DE1946823C - Process for stabilizing aqueous solutions of acrylic or methacrylic esters - Google Patents

Description

prevent. This is attributed to the influence of iron ions. which immigrate into the aqueous solutions, hierte aqueous methanol solution is carried out, which could also be confirmed by experiments. 60 is also the case that an aqueous solution,

If a liquid reaction mixture containing methyl methacrylate has been treated,
that in the production of methyl methacrylate by It is known that the bottom residue of the liquid

Esterification was incurred, distilled in a glass apparatus, reaction mixture from the esterification to Rückso, no significant polymerization was obtained in the distillate of the remaining methanol that was observed in the Verdes ester. BeIn ₁ addition of iron (III) - 65 esterification reaction is recycled, a water sulfate to the aqueous phase of the distillate is subjected to polymerized steam distillation. This, however, earths the ester immediately. The distillate held is also an aqueous solution. The invention is based on the finding that it contains methyl methacrylate.

Methvlacrylat is produced, for example, in such a way that SiI it Shflä Alid tt

For example, acrylate is produced in such a way that, however, 0.01 percent by weight of hydroquinone was used reacted with sulfuric acid to acrylamide and 0.02 percent by weight Natnumhexametaphos ^ at added with the addition of methanol and water. The aqueous phase of the Dotdfatfs pcrty iS id ie ifh Dül didn't merize, even when she was more ώ «« «« *

5 left to stand at 25 ° C. .It f "J ^ JJJ polymerization place when the waßnge 6hrs phase was maintained at 70 ⁰ C.

Example 2

The esterification according to ^^} ^ was dangerous

Steam distillation with superheated ^ f3? SL £ 130 ⁰ C distilled off. In this ^
Stainless steel sator

_au f _be safeguards or storage box. rt

he addition of methanol and water The iSter is made by simple distillation. In this case too, the distillate separates into an ester phase and an aqueous one phase in a condenser or decanter and both phases exist together.

In almost all of the cases mentioned, polymerization occurs immediately or after a few hours ? “Fif a common or stainless steel than Matter "is used for the devices and When a polymerization inhibitor is added on its own

Sd whereby a slurry or a gel _{generator of rustproof polymer forms that the device parts x 5} hydroquinone monomet ^ lather in each s, opfiE and a smooth operation makes impossible. . 0.01 ^ ^ch ^ ^oz lf ^ ^Z ^^ Se Polymerization is particularly pronounced, set. ^ R'ewaßngeP ^ edsp if a normal steel or a high temperature immediately una wn at 25 C in the Koifc.ensator

become dt. If apart from a polymer vessel. . use

inhibitor, however, a erfmdungsgemäßer additional _N, the experiment was re ^ he n Jerwendung -Jet is / polymerization -n cases mentioned can be completely the same capacitor, wherein goch "IM UE can be suppressed. This weight percent hydroquinone and _W! attributable _T fact that the additives used according to the invention apparently corroded the waunge ™ · «* filing with the formation of a complex compound a ₅ if they act for a month ^^ and thus the disadvantageous influence of iron 6 hours 7C C. Suppress ioria and the development of the effect Example 3

_d allow polymerization inhibitor. Esterification obtained according to Example 1,

If the additives used according to the invention das aus; en «Gefiterungg ^ ^ ^^

be used alone, they can polymerisation containing 30 hydroquinone "" rr α _laundri ßrigen

Don't prevent it. They must therefore in combination ^ J? XS hJHSn oSo36 g Eisend Nanon 11) -suL with a Polymensat.onsinhibitor used phase of the least ''^'s ^ ^u ™ ^e' f _{occurred immediately} Ic to. The Polymen- J used in the invention ^ KVIS aqueous phase san-.msinhibitor can be an inhibitor for d, eradikal.sche a [? ° * ™ 1 ^ q _{2 g of} sodium hexametaphosphate to polymerization, such as hydroquinone, hydroquinone mono- 35 however ^ rJ, 0Ig ^ wai _{isation instead} ,

Nuthyläther, Pyrogallol or Resorcm ^ which were set found to _{stand for} ζ month.

M d plitihibitors even if the waunge

relaxed »w» «^ _{then kejne Po} , _yme risation instead,

ver containing solution, ...,. . ", -" "- n place of sodium hexametophosphate sodium

me additional compounds and the polymerization 40 ^if _r f ⁿ _t ™ _p ^v _n ° "'; _{orden war} inhibitors can either be used individually or in a umsilicate. any combination of two or more cones ρ ie 1 4

indications can be used. _{The esterification product} obtained in Example 1

The invention is not only ^{distilled to aqueous solutions 1} ^ f KSi The soil residue was

of methyl methacrylate or methyl acrylate, but 45 ^ "" ^ Snsato'r i «s stainless steel one also applies to other esters of methacrylic acid and the over a £ ™ j £ ^r _{underwoifenf with} 0.01 Ge acrylic acid applicable and to the trap in which WasKrdamptaes «1 ^ ^ p ^, ^

d, cse Fster together with an upstream phase wäßngen f ^^^ ^^ _least illat polymerized immediately

i ^^ B ^ enrü ^ a ^ s

Nuthyläther, Pyrogallol or Resorcm ^ D The optimum amount of the polymerization inhibitor is 0.1 to 0.05 percent by weight, based on the containing solution

Invention is illustrated by the examples. ₅ o at J ^ B ^ i ^^^^

Addition of 0.01 percent by weight of resorcinol and B ρ ice ie 1 1 _{0 05 wt} i _c htsprozent sodium tripolyphosphate sawn

the a _US 1 Mon, Ace.on-

^IS

water added to the esterification. The esterhaltige product was distilled at 100 ⁰ C of a capacitor made of stainless steel, while hydroquinone was added in an amount of 0.03 percent by weight, based on the distillate, is added. The distillate separated into an ester phase and a water phase. The aqueous phase polymerized immediately at 25 ° C in the condenser and in a Dekantiergefaß _ and übetrug polymerization on ester 6 _S

would.

Example 5

DJ same esterification was repeated under Using the same capacitor. To the distillate

_{ß M} ■, _{χ obtained} e esterification product The ß ^e ^ ¹⁵ f ^e _e 7 _G , _acondenser distilled, where ^ ^β pyrogallol, based on the

_urde ^y _n . ^g _The crude Esterphase of, _{cozy Vo} i _{umen wate} r

^ _extraction device off ^ ^ _{after 5 hours}

£ 0

Dest y at
Des ^^, Hats
extracted, wöbe.

Methanol solution.

If, on the other hand, the crude ester phase was used in the same extraction device with an equal amount of water extracted with a content of 0.01 percent by weight sodium hexametaphosphate, no polymerization took place instead, even if the extraction has been carried out for more than 6 months. Even when in use of hydroquinone as a polymerization inhibitor Instead of pyrogallol, it was possible to continue working for more than 6 months without polymerization. Also at Use of sodium tetrapolyphosphate instead of sodium hexametaphosphate did not result in any polymerization instead of

Example 6

»5

Fs was an aqueous solution obtained by extracting crude methyl methacrylate with methanol-water using a countercurrent glass extractor with the addition of 0.03 percent by weight Hydroquinone had been obtained in a stainless steel still to remove Distilled methanol. The dissolved methyl methacrylate polymerized immediately in the preheater and in the still, which caused considerable difficulties.

In the distillation of the same aqueous methanol as solution with the addition of 0.03 percent by weight sodium tripolyphosphate no polymerization took place even when the process was continued for 6 months would. The same result was obtained when using potassium hexametaphosphate in place obtained from sodium tripolyphosphate.

Example 7

There were 2MoI acrylonitrile at 100 ⁰ C hydrolyzes 1 hour by the addition of 3 MoI of 85% sulfuric acid and 0.5 g of copper powder. The temperature was raised to 140 to 150 ⁰ C. The hydrolyzate was esterified by adding 6 moles of methanol and 9 moles of water. The esterification product was then distilled through a stainless steel condenser while 0.01 weight percent hydroquinone, based on the distillate, was added. The aqueous phase of the crude ester distillate polymerized immediately.

In contrast, when the esterification is distilled with the same capacitor, but 0.01 weight percent hydroquinone and 0.05 weight percent sodium silicate is added, based on the distillate, the aqueous phase then unpolymerized of the crude ester even when more than one _Mon:; (stopped. The same result was obtained when potassium silicate was used.

Example 8

An aqueous solution containing 4 percent by weight of pure methyl acrylate and the additives mentioned in Table I is placed in a test tube which is sealed. The content is Warming to 8O ⁰ C and determines the light-off time. The light-off time; ϊ defines the time that elapses before the beginning of the polymerization process to become cloudy. \ X, c results are shown in Table I.

Table I.

attempt
No. Polymerization inhibitor Amount added
ppm Light-off time
Minutes 1
2
3
4th Blind test
Hydroquinone
Sodium hexametaphosphate
Hydroquinone
and sodium hexametaphosphate 5000
5000
250
250 20th
60
120
j> 480

Example 9

An aqueous solution containing 5 percent by weight ethyl methacrylate, the inhibitor listed in Table II, and a piece of heat-treated stainless steel as a polymerization promoter is placed in a test tube which is sealed. The contents are ^{heated to 70 °} C. and the light-off time is determined. The results are compiled in tables.

Table II

Attempt-
No. Polymerization inhibitor Amount added
ppm Light-off time
Minutes 1
2
3 Hydroquinone monomethyl ether
Hydroquinone monomelhyl ether
(NaPO ₃ ),
Hydroquinone monomethyl ether
Na ₂ SiO ₃ 300
100
100
100
100 <1
}> 240
j> 240

Example 10 with their effect on polymerization inhibitors

Inhibitor mixtures which contain a component used according to the invention, Example 9 was repeated instead of ethyl 65, as well as with the invention

However, methyl methacrylate was used. The polymerization temperature was 80 ° C. The known ones listed in Table III were used used inhibitor mixtures compared. The surprising inhibitory effect is from Table IU evident.

1 946 823 \
7 ^ Amount added
ppm 8th Light-off time
Minutes Table III 200 8th Attempt-
No. Polymerization inhibitor ι 2-mercapto-5- (3 ', 4', 5'-trioxypheayl) - 200 3 1,3,4-oxadiazole 200 5 2 Semicarbazide 200 5 3 Acetone thiosemicarbazone 4th 7,8-dihydrodinaphth- 200 5 (l, 2-b: 2 \ l'-f) -azepine 200 <1 5 2,2'-dioxybenzalazine 200 <1 6th Butyl hydroxyanisole 200 <1 7th Dibutyl hydroxytoluene 100 \ 10 δ Hydroquinone monomethyl ether 100 J 10 9 Hydroquinone monomethyl ether 100 \ ₁₀ Citric acid 100 J ¹⁰ '10 Thiodipropionic acid 100 Hydroquinone monomethyl ether 100 11th Hydroquinone monomethyl ether 100
100 \ > 240 (NaPO ₃ ) e 100 12th Hydroquinone monomethyl ether
Na ₅₁ SiO ₃ 100 J> ²⁴⁰ 13th Hydroquinone monomethyl ether 100 Sodium pyrophosphate 100 J ^> 14th Hydroquinone monomethyl ether Sodium tetrametaphosphate

Claims (1)

adverse effect of iron ions does not occur Patent claim and, moreover, the polymerization of acrylic and Methacrylic acid esters are successfully suppressed A process for stabilizing aqueous solutions can be used if the aqueous solutions, in addition to one of the polymerization inhibitors mentioned of acrylic acid or methacrylic acid esters with 5, also certain hydroquinone, hydroquinone monomethyl, other compounds are added,
Rogallol and / or resorcinol as a polymerization object of the invention is thus a process inhibitors and synergistic substances, to stabilize aqueous solutions of acrylic acid by means of the fact that the or methacrylic acid esters with hydroquinone hydro solution in addition to the polymerization inhibitor as xo quinone monomethyl ether, pyrogallol and / or resorcinol synergistic substances 0.01 to 0.05 weight as Polymerization inhibitors and synergistic percentages, based on the substances containing the ester, which is characterized. that solution, sodium pyrophosphate, sodium tripoly- man of the solution apart from the polymensaöonsinhibitor phosphate, potassium tripolyphosphate, sodium tetra- as synergistic substances 0.01 to 0.05 polyphosphate, sodium tetrametaphosphate, sodium 15 percent by weight, based on the solution containing the ester hexametaphosphate phosphate , Sodium pyrophosphate, sodium polyphos sodium silicate and / or potassium silicate added. phate, potassium tripolyphosphate, sodium tetrapolyphosphate phate, sodium tetrametaphosphate, sodium hexametaphosphate, Potassium hexametaphosphate, sodium silicate 20 and / or potassium silicate added. "Aqueous solutions" mean water here Understood systems in which phases of the ester are present together with an aqueous phase or in Acrylic and methacrylic acid esters can be present during which the esters are in the form of aqueous solutions for their preparation or purification under the influence. These aqueous solutions usually contain other components, such as methanol, which polymerize easily from air, light, heat or from peroxides. The tendency to polymerize is about methacrylic acid. For large-scale Hersonders pronounced in aqueous solutions that this position of these esters were various processes containing esters, eg. B. in systems where this is suggested. In all of these processes, however, ester is used together with an aqueous phase or a greater or lesser amount of such aqueous phase
be in the form of an aqueous solution. Apparently solutions are used, which is explained in more detail below migrate into such aqueous phases or solutions. slightly iron ions, to which these esters are sensitive. Methyl methacrylate is usually produced in such a way that are. For example, these esters polymerize immediately that Acetoneyanhydrin reacted acrylamide sulphate with sulfuric acid to Methwenn conventional steel as a material for the devices 35 and subsequently is used where such mixtures or solutions is esterified by addition of methanol and water ■ ^f ryl- or methacrylic acid esters are present . The ester is from the reaction mixture either polymerisability of the ester is even promoted, by simple distillation or by steam, if the devices are separated from corrosion-resistant distillation with superheated steam; chrome steel that only dissolves so little 40 In both cases the distillate contains an ester phase it is found that virtually no metal ions are found and an aqueous phase because the ester can become an azeotrope. Aqueous solutions that form this ester boiling mixture with water and contain both will be present separately in all phases proposed so far in the distillate, the z. B. obtained by manufacturing processes for the esters. In addition, decanting is separated. becomes industrially common steel or 45 The obtained crude methyl methacrylate contains corrosion-resistant steel as a device material methanol and water, which is constantly used with methyl, methacrylate simmer. Therefore, if the separation from To the polymerization of acrylic or methacrylic economic reasons is not immediately through To inhibit acid esters, a wide variety of distillation can be done before distilling Polymerization inhibitors are used, such as hydro- so methanol with water or an aqueous solution quinone, hydroquinone monomethyl ether, pyrogallol, an inorganic salt, e.g. B. by continuous Resorcinol and methylene blue. These known poly countercurrent extraction or in a mixed-settling merization inhibitors are especially ex-systems in anhydrous devices or by extractive distillation useful that are used for storage and traction. Here lies the methyl methacrylate Serve to transport the ester. In aqueous solutions, 55 in the device together with the aqueous phase which contain the esters, this polymerization before and is also in the separated aqueous do not inhibit the premature polymerisation dissolving methanol solution.