Method for producing high-purity magnesium oxide

Abstract

The present invention provides a method for converting magnesium chloride to magnesium oxide, comprising the steps of: The method comprises subjecting a magnesium chloride solution to a spray-drying step at a temperature of 300-475°C to form a spray-dried product containing 10-80% by weight of magnesium oxide and 20-90% by weight of magnesium hydroxychloride and magnesium chloride, and subjecting the product of the spray-drying step to a roasting step in the presence of water at a temperature of 600-900°C in a roaster to form a product containing at least 98% by weight of MgO and less than 2% by weight of magnesium hydroxychloride and magnesium chloride, wherein the percentages of MgO, magnesium hydroxychloride, and magnesium chloride are calculated as the sum of MgO, magnesium hydroxychloride, and magnesium chloride. The method preferably comprises at least 98% by weight of MgO and less than 2% by weight of magnesium hydroxychloride and magnesium chloride, calculated on the total solid product. The present invention also relates to high-purity magnesium oxide obtainable by the method of the present invention.

Description

[Technical Field]

[0001] The present invention relates to a method for producing high purity magnesium oxide from a magnesium chloride solution. The present invention also relates to an integrated process comprising a fermentation step, a separation step, and a step for converting the magnesium chloride solution into high purity magnesium oxide. [Background technology]

[0002] Methods for producing carboxylic acids through fermentation are known in the art. In these methods, a base is often added to maintain the pH of the fermentation medium at a desired value. This results in the carboxylic acid being obtained in the form of a salt, e.g., a magnesium salt. When the carboxylic acid is recovered, a salt solution, e.g., a magnesium salt solution, is obtained, which requires further treatment. Preferably, the salt solution is treated to form a substance suitable for reuse in an earlier step of the fermentation. In particular, it is preferred to treat the salt solution to form a base that can be used for pH control in the fermentation.

[0003] For example, WO 00 / 17378 describes a method for producing lactic acid in which a magnesium lactate solution is prepared in a fermentation process. The magnesium lactate solution is acidified with HCl to produce a solution containing lactic acid in a magnesium chloride solution. The lactic acid is recovered from the solution. The resulting magnesium chloride solution can be processed by subjecting it to a pyrohydrolysis step at a temperature of at least 500°C to react the magnesium chloride with water to produce magnesium oxide powder and hydrochloric acid. The heat required for the pyrohydrolysis reaction is provided by in situ combustion of fuel.

[0004] WO 2013 / 025106 describes a method for producing carboxylic acids through a process that includes acidifying a magnesium salt of a carboxylic acid with HCl to form an acid and magnesium chloride solution, and isolating the acid from the solution through precipitation. It is indicated that the magnesium chloride solution can be processed through thermal decomposition.

[0005] WO 2013 / 093028 describes a method for producing carboxylic acids through a process that includes acidifying a magnesium salt of a carboxylic acid with HCl to form an acid and magnesium chloride solution, and isolating the acid from the solution through extraction and subsequent back-extraction. It is indicated that the magnesium chloride solution can be processed through thermal decomposition.

[0006] In the above cited document, the magnesium chloride solution is treated by subjecting the solution to a pyrolysis step in which magnesium chloride reacts with water from the solution to form solid magnesium oxide and a gas stream containing water and HCl.

[0007] A problem with the pyrolysis processes described in these documents is that the magnesium oxide recovered from the spray drying step may be of insufficient purity for it to be reused in the fermentation process either directly or after conversion to magnesium hydroxide. More specifically, it has been found that the chloride content in the magnesium oxide content is very high, which can have a detrimental effect on the fermentation process.

[0008] For example, it has been found that when a magnesium chloride solution is subjected to a spray drying process at a temperature of 500-600°C in a spray dryer, a product is formed that contains 97% by weight of magnesium oxide, the remainder being magnesium chloride and magnesium hydroxychloride. In this context, it should be noted that during fermentation, magnesium oxide (or its derivative, magnesium hydroxide) is added to the process in amounts of the order of 1 mole of magnesium per mole of carboxylic acid formed. This means that even trace amounts of contaminants in the magnesium oxide will be present in significant amounts in the fermentation medium. Summary of the Invention [Problem to be solved by the invention]

[0009] Therefore, there is a need in the art for a method for producing high purity magnesium oxide from a magnesium chloride solution. The present invention provides such a method. [Means for solving the problem]

[0010] The present invention provides a method for converting magnesium chloride to magnesium oxide, comprising the steps of: subjecting the magnesium chloride solution to a spray drying step in a spray dryer at a temperature of 300-475°C resulting in the formation of a spray dried product comprising 10-80% by weight of magnesium oxide and 20-90% by weight of the sum of magnesium hydroxychloride and magnesium chloride; subjecting the product of the spray drying step to a roasting step in the presence of water in a roaster at a temperature of 600-900°C, resulting in the formation of a product comprising at least 98% by weight of MgO and less than 2% by weight of the sum of magnesium hydroxychloride and magnesium chloride, wherein the percentages of MgO, magnesium hydroxychloride, and magnesium chloride are calculated as the sum of these three compounds; The method further comprises the steps of:

[0011] It has been found that the combination of a relatively mild spray drying process with a high temperature roasting process makes it possible to obtain high purity magnesium oxide in an efficient manner. Further advantages resulting from the present invention and specific embodiments thereof will become apparent from the further description.

[0012] More specifically, a process according to the present invention involving a spray-drying temperature of 300-475°C followed by roasting at a temperature of 600-900°C has been found to result in the formation of a product containing at least 98% by weight of MgO and less than 2% by weight of the sum of magnesium hydroxychloride and magnesium chloride, where the percentages of MgO, magnesium hydroxychloride, and magnesium chloride are calculated as the sum of these three compounds. The product of the spray-drying process carried out at a temperature of 500-600°C has a significantly lower chloride content, and when subjected to a roasting process under the same conditions, a magnesium oxide product with the same chloride content is obtained. Surprisingly, the product obtained from spray-drying at 300-475°C, despite its higher chloride content, appears to be convertible to high-purity MgO under the same conditions as the product obtained from spray-drying at 500-600°C. In the process of the present invention, the product of the spray-drying process is fed directly to the roasting process without any intermediate steps, such as washing or rehydration steps.

[0013] It should be noted that the production of high-purity magnesium oxide has also been described outside the context of fermentation processes. For example, Chinese Patent Application Publication No. 110015671 describes a method for producing high-purity magnesium oxide in which bischofite (MgCl 6H O) is dehydrated by spray drying the bischofite solution at 650-750 °C to form anhydrous magnesium chloride, which is then reacted with water in a rotary kiln to produce magnesium oxide. Thus, in this document, the spray drying step is carried out at a much higher temperature than in the method according to the present invention and is used to produce anhydrous magnesium chloride, but not to partially convert the magnesium chloride into a product containing a specific amount of magnesium oxide and magnesium (hydro)chloride. Chinese Patent Application Publication No. 100417596 describes a method for producing high-purity magnesium oxide in which magnesium chloride hydrate is subjected to a pyrolysis step at a temperature of 400-600 °C in a sealed pyrolysis stove for 0.5-3 hours. The product is subjected to a water washing step to remove aqueous impurities. In this step, the MgO is converted to Mg(OH). After the solid-liquid separation step, the product is subjected to a roasting step at a temperature of 500-700°C for 1.5-3.5 hours.

[0014] The method is described in more detail below.

[0015] Hereinafter, reference will be made to the following figures, but without being limited by them: [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 illustrates a method according to the present invention. [Figure 2] FIG. 2 shows a method according to the invention in combination with a fermentation process. [Figure 3] FIG. 3 shows the method according to the invention in an integrated process for the production of carboxylic acids. DETAILED DESCRIPTION OF THE INVENTION

[0017] The first step in the process according to the invention is to subject the magnesium chloride solution to a spray drying process in a spray dryer at a temperature of 300-475°C, resulting in the formation of a spray dried product comprising 10-80% by weight of magnesium oxide and 20-90% by weight of the sum of magnesium hydroxychloride and magnesium chloride, calculated on total solid product.

[0018] Preferably, the first step comprises subjecting the magnesium chloride solution to a spray drying step in a spray dryer at a temperature of 300-475°C, resulting in the formation of a spray dried product comprising 30-80% by weight of magnesium oxide and 20-70% by weight of magnesium hydroxychloride and magnesium chloride in total.

[0019] The magnesium chloride solution subjected to the spray-drying step in the method according to the present invention generally has a magnesium chloride concentration of 5 to 48% by weight, particularly 15 to 48% by weight. If the magnesium chloride solution has a low concentration, for example, less than 5% by weight or less than 15% by weight, the amount of water to be evaporated in the spray-drying step is large, making the method unattractive from an energy standpoint. On the other hand, at magnesium chloride concentrations above 48% by weight, there is a risk of magnesium chloride precipitation in the spray-drying nozzle. In general, it is preferred that the magnesium chloride solution have a concentration as high as possible without causing magnesium chloride precipitation in the nozzle. Therefore, it is preferred that the magnesium chloride solution have a magnesium chloride concentration of 18 to 48% by weight, particularly 23 to 48% by weight, more particularly 30 to 48% by weight, and even more particularly 35 to 47% by weight.

[0020] Since the objective of the magnesium chloride solution used in the method according to the invention is to prepare magnesium oxide with high purity, it is preferred that the solution contains only limited amounts of other compounds than magnesium chloride and water, more particularly that the magnesium chloride solution contains at least 95% by weight, in particular at least 98% by weight, more particularly at least 99% by weight of magnesium chloride and water.

[0021] The temperature of the magnesium chloride solution fed to the spray-drying process is not critical and can vary from room temperature to 140°C. Higher temperatures and more concentrated magnesium chloride solutions are preferred, as they result in less energy consumption in the spray-drying process. Higher temperatures can be obtained in a manner known in the art, for example by heating the solution in a heat exchange process using a hot gas or hot liquid. It may be preferable for the magnesium chloride solution fed to the spray-drying process to have a temperature of 50 to 140°C, particularly 70 to 135°C, more particularly 90 to 130°C.

[0022] The magnesium chloride solution is fed to the spray drying process at a temperature of 300-475°C, preferably 350-450°C, in the spray drying apparatus. Spray drying methods and apparatus are known in the art. In the spray drying apparatus, the feed to be spray dried is fed to a spray tower and atomized through a nozzle to form small droplets. The droplets fall through a hot gas, solidifying in the process as water evaporates. Furthermore, the magnesium chloride is partially converted to magnesium oxide.

[0023] In the method according to the invention, the spray drying step is carried out at a temperature of 300 to 475°C, preferably 350 to 450°C. The temperature is determined at the location of the spray drying nozzle. If the temperature is too low, the conversion of magnesium chloride to magnesium oxide will be insufficient. If the temperature is too high, too much magnesium chloride may be formed, which will have a detrimental effect on the purity of the final product. The temperature is preferably 350 to 450°C, in particular 375 to 450°C, more in particular 375 to 420°C. The temperatures indicated here are gas temperatures.

[0024] The residence time in the spray drying apparatus, defined as the time from the moment the droplets leave the nozzle to the moment the solid particles reach the bottom of the unit, is generally 1 to 60 seconds, particularly 3 to 30 seconds. Residence time is governed by the height of the spray tower and the flow rate and direction of any gas streams fed to the spray tower.

[0025] A desired conversion rate can be obtained in the spray drying process by selecting a suitable combination of temperature and residence time to achieve the desired conversion rate. Higher temperatures and longer residence times will result in higher conversion rates. Based on common general knowledge and the teachings of this specification, it is within the skill of the art to determine a suitable combination of residence time and temperature to achieve the desired conversion rate.

[0026] Depending on the configuration of the spray dryer, the particles may have a residence time at the bottom of the spray dryer before being transferred to the roaster. It has been found that a residence time at the bottom of the spray dryer does not substantially affect the conversion rate, presumably because the particles are not in intensive contact with the hot gas. However, for reasons of processing efficiency, it is generally preferred that the particles have a residence time at the bottom of the spray dryer of 60 minutes or less, particularly 30 minutes or less, more particularly 15 minutes or less, or 10 minutes or less, or 5 minutes or less.

[0027] In the spray drying process, gas is fed into the unit to provide the necessary temperature and airflow. The nature of the gas is not critical. Typically, hot combustion gas is provided, for example, by burning natural gas, biogas, hydrogen, or syngas. Gas is also removed from the unit. The gas removed from the unit contains HCl produced by the decomposition of magnesium chloride to magnesium oxide. The gas removed from the unit also contains moisture evaporated from the particles.

[0028] The spray-drying step produces solid particles containing 10 to 80 wt. % magnesium oxide, particularly 30 to 80 wt. % magnesium oxide, and 20 to 90 wt. % magnesium hydroxychloride and magnesium chloride, calculated as the total solids content, particularly 20 to 70 wt. If the conversion to magnesium oxide is too low, it will be impossible to achieve a conversion to magnesium oxide of at least 98 wt. % in the second step. If the conversion to magnesium oxide is greater than 80 wt. %, process efficiency will be affected. Preferably, the product from the spray drying step comprises 40-80 wt.% magnesium oxide and 20-60 wt.% combined magnesium hydroxychloride and magnesium chloride, particularly 45-75 wt.% magnesium oxide and 25-55 wt.% combined magnesium hydroxychloride and magnesium chloride, more particularly 50-70 wt.% magnesium oxide and 30-50 wt.% combined magnesium hydroxychloride and magnesium chloride, and even more particularly 55-70 wt.% magnesium oxide and 45-30 wt.% combined magnesium hydroxychloride and magnesium chloride, all calculated on total solids. Conversion can be determined by selecting a suitable spray drying temperature and residence time.

[0029] The product from the spray drying step is subjected to a roasting step in the presence of water at a temperature of 600-900°C in a roaster, resulting in the formation of a product containing at least 98% by weight of MgO and less than 2% by weight of magnesium hydroxychloride and magnesium chloride (calculated as the sum of these three compounds). Temperatures below 600°C are not sufficient to achieve the required conversion within a reasonable time frame. Higher temperatures shorten the time required to achieve the desired conversion, so temperatures of at least 700°C, and especially at least 750°C, are preferred. Temperatures above 900°C require high energy input and are therefore generally unattractive from a commercial standpoint. Furthermore, the product becomes less reactive. The roaster temperature may preferably be 850°C or less.

[0030] The residence time in the unit is selected to obtain the desired conversion at the desired temperature. As will be apparent to those skilled in the art, lower temperatures will require longer residence times to obtain the desired conversion. Typically, the residence time in the roaster is between 10 minutes and 4 hours, more specifically between 15 minutes and 2 hours, and in some embodiments, between 30 minutes and 90 minutes. Based on common general knowledge and the teachings herein, it is within the skill of those skilled in the art to determine the appropriate combination of residence time and temperature to achieve the desired conversion.

[0031] The roasting step is carried out in the presence of water to allow the reaction of magnesium chloride and magnesium hydroxychloride to magnesium oxide. The amount of water is not critical as long as there is enough water to allow the reaction to occur. Excess water is easily removed with the roasting gas. As a general range, values ​​of 0.1 to 50 mol % of water, particularly 0.1 to 15 mol % of water, more particularly 0.1 to 10 mol % of water, calculated on the composition of the roasting gas fed to the roasting step, can be mentioned.

[0032] Gas is fed to the unit to provide the required temperature during the torrefaction step. The nature of the gas is not critical. In one embodiment, hot combustion gas is supplied, for example, from the combustion of natural gas, biogas, hydrogen, and syngas. The advantage of this source is that the gas stream essentially contains water. Gas is also removed from the unit. The gas removed from the unit contains HCl, produced by the decomposition of the magnesium (hydroxyl) chloride to magnesium oxide, in an amount of, for example, 0.3 to 5 mol %, calculated on the composition of the gas leaving the unit.

[0033] The product obtained from the process according to the invention comprises at least 98% by weight of MgO and less than 2% by weight of the sum of magnesium hydroxychloride and magnesium chloride (calculated as the sum of these three components). The process according to the invention is capable of producing magnesium oxide of even higher purity, for example comprising at least 98.5% by weight of MgO and less than 1.5% by weight of the sum of magnesium hydroxychloride and magnesium chloride, or even at least 99% by weight of MgO and less than 1% by weight of the sum of magnesium hydroxychloride and magnesium chloride (calculated as the sum of these three components).

[0034] Depending on the composition of the starting materials, the solid product may contain further contaminants. However, it is preferred that the sum of MgO, magnesium hydroxychloride, and magnesium chloride accounts for at least 95% by weight of the solid product, particularly at least 98% by weight, and more particularly at least 99% by weight. It is particularly preferred that the solid product contains at least 98% by weight of MgO and less than 2% by weight of magnesium hydroxychloride and magnesium chloride, calculated on the total solid product. It is particularly preferred that the process according to the invention produces even higher purity magnesium oxide, for example, containing at least 98.5% by weight of MgO and less than 1.5% by weight of magnesium hydroxychloride and magnesium chloride, or even at least 99% by weight of MgO and less than 1% by weight of magnesium hydroxychloride and magnesium chloride, calculated on the total solid product.

[0035] The method according to the present invention has been found to result in magnesium oxide product particles having a relatively narrow particle size distribution. The particle size distribution can be characterized by the D-values ​​D10, D50, and D90. D10 is the diameter at which 10% of the sample mass is made up of particles with a diameter below this value. D50 is the diameter at which 50% of the sample mass has a diameter below this value and 50% of the sample mass has a diameter above this value. D90 is the diameter at which 90% of the sample mass has a diameter below this value. The D-values ​​can be determined by methods known in the art, such as laser diffraction on a dispersion of the product in a saturated MgO solution.

[0036] In one embodiment, the particles obtained by the process according to the invention have a D50 lying between 0.5 and 20 microns, in particular between 2 and 10 microns.

[0037] The magnesium oxide obtained by the method according to the present invention has high reactivity, as can be quantified by citric acid reactivity. More specifically, the magnesium oxide has a citric acid reactivity of 75 to 400 seconds, preferably 100 to 350 seconds, and specifically 150 to 300 seconds. The citric acid reactivity is determined as follows: A 0.4 eq / L or 25.61 g / L citric acid solution containing phenolphthalein (30 mg) as an indicator is prepared. The acid solution is shaken at 30°C for at least 1 hour. 1±0.01 g of powdered MgO sample is transferred to 50 ml of the acid solution at 30°C and shaken until the color of the slurry changes from white to pink. The time it takes for the slurry to change color is the citric acid reactivity. This method is similar to that described by EM van der Merwe, Hydration of medium reactive industrial magnesium oxide with magnesium acetate, thermogravimetric study, Journal of Thermal Analysis and Calorimetry, Vol 77 (2004) 49-56.

[0038] The present invention also relates to a novel magnesium oxide product characterized by the following parameters: The magnesium oxide product comprises at least 98% by weight MgO and less than 2% by weight sum of magnesium hydroxychloride and magnesium chloride, calculated on total solid product, particularly at least 98.5% by weight MgO and less than 1.5% by weight sum of magnesium hydroxychloride and magnesium chloride, calculated on total solid product, more particularly at least 99% by weight MgO and less than 1% by weight sum of magnesium hydroxychloride and magnesium chloride, calculated on total solid product. The magnesium oxide product has a D50 lying between 0.5 and 20 microns, especially between 2 and 10 microns. The magnesium oxide product has a citric acid reactivity of 75 to 400 seconds, preferably 100 to 350 seconds, specifically 150 to 300 seconds.

[0039] The product preferably contains less than 0.5 wt. % of other components other than MgO, magnesium hydroxychloride, and magnesium chloride, especially less than 0.1 wt. The high purity and reactivity of the novel magnesium oxide product make it attractive for a variety of applications.

[0040] Spray drying and torrefaction equipment is known in the art and does not require further description herein. Equipment including both a spray drying zone and a torrefaction zone is also known in the art. See, for example, U.S. Pat. No. 6,214,310 and U.S. Patent Application Publication No. 2002 / 0159946.

[0041] U.S. Patent No. 6,214,310 focuses on the regeneration of pickling acid used in steel production. It describes a process in which partial conversion of metal salts occurs in a spray-drying zone, with final conversion occurring in a roasting zone. The spray-drying zone operates at a temperature of 500-600°C. The conversion of magnesium chloride is not described, and the conversion rate in the spray-drying zone is not specified.

[0042] US Patent Application Publication No. 2002 / 0159946 describes a spray roasting process in which a metal salt solution is sprayed and the water is evaporated in a first stage to form metal salt particles, which are then heated at low temperatures in a conversion stage to convert the salts to oxides.

[0043] The method according to the present invention produces magnesium oxide with high purity and low chloride content, which is suitable for use as a neutralizing agent in a fermentation process for the production of carboxylic acids. Therefore, the present invention also relates to a method for producing carboxylic acids through fermentation using magnesium oxide obtained through the method according to the present invention. The present invention also relates to an integrated process comprising a fermentation step, a separation step, and a step for converting a magnesium chloride solution to high-purity magnesium oxide and feeding the magnesium oxide as a neutralizing agent to a fermentation medium directly or after conversion to magnesium hydroxide. These embodiments will be explained in more detail below.

[0044] In one embodiment, the present invention provides a method for producing a carboxylic acid, comprising: 1. Converting magnesium chloride to magnesium oxide by a process comprising the steps of: subjecting a magnesium chloride solution to a spray-drying step in a spray dryer at a temperature of 300-475°C, preferably 350-450°C, resulting in the formation of a spray-dried product comprising 10-80% by weight, in particular 30-80% by weight, of magnesium oxide and 20-90% by weight, in particular 20-70% by weight, of a sum of magnesium hydroxychloride and magnesium chloride; and subjecting the product of the spray-drying step to a roasting step in a roaster at a temperature of 600-900°C in the presence of water, resulting in the formation of a magnesium oxide product comprising at least 98% by weight of MgO and less than 2% by weight of a sum of magnesium hydroxychloride and magnesium chloride (percentages calculated as defined above); feeding the magnesium oxide product, which contains at least 98% by weight of MgO and less than 2% of the sum of magnesium hydroxychloride and magnesium chloride (percentages calculated as defined above), either as such or after a step of converting the magnesium oxide product to magnesium hydroxide by reacting it with water, as a neutralizing agent to a fermentation process, which comprises fermenting a carbon source by a microorganism in a fermentation medium to form a carboxylic acid, which is at least partially converted by the neutralizing agent, resulting in the formation of a magnesium carboxylate salt. The method further comprises the steps of:

[0045] The amount of magnesium base added during the fermentation process is generally between 0.1 and 4 moles of magnesium base per mole of carboxylic acid, more particularly between 0.2 and 2 moles of magnesium base per mole of carboxylic acid.

[0046] As indicated above, the product magnesium oxide obtained by the process according to the present invention can be used as is. It can also be used after conversion to magnesium hydroxide by reaction with water. The step of converting magnesium oxide to magnesium hydroxide through reaction with water can be carried out by methods known in the art.

[0047] Thus, the above-described method produces a fermentation medium containing magnesium carboxylate. The method according to the present invention also includes: subjecting the magnesium carboxylate to an acidification step, wherein the magnesium carboxylate is contacted with HCl in an aqueous environment to form an aqueous mixture comprising a carboxylic acid and magnesium chloride; subjecting said aqueous mixture containing carboxylic acid and magnesium chloride to a separation step to form an effluent containing carboxylic acid and an aqueous magnesium chloride solution. may include the further step of:

[0048] The magnesium chloride solution obtained from the separation step can be fed to the method according to the present invention. However, the magnesium chloride aqueous solution obtained from the separation step will generally have a relatively low concentration. Therefore, it may be preferable to subject the magnesium chloride aqueous solution obtained from the separation step to one or more concentration steps in which water is evaporated to obtain a more concentrated solution, which is then fed to the spray-drying step. In one embodiment, an aqueous magnesium chloride solution having a magnesium chloride concentration of 10 to 30% by weight is subjected to a concentration step in which water is evaporated to obtain a concentrated magnesium chloride solution having a magnesium chloride concentration of 15 to 48% by weight, particularly 35 to 47% by weight, which is then fed to the spray-drying step.

[0049] The one or more concentration steps can be carried out by methods known in the art, which do not require further explanation here.

[0050] As described above, an HCl-containing gas stream is recovered from the spray-drying process and the roasting process. In one embodiment, at least a portion of the HCl from one or both of these units is supplied to the acidification process, where a magnesium carboxylate is contacted with HCl in an aqueous environment to form an aqueous mixture containing a carboxylic acid and magnesium chloride. The HCl can be supplied to the acidification process in gaseous form. However, it is also possible to absorb HCl from the HCl-containing gas stream into water to form an aqueous HCl solution, and then supply the aqueous HCl solution to the acidification process.

[0051] The various steps in the integrated process, additional to the treatment of the magnesium chloride solution, will be described below.

[0052] In a first step, a carbon source is subjected to a fermentation process to form a carboxylic acid, wherein the fermentation process comprises fermenting the carbon source by a microorganism in a fermentation broth to form a carboxylic acid, and neutralizing at least a portion of the carboxylic acid by adding a magnesium base selected from magnesium oxide and magnesium hydroxide, thereby obtaining a magnesium carboxylate.

[0053] Fermentation processes for the production of carboxylic acids are known in the art and do not require further explanation herein. It is within the skill of the art to select a suitable fermentation process using common general knowledge depending on the desired acid to be produced, the carbon source and the available microorganisms.

[0054] The product of the fermentation process is a fermentation broth, which is an aqueous liquid containing magnesium carbonate, biomass, and optionally further components such as impurities such as sugars, proteins, and salts.

[0055] If desired, the fermentation broth can be subjected to a biomass removal step, such as a filtration step, before further processing. This is generally preferred to improve product quality. Depending on the carboxylic acids produced, another intermediate step can be separation of the solid reaction product, e.g., magnesium carboxylate, from the fermentation broth before, after, or simultaneously with biomass removal, and optionally subjecting the magnesium carboxylate to a washing step.

[0056] Depending on the carboxylic acids produced, another intermediate step may be to subject the fermentation broth to a concentration step to increase the concentration of magnesium carboxylates in the composition prior to acidification, which may be carried out before, after, or simultaneously with biomass removal.

[0057] Other intermediate steps, such as purification steps, can be carried out as desired, as will be apparent to those skilled in the art.

[0058] The next step in the integrated process according to the present invention is subjecting the magnesium carboxylate to an acidification step (sometimes referred to as the acidification step), in which the magnesium carboxylate is contacted with HCl in an aqueous environment to form an aqueous mixture comprising a carboxylic acid and magnesium chloride.

[0059] There are various ways in which this process can be accomplished.

[0060] The acidification step is typically carried out by contacting the carboxylate salt with an acidic HCl solution, however, in some embodiments, it may also be possible to contact the carboxylate salt with gaseous HCl.

[0061] The carboxylate salt can be in solid form and / or dissolved form. In one embodiment, the carboxylate salt is prepared in solid form. In this case, the acidification step is carried out by contacting the carboxylate salt with an acidic solution. Therefore, the advantage of preparing the aqueous mixture from the carboxylate salt in solid form is that a very high carboxylic acid concentration can be obtained, for example, at least 15% by weight, particularly at least 25%, for example, up to 50% by weight, or for example, up to 40% by weight.

[0062] The carboxylate salt may also be in dissolved form, typically as part of an aqueous solution, in which case the acidification step may be carried out by contacting the carboxylate salt with an acidic solution or an acidic gas.

[0063] The acidification step can also be carried out on a mixture of carboxylic acids and carboxylate salts. Such a mixture can be obtained, for example, in a low pH fermentation. The mixture can be, for example, an aqueous suspension.

[0064] When the carboxylate salt is acidified by contacting it with an acidic HCl solution, it preferably has as high an acid concentration as possible. Such a high acid concentration results in an aqueous mixture with a high carboxylic acid concentration, which is desirable. Therefore, the acid solution contains at least 5 wt. %, more preferably at least 10 wt. %, and even more preferably at least 20 wt. % of acid, based on the total weight of the acid solution.

[0065] Acidification is typically carried out using an excess of acid. The excess is preferably small so that the resulting aqueous mixture is not highly acidic, which may be undesirable in terms of further processing such a mixture. For example, the excess of acid used may be such that the resulting aqueous mixture has a pH of 2 or less, preferably a pH of 0 to 1.

[0066] When gaseous HCl is used, the gaseous HCl can be contacted by contacting the gaseous HCl with a carboxylate solution or suspension. In particular, the HCl gas can be bubbled through the solution or suspension.

[0067] Preferably, acidification is carried out at a temperature below 75° C. At higher temperatures, it becomes uneconomical to adapt the equipment to the harsh conditions of an acidic environment at high temperatures.

[0068] The acidification step results in the formation of an aqueous liquid comprising carboxylic acid and magnesium chloride, which is subjected to a separation step, optionally after intermediate processing steps have been carried out, such as a concentration step.

[0069] Suitable separation processes are known in the art, and the nature of the process used will depend on the nature and properties of the acid.

[0070] If the carboxylic acid is present in whole or in part as a solid in the aqueous liquid, separation can occur using conventional solid-liquid separation methods such as filtration, centrifugation, and the like.

[0071] If the carboxylic acid is present in whole or in part as a separate organic phase in the aqueous liquid, separation can occur using conventional liquid-liquid separation methods, such as decantation, settling, centrifugation, plate separators, coalescers, and hydrocyclones. To improve separation efficiency, an extraction solvent can be added. Combinations of different methods and devices can also be used.

[0072] If the carboxylic acid is present dissolved in the aqueous liquid, separation can occur using, for example, extraction with a suitable extraction solvent.

[0073] When an extractant is present in the process according to the invention, the extractant (which may also be referred to as an extractant) is substantially immiscible with water. The use of an extractant results in the formation of a two-phase system during the separation step, comprising a liquid organic layer containing the extractant and carboxylic acid, and an aqueous layer containing dissolved magnesium chloride.

[0074] Examples of suitable extractants are aliphatic and aromatic hydrocarbons, such as alkanes and aromatic compounds, ketones, and ethers. Mixtures of various compounds may also be used.

[0075] Examples of suitable aliphatic alkanes are C5 to C10 linear, branched, or cyclic alkanes, such as octane, hexane, cyclohexane, 2-ethyl-hexane, and heptane.

[0076] Examples of suitable aromatic compounds are C6-C10 aromatic compounds such as toluene, xylene and ethylbenzene.

[0077] Examples of suitable ketones in the present invention are C5+ ketones, more particularly C5-C8 ketones. C5+ denotes a ketone having at least 5 carbon atoms. The use of C9+ ketones is less preferred. The use of methyl-isobutyl-ketone (MIBK) has been found to be particularly attractive.

[0078] Examples of suitable ethers are C3-C6 ethers, such as methyl tert-butyl ether (MTBE) and diethyl ether (DEE).

[0079] After extraction, the carboxylic acids can be separated from the extraction solvent, if desired. In one embodiment, this can be done by removing the extraction solvent by evaporation. In another embodiment, the carboxylic acids can be recovered from the extraction solvent by extraction with water or another aqueous liquid.

[0080] After separating the carboxylic acid from the salt, the carboxylic acid can be processed as desired. Examples of further processing steps include purification steps such as washing, activated carbon treatment, recrystallization, distillation, and filtration. If the carboxylic acid is lactic acid, it can be converted into lactide and PLA.

[0081] Accordingly, the present invention also provides a method for producing a carboxylic acid, comprising the steps of: subjecting a carbon source to a fermentation process to form a carboxylic acid, the fermentation process comprising fermenting the carbon source with a microorganism in a fermentation broth to form a carboxylic acid, and neutralizing at least a portion of the carboxylic acid by adding a magnesium base selected from magnesium oxide and magnesium hydroxide, thereby obtaining a magnesium carboxylate; subjecting the magnesium carboxylate to an acidification step, wherein the magnesium carboxylate is contacted with HCl in an aqueous environment to form an aqueous mixture comprising a carboxylic acid and magnesium chloride; subjecting said aqueous mixture comprising carboxylic acid and magnesium chloride to a separation step to provide a carboxylic acid and a magnesium chloride solution separated therefrom; subjecting the magnesium chloride solution to a spray drying step at a temperature of 300 to 475°C, resulting in the formation of a spray dried product comprising 10 to 80% by weight of magnesium oxide and 20 to 90% by weight of the sum of magnesium hydroxychloride and magnesium chloride; subjecting the product of the spray drying step to a roasting step in the presence of water in a roaster at a temperature of 600-900°C, resulting in the formation of a product comprising at least 98% by weight of MgO and less than 2% by weight of the sum of magnesium hydroxychloride and magnesium chloride, wherein the percentages of MgO, magnesium hydroxychloride and magnesium chloride are calculated as the sum of MgO, magnesium hydroxychloride and magnesium chloride; The method further comprises the steps of:

[0082] As will be apparent to one skilled in the art, the additional steps and embodiments described herein also apply to this method.

[0083] The nature of the carboxylic acid produced is not critical to the integrated process according to the present invention.

[0084] In one embodiment, the carboxylic acid is a monotricarboxylic acid, ditricarboxylic acid, or tricarboxylic acid containing at least two but not more than eight carbon atoms (C2-C8 carboxylic acid). In one embodiment, the carboxylic acid is selected from the group consisting of lactic acid, succinic acid, propionic acid, 3-hydroxypropionic acid, 2-hydroxybutyric acid, 3-hydroxybutyric acid, and 4-hydroxybutyric acid, citric acid, fumaric acid, itaconic acid, adipic acid, acrylic acid, levulinic acid, maleic acid, 2,5-furandicarboxylic acid, mandelic acid, malic acid, and tartaric acid. Preferably, the carboxylic acid is selected from the group consisting of lactic acid, succinic acid, propionic acid, 3-hydroxypropionic acid, 2-hydroxybutyric acid, 3-hydroxybutyric acid, and 4-hydroxybutyric acid, and citric acid.

[0085] In one embodiment, the carboxylic acid is selected from monocarboxylic acids having 2 to 6 carbon atoms. In one embodiment, the monocarboxylic acid having 2 to 6 carbon atoms does not contain a hydroxyl group. Within this group, examples of suitable acids are propionic acid, acrylic acid, butyric acid, and valeric acid.

[0086] In another embodiment, the monocarboxylic acid contains at least one hydroxyl group. Within this group, in one embodiment, it may be preferable to select the acid from the group consisting of lactic acid, glycolic acid, 3-hydroxypropionic acid, 2-hydroxybutyric acid, 3-hydroxybutyric acid, and 4-hydroxybutyric acid. Within this group, it may be preferable to select the acid from the group consisting of glycolic acid, 3-hydroxypropionic acid, and 2-hydroxybutyric acid, 3-hydroxybutyric acid, and 4-hydroxybutyric acid. In a further embodiment, it may be preferable that the acid is lactic acid.

[0087] In another embodiment, the carboxylic acid is a polycarboxylic acid, more particularly a di- or tricarboxylic acid containing at least two but not more than six carbon atoms (C2-6 carboxylic acid). In one embodiment, the polycarboxylic acid is selected from the group consisting of succinic acid, citric acid, fumaric acid, itaconic acid, adipic acid, maleic acid, 2,5-furandicarboxylic acid, malic acid, and tartaric acid. Preferably, the polycarboxylic acid is selected from the group consisting of succinic acid, citric acid, fumaric acid, itaconic acid, adipic acid, and 2,5-furandicarboxylic acid. The polycarboxylic acid may be selected from succinic acid, fumaric acid, itaconic acid, and 2,5-furandicarboxylic acid in particular.

[0088] Various aspects of the present invention are illustrated by, but not limited to, the figures described below.

[0089] FIG. 1 illustrates a process according to the present invention. In FIG. 1, a magnesium chloride solution is fed to a spray-drying apparatus (2) via line (1). A hot gas stream is fed via line (3), and an HCl-containing gas stream is removed via line (4). In the spray-drying apparatus, the magnesium chloride solution is converted to a spray-dried product containing 10-80% by weight, particularly 30-80% by weight, of magnesium oxide and 20-90% by weight, particularly 20-70% by weight, of magnesium hydroxychloride and magnesium chloride combined. The spray-dried product is removed from the spray-drying apparatus via line (5) and fed to a roaster (6). A hot gas stream is fed to the roaster (6) via line (7), and an HCl-containing gas stream is removed via line (8). If desired, the HCl-containing gas removed from the roaster (6) via line (8) can be partially or completely fed to the spray-drying apparatus (2).

[0090] The product from the roaster, comprising at least 98% by weight magnesium oxide and less than 2% by weight magnesium hydroxychloride and magnesium chloride combined, is removed via line (9).

[0091] Figure 2 shows the combination of the method according to the present invention shown in Figure 1 with a fermentation process. In Figure 2, the magnesium oxide product removed from the roaster through line (9) is fed to a fermentation unit (10). This can be done directly or after conversion of the magnesium oxide product to magnesium hydroxide by reaction with water in a unit not shown. The fermentation unit (10) is fed with a carbon source and, optionally, further components, such as nutrients, through lines not shown. In the fermentation process in the fermentation unit (10), the carbon source is fermented by microorganisms in a fermentation broth to form carboxylic acids. At least a portion of the carboxylic acids is neutralized with the magnesium base, the magnesium product obtained from the roaster, either directly or after conversion to magnesium hydroxide. The fermentation process in the presence of a magnesium base results in a fermentation medium containing magnesium carboxylate, which is removed from the fermentation unit (10) through line (11).

[0092] FIG. 3 shows a further integrated process according to the invention, based on the method shown in FIG. 2. In the process of FIG. 3, the fermentation medium containing magnesium carboxylate salts is fed to an acidification step (12) via line (11). Intermediate steps, such as biomass removal or concentration, can be performed but are not shown. In the acidification step (12), the magnesium carboxylate is contacted with HCl in an aqueous environment to form an aqueous mixture containing carboxylic acid and magnesium chloride. The HCl is fed via line (13). In the diagram, the HCl fed via line (13) is a combination of HCl obtained from the spray dryer (1) via line (4) and HCl obtained from the roaster (6) via line (8). It will be apparent that it is also possible to use only one of these streams or to feed the streams separately to the acidification step (12). The HCl can be fed in the form of an HCl-containing gas stream obtained directly from the spray dryer (1) and / or the roaster (6). It may also be provided in the form of an aqueous solution obtained by absorbing the HCl-containing gas stream into an aqueous liquid (e.g., water), which occurs in an absorption step (not shown).

[0093] The aqueous mixture containing carboxylic acid and magnesium chloride is fed via line (14) to a separation step (15), which may be carried out as described above. Separation step (15) results in an effluent containing carboxylic acid and a magnesium chloride solution. The product carboxylic acid is removed via line (16). The magnesium chloride solution is removed via line (1) and fed to the spray dryer, as described above in the context of FIG. 1.

[0094] As will be apparent to one skilled in the art, only a portion of the HCl produced in the spray dryer or roaster can be fed to the acidification step and / or HCl can be fed from other sources. Similarly, it will be apparent that only a portion of the magnesium oxide product produced in the roaster can be fed to the fermentation step.

[0095] It will be clear to the skilled person that in the method according to the invention, preferred embodiments of the various steps can be combined, except where they are mutually exclusive.

[0096] The present invention is further illustrated by, but not limited to, the following examples.

[0097] Example 1: Method according to the invention A 37-43 wt % magnesium chloride solution was fed into a spray dryer and spray dried at a temperature of 350-420° C. The product from the spray drying process contained 50 wt % magnesium oxide and 50 wt % magnesium chloride and magnesium hydroxychloride in total.

[0098] The product from the spray drying step was subjected to a roasting step at 800°C for 30 minutes to yield a product containing 99.2 wt% magnesium oxide and 0.8 wt% combined magnesium chloride and magnesium hydroxychloride, calculated on total solid product.

[0099] Example 2: Comparative Example Method A 37-43 wt% magnesium chloride solution was fed into a spray dryer and spray dried at a temperature of 500°C. The product from the spray drying process contained 97 wt% magnesium oxide and 3 wt% magnesium chloride and magnesium hydroxychloride in total. Therefore, this product did not have the required purity.

[0100] In order to obtain a magnesium oxide product with the required purity of at least 98% by weight, it was found necessary to carry out a roasting step at 800°C for 30 minutes, resulting in a product containing 99.2% by weight of magnesium oxide and 0.8% by weight of magnesium chloride and magnesium hydroxychloride combined.

[0101] Thus, a comparison of Example 1 and Example 2 according to the present invention shows that spray drying at 500°C is insufficient to obtain the desired purity, and that the combination of spray drying and roasting with a given conversion in the spray drying step allows the use of lower temperatures in the spray drying step, and therefore lower energy consumption. The present invention may be configured as follows. [Section 1] 1. A process for converting magnesium chloride to magnesium oxide, comprising: subjecting the magnesium chloride solution to a spray drying step at a temperature of 300-475°C resulting in the formation of a spray dried product comprising 10-80% by weight of magnesium oxide and 20-90% by weight of the sum of magnesium hydroxychloride and magnesium chloride; subjecting the product of the spray drying step to a roasting step in the presence of water in a roaster at a temperature of 600-900°C, resulting in the formation of a product comprising at least 98% by weight of MgO and less than 2% by weight of the sum of magnesium hydroxychloride and magnesium chloride, wherein the percentages of MgO, magnesium hydroxychloride and magnesium chloride are calculated as the sum of MgO, magnesium hydroxychloride and magnesium chloride; The method. [Section 2] Item 1. The method according to Item 1, wherein the first step is a step of subjecting a magnesium chloride solution to a spray-drying process at a temperature of 350 to 450°C in a spray-drying apparatus to form a spray-dried product containing 30 to 80% by weight of magnesium oxide and 20 to 70% by weight in total of magnesium hydroxychloride and magnesium chloride. [Section 3] Item 3. The method according to Item 1 or 2, wherein the magnesium chloride solution to be subjected to the spray-drying step has a magnesium chloride concentration of 5 to 48% by weight, preferably 15 to 48% by weight, particularly 18 to 48% by weight, more particularly 23 to 48% by weight, even more particularly 30 to 48% by weight, and even more particularly 35 to 47% by weight. [Section 4] Item 4. The method according to any one of Items 1 to 3, wherein the spray drying is carried out at a temperature of 375 to 450°C, particularly 375 to 420°C. [Section 5] 5. The method of any one of items 1 to 4, wherein the product from the spray drying step comprises 40 to 80 wt. % magnesium oxide and 20 to 60 wt. % of the sum of magnesium hydroxychloride and magnesium chloride, particularly 45 to 75 wt. % magnesium oxide and 25 to 55 wt. % of the sum of magnesium hydroxychloride and magnesium chloride, more particularly 50 to 70 wt. % magnesium oxide and 30 to 50 wt. % of the sum of magnesium hydroxychloride and magnesium chloride, and even more particularly 55 to 70 wt. % magnesium oxide and 45 to 30 wt. % of the sum of magnesium hydroxychloride and magnesium chloride, all calculated based on total solids content. [Section 6] Item 6. The method according to any one of Items 1 to 5, wherein the temperature in the roaster is 700°C to 850°C, particularly 750°C to 850°C. [Section 7] 7. The method according to any one of items 1 to 6, wherein the product from the roasting step comprises, calculated as the sum of MgO, magnesium hydroxychloride, and magnesium chloride, at least 98.5 wt% MgO and less than 1.5 wt% sum of magnesium hydroxychloride and magnesium chloride, or even at least 99 wt% MgO and less than 1 wt% sum of magnesium hydroxychloride and magnesium chloride, and the product from the roasting step comprises, calculated as the total solids content, at least 98 wt% MgO and less than 2 wt% sum of magnesium hydroxychloride and magnesium chloride, preferably at least 98.5 wt% MgO and less than 1.5 wt% sum of magnesium hydroxychloride and magnesium chloride, or at least 99 wt% MgO and less than 1 wt% sum of magnesium hydroxychloride and magnesium chloride. [Section 8] A magnesium oxide product characterized by the following parameters: The magnesium oxide product comprises at least 98 wt.% MgO and less than 2 wt.% of the sum of magnesium hydroxychloride and magnesium chloride, particularly at least 98.5 wt.% MgO and less than 1.5 wt.% of the sum of magnesium hydroxychloride and magnesium chloride, more particularly at least 99 wt.% MgO and less than 1 wt.% of the sum of magnesium hydroxychloride and magnesium chloride, calculated on total solids product. the magnesium oxide product has a D50 of 0.5 to 20 microns, particularly 2 to 10 microns; The magnesium oxide product has a citric acid reactivity of 75 to 400 seconds, preferably 100 to 350 seconds, specifically 150 to 300 seconds. [Section 9] A method for producing a carboxylic acid, comprising providing, as a neutralizing agent in a fermentation process, the magnesium oxide according to Item 8, or the magnesium oxide obtainable by the method according to any one of Items 1 to 7, or the magnesium oxide obtained by the method according to any one of Items 1 to 7, either as such or after a step of converting the magnesium oxide product into magnesium hydroxide by reacting it with water, wherein the fermentation step comprises fermenting a carbon source by a microorganism in a fermentation medium to form a carboxylic acid, and the carboxylic acid is at least partially converted by the neutralizing agent, resulting in the formation of a magnesium carboxylate salt. [Section 10] subjecting the magnesium carboxylate to an acidification step, wherein the magnesium carboxylate is contacted with HCl in an aqueous environment to form an aqueous mixture comprising a carboxylic acid and magnesium chloride; subjecting said aqueous mixture containing carboxylic acid and magnesium chloride to a separation step to form an effluent containing carboxylic acid and an aqueous magnesium chloride solution. Item 10. The method according to Item 9, further comprising the step of: [Section 11] Item 11. The method according to item 10, wherein after the separation step, the carboxylic acid is subjected to a purification step, for example, a purification step selected from washing, activated carbon treatment, recrystallization, distillation, and filtration. [Section 12] Item 12. The method of item 10 or 11, wherein a biomass removal step is performed between the fermentation step and the acidification step. [Section 13] Item 13. The method according to any one of Items 10 to 12, wherein at least a portion of the HCl produced in one or more of the spray drying step and the roasting step is provided to the acidifying step. [Section 14] Item 14. The method according to any one of items 1 to 13, wherein the carboxylic acid is a monocarboxylic acid, dicarboxylic acid or tricarboxylic acid containing at least 2 but not more than 8 carbon atoms, in particular selected from lactic acid, succinic acid, 2,5-furandicarboxylic acid. [Section 15] The carboxylic acid is lactic acid, which is then converted to lactide or polylactide. 15. The method according to any one of Items 10 to 14, wherein [Section 16] 1. A method for producing a carboxylic acid, comprising: subjecting a carbon source to a fermentation process to form a carboxylic acid, the fermentation process comprising fermenting the carbon source with a microorganism in a fermentation broth to form a carboxylic acid, and neutralizing at least a portion of the carboxylic acid by adding a magnesium base selected from magnesium oxide and magnesium hydroxide, thereby obtaining a magnesium carboxylate; subjecting the magnesium carboxylate to an acidification step, wherein the magnesium carboxylate is contacted with HCl in an aqueous environment to form an aqueous mixture comprising a carboxylic acid and magnesium chloride; subjecting said aqueous mixture comprising carboxylic acid and magnesium chloride to a separation step to provide a carboxylic acid and a magnesium chloride solution separated therefrom; subjecting the magnesium chloride solution to a spray drying step at a temperature of 300 to 475°C, resulting in the formation of a spray dried product comprising 10 to 80% by weight of magnesium oxide and 20 to 90% by weight of the sum of magnesium hydroxychloride and magnesium chloride; subjecting the product of the spray drying step to a roasting step in the presence of water in a roaster at a temperature of 600-900°C, resulting in the formation of a product comprising at least 98% by weight of MgO and less than 2% by weight of the sum of magnesium hydroxychloride and magnesium chloride, wherein the percentages of MgO, magnesium hydroxychloride and magnesium chloride are calculated as the sum of MgO, magnesium hydroxychloride and magnesium chloride; The method, comprising the steps of:

Claims

1. 1. A process for converting magnesium chloride to magnesium oxide, comprising: subjecting the magnesium chloride solution to a spray drying step at a temperature of from 300 to 475°C resulting in the formation of a spray dried product comprising 10 to 80% by weight of magnesium oxide and 20 to 90% by weight of the sum of magnesium hydroxychloride and magnesium chloride; subjecting the product of the spray drying step to a roasting step in the presence of water at a temperature of 600-900°C in a roaster to result in the formation of a product comprising at least 98% by weight of MgO and less than 2% by weight of the sum of magnesium hydroxychloride and magnesium chloride, wherein the percentages of MgO, magnesium hydroxychloride and magnesium chloride are calculated as the sum of MgO, magnesium hydroxychloride and magnesium chloride; The method.

2. 2. The method of claim 1, wherein the first step is to subject the magnesium chloride solution to a spray drying process in a spray dryer at a temperature of 350-450°C, resulting in the formation of a spray-dried product comprising 30-80% by weight of magnesium oxide and 20-70% by weight of magnesium hydroxychloride and magnesium chloride combined.

3. 3. The method according to claim 1 or 2, wherein the magnesium chloride solution subjected to the spray drying step has a magnesium chloride concentration of 5 to 48% by weight.

4. The method according to any one of claims 1 to 3, wherein the spray drying is carried out at a temperature of from 375 to 450°C.

5. 5. The method of any one of claims 1 to 4, wherein the product from the spray drying step comprises 40 to 80 wt. % magnesium oxide and 20 to 60 wt. % of the sum of magnesium hydroxychloride and magnesium chloride, all calculated on total solids content.

6. The method of any one of claims 1 to 5, wherein the temperature in the roaster is from 700°C to 850°C.

7. 7. The method of any one of claims 1 to 6, wherein the product from the roasting step comprises at least 98.5 wt. % MgO and less than 1.5 wt. % of the sum of magnesium hydroxychloride and magnesium chloride, calculated as the sum of MgO, magnesium hydroxychloride and magnesium chloride.

8. 8. A method for producing carboxylic acids, comprising the step of feeding magnesium oxide obtained by the method according to any one of claims 1 to 7, either as such or after a step of converting said magnesium oxide product to magnesium hydroxide by reacting said magnesium oxide product with water, to a fermentation step as a neutralizing agent, wherein said fermentation step comprises fermenting a carbon source by a microorganism in a fermentation medium to form carboxylic acids, which are at least partially converted by said neutralizing agent, resulting in the formation of magnesium carboxylate salts.

9. subjecting the magnesium carboxylate to an acidification step, wherein the magnesium carboxylate is contacted with HCl in an aqueous environment to form an aqueous mixture comprising a carboxylic acid and magnesium chloride; subjecting said aqueous mixture containing carboxylic acid and magnesium chloride to a separation step to form an effluent containing carboxylic acid and an aqueous magnesium chloride solution. The method of claim 8 further comprising the step of:

10. 10. The method of claim 9, wherein after the separation step, the carboxylic acid is subjected to a purification step selected from washing, activated carbon treatment, recrystallization, distillation, and filtration.

11. 11. The method of claim 9 or 10, wherein a biomass removal step is performed between the fermentation step and the acidification step.

12. 12. The method of any one of claims 8 to 11, wherein the carboxylic acid is a monocarboxylic, dicarboxylic or tricarboxylic acid containing at least 2 but not more than 8 carbon atoms.

13. The method of claim 12, wherein the carboxylic acid is selected from lactic acid, succinic acid, and 2,5-furandicarboxylic acid.

14. 14. The method of claim 13, wherein the carboxylic acid is lactic acid, which is then converted to lactide or polylactide.

15. 1. A method for producing a carboxylic acid, comprising: subjecting a carbon source to a fermentation process to form a carboxylic acid, the fermentation process comprising fermenting the carbon source with a microorganism in a fermentation broth to form a carboxylic acid, and neutralizing at least a portion of the carboxylic acid by adding a magnesium base selected from magnesium oxide and magnesium hydroxide, thereby obtaining a magnesium carboxylate; subjecting the magnesium carboxylate to an acidification step, wherein the magnesium carboxylate is contacted with HCl in an aqueous environment to form an aqueous mixture comprising a carboxylic acid and magnesium chloride; subjecting said aqueous mixture comprising carboxylic acid and magnesium chloride to a separation step to provide a carboxylic acid and a magnesium chloride solution separated therefrom; subjecting the magnesium chloride solution to a spray drying step at a temperature of from 300 to 475°C resulting in the formation of a spray dried product comprising 10 to 80% by weight of magnesium oxide and 20 to 90% by weight of the sum of magnesium hydroxychloride and magnesium chloride; subjecting the product of the spray drying step to a roasting step in the presence of water at a temperature of 600-900°C in a roaster to result in the formation of a product comprising at least 98% by weight of MgO and less than 2% by weight of the sum of magnesium hydroxychloride and magnesium chloride, wherein the percentages of MgO, magnesium hydroxychloride and magnesium chloride are calculated as the sum of MgO, magnesium hydroxychloride and magnesium chloride; The method, comprising the steps of:

16. The method of claim 15, wherein at least a portion of the HCl produced in one or more of the spray drying and roasting steps is supplied to the acidification step.

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