Method for recovering o-aminophenol

Abstract

The invention relates to a method for recovering o-aminophenol, comprising: (i) purifying aniline in a distillation column to produce an aniline product stream comprising greater than 80% aniline, and a slurry residue stream comprising o-aminophenol and 5 - 40 wt. % aniline; (ii) cooling the residue stream to 80 – 25 °C to form a slurry residue; (iii) filtering the slurry residue to separate crude o-aminophenol solids from liquid waste; dissolving the crude o-aminophenol solids in solvent; (v) cooling the dissolved crude o-aminophenol to 15 – 35 °C; and (vi) recrystallizing o-aminophenol from dissolved crude o-aminophenol solids in solvent.

Description

[0001] METHOD FOR RECOVERING O-AMINOPHENOL

[0002] FIELD

[0003] The invention relates to a process for recovering o-aminophenol from a process to produce aniline, by creating a slurry residue from which o-aminophenol can be separated through filtration, then is dissolved in a solvent and recrystallized.

[0004] BACKGROUND OF THE INVENTION

[0005] Aniline is an important intermediate product, in the manufacture of diisocyanates and polyisocyanates in the diphenylmethane (MDI) series, and is manufactured on an industrial scale usually by the catalytic hydrogenation of nitrobenzene in the gas or liquid phase (see, for example, DE-A 2201528, U.S. Pat. No. 3,136,818, EP-A- 0696573 and EP-A-0696574). Methods of manufacturing aniline are described in EP 0944578 A2, as an isothermal mode of operation, and in EP 0696 574 Bl, EP 0696573 Bl and EP 1882681 Al, as an adiabatic mode of operation. In this reaction, in addition to the target product aniline, secondary components such as, for example, phenol or aminophenols are also formed which have to be removed prior to further use of the aniline in subsequent processes.

[0006] What is common to the described isothermal processes for producing aniline is that the starting material nitrobenzene is vaporized at elevated temperature in the hydrogen stream. The reaction is generally conducted such that the gaseous nitrobenzene / hydrogen mixture is passed into the hydrogenation reactor and reacted here over the fixed-bed catalyst, optionally with a downstream post -reactor, at elevated temperature and atmospheric pressure. The heat of reaction liberated is removed from the reactor via a heat exchanger and generally used for steam generation.

[0007] The gas / liquid separation is carried out with multistage condensation to separate hydrogen gas from liquid. The condensed-out reaction products separate into an organic phase (crude aniline) and an aqueous phase (aniline water) and these are subjected to further processing separately. The crude aniline also comprises water and organic by-products in dissolved form which are separated off by distillation. Initially, a column is used to distill off the low-boiling secondary components (for example cyclohexylamine, cyclohexanone, benzene) overhead and the water in the sidestream as an aniline-water azeotrope.

[0008] The bottom distillation product (aniline-high-boilers) is freed of the high-boiling byproducts (for example N-cyclohexylaniline, N,N-diphenylamine, o-aminophenol) in a second distillation column. The pure aniline is distilled off overhead. The high-boilers accumulate in the bottom and may be further concentrated in a third distillation column (residue column). Part of the aniline is recovered at the top of the residue column and the bottoms from the residue column are transferred into a residue container or pipelined to the incineration. Here, a residual aniline content serves as solvent to maintain the pumpability of the residue, as the incineration is typically in a different location or in a different facility. In addition, the residue is transferred through heated pipeline and stored at elevated temperature to avoid precipitates. The high-boilers together with the diluent residual aniline are supplied from the residue container to an incineration step.

[0009] It is important to achieve a high yield of the desired aniline product which means avoiding by-products in the reaction and minimizing production losses in the plant. Such losses may arise in the distillation of the product. This makes concentrating the high-boiling secondary components in the bottom residue difficult without the residue solidifying or parts thereof precipitating and forming undesired precipitates. The coveyability of the residue discharge stream worsens with increasing depletion of aniline content to the point of blocking of pipes due to solidification of high boiler residue components. A significant proportion of aniline product is therefore always incinerated with the high boiler residue. Notably, the aniline in this liquid waste may be about half of the content, to keep the liquid flowable in the process.

[0010] EP 0 696 574 Bl discloses in examples 9 and 10 a process in which the product of nitrobenzene hydrogenation including the water of reaction is distilled in a distillation column and the bottom product of the distillation column is diluted with the aniline- rich phase obtained after phase separation of the condensate of the top product of the same distillation column.

[0011] EP 1 005 888 Bl describes a rinsing apparatus for removing residues from the bottoms outlet of an evaporation apparatus and the use of said rinsing apparatus for the distillative work-up of salt-containing solutions. It is a disadvantage that the used rinsing agent again entails a certain cost and inconvenience to the extent that it needs to undergo costly incineration. Moreover, such a rinsing apparatus is unsuitable when high temperatures prevail at the bottom of the column and therefore high-boiling solvents would need to be used or the bottom would need to be cooled in order to carry out the rinsing operation without vaporization of the rinsing agent. In the process described, preference is given to using water, which, however, is only of limited suitability as a washing agent for organic residues. In addition, it is not always possible in practice to avoid washing agent entering the column and impairing the quality of the top product and / or the further work-up of the top product.

[0012] US Pat. No. 9,682,917 describes a process to recover more aniline from the residue discharge bottom and blending with methanol-water mixture. The distillation column is operated such that discharge residual bottom contains greater than 5 wt. % to less than 70 wt. % aniline based on the total weight of the bottom product. The residual discharge is then diluted with methanol water from methylenediphenylamine (MDA) production plant to keep it in the solution form.

[0013] US Pat. No. 9,115,049 describes a similar process in which aniline content in the residual bottom is reduced, and to the final discharge bottom the technical grade methanol is added under gauge pressure of from 15 to 20 bar. The residual discharge after blending with methanol discharged through heated pipeline kept at 60 °C or above.

[0014] In both of the above described processes, the addition of additional low boiler compound or mix of low boiler compounds is required to keep residue in the solution form. Though more aniline can be recovered from residual discharge but overall waste generation on the weight basis might be the same as aniline is replaced by a low boiler compound or a mix of low boiler compounds. Additional infrastructure cost and cost for the low boiler compound is also required.

[0015] US Pat. Appl. Pub. No. 2022 / 0348533 Al describes using an extraction step, where phenolic compounds including aminophenols are removed prior to distilling the aniline. This not only requires an additional step, but also an alkali metal hydroxide must be added, in addition to an alkali metal salt. Then, acid is added in a neutralization, or an acidification, step to bring the phenolate salts back to organic form, where it is then combined with the bottom discharge from distillation and typically incinerated as waste. This process suffers from many of the same drawbacks, in that it requires additional process equipment and raw materials for the extraction step, and the aminophenol ends up combined with the other phenol products to be incinerated, rather than in a form where it may be recovered. The process does not recognize that aminophenol is a valuable target product in its own right but is rather only concerned with removing the aminophenol from the aniline produced. Consequently, the application teaches that precipitation of aminophenols should be avoided.

[0016] CN 115 318 280 A discloses a method for regenerating and recovering a catalyst from aniline tar and producing o-aminophenol as a by-product. In this process, (1) Aniline tar is mixed with an extraction solvent comprising benzene, short-chain aliphatic hydrocarbons and optionally a benzene derivative, extracted under stirring, and then the liquid phase and the solid phase are separated by filtration; (2) the solid phase obtained in step (1) is mixed with an activator, wherein the activator comprises benzene, a short-chain aliphatic hydrocarbon and an optional benzene derivative, the mixture is heated under high-speed stirring for activation, and then the liquid phase and the solid phase are separated by filtration, wherein the solid phase is dried in an inert gas to obtain a dry solid; and (3) the dried solid obtained in step (2) is added to a sublimation desublimator, and heated to 120-220° C in at subatmospheric pressure for sublimation. O-aminophenol is obtained by desublimation of the sublimated gas, and the catalyst is recovered from the residual solid at the bottom of the sublimator.

[0017] Furthermore, the requirement of running a process where a portion of the target production product must be added to the waste, inherently means running a less efficient process. Combined with the increasing costs of waste incineration and remove, there is a need to reduce overall waste, while increasing efficiencies and looking for new and creative ways to develop sustainable chemical processes.

[0018] SUMMARY OF THE INVENTION

[0019] The present invention describes a process for recovering o-aminophenol, comprising: (i) purifying aniline in a distillation column to produce an aniline product stream comprising greater than 80 wt. % aniline, and a residue stream comprising o- aminophenol and 5 - 40 wt. % aniline; (ii) cooling the residue stream to 80 - 25 °C to form a slurry residue; (iii) filtering the slurry residue to separate crude o-aminophenol solids from liquid waste; (iv) dissolving the crude o-aminophenol solids in solvent; (v) cooling the dissolved crude o-aminophenol in solvent to 15 - 35 °C; and (vi) recrystallizing o-aminophenol from dissolved crude o-aminophenol solids in solvent.

[0020] In another embodiment, the purifying aniline step comprises a first distillation column and a second distillation column, wherein the first distillation column comprises two output streams during operation: an aniline product stream and a bottom stream, wherein the bottom stream enters the second distillation column and the slurry residue emanates from the second distillation column.

[0021] In other embodiments, the residue stream is cooled to between 50 and 25 °C, most preferably between 35 and 25°C. In others, the slurry residue comprises of 5-35 wt. % of solids, preferably between 25-35 wt. %, based on the total weight of the slurry residue. In more embodiments, the slurry residue comprises 10-40 wt. %, preferably 25-40 wt. % aniline, more preferably 30-40 wt. % aniline. In addition, the slurry residue comprises 2 - 20 wt. % o-aminophenol. Also, the slurry residue may comprise 5 - 25 wt. % phenylcyclohexylamine. In a different embodiment, the slurry residue comprises 1 - 15 wt. % diphenylamine. In yet another, the slurry residue comprises less than 1 wt. %, preferably less than 0.5 wt. % most preferably less than 0.1 wt. %, 4- aminodiphenylamine. In still another embodiment, the slurry residue comprises less than 10 ppm of catalyst, and the catalyst may be a copper, palladium or platinum catalyst.

[0022] In another embodiment, the process comprises (vii) washing crude o-aminophenol with water, toluene or benzene. In this embodiment, the (vii) washing may occur after step (iii) filtering, but before step (iv) dissolving. In an embodiment where the solvent is a waterethanol co-solvent, the ratio of waterethanol may be 10:90 to 50:50, more preferably 10:90 - 30:70 by weight. In one of these embodiments, the solvent may be heated to 60 - 90 °C.

[0023] In different embodiments, the solvent may be water, and it may be heated to 90 - 100 °C. In this embodiment, the process may further comprise (viii) filtering dissolved crude o-aminophenol, after step (iv) dissolving but before step (v) cooling.

[0024] In additional embodiments, the liquid waste separated in step (iii) has a viscosity of less than 200 cP at 25 °C, pursuant to ASTM D4889-15. Additionally, the liquid waste separated in step (iii) may remain in the liquid form at or above 25 °C, preferably for at least one week.

[0025] BRIEF DESCRIPTION OF DRAWINGS

[0026] FIG 1 is a process flow diagram of a continuous process of an embodiment of the present invention. FIG. 2 is a process flow diagram of a continuous process of another embodiment of the present invention.

[0027] DETAILED DESCRIPTION

[0028] The present invention describes the process to minimize aniline losses by recovering more aniline, which was previously discharged as part of the residual bottom waste stream, and to recover o-aminophenol as a byproduct from the residual waste. The advantage of this process over previously described processes is that it does not require additional low boiler compounds to keep the final residual discharge in the liquid form and valuable o-aminophenol can be recovered from the residual waste. The reduced liquid waste can then be stored and transported at room temperature without any issues stemming from the solidification of liquid waste. The additional advantage of process of this invention is that valuable o-aminophenol will be isolated from the residual waste. O-aminophenol s is an important intermediate for synthesis of photographic developers, dyes, stain, pharmaceutical intermediates, heterocyclic systems such as oxyquinolines, phenoxazines, and benzoxazole.

[0029] The residual discharge from the aniline production contains high boiler impurities and a majority of those high boiler impurities are N-methylaniline, toluidine, o- phenylenediamine, dicyclohexylamine, aminophenol isomers, m-phenylenediamine, phenylcyclohexylamine, phenylcyclohexylamine, diphenylamine and other high boiler impurities. According to Table 1 below, these high boiler impurities are either solids or liquids at room temperature when they are in their pure form. The impurities which are solid at room temperature would possibly cause the solidification of aniline residue discharge. The solubility study of impurities in pure aniline showed that aminophenol isomers have a very low saturation point in aniline compared to other impurities. The solubility study showed that aminophenol impurities can easily precipitate out of the aniline solution at low concentration, while other impurities may remain in solution with the aniline. The aminophenol impurities could be responsible for solidification of aniline residual discharge when residue is stored or transferred at room temperature, or when the aniline content in the residual discharge is decreased. Of the 2-aminophenol, 3-aminophenol and 4-aminophenol isomers, the 2-aminophenol is formed as a major impurity in the aniline process. The 2-aminophenol is a major isomer present in the residual discharge whereas other isomers 3-aminophenol and 4-aminophenol are found in less than 1 wt. % of the residue discharge. Therefore the 2-aminophenol impurity may be responsible for solidification of aniline residual discharge when the residue is stored or transferred at room temperature, or when the aniline content in the residual discharge is decreased. The isolation of 2-aminophenol from residual discharge can resolve the issue of solidation of residue. With the isolation of 2-aminophenol from residual discharge, more aniline can be recovered from the residue, and the residue can be stored and transported at room temperature. The valuable 2-aminophenol, referred to herein as o-aminophenol, can be recovered as a by-product from the waste.

[0030] Table 1: Impurities Found in Aniline Production

[0031] In the process scheme according to FIG. 1, crude aniline arrives in a distillation column 110, either directly from a production plant, or indirectly from an intermediate storage or phase separation container, as material stream 100. The purifying distillation column 110 is operated at reduced pressure; the necessary vaporization energy can be supplied via continuous evaporators heated with steam. The necessary reduced pressure is established with a liquid ring pump. Aniline water serves as the operating liquid for the vacuum pumps.

[0032] Low-boiling distillation products are withdrawn from the column 110 as top stream 112 and some of them are condensed. The organic, aniline-rich part of the condensate is returned to the top of the column via a phase separator 114, as material stream 118. The aqueous part of the condensate is recycled back into a different part of the process, or to a different process, as material stream 120.

[0033] Pure aniline is taken off of column 110 as material stream 122. Some of the pure aniline is re-introduced to the column as reflux stream 124 using pure aniline pumps. The remainder is discharged in product stream 126 comprising greater than 80 wt. % aniline, which is later allowed to cool. The concentrated high-boilers remain in the column bottom. They are discharged as material stream 130, while a portion stream 132 may be reboiled and reintroduced into the column bottom, and the remainder material stream 134 must be cooled in step 136 to form a slurry. The material is slowly cooled or quench cooled with or without stirring, preferably in a jacketed reactor or storage tank / vessel.

[0034] Material stream 134 is a slurry at room temperature, meaning it is a suspension of solids in liquid at room temperature. Material stream 134, also referred to herein as the slurry residue, forms a slurry between 80 and 25 °C, preferably between 50 and 25 °C, and more preferably between 35 and 25°C. Upon cooling of the slurry residue bottom to within one of these ranges, the slurry is formed. The 2-aminophenol solids start precipitating out of solution below 80 °C. After cooling, the slurry of material stream 138 comprises 5 - 35 wt. % of solids, preferably between 25 - 35 wt. %.

[0035] This material stream 138 is a slurry residue comprising o-aminophenol and less than 40 wt. % aniline, preferably less than 25 wt. %, aniline. In a preferred embodiment, material streams 130 and 138 may comprise 2 - 20 wt. % o-aminophenol, 5 - 40 wt. % aniline, 5 - 25 wt. % phenylcyclohexylamine, and 1 - 15 wt. % diphenylamine. In the invention the residue column is operated such that the aniline in the discharge residue, material stream 130 and 138, would be 5 - 40 wt. %, preferably 10 - 40 wt. %, of the residue. The composition of other components in material stream 130 and 138 may be 1 - 3 wt. % phenol, less than 0.1 wt. % toluidine, less than 0.1 wt. % o- phenylenediamine, 2 - 5wt. % m-phenylene-diamine, 0.1 - 2 wt. % 4-aminophenol and other high boiler impurities. In other embodiments, the slurry residue comprises 25-40 wt. % aniline, preferably between 30-40 wt% aniline, or at least 5 wt. % aniline. In others, the slurry residue comprises at least 2 wt. % o-aminophenol. The slurry residue may also comprise at least 5 wt. % phenylcyclohexylamine, or at least 1 wt. % diphenylamine.

[0036] In another embodiment, material streams 130 and 138 comprise less than 1 wt. %, preferably less than 0.5 wt. %, more preferably less than 0.1 wt. % 4- aminodiphenylamine. It was found that a higher amount of 4-aminodiphenylamine prevented the waste stream from forming a slurry. Instead, the higher amount of 4- aminodiphenylamine in the waste stream made it form a viscous liquid, instead of a slurry residue. This resulted in a much less effective filtering step to recover the o- aminophenol. Therefore, a higher amount of 4-aminodiphenylamine is not recommended.

[0037] Material stream 130 preferably comprises less than 10 ppm of catalyst, which may be present from an upstream process in which aniline is produced. The catalyst may be a copper, palladium or platinum catalyst.

[0038] Referring again to FIG. 1, Material stream 138 enters filtering step 140, where the slurry residue in material stream 138 is separated into filtrate material stream 144 comprising crude o-aminophenol solids, and filtrate liquid residue stream 142, comprising residual aniline as well as the other impurities, which are either liquid or are highly soluble in the liquid aniline stream. In filtering step 140, the crude 2- aminophenol solids are isolated from the slurry in material stream 138 by filtration such as by centrifuge or filter press or vacuum filters, such as rotary drum vacuum filters. The liquid residue 142 obtained from the filtrate remains in the liquid state with viscosity of less than 200 cP at 25 °C, the viscosity measured with Bookfield viscometer DV-I Prime, pursuant to ASTM D4889-15. The filtrate liquid residue 142 may then be stored at room temperature above 20 °C and transported without requirement of a heat traced piping system. Filtrate residue 142 remains in the liquid form at or above 25 °C, preferably for at least one week.

[0039] The crude 2-aminophenol in filtrate 144 is next dissolved in a solvent in dissolution step 150. Solvent is added in material stream 152, creating a dissolved material stream 154. The solvent may be water or ethanol or a water-ethanol co-solvent system preferably, a water-ethanol co-solvent system. The ratio of water to ethanol in the water-ethanol co-solvent system is preferably 10:90 to 50:50, more preferably 10:90 to 30:70, measured by weight of water to the weight of ethanol in the solvent. The amount of solvent used in dissolution step 150 is preferably 3 to 10 parts, more preferably 3 - 5 parts, solvent for each part by weight of crude 2-aminophenol, the weight of material stream 144. When the solvent used is either ethanol or a water-ethanol co-solvent, the crude 2-aminophenol material stream 144 is dissolved at 60 - 90 °C in dissolution step 150. When the solvent is water the crude 2-aminophenol material stream 144 is dissolved at 90 - 100 °C in dissolution step 150. The amount of water used for recrystallization is 5 to 50 parts, preferably 10 - 20 parts by weight per part by weight of the crude 2-aminophenol material stream 144.

[0040] After dissolution step 150, the dissoved o-aminophenol material stream 154 enters cooling step 156, where material stream 154 is cooled to preferably 15 - 35 °C, to allow the o-aminophenol to precipitate out of solution as o-aminophenol crystals in material stream 158. When water is used as the solvent, the solution may be filtered in an additional step (not shown) at above 90 °C., before it enters cooling step 156 to filter out impurities that may be insoluble in the water. The crystallized 2-aminophenol is then recovered from material stream 158 by filtration in filtration step 160, as crystallized 2-aminophenol product stream 164, while the liquid filtrate waste is removed as material stream 162. The filtration may be done by centrifuge or a filter press or vacuum filter, including a rotary drum vacuum filter. In some embodiments, the solvent dissolution and cooling steps may be done by a single piece of equipment, such as a crystallizer.

[0041] In another embodiment in the process scheme according to FIG. 2, crude aniline arrives either directly from a production plant or intermediate storage as material stream 200 to a first distillation column 210. The first distillation column 210 is operated at reduced pressure; the necessary vaporization energy can be supplied via continuous evaporators heated with steam. The low-boiling aniline distillation product stream is withdrawn from column 210 as top stream 212 and condensed. A portion of the condensed aniline product stream is returned to the top of the column column as reflux using pure aniline pumps, as material stream 218, while the remainder is produced as aniline product stream 220.

[0042] The bottoms of the first distillation column 210 that are enriched with high boilers are conveyed as material stream 224 into second distillation column 230 for further concentration, while a portion is refluxed back to the first distillation column as material stream 226. The second distillation column 230 likewise operates at reduced pressure. The necessary vaporization energy can be supplied via a falling-film evaporator heated with steam. At the top of the column, aniline vapor passes over as material stream 232 and is condensed out in a condenser. Some of the condensate is introduced to the top of the column as reflux in material stream 234 using distillate pumps. Depending on quality, the remaining condensate in material stream 236 can either be discharged via a heat exchanger or admixed with the feed stream of the first distillation column 210 as material stream 200.

[0043] The concentrated high-boilers remain in the bottom of second distillation column 230, discharged as material stream 240. A portion stream 242 may be reboiled and reintroduced into the bottom of second distillation column 230, while the remainder proceeds as material stream 244 to filtration step 250 as described below. The contents and characterization of material stream 240 may be the same as described above as in material stream 130 in association with FIG. 1.

[0044] Referring back to FIG. 2, Material stream 244 is cooled in step 246 to form a slurry. Various methods of cooling are described above. Material stream 244 is a slurry at room temperature, and is also referred to herein as the slurry residue. It forms a slurry between 80 and 25 °C, preferably between 50 and 25 °C, and more preferably between 35 and 25°C. Upon cooling of the slurry residue bottom to within one of these ranges, the slurry is formed. The 2-aminophenol solids start precipitating out of solution below 80 °C. After cooling, the slurry of material stream 248 comprises 5 - 35 wt. % of solids, preferably between 25 - 35 wt. % when it enters filtering step 250, where the slurry residue in material stream 244 or 248 is separated into filtrate material stream 254 comprising crude o-aminophenol solids, and filtrate liquid residue stream 252, comprising residual aniline as well as the other impurities, which are either liquid or are highly soluble in the liquid aniline stream. In filtering step 250, crude 2- aminophenol solids are isolated from the slurry in material stream 244 or 248 by filtration. The liquid residue 252 obtained from the filtrate remains in the liquid state.

[0045] The crude 2-aminophenol solids isolated through filtration in material stream are optionally further washed in washing step 260 with water, toluene or benzene entering as washing fluid in material stream 262. The washing fluid is preferably benzene, which may be recovered as benzene waste in the aniline production process. The washed benzene or other fluid in material stream 264 may be then feed to another part of the aniline production process. The washed 2-aminophenol in material stream 266 is the sent to dissolution step 270, wherein it is mixed with a solvent in material stream 272, creating dissolved 2-aminophenol material stream 274. When water is used as the solvent, the solution may be filtered in an additional step (not shown) at above 90 °C., before it enters cooling step 276 to filter out impurities that may be insoluble in the water. After dissolution step 270, the dissoved o-aminophenol material stream 274 enters cooling step 276, where material stream 274 is cooled to preferably 15 - 35 °C, to allow the o-aminophenol to precipitate out of solution as o-aminohenol crystals in material stream 278. Material stream 278 is sent to filtration step 280, where the material is filtered to create filtrate stream 282 and recrystallized product stream 284. Dissolution step 270, cooling step 276 and filtration step 280 are described as dissolution step 150, cooling step 156 and filtration step 160 above in FIG. 1.

[0046] In an embodiment, the slurry residue comprises very little, or no, 4- aminodiphenylamine. 4-Aminodiphenylamine, also known as N-phenyl-p- phenylenediamine, is an impurity formed in the liquid phase hydrogenation of mononitrobenzene, and can be detrimental to the invention. It was found that the presence of too much 4-aminodiphenylamine in the distillate bottom resulted in a viscous liquid rather than a slurry residue. This causes the subsequent filtration step to become less effective at separating the 2-aminophenol from the slurry residue.

[0047] 4-aminodiphenylamine impurity that may result from liquid phase hydrogenation of mononitrobenzene. It has been found that in gas phase hydrogenation, using an adiabatic process with a fixed bed catalyst system or an isothermal process, 4- aminodiphenylamine is present as an impurity at very low amounts. The catalyst activity and process parameters in gas phase hydrogenation does not lead to formation of 4-aminodiphenylamine as a major impurity.

[0048] Preferably, there is no extraction step in the process to recover o-aminophenol. Such a process that includes extraction requires additional process equipment and materials, including an alkali metal hydroxide, an alkali salt solution, and acid, such as hydrochloric acid. More preferred, there is no extraction step between steps (i) and (iv) of the claimed invention. In this embodiment, as the material stream flows from step (i) distillation, to step (ii) cooling, to step (iii) filtering, to step (iv) dissolving, to step (v) cooling, to step (vi) recrystallizing, there is no extraction step within any of these steps or any step in between these steps, as the material flows from steps (i) to (vi), inclusive. In another embodiment, there is no extraction with non polar solvents, such as benzene, derivatives of benzene, and aliphatic hydrocarbons, such as hexane and cyclohexane. Furthermore, processes that use such extraction steps typically combine phenolic waste, making it more difficult to separate o-aminophenol from the other phenolic compounds. To recover o-aminophenol, it would require additional equipment and materials, such as acid and a mixer-settler apparatus.

[0049] Examples

[0050] Inventive Example 1

[0051] The aniline residue containing about 54.4% of aniline was collected from a bottom of a distillation column used to produce aniline. This sample was then distilled to create a simulated residue bottom stream that contains less than 40% aniline, along with the remaining impurities of the residue bottom stream that is expected to be present in the process of the invention. Distillation experiments were carried out in 500 mL three neck flask quipped with distillation head with 4.5 inch Vigroux column, under reduced pressure of 5.3-6.6 kPa (or 40-50 torr) and at 120-125 °C temperature.

[0052] The aniline residue containing 54% aniline was added to 500 mL 3-neck flask equipped with thermometer, stirrer and distillation take off adapter connected to a condenser. The aniline was distilled to obtain distillate bottom with a composition of 39% aniline, 19.5% 2-aminophenol, 7.7% phenylcyclohexylamine and other high boiler impurities. The distillate bottom represents material stream 130, a discharge of distillation column 110 or material stream 240, a discharge of distillation column 230 according to the invention. About 45 wt% of the aniline was recovered from the distillate bottom.

[0053] The distillate bottom was then quench cooled to 25-30 °C to generate slurry containing 26.5% of solids. The slurry was filtered under reduced pressure to give crude 2- aminophenol solids at top and the liquid residue as a filtrate. The viscosity of the filtrate residue was 19 cp at 25 °C, and no solidification of the residue was observed when stored at 25-30 °C for over a week.

[0054] The crude 2-amiophenol was further purified by recrystallization from water-ethanol co-solvent mixture (10:90). Three parts by weight of solvent was used for per part by weight of solids and the resulted solution was heated to reflux (between 60-90 °C) with stirring then cooled to 10-20 °C to induce the crystallization of 2-aminophneol. The crystals were recovered by filtration, sequentially washed with water / ethanol 50:50 cosolvent then with water and dried in oven to obtain 2-aminophenol with 99.2% purity with a recovery of about 80%. The distillation, recrystallization, drying and storage in the experiments were carried out under nitrogen blanket. The composition of residual samples and purity of 2-aminophenol was determined by gas chromatography using area percent method. The percent solids in the slurry was calculated based on the weight of solids filtered and the weight of the liquid filtrate. The viscosity of residue measured by Brookfield rotating viscometer DV-I Prime at 25°C, pursuant to ASTM D4889-15.

[0055] Inventive Example 2

[0056] The aniline residue containing about 52.6% of aniline was collected from a bottom of a distillation column used to produce aniline, as described in Example 1. The aniline residue containing 52.6% aniline was distilled as described above for Example 1 to obtain a distillate bottom with a composition of 9.7% aniline, 10% 2-aminophenol, 23.6% phenylcyclohexylamine and other high boiler impurities. The distillate bottom represents material stream 130, a discharge of distillation column 110 (Fig. 1) or material stream 240, a discharge of distillation column 230 (Fig. 2) according to the invention. 94 wt% of aniline was recovered from the distillate bottom.

[0057] The distillate bottom was then quench cooled to 25-30 °C to generate slurry containing 25% of solids. The slurry was filtered under reduced pressure to give crude 2- aminophenol solids at top and the liquid residue as filtrate. The viscosity of residue was 132 cp at 25 °C, and no solidification of the residue was observed when stored at 25-30 °C for over a week. The crude 2-amiophenol was washed with recycled benzene (benzene waste from aniline production) and further purified by recrystallization from water. Twenty parts of water was used for per part of solids and the resulted solution was heated to reflux with stirring then filtered hot at greater than or equal to 90 °C. The filtrate solution was then allowed to cool to 20 °C to induce the crystallization of 2- aminophenol. The crystals were recovered by filtration, washed with water and dried in oven to obtain 2-aminophenol with 99.1% purity.

[0058] Comparative Example 3 (impact of 4-aminodiphenylamine)

[0059] The impact of 4-aminodiphenylamine on the process of isolating 2-aminophenol from the aniline residue and increased recovery of aniline from the residue was analyzed by carrying out controlled experiments using a residue bottom doped with 4- aminodiphenylamine. The aniline residue containing about 50% of aniline which was collected from the bottom of an aniline distillation column. The distillation experiments and slurry formation performed to simulate impact of 4-aminodephylamine on the proposed process according to invention. The aniline residue containing 49.4% aniline was added to 500 m 3-neck flask equipped with thermometer, stirrer and distillation take off adapter connected to a condenser. The aniline residue was spiked with 81 gm of N-phenyl-p-phenylenediamine. The aniline was distilled under reduced pressure of 5.3-6.6 kPa (or 40-50 torr) at 120- 125 °C temperature to obtain distillate bottom with a composition of 6.7% aniline, 8.0% 2-aminophenol, 17.8% phenylcyclohexylamine, 29% N-phenyl-p-phenylenediamine and other high boiler impurities.

[0060] The distillate bottom was then quench cooled down to 25-30 °C to generate slurry. However, a highly viscous solution was obtained. The distillate bottom was kept at 25 °C overnight, and then 5-10 °C for more than 5 hours to generate solids. The filtration of viscous solution took more than 6 hours and very fine solids were obtained. The presence of 4-aminodiphenylamine impurity was found to negatively impact slurry formation and thus the subsequent isolation of 2-aminophenol from the residue bottom.

[0061] Comparative Example 4 (impact of 4-aminodiphenylamine) In another control experiment, the aniline residue containing 49.4% aniline was added to 500 mL 3-neck flask equipped with thermometer, stirrer and distillation take off adapter connected to a condenser and spiked with 105 gm of N-phenyl-p- phenylenediamine. The aniline was distilled under reduced pressure of 5.3-6.6 kPa (or 40-50 torr) at 120- 125 °C temperature to obtain distillate bottom with a composition of 24.4% aniline, 10.6% 2-aminophenol, 6.8% phenylcyclohexylamine, 34% N- phenyl-p-phenylenediamine and other high boiler impurities. The distillate bottom was then quench cooled down to 25-30 °C to generate a slurry, however a highly viscous solution was obtained. The distillate bottom was kept at 25 °C overnight then 5-10 °C for more than 5 hours to generate solids. The filtration of viscous solution took more than 6 hours and very fine solids were obtained.

[0062] The aniline in the residue discharge is generally maintained between 50-60% wt% so that it can be kept flowable. A great deal of aniline is lost when the distillation apparatus i.e. distillation column 110 (shown in Fig. 1 ) or residual column 230 (shown in Fig. 2) connected to aniline process is operated without recovering o-aminophenol according to the invention. These aniline losses can be significantly reduced according to the invention. In addition, according to the invention, aniline waste can be handled in a liquid state without addition of external chemical / material and o-aminophenol can be isolated as a byproduct from the aniline waste with the process of the invention.

[0063] Examples 1 and 2 illustrates that 45 to 94 wt% of aniline was recovered from the aniline waste with the inventive process. These examples show that aniline losses can be siginifincantly reduced with the inventive process. As shown in examples 1 and 2, liquid waste separated from the filtration step of crude o-aminophenol can be stored at or above 25 °C in the liquid state without addition of external material or solvent.

[0064] O-aminophenol was isolated as a byproduct with >99% purity by recryallization from water: ethanol co-solvent with very good overall recovery of about 80% as shown example 2. O-aminophenol can also be purified by recrystallization from water as shown in example 2. 4-aminodiphenylamine is a major impurity in the liquid phase hydrogenation of mononitrobenzene but it is a minor impurity in gas phase hydrogenation of the nitrobenzene. 4-aminodiphenylamine impurty was shown to have a negative impact on the inventive process. The control experiments in example 3 and 4 show that 4- aminodiphenylamine negatively impacts slurry formation, forming instead a highly visocus liquid was obtained after cooling of residue.

Claims

Claims1. A process for recovering o-aminophenol, comprising:(i) purifying aniline in a distillation column to produce an aniline product stream comprising greater than 80 wt. % aniline, and a residue stream comprising o-aminophenol and 5 - 40 wt. % aniline;(ii) cooling the residue stream to 80 - 25 °C to form a slurry residue;(iii) filtering the slurry residue to separate crude o-aminophenol solids from liquid waste;(iv) dissolving the crude o-aminophenol solids in solvent;(v) cooling the dissolved crude o-aminophenol in solvent to 15 - 35 °C; and(vi) recrystallizing o-aminophenol from dissolved crude o-aminophenol solids in solvent.

2. The process of claim 1, where the purifying aniline step comprises a first distillation column and a second distillation column, wherein the first distillation column comprises two output streams during operation: an aniline product stream and a bottom stream, wherein the bottom stream enters the second distillation column and the slurry residue emanates from the second distillation column.

3. The process of claims 1 or 2, where the residue stream is cooled to between 50 and 25 °C, most preferably between 35 and 25°C.

4. The process of any of the preceding claims, wherein the slurry residue comprises of 5-35 wt. % of solids, preferably between 25-35 wt. %, based on the total weight of the slurry residue.

5. The process of any of the preceding claims, wherein the slurry residue comprises 10-40 wt. %, preferably 25-40 wt. % aniline, more preferably 30-40 wt. % aniline.

6. The process of any of the preceding claims, wherein the slurry residue comprises 2 - 20 wt. % o-aminophenol.

7. The process of any of the preceding claims, wherein the slurry residue comprises 5 - 25 wt. % phenylcyclohexylamine.

8. The process of any of the preceding claims, wherein the slurry residue comprises 1 - 15 wt. % diphenylamine.

9. The process of any of the preceding claims, wherein the slurry residue comprises less than 1 wt. %, preferably less than 0.5 wt. % most preferably less than wt. 0.1%, 4-aminodiphenylamine.

10. The process of any of the preceding claims, wherein the slurry residue comprises less than 10 ppm of catalyst.

11. The process of claim 10, wherein the catalyst is a copper, palladium or platinum catalyst.

12. The process of any of the preceding claims, further comprising (vii) washing crude o-aminophenol with water, toluene or benzene.

13. The process of claim 12, wherein (vii) washing occurs after step (iii) filtering, but before step (iv) dissolving.

14. The process of any of the preceding claims, wherein the solvent is a water: ethanol co-solvent, preferably wherein the ratio of waterethanol is 10:90 to 50:50, more preferably 10:90 to 30:70 by weight.

15. The process of claim 14, wherein the solvent is heated to 60 - 90 °C.

16. The process of any of claims 1-13, wherein the solvent is water.

17. The process of claim 16, wherein the solvent is heated to 90 - 100 °C.

18. The process of claim 17, where the process further comprising (viii) filtering dissolved crude o-aminophenol, after step (iv) dissolving but before step (v) cooling.

19. The process of any of the above claims, where the liquid waste separated in step (iii) has a viscosity of less than 200 cP at 25 °C, pursuant to ASTM D4889-15.

20. The process of any of the above claims, where the liquid waste separated in step (iii) remains in the liquid form at or above 25 °C, preferably for at least one week.

21. The process of any of the above claims, wherein there is no extraction step in the process to recover o-aminophenol.

22. The process of any of the above claims, wherein there is no extraction step in steps (i) through (vi) or in between any of those steps, in the process to recover o-aminophenol.

23. The process of any of the above claims, wherein there is no extraction step with benzene, derivatives of benzene, or aliphatic hydrocarbons, such as hexane and cyclohexane, in the process to recover o-aminophenol; preferably there is no extraction step with any non polar solvents in the process to recover o- aminophenol.

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