ES2302470B1 - SYSTEM AND METHOD FOR RECOVERY OF ACETIC ACID DURING THE PRODUCTION OF TEREFTALIC ACID. - Google Patents

Abstract

Acid recovery system and method acetic acid during the production of terephthalic acid.

A distillation system and method is disclosed to recover Acetic Acid from a stream containing Acid Acetic and water generated during the production of Terephthalic Acid. The invention includes a dehydration column that uses azeotropic distillation. To recover Acetic Acid in conjunction with a condenser system to recover energy. The dehydration column operates with a pressure of at least 1.2 Absolute Kg / cm2 or higher at the head of the column. He condensing system is a steam generator that condenses steam in a stream of concentrated acetic acid while generating Low pressure steam of 0.6 to 2.0 Kg / cm2 absolute.

Description

Acid recovery system and method acetic acid during the production of terephthalic acid.

Background of the invention

The invention is designed for processes chemicals used in the distillation of chemical compounds Industrial More specifically, the invention is directed to the acetic acid recovery during acid production terephthalic

Terephthalic acid is useful in a large variety of industrial applications and chemical processes. He terephthalic acid, for example, serves as a raw material for production of polyester fibers such as plastic and Dacron ™, which are used in textile and container production. Polyethylene terephthalate (PET) is a type of polyester or Mylar? And a high strength resin that is very useful in an endless number of industrial and consumer applications. The bottles of soft drinks and water, as well as jars and plastic containers which are used in the transport of consumer goods and of Food distribution, are manufactured from this resin.

Normally, teraphthalic acid is produced by a reaction of paraxylene and molecular oxygen in the presence of catalysts. During the production process, acetic acid is used as a solvent for teraphthalic acid. Acetic acid is diluted in water during the oxidation process in a section of reactors of a teraphthalic acid plant during the production cycle. Next, a part of the stream of acetic acid and water is sent to a dehydration unit to eliminate that water generated in the reactor that will serve to recycle or
Discard.

In terephthalic acid plants have employed three different methods to separate acetic acid and the water so that acetic acid can return to the reactor to be reused while the water generated by the reaction is sent to the sewage treatment facility for your insurance processing One of them is by distillation conventional, in which the uneven boiling point of Components facilitates the separation of acetic acid and water. He azeotropic distillation method makes use of some agents separators to form azeotropes with acetic acid and water, facilitating the change in energy requirements for your treatment. The liquid-liquid extraction is the last method for the separation of acetic acid and water during the production of terephthalic acid.

Distillation has been used mostly as a main operation group for acid recovery Acetic from the waters. In such processes, one or more are used towers to process a number of different currents acetic acid concentrations in order to recover it for possible future uses in oxidation processes. The products used in the distillation tower are a stream of acetic acid concentration at the bottom and a stream of pure water on top, ideal to minimize loss of the valuable acetic acid solvent. One more stream of water pure would also reduce the weight in the facilities for the wastewater treatment thus preventing spills accidental chemicals

However, the distillation of acetic acid and the water is not too efficient because the characteristics of the vapor-liquid balance in the acetic acid-water system are very little adequate. Conventional distillation systems require the use of a large number of theoretical phases, such as new trays, and a large number of reflux, as is the case with the high consumption of energy, to obtain relatively low levels of acetic acid, ranging between 0.5-0.8 wt% in distilled water in the top Then the wastewater is processed from the top to recover certain by-products, and They are then sent to the water treatment facilities residuals where the rest of acetic acid will be neutralized and will employ later.

The use of conventional distillation implies high investment costs due to the large dimensions of the tower and column equipment and a high operating cost because of the large amounts of steam consumed during the process. In addition, the traditional process scheme does not allow obtaining a economically a distillation that is completely free of acetic acid. This limitation, in turn, presents problems operations that include the costs associated with the operation that results from acetic acid losses, the costs associated with acetic acid treatment in wastewater, limitations of the capacity of the lower facilities in the treatment of wastewater and environmental problems that are in continued boom due to the increasingly stringent levels of Limitation of emissions to the environment.

An effort has been made to look for alternatives that help minimize the high operating costs associated with the conventional distillation process for acid separation acetic and water. The processors and chemical companies have resorted to azeotropic distillation including the addition of a selective alkyl acetate, such as isobutyl acetate (IBA), the  normal butyl acetate (NBA), normal propyl acetate (NPA), etc. as a separating agent for azeotropic distillation for the dehydration column. The separating agent forms an azeotrope of low boiling with water and, consequently, improves the relative volatility of the separation between acetic acid and azeotrope of alkyl acetate-water. This reduces the needs of the energy or theoretical phase for it separation. Compared to conventional distillation, the proposed azeotropic distillation normally reduces the energy consumption (for example, steam), between 20% and 40% at the dehydration column while providing a relatively low acetic acid concentration, 330-800 ppm (parts per million), in the water distilled Generally, the azeotropic distillation column operates at an environmental pressure in terephthalic acid plants in All previous systems.

A great effort has also been perceived in the use of liquid-liquid extraction with agents special extractives in acetic acid recovery from water streams to contain only 0.1% wt of acetic acid at 20% acetic acid. Some of the agents that most frequently used are acetates, aminos, ketones and phosphine oxides, as well as mixtures of this type. Once the extraction phase is complete, a complicated series of distillation phases to recover the acid and to circulate the extractive agent back to the phase Extraction

In view of a loss of energy like this, which derives from the use of traditional distillation systems, which what is needed is a distillation system that is energetically Efficient and produce less waste and unwanted by-products. The system should also recycle both energy and Initial products in a way that respects the environment. He distillation system and its process should also be easily modifiable in existing chemical process systems to Expand current plants. In addition, the recovery system it should be able to install easily, avoiding large expenses of capital.

For these reasons, it would be advisable to use less energy in a distillation system for acid recovery acetic and generate more energy for other uses within the plant. The system should allow to save chemical substances and material First hand, result in a lower loss of acetic acid And save money. Such systems and methods should also be able to be applied in a wide variety of chemical processes in what refers to a large number of industrial chemical compounds. In addition, the system should be simple and less expensive to manufacture at the same time that it should be compatible with conventional systems and processes.

Summary of the Invention

A distillation system is revealed for recover acetic acid from water during acid production teraphthalic comprising a dehydration column with a head section in which it includes a condenser or generator steam. The dehydration column has at least one current inlet feed containing a mixture of acetic acid and of water generated during the production of teraphthalic acid where acetic acid is a solvent for production and water is a byproduct of the reaction that produces acid teraphthalic

The dehydration column has an agent separator for azeotropic distillation of teraphthalic acid. In an inclusion, the separating agent may be acetate N-Butyl In another, the separator is acetate I-butyl or a mixture of acetate I-butyl and N-butyl acetate. The distillation column has a head pressure of at least 1.2 kg / cm2 absolute, but may become greater.

The lower output current of the column it has a higher concentration of acetic acid than the current of input power.

In addition the distillation system has a condenser to separate acetic acid from water. The current of column head steam has a lower dilute acetic acid concentration that at least one stream Input power. The condenser condenses a vapor from the top of the dehydration column to generate a low pressure steam. The low pressure steam generated has a pressure of at least 0.6 kg / cm2 absolute, but can reach pressures greater than 2.0 kg / cm2 absolute.

A distillation method is also revealed for recover acetic acid from water during acid production teraphthalic The method comprises the stages in which provides a water inlet feed stream that It contains acetic acid and the feed stream is distilled from entry into an azeotropic dehydration column that presents A head in a stream of steam. The steam stream is dragged through the use of acetate N-butyl or I-butyl acetate, or A mixture of both. Thus, the steam stream condenses to separate acetic acid from water and thus provide a output current at the bottom that has a acetic acid concentration more diluted than the stream of input power.

The present invention is a further improvement of the azeotropic distillation process for separating acetic acid from water in the teraphthalic acid plant (PTA) while generating steam through energy recovery. In the invention, both isobutyl acetate (IBA) and normal butyl acetate (NBA) are used, as well as their combinations as separating agents in the acetic acid distillation column at an operating head pressure equivalent to 1 , 3 kg / cm2 absolute or greater. The invention includes a steam generation system above the dehydration column in order to recover the energy in the form of steam by condensing the head steam leaving the dehydration column and generating a low pressure steam stream at 0 , 6 - 2.0 kg / cm2 absolute for various uses at the bottom. Based on conventional distillation devices, the content of acetic acid in the water at the top can be reduced from more than 7000 ppm to approximately 300-800 ppm. An additional reduction in acetic acid content (up to 150 ppm or less) can be achieved by using high-performance total transfer equipment such as multi-perforated valves, trays and high capacity pipes that conduct the gas or fluid down into the column without the additional consumption of
steam.

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When using devices and equipment total transfer in these plants with the specifications and existing separation needs, the present invention reduces significantly re-boiling expense (per example, steam consumption) required for said separation. Yes we compare it with conventional distillation, the present system and method normally requires between 20 and 40% less energy than that of conventional distillation. The present invention, combined with considerably lower energy consumption during the acetic acid and water separation, significantly reduces the acetic acid in the water from the top, usually from 0.5% -0.8% up to 300-800 ppm, or even less.

The invention has even greater advantages when applied to substitution or reform columns for dehydration of acetic acid by distillation conventional. Not only is the consumption of energy, but also the loss of acetic acid during the distillation, which is significantly reduced before sewage treatment. Some energy is recovered by generating steam and helps reduce loads and operating costs in water treatment facilities existing residuals.

This invention refers to a new method to recover acetic acid, which is the solvent used usually in the production of teraphthalic acid and also a source of recoverable waste in other industrial processes of similar importance. The system and method also provide a significant reduction over the total energy consumption of a plant and allows an increase in capacity in existing plants. A plant, according to the present invention, generates a Vapor pressure of 0.6 kg / cm2 absolute or even higher for generate additional energy and was used inside the plant. With these improvements, the teraphthalic acid plant also minimizes the wastewater treatment installation requirements and eliminates the problems of emission of organic compounds that currently exist in most of the production plants of teraphthalic acid In one embodiment, the invention provides a modification to the distillation of acetic acid in conjunction with an azeotropic distillation system so that it manufacture at an operating pressure higher than the environmental pressure, thus allowing energy saving and recovery of a greater amount of acetic acid.

The invention also offers its benefits. economic in the construction of new acid plants teraphthalic, where the total energy consumption of the invention is the lowest among all current and previous methods. The present invention is also especially useful in the processes of modernization in which existing plants are updated with new components during reconversion or maintenance regular. This system and method can also be projected on plants of newly constructed teraphthalic acid.

These and other objectives and accomplishments of the invention would come to be appreciated and understood better when considered in conjunction with the description and schemes that presented below. However, it should be taken in consideration as the following description, in the same way as notes the predominant achievements and numerous details specific, given by way of illustration and not limitation. They can various changes and modifications be made as regards to the invention, without having to take as a starting point the perspective of the present work. All these possible changes are collected in the invention.

Brief description of the figures

Figure 1 is a functional scheme that explains briefly several units of the process that is carried out in a normal plant during the acid production process terephthalic

Figure 2 illustrates a diagram of the process of manufacturing that takes place in a dehydration column of terephthalic acid in which a conventional distillation is used normally found in terephthalic acid plants previous.

Figure 3 shows an outline of the process of manufacture of an acetic acid dehydration column in the that a current azeotropic distillation is used under a pressure environmental in terephthalic acid plants.

Figure 4 is an outline of the assembly of the acetic acid recovery system under the lines of the present invention, in which the distillation column is provided azeotropic of a condenser. This capacitor is a system of roof steam generation that produces a low steam Pressure.

Figure 5 shows a diagram of the process of steam manufacturing that is generated by using a conventional distillation process.

Figure 6 is a diagram of the process of steam generation manufacturing from only section of reaction and its use in a terephthalic acid plant conventional.

Figure 7 shows a diagram of the process of manufacture of steam generation from the reaction section and, in turn, from the steam generator in the process of dehydration during the production of terephthalic acid.

Description of specific embodiments

The invention arose following an observation which showed that large amounts of energy were consumed during The terephthalic acid production system. In addition to the expense of energy, as soon as the recycling process was reached, where Acetic acid type solvents did not recover and were sent to water treatment facilities residuals, thereby increasing energy needs due to a greater demand for manufacturing process outside the scope of the plant system.

Normally, an industrial chemical from Terephthalic acid type is produced during the multiple degrees of fractionation where the heaviest liquids are distilled with lighter vapors. A distillation column is used that is composed of a cylindrical tower that stores numerous internal components to boost the interaction between the liquid and the steam

Conventional tower tools include sieves and valve reservoirs, random type packaging and properly structured and any combination of this type. Preferably, the tower's high power tools are will use in the production of terephthalic acid according to the present invention This includes advanced diffusion valves of the type of perforated valves, as disclosed in patent no. 6,145,816 (USA), whose full disclosure is incorporated by way of reference. You can also use a vertical downpipe and substances that increase the bubbling capacity to increase the efficiency and capacity of the distillation column.

If we look now at the figures in which the numbers represent similar components, figure 1 is a schematic diagram of the manufacturing process of a typical plant Terephthalic acid production. The main sections of the Plant consist of the following sections or units: reaction (2), crystallization (3), drying (4), purification (5), and dehydration (1). The water treatment facility residuals (6) is the last component for the process in a terephthalic plant.

The feed tank or steam outlet It consists of paraxylene (73) and molecular oxygen, such as air (71) which, together with a catalyst (71), is introduced into the reaction section (2) or in the reactor. PTA terephthalic acid (95) is a product of the reactor. The product and water are produced according to the following chemical reaction:

one

Terephthalic acid product is sent to the crystallization (3), drying (4) and purification units (5) to carry out a downstream flow procedure to produce purified terephthalic acid (95). Water (81) generated from the reaction and the solvent used in the reaction, that is, acetic acid (82), are sent to the section of dehydration to recover acetic acid (92) and return it to the reaction section for reuse. Acid MTA (96) medium grade terephthalic can also be produced and recovered before a next purification in terephthalic acid during the reaction process. Water (94) is sent at wastewater treatment facilities to be able to Get rid of her.

Normally, the heat that is generated in the previous exothermic reaction to produce terephthalic acid is recover by generating medium pressure steam (93). He medium pressure steam is generally used in the section of dehydration The present invention relates to the section of dehydration

Figure 2 shows a typical scheme of manufacturing process that uses a distillation method Conventional for the dehydration of acetic acid in the section of dehydration of the terephthalic acid production plant. The conventional distillation system incorporates a generator of steam in order to recover part of the steam for its reuse

The dehydration column (200) normally includes trays (290) and a reboiler (202). The currents of water (281) containing acetic acid solvent (282) and a small amount of organic by-product (283), methyl acetate, they are incorporated into the dehydration column (200) that normally It consists of about 70 to 90 distillation trays. Acetic acid (292), usually at a concentration of 92-95 wt %, is recovered from the lower part of the dehydration column (200) and returned to the reaction section.

Water, organic byproduct, acetate methyl and any acetic acid that could not be recovered (normally at a concentration of 0.5-0.8 wt%) they leave the upper part of the column (200) in the form of vapors (299). Next, a vapor condenser (220) condenses the outgoing steam from the top of the distillation column with boiled water (274). The vapor condenser of the upper part of the column (220) produces a low pressure steam (291) during the condensation to recover part of the energy so that This is recycled in the plant for different uses. Usually, a dehydration column generates a low pressure steam (Normally 0.6 - 0.7 Kg./cm^{2} gr.) at its highest part.

The condensation of outgoing steam from the part high of the column (299) that arises then, is incorporated into a steam condenser (233). A secondary capacitor (231) concentrate the accumulation with a non-condensable vapor that is vented with ventilation ducts (285). Part of the reflux that arises at that time it is returned to column (200) as Reflux.

The remaining reflux part is incorporated into a downstream stream to the methyl acetate column (210) to separate the organic by-product, methyl acetate (283) as a salient product from the top of the column and water and acetic acid as products from the lower part of the spine. Column (210) contains a condenser (211), a tube of condensation or a steam collector (213) and a reboiler (212). The stream of water (284) containing acetic acid is sent more late to sewage treatment facilities to to get rid of it later. The methyl acetate (283) is incorporates back into the reactor for recycling.

Normally, part of the medium pressure steam generated in the reaction section provides a source of heat to the reboiler (202) of the dehydration column (200) for use during the separation of acetic acid from water. The equilibrium of steam is used as steam generation or for others purposes, as illustrated in Figure 5. Approximately 50% of the generated medium pressure steam is used for the needs distillation in the dehydration section for this method of conventional distillation

Figure 3 shows a typical diagram of the manufacturing process using azeotropic distillation anterior with separating agents such as isobutyl acetate (IBA) or normal butyl acetate (NBA) in the dehydration section of a typical terephthalic acid plant.

Water streams (381) that contain the acetic acid solvent (382) and a small portion of Organic by-product (383), methyl acetate, are incorporated into the dehydration column (300). Column (300) has a condenser (301) and a reboiler (302). Normally, the column of dehydration (300) consists of about 60-70 trays distillation (390) operating at ambient pressure or almost environmental. Acetic acid (392), usually at a concentration 92-95 wt%, occurs from the bottom of the dehydration column (300) and returned to the section of reaction. Water, forming a low boiling azeotrope, together with small amounts of unrecovered acetic acid and of the reaction of the by-product, methyl acetate, leave the upper part of the column in the form of steam (399). An azeotrope is a mixture of  pure components with a constant boiling point and not can be easily separated by distillation conventional. The boiling point of the azeotrope is lower than the boiling points of any of the two components cigars

Then the steam coming out of the part column top (399) is condensed and incorporated into the decanter (340). The condensate of the liquid formed from steam (399) passes generates two phases, an organic phase and a water phase. The organic phase and acetic acid are combined with an agent separator or separating agent of the type of IBA or NBA from the composition of the separating agent (375) in the decanter (440). Part of the organic phase that contains the separating agent and the Organic by-product with acetic acid is returned to the column (300) as a reflux for recycling.

The remaining part of the organic phase is incorporates the acetate column in a downstream stream of methyl (310) to separate the organic by-product, that is, the methyl acetate from the separating agent. Acetate column methyl (310) is generally a distillation column with trays (390). The column (310) has a condenser (311), a tube of condensation or a steam collector (313) and a reboiler (312). Methyl acetate (383) is recovered in the upper part and sent back to the reaction section. The separating agent is a bottom product of the methyl acetate column (310) and recycle in the decanter (340).

The water phase of the decanter (340) containing the water, the separating agent, the methyl acetate dissolved in the water phase and a small amount of acetic acid (usually at 300-800 ppm) is then sent to the column of distillation of the lower part (330) to separate the methyl acetate and acetic acid. The distillation column (330) has a condenser (331), a condensation tube or a steam collector (333) and a reboiler (332). The methyl acetate is separated as a leaving product from the top of the distillation column that is sent to the methyl acetate column (310) to separate the methyl acetate and the separating agent. The liquid product (384) of the product from the bottom of the column (330) containing small amounts of unrecovered acetic acid is then sent to the wastewater treatment facilities to dispose of it further.
ahead.

There are two main advantages in the azeotropic distillation versus conventional distillation, specifically, the following: 1) lower energy consumption or steam (between 20 and 40%) and 2) a lower loss of acetic acid in wastewater treatment facilities (between a 0.5 and 0.8 wt% in wastewater). In comparison, the Acetic acid loss is normally 300-800 ppm with azeotropic distillation versus 7000-7500 ppm used in a distillation conventional.

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Conventional dehydration towers of azeotropic distillation used previously in plants Terephthalic acid production occurs at an environmental pressure.  Due to the low azeotropic boiling temperature, the heat recovery from the top of the column is not viable and therefore no steam generation systems are used during a typical azeotropic distillation in the plants of dehydration of acetic acid and terephthalic acid. In this way, the energy that could be used in other cases is not recovered, increasing, thus, the total energy consumption in the plant.

Normally, part of the medium pressure steam generated in the reaction section (not shown) provides a heat source to the reboiler (302) of the dehydration column (301) for the necessary separation of acetic acid from water. He steam balance is used as a steam generating power or for other purposes, as shown in Figure 6. Only approximately thirty percent (30%) of the average steam generated pressure is used for distillation needs in the dehydration section during azeotropic distillation previous.

Figure 4 shows a diagram of the process of manufacture of the invention, in which both a azeotropic distillation with separating agents to form azeotropes, as a vapor and heat recovery system in the dehydration section of the terephthalic acid plant. The The present invention shows improvements in distillation systems azeotropic by generating steam during separation of acetic acid and water in the production distillation phase of terephthalic acid. Isobutyl acetate (IBA) or acetate normal butyl (NBA) or the mixture of both is used as an agent acetic acid dehydration column separator. The column has an operating pressure at the top of 1.3 kg / cm2 absolute or greater. A steam generation system is places at the top of the dehydration column to recover steam energy by condensing steam protrusion from the top of the distillation column. This steam it is a low pressure vapor (about 0.6 - 2.0 kg / cm2) Absolutes). Acetic acid is recovered from the system in quantities Approximately 300-800 ppm.

A system based on the present invention that incorporated into an existing transfer plant would reduce the functions of the reboiler (for example, steam consumption) necessary for the separation process. In comparison with the previous methods, energy consumption is reduced by a 20-50% while maintaining a low loss of acetic acid in wastewater (0.5-0.8 wt% and 300-800 ppm or lower). When combined with advanced devices of mass transfer, of the type of perforated valves, tubes Advanced down verticals and tower tools or Any high performance equivalent, acid loss Acetic can be reduced to just 150 ppm or less.

Turning now to figure 4, the currents of water (481) containing acetic acid solvent (482) and small amounts of organic by-product (483), acetate methyl, incorporated into a dehydration column (400). In a embodiment, the dehydration column (400) consists of, at less, 60 distillation trays (490). The column operates at a higher pressure of 1.3 kg / cm2 absolute in the upper part of the dehydration column (400). Acetic acid (492), normally at a concentration of 92-95 wt%, it produced from the lower part of the dehydration column (400) and It is returned to the reaction section. The water, after forming a low pressure azeotrope, along with small amounts of acid acetic not recovered and reaction by-products that include in methyl acetate leave the top of the column (400) in steam form (499). A steam generator or condenser of the upper part (420) condenses the outgoing steam from the upper part of the dehydration column (499). The high part condenser (420) has a secondary capacitor (421) that also condenses the outgoing steam from the top of the column (499) with some steam non-condensable ventilated with ventilation ducts (485). Water Boiler supply (474) is supplied to the system for generate the steam necessary to maintain the different units, as the condenser of the high part.

Liquid condensate formed from steam (499) is incorporated into the decanter (440) and forms two phases liquids, a liquid phase and another water phase. The organic phase and The acetic acid is combined with an IBA or NBA separating agent from the composition of the separator (475) in the decanter (440). Part of this mixture is returned to column (400) as Reflux.

The remaining part of the organic phase is incorporates in an upstream stream to the acetate column of methyl (410) to separate the organic by-product, that is, the methyl acetate separating agent. The acetate column of methyl (410) is generally a distillation column with trays (490). The column (410) has a condenser (411), a tube of condensation or a steam collector (413) and a reboiler (412). Methyl acetate (483) is recovered in the upper part and recycled in the reaction section. The separating agent is a product of the methyl acetate column (410) and returned to the decanter (440).

The water phase of the decanter (440) that it contains the water, the separating agent or methyl acetate that is dissolve in the water phase and a small amount of acetic acid (normally 300-800 ppm) is then incorporated at a distillation column downstream (430) to separate the methyl acetate and acetic acid. Distillation column (430) is generally a distillation column with trays (490). The column (430) has a condenser (431), a tube of condensation or steam collector (433) and a reboiler (432). He methyl acetate separates as a product from the top that it is later sent to the methyl acetate column (410) to separate the methyl acetate and the separating agent. The water of product from the bottom of the column (430) that contains small amounts of acetic acid not recovered, is sent to sewage treatment facilities to get rid of she.

\hbox{anteriores de  destilación azeotrópica utilizados en
plantas de ácido tereftálico.}

While the operating pressure of the highest column disclosed in the present invention is not significantly different from energy consumption or acetic acid losses when compared to previous azeotropic distillation systems operating at an ambient pressure, the present invention It generates a valuable low pressure steam in a condenser (420) at a pressure of 0.6-2.0 kg / cm2 due to the higher initial operating pressure. Unlike the previous azeotropic distillation, the present system and method allows the temperature of the upper part of the azeotropic distillation column to be high enough to generate the low pressure steam (498) that can be used for the generation of force or for many other uses. Steam generation, although at low pressure, is not viable in systems

 \ hbox {previous azeotropic distillation used in
terephthalic acid plants.} 

Generally, part of the medium pressure steam generated in the reaction section (not shown) provides a heat source to the reboiler (402) of the dehydration column (400) for the necessary separation of acetic acid and water. He steam balance is used as a steam generating power or for many other uses, as shown in figure 7. In the previous azeotropic distillations only less than thirty percent (30%) of the medium pressure steam generated for the distillation needs in the section of dehydration

The main advantages of this invention versus conventional distillation methods and azeotropic distillation schemes in acid plants Terephthalic generate a number of benefits that include:

one.

A lower energy consumption (e.g. steam) and savings of at minus 20-40%.

2.

A less loss of acetic acid in treatment facilities of 0.5-08 wt% wastewater in the waters residuals according to conventional distillation, versus 300-800 ppm or less in distillation azeotropic

3.

A total energy recovery by generating steam from low pressure of at least 0.6-2.0 kg / cm2 for the power generation or other uses in the plant.

Once the invention has been described in a general way, The following example, which is only presented as a illustration and not as a possible limitation unless indicated, It can help us achieve a higher level of understanding.

Example

In a typical 350,000 production plant MTA of terephthalic acid, several methods of comparing dehydration of acetic acid, more specifically, distillation conventional, azeotropic distillation operating at a pressure Environmental and invention. The following table summarizes the Main benefits of typical design and production:

2

3

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As illustrated in the table above, a dehydration column using conventional distillation with a fractionation of 90 trays consumes the highest amount of medium pressure steam at 60 T / h during dehydration, using, in this way, a greater total energy. The use and consumption of this vapor is greater than that of azeotropic distillation conventional and is given by the present invention. However the energy consumed during dehydration normally recovers by generating low pressure steam from the section upper dehydration column. Consequently, the loss of acetic acid resulting from the use of the method of conventional distillation is considerably higher than that of the conventional azeotropic distillation and the present invention.

Theoretically, it is possible to increase the reflux of the column or the number of fractionation trays for further reduce the loss of acetic acid in the streams of water during conventional distillation. However, it does not work out economically justifiable due to the exponential costs each increasingly higher in energy consumption and / or higher investment of capital, since a greater number of subjects is needed premiums for building columns.

In comparison, in a dehydration column in which an azeotropic distillation equipped with 70 is used fractionation trays, energy consumption is approximately 70% of that occurs during a distillation conventional. In addition, the loss of acetic acid is seen considerably reduced when we contrast it with that of the conventional distillation, as can be seen in the table previous. The disadvantage of this proposal is that, due to a lower operating pressure in azeotropic distillation, it is not feasible to recover energy through steam generation during distillation.

On the contrary, the present invention offers not only the lowest energy consumption but also provides the lower loss of acetic acid. In one embodiment, the system and Terephthalic acid production method presented in this invention is equipped with seventy (70) trays of division. In another embodiment, the system consists of ninety (90) fractionation trays.

In addition, due to high pressures operating in the upper part of the dehydration column, the The present invention also allows the recovery of a greater amount of energy that is recovered with the systems earlier through the generation of higher and lower steam pressure simultaneously. This low pressure steam can recycled and returned to the system for as many uses within the plant thus allowing greater energy savings.

As shown in any of the embodiments of the present invention, the total loss of acid acetic remains low as in a typical azeotropic distillation and compared to a conventional distillation. The invention combines both the benefits of conventional distillation and those of azeotropic distillation in an original way to generate important economic benefits on systems and methods previous. Energy saving and recovery of greater quantity of raw materials and chemical compounds could be used both in the construction of new plants and in modernization projects

Returning now to the figures 5-7, the circulation and generation of steam in the Terephthalic acid plant are shown under various schemes operational Figure 5 represents a steam circulation generated by a steam generation system in a distillation conventional for use within the plant. The system generates both medium pressure steam (593) and low pressure steam (591).

The reaction unit (502) produces a vapor of medium pressure (593) at a pressure of 3.5-5.0 Kg./cm g. Most medium pressure steam (593) is consumed practically in the dehydration section (501) to use it during the distillation of acetic acid and water. Average steam pressure (593) also turns the turbine (560) in order to generate the force inside the plant to be able to use it when operating the compressor (562) and for many other uses (507).

Low pressure steam (591) is generated by the dehydration section (501) at a usual pressure of 0.5-0.8 Kg./cm^{2} absolute during the distillation of acetic acid and water. Next, the Low pressure steam (591) to steam turbine (560) to generate  steam in an additional way and use it in various ways within plant.

Unlike conventional distillation, the Figure 6 shows the circulation of steam generation and its use in a terephthalic acid production plant during the azeotropic distillation. The system only generates steam on average pressure (693) at a usual pressure of 3.5-6.0 Kg./cm g. Medium pressure steam (693) is produced in the section reaction (602) of the plant and is consumed. mainly in the dehydration section (601) to be used in the distillation of acetic acid and water. Steam (693) is also used in the turbine (660) for the generation of greater power and for its consumption in the crystallization section and for many other uses (607).

With regard to Figure 7, a diagram of the steam generation process according to the system of the present invention. The system generates steam on average pressure (793) and low pressure steam (791) in one way simultaneous.

The reaction unit (702) produces steam from medium pressure (793) at a pressure of 3.5-5.0 Kg./cm g. Medium pressure steam (793) is consumed in the section dehydration (701) so that it can be used during distillation of acetic acid and water. Medium pressure steam (793) is also used in the turbine (760) for the generation of a greater power in the plant and to be able to use it when operating the compressor (562), in addition to many other uses (507).

Therefore, in accordance with this invention, a terephthalic acid production plant and a system and method provide several advantages compared to a conventional distillation method and distillation scheme azeotropic This system requires a smaller amount of energy and Less steam consumption. Acid recovery is carried out acetic so high that there is a minor loss of acetic acid for be processed in water treatment facilities residual Also, dehydration of acetic acid during Terephthalic acid production generates a low pressure vapor more useful for generating greater power and for many others applications.

The previous description of the embodiment of the invention has been presented for illustrative purposes and descriptive It is not intended to be exhaustive or limit the possibilities of the invention in the indicated ways. Obviously, numerous modifications and variations will be evident to the ears of those professionals specialized in this matter. Be It is intended that the scope of this invention be defined in accordance with the following claims and their equivalents.

All publications and applications of the patents mentioned in this specification are incorporated here by reference as if each of the publications or patent applications were specifically and individually indicated to be incorporated by express reference.

While the invention has been described with Regarding its main realization, it will be appreciated that They may include those other alternative embodiments. By example, with respect to the set of embodiments explicitly described, as well as the other embodiments of the invention, are you can incorporate a different distillation system that includes Different designs and layouts of the trays. They can also other modifications of the columns that include multiple phases and uses of the separating agents alternately. These and many other modifications can be added to the embodiment revealed above without taking as starting point the subject of the invention.

Claims (22)

1. A distillation system to recover water acetic acid during the production of teraphthalic acid which includes:

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A dehydration column containing a section of head;

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To the minus an input feed stream containing acid acetic and water;

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A separating agent;

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A condenser to separate acetic acid from water.

2. The distillation system according to the claim 1 wherein the dehydration column is a azeotropic dehydration column. 3. The distillation system according to the claim 1 wherein the dehydration column contains a lower output current and an output current of head. 4. The distillation system according to the claim 3 wherein the lower output current has a higher concentration of acetic acid than that of at least one input power current. 5. The distillation system according to the claim 3 wherein the head output current has a concentration of acetic acid less diluted than that of less, an input power current. 6. The distillation system according to the claim 1 wherein the condenser condenses a vapor of the high part of the dehydration column to generate a vapor of low pressure. 7. The distillation system according to the claim 6 wherein the low pressure steam generated has a pressure of at least 0.6 Kg./cm^{2} absolute. 8. The distillation system according to the claim 6 wherein the low pressure steam generated has a pressure from 0.7 kg / cm 2 - 2.0 kg / cm 2 absolute. 9. The distillation system according to claim 1 wherein the separating agent is acetate N-Butyl 10. The distillation system according to the claim 1 wherein the separating agent is acetate I-Butyl 11. The distillation system according to the claim! in which the separating agent is a mixture of N-butyl acetate and acetate I-Butyl 12. The distillation system according to the claim 1 wherein the distillation column has a head pressure of at least 1.2 kg / cm2 absolute. 13. The distillation system according to the claim 1 wherein the distillation column has a head pressure greater than 1.2 kg / cm2 absolute. 14. A distillation method to recover water acetic acid during the production of terephthalic acid that you understand:

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The provision of a water inlet feed stream that contain acetic acid;

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The distillation of the input feed stream in a azeotropic dehydration column that has a section of head within a stream of steam;

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Steam separation;

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Condensation of the steam stream to separate acetic acid from water; Y

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A output to a lower current that has a higher concentration of acetic acid that the input and other feed current to a head output current has an acid concentration acetic more diluted than the feed stream of entry.

15. The distillation method according to the claim 14 wherein the separating agent uses acetate N-Butyl 16. The distillation method according to the claim 14 wherein the separating agent uses acetate I-Butyl 17. The distillation method according to the claim 14 wherein the separating agent uses acetate I-butyl and N-butyl acetate. 18. The distillation method according to the claim 14 wherein the condensation stage generates a low pressure steam. 19. The distillation method according to the claim 18 wherein the low pressure steam is at least at 0.6 Kg./cm^{2} absolute. 20. The distillation method according to the claim 18 wherein the low pressure steam is from 0.7 kg / cm2 absolute up to 2.0 kg / cm2 absolute. 21. The distillation method according to the claim 14 wherein the distillation step has a head pressure of at least 1.2 kg / cm2 absolute. 22. The distillation method according to the claim 14 wherein the distillation step has a head pressure greater than 1.2 kg / cm2 absolute.