Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C57/00—Unsaturated compounds having carboxyl groups bound to acyclic carbon atoms
  • C07C57/02—Unsaturated compounds having carboxyl groups bound to acyclic carbon atoms with only carbon-to-carbon double bonds as unsaturation
  • C07C57/03—Monocarboxylic acids
  • C07C57/04—Acrylic acid; Methacrylic acid
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
  • C07C51/42—Separation; Purification; Stabilisation; Use of additives
  • C07C51/43—Separation; Purification; Stabilisation; Use of additives by change of the physical state, e.g. crystallisation
  • C07C51/44—Separation; Purification; Stabilisation; Use of additives by change of the physical state, e.g. crystallisation by distillation

Definitions

• the present invention relates to the production of polymer grade acrylic acid, commonly referred to as glacial acrylic acid.
• Ex-propylene acrylic acid production processes implement, after leaving the propylene oxidation reactors, various purification steps which may differ in their sequence depending on the process:
• Each step thus produces a quality of acrylic acid which differs in the content of residual impurities which will remain therein.
• These impurities will limit the acrylic acid obtained to a particular type of application.
• the quality of acrylic acid (AA) is i.e. its content of different impurities will play a big role in subsequent polymerization processes.
• the manufacturers manufacturing this acrylic acid then bring into play additional purification steps to transform the so-called technical acrylic acid (Aat) into “standard” acrylic acid which is usually called glacial acrylic acid (AAg) or grade acrylic acid. polymer.
• the finishing column used should then separate the light products (water, acetic) with the flow of acrylic acid, but also that of the heavy products (furfural, benzaldehyde) with the latter, in the same column.
• the number of separation stages and consequently of Dual Flow type plates then increases significantly, which would lead to a pressure drop and a rise in the column bottom temperature which is not compatible with the thermosensitive nature of acrylic acid.
• Glacial acrylic acid can also be obtained by an additional distillation operation combined with a chemical treatment to remove the aldehydes.
• amines may be employed, and more particularly compounds of the hydrazine family, as described in US Patents 3,725,208 or US 7,393,976. Generally, these compounds can be used as such or in the form of their salts or hydrates.
• Document WO 2017/050583 complements the solvent-free processes described in WO 2015/126704 and WO 2008/033687 by proposing the addition of a step of treatment of aldehydes using a chemical agent, carried out in a section of purification comprising a dehydration column, and a finishing column (or purification column), preferably inside said purification section, or alternatively in an additional purification section by distillation with one or two distillation columns, and allowing to lead to a quality of glacial acrylic acid.
• the chemical treatments which are described in the state of the art all have the drawback of generating water during the reaction of the aldehydes with the chemical reagent.
• a separating wall column as a purification / finishing column in a process for recovering acrylic acid using two distillation columns in the absence of external organic solvent.
• the particular configuration of the separating wall column that is to say when the separating wall is contiguous with the upper dome of the column in the upper part, and not contiguous with the bottom of the column in the lower part, allows to improve the energy balance of the process while improving the technical quality of the acrylic acid recovered.
• the technical acrylic acid extracted at the top of the column with a separating wall can be subjected to an additional treatment by fractional crystallization, or by distillation optionally in the presence of a compound which reacts with the residual aldehydes, resulting in an acrylic acid quality of polymer grade. Due to the improved technical quality, further purification to produce a polymer grade is simplified. Moreover, under certain conditions of use of the separating wall column, it was observed that an acrylic acid of polymer grade, meeting specifications concerning the residual content of aldehydes such as furfural or benzaldehyde, and of protoanemonin, can be extracted directly at the head of the separating wall column. However, the implementation of a separator wall distillation column remains complex and specific.
• the present invention relates to a process for the manufacture of glacial acrylic acid from a technical acrylic acid comprising low-content aldehyde compounds, said process comprising a distillation carried out in a distillation unit in the absence of a processing chemical reagent.
• aldehydes producing a polymer grade acrylic acid stream which is withdrawn by a side outlet of the distillation unit, a stream comprising essentially light compounds being extracted at the top of the distillation unit, and a stream of technical acrylic acid comprising heavy compounds being recovered at the bottom of the distillation unit.
• the process of the invention does not use a separator wall distillation column.
• the distillation unit comprises a single E12 distillation column equipped with a side draw-off.
• column E12 has a number of theoretical plates of between 15 and 30, preferably between 20 and 25.
• the distillation unit comprises a first distillation column El whose flow generated at the top feeds a second distillation column E2 equipped with a lateral draw-off.
• each of the columns E1 and E2 comprises a number of theoretical plates of between 8 and 15, preferably between 10 and 12.
• the acrylic acid subjected to the process according to the invention is a technical grade acrylic acid with a mass content of greater than 99.5%, comprising a low content of aldehydes such as furfural, benzaldehyde and acrolein, and which may contain light compounds such as acrolein, acetic acid or water;
• the process according to the invention makes it possible to produce a flow of acrylic acid purified meeting high quality criteria allowing its use in the manufacture of acrylic polymers of high molecular weight, in the absence of addition of chemical compound for treating aldehydes.
• polymer grade acrylic acid obtained according to the process of the invention can be characterized as follows:
• the invention thus overcomes the drawbacks of the methods of the prior art, by eliminating the use of a CMR classified product in the manufacture of polymer grade acrylic acid from technical grade acrylic acid. As a result, the formation of water associated with reactions between amino compounds such as hydrazine and aldehydes or unsaturated acids is avoided, and fouling problems due to the use of chemical reagents do not occur.
• the residual product resulting from the distillation of technical acrylic acid with a view to obtaining acrylic acid of polymer grade, recovered at the bottom of the distillation unit, can be advantageously recycled to an esterification workshop. manufacturing C 1 -C 8 acrylic esters, without additional purification which would be required if a chemical aldehyde treatment agent was used.
• the invention also has one, or preferably, several of the advantageous characteristics listed below:
• the distillation unit has at least one reflux at the top, in particular a reflux at the top of the distillation column E 12 or the column E2 equipped with a side draw-off.
• the distillation unit has at the head a condenser which can be total or partial, which allows to condense at least partially the distilled stream rich in light compounds.
• the condensed flow is returned at least in part to the top of column E12 or E2 equipped with a lateral withdrawal.
• the non-condensed part is eliminated, for example by sending it to an incinerator before final discharge to the atmosphere, or can be recycled upstream of the process, for example in the column for absorption of acrylic acid from the gases. reaction.
• the part of the condensed stream which is not recycled to reflux in the column can be eliminated, or preferably recycled upstream of the purification process, or be used for the manufacture of acrylic esters.
• the side draw-off includes a condenser which cools the acrylic acid to a temperature of around 30 ° C before storage.
• At least one phenolic polymerization inhibitor is introduced at the level of the condenser associated with the lateral withdrawal, preferably hydroquinone methyl ether (EMHQ), in an adequate quantity to protect the condensed stream against polymerization at the level of the condenser, in the storage tank and during transport before use of acrylic acid, and meeting the requirements of reactivity in polymerization.
• EMHQ hydroquinone methyl ether
• the lateral withdrawal is preferably carried out in the first third of the top of the column E12 or E2.
• At least one phenolic polymerization inhibitor preferably EMEH is introduced at the top of the columns E2 and E12 upstream of the condenser, so as to prevent the formation of polymer during the condensation of the distilled gas mixture and into the column, thanks to the presence of this inhibitor in the liquid reflux returned to the top of the column.
• polymerization inhibitors in particular non-phenolic polymerization inhibitors, can be sent alone or in combination, to a plate located under the side draw-off of columns E2 or E12 and / or at the top of column El .
• the inhibitors involved are those employed by those skilled in the art for the purification of acrylic acid.
• Air or depleted air is injected at the bottom of the distillation unit, in column E12 or El, preferably in a volume proportion of 0.1 to 0.5% of oxygen relative to the total flow of distilled AA.
• the mass ratio between the flow withdrawn laterally and the feed flow is between 60 and 90%, preferably between 70% and 80%.
• the mass ratio between the flow withdrawn at the bottom and the feed flow is between 10% and 40%, preferably between 20% and 30%.
• the stream recovered at the bottom of the distillation unit is advantageously recycled to an esterification unit without additional treatment.
• the reflux rate which can be defined as the recycling flow rate from the column head to the column, relative to that of lateral withdrawal, is between 1.5 and 4, preferably between 2 and 3, for example is equal to 2.5. Under these conditions, it is possible to obtain a good compromise between the column size and the number of separation stages to be used and the energy to be used to ensure this separation.
• the technical acrylic acid subjected to the process according to the invention contains a mass content of total aldehydes (furfural, benzaldehyde and acrolein) of less than 0.1%.
• the method according to the invention is operated in continuous or semi-continuous mode, preferably in continuous mode.
• FIG. 1 block diagram of the process according to a first embodiment of the invention
• FIG. 2 block diagram of the process according to a second embodiment of the invention.
• polymer grade and the term “glacial” have the same meaning and indicate that acrylic acid meets high quality criteria allowing its use in the manufacture of (meth) acrylic polymers of high quality. molecular weight.
• chemical aldehyde treatment agent or "chemical aldehyde treatment reagent” means a chemical compound which forms heavier reaction products with aldehydes which become more easily separable from acrylic acid by distillation.
• chemical treatment is understood to mean the treatment carried out using an agent for the chemical treatment of aldehydes.
• This type of treatment and the compounds which can be used are well known in the state of the art, without the reactions or complexations implemented being completely identified.
• the main purpose of the mode of action is to form reaction products heavier than the aldehydes to be treated.
• This term of chemical treatment agent for aldehydes excludes polymerization inhibitors which, although they may have a minor effect on aldehydes, are generally introduced for the sole purpose of stabilizing fluxes containing acrylic derivatives vis-à-vis polymerization, these polymerization inhibitors can therefore be present in acrylic acid subjected to the process according to the invention.
• external organic solvent denotes any organic compound in which acrylic acid is soluble and whose origin is external to the process, used as an absorption, extraction or azeotropic distillation solvent.
• azeotropic solvent denotes any organic solvent having the property of forming an azeotropic mixture with water.
• non-condensable or “non-condensable” refers to compounds whose boiling point is below a temperature of 20 ° C at atmospheric pressure.
• a polymer grade acrylic acid can be obtained by a simple operation of distilling a technical acrylic acid, without resorting to chemical treatment of the aldehydes.
• This distillation operation can follow the various methods of manufacturing solvent-free technical acrylic acid, described for example in documents EP 2 066 613, WO 2015/126704, WO 2008/033687, or using so-called external solvents such as WO 2010/031949.
• Acetic acid ⁇ 0.25%, preferably ⁇ 0.10%, for example ⁇ 0.05%
• Acrolein ⁇ 0.02%, preferably ⁇ 0.01%
• protoanemonin ⁇ 0.02% preferably ⁇ 0.01%, for example ⁇ 0.005%.
• said stream of technical acrylic acid is sent to a single distillation unit from which an acrylic acid free of most of the residual aldehydes is withdrawn laterally, corresponding to the desired polymer or ice grade defined as follows :
• the distillation unit The distillation unit
• the process for making glacial acrylic acid from technical acrylic acid with low aldehyde compounds consists of a distillation carried out in a single distillation unit which is free of a separator wall distillation column.
• the column E12 is equipped with a lateral draw-off and comprises a number of theoretical plates between 15 and 30, preferably between 20 and 25.
• This column single operates under a reduced pressure generally between 20 mm Hg and 150 mm Hg, preferably between 30 mm Hg and 100 mm Hg.
• Column E 12 consists of any type of trays and / or bulk internals and / or structured packings available for the rectification of mixtures and suitable for the distillation of polymerizable compounds.
• distillation column can be a conventional distillation column which may comprise at least one packing, such as for example a bulk packing and / or a combination of sections equipped with loose and structured packings, and / or trays such as for example perforated trays, plates with fixed valves, plates with movable valves, plates with domes, or combinations thereof.
• packing such as for example a bulk packing and / or a combination of sections equipped with loose and structured packings, and / or trays such as for example perforated trays, plates with fixed valves, plates with movable valves, plates with domes, or combinations thereof.
• column E12 is equipped with perforated trays.
• Stabilization of column E12 is generally carried out using stabilizers well known to those skilled in the art, possibly with injection of air or oxygen-depleted air.
• the feed to column E12 takes place in the first quarter of the bottom of the column, preferably at a level of a plate ranging from plates 2 to 7, preferably plates 3 to 5.
• a gaseous fraction rich in light compounds such as acrolein, acetic acid and water is distilled at the top of the column and eliminated after condensation and possibly additional treatment, or recycled upstream of the purification process. , or used for the manufacture of acrylic esters.
• these light non-condensing compounds can be sent directly in gaseous form to a vent treatment unit.
• the polymer grade acrylic acid is withdrawn in the liquid phase or in the gas phase, preferably from the first third of the top of the El 2 column, in particular between the theoretical trays 1 to 5 trays located below the column head.
• the polymer grade acrylic acid is withdrawn in the liquid phase.
• a flow of acrylic acid comprising most of the heavy impurities (in particular furfural, benzaldehyde, protoanemonin and non-phenolic inhibitors) separated from the flow of acrylic acid feeding column E1 2, can be advantageously recycled.
• the heavy impurities in particular furfural, benzaldehyde, protoanemonin and non-phenolic inhibitors
• the mass ratio between the flow withdrawn laterally and the feed flow of column E12 is between 60 and 90%, preferably between 70% and 80%.
• the mass ratio between the flow withdrawn at the bottom and the feed flow for column E12 is between 10% and 40%, preferably between 20% and 30%.
• column E12 is equipped with a condenser and a liquid feed at the top, which ensures liquid reflux in the column.
• the reflux rate which can be defined as the recycling flow rate from the column head to the column relative to that of lateral withdrawal is between 1.5 and 4, preferably between 2 and 3, for example is equal to 2.5.
• the light compounds at the top of the column are preferentially eliminated in the gas phase after a partial condensation operation.
• the distillation unit comprises two distillation columns El and E2 fluidly connected to each other by the gas flow distilled at the top of the column El which feeds at the bottom column E2.
• Each of the columns E1 and E2 comprises a number of theoretical plates of between 8 and 15, preferably between 10 and 12.
• Columns E1 and E2 are generally conventional distillation columns which may comprise at least one packing, such as for example a bulk packing and / or a structured packing, and / or trays such as for example perforated trays, valve trays. fixed, movable valve trays, domed trays, or their combinations.
• the columns E1 and E2 are equipped with perforated trays.
• Columns E1 and E2 operate under a reduced pressure generally between 20 mm Hg and 150 mm Hg, preferably between 30 mm Hg and 100 mm Hg.
• the feed to column E1 is preferably carried out in the first quarter of the bottom of the column, preferably at the level of a plate ranging from plates 2 to 7, preferably plates 3 to 5.
• the gas phase generated at the top of column El feeds column E2 in the first quarter of the bottom of the column, preferably at a level of a plate located going from plates 1 to 3 of this column.
• a gaseous fraction essentially entraining light compounds such as acrolein, acetic acid and water is distilled at the head of column E2, and recovered after condensation to be treated in a biological station or when only uses a partial condenser these light compounds are sent directly to a vent treatment unit.
• At least part of the flow condensed at the top of column E2 is sent as reflux to column E2 and consequently to column El.
• the reflux rate which can be defined as the recycling flow rate from the top of column E2 to column E2 relative to that of lateral withdrawal from column E2 is between 1.5 and 4, preferably between 2 and 3 , for example is equal to 2.5.
• the polymer grade acrylic acid is withdrawn in the liquid phase or in the gas phase, preferably at the first third of the top of the column E2, in particular between the theoretical plates 1 to 5 plates below the column head.
• the polymer grade acrylic acid is withdrawn in the liquid phase.
• the mass ratio between the flow withdrawn laterally from column E2 and the feed flow from column El is between 60 and 90%, preferably between 70% and 80%.
• the ratio between the flow withdrawn at the bottom of column El and the feed flow for column El is between 10% and 40%, preferably between 20% and 30%.
• the flow from the bottom of column E2 is sent in liquid form to the top of column El
• an acrylic acid stream comprising most of the heavy impurities (in particular furfural, benzaldehyde, protoanemonin and non-phenolic inhibitors) separated from the acrylic acid stream feeding the El column, can be advantageously recycled as a technical grade of acrylic acid to an esterification unit, without additional purification.
• the energy consumption in the process according to the invention is generally higher than that necessary in a separation using hydrazine or its derivatives to treat the aldehydes. This additional energy cost is however largely offset by the gain obtained due to the absence of production stoppages and cleaning and maintenance operations following the fouling associated with the use of an amino compound, and especially by the absence of CMR product. and its restrictive industrial environment.
• the percentages are expressed as percentages by mass.
• ACO acrolein
• a technical grade acrylic acid stream is subjected to a distillation operation using two columns E3 and E4 in series in the presence of hydrazine hydrate.
• the first column E3 (with 12 theoretical stages, and operating under a pressure of 45 mm Hg)) is fed by the flow of acrylic acid to be purified and hydrazine as an amino compound reacting with aldehydes, at the level of the theoretical plateau. 3 counted from the bottom of the column. At the top of column E3 (topping column), light impurities such as water generated during the reaction of hydrazine with aldehyde impurities and acetic acid are removed. The mass reflux rate of this column / distillate flow rate is set between 0.5 and 0.7.
• the bottom flow from the E3 topping column feeds a second E4 distillation column (with 12 theoretical stages and operating at a pressure of 8500 Pa).
• Column E4 carries out, at the top, the distillation of the purified acrylic acid, and, at the bottom, the elimination of the heavy compounds, comprising in particular the reaction products of hydrazine with the aldehyde impurities and with acrylic acid ( excess reagent).
• the supply to this column is carried out under the first plate at the bottom of the column.
• acrylic acid meeting the specifications of a polymer grade is obtained at the top of the second column E4, in a proportion of 17,510 kg to 22,525 kg of acid. technical acrylic powered.
• the overall energy cost for the operation of the 2 columns has been estimated at 4.54 Gcal / h.
• the content of acrylic acid is 99.9% and the impurities furfuraldehyde, benzaldehyde and acrolein are present at a content of less than 1 ppm.
• the column bottom stream E4 contains the compounds resulting from the reaction of hydrazine with aldehydes and from side reactions with acrylic acid. This flow rich in acrylic acid is unsuitable for the manufacture of esters.
• Example 1 The process setup of Example 1 is used, but no addition of hydrazine hydrate is made.
• a configuration as shown in Figure 1 is used for the simulation of the process according to the invention.
• Column E12 has 24 theoretical trays and it is equipped at the head with a partial condenser and a side draw-off at tray No. 5 counted from the column head.
• Column E12 is fed with a flow of technical acrylic acid, without adding any agent for treating the aldehydes.
• the column operates under a pressure of 100 mm Hg.
• the temperature at the side draw-off is 90 ° C, and that at the bottom of 111 ° C.
• Table 3 below collates the mass composition of the various streams.
• the flow withdrawn laterally corresponds to an acrylic acid of polymer grade.
• the energy consumption in this configuration is 7.15 Gcal / h at the boiler.

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