MXPA95002339A - Production of acrylic acid of pure grade - Google Patents

Abstract

The present invention provides a continuous process for producing a pure grade of acrylic acid having residual aldehyde levels under 10 parts per million. The process applies two selected groups of amines (chosen from the groups consisting of primary arylamines, hydrazines, alkylenepolyamines and alpha-amino acids) at different points of the continuous process.

Description

PROCEDURE TO PRODUCE ACRYLIC ACID OF PURE GRADE This invention relates to a process for purifying acrylic acid. More specifically, the process is a continuous process, which supplies the pure grade acrylic acid, which contains very low levels of residual aldehyde. In the manufacture of acrylic acid by the catalytic oxidation of propylene, initially acrylic acid ("AA") and oxidation by-products are obtained in an aqueous solution of AA, before further purification. In the "extraction / distillation procedure", it is extracted the aqueous solution of the AA with a suitable organic solvent, which supplies an extract of the AA, which is distilled azeotropically and dehydrated, thus removing the water from the extract and recovering the organic solvent for recycling. In another purification procedure, a "direct distillation process", the extraction step of the aqueous solution is ignored and the azeotropic distillation and dehydration are applied directly to the aqueous solution of the AA. By any procedure, the resulting dehydrated AA or "crude" AA contains impurities from Acid, such as acetic acid, maleic acid and maleic anhydride, and also contains aldehyde impurities, such as acrolein, furfural and benzaldehyde, and other oxidation byproducts. The acetic acid can be removed from the dehydrated AA by fractional distillation, to give an AA with a low content of acetic acid, also referred to as "crude" AA, which still contains other components. In the extraction process, some of the impurities of maleic acid and other acids are discarded into the wash water and thus contribute to costly waste treatment. In the direct distillation process, these same impurities become an organic waste oil, which can be burned for its fuel value. Thus, while both processes are commercially practiced, the direct distillation method is preferred for recent plants, although its use increases the difficulty of purifying AA containing appreciable levels of maleic acid and maleic anhydride. The present invention can be used with both processes and is particularly advantageous in the direct distillation process. Conventional fractional distillation of the 'AA i crude ("CAA") is capable of removing most of the impurities of maleic acid and maleic anhydride and other high-boiling impurities, such as terephthalic acid, thus providing a distilled AA , which is useful as the starting material for producing acrylate esters or some polymers. However, conventional fractional distillation alone is not effective in reducing aldehydes to the levels necessary for a pure grade acrylic acid ("PGAA") useful for producing polymers having average molecular weights greater than those of the polymers obtained from AA distilled. To obtain the PGAA, the CA from the extraction / distillation or direct distillation process must be purified beyond that achieved by conventional fractional distillation, because the residual impurities, particularly the aldehydes, interfere with the reactions of I. polymerization; the aldehyde levels should individually be below about ten parts per million (ppm), more preferably below five ppm and especially preferred below one ppm. PGAA having these aldehyde levels is useful in the production, for example, of super-absorbent polymers and efficient polymers as dispersants for drilling muds of oil wells and as flocculating agents. It is known that aldehydes can be reduced to ppm levels in the AA, by distilling the AA in the presence of similar amines or co-positions. For example, the Research Disclosure of E. U. A., No. 167066, reveals that furfural is reduced to less than 1 ppm by treating crude acrylic acid or distillate with small amounts of phloroglucinol, ortho (o-) phenylenediamine or aniline.; these amines are believed to form a complex with or decompose the furfural to give a product which can then be separated by fractional distillation. U.S. Patent No. 3,725,208 ("" 208") discloses that at least one of the following: sulfuric acid, hydrazine, phenylhydrazine, aniline, monoethanolamine, ethylene diamine or glycine, when added in batches to partially purify (presumably by pre distillation) the "crude grade" acrylic acid, which contains aldehydes and the resulting mixture is heated for 3 hours at 70 ° C before the fractional distillation, and produces a distillate of A containing reduced levels of aldehydes. , No. 4,828,652 ("" 652") teaches that aminoguanidine or its salts are effective when used in ratios of 1 to 3 moles per mole of aldehyde and with at least 1 to 1.5 hours of residence times before fractional distillation of a "technical grade" (again, presumably a distilled grade) of the crude grade AA. However, there are problems with the aforementioned methods for reducing aldehyde. For example, known methods use so-called single or single-step amine addition to the crude grades of AA or a distilled grade of a crude AA, and require appreciable residence times prior to distillation, as disclosed in the patent. '652. That patent too? describes that previous efforts requiring an excess of about 4 moles of hydrazine per mole of aldehyde, and special distillation conditions, to achieve an I content of the furfural below 5 ppm; likewise, under these conditions, the distillation column becomes coated with by-products. Although the '208 patent discloses that amines, such as aniline, monoethanolamine and ethylenediamine, can be used, with the described conditions the lowest residual aldehyde contents are obtained only with the hydra ^^. Zinc or phenylhydrazine and high levels and long residence times are required to achieve a low level of aldehyde. There are additional problems when maleic acid and maleic anhydride are present; when their combined levels exceed about 0.1% by weight In the CAA, the massive formation of solids with the excess of amine used in the batch or continuous method can occur. These solids can clog the equipment and cause downtimes for cleaning. Additionally, due to the competitive reaction of the amine with the maleic anhydride, Excessive amounts of amine need to be added, because the reaction with maleic anhydride is kinetically favored over the reaction with furfural and benzaldehyde. The reaction with the maleic anhydride can be avoided by the previous distillation of CAA, but this is a expensive stage that would be beneficially eliminated. In addition, it has been found that another problem arises if the amine is added only to the top or near the top of the fractional distillation column, while the CAA is distilled; the addition of the amine in this way causes excessive polymer and other solids formed within the column when the CAA contains more than about 10 ppm of the acrolein. Thus, there is a need for an efficient process, particularly a continuous process, to produce PGAA from CA, when this CAA contains not only aldehydes but also the typical impurities mentioned above, in particular maleic acid and maleic anhydride. We have discovered a continuous, economic process to reduce aldehydes in the CAA that contains substantial levels of acrolein, furfural and maleic acid and anhydride. The process supplies a PGAA that is less than 10 ppm, and is capable of delivering less than 1 ppm, of any individual residual aldehyde, without requiring CAA prior distillation to remove the maleic anhydride. The characteristics of the The invention is also applicable to the previous stages of the process, associated with the preliminary sources of the AA, as shown below. Also, the process of the invention prevents clogging of the equipment with the polymer and other solids. The process also provides the PGAA with levels of maleic anhydride below 100 ppm and advantageously provides the minimum use of expensive amines and the minimum generation of new waste materials, compared to known processes. Broadly described, the process of the invention uses two selected groups of amines at different points in the continuous process in the delivery of the PGAA. In one embodiment, one or more amines from a selected group of the amines (Group A) is added to the CAA to supply a loading stream of the crude acrylic acid. Within this * 10 CAA load current, the Group A amine reacts rapidly with acrolein and other "light" aldehydes (aldehydes with a boiling point lower than that of AA), effectively removing them from the volatilization in the column. The load current of the AC is fed to a column of fractional distillation and distilled. The fractionation power of the column retains maleic acid, maleic anhydride and boiling point components * elevated, such as terephthalic acid, near the bottom of the column. Concurrently with the distillation of the CAA charging current, an amine loading stream of one or more amines from another selected group of amines (Group B), is introduced into or near the top of the column, to facilitate the removal of any 1 • residual residual volatile aldehyde, particularly the furfural, and the malefic anhydride. The resulting distillate, which may include polymerization stabilizers, is PGAA. More specifically, a continuous process for producing a pure grade acrylic acid (PGAA) is provided, which comprises the steps of: a) feeding a final charge column of the raw acrylic acid at a temperature of 25 to a final distillation column. at 100ac, this charge current comprises: i) a crude acrylic acid and ii) a minimum effective level of a molar ratio of 0.1 to 2.0, based on the total moles of the aldehydes and the maleic acid and the maleic anhydride in the crude acrylic acid, of one or more amines of Group A, selected from the group consisting of: i) a primary arylamine, of structure (I): and X2 are selected from the group consisting of H, NR2, OR, Cl and R, wherein R is selected from H or C ^ -Cg alkyl; ii) a hydrazine,. optionally its hydrate, of the structure R2-NH-NH2 wherein R2 is selected from H, phenyl, 4-nitrophenyl or 2,4-dinitrophenyl; iii) an alkylene polyamine of structure (II): R3 - N4 (II) in which R3 is selected from H or an alkyleneamine Cl-C6 and R4 is an alkyleneamine C ^ -Cg and iv) an a-amino acid, selected from the group consisting of structure III: NH2 R5 - N C02H (III) H 30 # in which R5 is selected from H, R or R4 arginine, aspartic acid, glutamic acid, histidine and methionine; b) feeding concurrently to an upper portion of the final distillation column, an amine loading stream, comprising a minimum effective level of a molar ratio of 0.01 to 1.0, based on the total moles of the aldehydes and the acid and maleic anhydride in the crude acrylic acid, of one or more amines of Group B, selected from the group consisting of o-, m-, p-phenylenediamine, 4-nitrophenylhydrazine and 2,4-dinitrophenylhydrazine; and c) fractionally distill the charge stream of the crude acrylic acid through the final column of distilla¬ tion, distilling and separating the PGAA, which has a residual individual aldehyde content of less than 10 ppm.

The continuous process can also be carried out by adding the amine from Group A to a preliminary column, used in preparing the CAA, for example the azeotropic distillation column or an acetic acid removal column. The resulting CAA is fed to the distillation column, while concurrently feeding the Group B amine to the upper portion of this final column of distillate and distill and separate the PGAA.

# Cone was previously described, the CAA is the dehydrated AA and typically contains the following acids and aldehydes in the indicated weight amounts: for example, acrolein, which varies from several ppm to about 300 ppm; benzaldehyde and furfural, each from 200 to 400 ppm; maleic acid and maleic anhydride (combined) up to about 1.0% by weight (and measured as maleic acid); and other components, such as acetic acid and terephthalic acid. The aqueous solutions of AA and AA extract, are the AA sources that precede the CAA and contain the same acids and aldehydes as the CAA, and v water. Upon obtaining the charge current from the CAA (or other AA source), the Group A amine can be added to the CAA (or other source of AA) or in net form or as a solution in a suitable solvent, such as water or a saturated carboxylic acid, such as propionic acid, * hexanoic or valeric. The amine of Group A is selected from. the amines previously described and are as defined here. The R - the alkyl group of the structure (I) of the primary arylamine is a C ^ -Cg alkyl, that is to say an alkyl group containing from 1 to 6 carbon atoms in any isomeric form, such as methyl, ethyl, propyl, isopropyl, n-, iso- or sec. -butyl, hexyl and its isomers. The Disubstituted primary arylamines, such as diamino- • toluenes and dimethylanilines, are also effective. The hydrazines (or hydrates) of R2-NH-NH2 have been defined; the hydrate has the advantage of ease and safety in handling. The alkylene group C ^ -Cg, R3 and R4 / of the alkylene polyamine contains from 1 to 6 carbon atoms, such as the methylene, ethylene, propylene, butylene, hexylene group, and their isomers, and carries a primary amine . Examples of the alkylene polyamine of structure II include ethylenediamine, diethylenetriamine and dipropylenetriamine. ? '10 The alpha-amino acid is as described above. The Group A amine is selected to be fast and substantially irreversible with acrolein and other light aldehydes present in the CAA or other sources of the AA that precede [a ^ CAA * The "most of the amines in Group A react in line as the CAA or another source of AA is conducted, with the amine, to a distillation column; Provision can also be made to prolong the time of »Residence by methods known in the art, such as by the use of a buffer tank in the cargo line conti¬ nua. While relatively expensive amines, such as phenylenediamines, are included in Group A, it is preferred to use less expensive amines, such as aniline, o-i methylaniline, hydrazine hydrate, diethylenetriamine, lysine, methionine and glycine, which They are particularly effective¬ ces with acrolein. (alkyl-amines, such as butyl-amine, were found to have lower reaction regimes and require higher usage levels than, for example, aniline and other "fast reaction" amines and, therefore, do not include as the amines of Group A). Generally, these Group A amines and their mixtures are liquid at temperatures below 702C and are easy to use. For reasons of cost, efficiency, availability and ease of handling, those preferred Group A amines for use in the invention include aniline, o-, m- and hydrazine and hydrazine hydrate, diethylenetriamine, glycine, lysine and methionine; more preferred, due to their cost and efficacy in reducing acrolein impurities, are aniline, o-methylaniline, hydrazine, hydrazine hydrate: I aniline is the most preferred. 15 At the same time that the charging current of the CAA is fed to the final distillation column, one or more amines from Group B are fed, either as a net or as a * solution, cone was described for the addition of the amine Group A, at the top portion of the same column, is say, it is fed to the top or within 30% of the top of the column, and always upstream of the CAA load current. Effective Group B amines are those indicated above and are selected to react, rapidly and I essentially irreversibly, with furfural. Amines Preferred Group B, due to their cost, availability and efficiency, include meta-phenylenediamine, 4-nitro-phenylhydrazine and 2,4-dinitrophenylhydrazine; of them, the most preferred is meta-phenylenediamine. PGAA having an individual residual aldehyde level of less than 5 ppm is easily achieved with the use of the preferred amines and less than 1 ppm is achieved with the use of the most preferred amines. Another embodiment of the invention, which uses the same groups of amines in a similar manner, is the addition of one or more amines from Group A to the AA source, for example. to an aqueous solution of AA, to form a charge stream from the AA source, which is fed to an azeotropic dehydration column. After dehydration, the resulting CAA has a low acrolein content (< 10 ppm) and is dried. The AA source can also be an extractant, that is, an aqueous solution of A, which has been extracted with a suitable organic solvent; the resulting extract of AA is fed to the azeotropic dehydration column instead of the aqueous solution of acrylic acid. It is also possible to feed the amine of Group A to the azeotropic dehydration column as a separate stream as any source of AA to the column. The resulting CAA with low acrolein (now dehydrated) is then fed, optionally, to another fractional distillation column for the removal of the acetic acid, thus providing a CAA with low acrolein, which has a low acetic acid content (< 2,000 ppm), or directly to the final distillation column, ie a high purity acrylic acid distillation column, where steps b) and c), described above, are carried out. An advantage of adding the Group A amine to an aqueous solution of AA or extract is that any solution does not contain the maleic acid in its anhydride form, thus not wasting the amine of Group A for its reaction with maleic anhydride. Thus, a continuous process for producing pure grade acrylic acid (PGAA) is also provided, which comprises the steps of: a) feeding a first charging stream from the acrylic acid source to a first distillation column at a temperature of 25 to 1002C, this charge stream comprises: i) a source of acrylic acid, selected from the group consisting of an aqueous solution of acrylic acid and an extract of acrylic acid; ii) an effective minimum level of a molar ratio of 0.1 to 2.0, based on the total moles of the aldehydes and maleic acid and the anhydride, maleic in the acrylic acid source, of one or more amines in Group A, selected from the same group A of amines described in paragraph a) section ii) above; b) dehydrating the charge stream from the acrylic acid source to supply a crude acrylic acid, with low acrolein, having an acrolein content of less than 10 ppm; c) distilling and separating, optionally, the acetic acid from the crude acrylic acid with low acrolein, to supply a crude acrylic acid with low acrolein, which has a reduced level of acetic acid; d) subsequently feed the final distillation column; i), the crude acrylic acid with low acrolein, and ii) concurrently, to an upper portion of the final distillation column, an amine loading stream, comprising a minimum effective level of molar ratio of 0.01 to 1.0, based on in the total moles of aldehydes and maleic acid and maleic anhydride in the crude acrylic acid with low acrolein, of one or more amines of Group B, selected from the group consisting of o-, m- and p-phenylenediamine, 4-nitro-phenylhydrazine and 2,4-dinitrophenylhydrazine; and e) fractionating crude acrylic acid with low acrolein fractionally through the final distillation column, distilling and separating the PGJAA having a residual individual aldehyde content of less than 10 ppm. Another embodiment of the invention, which uses the same groups of amines in a similar manner, is the addition of one or more amines from Group A to a CAA having a high level (> 2,000) of acetic acid. This charging stream of the CAA containing a high level of acetic acid, can be fed to a distillation column of acetic acid, t 'ie the distillation column used to efficiently reduce, by distillation, the acetic acid from the CAA. The distillation of the CAA treated with the amines of Group A supplies a CAA with low acrolein (now also with low acetic acid). (Amines from Group A can be fed to the acetic acid removal column as a separate stream, as the CAA with high acetic acid is fed to the column). Subsequently, the CAA r with low acrolein is fed to a distillation column Finally, a column of distillation of acrylic acid with high purity, where the distillation steps, previously described, are carried out. Thus, a continuous process is additionally supplied to produce a pure grade acrylic acid (PGAA), comprising the steps of a) feeding a charging stream to a distillation column of acetic acid at a temperature of 25 to 100 ° C, the charging stream comprising, i) a crude acrylic acid with a high acid content acetic; and ii) a minimum effective level of one rela¬ molar ratio of 0.1 to 2.0, based on the total moles of aldehydes and maleic acid and maleic anhydride in the crude acrylic acid with high acetic acid content, of one or more amines of Group A, selected from the same group A of amines described in paragraph a), section ii) above; B) distilling and separating the acetic acid from the charging stream, to supply a crude acrylic acid, with low asrolein, having an acetic acid content of less than 2,000 ppm and an acrolein content < 10 ppm; c) sequentially feeding a final distillation column: i) the acid low acrolein and ii) concurrently to an upper portion of the final distillation column, an amine loading stream, comprising a minimum effective level of a molar ratio of 0.01 to 1.0, based on the total moles of the aldehydes and maleic acid and maleic anhydride in the crude acrylic acid with low acrolein, of one or more amines of Group B, selected from the group consisting of the o-, -, p-phenylenediamine, 4-nitrophenylhydrazine and 2,4-dinitrophenylhydrazine; and d) fractionally distilling the crude acrylic acid with low acrolein through the distillation column, distilling and separating the PGAA having a residual individual aldehyde content of less than 10 ppm. One advantage of these approaches that use, for example, or the aqueous sources of AA or CAA that are high in CAA, is that acrolein and other light aldehydes are removed earlier in the AA purification process, with the added benefit to reduce the trend? of the AA to be polymerized, while being purified, thus allowing a reduction in the level of the polymerization inhibitor during the subsequent process. Thus, Group A amines can be used effectively in the partial purification of acrylic acid in a continuous process step, before feeding the final fractional distillation column, which supplies the PGAA and somewhat avoiding the tendency of the acrylic acid to be polymerized , while it is being purified. The same preferred amines of Group A and Group B, used in the first embodiment described above and preferred in the aqueous solution of the source AA and the CAA modalities with high acetic acid content, according to the invention. The PGAA that has < 10 ppm residual individual aldehyde, preferably < 5 ppm, more preferably < 1 ppnf can be obtained from the processes described, preferred amines easily achieve < 5 ppm and more preferred achieve < 1 ppm. Any distillation of the invention is carried out under reduced pressure, typically less than 200 mm of Hg, with a bottom temperature of the column maintained below 1502C, preferably less than about 1002C, to minimize the loss of AA as a polymer. When the Group A amine is added to the CAA or other source of the AA, as described, the temperature of the load current% 1 containing AA must be greater than 25 ° C and preferably greater than 402C, up to a temperature of 100 ° -C, a temperature range of 40 to 80 ° C is preferred. At these temperatures, few solids are generated compared to temperatures of 152 C and below. The continuous processes of the invention are distinguished from the processes "in batches"; in the latter, a fixed amount of the CAA or a source of AA is charged to the distillation unit, reacted with a fixed amount of the amine to reduce the aldehyde content (by way of single or single addition). operation of the amine) and subsequently distill to supply a fixed amount of the purified product. Processes in batches, due to the time required for loading, reaction, distillation and cleaning, they are characteristically of a lower productivity than the continuous processes of the invention. The continuous processes of the invention are also distinguished from the "batch and continuous combined" processes where, in the latter, the treatment of the CAA or a source of the AA with an amine, to reduce the content of the aldehyde, is carried out first in a batch reactor and then the previously treated CAA, or other source, is continuously fed to a distillation column. The latter processes require additional reactors and storage vessels that are not necessary with the continuous process of this invention. The "minimum effective level" of one or more amines of the Group A, added to the loading of a distillation column i (or directly to the column itself) is determined by measuring "the content of the acrolein of the outlet (eg a distillate), which results from the distillation column or other unit to which the stream treated with the amine of Group A is fed. (In the mode where the amine of Group A is added at points in the process before the final distillation step, the content of acrolein is measured in a stream greater that contains the AA, produced by the unit, for example a bottom current, in which the current treated with the amines of Group A is fed.

In any case, the Group A amine is added to the unit's charge source, until the measured level of acrolein is below 10 ppm. The level of the Group A amine required to reduce the level of acrolein to < 10 ppm, is defined as the "minimum effective level" for The Group A amine (s) greater than the minimum effective level are usually necessary to achieve lower levels of the residual acrolein, such as 5 and 1 ppm, but all of the Amines in Group A use levels that are within the value previously specified. The minimum effective level of the Group B amine, which, in all modalities, is added to the upper portion of the distillation column, was determined by measuring the furfural content of the distillate from the column of final distillation. Then, increasing levels of the Group B amine are added to the final distillation column until the measured level of the furfural is < 10 ppm. The level of the amine of group B, required to reduce just the level of the furfural to < 10 ppm, is defined as the "minimum effective level" for the Group B amine (s). In any of the embodiments of the invention, the minimum effective level of the amines of Group B is determined after. determine the minimum effective level of Group A amines and as these Group A amines continue to be fed, minimum effective levels of Group B amines greater than the minimum effective level are usually necessary to achieve lower levels of residual furfural, such as 5 and 1 ppm, but all the amines in Group B use levels within the previously specified range. The PGAA resulting from all embodiments of the invention have residual individual aldehyde contents below 10 ppm.

EXAMPLES General Data 1 In the Examples and Comparative Examples, these abbreviations are used: CAA, crude acrylic acid; HQ, hydroquinone quinone; MeOH monomethyl hydroquinone ether; mPD, m-phenylenediamine; PTZ, phenothiazine. For the compositional analysis, gas chromatography for acrolein, benzaldehyde and furfural and high performance liquid chromatography for maleic acid and anhydride were used, both methods sensitive to < 1 ppm. The analytical results of the acid and maleic anhydride were combined because the analytical method converts any anhydride into the acid, thus, the results for the maleic acid and anhydride are reported as "maleic acid / anhydride". (When the maleic acid / anhydride is reported for the distillate, it is probably present as maleic anhydride, because it is known from the vapor pressure data that an amount * 10 negligible maleic acid distils at the top of the column, when the acrylic acid distils at the top of the column.) When the amines are added to the CAA or other AA sources, the aggregate amount is expressed as a ratio molar of the amine to the total moles of the acrolein, benzaldehyde, furfural and maleic acid / anhydride, measured in the charge current of the unit, to which the latter is added. In the case of distillation examples * tion, distillate analyzes were typically done as the average of two or more sample analyzes per hour, taken during the stable operation. Analyzes greater than 100 ppm were rounded to the two significant figures. Classification tests were performed by adding the indicated levels of amine to aliquots of a PGAA loading solution, to which they have been added the following impurities at the ppm levels indicated in # Examples: acrolein, benzaldehyde, furfural and maleic anhydride. (In Tables IV, acrolein, benzaldehyde, furfural and maleic acid / anhydride are denoted by the symbols A, B, F, and M, respectively, and the results are in ppm.) The aliquots containing the amine were stirred for thirty minutes at 23-252C and then analyzed immediately. After about five days at 23-25 ° C, the aliquots containing the amine were re-analyzed. Lcis control samples are those samples contaminated in which no amine was added. The following criteria were used for the classification tests, to estimate which amines will be useful as the amines of Group A or Group B in the invention. An amine was judged to be a useful amine of group A if reduces acrolein to < 10 ppm at a molar ratio of the amine up to 2. The amine is judged particularly effective if the reduction of acrolein occurred within 30 minutes, for an amine to be useful as the amine of the Group A, it is not necessary to reduce benzaldehyde levels and / or furfural. An amine was judged useful as a Group B amine if: i) it shows a reduction > 50% within 30 minutes at the level of the furfural at a molar ratio of the lower amine of 1. 0 e (ii), showed a reversibility of the reaction with the furfural i (in a molar ratio of the amine less than 1.0), Wr that generates, after about 5 days, less than 70% of the initial level of the furfural in the control sample.

Example 1: Preparation of the PGAA, where the Amine of the Group A is the Aniline and the Amine of the Group B is the mPD An Oldershaw column of fifteen trays of 2.54 cm was used, equipped with a boiler heated by steam. The CAA, which contains 85 ppm of acrolein, 220 ppm of benzaldehyde, 240 ppm of furfural and 7200 ppm of acid / maleic anhydride, it was previously heated by passing it through a heat exchanger. Aniline (0.5 molar ratio) was added to the next pre-heated CAA and the charging current flowing from the CAA was maintained at the desired temperature during charging to the "pot", i.e. container at the bottom of the column. The operating conditions for the column were; upper pressure of about 35 mm Hg; CAA regime, about 211 grams / hour; reflux ratio, of about 1.6; percent of the total charge removed as a distillate, approximately 86%; temperature ide the charge current of the CAA, about 50 ° .C; pot temperature, approximately 832C; and temperature of the upper part, about 65 ° C. For the inhibition of the polymerization, the following levels of the inhibitor were fed, based on the CAA regimen: 0.5% by weight of air to the kettle, about 0.1% of MeHQ * to the condenser, about 0.03% by weight of the PTZ and about 0.06% by weight of the HQ to the tray 11 (numbered from the bottom to the higher) . Concurrently, the mPD (0.08 molar ratio) was added in trays fifteen, in the upper part of the column. With stable conditions over a period of seven hours, the PGAA distillate contained consistently < 1 ppm of each of acrolein, benzaldehyde and furfural, and 2 ppm of acid / maleic anhydride. There was no problem with the * 10 formation of solids in the lines of load to the pot or inside it, nor was there any problem of polymers or other solids in the column.

Example 2: Preparation of the PGAA, where the Amina of Group A 15 is the Hydrate of Hydrazine and the Amina of Group B is the mPD The conditions of Example 1 were repeated, »Except that (i) the hydrazine hydrate was fed to the pot (molar ratio of 0.5) instead of the aniline, (ii) the mPD (molar ratio of 0.2) was fed to the tray eleven (iii) the CAA contained 91 ppm of acrolein, 210 ppm of benzaldehyde, 250 ppm of furfural and 6100 ppm of acid / maleic anhydride. With stable conditions for a period of two hours, the PGAA distillate consistently contained < 1 ppm of acrolein, benzaldehyde and furfural and 2 ppm of maleic acid / anhydride. There were no problems with the formation of solids in the pot or problems with any polymer or other solids in the column. Some minor solids were observed in the CAA load current line, but at a level that does not interfere with the continuous operation.

Comparative Example 1; Distillation of the CAA without the addition of the amine of Group A or B Comparative Example 1 used conditions similar to those described in Example 1, except that (i) no amine of Group A was fed into the pot, (ii) no No Group B amine was fed to the column and (iii) the CAA contained 66 ppm of acrolein, 230 ppm of benzaldehyde, 270 ppm of furfural and 6600 ppm of acid / maleic anhydride. With stable conditions for a period of ten eight hours, the distillate contained consisten-? 38 ppm of acrolein, 3 ppm of benzaldehyde, 91 ppm of furfural and 70 ppm of acid / maleic anhydride. There were no problems with the formation of solids in the load lines to the pot or in the pot itself, nor problems with any polymer or other solids in the column, but without the addition of the amine, 1 the levels of the impurities in the distillate exceeded by far those required for the PGJAA.

Comparative Example 2; Distillation of the CAA, where the Amine of Group A is the Aniline and there was no Addition of the Amine of the Group B The Comparative Example 2 used conditions similar to those described in Example 1, except that (i) aniline was fed to the pot ( molar ratio of 0.6), and (ii) the amine of Group B was not fed to the column. With stable conditions over a period of two hours, the distillate contained consistently < 1 ppm of acrolein, 1 ppm of benzaldehyde, 46 ppm of furfural and 58 ppm of acid / maleic anhydride. There were no problems with the formation of solids in the lines of load to the pot or inside the pot, not even j; there were problems with polymers or other solids inside - the spine. HA, YES, . although the charge of aniline to the pot sufficiently reduced the acrolein, it did not sufficiently reduce the furfural to provide a satisfactory PGAA.

Comparative Example 3; Distillation of the CAA where the Amine from Group A to Aniline and the Charge stream from CAA is at a Temperature of 23-253C Comparative Example 3 used conditions similar to those described in Example 1, except that: (i) the aniline the pot was fed (0.6 molar ratio), (ii) the Group B amine was not fed to the column, (iii) the CAA contained 91 ppm of acrolein, 210 ppm of benzaldehyde, 250 ppm of furfural and 6100 ppm of acid / maleic anhydride; and (iv) the charge current from the CAA to the column was maintained at a temperature of 23-25 ° C. Under these conditions, the CAA load line was clogged with solids after 4 hours, forcing the column to stop. The solids were identified by H-NMR spectroscopy as N-phenyl-maleic acid, the reaction product of aniline and maleic anhydride.

Comparative Example 4: Distillation of the CAA Without Amin of Group A and where the Amine of Group B is the mPD The Comparative Example 4 used conditions similar to those described in Example 1, except that (i) the amine was not fed from Group A to the pot, (ii) the mPD was fed to the column (molar ratio of 0.05), (iii) the CAA contained 69 ppm of the acrolein, 230 ppm of the benzaldehyde, 270 ppm of the furfural and 8100 of the acid / maleic anhydride, and (iv) the charging current of the CAA to the column was maintained at t a temperature of 23-252C. Under these conditions, the column suffered from the dense formation of polymers and other solids and, after 30 minutes, had to stop in a forced manner. Likewise, the distillate, just before the stop, contained 63 ppm of acrolein, <1 ppm of benzaldehyde, 4 ppm of furfural and 2 ppm of acid / maleic anhydride. Thus, the single feed of the amine to the upper * portion of the column was not satisfactory for the production of pure grade acrylic acid, PGAA, due to the formation of polymers and other solids in the column, which impede the continuous operation. The data showed that densa formation of polymers and other solids occurred within the column, in which no Group A amine was fed to the crude acrylic acid, CAA, but where the feed was carried out; of a Group B amine in the upper portion of the column. Comparative Example 5: Classification Tests Adding a Primary Ina Alkylamide to the PGAA Contaminated with Impurities In Comparative Example 5, the general procedure, previously described, was used to classify the tests, except that the amines used were the primary alkylamines. The results are given in Table I, in which the data show that the representative primary alkylamines, n-butylamine and tertiary octylamine, are not useful amines of Group A (or Group B). While primary alkylamines may have some utility in reducing acrolein, they are not effective in producing the PGAA. I Table 1 Classification Tests showing the Effect of the Primary Alkylamines in the Removal of Aldehyde in the I PGAA Contaminated Example 3: Classification Tests Adding Primary Arylamine to PGAA Contaminated with Impurities, to the CAA, and to the Acid Acid Aqueous Solution In Example 3, the general procedure, previously described, was used for the classification tests, except that (i ) the amines used were the primary arylamines and (ii) the amine was added to aliquots of any PGAA loaded with impurities, or to the CAA, or to the aqueous solution of acrylic acid. These AA sources were used and contain ppm levels of acrolein, benzaldehyde, furfural and maleic acid / anhydride, indicated in Table II. The aqueous solution of acrylic acid contained about 35% water. Based on the criteria previously described, the data from the classification test in Table II showed that the following primary arylamines were effective as the amines of Group A: aniline, m-phenylenediamine, p-phenylenediamine, 1,5-diaminonaphthalene, p-aminophenol, p-methoxyaniline, p-chloroaniline, o-methylaniline, m-methylaniline, p-methylaniline and p-nitroaniline. In addition, Table II shows that m-phenylenediamine is a remarkable amine of Group B; p-phenylenediamine was also useful as the amine of Group B.

* Table II Classification Tests Showing the Effect of Primary Arylamines in the Removal of Aldehyde in PGAA. CAA or a Aqueous Acid Aqueous Acid Solution * • Example 4: Classification Tests Exploring the Effect of Temperature on Addition of Aniline to PGAA Contaminated with Impurities (23-25ac and 60se) In Example 4, the general procedure, previously described for classification tests, was employed, except that (i) the amine used was the aniline, (ii) the test was conducted either at 23-252C or at 60QC and (iii) only the aliquots containing the aniline were analyzed once after 30 minutes. The results are given in Table III, the data show that the regimen of the reaction of the co-operators with the aniline, after thirty minutes, in the descending order was: acrolein > maleic anhydride > furfural > benzaldehyde This reactivity tends to be the same for 23-252C and for 602C. However, at 602C, the levels of benzaldehyde, furfural and maleic anhydride are greater than at 23-252C with the same level of aniline. As well as the advantage of lower solids (discussed above), higher temperatures, such as 50-60 ° C, are preferred when the Group A amine is added to the CAA or an AA source. Table III Classification Tests Showing the Effect of Temperature on the Removal of Aldehydes by Aniline in the Polluted PGAA Example 5; Classification Tests Adding Hydrazine Hydrate and 2,4-Dinitrophenylhydrazine to PGAA Contaminated with Impurities In Example 5, the general procedure, previously described for classification tests, was employed, except that the amines used were hydrazine and its compounds. derivatives. The results given in table IV show that both hydrazine hydrate and 2,4-dinitrophenyl idrazine are effective as the amines of Group A; the last amine was the notable amine of Group B. Table IV Effect of the Hydrazine Derivatives on the Removal of Aldehyde in the Polluted PGAA Example 6: Classification Tests Adding Alkylene Polyamine or α-Amino Acid to PGAA Contaminated with Impurities In Example 6, the general procedure described previously for the classification tests was used, except that the amines used were either the alkylene polyamines or the a-amino acids. Here, glycine was added in an aqueous solution. The results are given in Table V. ~ o_ f Y 10 The data from the classification test in Table V show that diethylenetriamine, glycine, lysine, arginine and histidine were eficases as are the amines of Group A.

Table V Effect of Alkylenepolyamines and a-Amino Acids on Removal of Aldehyde in the Polluted PGAA P

Claims (13)

NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and, therefore, the content of the following is claimed as property: CLAIMS 1. A continuous process to produce a pure grade acrylic acid (PGAA), this The step comprises the steps of: a) feeding a final charge stream of the raw acrylic acid to a final distillation column, at a temperature of 25 to 100 ° C, this charge stream comprises: i) a sulfur acid acid and ) a minimum effective level of a molar ratio of 0.1 to 2.0, based on the total moles of the aldehydes, maleic acid and maleic anhydride in the crude acrylic acid, of one or more amines of Group A, selected from the group of : i) a primary arylamine, of structure (I): I) in which Xx and X2 are selected from the group consisting of H, NR2, OR, Cl and R, wherein R is selected from H or Ci-Cg alkyl; ii) a hydrazine,. opsionally its hydrate, of the struture R2-NH-NH2, wherein R2 is selected from H, phenyl, 4-nitrophenyl or 2,4-dinitrophenyl; iii) an alkylene polyamine, of the structure H R3 - N - R4 (II) wherein R3 is selected from H or an alkyleneamine cl-ct and R4 is an alkyleneamine C ^ -CQ J and iv) an a-amino acid, selected from the group consisting of structure III: NH2 R5 - N - CO9H (III) H e R5 is selected from H, R or R4 arginine, aspartic acid, glutamic acid, histidine and methionine; b) feeding concurrently to an upper portion of the final distillation column, a sorbate of amine twine, which shows a minimum ef- fective level of a molar ratio of 0.01 to

1.0, is based on the total moles of the aldehydes and the and anhydride maléiso in the harsh asríliso srudo, one or more amines of Group B, selessionadas sonjunto sonsta of o-, m-, p-phenylenediamine, 4-nitrophenylhydrazine and 2,4-dinitrophenilhid azina; and c) fractionally distilling the loading stream of the crude acrylic acid through the final distillation column, distilling and separating the PGAA, which has a residual individual aldehyde content of less than 10 ppm.

2. The expediency, according to claim 1, in which the amine of Group A is separated from aniline, o-m-, p-methylaniline, hydrazine, hydrazine hydrate, diethylenetriamine, glisine, lysine or methionine, and the amine of Group B is m-phenylenediamine, 4-nitrophenylhydrazine or 2,4-dinitrophenylhydrazine.

3. The promotion, according to Claim 2, in which the Group A amine is selected from the aniline, o-methylaniline, hydrazine or hydrazine hydrate, and the Group B amine is the m-phenylenediamine.

4. The process according to claim 3, wherein the amine of Group A is aniline.

5. The process according to claim 1, wherein the loading stream of the crude acrylic acid is fed to the final distillation column at a temperature of 40 to 80 ° C.

6. A continuous process for producing a pure grade acrylic acid (PGAA), which comprises the steps of: a) feeding to a first distillation column a charging stream from a source of the crude asylis acid, at a temperature of 25 ° C; at 1002C, this charge stream from the acrylic acid source appears: i) a source of the acrylic acid, selected from the group consisting of an aqueous solution of acrylic acid and an acrylic acid extract; (ii) a minimum effective level of a molar ratio of 0.1 to 2.0, based on the total moles of the aldehydes and maleic acid and maleic anhydride in the raw acid source of one or more amines from Group A, selected of the set of: i) a primary arylamine, of structure (I): wherein X x and X 2 are selected from the group consisting of H, N 2, OR, Cl and R, wherein R is selected from H or Ci-Cg alkyl; ii) a hydrazine,. opsionally ex. hydrate, of the structure R2-NH-NH2 wherein R2 is selected from H, phenyl, 4-nitrophenyl or 2,4-dinitrophenyl; Iii) an alkylene polyamine of the struture (II): R3 N - R4 (II) in e R3 is cut to H or a al.uilena.nina 20 cl-c6 and R4 is an alkyleneamine C ^ -Cg; and iv) an α-amino acid, seleaded from the group consisting of structure III: * NH2 R5 N - COoH (III) H 10 wherein R5 is selected from H, R or R47 arginine, aspartic acid, glutamic acid, histidine and methionine; b) dehydrate the charge current from the acid source 15 acrylics to provide a strong syringe are low astrolein content, which has an asterole content of less than 10 ppm; s) distilling and separating, opsionally, the acetic acid from crude asrichose acid, with low acrolein content, 20 for supplying a sulfuric acid are low in asteroid in asleolein which has a redissolved level of the assesy acid; d) feed subsysuently to the final distillation column: i) acrylic acid, are low in astrolein content, and ii) are, respectively, at the upper portion of the distillation column, a sorbate of amine twine, which suffers a level minimum efisaz of a ß molar relasion of 0.01 to 1.0, are based on the total moles of aldehydes and maleic acid and maleic anhydride, in the acid crude asríliso are low acrolein content of one or more amines of Group B, selected from the group consisting of o-, m-, p-phenylenediamine, 4-nitrophenylhydrazine and 2,4-dinitrophenylhydrazine yie) distillate frassionally, the acidic asylase is low in asylate in asrolein, through the final ß? 10 of distillation, distilling and separating the PGAA that has an individual aldehyde, residual, minor 10 ppm.

7. The preparation according to claim 6, wherein the Group A amine is selected from aniline, o-, m-15, p-methylaniline, hydrazine, hydrazine hydrate, diethylenetriamine, glisine, lysine or methionine, and Group B amine is m-phenylenediamine, 4-nitrophenylhydrazine or 2,4-dinitrophenylhydrazine.

8. The prosedimiento, according to claim 7, in which the amine of group A selessiona of aniline, o-metilanilina ,. hydrazine or hydrazine hydrate, and the amine of Group B is m-phenylenediamine.

9. The improvement, according to claim 6, in which the twister soruent of the source of the stiff assyrid is fed to the final distillation column at a temperature of 40 to 80 ° C.

10. A continuous effort to produce the pure, pure-grade asphalt (PGAA), this step comprises the steps of: a) feeding a distillation column of acetic acid with a twister sorder, at a temperature of 25 to 100ac, this sorrent of serge somprende: i) an arid asríliso srudo, with a high content of the ß ~ 10 asetiso; ii) a minimum efisazle level of a molar ratio of 0.1 to 2.0, are based on the total moles of the aldehydes and the maleic acid and malefic anhydride in the crude acrylic acid, with high content of acetic acid, 15 of one or more amines of Group A, selected from the set of: i) a primary arylamine, of structure (I): Wherein X and X2 are sequestered from the group consisting of Hf 2 OR, Cl and R, wherein R is selected from H or C ^ -Cg alkyl; ii) a hydrazine,. optionally its hydrate, of the struture R2-NH-NH2, wherein R2 is selected from H, phenyl, 4-nitrophenyl or 2,4-dinitrophenyl; iii) an alkylene polyamine of structure (II): ß H R3 - N R4 (II) in which R3 is selessiona of H or an alkyleneamine C _C6 and R4 is an alkyleneamine Cx-Cg; and iv) an α-amino acid, selessionate of the group that plays the structure III: NH2 I 25 R5 - N - C02H (III) H 30 wherein R5 is selected from H, R or R4 'arginine, aspartic acid, glutamic acid, histidine and methionine; b) distilling and separating the acetic acid from the twister sor sorizer, to supply a crude crude asyllosis with low asrolein content, which has a content of asbestos nenor less than 2,000 ppm and an asterole content of less than 10 ppm; s) feed subserviently to the final solm 10 distillation; i) the crude acrylic acid with low acrolein content and ii) is, to the uppermost portion of the final distillation column, a charging stream of 15 amine, which comprises a minimum efisazle level of a molar relasion of 0.01 to 1.0, are based on the total moles of the aldehydes and the maleic acid and the maleic anhydride, in the acidic asrichis srudo are low asrolein, one or more amines Group, B, selected from the group consisting of o-, m-, p-phenylenediamine, 4-nitrophenylhydrazine and 2,4-dinitrophenylhydrazine; and d) fractionally distill crude acrylic acid with low acrolein content, through the final column of 25 distillation, distilling and separating the PGAA having a residual individual aldehyde content of less than 10 ppm.

11. The process according to claim 10, wherein the amine of group A is selected from the aniline, o-, -, p-methylaniline, hydrazine, hydrazine hydrate, diethylenetriamine, glycine, lysine or methionine, and the amine of the Group B is m-phenylenediamine, 4-nitrophenylhydrazine or 2,4-dinitrophenylhydrazine.

12. The process according to claim 11, wherein the amine of Group A is separated from the aniline, o-methylaniline, hydrazine or hydrazine hydrate, and the amine of Group B is m-phenylenediamine.

13. The prosedimiento, according to claim 10, in which the twister soruent is fed to the solumn of 15 distillation of the asystid acid at a temperature of 40 to 802C. ! H.H