Patent Description:
The present invention relates to a method for preparing an acrylic acid, and more particularly, to a method for preparing an acrylic acid by a dehydration reaction of a lactic acid, which effectively removes by-products while reducing an acrylic acid loss.

An acrylic acid is used as a polymer raw material used in fiber, adhesives, paint, fiber processing, leather, building materials, and the like, and its demand is growing. In addition, the acrylic acid is also used as a raw material of an absorbent resin and is industrially used a lot in absorbent articles such as paper diapers and sanitary napkins, agricultural and horticultural water retaining agents, industrial water stop materials, and the like.

A conventional method for preparing an acrylic acid is generally a method of oxidizing propylene in the air, but the method is a method of converting propylene into acrolein by a gaseous contact oxidation reaction and subjecting the acrolein to a gaseous contact oxidation reaction to prepare an acrylic acid, and the method produces an acetic acid as a by-product, which is difficult to separate from the acrylic acid. In addition, the method for preparing an acrylic acid using propylene uses propylene obtained by refining crude oil which is a fossil resource, as a raw material, and considering problems such as a recent rise in crude oil prices or global warming, the method has a problem in terms of raw material costs or environmental pollution.

Thus, a study on a method for preparing an acrylic acid from a carbon-neutral biomass raw material was conducted. For example, there is a method for preparing an acrylic acid (AA) by a gaseous dehydration reaction of a lactic acid (LA). This method is generally a method for preparing an acrylic acid by an intramolecular dehydration reaction of a lactic acid in the presence of a catalyst at a high temperature of <NUM> or higher. A reaction product including an acrylic acid is produced by the dehydration reaction of a lactic acid, and an unreacted lactic acid is included in the reaction product depending on a conversion rate. When an unreacted lactic acid is included in the reaction product, the economic feasibility of the process may be improved only by recovering the lactic acid in a separation process. However, since the lactic acid is rapidly oligomerized at a high concentration at a high temperature, it is difficult to recover the lactic acid. <CIT> discloses a process for the dehydration of lactic acid to yield acrylic acid.

An object of the present invention is to provide a method of effectively recovering an unreacted lactic acid from a reaction product produced by preparing an acrylic acid by a dehydration reaction of a lactic acid, and reusing the lactic acid, in order to solve the problems mentioned in the Background Art.

In one general aspect, a method for preparing an acrylic acid includes: dehydrating a lactic acid aqueous solution in a reaction unit to prepare a reaction product stream; passing the reaction product stream through a cooling unit and a refining unit sequentially and supplying a discharge stream from the refining unit to an acrylic acid separation column; and separating an unreacted lactic acid as a side discharge stream and separating the acrylic acid as an upper discharge stream in the acrylic acid separation column.

According to the method for preparing an acrylic acid of the present invention, in recovering a lactic acid from a reaction product including an acrylic acid, a recovery rate of an unreacted lactic acid may be increased by controlling the amount of exposure time to a high temperature in a high concentration state to minimize an oligomerization reaction of a lactic acid.

The term "stream" in the present invention may refer to a fluid flow in a process, or may refer to a fluid itself flowing in a pipe. Specifically, the stream may refer to both a fluid itself flowing in a pipe connecting each device and a fluid flow. In addition, the fluid may include any one or more components of gas, liquid, and solid.

Hereinafter, the present invention will be described in more detail for better understanding of the present invention, with reference to <FIG>.

According to the present invention, a method for preparing an acrylic acid is provided. More specifically, the method may include: dehydrating a lactic acid aqueous solution in a reaction unit <NUM> to prepare a reaction product stream; passing the reaction product stream through a cooling unit <NUM> and a refining unit <NUM> sequentially and supplying a discharge stream from the refining unit <NUM> to an acrylic acid separation column <NUM>; and separating an unreacted lactic acid as a side discharge stream and separating the acrylic acid as an upper discharge stream in the acrylic acid separation column <NUM>.

Specifically, a conventional method for preparing an acrylic acid is generally a method of oxidizing propylene in the air, but the method is a method of converting propylene into acrolein by a gaseous contact oxidation reaction and subjecting the acrolein to a gaseous contact oxidation reaction to prepare an acrylic acid, and the method produces an acetic acid as a by-product, which is difficult to separate from the acrylic acid. In addition, the method for preparing an acrylic acid using propylene uses propylene obtained by refining crude oil which is a fossil resource, as a raw material, and considering problems such as a recent rise in crude oil prices or global warming, the method has a problem in terms of raw material costs or environmental pollution.

In order to solve the problems of the conventional method for preparing an acrylic acid, a study on a method for preparing an acrylic acid from a carbon-neutral biomass raw material was conducted. For example, there is a method for preparing an acrylic acid (AA) by a gaseous dehydration reaction of a lactic acid (LA). This method is generally a method for preparing an acrylic acid by an intramolecular dehydration reaction of a lactic acid in the presence of a catalyst at a high temperature. A reaction product including an acrylic acid is produced by the dehydration reaction of a lactic acid, and an unreacted lactic acid is included in the reaction product depending on a conversion rate. When an unreacted lactic acid is included in the reaction product, the economic feasibility of the process may be improved only by recovering the lactic acid in a separation process. However, since the lactic acid is rapidly oligomerized at a high concentration at a high temperature, it is difficult to recover the lactic acid.

For this, in the present invention, in order to solve the conventional problems, a method of separating a lactic acid from a reaction product including an acrylic acid prepared by the dehydration reaction of a lactic acid, in which a time that a high concentration of a lactic acid is exposed to a high temperature is shortened to prevent oligomerization of a lactic acid, thereby improving a recovery rate of an unreacted lactic acid, is to be provided.

According to an exemplary embodiment of the present invention, a lactic acid aqueous solution is supplied to the reaction unit <NUM> and a dehydration reaction is performed to prepare a reaction product including an acrylic acid. Here, the dehydration reaction may be performed as a gas phase reaction in the presence of a catalyst. For example, the concentration of the lactic acid in the lactic acid aqueous solution may be <NUM> wt% or more, <NUM> wt% or more, or <NUM> wt% or more and <NUM> wt% or less, <NUM> wt% or less, <NUM> wt% or less, or <NUM> wt% or less. When the lactic acid is present at a high concentration, oligomers such as dimers and trimers are formed by an equilibrium reaction, so that the lactic acid may be used in the form of an aqueous solution having the concentration in the above range.

The reactor may include a reactor capable of a common dehydration reaction of a lactic acid, the reactor may include a reaction tube filled with a catalyst, and while a reaction gas including volatile components of a lactic acid aqueous solution as a raw material is passed through the reaction tube, a lactic acid may be dehydrated by a gaseous contact reaction to produce an acrylic acid. The reaction gas may further include any one or more dilution gases of water vapor, nitrogen gas, and air for adjusting a concentration, in addition to the lactic acid.

Operation conditions of the reactor may be common dehydration reaction conditions of a lactic acid. Here, the operation temperature of the reactor may refer to a set temperature of a heating medium or the like used for controlling the temperature of the reactor.

A catalyst used in the dehydration reaction of the lactic acid may include, for example, one or more selected from the group consisting of sulfate-based catalysts, phosphate-based catalysts, and nitrate-based catalysts. As a specific example, the sulfate may include Na<NUM>SO<NUM>, K<NUM>SO<NUM>, CaSO<NUM>, and Al<NUM>(SO<NUM>)<NUM>, the phosphate may include Na<NUM>PO<NUM>, Na<NUM>HPO<NUM>, NaH<NUM>PO<NUM>, K<NUM>PO<NUM>, K<NUM>HPO<NUM>, KH<NUM>PO<NUM>, CaHPO<NUM>, Ca<NUM>(PO<NUM>)<NUM>, AlPO<NUM>, CaH<NUM>P<NUM>O<NUM>, and Ca<NUM>P<NUM>O<NUM>, and the nitrate may include NaNO<NUM>, KNO<NUM>, and Ca(NO<NUM>)<NUM>. In addition, the catalyst may be supported on a support. The support may include one or more selected from the group consisting of, for example, diatomaceous earth, alumina, silica, titanium dioxide, carbides, and zeolite.

The reaction product prepared by the dehydration reaction of the lactic acid may further include water (H<NUM>O), gas by-products, low-boiling point by-products, high-boiling point by-products, and an unreacted lactic acid, in addition to the acrylic acid which is a desired product.

The method for preparing an acrylic acid by the dehydration reaction of the lactic acid may secure raw material competitiveness as compared with a conventional method of oxidizing propylene in the air and solve the problem of environmental pollution, but the conversion rate of the lactic acid is low and various by-products are produced to lower the yield of an acrylic acid. Therefore, it is necessary to develop a process for improving economic feasibility. For this, in the present invention, a method for improving economic feasibility by increasing the recovery rate of an unreacted lactic acid may be provided.

According to an exemplary embodiment of the present invention, the reaction product stream is passed through a cooling unit <NUM> and a refining unit <NUM> sequentially, and a discharge stream from the refining unit <NUM> may be supplied to an acrylic acid separation column <NUM> to recover a lactic acid.

According to an exemplary embodiment of the present invention, the cooling unit <NUM> may include one or more cooling towers, and the reaction product stream may be supplied to the cooling tower and cooled. Specifically, the reaction product prepared by the dehydration reaction of the lactic acid is a gas phase and may be condensed through the cooling tower. Gas by-products may be separated to the upper portion of the cooling tower and a liquid condensate may be discharged to the lower portion of the cooling tower, and the condensate may be supplied to the refining unit <NUM> at the rear end. Here, the gas by-products may include water, carbon monoxide, carbon dioxide, dilution gas, acetaldehyde, and the like as gas components.

According to an exemplary embodiment of the present invention, the refining unit <NUM> may include a water separation column and a low-boiling point separation column. For example, the water separation column may separate water from a reaction product by distillation or extraction.

When water is separated from the reaction product by extraction in the water separation column, a separate extractant is supplied to the water separation column, and the acrylic acid included in the reaction product stream may be separated as the upper discharge stream from the water separation column, using the extractant. In addition, a step for recovering the extractant may be further performed.

The extractant may include one or more selected from the group consisting of, for example, benzene, toluene, xylene, n-heptane, cycloheptane, cycloheptene, <NUM>-heptene, ethylbenzene, methylcyclohexane, n-butylacetate, isobutylacetate, isobutylacrylate, n-propylacetate, isopropylacetate, methylisobutylketone, <NUM>-methyl-<NUM>-heptene, <NUM>-methyl-<NUM>-heptene, <NUM>-methyl-<NUM>-heptene, <NUM>-ethyl-<NUM>-hexene, ethylcyclopentane, <NUM>-methyl-<NUM>-hexene, <NUM>,<NUM>-dimethylpentane, <NUM>-methyl-<NUM>-hexene, and isopropylbutylether. As a specific example, the extractant may be toluene.

A method of supplying the extractant to the water separation column and performing extraction may be any known method, and for example, any method such as cross current, counter current, and co-current may be used without particular limitation.

The reaction product stream and the extractant may be brought into contact in the water separation column, thereby separating an extract and an extraction residue solution. For example, the extract may be an acrylic acid dissolved in the extractant, and the extract may be discharged as an upper discharge stream from the water separation column. Here, the upper discharge stream from the water separation column may be supplied to a low-boiling point separation column after removing the extractant.

In addition, the extraction residue solution is wastewater including water and may be separated as a lower discharge stream from the water separation column. Here, aqueous by-products may be separated together with water in the lower portion of the water separation column and discharged.

The upper discharge stream from the water separation column is supplied to the low-boiling point separation column and low-boiling point by-products may be removed by distillation, and a reaction product from which the low-boiling point by-products have been removed may be discharged as the lower discharge stream from the low-boiling point separation column. Here, the discharge stream from the refining unit <NUM> supplied to the acrylic acid separation column <NUM> may be the lower discharge stream from the low-boiling point separation column.

The reaction product stream may be passed through the cooling unit <NUM> and the refining unit <NUM> sequentially to remove gas by-products, water, and low-boiling point by-products.

The discharge stream from the refining unit <NUM> may include an acrylic acid, an unreacted lactic acid, and high-boiling point by-products. The content of the unreacted lactic acid in the discharge stream from the refining unit <NUM> varies with the conversion rate of a lactic acid which is changed depending on the reaction and process conditions in the reaction unit <NUM>, and for example, may be <NUM> wt% or more, <NUM> wt% or more, or <NUM> wt% or more and <NUM> wt% or less, <NUM> wt% or less, or <NUM> wt% or less. As such, when the unreacted lactic acid is present in the reaction product, it should be recovered or removed in a separation process, but conventionally, it was difficult to recover the unreacted lactic acid and the unreacted lactic acid was removed with high-boiling point by-products in most cases, and in the present invention, the unreacted lactic acid is recovered at a high recovery rate to improve the economic feasibility of the process.

According to an exemplary embodiment of the present invention, the discharge stream from the refining unit <NUM> may be supplied to the acrylic acid separation column <NUM> to recover the lactic acid. Specifically, the acrylic acid separation column <NUM> may be for separating the acrylic acid from the reaction product, and recovering and reusing the unreacted lactic acid.

The operation conditions of the acrylic acid separation column <NUM> may be adjusted for increasing the separation efficiency in separating each component depending on the composition of the discharge stream from the refining unit <NUM>.

The operation pressure of the acrylic acid separation column <NUM> may be <NUM> kPa (<NUM> torr) or more, <NUM> kPa (<NUM> torr) or more, or <NUM> kPa (<NUM> torr) more and <NUM> kPa (<NUM> torr) or less, <NUM> kPa (<NUM> torr) or less, or <NUM> kPa (<NUM> torr) or less. When the acrylic acid separation column 10C is operated to the operation pressure in the above range, separation efficiency in separating each of the acrylic acid, the unreacted lactic acid, and the high-boiling point by-products in the acrylic acid separation column <NUM> may be high and a side reaction occurring at a high temperature may be suppressed.

The discharge stream from the refining unit <NUM> may be supplied to a stage at <NUM>% or more, <NUM>% or more, <NUM>% or more, or <NUM>% or more and <NUM>% or less, <NUM>% or less, or <NUM>% or less with respect to the total number of stages of the acrylic acid separation column <NUM>. Here, the total number of stages of the acrylic acid separation column <NUM> may be <NUM> to <NUM>. For example, when the total number of stages of the acrylic acid separation column <NUM> is <NUM>, a top stage may be a 1st stage and a bottom stage may be a 100th stage, and stages at <NUM>% to <NUM>% of the total number of stages of the acrylic acid separation column <NUM> may refer to 60th to 80th stages of the acrylic acid separation column <NUM>. A supply stage of the discharge stream from the refining unit <NUM> which is supplied to the acrylic acid separation column <NUM> is controlled to the above range, thereby increasing the separation efficiency of the acrylic acid, the lactic acid, and the high-boiling point by-products in the acrylic acid separation column <NUM>.

In the acrylic acid separation column <NUM>, the acrylic acid may be separated from the upper discharge stream, the lactic acid may be separated from the side discharge stream, and the high-boiling point by-products may be separated from the lower discharge stream.

The side discharge stream from the acrylic acid separation column <NUM> may be discharged to a stage at <NUM>% or more, <NUM>% or more, <NUM>% or more, or <NUM>% or more and <NUM>% or less, <NUM>% or less, or <NUM>% or less with respect to the total number of stages of the acrylic acid separation column <NUM>. The discharge stage of the side discharge stream from the acrylic acid separation column <NUM> is controlled to the above range, thereby separating a high-purity unreacted lactic acid to the side and recovering it, and thus, a time that the lactic acid is exposed to a high temperature may be minimized and a loss of a lactic acid discharged to a lower portion with the high-boiling point by-products may be minimized.

The content of the unreacted lactic acid included in the side discharge stream from the acrylic acid separation column <NUM> may be <NUM>% or more, <NUM>% to <NUM>%, or <NUM>% to <NUM>% of the content of the unreacted lactic acid included in the discharge stream from the refining unit <NUM>. The unreacted lactic acid separated as the side discharge stream from the acrylic acid separation column <NUM> may be mixed with the lactic acid aqueous solution and supplied to the reaction unit <NUM>. The unreacted lactic acid is recovered as the side discharge stream from the acrylic acid separation column <NUM> and reused in the reaction unit <NUM>, thereby improving the economic feasibility of the process.

The upper discharge stream from the acrylic acid separation column <NUM> passes through a condenser, and a part of the stream is refluxed to the acrylic acid separation column <NUM> and an acrylic acid may be separated from the rest of the stream. In addition, a part of the lower discharge stream from the acrylic acid separation column <NUM> passes through a reboiler and is refluxed to the acrylic acid separation column <NUM>, and high-boiling point by-products may be separated to the rest of the stream.

A flow rate ratio of the stream passing through the reboiler and being refluxed to the acrylic acid separation column <NUM> to the stream being not refluxed and separating the acrylic acid in the upper discharge stream from the acrylic acid separation column <NUM> may be <NUM> or more, <NUM> or more, or <NUM> or more and <NUM> or less, <NUM> or less, or <NUM> or less. As described above, the flow rate ratio of the stream passing through the lower reboiler and being refluxed to the stream being not refluxed and separating the acrylic acid in the upper discharge stream from the acrylic acid separation column <NUM> is controlled, thereby reducing a time that the unreacted lactic acid passes through the lower reboiler of the acrylic acid separation column <NUM> operated at a high temperature to prevent the progress of the oligomerization reaction of the lactic acid.

According to an exemplary embodiment of the present invention, in the method for preparing an acrylic acid, if necessary, devices such as a distillation column, a condenser, a reboiler, a valve, a pump, a separator, a mixer, and the like may be further installed.

Hereinabove, the method for preparing an acrylic acid according to the present invention has been described and illustrated in the drawings, but the description and the illustration in the drawings are the description and the illustration of only core constitutions for understanding of the present invention, and in addition to the process and devices described above and illustrated in the drawings, the process and the devices which are not described and illustrated separately may be appropriately applied and used for carrying out the method for preparing an acrylic acid according to the present invention.

Hereinafter, the present invention will be described in more detail by the examples. However, the following examples are provided for illustrating the present invention, and it is apparent to a person skilled in the art that various modifications and alterations may be made without departing from the scope of the present invention.

According to the process flow diagram illustrated in <FIG>, a process of preparing an acrylic acid was simulated, using an Aspen Plus simulator from Aspen Technology, Inc.

Specifically, a lactic acid aqueous solution and nitrogen (N<NUM>) as a dilution gas were supplied to a reaction unit <NUM> to prepare a reaction product including an acrylic acid (AA) by a dehydration reaction. The discharge stream from the reaction unit <NUM> including the reaction product stream was supplied to a cooling unit <NUM> to remove gas by-products, and the reaction product from which the gas by-products were removed was supplied to a refining unit <NUM>. Water and low-boiling point by-products were removed from the reaction product in the refining unit <NUM>, and a discharge stream from the refining unit <NUM> from which water and low-boiling point by-products were removed was supplied to a 15th stage of an acrylic acid separation column <NUM>. At this time, the total number of stages of the acrylic acid separation column <NUM> was <NUM>.

The upper discharge stream from the acrylic acid separation column <NUM> was passed through a condenser, and a part of the stream was refluxed to the acrylic acid separation column <NUM> and an acrylic acid was separated from the rest of the stream. In addition, a part of the lower discharge stream from the acrylic acid separation column <NUM> was passed through a reboiler and refluxed to the acrylic acid separation column <NUM>, and high-boiling point by-products were separated from the rest of the stream. In addition, a side discharge stream including an unreacted lactic acid was separated to a 13th stage of the acrylic acid separation column <NUM>, and the side discharge stream from the acrylic acid separation column <NUM> was mixed with the lactic acid aqueous solution and supplied to the reaction unit <NUM>. At this time, a flow rate ratio of a stream passing through the reboiler and being refluxed to the acrylic acid separation column <NUM> to a stream being not refluxed and separating the acrylic acid in the upper discharge stream from the acrylic acid separation column <NUM> was controlled to <NUM>.

The temperature, the pressure, and the flow rate (kg/hr) for each component in each stream are shown in the following Table <NUM>:.

The process was performed in the same manner as in Example <NUM>, except that the discharge stream from the refining unit <NUM> was supplied to a 10th stage of the acrylic acid separation column <NUM> and the side discharge stream including the unreacted lactic acid was separated to an 8th stage of the acrylic acid separation column <NUM>.

At this time, the temperature, the pressure, and the flow rate (kg/hr) for each component in each stream are shown in the following Table <NUM>:.

Specifically, a lactic acid aqueous solution and nitrogen (N<NUM>) as a dilution gas were supplied to a reaction unit <NUM> to prepare a reaction product including an acrylic acid (AA) by a dehydration reaction. The discharge stream from the reaction unit <NUM> including the reaction product stream was supplied to a cooling unit <NUM> to remove gas by-products, and the reaction product from which the gas by-products were removed was supplied to a refining unit <NUM>. Water and low-boiling point by-products were removed from the reaction product in the refining unit <NUM>, and a discharge stream from the refining unit <NUM> from which water and low-boiling point by-products were removed was supplied to a 3rd stage of an acrylic acid separation column <NUM>. At this time, the total number of stages of the acrylic acid separation column <NUM> was <NUM>.

The upper discharge stream from the acrylic acid separation column <NUM> was passed through a condenser, and a part of the stream was refluxed to the acrylic acid separation column <NUM> and an acrylic acid was separated from the rest of the stream. In addition, a part of the lower discharge stream from the acrylic acid separation column <NUM> was passed through a reboiler and refluxed to the acrylic acid separation column <NUM>, and high-boiling point by-products and an unreacted lactic acid were separated from the rest of the stream and supplied to a lactic acid recovery column <NUM>.

The upper discharge stream from the lactic acid recovery column <NUM> was passed through a condenser, and a part of the stream was refluxed to the lactic acid recovery column <NUM> and the unreacted lactic acid was recovered from the rest of the stream. In addition, a part of the lower discharge stream from the lactic acid recovery column <NUM> was passed through a reboiler and refluxed to the lactic acid recovery column <NUM>, and high-boiling point by-products were separated from the rest of the stream. The lactic acid recovered from the upper discharge stream from the lactic acid recovery column <NUM> was mixed with the lactic acid aqueous solution and supplied to the reaction unit.

Referring to Tables <NUM> to <NUM>, in Examples <NUM> and <NUM> in which the unreacted lactic acid was recovered from the reaction product by the method for preparing an acrylic acid according to the present invention, it was confirmed that the purity of the acrylic acid was <NUM>% to <NUM>%, and the recovery rate of the lactic acid was <NUM>% or more. In particular, in Example <NUM> in which the supply stage of the discharge stream from the refining unit <NUM> was controlled to a stage at <NUM>% to <NUM>% of the total number of stages of the acrylic acid separation column <NUM>, the discharge stage of the side discharge stream from the acrylic acid separation column <NUM> was controlled to a stage at <NUM>% to <NUM>%, and the flow rate ratio of the stream passing through the reboiler and being refluxed to the acrylic acid separation column <NUM> to the stream being not refluxed and separating the acrylic acid in the upper discharge stream from the acrylic acid separation column <NUM> was controlled to <NUM> to <NUM>, it was confirmed that the purity of the acrylic acid reached <NUM>%, and the recovery rate of the lactic acid was higher.

Claim 1:
A method for preparing an acrylic acid, the method comprising:
dehydrating a lactic acid aqueous solution in a reaction unit to prepare a reaction product stream;
passing the reaction product stream through a cooling unit and a refining unit sequentially and supplying a discharge stream from the refining unit to an acrylic acid separation column; and
separating an unreacted lactic acid as a side discharge stream and separating the acrylic acid as an upper discharge stream in the acrylic acid separation column.