounted in upright position. A carefully cleaned and dried elutriator sample ''. ... I
l ~, ~ - 13 -., ~
~ 3~
~! contalner tube, one inch in internal diameter and 8 inches in j length, with a layer of g]ass wool ahout 1 inch thick packed j lnto the bottom tl~ereoE, :Ls connected :in ~Iprlght posltion to the l)ottotll o~ the elutriator tube. /~ nLtrogen source at 5-10 pslg Ls connectecl through a neeclle control valve and a rotameter to the bottom oE the sample container tube. A J-shaped lead-off tube of 4-5 mm internal diameter is connected in inverted 1l position to the upper ball joint of the elutriator tube, the ;I straight side oE the~J" extending to within one inch of the bottom of a 500 ml graduated cylinder containing 450 ml of water. A door bell buz~er is attached to the curved portion ~' of the "J" and connected through a variac to a source of power.
`~1 A 50 ml burette containing the rubine solution is mounted above the top oE the graduated cylinder.
To begin the test, a bottle containing a portion of a production batch is thoroughly mixed by gently rolling and ' tumbling the bottle (when the contents of the bottle are shaken, the dust cloud that settles on the top interferes with reproducibility oE the test). A 50+ 0.1 gram sample is removed 'I
from the bottle and carefully poured into the elutriator sample tube, care being exercised to prevent the loss oE dust during the transfer and a camel's hair brush being used to transfer all particles into the sample container tube.
i 3~0 m] of rubine solution are added to the water in the i graduated cylinder. The vibration is started and adjusted by ' ~
Il having the vibrator bar strikin'g'sharply agaiinst the underside 'l of the J-shaped lead-off tube in the proximate center of the 1~ arc. When the buz~er is operating properly and suitably controlled by the variac, the operator can feel the vibrations l4 _ ~3~
when he p:Laces a flnger on the tube about 3 or 4 inches from the point where the v:ibr~tor bar stril~es it. IE the apparatus is clamped too firmly, the vibrations are daml)ened and ineEEective Eor dislodgirlg the dust that settles out and witl~ the Iead-oEE tul)e.
Tlle neeclLe valve whicil controls tlle nitrogen Elow througll the elutriltor columll ls opened carefulLy and rapidly and ad~justed to a E:Low rate oE 0.09425 cubic Eeet per minute. lhis flow rate is held constant throughout ¦ the run. ~s SOOIl as the nitrogen flow into the bottoM oE the elutriator I column and through the sodium dithionite sample is high enough to form a ¦ dust cloud, a timer is started.
ll ~t the instant that the rubine solution is decolorized, another ,' few mi]li:Liters oE rubine solution are added. The number of milliliters of rubine solution are noted at one-minute interva]s. The elutriator running is continued for approximately 5 minutes (~ one-half minute~. ~le volume of rubine solution is determined to the nearest 0.1 milliliter, and the time is determ:ined to the nearest 0.1 minute.
The dust index or dust rating is calculated as follows:
Millilit rs oE rublne solution x 30 = dust number ` Elapsed minutes In general, S02 addition is d:ivided into two portions. The "fast"
S02, comprising 80-85% of the total, is fed during the first 80 minutes;
1~ "slow" S02, comprising the remainder, is fed during the second 80 minutes;
and the reaction is allowed to "cook", with no additional feed being added !l other than the "scrub" alcohol-to prevent loss of volatile reactants, during the third 80 minutes.
Next, the extra water and methanol associate~ with the use of ~aOH
are reduced, and, finally, the amounts of reactants are scaled up to utiliæe ¦
the full volume of the reactor and to obtain maximum productivity per unit f available volumetric capacity. The laboratory and pilot plant experimental data for Na2C03 are presented in Examples 2, 3, ~, 6 and 7 and compared with "
Examples 1 and 5 for NaOII and with 15 examples for NaOI-I and Na2C03 in the prior art.
., i ~l - 15 -31 ~ 3~
I Examples l-4 __ !
Data and results for Examples 1-4 are listed in Table III. Example 1 plesents the average Eor seven runs using caust-ic soda at 99% purity in a 73%
gol.ut:ion ancl llO socli~ carbonate, accol-ding to n stanclard laboratory procedure wltll Laboratory scale equLpment, using the process described in U.S. Patent Nutnber 3,887,695. Example 2 presents the results Eor all equivalent amount of ¦
sodillm carbonate and the same amount oE water as in Example 1. Example 3 gives results for a lesser quantity of sodium carbonte and the same amount of water as in Example 2. Example 4 presents results for a still lesser amount of sodiunl carbonate and decreased amounts of both water and methanol.
As a typical procedure, Example 2 was prepared according to the following detailed steps.
To a stirred reactor is added 851 g. of methanol plus 38 g. of methyl formate. This charge is heated to 70C and maintained under a pressure of 35 PSIG with nitrogen.
A mixture of 828 g. of 96% sodium fonnate is mixed with 727 g. water and heated to the boiling point. The mixture is transferred to a stainless steel cyclinder, which is jacketed with 70 psig steam to maintain the solution at about 300F. The level in the feeder is measured by a float to which is attached a metal rod which protrudes from the top of the cylinder into a sight glass. The sight glass is calibrated in millimeters, so that the volume in the feeder is known with a good degree of accuracy. The feed rate i5 con-trolled by reading the feeder level every millimeter and comparing this with the calculated value.
A mixture of 1702 g. methanol, 76 g. methyl formate and 1307 g. of sulfur dioxide is placed in another stainless steel c~iinder equipped with a sight glass and meter stick, which also enables the volume to be known with good accuracy. The feed rate of the mixture is controlled by a rotameter. I
Five hundred and fifty-seven grams of sodium carbonate are weighed I
, I
li il .
Ij TABLE III
`! I
Laboratory Scale Dithionite Preparations Fx_mple_No. 1 _ _ _ 2_ 3 4 I Nc~Oll~ g. 424 -- -- --~l2' g' l55 __ __ __ ¦ Ntl2CO3, g. ~~ 557 517 501 ¦ }ICOONa (96%), g.787 828 828 819 ¦ H2O, g. 455 727 727 595 CH30H, g. 1702 1702 1702 1206 }ICOOC}~3, g. 76 76 76 76 2' g' 1282 1307 1282 1263 C}13OH (puddle), g.851 851 851 851 }~COOCH3 (puddle), g. 38 38 38 38 HCOONa (puddle), g.41 -- __ __ ,~
!! H2O (p~lddle)~ g~ 22 ~~
,I CH30H (scrub), g.450 500 450 450 Na2 24' g' 1429 1462 1416 1432 Assay, % 90.9 89.8 91.6 90.9 P~lre Na2S24' g- 1299 1313 1297 1301 Dust No. 175 453 97 238 Total Na equivalents 22.775 22.341 21.931 21.496 Total formate equivalents14.07314.073 14.073 13.94 Total SO2 equivalents 20.012 20.401 20.012 19.716 Total CH30H equivalents95-625 97.210 95-625 80.144 '`
* 99% purity, .
'l 73% solution l i l .
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, I
in-to five beakers of 100 g. each plus one beaker of 57 g. 'lhe feeding mechan-ism for soda ash consis-ts of two valves and a s~all hopper. m e hopper easily holds 100 g. The space be~ween the valve holds 11.1 g. Since 557 g. are to be :E~cl ove..r 79 nLinutes, 7.05 g. should be :Eed per nLirlute. At 11.1 g. per dump, the vaLve ~system shou1d be operated over every 1.57 minutes. A bleed of nitro-gen is l~l.intcain~-~d at the soda ash lnlet to prevent condensation from the reac--tion plugging -the inlet. (In later experiments, the nikro~en bleed was omitted, and the valve and :Eittings heated with electrical tape to prevent condensa-tion.) With the reactor contents at 70C, the SO2-methanol feed is started. !
~, After the SO2 concentration in the pot has reached 1~ (by calculation), the I timer is started and the feeds of sodium fornk~te solution and solid soda ash begun. Five percen-t of the sodium forma-te solution is fed in the first minute,~
and the rel~aining 95% fed over 79 minutes. The soda ash is fed over 79 minutes as a "fast SO2" feed rate. Eigh-ty-one percent o:E the SO2-methanol is fed over 80 minutes, and the remaining 19% fed over the :Eollowing 80 minutes at , progressively slower rates. At the end of 80 minu-tes, the SO2-methanol feed rate is reduced to a~lt 1/3 that of the fast So2 feed ra-te, and this flow rate is maintained for 20 minutes. The rate is then reduced to 26% of the fast SO2 feed rate for another 15 minutes and finally to 17% of the fast rate until the SO2-methanol solution runs out, which is generally at 160 minutes.
I The reaction temperature, which is at 70C a-t the start, is allowed I to reach 83C af-ter about 5 minutes. A -te~perature of 83C is ma~ntained thereafter until the end of the run.
~; After the slow S02 feed is finished.(at about 160 minutes), the n m is allowed to "cook" for another 80 minutes, or until a total of 240 minutes of run time. -During the entire run, a feed of 500 g. of methanol is fed to the scrubber to lessen the loss of volatile reac-tan-ts such as methyl formate and so2~
3~
., , Samp].es are taken o:E tlle react:i.on E:i:~trate a:Eter tlle East S2 Eeed , (80 ll~i.nutes), aftcr tlle. ~]ow S02 :Eeed ~:l(iO minlltes), antl at the end oE the runj (2~0 ml.llutes). A t(~l~ m:l. snmplt-~ is mlxed w:Ltll cln a:LIcal.:lne Eormaldeilydc solutioj (to tle Up b.isu:l.E:ite) and ls then titratecl w:itl~ 0.]. N stan(lard iod:ide solut:ion.l Th:is "tL.ter" is a measure o.E the sodium tl~iosulate content o:E the solution anq :i.s ti~ere:fore an indication oE the extent of decomposition of hydrosulfite.
The contents of the reactor are filtered through a glass-fritted Buchner funnel, maintaining an atmosphere of nitrogell above the product to prevent contact witll air. The product is washed with methanol and dried in a I vacuum :flask, under vacuum while heated in a hot water bath. The dried productj " is weighed to determ:ine the y:Lel.d, assayed Eor hydrosulfite purity, and a dust l number :is run plus a screen ana:Lys:is.
Examples 5-7 i Data and results Eor Examples 5-7 are listed in Table IV which shows¦
~, pilot plant results for a standard run using sodium hydroxi.de and for two runs ¦
using sodium carbonate. The reactor i.s equipped and operated as described in U.S. Patent Number 3~887,695. The sodium carbonate is 63% by weight of the ~i sodium formate. In Example 6, the amount of methanol is the same as in Example 5, but the amount o.E water that is present has been slightly increased. In Example 7, the amount of water has been reduced by 25% and the amount of metha-¦
nol has been reduced by 20% with respect to Example 6.
Comparative Ratios and Productivity Cal.culation for Labora-tory and Pilot Plant Examples and for Prior Art Examples In Tables V(a), V(b~, calculated ratios, based on equivalence values in Tables I-IV, and calculated yields, based on S02, fo~mate ion, and sodium ;' ion, are also given for both experimental runs and prior art examples. Finally, . calculated productivity in terms of reactor volume as pounds per hour per gallon are listed for one example and for each of the four prior art patents.
In general, productivity increased 18% by laboratory data and 20% by pilot plant data.
I, .
!
~3~ 38 ,j , T~!BLE IV
_lL~t P:Lant l)Ltl!:lollite _re~_r tions !~ N~ 5 _ 6 _ _ 7 ¦I Na()ll, parts 7l Na2C03, parts -- 83 83 ! U20, parts 98 116 87 i HCOONa, parts 138 138 138 CH30H, parts 50l 501 400 IICOOCH3, parts 18 18 18 I S02, parts 211.2 205.2 205.2 Na2S20~ (gross basis) 246 239 247.5 Na2S204 (100% basis) 226 222 228.7 Assay, % 92 92.7 92.4 Dust No. 100 206 102 Total Reaction Tilr.e, Mrs.4.0 4.0 4.0 Il Prodllctivity, pounds/gal.2.26 2.26 2.70 i, Total Na equivalents 3-704 3.514 3.514 Total formate equivalents 2.247 2.247 2.247 Total S02 equivalents 3.30 3.206 3.206 Total CH30H equivalents 15.937 15.937 12.784 '.1 .. ,' ,,~'. I
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, ' i It is clear that, in terms of sodium equivalence per S02 equivalence, there is a slight diEference between the two sodium hydrox:icle examples (1 and 5), the three sodLum carbonate examples (4, 6, ancl 7), ancl the four prlor art patents. ~mployment o~
socla asll enable6 use oF 3% less total soclLum ecluivalent/S02 etlulvaLellts over the best results In the prior art. Although the laboratory and pilot plant examples, using either sodium hydroxide or sodium carbonate, utilize a h:igher weight ratio of methanol to water than the four prior art examples, the five sodium carbonate ratios are somewhat lower than the two sodium hydroxide ratios among the laboratory and pilot plant examples.
As to the weight ratio of sulfur dioxide to water, the laboratory and pilot plant examples possess higher values than three of the four prior art patents. As to the equivalenct-! ratio of sulfur dioxlde to formate, the laboratory and pilot plant examples have distinctly higher values relative to prior art, for both sodium hydroxide and sodium carbonate.
It is on a yield basis and on a process productivity basis that the invention is most striking. In the laboratory series, substituting sodium carbonate for sodium hydroxide in Example 4 compared to Example 1 increased the efficiency of the process when based on all three raw materials. The productivity, as measured by the pounds of product prepared per hour per gallon of reaction solution, is also increased by the substitution. A
similar increase in process efficiencies and productivity is observed in Example 7 vs. Example 5 ln the pilot plant.
."' '''' , ', .
!
~3~
.1 i Tlle.se results are belleved to be noteworthy in view of the h:Lgh assay and low dust numbers for tile products of Examples 6 ancl i, as given in 'rable :tV, which are high:Ly useful as in- ¦
! dustriaJ bleaching agents.
~ dditional pilot plan~ results are presented in Table VI for a standard run with caustic soda and for two runs with soda ash in which the Na2CO3 is 62.9% by weight of the HCCOONa.
" Signif:icantly improved productivities, measured as pounds of 'I pure Na2S204 per gallon of reactor volume, were obtained in Examples 9 and :LO. Even though the amount of water which was used for dissolving the increased amount of sodium formate was s1ightly greater than the total amount of water used in Example 8 with the NaOH and with the ~ICOONa, the substitution of Na2CO3 for NaOH enabled the methanol to be reduced even though additional sulEur dioxide was used. Because of the relatively low density of methanol, this reduction saves considerable valuable space in a reactor.
In general, use of sodium carbonate as the principle source of supply for alkali in the process of this invention, as demonstrated in Examples -8-l0, enables less solvent and larger quantities of reactants to be used in a reactor so that pro-ductivity is significantly increased as compa~ed with the world-wide standard productivities obtained with sodium hydroxide as the principle souce of supply for al~ali. Less total sodium is thus required when soda ash is employed.
, ~3 ,i ¦ TABLE VI
Pi ot E'l~nt_DItllion te _repa ations ~I Example_~N,_Il_),er ,"__,_ 8,,_ __,, ,,,,_,_9_ _, 10 Na2(`O~, Ib ~ed -- L00 100 ¦ NaOll, :Ib ~ecl~ 70 UCOUNa, lb ed ** 132.5 159 159 ~! SO2, lb Eed 211.2 243.2 243.2 CH30H, lb fed 501 483 483 (Initial Puddle) (142) (164) (164) (With SO2) (284) (244) (244) ,, (Scrub) (75) (75) (75) il2O, lb fed 100 104 104 (With NaOU) (26) __ __ (With HCOONa) (74) (104) (104) ¦ HCOOCU3 18 ]6 16 ', Total Vol., gal 100 100 100 Filtrate Vo]., gal 87 84 84 ~', Product, lb 247 302 296 ,I roduct, % Na2S2O4 91.5 90.3 90.3 Pure Na2S24' lb 226 273 267 Productivity, ],b/gal 2.26 2.73 2.67 Yield: S02 Basis 78.7 82.5 80.8 Formate Basis - 66.6 67.0 65.7 Sodium Basis 70.2 74.2 72.7 Il Productivity (lb/gal/hr) 0.57 0.~68 0.68 ,l * 100% pure '~
I ** 100% pure , " - 25 -.,, ~.
1, !
. .
3~
lthough t-he Examples which follow are direc-ted towards -the use oE soda ash as a solid, i-t is to be underst-ood that this invention encompasses the addition oE water to soda ash witli a correspondln~ r~duction of water in other Eee~d streams. ~le lcey to the inventive contribution resicles in:
~(a) the-total water add~d to the reactor ancl (b) maintainill~ the met~lculol-to-water ratios previously set forth and not necessarily in the amowlt of water in an individual feed stream. I
Exarnple 11 This example illustrates the pre-reaction oE sodium carbonate and sulfur dioxide to Eorm a feed material.
Three separate feeds were prepared. Feed "A" was made by suspending ~83 parts by weight of sodium carbonate in 167 parts of methyl alcohol containing 9 parts methyl forma-te, and adding to the suspension 167 parts ~lof sulEur dioxide. Feed "B" was l~ade by dissolving 131 parts of sodium forrnate of approx~nately 96% purity in 93 parts water. Feed "C" was made by dissolving 35 parts sulfur dioxide in 35 parts methyl alcohol containing 2 parts methyl form~-te.
An ini-tial charge consisting of 115 parts methyl alcohol containing 6 parts methyl fonnate was placed in the reactor. m is charge was agi-tated ,land heated ~o a temperature of 65C and at a pressure of 20 psig. Then ,Feed "A" and Feed "B" were started simultaneously and at such a rate that the specified cruantity of each would be fed to the reactor in an 80-minute period.
Heating of the reactor contents continued untll a temperature of 83C was reached, at which time the heat was reduced -to main-tain a controlled reaction temperature of 83C. me time period fran 65 to 83 was approxirnately 10 minutes. Also after this sarne 10 minutës, the reactor pressure had reached 50 psig owing to the release of carbon dioxide gas frcm the reaction. me I
:
&~i , reaction pressure was theîeafter m~intained at 50 psig by controlled release of the carbon dioxide fon~d in -the reaction. m e released yas let the reac-tor thro~,~Jh Eirst a water-coo:led condenser (35C) Eollowed by a chilled ¦ conclens,_~ 10C), ~llen a chilled scrubbf~r Eed with lllethyl alcohol at a rate oE 0~26 parts per nuinute. The c~ndensate Erf~m the two condensers plus the effluent scrubber methanol bo-th re-entered the reactor.
~ -t the end oE the 80 minute period o eeding Feed "A" and Eeed "B"; ¦
Feed "C" was s-tartecl at a rate of 1.5 parts per minu-te~ The rate was reduced to 1.0 parts per minute after 15 minutes, and further reduced to 0.7 parts per minute after another 15 minutes~ The entire 72 parts o:E Feed "C" was consumed in 80 minutes. During this time, -the temperature and pressure within ¦
the reactor were maintained a-t 83C and 50 psig, respectively.
' rl~hese same conditions were maintained for an adclitional 70-minute i~ period af-ter the ca~,pletion of Feed "C". At this time, 230 minutes r,am the begir~ing in all, the reactor cantents were cool~ed to 60C and filtered. Then the filter cake was washed with 240 parts me-thyl alcohol, dried under vacuum ~I to yield a crystalline prc,duct of 240.5 parts by weight and 92.3% assay as sodium hydrosulfite.
E~ample 12 This example illustrates the use o sodium metcbisulEite as a eed mat,erial.
Again, three separa-te Eeeds were prepared. Feed "A" was made by , suspending 150 parts of sodi~n metabisulfite in 167 parts o methyl alcohol ; containing 9 parts of me-thyl formate, and adding to the suspension 67 parts of ¦
sulur dioxide. Feed "s" and Feed "C'! were ldentical ~o those described in I Example 11. ``` `
.1 .
, The feed schedules, reac-tion condi-tions, and -total reac-tion time were exactLy as described in Exc~mple 11. AEter Eiltering, washing, and dryincJ as in E`xample :Ll, a crystall:ine procluct of 238 ~ ~s by weight and ~ l.0% assay as sodi~ml hydroslllfite was obta.ined.
;1 As has heretofo2.e be~l stated, the novel process of this invention . results in increasecl productivity for a given reaction vessel per unit of time. r~lis increased productivity results f.rom the fac-t that it is possible, using the teachings of this invention, to utiliæe more of the reactor volume Eor the production of sodium dithionite than has heretofore been possible.
The inventive concept disclosed herein involves the use of less , wa-ter which in turn permits one to use less methanol while still keeping the proper range oE water to methanol in the reactor. By the use o:E less methanol,¦
there is more room in the reactor so that more product can be produced per batch. rlhe instan-t inventive concept embraces many alka.lis but sodium carbonate is preferred.
Because it will be readily apparent to those skilled in the I art that innumerable variations, modifications, applications, and extensions `; of the examples rmd principles hereinbefore set forth can be made without departing from the spirit and scope of the invention, what is herein defined as such scope and is desired to be protected should be measured, and the inv nt on should b limlt d, on y by t e following clalms.
, 1 ~ .
. . .
¦, These improvements comprise -the addition of ¦~sulfur dioxide-containing methanol and an alkaline agent to an aqueous solution of an alkali metal formate, the resulting aqueous l¦me-thanol solu-tion being held at a reaction temperature above the jjdehydration point oE a hydrated alkali metal dithionite in order to prevent the formation of crystals having water of crystalli-l¦zation occluded therewi-thin. The rate of addi-tion must ¦Icorrespond to the ra-te of production of dithionite; if too rapid, the dithioni-te ion decomposes, thus reducing yieldO
The improvements comprise absorbing sulfur dioxide in a ~! water-miscible alcohol as a first feed solution, dissolving ¦sodium hydroxide and sodium formate outside of the reactor in very hot water as a second feed solution, and feeding these two i solutions into a reactor which is held at 50-9~C and contains a small amount of the alcohol under superatmospheric pressure.
l ll .
Il - 3 -I' i I
_ 3 ~
~ High reactor concentrations are used -to ob-tain high I¦ production per unit of reactor volume and per unit of alcohol volume, and methyl forma-te (which can be a by-product of a previous reaction) ls dissolved :in tl~e me-thyl alcohol used as recipient in the reactor for the adcled solutiolls, particularly as t~u~ht irl U.s~ Pa-t. No. 3,~7,695.
~ lthoucJh each oE -these new~r processes uses sodium hydroxide as the source o alkali ancl barely mentions sodium ¦ carbonate therefor, it is noteworthy -that Japanese Patent Number 7,003/68 teaches absorption of sulfur dioxide in methanol to a suitable concentration and then gradually adding an alkaline ¦ a~ueous solution includiny both sodium formate and sodium carbonate which is 33% by weight of -the sodium formate. The yield is about 56% based on sulfur dioxide and 54% based on ¦ sodium.
Tables I and II give comparative experimental data and results ~or the lS examples of the four most pertinent United States prior art patents. Data on dust characteristics of the ¦¦ products are not available.
From the examples showing experirnental results in the ¦ prior art, it appears that: (a) sodium hydroxide has been routinely selected as the alkali source; (b) sodium carbonate has seldom been used but is often mentioned; and ~) in the few available examples that have employed sodium carbonate as the alkali source, the yield is decidedly inferior to sodium hydroxide in the production of sodium dithionite. Nevertheless, simply because sodium carbonate is considerably cheaper than sodium hydroxide, its use is highly desirable. Moreover, production rate ¦ per uni of reactor volum~ i5 a critically im nrtant economic ,1.~.~ ' s ~ ~L~L4~3~
. . .
, TABLE I
.
t!. s . 3.4 L L ~ 875 x . 3 ~.x. ~ !
¦ NaOtl, l~arts 23 21 20 30 ~¦ N~2C~3, parts __ __ __ __ I
¦ }l2, partg 200 240 13fi loo IICOONa, parts 80 90 70 75 Il Cl130M, parts 470 soo 386 424 I! ~COOC~13, parts -- _~
¦¦ 52, parts 80 87 72 loo . Na2S204 (gross/100% basis) 84/76.0 90l78.3 72/64.1 104/94.2 i Assay~ % 90-5 91.2 89.0 90.6 ' Temp. Range, C. 60.70 70 70 70 Total Reactlon T:ime, Hrs. 4.8 5.3 5.0 5.3 1~ Productivlty (lbs/llr/gal) -- -- -- 0.191 Total Na equ:ivalents1.751 1.848 1.529 1.853 Total formate equivalents 1.176 1.3231.029 1.103 l¦ Total S02 equivalents 1.249 1.3581.124 1.561 ¦¦ Total CH30H equivalents 14.669 15.60512.047 13.233 i , i'' .....
., , .
consideration in view of the reaction being relatively slow and requiring repetitive batch pressure reactions. Also, as commented upon in German Patent Number 2,000,877 and in U.S. Paten-t Number 3,8~7,695, it is difE.icult to enhance the productivity of the reaction system, particularly by decreasing the volume of alcohol with which the sulfur dioxide is added to the system, partly because water both accompanies caustic soda (generally added as a concentrated solution) and is chemically bound therewith and because the ratio of alcohol to water cannot be lowered without promoting the solubility of dithionite (dissolved dithionite immediately decomposes at the reaction pH, thereby causing a reduction in both yield and efficiency of the process).
SUMMARY OF THE INVENTION
It is accordin~ly an object o this invention to provide a process for the production of anhydrous alkali metal dithionites from sulfur dioxide and formates in which a substantial amount of sodium ion is supplied by sodium carbonate or by the reaction product of sodium carbonate with sulfur dioxide.
It is also an object to provide a batch process for dithionite production having high production per unit of reactor volume..
In accordance with the spirit and objectives of this invention, there is provided in a process for the production of anhydrous Na2S204 by introducing a~ueous sodium formate, a sulfur dioxide-methanol solution and a sodium compound into a reactor wherein, (a) the mekhanol-to water weight ratio is 4.2 to about 5.2; and (b) the S02-to-water weight ratio is 1.7 to about 2.4;
the improvement which comprises using sodium carbona-te as said sodium compound in the proportion of at least 50% by weight of said sodium formate, allowing reagen~s to react, and recovering said anhydrous Na2S20~. The sodium formate is dissolved preferably in water at about 120C and the sodium carbonate is preerably added as a dry powder to the recipient methanol so:Lutlon to wh.ich the SO2-methanol and a~ueous ormate solutions are :Eed. 'rhe methanol and the water are thus at a selected weight - 7a -ratio, and the water is the minimum amount required for dissol- I
ving the sodium formate at max:imum concentration and at elevated tempera~lre. The quarltities of s~llfur dioxide, methanol, so(li~l Eormate, watcl, nnd socliulll carbollate are pre~erably aclJusted so that the flxed reactor volume ;s Eully utilized.
Eacll tnetllalloL soLution Lncludes about 4% methyl formate. An add:itional amount of methanol is added to the reflux condenser to minimi~e loss oE methyl formate and other by-products. This additional amount is about 15% of the total methanol used.
The ratio oE methanol to water by weight is about 4.2 to 5.2.
The sulfur dioxide-to-methanol ratio on an equivalence basis is about 0.20 to 0.25. On a weight basis, the ratio of sulfur dioxide to water is about 1.7 to about 2.4. On an equivalence basis, the ratio oE sulfur dioxide to formate ion is about 1.4. On a weight basis, the sodium carbonate is about 60% Of the sodium formate; on an equivalence basis, the Na2CO3/HCOONa ratio is about 0.8.
On a sulfur dioxide basis, the yield is about 74-82~.
On a formate basis, the yield is about 53-59~. On a sodium basis, the yield is about 65-75%. On a basis of reactor volume, this process produces about 2.3 pounds per gallon and about 0.6 pounds per hour per gallon.
It was found that soda ash is at least 7% more e;fficient than caustic soda with respect to usage of Na2O in the process of this invention which is an improvement on U.S. Patent Number 3,887,695. Although the reaso~s are not ent`irely understood, it is thought that perhaps the very strong alkalinity of NaOH, which is preseDt when an lncremenL of the NaOh s~lution cont~cts , ~
?, ~ f the reaction medium and dissolves, results in the Eormation of some by-product, such as Na2SO3, wh:ich -is insoluble and largely unreactive. Soda ash, on tlle other hancl,ls not imn~ecl:Lately dLssolved wllen aclded ~nd thereEore tends to reLease its alka-LnLty at a slower rate.
I llowever,a comparative calculation of prior art results ! for Na20, on the basis of alkaline Na versus total Na added, can be mis:leacling for those examples (such as Example 4 in ' United States Patent 3,897,544) wherein no caustic soda is added, all sodium being supplied by sodium Eormate. The reason thereEor is that the process cannot be continued with recycled alcohol. To explain, the desired reaction requires one ! mol of formic acid and two mols oE bisulELte:
i !
I` HCOO}I + 2NaHSO3 - ~ Na~S204 -~ CO2 + 2H2 l' l When one adds S2 to sodium Eormate as :in Example 4 of United States Patent Number 3,897,544, one produces two mols of formic acid -Eor two mols of NaHSO3:
2 ~ 2S2 ~ 2HCooNa ~ ~ 2HCOOH + 2NaHSO3 The extra formic acid must react with excess methanol I to produce methyl formate. Otherwise, the excess formic acid il would cause the hydrosulfite to decompose. The problem occurs ~ when the methanol is recovered for the next ba~ch. It will now il contain much methyl formate, and could resul~.in a run with j severe decomposition if used according to Example 4 of United States 3,897,544 because of an excess o~- formic acid produced, which cannot be converted to methyl formate due to the latter already being present.
g The formulations in the examples given hereinafter, in wh.ich sodium formate is balanced with either NaOH or Na2CO3, are I based on the assumpti.on that -the methallol, containing methyl formate~, wi:l.l be .recoverecl.Erom a previous run so that the methyl 11l Eormate whl.ch iS added is nei-the:r consumed no.r produced. The ¦~ examples thus simulate normal commercial production i.n which the me-thyl alcohol is recycled ove.r and over.
In virgin batches such as the demonstrative examples of the prior art, in which caustic soda is used, methyl formate is no-t fed. Formate ion must consequently be supplied entirely from HCOONa, and NaO~ must be correspondingly reduced. ¦.
~ s a result of this, the recycle formulations in the ' following examples cannot be literally compared with the virgin formulations of the prior art examples. For this reason, comparisons are hereinafter made on a basis of total sodium use j even though the consumption of less total Na i.s less apparent because the sodium formate tends to l'dilutell the effect.
This process may be summarized as comprising the following steps:
(A) dissolving sodium formate in wa-ter at elevated temperatures and up to maximum concentra-tion -to form an aqueous I formate solution;
¦ (B) dissolving sulfur dioxide in methanol l (C) providing a recipient or puddle methanol solution 'I within a fixed reactor and adding there-to: ~.
1 (1) sodium carbonate,~preferably as a dry powder, according to a first specific schedule to provide at least a substantial proportion :; I
~?3~
of the alkali needed for the reaction, this sodium carbonate being at least 50% by weight oE the sod:ium Eormate when used as 100~ of th~ neecled alka:Li;
(2) the a~ueous formate solution according -to a second specific schedule, and (3) the SO2-methanol solution according to a third specific schedule in which about 80~ is added as a "fast" ~2 feed, the remainder as a "slow" SO2 feed at progressively slower addition rates. ¦~
As an improved soda ash embodiment, even better results are obtained by pre-reacting the sulfur dioxide with the sodium carbonate suspended in the methanol and -then adding the resultant slurry of sodium bisulfite in methanol along with the concentrated sodium formate solution to -the main reactor at a controlled rate. This embodiment produces sodium dithionite having acc~ptable particle size and dust properties and an assay that is a-t least as good as the product of the standard caus-tic process as disclosed in United States Patent 3,887,695 at a yield which is 22-25% greater than the yield of the standard caustic process while consuming about 3.0% less sulfur dioxide and about 8.6% less equivalent NaOH.
An addi-tional soda ash embodiment comprises slurrying sodium metabisulfite (representing the stoichi~metric reaction product of all of the soda ash with about half of the sulfur dioxide) with most of the methanol, and dissolving 60% of the other half of the SO2 in the methanol, and then adding this ll metabisulEite slurry to the main reactor along with the concentrated aqueous solu-tion of sodium formate. This second improvement produces sodium dlthionite with excellent par-ticle size alld clust properties at about 20~ improved yield as compared to tile standard caust,ic p.rocess according to U.S. Patent 3,897,544 while consuming about 5.4~ less equivalen-t sodium hydroxlde.
In contrast to prior art experimentation with Na2CO3, these results demonstrate that an opt:imum ratio of reactants and an optimum experimental procedure have been discovered for using sodium carbonate as the source of a substan-tial amount 1, of added alkali in the incremental reduction of sulfur dioxide with formate ion in aqueous methanolic solution.
The novel process of this invention is effective whether the alkali is in the form of sodium carbonatet sodium bicarbonate, sodium sulfite, sodium metabisulfite, or sodium hydroxide. However, i-t is particularly preferred to use sodium carbonate for a wide varie-ty of reasons including its relatively low cost.
DESCRIPTION OF THE INVENTION
Investigation of the feasibillty of substituting sodium carbonate for sodium hydroxide in a standardized process,as disclosed in ~nited States Patent Number 3,887,695 proceeded by making a direct substitution of an amount of Na2CO3 equivalent to the NaOH while maintaining the same amount o~ water, including .. .
:, .j il .
8~
the chemically bound water in the NaOH. Undesirable amounts of dust were obtained and the product was of lower purity. Next, `~ the amount oE soda ash was reduced, all other variables being llStallt. Th:l9 llllprOVed the purity of assay o~ the product and lowered the dust.
~¦ In one set oE experiments, clust was reduced from 350 to j 307 by adding 45 g. less Na2CO3 and was Eurther reduced to 215 by a five-minute delay in feeding the Na2CO3, but the most effective variab:Le for decreasing dust was found to be the SO2 "split" as shown by the following results for another set of experiments:
!
Split Dust Number Il , 82/18 196 l'l 83/17 1~7 The dustiness of production batches of sodium dithionite !
is checked with a colorimetric analytical method that uses a i !
rubine solution tomeasure the sodium dithionite dust in a sample., In this method, 0.0256 grams Na2S2O4 react with and decolorize 25 milliliters of rubine solution for determining the dust ratingl i of each production batch.
A dustometer apparatus is assembled for carrying out this¦
dust rating procedure. A carefully cleaned and dried elutriator tube, one inch in internal diameter and 34 inches in length and havillg a ball joint at each end thereof,~is mounted in upright position. A carefully cleaned and dried elutriator sample ''. ... I
l ~, ~ - 13 -., ~
~ 3~
~! contalner tube, one inch in internal diameter and 8 inches in j length, with a layer of g]ass wool ahout 1 inch thick packed j lnto the bottom tl~ereoE, :Ls connected :in ~Iprlght posltion to the l)ottotll o~ the elutriator tube. /~ nLtrogen source at 5-10 pslg Ls connectecl through a neeclle control valve and a rotameter to the bottom oE the sample container tube. A J-shaped lead-off tube of 4-5 mm internal diameter is connected in inverted 1l position to the upper ball joint of the elutriator tube, the ;I straight side oE the~J" extending to within one inch of the bottom of a 500 ml graduated cylinder containing 450 ml of water. A door bell buz~er is attached to the curved portion ~' of the "J" and connected through a variac to a source of power.
`~1 A 50 ml burette containing the rubine solution is mounted above the top oE the graduated cylinder.
To begin the test, a bottle containing a portion of a production batch is thoroughly mixed by gently rolling and ' tumbling the bottle (when the contents of the bottle are shaken, the dust cloud that settles on the top interferes with reproducibility oE the test). A 50+ 0.1 gram sample is removed 'I
from the bottle and carefully poured into the elutriator sample tube, care being exercised to prevent the loss oE dust during the transfer and a camel's hair brush being used to transfer all particles into the sample container tube.
i 3~0 m] of rubine solution are added to the water in the i graduated cylinder. The vibration is started and adjusted by ' ~
Il having the vibrator bar strikin'g'sharply agaiinst the underside 'l of the J-shaped lead-off tube in the proximate center of the 1~ arc. When the buz~er is operating properly and suitably controlled by the variac, the operator can feel the vibrations l4 _ ~3~
when he p:Laces a flnger on the tube about 3 or 4 inches from the point where the v:ibr~tor bar stril~es it. IE the apparatus is clamped too firmly, the vibrations are daml)ened and ineEEective Eor dislodgirlg the dust that settles out and witl~ the Iead-oEE tul)e.
Tlle neeclLe valve whicil controls tlle nitrogen Elow througll the elutriltor columll ls opened carefulLy and rapidly and ad~justed to a E:Low rate oE 0.09425 cubic Eeet per minute. lhis flow rate is held constant throughout ¦ the run. ~s SOOIl as the nitrogen flow into the bottoM oE the elutriator I column and through the sodium dithionite sample is high enough to form a ¦ dust cloud, a timer is started.
ll ~t the instant that the rubine solution is decolorized, another ,' few mi]li:Liters oE rubine solution are added. The number of milliliters of rubine solution are noted at one-minute interva]s. The elutriator running is continued for approximately 5 minutes (~ one-half minute~. ~le volume of rubine solution is determined to the nearest 0.1 milliliter, and the time is determ:ined to the nearest 0.1 minute.
The dust index or dust rating is calculated as follows:
Millilit rs oE rublne solution x 30 = dust number ` Elapsed minutes In general, S02 addition is d:ivided into two portions. The "fast"
S02, comprising 80-85% of the total, is fed during the first 80 minutes;
1~ "slow" S02, comprising the remainder, is fed during the second 80 minutes;
and the reaction is allowed to "cook", with no additional feed being added !l other than the "scrub" alcohol-to prevent loss of volatile reactants, during the third 80 minutes.
Next, the extra water and methanol associate~ with the use of ~aOH
are reduced, and, finally, the amounts of reactants are scaled up to utiliæe ¦
the full volume of the reactor and to obtain maximum productivity per unit f available volumetric capacity. The laboratory and pilot plant experimental data for Na2C03 are presented in Examples 2, 3, ~, 6 and 7 and compared with "
Examples 1 and 5 for NaOII and with 15 examples for NaOI-I and Na2C03 in the prior art.
., i ~l - 15 -31 ~ 3~
I Examples l-4 __ !
Data and results for Examples 1-4 are listed in Table III. Example 1 plesents the average Eor seven runs using caust-ic soda at 99% purity in a 73%
gol.ut:ion ancl llO socli~ carbonate, accol-ding to n stanclard laboratory procedure wltll Laboratory scale equLpment, using the process described in U.S. Patent Nutnber 3,887,695. Example 2 presents the results Eor all equivalent amount of ¦
sodillm carbonate and the same amount oE water as in Example 1. Example 3 gives results for a lesser quantity of sodium carbonte and the same amount of water as in Example 2. Example 4 presents results for a still lesser amount of sodiunl carbonate and decreased amounts of both water and methanol.
As a typical procedure, Example 2 was prepared according to the following detailed steps.
To a stirred reactor is added 851 g. of methanol plus 38 g. of methyl formate. This charge is heated to 70C and maintained under a pressure of 35 PSIG with nitrogen.
A mixture of 828 g. of 96% sodium fonnate is mixed with 727 g. water and heated to the boiling point. The mixture is transferred to a stainless steel cyclinder, which is jacketed with 70 psig steam to maintain the solution at about 300F. The level in the feeder is measured by a float to which is attached a metal rod which protrudes from the top of the cylinder into a sight glass. The sight glass is calibrated in millimeters, so that the volume in the feeder is known with a good degree of accuracy. The feed rate i5 con-trolled by reading the feeder level every millimeter and comparing this with the calculated value.
A mixture of 1702 g. methanol, 76 g. methyl formate and 1307 g. of sulfur dioxide is placed in another stainless steel c~iinder equipped with a sight glass and meter stick, which also enables the volume to be known with good accuracy. The feed rate of the mixture is controlled by a rotameter. I
Five hundred and fifty-seven grams of sodium carbonate are weighed I
, I
li il .
Ij TABLE III
`! I
Laboratory Scale Dithionite Preparations Fx_mple_No. 1 _ _ _ 2_ 3 4 I Nc~Oll~ g. 424 -- -- --~l2' g' l55 __ __ __ ¦ Ntl2CO3, g. ~~ 557 517 501 ¦ }ICOONa (96%), g.787 828 828 819 ¦ H2O, g. 455 727 727 595 CH30H, g. 1702 1702 1702 1206 }ICOOC}~3, g. 76 76 76 76 2' g' 1282 1307 1282 1263 C}13OH (puddle), g.851 851 851 851 }~COOCH3 (puddle), g. 38 38 38 38 HCOONa (puddle), g.41 -- __ __ ,~
!! H2O (p~lddle)~ g~ 22 ~~
,I CH30H (scrub), g.450 500 450 450 Na2 24' g' 1429 1462 1416 1432 Assay, % 90.9 89.8 91.6 90.9 P~lre Na2S24' g- 1299 1313 1297 1301 Dust No. 175 453 97 238 Total Na equivalents 22.775 22.341 21.931 21.496 Total formate equivalents14.07314.073 14.073 13.94 Total SO2 equivalents 20.012 20.401 20.012 19.716 Total CH30H equivalents95-625 97.210 95-625 80.144 '`
* 99% purity, .
'l 73% solution l i l .
. ' .
, I
in-to five beakers of 100 g. each plus one beaker of 57 g. 'lhe feeding mechan-ism for soda ash consis-ts of two valves and a s~all hopper. m e hopper easily holds 100 g. The space be~ween the valve holds 11.1 g. Since 557 g. are to be :E~cl ove..r 79 nLinutes, 7.05 g. should be :Eed per nLirlute. At 11.1 g. per dump, the vaLve ~system shou1d be operated over every 1.57 minutes. A bleed of nitro-gen is l~l.intcain~-~d at the soda ash lnlet to prevent condensation from the reac--tion plugging -the inlet. (In later experiments, the nikro~en bleed was omitted, and the valve and :Eittings heated with electrical tape to prevent condensa-tion.) With the reactor contents at 70C, the SO2-methanol feed is started. !
~, After the SO2 concentration in the pot has reached 1~ (by calculation), the I timer is started and the feeds of sodium fornk~te solution and solid soda ash begun. Five percen-t of the sodium forma-te solution is fed in the first minute,~
and the rel~aining 95% fed over 79 minutes. The soda ash is fed over 79 minutes as a "fast SO2" feed rate. Eigh-ty-one percent o:E the SO2-methanol is fed over 80 minutes, and the remaining 19% fed over the :Eollowing 80 minutes at , progressively slower rates. At the end of 80 minu-tes, the SO2-methanol feed rate is reduced to a~lt 1/3 that of the fast So2 feed ra-te, and this flow rate is maintained for 20 minutes. The rate is then reduced to 26% of the fast SO2 feed rate for another 15 minutes and finally to 17% of the fast rate until the SO2-methanol solution runs out, which is generally at 160 minutes.
I The reaction temperature, which is at 70C a-t the start, is allowed I to reach 83C af-ter about 5 minutes. A -te~perature of 83C is ma~ntained thereafter until the end of the run.
~; After the slow S02 feed is finished.(at about 160 minutes), the n m is allowed to "cook" for another 80 minutes, or until a total of 240 minutes of run time. -During the entire run, a feed of 500 g. of methanol is fed to the scrubber to lessen the loss of volatile reac-tan-ts such as methyl formate and so2~
3~
., , Samp].es are taken o:E tlle react:i.on E:i:~trate a:Eter tlle East S2 Eeed , (80 ll~i.nutes), aftcr tlle. ~]ow S02 :Eeed ~:l(iO minlltes), antl at the end oE the runj (2~0 ml.llutes). A t(~l~ m:l. snmplt-~ is mlxed w:Ltll cln a:LIcal.:lne Eormaldeilydc solutioj (to tle Up b.isu:l.E:ite) and ls then titratecl w:itl~ 0.]. N stan(lard iod:ide solut:ion.l Th:is "tL.ter" is a measure o.E the sodium tl~iosulate content o:E the solution anq :i.s ti~ere:fore an indication oE the extent of decomposition of hydrosulfite.
The contents of the reactor are filtered through a glass-fritted Buchner funnel, maintaining an atmosphere of nitrogell above the product to prevent contact witll air. The product is washed with methanol and dried in a I vacuum :flask, under vacuum while heated in a hot water bath. The dried productj " is weighed to determ:ine the y:Lel.d, assayed Eor hydrosulfite purity, and a dust l number :is run plus a screen ana:Lys:is.
Examples 5-7 i Data and results Eor Examples 5-7 are listed in Table IV which shows¦
~, pilot plant results for a standard run using sodium hydroxi.de and for two runs ¦
using sodium carbonate. The reactor i.s equipped and operated as described in U.S. Patent Number 3~887,695. The sodium carbonate is 63% by weight of the ~i sodium formate. In Example 6, the amount of methanol is the same as in Example 5, but the amount o.E water that is present has been slightly increased. In Example 7, the amount of water has been reduced by 25% and the amount of metha-¦
nol has been reduced by 20% with respect to Example 6.
Comparative Ratios and Productivity Cal.culation for Labora-tory and Pilot Plant Examples and for Prior Art Examples In Tables V(a), V(b~, calculated ratios, based on equivalence values in Tables I-IV, and calculated yields, based on S02, fo~mate ion, and sodium ;' ion, are also given for both experimental runs and prior art examples. Finally, . calculated productivity in terms of reactor volume as pounds per hour per gallon are listed for one example and for each of the four prior art patents.
In general, productivity increased 18% by laboratory data and 20% by pilot plant data.
I, .
!
~3~ 38 ,j , T~!BLE IV
_lL~t P:Lant l)Ltl!:lollite _re~_r tions !~ N~ 5 _ 6 _ _ 7 ¦I Na()ll, parts 7l Na2C03, parts -- 83 83 ! U20, parts 98 116 87 i HCOONa, parts 138 138 138 CH30H, parts 50l 501 400 IICOOCH3, parts 18 18 18 I S02, parts 211.2 205.2 205.2 Na2S20~ (gross basis) 246 239 247.5 Na2S204 (100% basis) 226 222 228.7 Assay, % 92 92.7 92.4 Dust No. 100 206 102 Total Reaction Tilr.e, Mrs.4.0 4.0 4.0 Il Prodllctivity, pounds/gal.2.26 2.26 2.70 i, Total Na equivalents 3-704 3.514 3.514 Total formate equivalents 2.247 2.247 2.247 Total S02 equivalents 3.30 3.206 3.206 Total CH30H equivalents 15.937 15.937 12.784 '.1 .. ,' ,,~'. I
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, ' i It is clear that, in terms of sodium equivalence per S02 equivalence, there is a slight diEference between the two sodium hydrox:icle examples (1 and 5), the three sodLum carbonate examples (4, 6, ancl 7), ancl the four prlor art patents. ~mployment o~
socla asll enable6 use oF 3% less total soclLum ecluivalent/S02 etlulvaLellts over the best results In the prior art. Although the laboratory and pilot plant examples, using either sodium hydroxide or sodium carbonate, utilize a h:igher weight ratio of methanol to water than the four prior art examples, the five sodium carbonate ratios are somewhat lower than the two sodium hydroxide ratios among the laboratory and pilot plant examples.
As to the weight ratio of sulfur dioxide to water, the laboratory and pilot plant examples possess higher values than three of the four prior art patents. As to the equivalenct-! ratio of sulfur dioxlde to formate, the laboratory and pilot plant examples have distinctly higher values relative to prior art, for both sodium hydroxide and sodium carbonate.
It is on a yield basis and on a process productivity basis that the invention is most striking. In the laboratory series, substituting sodium carbonate for sodium hydroxide in Example 4 compared to Example 1 increased the efficiency of the process when based on all three raw materials. The productivity, as measured by the pounds of product prepared per hour per gallon of reaction solution, is also increased by the substitution. A
similar increase in process efficiencies and productivity is observed in Example 7 vs. Example 5 ln the pilot plant.
."' '''' , ', .
!
~3~
.1 i Tlle.se results are belleved to be noteworthy in view of the h:Lgh assay and low dust numbers for tile products of Examples 6 ancl i, as given in 'rable :tV, which are high:Ly useful as in- ¦
! dustriaJ bleaching agents.
~ dditional pilot plan~ results are presented in Table VI for a standard run with caustic soda and for two runs with soda ash in which the Na2CO3 is 62.9% by weight of the HCCOONa.
" Signif:icantly improved productivities, measured as pounds of 'I pure Na2S204 per gallon of reactor volume, were obtained in Examples 9 and :LO. Even though the amount of water which was used for dissolving the increased amount of sodium formate was s1ightly greater than the total amount of water used in Example 8 with the NaOH and with the ~ICOONa, the substitution of Na2CO3 for NaOH enabled the methanol to be reduced even though additional sulEur dioxide was used. Because of the relatively low density of methanol, this reduction saves considerable valuable space in a reactor.
In general, use of sodium carbonate as the principle source of supply for alkali in the process of this invention, as demonstrated in Examples -8-l0, enables less solvent and larger quantities of reactants to be used in a reactor so that pro-ductivity is significantly increased as compa~ed with the world-wide standard productivities obtained with sodium hydroxide as the principle souce of supply for al~ali. Less total sodium is thus required when soda ash is employed.
, ~3 ,i ¦ TABLE VI
Pi ot E'l~nt_DItllion te _repa ations ~I Example_~N,_Il_),er ,"__,_ 8,,_ __,, ,,,,_,_9_ _, 10 Na2(`O~, Ib ~ed -- L00 100 ¦ NaOll, :Ib ~ecl~ 70 UCOUNa, lb ed ** 132.5 159 159 ~! SO2, lb Eed 211.2 243.2 243.2 CH30H, lb fed 501 483 483 (Initial Puddle) (142) (164) (164) (With SO2) (284) (244) (244) ,, (Scrub) (75) (75) (75) il2O, lb fed 100 104 104 (With NaOU) (26) __ __ (With HCOONa) (74) (104) (104) ¦ HCOOCU3 18 ]6 16 ', Total Vol., gal 100 100 100 Filtrate Vo]., gal 87 84 84 ~', Product, lb 247 302 296 ,I roduct, % Na2S2O4 91.5 90.3 90.3 Pure Na2S24' lb 226 273 267 Productivity, ],b/gal 2.26 2.73 2.67 Yield: S02 Basis 78.7 82.5 80.8 Formate Basis - 66.6 67.0 65.7 Sodium Basis 70.2 74.2 72.7 Il Productivity (lb/gal/hr) 0.57 0.~68 0.68 ,l * 100% pure '~
I ** 100% pure , " - 25 -.,, ~.
1, !
. .
3~
lthough t-he Examples which follow are direc-ted towards -the use oE soda ash as a solid, i-t is to be underst-ood that this invention encompasses the addition oE water to soda ash witli a correspondln~ r~duction of water in other Eee~d streams. ~le lcey to the inventive contribution resicles in:
~(a) the-total water add~d to the reactor ancl (b) maintainill~ the met~lculol-to-water ratios previously set forth and not necessarily in the amowlt of water in an individual feed stream. I
Exarnple 11 This example illustrates the pre-reaction oE sodium carbonate and sulfur dioxide to Eorm a feed material.
Three separate feeds were prepared. Feed "A" was made by suspending ~83 parts by weight of sodium carbonate in 167 parts of methyl alcohol containing 9 parts methyl forma-te, and adding to the suspension 167 parts ~lof sulEur dioxide. Feed "B" was l~ade by dissolving 131 parts of sodium forrnate of approx~nately 96% purity in 93 parts water. Feed "C" was made by dissolving 35 parts sulfur dioxide in 35 parts methyl alcohol containing 2 parts methyl form~-te.
An ini-tial charge consisting of 115 parts methyl alcohol containing 6 parts methyl fonnate was placed in the reactor. m is charge was agi-tated ,land heated ~o a temperature of 65C and at a pressure of 20 psig. Then ,Feed "A" and Feed "B" were started simultaneously and at such a rate that the specified cruantity of each would be fed to the reactor in an 80-minute period.
Heating of the reactor contents continued untll a temperature of 83C was reached, at which time the heat was reduced -to main-tain a controlled reaction temperature of 83C. me time period fran 65 to 83 was approxirnately 10 minutes. Also after this sarne 10 minutës, the reactor pressure had reached 50 psig owing to the release of carbon dioxide gas frcm the reaction. me I
:
&~i , reaction pressure was theîeafter m~intained at 50 psig by controlled release of the carbon dioxide fon~d in -the reaction. m e released yas let the reac-tor thro~,~Jh Eirst a water-coo:led condenser (35C) Eollowed by a chilled ¦ conclens,_~ 10C), ~llen a chilled scrubbf~r Eed with lllethyl alcohol at a rate oE 0~26 parts per nuinute. The c~ndensate Erf~m the two condensers plus the effluent scrubber methanol bo-th re-entered the reactor.
~ -t the end oE the 80 minute period o eeding Feed "A" and Eeed "B"; ¦
Feed "C" was s-tartecl at a rate of 1.5 parts per minu-te~ The rate was reduced to 1.0 parts per minute after 15 minutes, and further reduced to 0.7 parts per minute after another 15 minutes~ The entire 72 parts o:E Feed "C" was consumed in 80 minutes. During this time, -the temperature and pressure within ¦
the reactor were maintained a-t 83C and 50 psig, respectively.
' rl~hese same conditions were maintained for an adclitional 70-minute i~ period af-ter the ca~,pletion of Feed "C". At this time, 230 minutes r,am the begir~ing in all, the reactor cantents were cool~ed to 60C and filtered. Then the filter cake was washed with 240 parts me-thyl alcohol, dried under vacuum ~I to yield a crystalline prc,duct of 240.5 parts by weight and 92.3% assay as sodium hydrosulfite.
E~ample 12 This example illustrates the use o sodium metcbisulEite as a eed mat,erial.
Again, three separa-te Eeeds were prepared. Feed "A" was made by , suspending 150 parts of sodi~n metabisulfite in 167 parts o methyl alcohol ; containing 9 parts of me-thyl formate, and adding to the suspension 67 parts of ¦
sulur dioxide. Feed "s" and Feed "C'! were ldentical ~o those described in I Example 11. ``` `
.1 .
, The feed schedules, reac-tion condi-tions, and -total reac-tion time were exactLy as described in Exc~mple 11. AEter Eiltering, washing, and dryincJ as in E`xample :Ll, a crystall:ine procluct of 238 ~ ~s by weight and ~ l.0% assay as sodi~ml hydroslllfite was obta.ined.
;1 As has heretofo2.e be~l stated, the novel process of this invention . results in increasecl productivity for a given reaction vessel per unit of time. r~lis increased productivity results f.rom the fac-t that it is possible, using the teachings of this invention, to utiliæe more of the reactor volume Eor the production of sodium dithionite than has heretofore been possible.
The inventive concept disclosed herein involves the use of less , wa-ter which in turn permits one to use less methanol while still keeping the proper range oE water to methanol in the reactor. By the use o:E less methanol,¦
there is more room in the reactor so that more product can be produced per batch. rlhe instan-t inventive concept embraces many alka.lis but sodium carbonate is preferred.
Because it will be readily apparent to those skilled in the I art that innumerable variations, modifications, applications, and extensions `; of the examples rmd principles hereinbefore set forth can be made without departing from the spirit and scope of the invention, what is herein defined as such scope and is desired to be protected should be measured, and the inv nt on should b limlt d, on y by t e following clalms.
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Claims (24)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a process for the production of anhydrous Na2S2O4 by introducing aqueous sodium formate, a sulfur dioxide-methanol solution and a sodium compound into n reactor wherein, (a) the methanol-to-water weight ratio is 4.2 to about 5.2; and (b) the SO2-to-water weight ratio is 1.7 to about 2.4;
the improvement which comprises using sodium carbonate as said sodium compound in the proportion of at least 50% by weight of said sodium formate, allowing reagents to react, and recovering said anhydrous Na2S2O4.
the improvement which comprises using sodium carbonate as said sodium compound in the proportion of at least 50% by weight of said sodium formate, allowing reagents to react, and recovering said anhydrous Na2S2O4.
2. The process of claim 1, wherein said anhydrous Na2S2O4 is prepared within a fixed reactor volume, said methanol to said water having a weight ratio of 4.2 to about 5.2 and said sulfur dioxide and said water having a weight ratio of 1.7 to about 2.4, to impart improved productivity, as measured in yield weight of said sodium dithionite per hour per gallon, and less usage of sodium, comprising:
(a) pre-reacting said sodium carbonate with a portion of said sulfur dioxide while suspending said sodium carbonate in a portion of said methanol to form a slurry, and then adding said slurry directly to the reactor;
(b) using said water substantially only for dissolving said sodium formate;
(c) using a minimum amount of said methanol while maintaining said methanol:water weight ratio of 4.2 to about 5.2; and (d) adjusting quantities of said sulfur dioxide, said methanol, said sodium formate, said water, and said sodium carbonate so that said fixed reactor volume is fully utilized.
(a) pre-reacting said sodium carbonate with a portion of said sulfur dioxide while suspending said sodium carbonate in a portion of said methanol to form a slurry, and then adding said slurry directly to the reactor;
(b) using said water substantially only for dissolving said sodium formate;
(c) using a minimum amount of said methanol while maintaining said methanol:water weight ratio of 4.2 to about 5.2; and (d) adjusting quantities of said sulfur dioxide, said methanol, said sodium formate, said water, and said sodium carbonate so that said fixed reactor volume is fully utilized.
3. The improvement of claim 2, wherein a first portion of said minimum amount of said CH3OH is used for dissolving said SO2 to form an SO2-methanol solution.
4. The improvement of claim 3, wherein said first portion of said minimum amount of CH3OH in which said SO2 is dissolved to form said SO2-methanol solution is approximately 50% of said minimum amount of CH3OH.
5. The improvement of claim 4, wherein the weight ratio of said SO2 to said first portion of said minimum amount of CH3OH in said SO2-methanol solution is approximately 1:1.
6. The improvement of claim 5, wherein said methanol in said SO2-methanol solution contains a first amount of HCOOCH3.
7. The improvement of claim 6, wherein a second portion of said minimum amount of CH3OH, containing a second amount of HCOOCH3, forms a puddle solution which is held at about 70°F to receive and be admixed with said aqueous solution, said SO2-methanol solution, and said Na2CO3 as dry powder.
8. The improvement of claim 7, wherein said second portion of said minimum amount of CH3OH in said puddle solution is approximately 34% of said minimum amount of CH3OH.
9. The improvement of claim 8, wherein approximately 2.7 pounds of said Na2S2O4 are produced per gallon of said minimum amount of CH3OH.
10. The improvement of claim 9, wherein said Na2S2O4 is produced as pure product at at least 2.6 pounds per gallon of said fixed reactor volume.
11. The improvement of claim 2 wherein said Na2CO3 is pre-reacted, externally of said fixed reactor volume, with a portion of said SO2.
12. The improvement of claim 11 wherein said Na2CO3 and said portion of said SO2 are admixed with a portion of said CH3OH to form a bisulfite-methanol slurry which is fed to said fixed reactor volume along with the aqueous formate solution.
13. The improvement of claim 12 wherein the remaining portion of said SO2 is dissolved in the remaining portion of said CH3OH to form an SO2-methanol solution which is added to said fixed reactor volume.
14. The improvement of claim 13 wherein said remaining portion of said SO2 is about 20% of said SO2.
15. The process of claim 1 wherein the sulfur dioxide-methanol solution contains methyl formate.
16. The process of claim 15 wherein methyl alcohol and methyl formate are placed into said reactor prior to introducing said sulfur dioxide-methanol solution, said aqueous sodium formate and said sodium carbonate.
17. The process of claim 16 wherein the ratio of the equivalents of SO2 to the equivalents of formate is about 1.4.
18. The process of claim 16 wherein said sodium carbonate is added directly to the reactor as a dry powder.
19. The process of claim 16 wherein said sodium carbonate is pre-reacted with a portion of said sulfur dioxide-methanol solution to form a slurry which is added to said reactor.
20. The process of claim 19 wherein said slurry is formed by pre-reacting said sodium carbonate with a portion of said sulfur dioxide-methanol solution to form sodium metabisulfite in said methanol.
21. The process of claim 19 wherein said slurry is formed by pre-reacting said sodium carbonate with a portion of said sulfur dioxide-methanol solution and with water to form sodium bisulfite in said methanol.
22. The process of claim 19 wherein the addition of said slurry takes place during approximately the first 1/3 of the time required for said reaction to produce said anhydrous alkali metal dithionite.
23. The process of claim 19 wherein the addition of said aqueous sodium formate solution takes place approximately simultaneously with the addition of said slurry to said reactor.
24. The process of claim 19 wherein 80-85% by weight of said sulfur dioxide-methanol solution is pre-reacted with sodium carbonate and wherein the remaining 15-20% is introduced within the second 1/3 of the total reaction time.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US69946276A | 1976-06-24 | 1976-06-24 | |
| US80652777A | 1977-06-14 | 1977-06-14 | |
| US806,527 | 1977-06-14 | ||
| US699,462 | 1985-02-07 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1103888A true CA1103888A (en) | 1981-06-30 |
Family
ID=27106430
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA280,843A Expired CA1103888A (en) | 1976-06-24 | 1977-06-17 | Production of sodium dithionite from sulfur dioxide, sodium formate and sodium carbonate with minimum solvent |
Country Status (9)
| Country | Link |
|---|---|
| JP (1) | JPS6020321B2 (en) |
| CA (1) | CA1103888A (en) |
| DE (1) | DE2728316B2 (en) |
| FR (1) | FR2355775A1 (en) |
| GB (1) | GB1584626A (en) |
| IT (1) | IT1143585B (en) |
| MX (1) | MX147264A (en) |
| NO (1) | NO149884C (en) |
| SE (1) | SE418490B (en) |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3411875A (en) * | 1964-04-08 | 1968-11-19 | Mitsubishi Edogawa Kagaku Kk | Process for the production of anhydrous hydrosulfites |
| DE1592013B2 (en) * | 1966-05-16 | 1972-08-24 | Mitsubishi Edogawa Kagaku K K , Tokio | PROCESS FOR THE MANUFACTURING OF A WATER-FREE SODIUM HYPOSULPHITE |
| JPS4814316B1 (en) * | 1969-01-10 | 1973-05-07 | ||
| US3887695A (en) * | 1970-02-05 | 1975-06-03 | Virginia Chemicals Inc | Production of sodium hydrosulfite from formates |
| GB1461785A (en) * | 1973-03-30 | 1977-01-19 | Boc Ltd | Alkali metal dithionite manufacture |
-
1977
- 1977-06-17 CA CA280,843A patent/CA1103888A/en not_active Expired
- 1977-06-20 NO NO77772165A patent/NO149884C/en unknown
- 1977-06-21 GB GB25816/77A patent/GB1584626A/en not_active Expired
- 1977-06-22 SE SE7707235A patent/SE418490B/en not_active IP Right Cessation
- 1977-06-23 FR FR7719337A patent/FR2355775A1/en active Granted
- 1977-06-23 IT IT49962/77A patent/IT1143585B/en active
- 1977-06-23 DE DE2728316A patent/DE2728316B2/en active Granted
- 1977-06-24 MX MX169610A patent/MX147264A/en unknown
- 1977-06-24 JP JP52075360A patent/JPS6020321B2/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| SE7707235L (en) | 1977-12-25 |
| GB1584626A (en) | 1981-02-18 |
| DE2728316C3 (en) | 1990-08-23 |
| FR2355775B1 (en) | 1984-04-13 |
| JPS6020321B2 (en) | 1985-05-21 |
| FR2355775A1 (en) | 1978-01-20 |
| NO772165L (en) | 1977-12-28 |
| JPS5316388A (en) | 1978-02-15 |
| NO149884B (en) | 1984-04-02 |
| DE2728316B2 (en) | 1980-10-23 |
| SE418490B (en) | 1981-06-09 |
| IT1143585B (en) | 1986-10-22 |
| NO149884C (en) | 1984-07-11 |
| MX147264A (en) | 1982-10-29 |
| DE2728316A1 (en) | 1978-01-05 |
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