Method for preparing high-purity magnesium oxide

Abstract

The present invention relates to a method for converting magnesium chloride into magnesium oxide, comprising the following steps: - subjecting a magnesium chloride solution to a spray drying step in a spray drying device at a temperature of 300-475°C, thereby forming a spray-dried product containing 10-80wt.% of magnesium oxide and a total amount of 20-90wt.% of hydroxymagnesium chloride and magnesium chloride; - subjecting the product of the spray drying step to a roasting step in a roasting furnace at a temperature of 600-900°C in the presence of water, thereby forming a product containing at least 98wt.% of MgO and a total amount of less than 2wt.% of hydroxymagnesium chloride and magnesium chloride, wherein the percentages of MgO, hydroxymagnesium chloride and magnesium chloride are calculated based on the total amount of MgO, hydroxymagnesium chloride and magnesium chloride. Preferably, the product of the method of the present invention contains at least 98wt.% of MgO, and a total amount of less than 2wt.% of hydroxymagnesium chloride and magnesium chloride, calculated based on the solid product. The present invention also relates to a high-purity magnesium oxide product obtainable by the method according to the present invention.

Description

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

[0002] Methods for preparing carboxylic acids by fermentation are known in the art. In these methods, a base is usually added to keep the pH of the fermentation medium at a desired value. This results in the carboxylic acid being obtained in the form of a salt, such as a magnesium salt. After the carboxylic acid is recovered, a salt solution, such as a magnesium salt solution, is obtained, which requires further treatment. Preferably, the salt solution is treated to form a material suitable for recycling to an earlier step of the fermentation. In particular, it is preferred to treat the salt solution to form a base that can be used to control the pH in the fermentation.

[0003] For example, WO00 / 17378 describes a process for the preparation of lactic acid, wherein a magnesium lactate solution is prepared during a fermentation process. The magnesium lactate solution is acidified with HCl to obtain 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 treated by subjecting it to a thermal hydrolysis step at a temperature of at least 500° C., reacting the magnesium chloride with water to obtain magnesium oxide powder and hydrochloric acid. The heat required for the thermal hydrolysis reaction is provided by in situ combustion of a fuel.

[0004] WO2013 / 025106 describes a method for preparing a carboxylic acid by a process comprising acidifying a magnesium salt of a carboxylic acid with HCl to form an acid and a magnesium chloride solution, and separating the acid from the solution by precipitation. This indicates that the magnesium chloride solution can be treated by thermal decomposition.

[0005] WO2013 / 093028 describes a method for preparing a carboxylic acid by a process comprising acidifying a magnesium salt of a carboxylic acid with HCl to form an acid and a magnesium chloride solution, and separating the acid from the solution by extraction followed by stripping. This indicates that the magnesium chloride solution can be treated by thermal decomposition.

[0006] In the above cited references, a magnesium chloride solution is treated by providing the solution to a thermal decomposition step, wherein the magnesium chloride reacts with water in the solution to form solid magnesium oxide and a gas stream comprising water and HCl.

[0007] One problem with the thermal decomposition processes described in these references is that the magnesium oxide recovered from the spray drying step may not be of sufficient purity to be recycled directly to the fermentation process or to be recycled to the fermentation process after it has been converted to magnesium hydroxide. More specifically, it has been found that the chloride content in the magnesium oxide may be so high that the chloride has a deleterious effect on the fermentation process. For example, it has been found that when a magnesium chloride solution is subjected to a spray drying step in a spray drying apparatus at a temperature of 500-600°, a product having a magnesium oxide content of 97 wt.% is formed, the remainder being magnesium chloride and magnesium hydroxychloride. In this case, it should be noted that during the fermentation process, magnesium oxide (or its derivative magnesium hydroxide) is added to the process in an amount of approximately one mole of magnesium per mole of carboxylic acid. This means that even if there are small amounts of contaminants in the magnesium oxide, they will eventually enter the fermentation medium in large quantities.

[0008] Therefore, there is a need in the art for a method for preparing high-purity magnesium oxide from a magnesium chloride solution. The present invention provides such a method.

[0009] The present invention relates to a method for converting magnesium chloride into magnesium oxide, comprising the following steps

[0010] - subjecting the magnesium chloride solution to a spray drying step in a spray drying apparatus at a temperature in the range of 300-475° C., thereby forming a spray dried product comprising 10-80 wt. % of magnesium oxide and 20-90 wt. % of the total amount of magnesium hydroxychloride and magnesium chloride,

[0011] - subjecting the product of the spray drying step to a calcination step in a calcination furnace at a temperature of 600-900° C. in the presence of water, thereby forming a product containing at least 98 wt.% of MgO and less than 2 wt.% of the total amount of magnesium hydroxychloride and magnesium chloride, wherein the percentages of MgO, magnesium hydroxychloride and magnesium chloride are calculated based on the total amount of these three compounds.

[0012] It has been found that combining a relatively mild spray drying step with a high temperature calcination step can effectively obtain high purity magnesium oxide. Further advantages of the present invention and its specific embodiments will become apparent from the further description.

[0013] More specifically, it has been found that, according to the process of the present invention, a spray drying temperature of 300-475°C, followed by calcination at a temperature of 600-900°C, results in the formation of a product containing at least 98 wt.% of MgO and less than 2 wt.% of the total amount of magnesium hydroxychloride and magnesium chloride, wherein the percentages of MgO, magnesium hydroxychloride and magnesium chloride are calculated on the basis of the total amount of these three compounds. When the product of the spray drying step carried out at a temperature of 500-600°C (which therefore has a lower chloride content) is subjected to a calcination step under the same conditions, a magnesium oxide product having the same chloride content is obtained. Apparently, surprisingly, the product obtained by spray drying at 300-475°C can be converted into high purity MgO under the same conditions as the product obtained by spray drying at 500-600°C, despite its higher chloride content. In the process of the present invention, the product of the spray drying step is directly provided to the calcination step without any intermediate steps, such as washing or rehydration steps.

[0014] It is noteworthy that the production of high-purity magnesium oxide is also described outside the context of fermentation processes. For example, CN110015671 describes a method for preparing high-purity magnesium oxide, wherein bischofite (MgCl2·6H2O) is dehydrated at 650-750°C by spray drying of a bischofite solution to form anhydrous magnesium chloride, which is then reacted with water in a rotary kiln to form magnesium oxide. Therefore, in this reference, the spray drying step is carried out at a temperature much higher than the temperature in the method according to the present invention, and is used to prepare anhydrous magnesium chloride, rather than partially converting the magnesium chloride into a product containing a specific amount of magnesium oxide and magnesium chloride (hydrogen). CN100417596 describes a method for preparing high-purity magnesium oxide, wherein magnesium chloride hydrate is subjected to a pyrolysis step of 0.5-3 hours in a sealed pyrolysis furnace at a temperature of 400-600°C. The product undergoes a water washing step to remove aqueous impurities. In this step, MgO is converted into Mg(OH)2. After the solid-liquid separation step, the product is subjected to a calcination step at a temperature of 500-700°C for 1.5-3.5 hours.

[0015] This approach is discussed in more detail below.

[0016] In the following, reference is made to the following drawings, but the present invention is not limited thereto or thereby.

[0017] Figure 1 A method according to the invention is shown.

[0018] Figure 2 A method according to the invention is shown which incorporates a fermentation step.

[0019] Figure 3The process according to the invention is shown, which is integrated into a process for preparing carboxylic acids.

[0020] The first step in the process according to the present invention is a step of spray drying the magnesium chloride solution in a spray drying device at a temperature in the range of 300-475° C., thereby forming a spray-dried product containing 10-80 wt.% of magnesium oxide and 20-90 wt.% of the total amount of magnesium hydroxychloride and magnesium chloride, the above percentages being calculated based on the total solid product.

[0021] Preferably, the first step comprises spray drying the magnesium chloride solution in a spray drying device at a temperature in the range of 300-475° C., thereby forming a spray dried product containing 30-80 wt.% of magnesium oxide and 20-70 wt.% of the total amount of magnesium hydroxychloride and magnesium chloride.

[0022] In the process according to the invention, the magnesium chloride solution subjected to the spray drying step generally has a magnesium chloride concentration of 5-48 wt.%, in particular 15-48 wt.%. If the concentration of the magnesium chloride solution is lower, for example less than 5 wt.% or less than 15 wt.%, the amount of water to be evaporated in the spray drying step is too high, making the process unattractive from an energy point of view. On the other hand, when the magnesium chloride concentration is higher than 48 wt.%, there is a risk of magnesium chloride precipitation in the spray drying nozzle. Generally, it is preferred that the concentration of the magnesium chloride solution is as high as possible and that no magnesium chloride precipitation occurs in the nozzle. Therefore, it is preferred that the magnesium chloride concentration of the magnesium chloride solution is in the range of 18-48 wt.%, in particular 23-48 wt.%, more particularly 30-48 wt.%, and even more particularly 35-47 wt.%.

[0023] It is preferred that the magnesium chloride solution used in the process according to the invention contains only limited amounts of other compounds than magnesium chloride and water, since the aim is to produce high purity magnesium oxide. More specifically, it is preferred that the magnesium chloride solution preferably contains at least 95 wt.% of magnesium chloride and water, in particular at least 98 wt.%, more in particular at least 99 wt.%.

[0024] The temperature of the magnesium chloride solution supplied to the spray drying step is not critical and may vary between room temperature and 140°C. A higher temperature, more concentrated magnesium chloride solution is preferred as this may reduce energy consumption in the spray drying step. Higher temperatures may be achieved, for example, by heating the solution in a heat exchange step using hot gas or hot liquid in a manner known in the art. It may be preferred that the temperature of the magnesium chloride solution supplied to the spray drying step is in the range of 50-140°C, particularly in the range of 70-135°C, more particularly in the range of 90-130°C.

[0025] The magnesium chloride solution is provided to the spray drying device in the spray drying step at a temperature range of 300-475°C, preferably 350-450°C. Spray drying processes and devices are known in the art. In the spray drying device, the feed to be spray dried is provided to the spray tower and sprayed through a nozzle to form small droplets. The droplets fall through the hot gas and solidify during the evaporation of water. In addition, the magnesium chloride is partially converted into magnesium oxide.

[0026] In the process according to the invention, the spray drying step is carried out at a temperature in the range of 300-475° C., preferably 350-450° C. The temperature is determined at the location of the spray drying nozzle. If the temperature is too low, the conversion of magnesium chloride into magnesium oxide will be insufficient. If the temperature is too high, too much magnesium chloride may be formed, which will have an adverse effect on the purity of the final product. It is preferred that the temperature is in the range of 350-450° C., in particular 375 to 450° C., more particularly 375-420° C. The temperatures given here are gas temperatures.

[0027] The residence time in a spray drying apparatus, defined as the time between the moment the liquid droplets leave the nozzle and the moment the solid particles reach the bottom of the unit, is generally in the range of 1 to 60 seconds, in particular in the range of 3 to 30 seconds. The residence time depends on the height of the spray tower and on the flow rate and direction of any gas stream supplied to the spray tower.

[0028] By selecting a combination of temperature and residence time suitable for obtaining the conversion, a specified conversion can be obtained in the spray drying step. The higher the temperature and the longer the residence time, the higher the conversion. It is within the ability of those skilled in the art to determine the appropriate combination of residence time and temperature to achieve the desired conversion, based on common knowledge in the art and the teachings of this specification.

[0029] Depending on the configuration of the spray drying apparatus, the particles may have a certain residence time at the bottom of the spray dryer before being moved to the calciner. It has been found that the residence time at the bottom of the spray dryer does not have a significant effect on the conversion rate, probably because the particles are not in close contact with the hot gases. However, for reasons of process efficiency, it is generally preferred that the residence time of the particles at the bottom of the spray dryer is at most 60 minutes, in particular at most 30 minutes, more particularly at most 15 minutes, or at most 10 minutes, or at most 5 minutes.

[0030] During the spray drying step, gas is supplied to the unit to provide the necessary temperature and gas flow. The nature of the gas is not critical. Typically, hot combustion gas is provided, for example, by burning natural gas, biogas, hydrogen or synthesis gas. Gas is also withdrawn from the unit. The gas withdrawn from the unit contains the HCl produced when the magnesium chloride decomposes to magnesium oxide. The gas withdrawn from the unit also contains water evaporated from the particles.

[0031] The spray drying step produces solid particles comprising 10-80 wt.%, especially 30-80 wt.% of magnesium oxide, and 20-90 wt.%, especially 20-70 wt.% of the total amount of magnesium hydroxychloride and magnesium chloride, calculated on the total solid content. If the conversion rate to magnesium oxide is too low, it is not possible to achieve a magnesium oxide conversion rate of at least 98 wt.% in the second step. If the conversion rate to magnesium oxide is higher than 80 wt.%, the process efficiency will be affected. It is preferred that the product from the spray drying step contains 40-80 wt.% magnesium oxide and 20-60 wt.% of the total amount of magnesium hydroxychloride and magnesium chloride, in particular 45-75% magnesium oxide and 25-55% of the total amount of magnesium hydroxychloride and magnesium chloride, more in particular 50-70 wt.% magnesium oxide and 30-50 wt.% of the total amount of magnesium hydroxychloride and magnesium chloride, still more in particular 55-70 wt.% magnesium oxide and 45-30 wt.% of the total amount of magnesium hydroxychloride and magnesium chloride, all percentages calculated based on the total solids content. The conversion rate can be determined by choosing an appropriate spray drying temperature and residence time.

[0032] The product from the spray drying step is subjected to a roasting step in a roasting furnace in the presence of water at a temperature of 600-900° C., thereby forming a product containing at least 98 wt.% of MgO and less than 2 wt.% of the total amount of magnesium hydroxychloride and magnesium chloride, calculated on the basis of the total amount of these three compounds. Temperatures below 600° C. are insufficient to obtain the necessary conversion within a reasonable time frame. It is preferred that the temperature is at least 700° C., in particular at least 750° C., because higher temperatures will shorten the time required to obtain the desired conversion. Temperatures greater than 900° C. will require such high energy inputs that this is generally unattractive from a commercial point of view. In addition, the product is less reactive. It is preferred that the temperature in the roasting furnace is at most 850° C.

[0033] The residence time in the unit is selected so that the desired conversion rate is obtained at the desired temperature. It will be apparent to the technician that lower temperatures require longer residence times to achieve the desired conversion rate. Typically, the residence time in the roasting furnace will be between 10 minutes and 4 hours, more specifically between 15 minutes and 2 hours, and in some embodiments between 30 minutes and 90 minutes. According to the common knowledge of those skilled in the art and the teaching of this specification, it is within the capabilities of the technician to determine the appropriate combination of residence time and temperature to achieve the desired conversion rate.

[0034] The calcination step is carried out in the presence of water to allow the magnesium chloride and magnesium hydroxychloride to react to form 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 calcination gas. As a general range, 0.1-50 mol% of water, in particular 0.1-15 mol% of water, more particularly 0.1-10 mol% of water may be mentioned, calculated on the composition of the calcination gas supplied to the calcination step.

[0035] In the roasting step, gas is supplied to the unit to provide the necessary temperature. The nature of the gas is not important. In one embodiment, hot combustion gases, such as those produced by the combustion of natural gas, biogas, hydrogen and synthesis gas, are provided. An advantage of this source is that the gas stream itself contains water. Gas is also withdrawn from the unit. The gas withdrawn from the unit contains HCl produced by the decomposition of (hydroxy)magnesium chloride to magnesium oxide, for example, in an amount of 0.3-5 mol %, calculated based on the gas composition leaving the unit.

[0036] The product obtained according to the process of the present invention comprises at least 98 wt.% of MgO, and less than 2 wt.% of the total amount of magnesium hydroxychloride and magnesium chloride, calculated based on the total amount of these three components. The process according to the present invention can produce magnesium oxide of even higher purity, which comprises, for example, at least 98.5 wt.% of MgO, and less than 1.5 wt.% of the total amount of magnesium hydroxychloride and magnesium chloride, or even at least 99 wt.% of MgO, and less than 1 wt.% of the total amount of magnesium hydroxychloride and magnesium chloride, calculated based on the total amount of these three components.

[0037] Depending on the composition of the starting materials, the solid product may contain other contaminants. However, it is preferred that the total amount of MgO, hydroxychloride and magnesium chloride is at least 95 wt.%, in particular at least 98 wt.%, more particularly at least 99 wt.% of the solid product. It is particularly preferred that the solid product contains at least 98 wt.% of MgO, and less than 2 wt.% of the total amount of hydroxychloride and magnesium chloride, calculated on the solid product. It is particularly preferred that the process according to the invention can produce even higher purity magnesium oxide, which contains, for example, at least 98.5 wt.% of MgO, and less than 1.5 wt.% of the total amount of hydroxychloride and magnesium chloride, or even at least 99 wt.% of MgO, and less than 1 wt.% of the total amount of hydroxychloride and magnesium chloride, calculated on the total solid product.

[0038] It has been found that the process according to the invention can 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 consists 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, for example, by laser diffraction of a dispersion of the product in a saturated MgO solution.

[0039] In one embodiment, the particles obtained by the process according to the invention have a D50 in the range of 0.5 to 20 microns, in particular in the range of 2 to 10 microns.

[0040] The magnesium oxide obtained by the method according to the present invention has high reactivity, which can be quantified by citric acid reactivity. More specifically, magnesium oxide has a citric acid reactivity of 75-400s, preferably 100-350s, and specifically in the range of 150 to 300s. The citric acid reactivity is determined as follows: a citric acid solution (0.4eq / L / 25.61g / L) containing phenolphthalein (30mg) as an indicator is prepared. The acid solution is shaken at 30°C for at least one hour. A 1±0.01g powdered MgO sample is transferred to 50ml of an acid solution at 30°C and shaken until the slurry color changes from white to pink. The time required for the slurry to change color is the citric acid reactivity. The method is similar to the method described in 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.

[0041] The present invention also relates to a novel magnesium oxide product characterized by the following parameters:

[0042] - it contains at least 98 wt.% of MgO and less than 2 wt.% of the total amount of magnesium hydroxychloride and magnesium chloride, calculated on the total solid product, in particular at least 98.5 wt.% of MgO and less than 1.5 wt.% of the total amount of magnesium hydroxychloride and magnesium chloride, calculated on the total solid product, more in particular at least 99 wt.% of MgO and less than 1 wt.% of the total amount of magnesium hydroxychloride and magnesium chloride, calculated on the total solid product.

[0043] - its D50 is in the range of 0.5 to 20 microns, in particular in the range of 2 to 10 microns,

[0044] - It has a citric acid reactivity of 75-400s, preferably 100-350s and in particular between 150 and 300s.

[0045] The product preferably contains less than 0.5 wt.% of other components than MgO, magnesium hydroxychloride and magnesium chloride, especially less than 0.1 wt.% of other components.The new magnesium oxide product is attractive for a variety of uses due to its high purity and reactivity.

[0046] Spray drying and roasting devices are known in the art and need no further explanation here. Devices comprising a spray drying zone and a roasting zone are also known in the art. For example, reference is made to US6214310 and US2002 / 0159946.

[0047] US6214310 is concerned with the regeneration of pickling acids used in steel manufacturing. It describes a process in which a partial conversion of the metal salt is carried out in a spray drying zone and the final conversion is carried out in a roasting zone. The spray drying zone operates at a temperature of 500-600°C. The conversion of magnesium chloride is not described, nor is the conversion rate in the spray drying zone specified.

[0048] US 2002 / 0159946 describes a spray roasting process in which a metal salt solution is sprayed and water is evaporated in a first stage to form metal salt particles. The metal salt particles are subsequently heated at low temperature in a conversion stage to convert the salt into an oxide.

[0049] The method according to the invention produces magnesium oxide with high purity and low chloride content, which is suitable for use as a neutralizing agent in a fermentation process to prepare carboxylic acids. Therefore, the present invention also relates to a method for preparing carboxylic acids by fermentation using the magnesium oxide obtained according to the method of the invention. The present invention also relates to an integrated method comprising a fermentation step, a separation step and a step of converting a magnesium chloride solution into high-purity magnesium oxide and providing the magnesium oxide to the fermentation medium as a neutralizing agent directly or after conversion into magnesium hydroxide. These embodiments will be discussed in more detail below.

[0050] In one embodiment, the present invention relates to a method for preparing a carboxylic acid, comprising the steps of:

[0051] - converting magnesium chloride into magnesium oxide by a process comprising the steps of: subjecting a magnesium chloride solution to a spray drying step in a spray drying apparatus at a temperature in the range of 300-475° C., preferably 350-450° C., thereby forming a spray dried product comprising 10-80 wt.%, in particular 30-80 wt.% of magnesium oxide and 20-90 wt.%, in particular 20-70 wt.% of the total amount of magnesium hydroxychloride and magnesium chloride, and subjecting the product of the spray drying step to a roasting step in a roasting furnace at a temperature of 600-900° C. in the presence of water, thereby forming a magnesium oxide product comprising at least 98 wt.% of MgO and less than 2% of the total amount of magnesium hydroxychloride and magnesium chloride (the percentages are calculated as specified above);

[0052] - providing a magnesium oxide product comprising at least 98 wt.% of MgO and less than 2% of the total amount of magnesium hydroxychloride and magnesium chloride (percentages calculated as specified above) as a neutralizing agent to a fermentation step as such or after a conversion step of reacting the magnesium oxide product with water to convert it into magnesium hydroxide, the fermentation step comprising the step of fermenting a carbon source in a fermentation medium by means of a microorganism to form a carboxylic acid, wherein the carboxylic acid is at least partially converted by the neutralizing agent to form a magnesium carboxylate salt.

[0053] The amount of magnesium base added during the fermentation step is typically in the range of 0.1 to 4 moles of magnesium base per mole of carboxylic acid, more specifically in the range of 0.2 to 2 moles of magnesium base per mole of carboxylic acid.

[0054] As mentioned above, the product magnesium oxide obtained by the method according to the present invention can be used as it is. It can also be used after being converted into magnesium hydroxide by reaction with water. The step of converting magnesium oxide into magnesium hydroxide by reaction with water can be carried out by methods known in the art.

[0055] Thus, the above method produces a fermentation medium containing magnesium carboxylate. The method according to the present invention may also include the following additional steps

[0056] - 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 carboxylic acid and magnesium chloride,

[0057] - subjecting the aqueous mixture comprising the carboxylic acid and the magnesium chloride to a separation step to form an effluent comprising the carboxylic acid and the aqueous solution of magnesium chloride

[0058] The magnesium chloride solution obtained from the separation step can be provided to the method according to the invention. However, in general, the magnesium chloride aqueous solution from the separation step has a relatively low concentration. Therefore, it may be preferred to subject the magnesium chloride aqueous solution from the separation step to one or more concentration steps, in which water is evaporated, thereby producing a more concentrated solution, which is provided to the spray drying step. In one embodiment, the magnesium chloride aqueous solution with a magnesium chloride concentration of 10-30 wt.% is subjected to a concentration step, in which water is evaporated, thereby producing a concentrated magnesium chloride solution with a magnesium chloride concentration of 15-48 wt.%, in particular 35-47 wt.%, which is then provided to the spray drying step.

[0059] The one or more concentration steps may be performed by methods known in the art and need no further explanation here.

[0060] As discussed above, a gas stream containing HCl is recovered from the spray drying step and the roasting step. In one embodiment, at least a portion of the HCl from one or both of these units is provided to an acidification step, wherein the magnesium carboxylate is contacted with the HCl in an aqueous environment to form an aqueous mixture comprising carboxylic acid and magnesium chloride. The HCl may be provided to the acidification step in gaseous form. However, it is also possible to absorb the HCl from the gas stream containing HCl into water to form an aqueous HCl solution, and to provide the aqueous HCl solution to the acidification step.

[0061] The individual steps in the integrated process other than treating the magnesium chloride solution are discussed below.

[0062] In the first step, the carbon source is subjected to a fermentation step to form carboxylic acids, the fermentation step comprising the steps of fermenting the carbon source in the fermentation broth by microorganisms to form carboxylic acids and neutralizing at least part of the carboxylic acids by adding a magnesium base selected from magnesium oxide and magnesium hydroxide to obtain magnesium carboxylate.

[0063] Fermentation processes for preparing carboxylic acids are known in the art and need no further description here. Using the common knowledge of those skilled in the art, it is within their capabilities to select a suitable fermentation process depending on the desired acid to be produced, the carbon source and the available microorganisms.

[0064] The product of the fermentation process is a fermentation broth, which is an aqueous liquid comprising magnesium carboxylate, biomass and optionally other components such as impurities such as sugars, proteins and salts.

[0065] If desired, the fermentation broth may be subjected to a biomass removal step, such as a filtration step, prior to further processing. This is generally preferred for improving product quality. Depending on the carboxylic acid produced, another intermediate step may be to separate the solid reaction product, such as magnesium carboxylate, from the fermentation broth before, after or simultaneously with the removal of the biomass, and optionally subject the magnesium carboxylate to a washing step.

[0066] Depending on the carboxylic acid produced, another intermediate step may be to subject the fermentation broth to a concentration step to increase the concentration of magnesium carboxylate in the composition prior to acidification. This step may be performed before, after or simultaneously with the removal of the biomass.

[0067] Other intermediate steps, such as purification steps, may be performed as desired, as will be apparent to those skilled in the art.

[0068] The next step of the integrated process according to the invention is to subject the magnesium carboxylate to an acidification step, sometimes also indicated as an acidification step, in which the magnesium carboxylate is contacted with HCl in an aqueous environment to form an aqueous mixture comprising carboxylic acid and magnesium chloride.

[0069] There are many ways to accomplish this step.

[0070] The acidification step is typically performed by contacting the carboxylate salt with an acidic HCl solution. However, in some embodiments, the carboxylate salt may also be contacted with gaseous HCl.

[0071] The carboxylate may be in solid and / or dissolved form. In one embodiment, the carboxylate is provided in solid form. In this case, the acidification step is carried out by contacting the carboxylate with an acidic solution. The advantage of preparing the aqueous mixture from a carboxylate in solid form is that very high carboxylic acid concentrations can thus be obtained, for example at least 15 wt %, in particular at least 25 wt %, at most 50 wt %, or at most 40 wt % for example.

[0072] The carboxylate salt may also be in dissolved form, typically as part of an aqueous solution. In this case, the acidification step may be carried out by contacting the carboxylate salt with an acidic solution or an acidic gas.

[0073] The acidification step can also be carried out on a mixture of carboxylic acid and carboxylate. Such a mixture can be obtained, for example, in a low pH fermentation. The mixture can be, for example, an aqueous suspension.

[0074] When the acidification of the carboxylate is carried out by contacting it with an acidic HCl solution, it preferably has an acid concentration as high as possible. Such a high acid concentration will result in an aqueous mixture with a high carboxylic acid concentration, which is desirable. Therefore, the acidic solution comprises at least 5 wt%, more preferably at least 10 wt%, even more preferably at least 20 wt% of acid, based on the total weight of the acidic solution.

[0075] Acidification is usually performed 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 view of further processing of the mixture. For example, the excess acid used may result in a pH value of 2 or less, preferably a pH value of 0-1, for the resulting aqueous mixture.

[0076] In the case of using gaseous HCl, it can be contacted by contacting it with the carboxylate solution or suspension. In particular, HCl gas can be blown through the solution or suspension.

[0077] Preferably, the acidification is carried out at a temperature of 75° C. or lower. At higher temperatures, it becomes uneconomical to subject the equipment to the harsh conditions of an acidic environment at high temperatures.

[0078] The acidification step results in the formation of an aqueous liquid comprising carboxylic acid and magnesium chloride. Optionally, after undergoing an intermediate treatment step such as a concentration step, the aqueous liquid is subjected to a separation step.

[0079] Suitable separation procedures are known in the art. The nature of the procedure used depends on the identity and properties of the acid.

[0080] When the carboxylic acid is present in whole or in part in the form of a solid in an aqueous liquid, it can be separated using conventional solid-liquid separation methods such as filtration, centrifugation, and the like.

[0081] When the carboxylic acid is present in whole or in part as a separate organic phase in an aqueous liquid, it can be separated using conventional liquid-liquid separation methods, such as decantation, sedimentation, centrifugation, use of plate separators, use of coalescers, and use of hydrocyclones. An extractant may be added to improve the separation efficiency. Combinations of different methods and apparatus may also be used.

[0082] Where the carboxylic acid is dissolved in an aqueous liquid, it can be isolated using, for example, extraction with a suitable extractant.

[0083] When an extractant is present in the process according to the invention, the extractant (which may also be indicated as extractant) is substantially immiscible with water. The use of an extractant results in the formation of a two-phase system during the separation step, which comprises a liquid organic layer containing the extractant and the carboxylic acid and an aqueous layer containing the dissolved magnesium chloride.

[0084] Examples of suitable extractants are aliphatic and aromatic hydrocarbons, such as alkanes and aromatic compounds, ketones and ethers. It is also possible to use mixtures of various compounds.

[0085] Examples of suitable aliphatic hydrocarbons are C5-C10 straight-chain, branched or cyclic alkanes, such as octane, hexane, cyclohexane, 2-ethyl-hexane and heptane.

[0086] Examples of suitable aromatic compounds are C6-C10 aromatic compounds such as toluene, xylene and ethylbenzene.

[0087] Examples of suitable ketones in the present invention are C5+ ketones, more particularly C5-C8 ketones. C5+ represents a ketone having at least 5 carbon atoms. The use of C9+ ketones is less preferred, and the use of methyl-isobutyl-ketone (MIBK) has been found to be particularly attractive.

[0088] Examples of suitable ethers are C3-C6 ethers, such as methyl tert-butyl ether (MTBE) and diethyl ether (DEE).

[0089] After extraction, the carboxylic acid can be separated from the extractant as desired. In one embodiment, this can be accomplished by removing the extractant by evaporation. In another embodiment, the carboxylic acid can be recovered from the extractant by extraction with water or another aqueous liquid.

[0090] After separation of the carboxylic acid from the salt, the carboxylic acid can be processed as desired. Examples of further processing steps are purification steps, such as one or more of washing, activated carbon treatment, recrystallization, distillation and filtration. When the carboxylic acid is lactic acid, it can be converted into lactide and PLA.

[0091] Therefore, the present invention also relates to a method for preparing a carboxylic acid, which method comprises the following steps

[0092] - subjecting the carbon source to a fermentation step to form carboxylic acids, the fermentation step comprising the steps of fermenting the carbon source in the fermentation broth by a microorganism to form carboxylic acids and neutralizing at least part of the carboxylic acids by adding a magnesium base selected from magnesium oxide and magnesium hydroxide to obtain magnesium carboxylate,

[0093] - 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 carboxylic acid and magnesium chloride,

[0094] - subjecting the aqueous mixture comprising carboxylic acid and magnesium chloride to a separation step, thereby separating carboxylic acid and magnesium chloride solution therefrom,

[0095] - subjecting the magnesium chloride solution to a spray drying step at a temperature in the range of 300-475° C., thereby forming a spray dried product comprising 10-80 wt. % of magnesium oxide and 20-90 wt. % of the total amount of magnesium hydroxychloride and magnesium chloride,

[0096] - subjecting the product of the spray drying step to a calcining step in a calcining furnace at a temperature of 600-900° C. in the presence of water, thereby forming a product containing at least 98 wt.% of MgO and less than 2 wt.% of the total amount of magnesium hydroxychloride and magnesium chloride, wherein the percentages of MgO, magnesium hydroxychloride and magnesium chloride are calculated based on the total amount of MgO, magnesium hydroxychloride and magnesium chloride.

[0097] It will be apparent to the skilled person that other steps and embodiments described herein are also applicable to this method.

[0098] The nature of the carboxylic acid prepared is not critical for the integrated process according to the invention.

[0099] In one embodiment, the carboxylic acid is a mono-, di- or tri-carboxylic acid (C2-C8 carboxylic acid) comprising at least 2 but not more than 8 carbon atoms. In one embodiment, the carboxylic acid is selected from 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 lactic acid, succinic acid, propionic acid, 3-hydroxypropionic acid, 2-hydroxybutyric acid, 3-hydroxybutyric acid- and 4-hydroxybutyric acid and citric acid.

[0100] In one embodiment, the carboxylic acid is selected from monocarboxylic acids having 2 to 6 carbon atoms. In one embodiment, the monocarboxylic acids having 2 to 6 carbon atoms do not contain hydroxyl groups. In this group, examples of suitable acids are propionic acid, acrylic acid, butyric acid and valeric acid.

[0101] In another embodiment, the monocarboxylic acid contains at least one hydroxyl group. In this group, in one embodiment, the acid may preferably be selected from lactic acid, glycolic acid, 3-hydroxypropionic acid, 2-hydroxybutyric acid, 3-hydroxybutyric acid- and 4-hydroxybutyric acid. In another embodiment of this group, the acid may preferably be selected from glycolic acid, 3-hydroxypropionic acid and 2-hydroxybutyric acid, 3-hydroxybutyric acid- and 4-hydroxybutyric acid. In another embodiment, the acid may preferably be lactic acid.

[0102] In another embodiment, the carboxylic acid is a polycarboxylic acid, more particularly a dibasic or tribasic carboxylic acid (C2-6 carboxylic acid) comprising at least 2 but not more than 6 carbon atoms. In one embodiment, the polycarboxylic acid is selected from 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 succinic acid, citric acid, fumaric acid, itaconic acid, adipic acid and 2,5-furandicarboxylic acid. The polycarboxylic acid may be particularly selected from succinic acid, fumaric acid, itaconic acid and 2,5-furandicarboxylic acid.

[0103] The figures discussed below will illustrate various aspects of the present invention, but the present invention is not limited thereto or thereby.

[0104] Figure 1 The method according to the present invention is shown. Figure 1In the process, a magnesium chloride solution is supplied to a spray drying device (2) via a pipeline (1). A hot gas stream is supplied via a pipeline (3), and a gas stream containing HCl is withdrawn via a pipeline (4). In the spray dryer, the magnesium chloride solution is converted into a spray-dried product, which comprises 10-80 wt.%, in particular 30-80 wt.% of magnesium oxide; and 20-90 wt.%, in particular 20-70 wt.% of the total amount of magnesium hydroxychlorate and magnesium chloride. The spray-dried product is withdrawn from the spray dryer via a pipeline (5) and supplied to a roasting furnace (6). A hot gas stream is supplied to the roasting furnace (6) via a pipeline (7), and a gas stream containing HCl is withdrawn via a pipeline (8). If desired, part or all of the gas containing HCl withdrawn from the roasting furnace (7) via a pipeline (8) can be supplied to the spray drying device (2).

[0105] The product from the calciner, comprising at least 98 wt.% of magnesium oxide; and less than 2 wt.% of the total amount of magnesium hydroxychloride and magnesium chloride, is withdrawn via line (9).

[0106] Figure 2 Shows Figure 1 The combination of the method according to the invention and a fermentation process is shown. Figure 2 In the fermentation process of the fermentation unit (10), the magnesium oxide product extracted from the roaster via pipeline (9) is provided to the fermentation unit (10). This can be done directly, or it can be done in a unit not shown after the magnesium oxide product is converted into magnesium hydroxide by reaction with water. The fermentation unit (10) is provided with a carbon source and optional other components, such as nutrients, via a pipeline not shown. In the fermentation step of the fermentation unit (10), the carbon source is fermented by microorganisms in the fermentation broth to form carboxylic acids. At least part of the carboxylic acids are neutralized directly or after they are converted into magnesium hydroxide by magnesium base, which is a magnesium product from the roaster. The fermentation process in the presence of magnesium base produces a fermentation medium containing magnesium carboxylate, which is extracted from the fermentation unit (10) via pipeline (11).

[0107] Figure 3 A further integration method according to the present invention is shown, which is based on Figure 2 The method shown. Figure 3In the method, a fermentation medium containing a magnesium carboxylate salt is provided to an acidification step (12) via a pipeline (11). Intermediate steps such as biomass removal or concentration may 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. HCl is provided via a pipeline (13). In the figure, the HCl provided via pipeline (13) is a combination of HCl obtained from a spray dryer (1) via pipeline (4) and HCl obtained from a roaster (6) via pipeline (8). Obviously, it is also possible to use only one of these streams, or to provide a stream to the acidification step (12) separately. HCl can be provided in the form of a gas stream containing HCl obtained directly from the spray dryer (1) and / or the roaster (6). It can also be provided in the form of an aqueous solution obtained by absorbing a gas stream containing HCl into an aqueous liquid (e.g., water). This will be carried out in an absorption step (not shown).

[0108] The aqueous mixture comprising the carboxylic acid and magnesium chloride is provided to a separation step (15) via line (14). The separation step may be performed as described above. The separation step (15) produces an effluent comprising the carboxylic acid and a magnesium chloride solution. The product carboxylic acid is removed via line (16). The magnesium chloride solution is withdrawn via line (1) and provided to a spray dryer as described above. Figure 1 discussed in the context of.

[0109] It will be apparent to the skilled person that only a portion of the HCl produced in the spray dryer or roaster may be provided to the acidification step, and / or HCl from other sources may also be provided. Likewise, it will be apparent that only a portion of the magnesium oxide product produced in the roaster may be provided to the fermentation step.

[0110] It is clear to a person skilled in the art that in the method according to the invention the preferred embodiments of the various steps can be combined unless they are mutually exclusive.

[0111] The present invention is further illustrated by the following examples, but the present invention is not limited thereto or thereby.

[0112] Example 1 - Method according to the invention

[0113] The spray dryer is provided with a 37-43 wt.% magnesium chloride solution and spray dried at a temperature of 350-420° C. The product of the spray drying step contains 50 wt.% magnesium oxide, and a total of 50 wt.% magnesium chloride and magnesium hydroxychloride.

[0114] The product of the spray drying step was subjected to a calcination step at 800°C for 30 minutes to obtain a product containing 99.2 wt.% of magnesium oxide and a total of 0.8 wt.% of magnesium chloride and magnesium hydroxychloride, the above percentages being calculated based on the total solid product.

[0115] Example 2 - Comparative Method

[0116] A 37-43 wt.% magnesium chloride solution is provided to the spray dryer and spray dried at a temperature of 500° C. The product of the spray drying step contains 97% magnesium oxide and a total of 3 wt.% magnesium chloride and magnesium hydroxychloride. Therefore, the product does not reach the required purity.

[0117] In order to obtain the required magnesium oxide product having a purity of at least 98 wt.%, it was found necessary to carry out a calcination step at 800°C for 30 minutes, thereby obtaining a product containing 99.2 wt.% magnesium oxide and a total of 0.8 wt.% magnesium chloride and magnesium hydroxychloride.

[0118] Therefore, the comparison between Example 1 according to the present invention and Comparative Example 2 shows that spray drying at 500°C is not sufficient to obtain the desired purity, and the combination of spray drying and calcination with a specified conversion rate in the spray drying step allows the use of lower temperatures in the spray drying step, thereby reducing energy consumption.

Claims

1. A method for converting magnesium chloride into magnesium oxide, comprising the following steps: - subjecting the magnesium chloride solution to a spray drying step at a temperature in the range of 300-475° C., thereby forming a spray dried product comprising 10-80 wt.% of magnesium oxide and 20-90 wt.% of magnesium hydroxychloride and magnesium chloride in total, - subjecting the product of said spray drying step to a calcination step in a calcination furnace at a temperature of 600-900° C. in the presence of water, thereby forming a product containing at least 98 wt.% of MgO and less than 2 wt.% of magnesium hydroxychloride and magnesium chloride in total, The percentages of MgO, hydroxymagnesium chloride and magnesium chloride are calculated based on the total amounts of MgO, hydroxymagnesium chloride and magnesium chloride.

2. The method according to claim 1, wherein the first step comprises spray drying the magnesium chloride solution in a spray drying device at a temperature in the range of 350-450° C., thereby forming a spray-dried product containing 30-80 wt.% of magnesium oxide and a total amount of 20-70 wt.% of magnesium hydroxychloride and magnesium chloride.

3. The method according to any one of claims 1-2, wherein the magnesium chloride solution provided to the spray drying step has a magnesium chloride concentration of 5-48 wt.%.

4. The method according to any one of claims 1-2, wherein the magnesium chloride solution provided to the spray drying step has a magnesium chloride concentration of 15-48 wt.%.

5. The method according to any one of claims 1-2, wherein the magnesium chloride solution provided to the spray drying step has a magnesium chloride concentration of 18-48 wt.%.

6. The method according to any one of claims 1-2, wherein the magnesium chloride solution provided to the spray drying step has a magnesium chloride concentration of 23-48 wt%.

7. The method according to any one of claims 1-2, wherein the magnesium chloride solution provided to the spray drying step has a magnesium chloride concentration of 30-48 wt.%.

8. The method according to any one of claims 1-2, wherein the magnesium chloride solution provided to the spray drying step has a magnesium chloride concentration of 35-47 wt.%.

9. The method according to any one of claims 1-2, wherein the spray drying is carried out at a temperature in the range of 375 to 450°C.

10. The method according to any one of claims 1-2, wherein spray drying is carried out at a temperature in the range of 375 to 420°C.

11. The process according to any one of claims 1 to 2, wherein the product from the spray drying step comprises 40-80 wt.% magnesium oxide and a total of 20-60 wt.% magnesium hydroxychloride and magnesium chloride, all percentages being calculated based on the total solids content.

12. The process according to any one of claims 1 to 2, wherein the product from the spray drying step comprises 45-75 wt.% magnesium oxide and a total of 25-55 wt.% magnesium hydroxychloride and magnesium chloride, all percentages being calculated based on the total solids content.

13. The process according to any one of claims 1 to 2, wherein the product from the spray drying step comprises 50-70 wt.% magnesium oxide and a total of 30-50 wt.% magnesium hydroxychloride and magnesium chloride, all percentages being calculated based on the total solids content.

14. The process according to any one of claims 1 to 2, wherein the product from the spray drying step comprises 55-70 wt.% magnesium oxide and a total of 45-30 wt.% magnesium hydroxychloride and magnesium chloride, all percentages being calculated based on the total solids content.

15. The method according to any one of claims 1-2, wherein the temperature in the calcining furnace is in the range of 700°C to 850°C.

16. The method according to any one of claims 1-2, wherein the temperature in the calcining furnace is in the range of 750°C to 850°C.

17. The process according to any one of claims 1 to 2, wherein the product of the calcining step comprises at least 98.5 wt.% MgO and less than 1.5 wt.% of magnesium hydroxychloride and magnesium chloride in total; or even at least 99 wt.% MgO and less than 1 wt.% of magnesium hydroxychloride and magnesium chloride in total, calculated on the total amount of MgO, magnesium hydroxychloride and magnesium chloride; or the product of the calcining step comprises at least 98 wt.% MgO and less than 2 wt.% of magnesium hydroxychloride and magnesium chloride in total; calculated on the total solid product.

18. The process of claim 17, wherein the product of the calcining step comprises at least 98.5 wt.% MgO and less than 1.5 wt.% total magnesium hydroxychloride and magnesium chloride; calculated on the total solid product.

19. The process of claim 17, wherein the product of the calcining step comprises at least 99 wt.% MgO and less than 1 wt.% of magnesium hydroxychloride and magnesium chloride in total, calculated on the total solid product.

20. A magnesium oxide product obtained by the method according to any one of claims 1 to 19, characterized in that The following parameters: - it contains at least 98 wt.% of MgO and less than 2 wt.% of magnesium hydroxychloride and magnesium chloride in total, all percentages being calculated based on the total solid product, - Its D50 is in the range of 0.5 to 20 microns, -It has a citric acid reactivity between 75-400s.

21. The magnesium oxide product of claim 20, wherein - It contains at least 98.5 wt.% of MgO and less than 1.5 wt.% of magnesium hydroxychloride and magnesium chloride in total, all percentages being calculated based on the total solid product.

22. The magnesium oxide product of claim 20, wherein - It contains at least 99 wt.% of MgO and less than 1 wt.% of magnesium hydroxychloride and magnesium chloride in total, all percentages being calculated on the basis of the total solid product.

23. The magnesium oxide product of claim 20, wherein - Its D50 is in the range of 2 to 10 microns.

24. The magnesium oxide product of claim 20, wherein -It has a citric acid reactivity between 100-350s.

25. The magnesium oxide product of claim 20, wherein -It has a citric acid reactivity between 150-300s.

26. A method for preparing a magnesium carboxylate, comprising the steps of: The magnesium oxide obtained by the method of any one of claims 1 to 19 is provided as a neutralizing agent to a fermentation step as it is or after a conversion step of reacting the magnesium oxide product with water to convert it into magnesium hydroxide, the fermentation step comprising a step of fermenting a carbon source in a fermentation medium by a microorganism to form a carboxylic acid, wherein the carboxylic acid is at least partially converted by the neutralizing agent to form a magnesium carboxylate.

27. A method for preparing a carboxylic acid comprising the steps of: - providing a magnesium carboxylate according to claim 26, - 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 carboxylic acid and magnesium chloride, - subjecting the aqueous mixture comprising the carboxylic acid and the magnesium chloride to a separation step to form an effluent comprising the carboxylic acid and the aqueous solution of magnesium chloride.

28. The process according to claim 27, wherein after the separation step, the carboxylic acid is subjected to a purification step.

29. The method of claim 28, wherein the purification is selected from the group consisting of washing, activated carbon treatment, recrystallization, distillation and filtration.

30. The method according to any one of claims 27-29, wherein a biomass removal step is performed between the fermentation step and the acidification step.

31. The process according to any one of claims 27-29, 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 acidulation step.

32. The method of any one of claims 27-29, wherein the carboxylic acid is a mono-, di- or tricarboxylic acid comprising at least 2 but not more than 8 carbon atoms.

33. The method of claim 32, wherein the carboxylic acid is a carboxylic acid selected from lactic acid, succinic acid, and 2,5-furandicarboxylic acid.

34. The method of any one of claims 27-29, wherein the carboxylic acid is lactic acid, which is subsequently converted to lactide or polylactide.

35. A method for preparing a carboxylic acid comprising the steps of: - subjecting the carbon source to a fermentation step to form carboxylic acids, the fermentation step comprising the steps of fermenting the carbon source in the fermentation broth by a microorganism to form carboxylic acids and neutralizing at least part of the carboxylic acids by adding a magnesium base selected from magnesium oxide and magnesium hydroxide to obtain 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 carboxylic acid and magnesium chloride, - subjecting the aqueous mixture comprising carboxylic acid and magnesium chloride to a separation step, thereby separating carboxylic acid and magnesium chloride solution therefrom, - subjecting the magnesium chloride solution to a spray drying step at a temperature in the range of 300-475° C., thereby forming a spray dried product comprising 10-80 wt.% of magnesium oxide and 20-90 wt.% of magnesium hydroxychloride and magnesium chloride in total, - subjecting the product of the spray drying step to a roasting step in a roasting furnace at a temperature of 600-900° C. in the presence of water, thereby forming a magnesium oxide product containing at least 98 wt.% of MgO and less than 2 wt.% of magnesium hydroxychloride and magnesium chloride in total, wherein the percentages of MgO, magnesium hydroxychloride and magnesium chloride are calculated based on the total amounts of MgO, magnesium hydroxychloride and magnesium chloride, and - Magnesium oxide is provided to the fermentation medium as a neutralizing agent either as such or after a conversion step in which the magnesium oxide product is converted into magnesium hydroxide by reaction with water.

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