Process for purifying crude methanol

Abstract

The invention relates to a method for purifying crude methanol. Specifically, the present invention relates to heavy oil obtained from a crude methanol side stream derived from chemical broadleaf wood pulping wherein the heavy oil is produced by a process comprising: an acidification step comprising mixing the crude methanol side stream with an acidic aqueous solution and heating to vaporize low boiling sulfur-containing compounds, providing an acidified crude methanol; a separation step comprising separating a liquid top phase, a liquid aqueous intermediate phase and a liquid bottom phase from the acidified crude methanol; and collecting the liquid bottom phase as a heavy oil wherein the heavy oil contains less than 65% terpenes and at least 40% sulfur-containing compounds as analyzed by GC / MS. The process of the present invention can prevent precipitation occurring when purifying a crude methanol stream from softwood pulp.

Description

[0001] This application is a divisional application of international application PCT / FI2021 / 050464, which entered the Chinese national phase on December 29, 2022, with application number 202180046337.4 and invention name “Method for purifying crude methanol”. Technical Field

[0002] The present invention generally relates to the purification of crude methanol obtained in industrial processes. The present invention particularly, but not exclusively, relates to a method for purifying crude methanol obtained in chemical pulping and the use of components obtained from such crude methanol. Background Art

[0003] This section provides useful background information but does not constitute an admission that any of the techniques described herein represent the state of the art.

[0004] Methanol is formed during kraft cooking when lignin is hydrolyzed in alkali. In addition to methanol, the cooking also produces organic sulfur compounds such as methyl mercaptan, dimethyl sulfide and dimethyl disulfide as sulfide and hydrosulfide ions react with lignin.

[0005] During the cooking process, a large amount of methanol ends up in the black liquor, and because methanol is very volatile, it evaporates with water into the evaporator fouling condensate to be recovered as crude methanol. Crude methanol is also recovered from other points in the pulping process, for example from the condensate of the digester off-gas. The fouling condensate can be treated at the fouling condensate stripper by stripping methanol from the condensate, after which methanol can be liquefied from the stripper off-gas to crude methanol in a methanol column, which reduces the water content of the crude methanol.

[0006] The fouling condensate also contains low-boiling volatile sulfur compounds such as H2S, methyl mercaptan, dimethyl sulfide, but also other less volatile sulfur compounds. When processed in the stripper, these end up in crude methanol. In the case of methanol recovery during the digestion of spruce or pine for softwood pulping, the crude methanol contains turpentine and ammonia as well as the sulfur compounds mentioned above.

[0007] Since the crude methanol obtained in the chemical pulping of softwood contains a complex mixture of impurities, it is necessary to remove the impurities before using the methanol. After acidification and dilution, the solubility of the softwood turpentine present in the crude methanol decreases and the different phases can be separated by decantation. After acidification, the heavier bottom phase can be collected, while the methanol and turpentine remain in the upper phase. A portion of the turpentine may still be dissolved or entrained in the crude methanol. The turpentine can be removed from the crude methanol in an extraction column.

[0008] Some methods for purifying methanol from sulfur compounds and other compounds have been described. For example, FI52710 describes a method in which methanol is treated with an acid to precipitate salts and volatile sulfur compounds such as H2S, methyl mercaptan and dimethyl sulfide are removed as a lighter fraction, while methanol remains in the heavier bottom fraction. In addition, the remaining sulfur compounds are treated with an oxidizing agent to make them more volatile and easier to separate by distillation.

[0009] Metso Power AB proposed another methanol purification process in US 8,440,159, in which the acid is acidified with sulfuric acid and the salt formed is kept dissolved below the precipitation point by dilution with water. After acidification, the methanol is evaporated and processed as described in FI52710.

[0010] WO 2015 / 053704 of Andritz Oy describes a process in which crude methanol is first acidified to evaporate H2S, methyl mercaptan and dimethyl sulfide. Thereafter, the crude methanol is washed with a non-polar organic solvent to further purify the methanol. Finally, water, acetone and ethanol in the washed methanol are reduced by distillation.

[0011] One problem with purifying a crude methanol stream from softwood pulp is that precipitates formed during the acidulation step of the crude methanol can also adhere to and grow on equipment surfaces exposed to the acidulated crude methanol. When such precipitates form under process conditions, they need to be removed, resulting in undesirable plugging and process interruptions.

[0012] An object of the present invention is to provide a method for preventing precipitation when purifying crude methanol obtained as a by-product in Kraft pulping of softwood. Summary of the invention

[0013] The claims define the scope of protection. Any examples and technical descriptions of devices, products and / or methods in the specification and / or drawings that are not covered by the claims are not presented as embodiments of the present invention, but are presented as background technology or examples to help understand the present invention.

[0014] According to a first exemplary aspect, there is provided a heavy oil obtainable from a crude methanol side stream derived from chemical hardwood pulping, wherein the heavy oil is produced by a process comprising the steps of:

[0015] an acidification step, the acidification step comprising mixing the crude methanol side stream with an acidic aqueous solution and heating to evaporate low boiling sulfur compounds to provide acidified crude methanol;

[0016] a separation step comprising separating a liquid top phase, a liquid aqueous middle phase, and a liquid bottom phase from the acidified crude methanol; and

[0017] The liquid bottom phase was collected, which had a mass of about 1010 kg / m 3 Heavy oil of density.

[0018] According to a second example aspect, there is provided a method of producing heavy oil, the method comprising:

[0019] providing a crude methanol stream derived from hardwood pulp;

[0020] an acidification step, the acidification step comprising mixing the crude methanol side stream with an acidic aqueous solution and heating to evaporate low boiling sulfur compounds to provide acidified crude methanol;

[0021] a separation step comprising separating a liquid top phase, a liquid aqueous middle phase, and a liquid bottom phase from the acidified crude methanol; and

[0022] The liquid bottom phase was collected, which had a mass of about 1010 kg / m 3 Heavy oil of density.

[0023] In one embodiment of the method of the second aspect, the method is used to produce the heavy oil of the first aspect. Figure 2 shown.

[0024] According to a third exemplary aspect, there is provided a method for purifying crude methanol obtained in chemical pulping, the method comprising:

[0025] - Providing crude methanol obtained as a by-product of chemical pulping;

[0026] - acidifying the crude methanol with an acidic aqueous solution to provide acidified methanol;

[0027] - mixing the heavy oil into acidulated methanol to provide a methanol mixture; and

[0028] - distilling or evaporating the methanol mixture to recover the methanol.

[0029] In one embodiment of the third aspect, the crude methanol is obtained from chemical pulping of softwood. The method for purifying the crude methanol is shown in Figure 3 middle.

[0030] In another aspect, there is provided the use of heavy oil in the purification of crude methanol obtained in chemical pulping. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Some example embodiments will be described with reference to the accompanying drawings, in which:

[0032] Figure 1 One embodiment of a system for producing heavy oil is shown;

[0033] Figure 2 A flow chart showing a method of producing heavy oil; and

[0034] Figure 3 A flow chart of a method for purifying crude methanol according to one embodiment of the present method is shown. DETAILED DESCRIPTION OF THE INVENTION

[0036] In the following description, the same reference numerals denote the same elements or steps.

[0037] When softwood or hardwood is treated in chemical pulping, the resulting crude methanol or crude methanol stream can be treated by acidulating the crude methanol. Optionally, the crude methanol stream can also be diluted with water. The chemical composition of the crude methanol obtained from the chemical pulping process varies depending on the type of wood used in the pulping and the process parameters. Therefore, the crude methanol stream components obtained from softwood pulping may have different characteristics and behave in a different way in the acidulation step and the optional dilution step when compared to the crude methanol stream components obtained from hardwood pulping.

[0038] Heavy oil production

[0039] It has now surprisingly been found that components dissolved in crude methanol from softwood pulp tend to form solid precipitates after acidification and that this precipitation can be prevented by using heavy oil obtained from the crude methanol stream from hardwood pulp by the process of the invention.

[0040] Without being bound by any theory, it can be assumed that the components found in the recovered heavy oil are formed during the hardwood pulping process and some additional chemical transformation occurs during the acidification and / or heating steps. During the black liquor evaporation step of the pulping process, the heavy oil components follow the methanol and during the purification process they separate into different phases due to acidification and are collected.

[0041] Examples of heavy oils include hardwood oil, birch oil, eucalyptus oil, mixtures of the oils in any proportion, and components that can be separated from the oils and mixtures. Other examples of heavy oils include: oils or compounds synthesized during acidification or heating (distillation and evaporation); and sulfur-containing compounds produced during cooking processes.

[0042] The term "heavy oil composition" refers to a composition comprising any amount of heavy oil or a component thereof.

[0043] As used herein, the term "comprising" includes the broad meanings of "including," "containing," and "comprising," as well as the narrow expressions "consisting of" and "consisting only of."

[0044] Birch oil as an example of heavy oil may contain aliphatic or cyclic sulfur-containing compounds having 2 to 4 sulfur atoms and have a molecular weight ranging from 50 to 200.

[0045] In one embodiment, the crude methanol stream is a side stream derived from softwood chemical pulping.

[0046] A crude methanol stream refers to a stream of crude methanol, such as a stream produced in a continuous process.

[0047] In one embodiment, the crude methanol is mixed with an acid to form a salt solution.Salts such as ammonium salts can be removed by methods known in the art such as sedimentation.

[0048] In one embodiment, the heavy oil has a mass fraction of about 1010 kg / m at 20°C. 3 density.

[0049] When the heavy oil is collected in the method, the temperature during collection is 50-80°C.

[0050] In one embodiment, the crude methanol has a mass fraction of about 800 kg / m at 20°C. 3 density.

[0051] In one embodiment, the heavy oil is rich in organic sulfur compounds compared to the crude methanol side stream.

[0052] Other examples of heavy oils include oils or compounds synthesized from heavy oils such as birch oil during acidulation, heating, distillation, and / or evaporation.

[0053] The amount of terpenes increases in softwood cooking, whereas their amount is lower in hardwood cooking. Hardwood and softwood operations are usually carried out simultaneously in chemical pulping, so streams such as methanol streams produced in these operations may be mixed. Thus, when the composition of, for example, a hardwood methanol stream or heavy oil is analyzed, the results of the analysis may reveal components formed in the previous softwood operation. However, the reduction in the amount of typical softwood turpentine components in heavy oil or crude methanol from hardwood cooking indicates that the content of such components in softwood turpentine is much higher. For example, the content of terpenes in heavy oil is lower.

[0054] Particularly, when heavy oil is produced according to the method of the present invention, the amount of sesquiterpenes increases.

[0055] GC / MS analysis can be performed following a recent description of heavy oils in hardwood crude methanol (Niemelä 2020). For MS identification, commercial MS databases can be used, as well as a large number of spectra from previous studies and published sources, including the NIST Chemistry WebBook (https: / / webbook.nist.gov). Additional MS data searches from the literature can be performed to help identify certain compounds. For comparison, a large number of MS data files from several previous methanol analyses can be examined. Table 1 shows the results of the chemical analysis of the heavy oils and the comparison with the softwood turpentine.

[0056] As will be appreciated by those skilled in the art, it is impractical to characterize the heavy oil composition of the present invention by its exact chemical composition, since it may contain hundreds of different compounds, some of which may be volatile or susceptible to degradation. Instead, the present invention characterizes the heavy oil by reference to its method of manufacture. Other chemical and physical parameters are also used to characterize the heavy oil and distinguish it from, for example, softwood turpentine and crude methanol streams. For example, the presence or absence of certain components of the heavy oil, or changes in their concentration, compared to crude methanol streams or softwood turpentine, serves as a chemical property that is an inherent feature of the heavy oil of the present invention. One skilled in the art can readily determine the presence or absence of such a feature in the heavy oil or in another substance.

[0057] In one embodiment, the heavy oil has a reduction in at least one of alpha-pinene, beta-pinene, nitrogen compounds, and sulfur- and nitrogen-containing compounds compared to crude methanol.

[0058] In one embodiment, the heavy oil contains at least 20% sulfur-containing compounds by GC / MS analysis; and preferably contains more than 30% sulfur-containing compounds by GC / MS analysis.

[0059] In one embodiment, the heavy oil comprises less than 65% terpenes and at least 40% sulfur-containing compounds by GC / MS analysis; and preferably contains 1-10% terpenes and 40-50% sulfur-containing compounds by GC / MS analysis.

[0060] In one embodiment, the heavy oil contains 1 to 3.5%, preferably 1.5 to 2.5%, most preferably about 1.8% β-pinene by GC / MS analysis.

[0061] In one embodiment, the heavy oil comprises oil derived from crude methanol obtainable from hardwood pulping.

[0062] In one embodiment, the heavy oil is produced from a mixture of crude methanol derived from hardwood pulp and from softwood pulp. Preferably, the mixture mainly contains crude methanol derived from hardwood pulp. However, the crude methanol derived from softwood pulp in the mixture does not hinder the production of heavy oil, because the method of the present invention can separate heavy oil from such a mixture.

[0063] In one embodiment, when heavy oil is used for crude methanol purification, the addition amount of the heavy oil is selected from the following range: 0.0001 to 5 mass %, preferably 0.001 to 5 mass %, more preferably 0.001 to 4 mass %, most preferably 0.001 to 1 mass %, based on the total mass of the methanol mixture.

[0064] Figure 1 An embodiment of a system for producing heavy oil is shown. Figure 2 The relevant elements of system 100 are described in detail in connection with the corresponding method for producing heavy oil.

[0065] The system 100 has an acidification unit 110, wherein a crude methanol stream 111 derived from hardwood pulp is fed to the acidification unit 110. An acid stream 112 is fed to the acidification unit 110 to acidify the crude methanol in the acidification unit 110. The acidification of the crude methanol stream 111 is also shown as an acidification step 320 including the optional addition of water. Figure 2 middle.

[0066] Volatiles 113 are optionally removed from the acidulation unit 110. Optionally, turpentine 115 is also removed and directed to a turpentine recovery unit 1151.

[0067] The heavy oil 116 can optionally be recovered from the acidification unit to a heavy oil recovery unit 1161, which can also be used for liquid phase separation after acidification. Because the acidification of the crude methanol stream in the acidification unit 110 results in the separation of a brine solution, salts such as ammonium salts can be removed. Figure 2 Phase separation 325 is shown occurring in the acidulation unit 110, and the heavy oil can be recovered as a bottom phase after the liquid phase settles 1161. A lighter methanol-containing phase is formed as an acidulated crude methanol stream 114 above the liquid bottom phase.

[0068] The acidified crude methanol stream 114 is fed to a distillation unit 120 to separate volatiles 1131 by distillation 330. Optionally, a salt solution 1171 comprising ammonium sulfate formed during the distillation is removed, such as Figure 2 As shown in step 328.

[0069] The crude methanol distillate 124 is fed from the distillation unit 120 to a buffer tank 130, wherein water 131 is optionally fed to the buffer tank 130. When the water 131 is added, the crude methanol distillate 124 is diluted, also as Figure 2 The dilution 340 results in phase separation of the liquid phase ( Figure 2 350 in step 350), from which the heavy oil 132 can be recovered to the heavy oil recovery unit 1321, and the purification of methanol 360 can be continued by feeding the crude methanol and water feed 134 to the extraction column 140.

[0070] The optional addition of water is useful to prevent precipitation of ammonium sulfate, as methanol reduces its solubility. The chemical composition of crude methanol may vary from industrial process to industrial process, and for situations when the ammonium sulfate concentration exceeds its solubility level, the optional addition of water can be used to optimize the process.

[0071] Feed 141 originating from extraction column 140 is optionally fed to optional solvent stripping unit 145, to which steam 1453 can be fed. Gaseous feed 1451 is directed to a rich gas system, and aqueous condensate 1452 is removed. Feed 142 containing aliphatic paraffin oil can be returned to the extraction column.

[0072] A feed 143 containing methanol, ethanol, acetone and water is introduced from the extraction column into a series of distillation columns 150, 160, 170, wherein acetone and volatile impurities 151 are first removed from the methanol, ethanol and water feed 152 in distillation column 150, then water 162 is separated from the methanol and ethanol feed in distillation column 160, and methanol feed 171 is separated from less volatile impurities such as propanol, butanol and ethanol feed 172 in distillation column 170.

[0073] Figure 2 A flow chart for heavy oil production is shown. Briefly, a crude methanol stream 310 derived from hardwood pulp is provided and acidified 320, optionally with the addition of water. When the acid 320 is added, methyl mercaptan (MM) and H2S may evaporate. In existing processes, dimethyl sulfide (DMS) is also removed in a distillation column ("sulfur column") along with MM and H2S. Salts are removed as a salt solution 328, and the different liquid phases are separated 325. The heavy bottom phase containing the heavy oil is recovered 1161, the acidified crude methanol stream is distilled 330 and the resulting distillate is optionally diluted 340 with water, which results in a liquid phase separation 350. The heavy bottom phase containing the heavy oil is recovered 1321, and the lighter phase containing methanol is sent to methanol purification 360. The methanol purification step 360 includes Figure 1 All steps are performed downstream of the buffer tank 130.

[0074] In one embodiment, the acidification step 320 is performed by using an aqueous solution of a strong acid, preferably 10 to 98 wt % H2SO4. Optionally, water is added. Adding water is particularly advantageous when using a strong acid such as 98 wt % H2SO4. Acidification results in the formation of ammonium salts.

[0075] In one embodiment of the method for producing heavy oil, Figure 2 As shown, the crude methanol side stream contains less than 50% terpenes and less than 20% sulfur-containing compounds by GC / MS analysis; and preferably contains less than 45% terpenes and less than 15% sulfur-containing compounds by GC / MS analysis.

[0076] In one embodiment of the method for producing heavy oil, Figure 2 As shown, it also includes: diluting the middle phase; optionally diluting the obtained distillate with water to separate the phases; and recovering the heavy bottom phase containing heavy oil 1321. Thus, by collecting the heavy oil after the distillation step 330, the recovery of heavy oil can be further enhanced.

[0077] In other embodiments, the heavy oil is recovered only after distillation, ie the first recovery step 1161 before distillation is omitted and only the recovery point 1321 is used.

[0078] Purification of crude methanol

[0079] Crude methanol from softwood pulp accelerates the formation of precipitates at low pH values ​​below 5, indicating that this is an acid-catalyzed reaction. Temperatures above 50° C. further accelerate the formation of precipitates. Acidification of the crude methanol stream also serves to evaporate volatile sulfur compounds and keep NH3 in solution.

[0080] By adding the heavy oil of the present invention, the formation of precipitates in crude methanol can be prevented.

[0081] In alternative or additional embodiments, prior to the start of the methanol purification process, for example, after removing the foulant condensate from the stripper ( Figure 3 During or after methanol recovery (not shown in FIG), heavy oil is added to the crude methanol derived from softwood pulp.

[0082] In another embodiment, the heavy oil is mixed with crude methanol after acid mixing but before distillation, such as Figure 3 In the case where the crude methanol is diluted with water, the heavy oil can be added before or after the addition of water. In a preferred embodiment, the heavy oil is added after the turpentine is separated to ensure that the heavy oil does not dissolve in the turpentine.

[0083] The acidification step can be followed by heating to evaporate volatiles such as H2S, mercaptans and dimethyl sulfide from the methanol-containing phase, which are then recovered as distillate from the distillation column.

[0084] In a preferred embodiment, the crude methanol purification method includes distillation and evaporation by using a multi-stage distillation and evaporation process including a series of distillation columns. In this method, heavy oil can be added to the methanol-containing feed before the distillation or evaporation step begins. Thus, the heavy oil can be added at least once before the multi-stage distillation process begins, it can be added before the start of each individual distillation step in the series of distillation columns, or it can be added before the start of a specific distillation step.

[0085] The precipitate is formed primarily when methanol is evaporated / distilled from the salt solution. As the methanol content becomes lower during the evaporation / distillation process, the temperature rises and the solubility of the precipitated compound decreases. In a preferred embodiment, heavy oil is added or fed just before this step, i.e., before the temperature starts to rise due to the reduction in methanol content.

[0086] When the heavy oil is added before the start of the distillation or evaporation step, the dosage thereof can be selected within the range of 0.5 to 50 L / day.

[0087] In a preferred embodiment, the first distillation column is configured to separate water containing dissolved (NH4)2SO4.

[0088] In a preferred embodiment, the second distillation column is configured to separate compounds that are more volatile than methanol, such as acetone.

[0089] In a preferred embodiment, the third distillation column is configured to separate water.

[0090] In a preferred embodiment, the fourth distillation column is configured to separate compounds that are less volatile than methanol, such as ethanol.

[0091] As shown in the following examples, when heavy oil is added to the crude methanol stream obtained from softwood pulp, the resulting crude methanol mixture remains clear, and no precipitation is observed during the distillation process. Thus, the crude methanol mixture can be directly distilled without the need for other steps to remove the precipitate. Typically, when using the purification method of the prior art to purify crude methanol by distillation, precipitates are seen in the distillation tower and the crude methanol liquid, and the precipitate must be removed before distillation.

[0092] Figure 3A flow chart showing an overview of the method for purifying crude methanol using heavy oil of the present invention. In step 510, crude methanol is provided, and heavy oil is added 530 before the distillation step 540. After obtaining a methanol mixture with the added heavy oil, the methanol mixture is distilled in step 540, and methanol is recovered in step 550.

[0093] In a preferred embodiment, the addition of heavy oil is controlled so that no significant phase separation occurs when it is mixed with acidified crude methanol, which is beneficial to enhancing the ability of heavy oil to resist precipitation.

[0094] exist Figure 3 In the embodiment of the present invention, the optional acidification step 520 is shown as a dashed box, and when this step is used, the heavy oil is added to the acidified crude methanol before or after the acidification step 520, as shown by the dashed arrow. In this embodiment, one or two addition points can be used. It is preferred to add the heavy oil after acidification.

[0095] Under the conditions where the process of the present invention involves the use of heavy oil, the methanol purification process is simplified because the crude methanol mixture containing the heavy oil can be directly distilled.

[0096] In one embodiment, the crude methanol stream 510 mainly comprises methanol, wood extractives, sulfur-containing compounds and optional nitrogen-containing compounds. The amounts of these components may vary depending on the type of wood used in pulping and the process parameters of pulping. Typically, in the crude methanol derived from softwood pulp, the amounts of water, wood extractives, sulfur-containing compounds and nitrogen-containing compounds are in the range of 15 to 30 mass %.

[0097] The methanol content of the crude methanol derived from softwood pulp is in the range of 70 to 85% by mass.

[0098] In one embodiment, the wood extract present in crude methanol comprises terpenes, preferably monoterpenes and sesquiterpenes.

[0099] The crude methanol stream may also contain sulfur-containing compounds and nitrogen-containing compounds. Sulfur compounds and sulfur-containing compounds refer to organic compounds containing at least one sulfur atom as a heteroatom but no nitrogen. Nitrogen-containing compounds and nitrogen compounds refer to organic compounds containing at least one nitrogen atom as a heteroatom but no sulfur. Sulfur-nitrogen compounds refer to organic compounds containing at least one sulfur atom and at least one nitrogen atom as heteroatoms.

[0100] In one embodiment, the crude methanol is obtained from chemical pulping of softwood, hardwood or a mixture thereof.In a preferred embodiment, the crude methanol comprises crude methanol derived from chemical pulping of softwood.

[0101] In another embodiment, the heavy oil does not contain nitrogen-containing compounds, such as pyrroles and amines, that are typically present in crude methanol obtained from softwood pulping.

[0102] In one embodiment, the methanol mixture is a single-phase solution, dispersion or two-phase mixture. In a two-phase system, each phase can be dispersed or undispersed, and the crude methanol is mainly in one phase, but it may contain some dispersion (not necessarily visible). However, as the crude methanol is acidified and / or water is added, the solubility of terpenes, for example, decreases and they form a more obvious dispersion. In a preferred embodiment, the methanol mixture is a single-phase solution. Adding dilution water can reduce the solubility of terpenes. In one embodiment, only a strong acid is added, and the acid will be consumed by forming a white ammonium salt precipitate.

[0103] Preferably no precipitation is seen in the methanol mixture after addition of the heavy oil.

[0104] In one embodiment, the crude methanol is acidified to a pH value below 7, preferably to a pH value below 5, before distillation or evaporation. In another embodiment, the methanol mixture is distilled immediately after acidification, i.e. the methanol mixture can be distilled without removing the precipitate and without decanting or settling the phases.

[0105] In one embodiment, the light turpentine phase is removed prior to distillation.

[0106] In one embodiment, heavy oil is added to the crude methanol prior to distillation or evaporation.

[0107] In one embodiment, the heavy oil is added to the crude methanol after acidification.

[0108] In one embodiment, the ammonium sulfate is removed as a solution.Since salts such as ammonium salts remain dissolved during the evaporation and / or distillation process, they can be easily removed as a bottoms product.

[0109] In one embodiment, the amount of heavy oil added is selected from the following ranges based on the total mass of the methanol mixture: 0.0001 to 5 mass%, preferably 0.001 to 5 mass%, more preferably 0.001 to 4 mass%, and most preferably 0.001 to 1 mass%. In the case of using a plurality of distillation columns in series, the amount can be added before the first, at least one, a part of, or each distillation column.

[0110] In one embodiment of the process, the methanol is recovered by distillation using multiple distillation columns connected in series.

[0111] In one embodiment, crude methanol stream 510 is obtained from chemical pulping of softwood or hardwood or a mixture thereof. Crude methanol obtained from softwood pulping is particularly advantageous in the present invention.

[0112] In one embodiment, the crude methanol is acidified prior to distillation or evaporation. Preferably, the acidified crude methanol is distilled or evaporated without a precipitate removal step and / or a decantation step.

[0113] In one embodiment of softwood crude methanol purification, the turpentine fraction is removed after adding dilution water. In one embodiment, the turpentine content is about 10% in the crude methanol derived from softwood. In the absence of dilution water, the turpentine remains dissolved and then follows the methanol into the extraction column.

[0114] In one embodiment, the methanol mixture obtained after adding the heavy oil is clear or substantially clear.The clarity of the methanol mixture can be verified, for example, by simple visual inspection.

[0115] It is clear to those skilled in the art that it is possible to modify Figure 2 and 3 The method described can be used to further control or improve certain steps of the method or the products obtained therefrom. For example, the products obtained by the method can be used for further purification, separation, derivatization or for at least one chemical transformation step to separate the components present in the product, or chemically transform them into other products. DETAILED DESCRIPTION

[0116] Example

[0117] In order to compare the performance of the crude methanol purification method of the present invention with the performance of the method performed according to the prior art, the following experiment was conducted.

[0118] Heavy oil production

[0119] The results of the analysis of the heavy oil are summarized in Table 1. The results show that the heavy oil of the present invention is characterized by an unusually high content of sulfur compounds. The content of sesquiterpenes is also high and significantly different compared to, for example, softwood turpentine.

[0120] Table 1. Chemical analysis of heavy oil and softwood turpentine

[0121]

[0122] Comparative Example 1

[0123] In a 500 mL glass, 300 mL of acidified crude methanol derived from softwood pulp and containing aqueous ammonium sulfate was boiled at atmospheric pressure to simulate the conditions of the first distillation column after methanol acidification. During the boiling of methanol water, the formation of a solid precipitate was noted, similar to that described in previous publications on methanol purification methods. The solid precipitate was insoluble in common solvents tested, such as acetone, sulfuric acid, hydrochloric acid, paraffin oil, or NaOH.

[0124] Example 2

[0125] As in Comparative Example 1, the test started with a crude methanol sample derived from softwood pulp. Before heating and boiling, 1 g of heavy oil (birch oil) was added. No precipitation was observed during boiling and methanol evaporation. Therefore, the heavy oil prevented precipitation.

[0126] Furthermore, it was found that heavy oil was able to dissolve the solid precipitate formed in Comparative Example 1. A heavily fouled distillation column used for purification of crude methanol from softwood operations could be cleaned with crude methanol containing heavy oil: after a few days of using hardwood crude methanol, most of the liquid exposed parts of the column were almost clean. Thus, the addition of heavy oil effectively prevented precipitation and even dissolved previously formed precipitates.

[0127] The foregoing description has provided a complete and detailed description of the best mode currently contemplated by the inventor for carrying out the invention by way of non-limiting examples of specific embodiments and implementations. However, it is clear to those skilled in the art that the invention is not limited to the details of the foregoing implementations, but can be implemented in other implementations using equivalent means or in different combinations of implementations without departing from the characteristics of the invention.

[0128] In addition, some features of the exemplary embodiments disclosed above may be used advantageously without corresponding use of other features. Therefore, the above description should be regarded as merely illustrating the principles of the present invention, rather than limiting it. Therefore, the scope of the present invention is limited only by the claims.

Claims

1. A heavy oil obtained from a crude methanol side stream derived from chemical hardwood pulping, wherein the heavy oil is produced by a process comprising the steps of: an acidification step comprising mixing the crude methanol side stream with an acidic aqueous solution and heating to vaporize low boiling sulfur compounds to provide acidified crude methanol; a separation step comprising separating a liquid top phase, a liquid aqueous middle phase, and a liquid bottom phase from the acidified crude methanol; and The liquid bottom phase was collected as heavy oil, According to GC / MS analysis, the heavy oil contains less than 65% of terpenes and at least 40% of sulfur-containing compounds.

2. The heavy oil of claim 1, wherein the heavy oil is rich in organic sulfur compounds compared to the crude methanol side stream.

3. A method for producing heavy oil, the method comprising: providing a crude methanol stream derived from hardwood pulp; an acidification step comprising mixing the crude methanol side stream with an acidic aqueous solution and heating to vaporize low boiling sulfur compounds to provide acidified crude methanol; a separation step comprising separating a liquid top phase, a liquid aqueous middle phase, and a liquid bottom phase from the acidified crude methanol; and The bottom phase is collected as heavy oil, According to GC / MS analysis, the heavy oil contains less than 65% of terpenes and at least 40% of sulfur-containing compounds.

4. The process of claim 3 wherein the crude methanol side stream contains less than 50% terpenes and less than 20% sulfur compounds by GC / MS analysis.

5. The process of claim 3 or 4, wherein the crude methanol side stream contains less than 45% terpenes and less than 15% sulfur compounds by GC / MS analysis.

6. A method for purifying crude methanol obtained in chemical pulping, the method comprising: Providing crude methanol obtained as a by-product of chemical pulping; acidifying the crude methanol with an acidic aqueous solution to provide acidified methanol; mixing the heavy oil according to any one of claims 1 to 2 into acidified methanol to provide a methanol mixture; and The methanol mixture is distilled or evaporated to recover the methanol.

7. The process of claim 6, wherein the crude methanol comprises methanol, wood extractives, sulfur-containing compounds and optionally nitrogen-containing compounds.

8. The process according to claim 6 or 7, wherein the crude methanol is obtained from chemical pulping of softwood, hardwood or a mixture thereof.

9. The process according to claim 6 or 7, wherein the methanol mixture is a single-phase solution, dispersion or a two-phase mixture.

10. The process according to claim 6 or 7, wherein the methanol mixture is a two-phase system having a liquid top phase and a liquid bottom phase, wherein the liquid bottom phase contains ammonium sulfate, and wherein the liquid bottom phase is at least partially removed before distillation or evaporation.

11. The process according to claim 6 or 7, wherein the crude methanol is acidified to a pH value below 7 before distillation or evaporation.

12. The method according to claim 6 or 7, wherein the heavy oil is added to the crude methanol before distillation or evaporation.

13. The method according to claim 6 or 7, wherein the amount of the heavy oil added is 0.0001 to 5% by mass based on the total mass of the methanol mixture.

14. The method according to claim 13, wherein the heavy oil is added in an amount of 0.001 to 5% by mass based on the total mass of the methanol mixture. 15 . The method according to claim 14 , wherein the heavy oil is added in an amount of 0.001 to 4% by mass based on the total mass of the methanol mixture. 16 . The method according to claim 15 , wherein the heavy oil is added in an amount of 0.001 to 1% by mass based on the total mass of the methanol mixture.

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