Method of treating crude methanol

Abstract

The present technology relates to a method of treating crude methanol comprising the steps in temporal order of distilling the crude methanol to remove at least a portion of one or more sulphurous compounds from the crude methanol and provide a methanol-rich stream, contacting the methanol-rich stream with an oxidant, whereby at least a part of the sulphur compounds in the stream is oxidized, and contacting the methanol-rich stream with an acidifying agent, whereby ammonia present in the stream reacts to form ammonium sulphate in a methanol- rich stream, essentially free of polymerised terpenes.

Description

Method of Treating Crude MethanolTECHNICAL FIELD

[0001] The present invention relates to a method of treating crude methanol. The present invention further relates to a system for treating crude methanol. Still further, the present invention relates to a use of a system for carrying out a method of treating crude methanol.BACKGROUND

[0002] In a pulp mill methanol is mainly formed during sulphate cooking by alkali-catalysed elimination of methanol from 4-O-methylglucuronic acid residues in hemicellulose. Methanol is also formed by oxidation reactions in phenolic lignin during Ch-delignification. Methanol yield is around 6- 15 kg / ADT depending on the wood type and pulping process. Cooking also produces organic sulphur compounds, as the sulphide- and hydrogen sulphide ions react with lignin. Methanol and other volatile compounds formed during cooking end up in black liquor, a by-product of the cooking process, which comprises an aqueous solution of lignin residues, hemicellulose and inorganic chemicals as well as organic and inorganic solids. Due to methanol’s high volatility, it vaporises with water and other volatiles and condenses in the evaporation plant’s foul liquor.

[0003] Pulp mill produces foul liquor as a result of black liquor evaporation. This foul liquor is stripped, in order to generate beter quality stripped liquor having a total reduced sulphur (TRS) content of < 5 mg / L As a result of the stripping, methanol from the foul liquor ends up in stripper off-gases, which are taken to the methanol liquefaction plant. In the methanol liquefaction plant, methanol concentration is increased to 60 - 80%.

[0004] In addition to methanol, foul liquor contains volatile sulphur compounds such as hydrogen sulphide (H2S), methyl mercaptan (MM), dimethyl sulphide (DMS) and dimethyl disulphide (DMDS). A portion of the volatile sulphur compounds are found in the methanol, which is called crude methanol, after stripping while a larger portion is found in concentrated non-condensable gases after stripping. The foul liquor still further comprises less-volatile sulphur compounds, which remain with methanol when treated in the stripper. The amount of less-volatile sulphur compounds in the foul liquor is a fraction of that of volatile sulphur compounds. The recovered methanol concentration is fairly high (>74 w-%, by weight of crude methanol), but as mentioned, it contains sulphur compounds normally over 5 w-%, by weight of crude methanol. Water, ethanol, acetone, ammonia (NH3) and turpentine compounds are the other main impurities. Methods have been developed to remove nitrogen and sulphur and provide purified methanol. Using methods of the prior art involving acidification of a liquor followed by oxidation of the liquor, however, results in the consumption of large amounts of oxidant and in the formation of polymerised terpene compounds, sticky stuff, which foul, e.g., distillation columns resulting in plant shutdowns for regular periodic cleaning.SUMMARY

[0005] The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0006] According to a first aspect of the present invention there is provided method of treating crude methanol, the method comprising the steps in temporal order of distilling the crude methanol to remove at least a portion of one or more sulphurous compounds from the crude methanol and provide a methanol-rich stream, contacting the methanol-rich stream with an oxidant, whereby at least a part of the sulphur compounds in the stream is oxidized to their oxidized forms; and contacting the oxidised stream with an acidifying agent, whereby ammonia present in the stream reacts to form ammonium sulphate in a methanol-rich stream.

[0007] According to second aspect of the present invention there is provided a system of treating crude methanol. The system comprises a distillation column, an oxidation unit and an acidification unit. The distillation column has an inlet for receiving crude methanol, an outlet for a distillate, and an outlet for a methanol-rich stream. The oxidation unit has a first inlet for receiving a methanol-rich stream, a second inlet for receiving an oxidant, and an outlet for feeding the contents of the oxidation unit to the acidification unit. The acidification unit has an inlet for receiving a feed of a methanol-rich stream from the outlet of the oxidation unit, a second inlet for receiving an acidifying agent, and an outlet for an acidified methanol-rich stream.

[0008] According to a third aspect of the present invention there is provided a use of a system according to the second aspect for carrying out a method of the first aspect

[0009] Considerable benefits are gained with the aid of the present invention. A simple, easy to apply inexpensive treatment, industrially applicable under moderate conditions provides a treated methanol stream that is essentially free of polymerised terpenes, which foul mill equipment, such as distillation columns. Distillation of the crude methanol prior to oxidation reduces the charge of oxidant that is required.

[0010] Other features and advantages will become apparent from the following description.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIGURE 1 is a flow chart illustrating treating crude methanol in accordance with at least some embodiments.

[0012] FIGURE 2 is a flow chart illustrating treating crude methanol in accordance with at least some embodiments.

[0013] FIGURE 3 is a flow chart illustrating treating crude methanol in accordance with at least some embodiments.

[0014] FIGURE 4 is a flow chart illustrating treating crude methanol in accordance with at least some embodiments.EMBODIMENTS

[0015] For the purposes of embodiments of the present invention, crude methanol may be taken to mean any alkaline liquor from a pulp mill comprising methanol for example liquified stripper off gases (gases from foul liquor stripping), liquefied methanol, crude methanol from a methanol plant, foul liquor, or any type of liquor or condensate, such as foul condensate or condensate formed from stripper off gases etc. Indeed embodiments of the method are not limited to liquors from pulp mills but include any alkaline liquid comprising methanol and one or more sulphurous compounds e.g. hydrogen sulphide and sulphurous organic compounds such as methyl mercaptan (MM) and dimethyl sulphide (DMS), as well as ammonia, acetone, alcohols such as ethanol, and extractives such as turpentine and other non- structural components of lignocellulosic material.

[0016] In embodiments, streams are described as being essentially free of polymerised terpenes. For the purposes embodiments of the present invention, “essentially free” means that any presence of polymerised terpenes is so low that fouling of equipment is at such a minimal level that no maintenance beyond that which is normal is required.DETAILED DESCRIPTION

[0017] The present invention relates to a method of treating crude methanol. The method comprises the steps in temporal order of distilling the crude methanol to remove at least a portion of one or more sulphurous compounds from the crude methanol and provide a methanol-rich stream, contacting the methanol-rich stream with an oxidant, whereby at least a part of the sulphur compounds in the stream is oxidized to their oxidized forms; and contacting the oxidised stream with an acidifying agent, whereby ammonia present in the stream reacts to form ammonium sulphate in a methanol-rich stream. The methanol-rich stream is essentially free of polymerised terpenes.

[0018] FIGURE 1 is a flow diagram illustrating a method and system of treating crude methanol in accordance with at least some embodiments of the present invention.

[0019] Crude methanol 10 is optionally diluted with water and fed into a decanting unit 200. Turpentine 20 is decanted from the decanting unit and directed to further processing. The crude methanol with reduced turpentine content 300 is then fed from the decanting unit into and distilled in a distillation column 100 having an outlet for sulphurous compounds 30 and an outlet for a methanol-rich stream 310. The methanol-rich stream 310 is fed from the distillation column 100 into an oxidation unit 101 where it is contacted with an oxidant 40 providing an oxidised stream 320 which is optionally diluted with water and led to a further decanting unit 102. Further turpentine 50 is decanted from the oxidised stream320 in the further decanting unit 102 and the oxidised stream with reduced turpentine content 330 is fed from the further decanting unit 102 into an acidification unit 103. The oxidised stream with reduced turpentine content 330 is then contacted with an acidifying agent 60 and an acidified methanol-rich stream 340 is led from the acidification unit 103 to further processing. The acidified methanol-rich stream 340 is essentially free of polymerised terpenes.

[0020] FIGURE 2 is a flow diagram illustrating a method and system of treating crude methanol in accordance with at least some embodiments of the present invention.

[0021] Crude methanol 10 is optionally diluted with water and fed into a decanting unit 200. Turpentine 20 is decanted from the decanting unit 200 to provide a crude methanol with reduced turpentine content 300. The crude methanol with reduced turpentine content 300 is then fed from the decanting unit into and distilled in a distillation column 100 having an outlet for sulphurous compounds 30 and an outlet for a methanol-rich stream 310. The methanol-rich stream 310 is fed from the distillation column 100 into an oxidation unit 101, where it is contacted with an oxidant 40. One stream 70 of oxidation products is led to further processes, and an oxidised stream 350 is optionally diluted with water and led to a further decanting unit 102. Further turpentine 50 is decanted to provide a decanted oxidised stream with reduced turpentine content 360 free of oxidation product 70, which stream 360 is led from the further decanting unit 102 to an acidification unit 103 where it is contacted with an acidifying agent 60. An acidified methanol-rich stream 370 comprising mainly alcohols and acetone and ammonium sulphate is directed to a second distillation column. The acidified methanol-rich stream 370 is distilled, ammonium sulphate is recovered 80, providing a distilled methanol-rich stream 380. The distilled methanol-rich stream 380 is essentially free of polymerised terpene compounds and ammonium sulphate.

[0022] FIGURE 3 is a flow diagram illustrating a method and system of treating crude methanol in accordance with at least some embodiments of the present invention.

[0023] Crude methanol 10 is optionally diluted with water and fed into a decanting unit 200. Turpentine 20 is decanted from the decanting unit 200 to provide a crude methanol with reduced turpentine content 300. The crude methanol with reduced turpentine content 300 is then fed from the decanting unit into and distilled in a distillation column 100 having an outlet for sulphurous compounds 30 and an outlet for a methanol-rich stream 310. The methanol-rich stream 310 is fed from the distillation column 100 into an oxidation and acidification unit 104. The crude methanol with reduced turpentine content 300 is then first contacted with an oxidant 40 and subsequently contacted with an acidifying agent 60, whereby an acidified methanol-rich stream 390 is formed and directed to further processing. The acidified methanol-rich stream 390 is essentially free of polymerised terpenes.

[0024] FIGURE 4 is a flow diagram illustrating a method and system of treating crude methanol in accordance with at least some embodiments of the present invention.

[0025] Crude methanol 10 is fed into and distilled in a distillation column 100 having an outlet for sulphurous compounds 30 and an outlet for a non decanted methanol-rich stream 400. The non decanted methanol-rich stream 400 is fed from the distillation column 100 into an oxidation unit 101, where it is contacted with an oxidant 40. An oxidised stream 410 is led from the oxidation unit 101 to an acidification unit 103 where it is contacted with an acidifying agent 60, whereby an acidified methanolrich stream 420 is formed and directed to further processing. The acidified methanol-rich stream 420 is essentially free of polymerised terpenes.

[0026] FIGURE 5 is a flow diagram illustrating a method and system of treating crude methanol in accordance with at least some embodiments of the present invention.

[0027] Crude methanol 10 is optionally diluted with water and fed into a decanting unit 200. Turpentine 20 is decanted from the decanting unit 200 to provide a crude methanol with reduced turpentine content 300. The crude methanol with reduced turpentine content 300 is then fed from the decanting unit into and distilled in a distillation column 100 having an outlet for sulphurous compounds 30 and an outlet for a methanol-rich stream 310. The methanol-rich stream 310 is fed from the distillation column 100 into an oxidation unit 101, where it is contacted with an oxidant 40. One stream 70 of oxidation products is led to further processes, and an oxidised stream 350 is optionally diluted with water and led to a further decanting unit 102. Further turpentine 50 is decanted to provide a decanted oxidised stream with reduced turpentine content 360 free of oxidation product 70, which stream 360 is led from the further decanting unit 102 to an acidification unit 103 where it is contacted with an acidifying agent 60. An acidified methanol-rich stream 370 comprising mainly alcohols and acetone and ammonium sulphate is directed to a mechanical separation unit 106 where oil 90 and optionally turpentine are separated from the stream 370 to provide a mechanically treated methanol stream 430 which is directed to a second distillation column 105. The mechanically treated methanol stream 430 is distilled, ammonium sulphate is recovered 80, providing a distilled methanol-rich stream 440. The distilled methanol-rich stream 440 is essentially free of polymerised terpene compounds and ammonium sulphate.

[0028] As described above, the present technology relates to a method of treating crude methanol. The method comprises the steps in temporal order of distilling the crude methanol to remove at least a portion of one or more sulphurous compounds from the crude methanol and provide a methanol-rich stream, contacting the methanol-rich stream with an oxidant, whereby at least a part of the sulphur compounds in the stream is oxidized, and contacting the methanol-rich stream with an acidifying agent, whereby ammonia present in the stream reacts to form ammonium sulphate in an acidified methanolrich stream. The acidified methanol-rich stream is essentially free of polymerised terpenes. It has surprisingly been found that by distilling the crude methanol before carrying out an oxidation step the amount of oxidant needed to oxidise sulphurous compounds is reduced by almost half. Oxidising the methanol-rich stream before an acidification step provides an additional benefit that terpenes remaining in the methanol-rich stream are far less likely to polymerise forming a sticky stuff comprisingpolymerised terpenes. It has been found that the amount of polymerised terpenes in a liquor in which an acidification step is carried out before an oxidation step is at such a level that fouling of mill equipment, for example distillation columns, demands regular and periodic cleaning.

[0029] As mentioned above the crude methanol may contain hydrogen sulphide and sulphurous organic compounds. Such compounds include methyl mercaptan (MM) and dimethyl sulphide (DMS). In the distilling step the sulphurous compound content of the raw methanol, for example in an embodiment at least a portion of the H2S is removed from the raw methanol. In another embodiment at least a portion of the MM is removed. In a further embodiment at least a portion of DMS is removed. In one embodiment at least a portion of DMDS is removed. Removal of at least one or more sulphurous compounds from the crude methanol has been found to reduce the oxidant charge required in the oxidation step by up to 50%, typically by 20 to 50 %. In the oxidation step, remaining sulphurous compounds or at least a portion thereof are oxidised for example methyl mercaptan (MM) is oxidised to dimethyl disulphide (DMDS), which is in turn oxidised to dimethyl sulphoxide, hydrogen sulphide is oxidised to sulphur dioxide, dimethyl disulphide is oxidised to dimethyl sulphoxide and dimethyl sulphoxide is in turn oxidised to dimethyl sulphone. Another possible oxidation product of MM and DMDS is methane sulfonic acid. It is speculated that the generation of sulphate ions in the oxidation phase reduces the amount of acidifying agent needed in the acidification phase for the protonation of ammonia (NH3). In the acidification stage ammonia reacts to form ammonium sulphate. Optionally, water is added to maintain the concentration of ammonium sulphate below the concentration at which it precipitates.

[0030] In one embodiment the methanol-rich stream is directed to further processing after the acidifying step. In an embodiment ammonium sulphate is removed from the methanol-rich stream, whereby ammonium sulphate is recovered and a liquid comprising methanol is recovered. Recovered ammonium sulphate has a plethora of uses, for example the ammonium sulphate can be used as a fertilizer, a food additive, a flame retardant, an ingredient in vaccines, a cleaning additive, a pH buffer, a binding material in wall board, a dough conditioner in bread products. There are many other uses of ammonium sulphate for which the recovered ammonium sulphate would be suitable. The recovered liquid comprising methanol can be used in a number of applications. In a pulp mill the recovered liquid comprising methanol can be used as fuel in a lime kiln, as an auxiliary fuel in burners or in a recovery boiler. Using the recovered liquid comprising methanol as a fuel in a recovery boiler helps reduce sulphur and NOx emissions of the recovery boiler, which becomes a more and more desirable aim as environmental legislation becomes more and more stringent. The recovered liquid comprising methanol is also suitable for use, e.g., as a fuel outside the confines of a pulp mill. Optionally, the recovered liquid comprising methanol can be processed further, for example distilled, to remove alcohols such as ethanol, and acetone from the methanol and provide a purified methanol stream which is suitable for converting into various industrially-useful chemicals as well as being ideal for fuel.

[0031] In one embodiment the crude methanol starting material is diluted with water. In an embodiment the water: crude methanol ratio is in the range of 1.0 - 1.5:1, by weight of the crude methanol, preferably 1.3: 1. In a further embodiment turpentine is decanted from the crude methanol before the distilling step. The further step of decanting turpentine from the crude methanol provides the additional benefit of removing at least a portion of the terpenes and at least a portion of heavier sulphur compounds from the liquor. As a natural consequence, reactions between sulphur compounds and oxidants are reduced whereby the amount of oxidant added to the liquor for the oxidation of sulphurous compounds may be reduced. The step of diluting the liquor with water before distilling facilitates and improves the decantation of turpentine in an embodiment.

[0032] Acidification of the methanol-rich stream lowers its pH. In one embodiment the pH of the oxidised liquor is adjusted to a pH in the range of 5.0 - 6.0. Reducing the pH in the acidification step to a pH in the range of 5.0 - 6.0, suitably 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8 or 5.9 increases the yield of ammonium sulphate, whereby the amount of sulphate ions in solution is increased. Traditionally, pH has been reduced to a much lower level of about 2.0. Due to the distillation, and the oxidation prior to the acidification, a large portion of the low-boiling sulphurous compounds, such as hydrogen sulphide and MM, are no longer present in the methanol-rich stream and thus the amount of sulphurous compounds to be acidified are no longer present and less acid is required.

[0033] In a further embodiment, the acidified methanol-rich stream treated is mechanically in a mechanical treatment unit, e.g. by filtering and / or coalescing. Filtering removes oil droplets and optionally turpentine, and coalescing in a coalescer collects the small droplets into larger droplets that are then separated from the acidified methanol-rich stream by gravity. Removing the oil drops at this stage facilitates downstream further processing. Thus, in an embodiment the method comprises the further step of filtering and / or coalescing the acidified methanol-rich stream before further processing.

[0034] In one embodiment, the oxidant is selected from the group consisting of peroxide, typically hydrogen peroxide, oxygen, ozone, sodium hypochlorite, and a mixture thereof. In a preferred embodiment the oxidant is in liquid form, particularly suitable is hydrogen peroxide in liquid form. Oxidants in liquid form, such as hydrogen peroxide in liquid form are easier to handle than gaseous oxidants. In one embodiment the oxidant is added in a dose in the range of 4 to 8 % by weight of the crude methanol, typically 4.5 to 7.5 %, for example about 5 %, 6 %, or about 7 %. The charge of oxidant depends on the sulphur content of the feed to the oxidation unit. The amount of oxidant required is proportional to the amount of sulphur. In other words, if the crude methanol comes from a source with a high sulphur content, even after a distillation step the sulphur content may be higher than in crude methanol from a low sulphur source, e.g. sulphur in crude methanol from a eucalyptus pulp mill is higher than sulphur in crude methanol from a birch pulp mill. The charge of oxidant will be adjusted accordingly.

[0035] In a further embodiment the acidifying agent is selected from the group consisting of sulphuric acid, hydrochloric acid, nitric acid, phosphoric acid, ethanoic acid, methanoic acid, carbondioxide, sulphur dioxide, chlorine dioxide, waste liquid from chlorine dioxide production, acid bleach plant waste liquor, sodium sulphate bleaching filtrates such as A-stage bleaching, and a mixture thereof. In an embodiment, sulphuric acid is favoured due to its wide availability in pulp mills and can be produced from concentrated non-condensable gases (CNCG). The readily available sulphuric acid or that which can be produced from CNCGs has the further advantage of having fewer impurities than some of the other mentioned acidifying agents, i.e., filtrates.

[0036] In a still further embodiment the method is carried out at a temperature in the range of 35 °C - 60 °C, preferably 40 °C to 55 °C, suitably at a temperature of 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53 or 54 °C. The methanol, forming the most valuable part of the liquor has a boiling point of 64 °C. It is preferred that the methanol remains in the liquid form during treatment of the liquor and that none is lost in the gaseous form. Distilling in this temperature range allows for the removal of sulphurous compounds having boiling points around this temperature, e.g. DMS has a boiling point in the range of 35 to 41 °C

[0037] In an embodiment the method is carried out at ambient pressure, meaning that in an embodiment the pressure is not adjusted, in other words no pressure adjustment step is carried out.

[0038] Embodiments may be carried out in one or more vessels. In one embodiment the oxidising step and the acidifying step are carried out in the same vessel. Carrying out both oxidation and acidification in the same vessel improves the economy of the process in terms of both equipment costs and in terms of energy, for example, heat / vapour generated in the exothermic oxidation and acidification steps can be used to strip away the methanol in the same vessel. In a further embodiment the oxidising step and the acidifying step are carried out in different vessels. Carrying out the oxidation and acidification steps in different vessels provides greater control over the process since both steps are exothermic.

[0039] In embodiments in which the oxidising step and acidifying step are carried out in different vessels, it is necessary to transfer the oxidised methanol-rich stream from a first vessel to a second vessel. Thus, in an embodiment the oxidised methanol-rich stream is transferred from a first vessel to a second vessel.

[0040] As described above, in one embodiment the methanol-rich stream is directed to further processing. In one embodiment, further processing comprises distilling the acidified methanol-rich stream to provide a methanol-rich distillate and a residue comprising ammonium sulphate and oxidation reaction products. Typically, the distillation is carried out at a temperature in the range of 50 to 70 °C, whereby the temperature at the condenser is typically in the range of 64 to 68 °C, most usually in the range of 65 to 67 °C. In an embodiment the ammonium sulphate is separated from the oxidation reaction products. In a further embodiment the ammonium sulphate is recovered for further processing.

[0041] In addition to a method, the present technology also relates to a system of treating crude methanol. In an embodiment the system comprises a distillation column 100, an oxidation unit 101 andan acidification unit 103. The distillation column 100 has an inlet for receiving crude methanol 10, an outlet for a distillate 30, and an outlet for a methanol-rich stream 400. The oxidation unit 101 has a first inlet configured for receiving a methanol-rich stream 400, a second inlet for receiving an oxidant 40, an outlet for feeding the contents 410 of the oxidation unit 101 to the acidification unit 103. The acidification unit 103 has an inlet for receiving a feed of a methanol- rich stream 410 from the outlet of the oxidation unit 101 , a second inlet for receiving an acidifying agent 60, and an outlet for an acidified methanol-rich stream 420. The acidified methanol-rich stream is essentially free of polymerised terpenes.

[0042] In a further embodiment the system further comprises a first decanting unit 200 for receiving crude methanol 10 optionally diluted with water, said decanting unit 200 being for decanting turpentine 20 from the crude methanol 10 before feeding a crude methanol stream with a reduced turpentine content 300 from an outlet of the decanting unit 200 to the inlet of the distillation column 100.

[0043] In one embodiment the system further comprises a second decanting unit 102 for receiving a methanol-rich stream 320, 350 optionally diluted with water, from the oxidation unit 101, said second decanting unit 102 being for decanting further turpentine 50 before feeding the methanol-rich stream with a reduced turpentine content 330, 360 from an outlet of the decanting unit 102 to the acidification unit 103.

[0044] In an embodiment the oxidation unit 101 comprises a second outlet for removing oxidation products 70 from the oxidation unit 101. Typically, any solid oxidation products 70 are removed from the oxidation unit 101 before a further step is carried out.

[0045] In one embodiment the system comprises a second distillation column 105 for distilling a methanol- rich stream 370, 430 received from an outlet of an acidification unit 103 or a mechanical separation unit 106. The second distillation column 105 is equipped with a inlet for receiving a stream 370, 430, an outlet for ammonium sulphate 80 and an outlet for a distillate comprising a distilled methanol-rich stream 380, 440. As is familiar to those of skill in the art, the oxidation unit 101, the acidification unit may all comprise an agitator for mixing the contents of the said unit. Agitators may be selected from those known in the art for example suitable agitators include propellers, blades, anchors, turbines, paddles and helical agitators.

[0046] Further embodiments according to the present technology describe a system in which oxidation and acidification can be carried out in a single vessel. Thus, in an embodiment, the system of treating crude methanol 10, comprises a decanter 200, a distillation column 100 and an oxidation and acidification unit 104. The decanter 200 has a first inlet configured to receive the crude methanol 10, a first outlet for decanting turpentine 20, and a second outlet configured to feed a crude methanol with reduced turpentine content 300 to distillation column 100. The distillation column 100 has an inlet for receiving crude methanol with a reduced turpentine content 300, an outlet for a distillate 30, and an outlet for a methanol-rich stream 310. The oxidation and acidification unit 104 has a first inlet forreceiving a feed of a methanol-rich stream 310 from the distillation column 100, a second inlet for receiving an oxidant 40, a third inlet for receiving an acidifying agent 60 and an outlet for delivering an acidified stream 390 to further processing.

[0047] In an embodiment the oxidation and acidification unit 104 is configured to receive the oxidant 40 via the second inlet before it receives the acidifying agent 60 through the third inlet. In a further embodiment the oxidation and acidification unit 104 is configured so that the third inlet is closed when the second inlet is open to receive oxidant 40. In a still further embodiment the oxidation and acidification unit is configured so that the second inlet is closed when the third inlet is open to receive acidifying agent 60.

[0048] Also envisaged are embodiments in which any of the above-described embodiments of systems are used to carry out any of the above-described embodiments of methods.

[0049] The following examples illustrate at least some embodiments of the present technology.EXAMPLESExample 1

[0050] A crude methanol oxidation treatment process was simulated in laboratory experiments. Water was added to crude methanol in the ratio of 1.3 (1.3 water: 1 crude methanol by weight) and the formed turpentine layer was decanted from the top of the water phase. Hydrogen peroxide was added to the decanted methanol solution. Oxidation was performed for 1 hour at 50 °C with 9.8 w / w% H2O2 dosage by weight of crude methanol. The oxidized methanol solution was acidified with H2SO4 to adjust the pH to approximately 2.2. The acidified methanol solution was evaporated until temperature 95 °C was reached. The distillation residue left in the flask was filtered. As on outcome the evaporation flask was clear, and no solids was observed in the filter paper or gravimetrically measured.Example 2

[0051] To find the right operation zone for the peroxide charge, half the charge of the previous trial was tested as previously described. The peroxide charge was 4.9 w / w% H2O2. Red solids were observed after evaporation in the distillation flask and on the filter paper. The amount of solids gravimetrically measured was 0.65 % from crude methanol to distillation. The low residual peroxide charge (Table 1) with the visual outcome, indicated that the peroxide charge was not enough, and sticky solids would form in an industrial process with this charge if the sulphur content of the feed would remain the same.Example 3

[0052] Predistillation prior to oxidation eliminates solids formation and decreases the concentration of sulphuric compounds and additionally, decreases the consumption of chemicals. The proceduredescribed in Example 1 was repeated with an additional predistillation step after decanting and prior to oxidation. The predistillation was performed at approximately 40°C to distill light sulphuric compounds from the methanol-rich stream. The distilled stream was oxidized with hydrogen peroxide for 1 hour at 50°C with 5.1 w / w% H2O2 dosage by weight of predistilled methanol-rich stream. The H2O2 consumption was lowered due to oxidation. The oxidated stream was acidified with H2SO4 and evaporated. As an outcome in comparison to example 2 very little solids was observed in the filter paper, residual peroxide was higher, and the consumption was lowered as there was less sulphur in the feed due to predistillation. The amount of solids gravimetrically measured was 0.34 % from crude methanol to distillation. The comparison of experiments with and without distillation are shown in Table 1.Table 1 : Treatment of crude methanol with and without distillationINDUSTRIAL APPLICABILITY

[0053] Embodiments of the method find various uses in industry for example in pulp mills the embodiments may be applied to foul condensate, crude methanol or SOGs to oxidise sulphurous compounds, to remove turpentine and ammonia, e.g. by forming ammonium sulphate from unreacted ammonia. Embodiments allow the charge of oxidant to be reduced significantly while the formation of polymerised terpenes is greatly reduced or even eliminated. The oxidised compounds and ammonium sulphate are easily removable from the treated liquor for further processing, providing a methanol stream comprising further alcohols and acetone and being essentially free of polymerised terpenes which are known to foul columns and reactors.REFERENCE NUMBERS

Claims

CLAIMS1. A method of treating crude methanol (10), the method comprising the steps in temporal order of:• distilling the crude methanol (10) to remove at least a portion of one or more sulphurous compounds (30) from the crude methanol (10) and provide a methanolrich stream (310, 400),• contacting the methanol-rich stream (310, 400) with an oxidant (40), whereby at least a part of the sulphur compounds in the stream is oxidized, and• contacting the methanol-rich stream (350, 410) with an acidifying agent (60), whereby ammonia present in the stream reacts to form ammonium sulphate in an acidified methanol-rich stream (80, 340, 370, 390, 420).

2. The method according to claim 1, comprising the further step of directing the acidified methanolrich (340, 370, 390, 420) stream to further processing.

3. The method according to claim 1 or 2, comprising the further step of diluting the crude methanol (10) with water before distilling.

4. The method according to claim 1 to 3, comprising the further step of decanting turpentine (20) from the crude methanol (10) before distilling the crude methanol (10).

5. The method according to any of the preceding claims, comprising the further step of decanting further turpentine (50) before contacting the methanol-rich stream (340) with the acidifying agent (70).

6. The method according to any of the preceding claims, comprising adjusting the pH of the oxidised residue to a pH in the range of 5.0 - 6.0, suitably 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8 or 5.9.

7. The method according to any of the preceding claims, wherein the oxidant (40) is selected from the group consisting of hydrogen peroxide, peroxide, oxygen, ozone, sodium hypochlorite, and a mixture thereof.

8. The method according to any of the preceding claims, wherein the acidifying agent (60) is selected from the group consisting of sulphuric acid, hydrochloric acid, nitric acid, phosphoric acid, ethanoic acid, methanoic acid, carbon dioxide, sulphur dioxide, waste liquid from chlorine dioxide production, acid bleach plant waste liquor, sodium sulphate bleaching filtrates such as A- stage bleaching filtrate, and a mixture thereof.

9. The method according to any of the preceding claims carried out at a temperature in the range of 35 °C - 60 °C, preferably 40 °C to 55 °C, suitably at a temperature of 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53 or 54 °C.

10. The method according to any of the preceding claims carried out at ambient pressure.

11. The method according to any of the preceding claims, wherein the oxidising step and the acidifying step are carried out in the same vessel (104).

12. The method according to any of claims 1 to 10, wherein the oxidising step and the acidifying step are carried out in different vessels (101, 103).

13. The method according to claim 12, comprising the step of transferring the methanol-rich stream (320, 350, 410) after the oxidising from a first vessel (101) to a second vessel (103).

14. The method according to any of the preceding claims comprising the further step of mechanically treating (106), such as filtering and / or coalescing the acidified methanol-rich stream (340, 370, 390, 420) before further processing.

15. The method according to any of the preceding claims, wherein further processing comprises distilling the acidified methanol-rich stream to provide a methanol-rich distillate and a residue comprising ammonium sulphate and oxidation reaction products.

16. A system of treating crude methanol (10), characterized in that the system comprises:• a distillation column (100), an oxidation unit (101) and an acidification unit (102), wherein o The distillation column (100) has■ an inlet for receiving crude methanol (10),■ an outlet for a distillate (20), and■ an outlet for a methanol-rich stream (310, 400) o The oxidation unit (101) has■ a first inlet for receiving methanol- rich stream (310, 400),■ a second inlet for receiving an oxidant (40), and■ an outlet for feeding the contents of the oxidation unit (310) to the acidification unit (103), o The acidification unit (103) has■ an inlet for receiving a feed of a methanol-rich stream (330, 360, 410) from the outlet of the oxidation unit,■ a second inlet for receiving an acidifying agent (60), and■ an outlet for an acidified methanol-rich stream (340, 370, 390, 420).

17. The system according to claim 16 further comprising a first decanting unit (200) for receiving crude methanol (10), said decanting unit being for decanting turpentine (20) from the crude methanol (10) before feeding a crude methanol stream with reduced turpentine content (300) from an outlet of the decanting unit to the inlet of the distillation column (100).

18. The system according to claim 16 or 17 further comprising a second decanting unit (102) for receiving a methanol-rich stream (310) from the oxidation unit (101), said second decanting unit (102) being for decanting further turpentine (50) before feeding a methanol-rich stream with a reduced turpentine content (330) from an outlet of the decanting unit (102) to the acidification unit (103).

19. The system according to any of claims 16 to 18, characterized in that the oxidation unit comprises a second outlet for removing oxidation products (50) from the oxidation unit (101).

20. A system of treating crude methanol characterized in that the system comprises a decanter (200), a distillation column (100), and an oxidation and acidification unit (104), wherein• the decanter (200) has a first inlet configured to receive the crude methanol (10), a first outlet for decanting turpentine (20), and a second outlet configured to feed a crude methanol with reduced turpentine content (300) to distillation column (100);• the distillation column (100) haso an inlet for receiving crude methanol with a reduced turpentine content (300), o an outlet for a distillate (30), and o an outlet for a methanol-rich stream (310);• the oxidation and acidification unit (104) has a first inlet for receiving a feed of a methanol-rich stream (310) from the distillation column (100), a second inlet for receiving an oxidant (40) a third inlet for receiving an acidifying agent (60) and an outlet for delivering an acidified stream (390) to further processing.

21. The system according to claim 20 characterized in that the oxidation and acidification unit (104) is configured to receive the oxidant (40) via the second inlet before it receives the acidifying agent (60) through the third inlet.

22. The system according to claim 20 or 21 characterized in that the oxidation and acidification unit (104) is configured so that the third inlet is closed when the second inlet is open to receive oxidant (40).

23. The system according to any of claims 20 to 22 characterized in that the oxidation and acidification unit (104) is configured so that the second inlet is closed when the third inlet is open to receive acidifying agent (60).

24. The system according to any of claims 16 to 23 further comprising a filtering / coalescing unit (106) for receiving an acidified methanol stream (340, 370, 390, 420) from the outlet of the acidification unit (103, 104)25. Use of a system according to any of claims 16 to 23 for carrying out a method of any of claims 1 to 15.

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