Method of treating an alkaline liquor comprising methanol

Abstract

The present technology relates to a method of treating an alkaline liquor comprising methanol and one or more components selected from the group consisting of sulphurous organic compounds, hydrogen sulphide (H2S), ammonia, acetone, alcohols such as ethanol, extractives such as turpentine, and mixtures thereof. The method comprises the steps in temporal order of contacting the liquor with an oxidant, whereby at least a part of the sulphur compounds in the liquor are oxidized to their oxidized forms providing an oxidised liquor, and contacting the oxidised liquor with an acidifying agent, whereby ammonia present in the oxidised liquor reacts to form ammonium sulphate and provide an acidified liquor, essentially free of polymerised terpenes.

Description

Method of Treating an Alkaline Liquor Comprising MethanolTECHNICAL FIELD

[0001] The present invention relates to a method of treating an alkaline liquor comprising methanol. The present invention further relates to a system for treating an alkaline liquor comprising 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 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 an alkaline liquor comprising methanol. In addition to methanol, the alkaline liquor further comprises one or more components selected from the group consisting of sulphurous organic compounds, hydrogen sulphide ( H2S) , ammonia, acetone, alcohols such as ethanol, extractives such as turpentine, and mixtures thereof. The method comprising the steps in temporal order of contacting the liquor with an oxidant, whereby at least a part of the sulphur compounds in the liquor are oxidized to their oxidized forms providing an oxidised liquor, and contacting the oxidised liquor with an acidifying agent, whereby ammonia present in the oxidised liquor reacts to form ammonium sulphate and provide an acidified liquor, essentially free of polymerised terpenes.

[0007] According to further aspect of the present invention there is provided a system of treating an alkaline liquor comprising methanol. In addition to methanol, the alkaline liquor further comprises one or more components selected from the group consisting of sulphurous organic compounds, hydrogen sulphide (H2S), ammonia, acetone, alcohols such as ethanol, extractives such as turpentine, and mixtures thereof. The system comprises an oxidation unit and an acidification unit. The oxidation unit has an inlet configured for receiving the alkaline liquor and a second inlet configured for receiving an oxidant. The oxidation unit is adapted for oxidation reactions. The oxidation unit has an outlet for feeding the contents of the oxidation unit to an inlet of the acidification unit, said inlet being configured to receive a feed of an oxidised alkaline liquor from the oxidation unit. The acidification unit has a second inlet configured for receiving an acidifying agent. The acidification unit has an outlet configured to feed an acidified stream essentially free of polymerised terpenes to further processing.

[0008] 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 liquor that is essentially free of polymerised terpenes, which foul mill equipment, such as distillation columns.

[0009] Other features and advantages will become apparent from the following description.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIGURE 1 is flow chart illustrating a method of treating an alkaline liquor comprising methanol according to at least some embodiments.

[0011] FIGURE 2 is a flow chart illustrating a method of treating an alkaline liquor comprising methanol according to at least some embodiments.

[0012] FIGURE 3 is a flow chart illustrating a method of treating an alkaline liquor comprising methanol according to at least some embodiments.

[0013] FIGURE 4 is a flow chart illustrating a method of treating an alkaline liquor comprising methanol according to at least some embodiments.EMBODIMENTS

[0014] For the purposes of embodiments of the present invention, the liquor to be treated 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 components selected from the group consisting of sulphurous organic compounds, ammonia, acetone, alcohols such as ethanol, extractives such as turpentine and other non- structural components of lignocellulosic material, which liquid has not been treated in an acidification step.DETAILED DESCRIPTION

[0015] The present invention relates to a method of treating an alkaline liquor comprising methanol and one or more components selected from the group consisting of sulphurous organic compounds, hydrogen sulphide (EES), ammonia, acetone, alcohols such as ethanol, extractives such as turpentine, and mixtures thereof. The method comprises the steps in temporal order of contacting the liquor with an oxidant, whereby at least a part of the sulphur compounds in the liquor are oxidized to their oxidized forms providing an oxidised liquor, and contacting the oxidised liquor with an acidifying agent, whereby ammonia present in the oxidised liquor reacts to form ammonium sulphate and provide an acidified liquor, essentially free of polymerised terpenes.

[0016] FIGURE 1 is a flow diagram illustrating a method of treating an alkaline liquor in accordance with at least some embodiments of the present invention.

[0017] An alkaline liquor 10 comprising methanol and one or more components selected from the group consisting of sulphurous organic compounds, hydrogen sulphide (EES), ammonia, acetone, alcohols such as ethanol, extractives such as turpentine, and mixtures thereof is fed into a decanting unit 100 with water 20. Turpentine 30 is decanted from the decanting unit and directed to further processing. A decanted methanol stream 300 is then fed from the decanting unit 100 to an oxidation unit 101 where it is contacted with an oxidant 40 providing and oxidised stream 310 which is led to a further decanting unit 102 into which water 50 is added. Further turpentine 60 is decanted from the oxidised stream 310 in the further decanting unit 102 and the decanted oxidised stream 320 is fed from the further decantingunit 102 into an acidification unit 103. The decanted oxidised stream 320 is then contacted with an acidifying agent 70 and an acidified stream 80 is led from the acidification unit 103 to further processing. The acidified stream 80 is essentially free of polymerised terpenes.

[0018] FIGURE 2 is a flow diagram illustrating a method of treating an alkaline liquor in accordance with at least some embodiments of the present invention.

[0019] An alkaline liquor 10 comprising methanol and one or more components selected from the group consisting of sulphurous organic compounds, hydrogen sulphide (EES), ammonia, acetone, alcohols such as ethanol, extractives such as turpentine, and mixtures thereof is fed with water 20 into a decanting unit 100. Turpentine 30 is decanted from the decanting unit 100 to provide a decanted methanol stream 300. The decanted methanol stream 300 is fed from the decanting unit 100 into an oxidation unit 101, where it is contacted with an oxidant 40. One stream 90 of oxidation products is led to further processes, and an oxidised stream 330 is led to a further decanting unit 102. Water 50 is added to the further decanting unit 102 and further turpentine 60 is decanted to provide a decanted oxidised stream 340 free of oxidation product 90, which stream 340 is led from the further decanting unit 102 to an acidification unit 103 where it is contacted with an acidifying agent 70. An acidified stream 110 comprising mainly alcohols and acetone is directed to further processing and ammonium sulphate 120 is recovered and directed to further processing. The acidified stream 110 is essentially free of polymerised terpene compounds.

[0020] FIGURE 3 is a flow diagram illustrating a method of treating an alkaline liquor in accordance with at least some embodiments of the present invention.

[0021] An alkaline liquor 10 comprising methanol, and one or more components selected from the group consisting of sulphurous organic compounds, hydrogen sulphide (EES), ammonia, acetone, alcohols such as ethanol, extractives such as turpentine, and mixtures thereof is fed with water 20 into a decanting unit 100. Turpentine 30 is decanted from the decanting unit 100 to provide a decanted methanol stream 300. The decanted methanol stream 300 is fed from the decanting unit 100 into an oxidation and acidification unit 104. The decanted methanol stream 300 is then first contacted with an oxidant 40 and subsequently contacted with an acidifying agent 70, whereby an acidified stream 80 is formed and directed to further processing. The acidified stream 80 is essentially free of polymerised terpenes.

[0022] FIGURE 4 is a flow diagram illustrating a method of treating an alkaline liquor in accordance with at least some embodiments of the present invention.

[0023] An alkaline liquor 10 comprising methanol, and one or more components selected from the group consisting of sulphurous organic compounds, hydrogen sulphide (EES), ammonia, acetone, alcohols such as ethanol, extractives such as turpentine, and mixtures thereof is fed into an oxidation unit 101, where it is contacted with an oxidant 40. An oxidised stream 310 is led from the oxidation unit 101 to an acidification unit 103 where it is contacted with an acidifying agent 70, whereby an acidifiedstream 80 is formed and directed to further processing. The acidified stream 80 is essentially free of polymerised terpenes.

[0024] As described above, the present technology relates to a method of treating an alkaline liquor comprising methanol, and one or more components selected from the group consisting of sulphurous organic compounds, hydrogen sulphide (H2S), ammonia, acetone, alcohols such as ethanol, extractives such as turpentine, and mixtures thereof. The method comprises the steps in temporal order of contacting the liquor with an oxidant, whereby at least a part of the sulphur compounds in the liquor are oxidized to their oxidized forms providing an oxidised liquor, and contacting the oxidised liquor with an acidifying agent, whereby ammonia present in the oxidised liquor reacts to form ammonium sulphate and provide an acidified liquor, essentially free of polymerised terpenes. It has surprisingly been found that by carrying out an oxidation step before an acidification step, terpenes remaining in the liquor to be treated are far less likely to polymerise forming a sticky stuff comprising polymerised 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.

[0025] As mentioned above the alkaline liquor comprising methanol may contain hydrogen sulphide and sulphurous organic compounds. Such compounds include methyl mercaptan and dimethyl sulphide. In the oxidation phase methyl mercaptan (MM) is oxidised to dimethyl sulphide (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.

[0026] In one embodiment the alkaline liquor comprises methanol, ammonia, sulphurous organic compounds, hydrogen sulphide and one or more components selected from the group consisting of acetone, alcohols, such as ethanol, extractives such as turpentine, and mixtures thereof.

[0027] In one embodiment the acidified liquor is directed to further processing. In an embodiment ammonium sulphate is removed from the acidified liquor, 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 comprisingmethanol 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.

[0028] In one embodiment the liquor is diluted with water before contacting the liquor with the oxidant. The further step of diluting the liquor with water before contacting the liquor with the oxidant mitigates the exothermic effects of the step of contacting the liquor with the oxidant.

[0029] In a further embodiment turpentine is decanted from the liquor before the liquor is contacted with the oxidant. The further step of decanting turpentine from the liquor before contacting the liquor with the oxidant provides the additional benefit of removing at least a portion of the terpenes from the liquor. As a natural consequence, reactions between terpenes 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 contacting the liquor with the oxidant facilitates and improves the decantation of turpentine in an embodiment.

[0030] In one embodiment, the method comprises the further step of adding water to the oxidised liquor, and optionally decanting turpentine from the oxidised liquor before contacting the oxidised liquor with the acidifying agent. After adding water to the oxidised liquor, a portion of the remaining turpentine in the liquor separates from the liquor and is apt to be decanted from the liquor, thereby reducing the amount of terpenes in the liquor available to undergo unfavourable reactions in a subsequent acidification step, in which step polymerised terpenes are formed. As the amount of unfavourable reactions with terpenes is reduced, the amount of acidifying agent required to produce ammonium sulphate is reduced, still further improving the efficiency of the method. As mentioned above, the addition of water facilitates and improves the decantation of turpentine from the oxidised liquor. Additionally, the addition of water lowers heat release when adding acidifying agent ensuring that ammonium sulphate is not precipitated.

[0031] Acidification of the oxidised liquor lowers the pH of the liquor. In one embodiment the pH of the oxidised liquor is adjusted to a pH in the range of 2.0 - 6.5, preferably 2.0 - 3.0, suitably to a pH of 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8 or 2.9. Reducing the pH in the acidification step to a pH in the range of 2.0 - 6.5, preferably 2.0 - 3.0, suitably to a pH of 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8 or 2.9 increases the yield of ammonium sulphate, whereby the amount of free sulphate ions in the liquor is lowered.

[0032] 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 preferredembodiment 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 2 to 12% by weight of the crude methanol, typically 3 to 11 %, suitably 4 to 10%, for example 5, 6, 7, 8 or 9%.

[0033] 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, carbon dioxide, sulphur dioxide, waste liquid from carbon dioxide production, acid bleach plant waste liquor, sodium sulphate bleaching filtrates such as A-stage bleaching filtrate and chlorine bleaching filtrate, 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.

[0034] 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 non is lost in the gaseous form.

[0035] 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.

[0036] 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 values provides greater control over the process since both steps are exothermic.

[0037] In embodiments in which the oxidising step and acidifying step are carried out in different vessels, it is necessary to transfer the oxidised liquor from a first vessel to a second vessel. Thus, in an embodiment the oxidised liquor is transferred from a first vessel to a second vessel.

[0038] In addition to a method, the present technology also relates to a system of treating an alkaline liquor comprising methanol, and one or more components selected from the group consisting of sulphurous organic compounds, hydrogen sulphide (H2S), ammonia, acetone, alcohols such as ethanol, extractives such as turpentine, and mixtures thereof. Particularly, the technology also relates to a system of treating an alkaline liquor comprising methanol, ammonia, sulphurous organic compounds, hydrogensulphide and one or more components selected from the group consisting of acetone, alcohols, such as ethanol, extractives such as turpentine, and mixtures thereof.

[0039] In an embodiment the system comprises an oxidation unit 101 and an acidification unit 103. The oxidation unit 101 has a first inlet configured for receiving an alkaline liquor 10 comprising methanol and one or more components selected from the group consisting of sulphurous organic compounds, hydrogen sulphide (H2S), ammonia, acetone, alcohols such as ethanol, extractives such as turpentine, and mixtures thereof, a second inlet configured for receiving an oxidant 40, an outlet for feeding the contents 310 of the oxidation unit 101 to the acidification unit 103. The acidification unit103 has an inlet configured to receive a feed of an oxidised alkaline liquor 310 from the outlet of the oxidation unit 101, a second inlet configured for receiving an acidifying agent 70, and an outlet configured to feed an acidified stream 80 essentially free of polymerised terpenes to further processing.

[0040] In a further embodiment the system further comprises a first decanting unit 100 configured to receive alkaline liquor 10 comprising methanol, and one or more components selected from the group consisting of sulphurous organic compounds, hydrogen sulphide (H2S), ammonia, acetone, alcohols such as ethanol, extractives such as turpentine, and mixtures thereof and having an inlet for water 20 for decanting turpentine 30 from the alkaline liquor 10 before feeding the liquor from an outlet of the decanting unit 100 to the first inlet of the oxidation unit 101.

[0041] In one embodiment the system further comprises a second decanting unit 102 configured to receive an oxidised alkaline liquor from the oxidation unit 101 and having an inlet for water 50 for decanting further turpentine 60 from the oxidised alkaline liquor before feeding the oxidised alkaline liquor from an outlet of the decanting unit to the acidification unit 103.

[0042] In an embodiment the oxidation unit 101 comprises a second outlet, said second outlet configured to remove oxidation products 90 from the oxidation unit 101. Typically, oxidation products 90 are removed from the oxidation unit 101 before a further step is carried out.

[0043] In one embodiment the acidification unit 103 comprises a second outlet configured to remove ammonium sulphate 120 from the acidification unit. Typically, ammonium sulphate is removed from the acidified liquor 80 before the acidified stream is led to further processing.

[0044] 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 an alkaline liquor 10 comprising methanol, and one or more components selected from the group consisting of sulphurous organic compounds, hydrogen sulphide (H2S), ammonia, acetone, alcohols such as ethanol, extractives such as turpentine, and mixtures thereof, comprises a decanter 100 and an oxidation and acidification unit 104. The decanter 100 has a first inlet configured to receive the liquor 10, a second inlet for water 20, a first outlet for decanting turpentine 30, and a second outlet configured to feed a decanted liquor to the oxidation and acidification unit 104. The oxidation and acidification unit104 has a first inlet for receiving a feed of decanted liquor 300 from the decanter 100, a second inlet forreceiving an oxidant 40 a third inlet for receiving an acidifying agent 70 and an outlet for delivering an acidified stream 80 to further processing.

[0045] 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 70 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. 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 70.

[0046] The following examples illustrate at least some embodiments of the present technology.EXAMPLESExample 1

[0047] A crude methanol acidification 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. pH was adjusted to approximately 2 with sulphuric acid. The acidified methanol solution was evaporated until temperature 95 °C was reached. The liquid left on the evaporation flask was filtered. Sticky solids were left on the walls of the evaporation flask, and solid residue cake was left on the filtration funnel. Solid residues were collected from the evaporation flask and filtration funnel. Increasing the crude methanol / water ratio increased the solids formation further, and it was confirmed that solids form even with acidification to pH 6.

[0048] Experiments showed that no mechanical means or process adjustments would eliminate the tendency to solids formation in acidification process. Solids formation was observed even at room temperature without any heating and applying filtering and second decantation after acidification did not clearly decrease the solids formation.Example 2

[0049] It was confirmed in lab trials, that oxidation prior to acidification eliminates solids formation. The previously described procedure was repeated with an additional oxidation step after decanting and prior to acidification. Oxidation was performed for 1 hour at 50 °C with 3.9 w / w % H2O2 dosage by weight of crude methanol. The H2SO4 consumption was lowered because of oxidation. After evaporation no particle formation was observed. The comparison of experiments with and without oxidation are shown in Table 1.Table 1. The comparison of acidification with and without oxidation.INDUSTRIAL APPLICABILITY

[0050] 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 sulphuric compounds turpentine and ammonia and to form ammonium sulphate from unreacted ammonia. 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.

Claims

CLAIMS1. A method of treating an alkaline liquor (10) comprising methanol, ammonia, sulphurous organic compounds, hydrogen sulphide and one or more components selected from the group consisting of, acetone, alcohols such as ethanol, extractives such as turpentine, and mixtures thereof, the method comprising the steps in temporal order of:• contacting the liquor with an oxidant (40), whereby at least a part of the sulphur compounds in the liquor are oxidized to their oxidized forms providing an oxidised liquor (310); and• contacting the oxidised liquor (310) with an acidifying agent (70), whereby ammonia present in the oxidised liquor reacts to form ammonium sulphate and provide an acidified liquor (80), essentially free of polymerised terpenes.

2. The method according to claim 1, comprising the further step of directing the acidified liquor (80) to further processing.

3. The method according to claim 1 or 2, comprising the further step of diluting the liquor (10) with water before contacting the liquor (10) with the oxidizing agent (40).

4. The method according to claim 1 to 3, comprising the further step of decanting turpentine (30) from the liquor before contacting the liquor (10) with the oxidizing agent (40).

5. The method according to any of the preceding claims, comprising the further step of adding water (50) to the oxidised liquor, and optionally decanting turpentine (60) from the oxidised liquor before contacting the oxidised liquor (310) with the acidifying agent (70).

6. The method according to any of the preceding claims, comprising adjusting the pH of the oxidised liquor (310) to a pH in the range of 2.0 - 6.5, preferably 2.0 - 3.0, suitably to a pH of 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8 or 2.9.

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 (70) 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 carbon dioxideproduction, acid bleach plant waste liquor, sodium sulphate bleaching filtrates such as A-stage bleaching filtrate and chlorine 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 9, wherein the oxidising step and the acidifying step are carried out in different vessels (101, 103).

13. The method according to claim 11, comprising the step of transferring the oxidised liquor from a first vessel to a second vessel.

14. A system of treating an alkaline liquor comprising methanol, ammonia, sulphurous organic compounds, hydrogen sulphide and one or more components selected from the group consisting of, acetone, alcohols such as ethanol, extractives such as turpentine, and mixtures thereof, characterized in that the system comprises:• an oxidation unit (101) and an acidification unit (103), wherein o The oxidation unit (101) has■ a first inlet configured for receiving an alkaline liquor (10) comprising methanol, sulphurous organic compounds, hydrogen sulphide, ammonia, and turpentine,■ a second inlet configured for receiving an oxidant (40).■ an outlet for feeding the contents (310) of the oxidation unit (101) to the acidification unit (103), o The acidification unit (103) has■ an inlet configured to receive a feed of an oxidised alkaline liquor (310) from the outlet of the oxidation unit (101),■ a second inlet configured for receiving an acidifying agent (70), and■ an outlet configured to feed an acidified stream essentially free of polymerised terpenes (80) to further processing.

15. The system according to claim 14 further comprising a first decanting unit (100) configured to receive alkaline liquor and having an inlet for water (20) for decanting turpentine (30) from the alkaline liquor before feeding the liquor from an outlet of the decanting unit (100) to the first inlet of the oxidation unit (101).

16. The system according to claim 14 or 15 further comprising a second decanting unit (102) configured to receive an oxidised alkaline liquor from the oxidation unit (101) and having an inlet for water (50) for decanting further turpentine (60) from the oxidised alkaline liquor before feeding the oxidised alkaline liquor from an outlet of the decanting unit to the acidification unit (103).

17. The system according to any of claims 14 to 16, characterized in that the oxidation unit (101) comprises a second outlet, said second outlet configured to remove oxidation products (90) from the oxidation unit (101).

18. The system according to any of claims 14 to 17, characterized in that the acidification unit (103) comprises a second outlet configured to ammonium sulphate (120) from the acidification unit.

19. A system of treating an alkaline liquor comprising methanol, and one or more components selected from the group consisting of sulphurous organic compounds, hydrogen sulphide (H2S), ammonia, acetone, alcohols such as ethanol, extractives such as turpentine, and mixtures thereof, characterized in that the system comprises:• a decanter (100) and an oxidation and acidification unit (104), wherein o the decanter (100) has■ a first inlet configured to receive the liquor,■ a second inlet for water (20),■ a first outlet for decanting turpentine (30), and■ a second outlet configured to feed a decanted liquor to the oxidation and acidification unit (104) o the oxidation and acidification unit (104) has■ a first inlet for receiving a feed of decanted liquor from the decanter (100),■ a second inlet for receiving an oxidant,■ a third inlet for receiving an acidifying agent and an outlet for delivering an acidified stream to further processing.

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