Reducing acetic acid corrosivity

Abstract

A method for reducing the corrosivity of acetic acid recovered from a process of subjecting wood to a reaction with an acetylation fluid comprising acetic anhydride is disclosed. It has been found that such corrosivity can be reduced by removing terpenes chloride and terpenoids chloride from the acid. The method for implementing this includes crystallization by cooling.

Description

Technical Field

[0001] This invention relates to a method for reducing the corrosiveness of impure acetic acid. In particular, it relates to acetic acid recovered from acetylation fluids used for wood acetylation. Background Technology

[0002] Acetic acid is an important chemical reagent and industrial chemical. Its production and properties have been well confirmed.

[0003] One method for producing acetic acid is by reacting wood with an acetylation fluid containing acetic anhydride. The products of this reaction are acetylated wood and acetic acid. See, for example, WO 2009 / 095687. It describes a method for acetylifying wood by reacting it with an acetylation fluid typically containing acetic anhydride.

[0004] The acetylated fluid obtained by acetylation of wood with acetic anhydride contains a large amount of acetic acid. This acetic acid is a byproduct of wood acetylation, in which acetic anhydride undergoes an esterification reaction with the hydroxyl groups in the wood to produce acetic acid.

[0005] The reaction involved can be represented by the following equation: [wood]OH + CH3C(O)OC(O)CH3 → [wood]OC(O)CH3 + CH3C(O)OH. Therefore, this method of acetylation of wood effectively provides a source of acetic acid. The resulting acetic acid contains impurities, primarily wood extracts. As discussed in WO 2009 / 095687, this acetic acid is known to be sold as an industrial-grade acid.

[0006] In the case of acetic acid produced by the acetylation of wood, a particular problem is its corrosiveness. Steel subjected to prolonged contact with acetic acid exhibits an undesirable high rate of corrosion. This corrosiveness is a limiting factor for the potential uses of acetic acid, and this remains unremedied in the art to date.

[0007] This invention attempts to solve this particular problem. Summary of the Invention

[0008] In one aspect, the present invention provides a method for reducing the corrosiveness of acetic acid, said acetic acid being recovered from wood by subjecting it to a reaction with an acetylated fluid containing acetic anhydride, said method comprising removing chlorinated terpenes and chlorinated terpenoids from the acid.

[0009] In another aspect, the invention relates to the use of crystalline acetic acid for reducing the corrosiveness of acetic acid, said crystalline acetic acid being formed in a method comprising subjecting acetic acid recovered from wood acetylation to cooling and crystallizing, thereby separating the crystalline acetic acid from its respective mother liquor.

[0010] In another aspect, the present invention provides a method for producing acetic acid, the method comprising reacting an acetylated fluid containing acetic anhydride with wood to form esterified wood and a used acetylated fluid containing acetic acid, subjecting the used acetylated fluid to a step of separating acetic acid from acetic anhydride, and subjecting the acetic acid to a purification step of removing chlorinated terpenes and chlorinated terpenoids to form purified acetic acid, preferably determining the levels of chlorinated terpenes and chlorinated terpenoids in the purified acid by gas chromatography, and repeating the purification step and the determination step until the levels of chlorinated terpenes and chlorinated terpenoids are undetectable.

[0011] In another aspect, the present invention provides the use of acetic acid seed crystals for reducing the corrosiveness of acetic acid recovered from wood acetylation. Detailed Implementation

[0012] This invention is based on the insightful observation that chlorinated terpenes and chlorinated terpenoids significantly enhance the corrosivity of acetic acid recovered from wood acetylation. This insight contradicts conventional explanations for the cause of this corrosivity, which are particularly based on the presence of residual acetic anhydride in the recovered acetic acid. Furthermore, it has been shown that in the field of steel alloys, the corrosivity of acetic acid is related to the presence of ionic chlorides. However, this is not specific to acetic acid recovered from wood acetylation and therefore cannot be used to explain its particular corrosivity.

[0013] According to this disclosure, corrosivity is defined as the corrosion rate measured at 115°C for 316L stainless steel. This specifically refers to the corrosion rate measured using a standard method in which a steel sample is tested in 300 g of test liquid in a 1 L three-necked flask under air conditions. The flask is connected to a reflux cooler, thermocouple tube, and stopper. The test liquid is stirred at 70 rpm using a stir bar. The flask is heated by an oil bath, with the temperature measured approximately 1 cm above the sample in the test liquid. The apparatus is insulated. The sample tested is 316L stainless steel. The test temperature is 115°C. The test duration is at least 100 hours, with longer durations up to two weeks, applied to assessing the corrosivity of liquids with minimal corrosivity.

[0014] The foregoing insights present a novel and unexpected discovery that allows for better remedies for the corrosiveness of acetic acid recovered from wood acetylation. Therefore, in a broader sense, the present invention utilizes this discovery by reducing the corrosiveness of acetic acid through a step of removing chlorinated terpenes and chlorinated terpenoids from the acetic acid recovered from wood acetylation.

[0015] Terpenes are a large and diverse class of organic compounds produced by various plants, including trees. Terpenes are hydrocarbons. Terpenoids are modified terpenes containing additional functional groups, typically oxygen-containing. Terpenes exist as monoterpenes and oligoterpenes. In this disclosure, the term "chlorinated terpene" refers to a terpene having one or more chlorine substituents. The term "chlorinated terpenoid" refers to a modified terpene having one or more additional chlorine substituents.

[0016] Terpenes can be classified by the number of isoprene units in their molecules; the prefix in the name indicates the number of terpene units required to assemble the molecule. Hemiterpenes consist of one isoprene unit. Isoprene itself is considered the only type of hemiterpene, but oxygen-containing derivatives such as prenol and isovaleric acid are hemiterpenoids. Monoterpenes consist of two isoprene units and have the molecular formula C1. 10 H 16 Examples of monoterpenes and monoterpenoids include geraniol, terpineol, limonene, myrcene, linalool, or pinene. Iridoids are derived from monoterpenes. Sesquiterpenes consist of three isoprene units and have the molecular formula C1. 15 H 24 Examples of sesquiterpenes and sesquiterpene compounds include humulene, farnesene, and farnesol. Diterpenes consist of four isoprene units and have the molecular formula C2. 20 H 32 Examples of diterpenes and diterpenoids include caffeol, cardamomol, coniferene, and taxadiene. Disesquiterpenes (terpenes with 25 carbons and five isoprene units) are rare relative to other sizes. An example of a disesquiterpene is geranylfarnesol. Triterpenes consist of six isoprene units and have the molecular formula C2. 30 H 48 Sesquarterpenes are composed of seven isoprene units and have the molecular formula C2. 35 H 56 Examples of trisesquiterpenes are ferrugicadiol and tetraprenylcurcumene. Tetraterpenes contain eight isoprene units and have the molecular formula C2. 40 H 64 .

[0017] Common chlorinated terpenes include borneol chloride, borneol chloride, isoborneol chloride, pinene hydrochloride, dipeptene hydrochloride, their isomers or derivatives.

[0018] The method of this invention uses acetic acid with reduced corrosiveness, which is a used acetylation fluid recovered from any acetylation process of wood containing terpenes. In the case of any such wood, hydrochlorinated terpenes may form under the harsh conditions applicable during acetylation. Not wishing to be bound by theory, the inventors believe that, for example, borneol chloride and ferruginol chloride are readily formed from β-pinene and to a lesser extent from α-pinene.

[0019] Such wood acetylation methods include liquid-phase methods, gas-phase methods, and combinations thereof. Typically, the wood to be acetylated is impregnated with an acetylation fluid and subjected to one or more heating steps, usually under elevated pressure. The acetylation fluid can be acetic acid, acetic anhydride, or a combination thereof. Typically, the acetylation fluid used will contain byproducts from wood acetylation, extractable components from the wood such as terpenes and / or terpenoids, and an excess of the acetylation fluid. Typically, when the acetylation fluid contains acetic anhydride, the byproduct is acetic acid. The excess acetylation fluid will typically be acetic anhydride, acetic acid, or both.

[0020] Typically, in acetylation methods that produce a combination of acetic anhydride and acetic acid as the acetylation fluid used, it is desirable to first separate the acetic acid from the acetic anhydride. This is usually done by distillation. As described in the art, such distillation will produce acetic acid in which wood-derived impurities such as terpenes and / or terpenoids are not removed, or at least not sufficiently removed.

[0021] In one embodiment, the acetylated fluid used, after undergoing steps to remove chlorinated terpenes and chlorinated terpenoids, contains acetic anhydride in addition to acetic acid. The presence of acetic anhydride, particularly in combination with chlorinated terpenes, results in a synergistically increased corrosivity.

[0022] In one embodiment, the acetylated fluid used has already undergone a step of removing acetic anhydride before undergoing the steps of removing chlorinated terpenes and chlorinated terpenoids. It is understood that the removal of acetic anhydride is suitably accomplished by distillation.

[0023] In one embodiment of interest, the step of removing chlorinated terpenes includes subjecting acetic acid to solvent extraction to remove the chlorinated terpenes. Such solvent extraction can be carried out, for example, by a method disclosed in WO 2009 / 114070. This method involves forming a separating composite extraction medium by adding water and an organic solvent substantially immiscible with acetic acid to acetic acid. This results in the impurities being concentrated in the organic phase, while acetic acid can be recovered from the aqueous phase.

[0024] A preferred method for removing chlorinated terpenes from acetic acid containing these impurities is to subject the acetic acid to cooling below its melting point, whereby crystals form, and then separate the crystals from the fluid. See WO 2022 / 23452.

[0025] In this method, a fluid containing recovered acetic acid, i.e., the used acetylated fluid or acetic acid separated from such a fluid, is cooled to below the melting point of acetic acid. The melting point is 16.6°C, and cooling will typically be performed at temperatures below this temperature, for example, to a range of 0°C to 16°C, such as 10°C to 15°C. Lower temperatures can generally be applied, and this method will be used where the acetylated fluid has a lower freezing point, for example, where there are large quantities of compounds with lower melting points, such as water and / or acetic anhydride. Those skilled in the art will be able to determine the freezing point of any fluid, such as the used acetylated fluid, without difficulty.

[0026] In the cooling crystallization method of this embodiment, it is preferable to recycle the liquid remaining after crystallization, i.e., the mother liquor, rather than discarding it after each round of crystallization. The recirculated fluid is thus replenished with freshly recovered acetylated fluid. This has the advantage of reducing waste and makes the method more economical. In a preferred embodiment, such mother liquor is recirculated at least 20 times, for example at least 50 times, for example from 20 to 200 times, preferably from 50 to 100 times. After such recirculation, as a result of repeated crystallization of acetic acid, the concentration of any liquids that may be present besides acetic acid will increase. For example, if there is 0.1% water in the freshly recovered acetylated fluid, it will rise to more than 5% after 60 recirculations in the mother liquor. In fact, water can be considered an impurity, which exists in a relatively high concentration in acetic acid compared to other impurities and will accumulate in the mother liquor (as will all other non-freezing molecules). Such mixing of freshly recovered acetylated fluid with the recirculated mother liquor can occur in batches from a collection container of the used acetylated fluid. The crystallization process is preferably carried out as a continuous process. Therefore, freshly recovered used acetylated fluid can still be added in batches or as a continuous feed.

[0027] The other liquid is typically acetic anhydride or water. The former is present as a result of the original composition of the acetylation fluid, and its amount depends on the degree to which such anhydride is optionally removed before subjecting the used acetylation fluid to the crystallization method of the present invention. Water may be present depending on the concentration of acetic acid and / or acetic anhydride used as the wood acetylation fluid. Water may be added to quench the anhydride. This reduces the risk of anhydride-based corrosion in the crystallization equipment, as such quenching will effectively remove the anhydride. Catalysts, as known to those skilled in the art, may be added to accelerate the reaction between water and acetic anhydride.

[0028] Cooling can be carried out in any suitable container or tube that allows crystal formation. A technician familiar with suitable equipment, such as a scraped-wall crystallizer, will understand that the crystallization equipment will allow cooling for this method to be implemented. Typically, the formed crystals will be subjected to washing, usually in a washing column, for example to remove the liquid film of the mother liquor that would normally remain in the molten crystallization. A technician familiar with operating the crystallization equipment will also be familiar with its operation.

[0029] No special measures are required to complete crystallization. If necessary, the process can be aided by adding a small amount, such as less than 10% by weight, less than 5% by weight, or 1% to 3% by weight of a suitable contaminant (e.g., water or acetic anhydride). The technician will be familiar with techniques that promote crystallization, such as scraping the walls of the crystallizer, as with a scraper.

[0030] Crystallization can be advantageously promoted by the presence of one or more acetic acid seed crystals. Such seed crystals can be added to the fluid at a temperature approximately equal to or below the melting point of acetic acid. The seed crystals are typically obtained and stored in advance. Advantageously, they can also be obtained in situ in the method of the present invention.

[0031] In one interesting embodiment, crystallization is carried out in two stages. Thus, in the first step, in the case of crystal formation, the recovered acetylation fluid is cooled to below the melting point of acetic acid. This step can be carried out as described above with or without seed crystals. Subsequently, in the second step, a first portion of the crystals, typically obtained after washing away any film from the residual feed liquid, is melted to obtain an acetic acid melt. Since not all the crystals melt, the second portion is retained. The acetic acid melt is recycled and cooled again to below the melting point of acetic acid. This cooling is carried out in the presence of at least partially retained crystals, thus the second crystallization step is carried out in the presence of seed crystals. The recycled melt can be cooled as is, or after being combined with an additional amount of used acetylation fluid recovered from the wood acetylation process (from the same process operation, or from its different operation, or—for example, from different processes if multiple acetylation reactors operate in parallel). The aforementioned process can be repeated to provide multiple washing and recrystallization steps, typically resulting in a greater degree of purity.

[0032] In the two-stage implementation, the first portion (i.e., the crystals to be remelted) typically contains more than 50% of the crystals formed in the first step. Preferably, the first portion contains 60% to 99% of the crystals formed in the first step, and more preferably 85% to 95% of the crystals formed in the first step. If necessary, any third and subsequent stages can be performed: after crystallization in the second step, a portion of the subsequently formed crystals can be remelted, and the process can continue as described above. Therefore, the wood acetylation and recovery of the acetylated fluid using the purification method of this embodiment of the invention can be an ongoing continuous or semi-continuous operation.

[0033] In another embodiment of interest, the seed crystal is added separately, for example, provided by a reservoir, without requiring remelting of the crystal obtained from the same acetylated fluid in the crystallization process. One advantage of this embodiment is that it more readily facilitates crystallization in a continuous process. It will be understood that a continuous process can also advantageously include both remelting and recrystallization.

[0034] Combinations of the aforementioned embodiments are also conceivable. Therefore, at any stage, the seed crystal can be selected from either a storage container or from in-situ crystal formation. For example, in the first stage, the seed crystal can be provided by a storage container, and in one or more subsequent stages, the seed crystal can be obtained by retaining the partially formed crystal without remelting.

[0035] In the preferred method of cooling crystallization, the formed acetic acid crystals play a crucial role in obtaining acetic acid from which chlorinated terpenes and chlorinated terpenoids have been removed. This is reflected in another aspect of the invention, relating to the use of crystalline acetic acid. Hereinafter, acetic acid crystals are formed in a process comprising subjecting acetic acid recovered from wood acetylation to cooling crystallization. These crystals consist of pure acetic acid and are solids obtained from a liquid phase (i.e., the mother liquor from which the crystals are obtained). The crystals are then used as a carrier for separating pure acetic acid from the mother liquor containing impurities. In the present invention, this use is for a purpose previously unknown, namely, for reducing the corrosiveness of acetic acid. In particular, this use is for the purpose of reducing the corrosiveness of acetic acid by separating it from chlorinated terpenes and chlorinated terpenoids.

[0036] In the embodiments for forming the aforementioned acetic acid crystals, as described above, acetic acid seed crystals may be added to initiate and / or promote crystallization. Therefore, the application of such seed crystals is intended to remove chlorinated terpenes and chlorinated terpenoids from acetic acid, thereby reducing the latter's corrosiveness. This reflects the use of acetic acid crystals by adding them to fluids containing acetic acid recovered from wood acetylation to reduce the corrosiveness of acetic acid.

[0037] In another aspect, the present invention provides a method for producing acetic acid. This method involves reacting an acetylated fluid containing acetic anhydride with wood. The acetic anhydride undergoes an esterification reaction with the hydroxyl groups in the wood, thereby producing acetic acid. This can be represented by the following formula:

[0038] [Wood]–OH+CH3–C(=O)–O–C(=O)–CH3→[Wood]–O–C(=O)–CH3+CH3–C(=O)–OH

[0039] Therefore, this method of acetylation of wood effectively produces acetic acid. As discussed above, this acetic acid is purified, meaning it may undergo a purification step after separation from any residual acetic anhydride to form purified acetic acid. According to the invention, the method is carried out in such a way that it ensures the removal of substances that the inventors have wisely identified as causes of corrosivity, namely chlorinated terpenes and chlorinated terpenoids. This is reflected in the process steps including determining the levels of chlorinated terpenes and chlorinated terpenoids in the purified acid. Where detectable levels are present, the method of the invention requires repeating the purification step. Thereafter, the method includes a step of again determining the levels of chlorinated terpenes and chlorinated terpenoids. This series of steps is repeated until the levels of chlorinated terpenes and chlorinated terpenoids are undetectable.

[0040] Typically, the levels of chlorinated terpenes and chlorinated terpenoids are determined by techniques, preferably gas chromatography, with a detection limit of up to 1 ppm, preferably up to 0.5 ppm.

[0041] Preferably, the levels of chlorinated terpenes and chlorinated terpenoids are determined by gas chromatography, more preferably using dodecane as an internal standard and a flame ionization detector.

[0042] The method for reacting wood with an acetylated fluid containing acetic anhydride is typically carried out according to an optimized acetylation method as known in the art. A preferred method includes the following steps:

[0043] - Provide timber (solid wood or timber components);

[0044] - Control, and adjust if necessary, the moisture content of the wood or wood components;

[0045] - Impregnate wood or wood components with acetylated fluid;

[0046] - subject impregnated wood or wood components to one or more heating steps to achieve acetylation of the wood components;

[0047] - Separate acetylated wood or wood components from excess acetylated fluid.

[0048] In an embodiment of interest, acetylation is performed according to any of the acetylation methods described in WO 2009 / 095687, WO 2011 / 95824, WO2013 / 117641, WO 2013 / 139937 or WO 2016 / 008995, the disclosure of which is incorporated herein by reference.

[0049] Acetylation reactions are typically carried out at temperatures between 120°C and 200°C, for example, 160°C to 180°C. The duration of acetylation treatment usually ranges from 30 minutes to 3 hours. For a given reactor setup and depending on the type of wood to be acetylated, technicians can optimize the time and temperature conditions.

[0050] The wood to be acetylated is in the form of wood elements or solid wood, and also includes wood veneers. Wood elements can preferably be, for example, wood chips, wood strips, or wood particles. The wood is preferably a non-durable species, such as softwood, like conifers, typically spruce, pine, or fir, or a non-durable hardwood. Non-limiting examples of suitable types of wood include spruce, Sitka spruce, coast pine, Scots pine, radiata pine, eucalyptus, red alder, European alder, beech, birch, spruce, black pine, Chinese pine, red pine, southern yellow pine, Japanese cedar (sugi), and hemlock. Monocotyledonous plants, such as palm trees, and other hardwoods, such as paulownia, teak, maple, oak, and white oak, are also suitable.

[0051] Typically, the wood to be acetylated is not wood pulp. Specifically, the wood acetylation process differs from processes involving chemical reactions that form new materials and / or shapes from wood-based starting materials such as pulp, for example, the production of nanocellulose from cellulose-based starting materials. Essentially, the wood acetylation process is used to preserve the wood (solid wood, wood veneer, wood components) in its original shape and only alters the wood to the extent that it becomes acetylated. In particular, unlike the case of nanocellulose, acetylated wood contains hemicellulose, and especially lignin, in addition to cellulose. The purpose of wood acetylation is to acetylate these wood components, resulting in the presence of acetylated cellulose, acetylated hemicellulose, and acetylated lignin.

[0052] The table below shows typical dimensions for acetylated wood components.

[0053] Table 1

[0054] In some embodiments, the wood element has a length of 1.0 mm to 75 mm, a width of 0.05 mm to 75 mm, and a thickness of 0.05 mm to 15 mm.

[0055] In alternative embodiments, the wood is solid wood or veneer of wood and preferably has a length or width of at least 8 cm. The thickness is preferably at least 1 mm. In some embodiments, the wood has a width of 2 cm to 30 cm, a thickness of 2 cm to 16 cm, and a length of 1.5 m to 6.0 m. In other embodiments, the wood has a thickness of at least 1 mm, a width of 20 cm to 2.5 m, and a length of 20 cm to 6 m.

[0056] In summary, methods for reducing the corrosivity of acetic acid recovered from a process in which wood is subjected to reaction with an acetylating fluid containing acetic anhydride are disclosed. It has been found that such corrosivity can be reduced by removing chlorinated terpenes and chlorinated terpenoids from the acid. Methods for achieving this include, among others, cooling crystallization.

[0057] The present invention is illustrated by reference to the following non-limiting test examples.

[0058] Examples

[0059] The corrosivity of several test liquids was determined on stainless steel specimens according to the following setup:

[0060] - Specimen in a 1 L three-neck flask

[0061] - Flask connection:

[0062] ○ Reflux condenser

[0063] ○ Thermocouple tube

[0064] ○ Plug

[0065] - Stirring of the test liquid by a magnetic stirrer

[0066] - Heating of the flask by an oil bath

[0067] - Measuring the temperature about 1 cm above the specimen in the test liquid

[0068] - The apparatus is insulated

[0069] - Specimen = stainless steel 316L

[0070] - Temperature = 115 °C

[0071] - Duration = 100 hours (or longer, up to two weeks, to evaluate the corrosivity of liquids with little corrosivity)

[0072] - Stirring = 70 rpm

[0073] - Environment = air

[0074] - Test liquid = 300 g

[0075] Test liquid:

[0076] (A) Impure acetic acid recovered from the acetylation of radiata pine;

[0077] (B) Test liquid (A) with 0.5% water added;

[0078] (C) Commercial glacial acetic acid;

[0079] (D) Commercial glacial acetic acid containing chlorinated terpenoids;

[0080] (E) Commercial acetic acid with added pinene;

[0081] (F) Commercial glacial acetic acid with added terpenes and acetic anhydride;

[0082] (G) Commercial glacial acetic acid with added chlorinated terpenes and acetic anhydride;

[0083] (H) Commercial glacial acetic acid containing chlorinated terpenoids was added in a reduced amount compared to the test liquid (D);

[0084] (I) Commercial glacial acetic acid with added sodium chloride;

[0085] (J) Commercial glacial acetic acid with added acetic anhydride;

[0086] (K) Test liquid (A) purified by melt crystallization;

[0087] (L) Test liquid (A) subjected to azeotropic distillation together with water;

[0088] The results are given in Table 2 below ("nd" = not detected). Table 2

Claims

1. A method for reducing the corrosiveness of acetic acid, said acetic acid being recovered from a process of subjecting wood to a reaction with an acetylated fluid containing acetic anhydride, said method comprising removing chlorinated terpenes and chlorinated terpenoids from said acid.

2. The method of claim 1, further comprising cooling the acetic acid to below its melting point, thereby forming crystals, and separating the crystals from the fluid.

3. Acetic acid seed crystals are used to reduce the corrosiveness of acetic acid recovered from wood acetylation.

4. Use of a crystalline acetic acid for reducing the corrosiveness of acetic acid, said crystalline acetic acid being formed in a method comprising subjecting acetic acid recovered from wood acetylation to cooling and crystallizing, thereby separating the crystalline acetic acid from its respective mother liquor.

5. An acetic acid crystal for use in reducing the corrosiveness of acetic acid by adding it to a fluid containing acetic acid recovered from wood acetylation.

6. A method for producing acetic acid, the method comprising reacting an acetylated fluid containing acetic anhydride with wood to form esterified wood and a used acetylated fluid containing acetic acid, subjecting the used acetylated fluid to a step of separating acetic acid from acetic anhydride, subjecting the acetic acid to a purification step of removing chlorinated terpenes and chlorinated terpenoids to form purified acetic acid, determining the levels of chlorinated terpenes and chlorinated terpenoids in the purified acid, and repeating the purification step and the determination step until the levels of chlorinated terpenes and chlorinated terpenoids are undetectable.

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