A method for preparing chemically modified bicarbonate particles

Abstract

The present invention relates to a method for preparing chemically modified bicarbonate particles. The present disclosure relates to a method for chemically modifying particles of bicarbonate in a co-rotating twin-screw extruder and to the chemically modified bicarbonate particles prepared thereby. The present disclosure also relates to a method for controlling the amount of carbonate formed during the chemical modification of bicarbonate particles.

Description

[0001] This application is a divisional application of a patent application with the application number 201980085306.2, the filing date of December 20, 2019, the priority date of December 20, 2018, and the invention title of "A method for preparing chemically modified bicarbonate particles". Technical Field

[0002] The present disclosure relates to a method for preparing chemically modified bicarbonate particles in a twin-screw extruder and chemically modified bicarbonate particles prepared therefrom. Background Art

[0003] Bicarbonates are widely used in many products in the food, pharmaceutical, and nutritional industries. The most popular are the alkali metal bicarbonates. There are many different methods for commercially producing bicarbonates. Bicarbonates are reactive components and a source of carbon dioxide.

[0004] When sodium bicarbonate particles are heated to above about 80 °C, they undergo thermal decomposition to form sodium carbonate, water, and carbon dioxide.

[0005] 2NaHCO 3 →Na 2 CO 3 +H 2 O+CO 2

[0006] Sodium carbonate acts as a drying agent layer on the sodium bicarbonate particles. It increases the resistance of sodium bicarbonate to moisture. It is known to heat sodium bicarbonate to partially convert it to sodium carbonate by conventional methods (such as heating in a tray or fluidized bed heating) to prepare surface-modified sodium bicarbonate or passivated sodium bicarbonate. The conventional methods are time-consuming or expensive batch processes.

[0007] In the above batch process, removing the water generated due to the decomposition of sodium bicarbonate and the formation of sodium carbonate is cumbersome. The percentage of conversion of sodium bicarbonate to carbonate is inconsistent. Sodium carbonate acts as a drying agent and also passivates the reactive sodium bicarbonate. Changes in the content of sodium carbonate result in changes in the degree of passivation. The reported literature shows that there is no effective lean manufacturing process for passivating bicarbonates in an extruder that can control the degree of passivation without considering too many operating parameters. What is desired is to prepare modified bicarbonates by a simpler, cost-effective, commercially viable, and fast method suitable for continuous manufacturing. Summary of the Invention

[0008] The present disclosure relates to a method for chemically modifying particles of bicarbonate in a co-rotating twin-screw extruder. The method includes: feeding the particles into the feed zone of the extruder; treating the fed particles in the heat treatment zone of the extruder at a temperature in the range of 200 °C to 350 °C for a residence time in the range of 3 to 20 seconds to convert 3% to 40% w / w of the bicarbonate present in the fed particles into carbonate, thereby chemically modifying the particles, and collecting the chemically modified particles from the extruder.

[0009] The present disclosure also relates to chemically modified bicarbonate particles. The particles comprise bicarbonate and carbonate. The pH of a 5% aqueous solution of the particles is in the range of 9.25 to 9.6, and the water activity is in the range of 0.05 - 0.3 a w .

[0010] The present disclosure further relates to chemically modified bicarbonate particles. The particles comprise (comprise of) bicarbonate and carbonate. The pH of a 5% aqueous solution of the particles has a standard deviation of no more than 0.1. The standard deviation is calculated by measuring the pH of at least 10 different samples of the chemically modified particles.

[0011] The present disclosure also relates to a method for controlling the amount of carbonate formed during the chemical modification of bicarbonate particles. The method includes: feeding the particles of bicarbonate into the feed zone of the extruder, treating the fed particles in the heat treatment zone of the extruder for a residence time in the range of 5 to 20 seconds to convert 3% to 40% w / w of the bicarbonate present in the fed particles into carbonate, thereby chemically modifying the particles, and collecting the chemically modified particles from the extruder. The amount of bicarbonate converted to carbonate is controlled by maintaining the temperature of the heat treatment zone in the range of 200 °C to 350 °C. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1A Shows a scanning electron micrograph of the chemically modified sodium bicarbonate of Example 2.

[0013] Figure 1B Shows a scanning electron micrograph of commercially available surface-modified sodium bicarbonate. DETAILED DESCRIPTION

[0014] For the purpose of promoting an understanding of the principles of the present disclosure, reference is now made to the embodiments and specific language is used to describe them. However, it should be understood that the scope of the present disclosure is not thereby intended to be limited, and such changes and further modifications of the disclosed compositions and methods, and such further applications of the principles of the present disclosure therein, are contemplated as would normally occur to one of ordinary skill in the art to which the present disclosure pertains.

[0015] Those skilled in the art will understand that the foregoing general description and the following detailed description are exemplary and explanatory of the present disclosure, and are not intended to limit it.

[0016] References throughout this specification to "one embodiment", "an embodiment", or similar language mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, the appearances of the phrases "in one embodiment", "in an embodiment", and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

[0017] The present disclosure relates to a method of chemically modifying particles of bicarbonate in a co-rotating twin screw extruder. The method comprises: feeding the particles into the feed zone of the extruder, treating the fed particles in the heat treatment zone of the extruder at a temperature in the range of 200 °C to 350 °C for a residence time in the range of 3 to 20 seconds to convert 3% to 40% w / w of the bicarbonate present in the fed particles to carbonate, thereby chemically modifying the particles, and collecting the chemically modified particles from the extruder.

[0018] In the disclosed method, the amount of bicarbonate converted to carbonate can be controlled by maintaining the temperature of the heat treatment zone in the range of 200 °C to 350 °C. According to one embodiment, the heat treatment zone is maintained at a temperature in the range of 200 °C to 300 °C.

[0019] According to one embodiment, by maintaining the temperature of the heat treatment zone at 200 °C, 11 - 14% w / w of the bicarbonate is converted to carbonate. In another embodiment, by maintaining the temperature of the heat treatment zone at 225 °C, 15 - 19% w / w of the bicarbonate is converted to carbonate. In yet another embodiment, by maintaining the temperature of the heat treatment zone at 275 °C, 26 - 29% w / w of the bicarbonate is converted to carbonate. In another embodiment, by maintaining the temperature of the heat treatment zone at 300 °C, 35 - 39% w / w of the bicarbonate is converted to carbonate.

[0020] Bicarbonate is a salt that undergoes a reversible reaction to form carbonate, water, and carbon dioxide. Examples of bicarbonates suitable for this method include, but are not limited to, carbonate-containing compounds such as potassium bicarbonate, sodium bicarbonate, and calcium bicarbonate and / or mixtures thereof. According to one embodiment, the bicarbonate is sodium bicarbonate. In another embodiment, the bicarbonate is potassium bicarbonate.

[0021] According to one embodiment, the particles are fed into the feed zone of the extruder at a feed rate in the range of 100 g / min to 700 g / min. In one embodiment, the feed rate is in the range of 300 g / min to 600 g / min. In another embodiment, the feed rate is in the range of 400 g / min to 600 g / min.

[0022] According to one embodiment, the size of the particles fed into the feed zone is less than or equal to 400 microns. In another embodiment, the size is less than or equal to 250 microns.

[0023] According to one embodiment, the residence time is in the range of 8 to 20 seconds. According to a specific embodiment, the residence time is in the range of 5 to 20 seconds.

[0024] According to one embodiment, 10% to 40% w / w of the bicarbonate is converted to carbonate. According to another embodiment, 15% to 30% w / w of the bicarbonate is converted to carbonate. The modification mainly occurs on the surface of the particles.

[0025] According to one embodiment, the pH of a 5% aqueous solution of the chemically modified bicarbonate particles collected from the extruder is in the range of 8.6 to 9.6. According to one embodiment, the pH is in the range of 9.2 to 9.4. The pH is measured at regular intervals. According to one embodiment, the pH is calculated at intervals of 10 minutes and 30 minutes.

[0026] According to one embodiment, the standard deviation of the pH of a 5% aqueous solution of the chemically modified bicarbonate particles does not exceed 0.1. The standard deviation is measured by measuring the pH of at least 10 different samples of the chemically modified particles.

[0027] According to one embodiment, the relative standard deviation of the pH of a 5% aqueous solution of the chemically modified bicarbonate particles collected at regular time intervals is less than 1%. According to one embodiment, the pH is calculated at intervals of 10 minutes and 30 minutes.

[0028] According to one embodiment, at a constant temperature selected from the range of 200 °C to 350 °C, the chemically modified particles have a uniform pH such that the relative standard deviation of the pH values of 5% aqueous solutions of aliquots or samples of the chemically modified particles at regular time intervals is less than 1%. According to one embodiment, the pH is calculated at intervals of 10 minutes and 30 minutes.

[0029] According to one embodiment, only the heat treatment zone is heated. The lengths of the feed zone and the heat treatment zone are fixed according to the selected temperature. According to one embodiment, the extruder has an additional conveying zone. According to one embodiment, the feed zone and / or the conveying zone are not heated. According to one embodiment, the hot feed zone and / or the conveying zone are maintained at room temperature.

[0030] The extruder includes one or more screw elements. According to one embodiment, the extruder includes a plurality of screw elements. In a particular embodiment, the extruder contains only forward conveying screw elements. According to one embodiment, the screw speed is in the range of 300 to 600 rpm.

[0031] The extruder is provided with means for controlling the temperatures of the feed zone, the heat treatment zone, and the conveying zone (if present). It is also provided with means for adjusting the screw speed. It further has a human-machine interface for controlling the processing conditions.

[0032] The feed zone can be connected upstream to a side feeder, and the side feeder can in turn be connected upstream to a hopper. Alternatively, the feed zone can be directly connected to the hopper.

[0033] A collection container can be connected to the outlet end of the extruder for collecting the chemically modified particles. In another example, the collection container can be connected to a diverter valve, which can in turn be connected upstream to the outlet end of the extruder and downstream to the collection container. In another example, a screw conveyor is provided to collect and convey the chemically modified particles from the extruder to the collection container or to a tray.

[0034] The particles being fed and processed, as well as the gaseous by-products, should be discharged or metered towards the outlet of the extruder without any backflow or stagnation. This can be achieved by using one or more side feeders placed perpendicular to the feed zone or at any other angle, such that they create an air lock and prevent the backflow of vapors and / or gaseous by-products formed during the processing of the particles. Additionally, the particles can be force-fed to create a positive displacement of the particles and by-products away from the feed zone.

[0035] Examples of suitable twin-screw extruders include, but are not limited to, the Omega series of extruders manufactured by STEER Engineering Private Limited.

[0036] The present disclosure also relates to chemically modified bicarbonate particles. The particles contain bicarbonate and carbonate. A 5% aqueous solution of the chemically modified particles has a pH in the range of 8.6 to 9.6. The particles have a water activity in the range of 0.05 - 0.3a w

[0037] According to one embodiment, the pH of the chemically modified particles is in the range of 9.2 to 9.6. According to one embodiment, the pH of the chemically modified particles is in the range of 9.25 to 9.6

[0038] A bicarbonate is a salt that undergoes a reversible reaction to form a carbonate, water, and carbon dioxide. Examples of bicarbonates suitable for the method include, but are not limited to, carbonate-containing compounds such as potassium bicarbonate, sodium bicarbonate, and calcium bicarbonate, and / or mixtures thereof. According to one embodiment, the bicarbonate is sodium bicarbonate. In another embodiment, the bicarbonate is potassium bicarbonate.

[0039] The pH is measured at regular intervals. According to one embodiment, the pH is measured at intervals of 10 minutes and 30 minutes.

[0040] According to one embodiment, the particles have a water activity in the range of 0.05 - 0.3a w .

[0041] The present disclosure also relates to chemically modified bicarbonate particles comprising a bicarbonate and a carbonate, wherein the pH of a 5% aqueous solution of the particles has a standard deviation of no more than 0.1. The standard deviation is calculated by measuring the pH of at least 10 different samples of the chemically modified particles.

[0042] According to one embodiment, the relative standard deviation of the pH of a 5% aqueous solution of the chemically modified particles collected at regular intervals is less than 1%.

[0043] The chemically modified particles obtained from the process are dry, passivated, and free-flowing.

[0044] The chemically modified bicarbonate particles can be packaged and stored in aluminum bags of various capacities.

[0045] The invention is further illustrated by the following examples, which are used to illustrate the invention and do not limit the scope of the invention. Although the invention has been described in terms of its specific embodiments, certain modifications and equivalents will be apparent to those skilled in the art and are intended to be included within the scope of the invention.

[0046] A method of chemically modifying bicarbonate particles in a co-rotating twin-screw extruder is disclosed. The method includes: feeding the particles into the feed zone of the extruder; treating the fed particles in the heat treatment zone of the extruder at a temperature in the range of 200°C to 350°C for a residence time in the range of 3 to 20 seconds to convert 3% to 40% w / w of the bicarbonate present in the fed particles into a carbonate, thereby chemically modifying the particles; and collecting the chemically modified particles from the extruder.

[0047] A method is disclosed in which the pH of a 5% aqueous solution of the collected particles is in the range of 8.6 to 9.6.

[0048] A method is disclosed in which, at a constant temperature selected from the range of 200 °C to 350 °C, the method provides chemically modified particles having a uniform pH such that the relative standard deviation of the pH value of a 5% aqueous solution of aliquots of the particles collected from the extruder at regular time intervals is less than 1%.

[0049] A method is disclosed in which the collected particles have a water activity in the range of 0.05 - 0.3a w of.

[0050] A method is disclosed in which the bicarbonate is selected from sodium bicarbonate and potassium bicarbonate.

[0051] A method is disclosed in which the method provides a conversion of 10% to 40% w / w of bicarbonate to carbonate.

[0052] A method is disclosed in which the method provides a conversion of 15% to 30% w / w of bicarbonate to carbonate.

[0053] A method is disclosed in which the particles of bicarbonate are fed into the feed zone at a feed rate in the range of 100 g / min to 700 g / min.

[0054] Chemically modified bicarbonate particles are disclosed. The chemically modified bicarbonate particles comprise bicarbonate and carbonate, wherein a 5% aqueous solution of the particles has a pH in the range of 9.25 to 9.6 and a water activity in the range of 0.05 - 0.3a w of.

[0055] Chemically modified bicarbonate particles are disclosed. The chemically modified bicarbonate particles comprise bicarbonate and carbonate, wherein the pH of a 5% aqueous solution of the particles has a standard deviation of no more than 0.1; wherein the standard deviation is calculated by measuring the pH of at least 10 aliquots of the chemically modified bicarbonate particles.

[0056] A method for controlling the amount of carbonate formed during the chemical modification of bicarbonate particles is disclosed. The method comprises: feeding particles of bicarbonate into the feed zone of an extruder, treating the fed particles in the heat treatment zone of the extruder for a residence time in the range of 3 to 20 seconds to convert 3% to 40% w / w of the bicarbonate present in the fed particles to carbonate, thereby chemically modifying the particles, and collecting the chemically modified particles from the extruder, wherein the amount of bicarbonate converted to carbonate is controlled by changing the temperature of the heat treatment zone in the range of 200 °C to 350 °C.

[0057] There is disclosed a method in which 11 - 14% w / w of a bicarbonate is converted to a carbonate by maintaining the temperature of a heat treatment zone at 200 °C.

[0058] There is disclosed a method in which 15 - 19% w / w of a bicarbonate is converted to a carbonate by maintaining the temperature of a heat treatment zone at 225 °C.

[0059] There is disclosed a method in which 26 - 29% w / w of a bicarbonate is converted to a carbonate by maintaining the temperature of a heat treatment zone at 275 °C.

[0060] There is disclosed a method in which, by maintaining the temperature of a heat treatment zone at 300 °C, 35 - 39% w / w of a bicarbonate is converted to a carbonate.

[0061] The present invention includes the following embodiments

[0062] 1. A method for chemically modifying particles of a bicarbonate in a co - rotating twin - screw extruder, the method comprising:

[0063] Feeding the particles into the feed zone of the extruder;

[0064] Treating the fed particles in a heat treatment zone of the extruder at a temperature in the range of 200 °C to 350 °C for a residence time in the range of 3 to 20 seconds to convert 3% to 40% w / w of the bicarbonate present in the fed particles to a carbonate, thereby chemically modifying the particles; and

[0065] Collecting the chemically modified particles from the extruder.

[0066] 2. The method according to item 1, wherein a 5% aqueous solution of the collected particles has a pH in the range of 8.6 to 9.6.

[0067] 3. The method according to item 1, wherein at a constant temperature selected from the range of 200 °C to 350 °C, the method provides chemically modified particles having a uniform pH such that the relative standard deviation of the pH values of 5% aqueous solutions of aliquots of the particles collected from the extruder at regular time intervals is less than 1%.

[0068] 4. The method according to item 1, wherein the collected particles have a water activity in the range of 0.05 - 0.3a w of.

[0069] 5. The method according to item 1, wherein the bicarbonate is selected from sodium bicarbonate and potassium bicarbonate.

[0070] 6. The method according to item 1, wherein the method provides a conversion of 10% to 40% w / w of the bicarbonate to a carbonate.

[0071] 7. The method according to item 1, wherein the method provides a conversion of 15% to 30% w / w of bicarbonate to carbonate.

[0072] 8. The method according to item 1, wherein the bicarbonate particles are fed into the feed zone at a feed rate in the range of 100 g / min to 700 g / min.

[0073] 9. Chemically modified bicarbonate particles, comprising:

[0074] Bicarbonate and carbonate, wherein a 5% aqueous solution of the particles has a pH in the range of 9.25 to 9.6 and a water activity in the range of 0.05 - 0.3a w of.

[0075] 10. Chemically modified bicarbonate particles, comprising:

[0076] Bicarbonate and carbonate, wherein the pH of a 5% aqueous solution of the particles has a standard deviation of not more than 0.1; wherein the standard deviation is calculated by measuring the pH of at least 10 aliquots of the chemically modified bicarbonate particles.

[0077] 11. A method for controlling the amount of carbonate formed during the chemical modification of bicarbonate particles, the method comprising:

[0078] Feeding particles of bicarbonate into the feed zone of an extruder;

[0079] Treating the fed particles in the heat treatment zone of the extruder for a residence time in the range of 3 to 20 seconds to convert 3% to 40% w / w of the bicarbonate present in the fed particles to carbonate, thereby chemically modifying the particles; and

[0080] Collecting the chemically modified particles from the extruder;

[0081] wherein the amount of bicarbonate converted to carbonate is controlled by changing the temperature of the heat treatment zone in the range of 200°C to 350°C.

[0082] 12. The method according to item 11, wherein 11 - 14% w / w of the bicarbonate is converted to carbonate by maintaining the temperature of the heat treatment zone at 200°C.

[0083] 13. The method according to item 11, wherein 15 - 19% w / w of the bicarbonate is converted to carbonate by maintaining the temperature of the heat treatment zone at 225°C.

[0084] 14. The method according to item 11, wherein by maintaining the temperature of the heat treatment zone at 275 °C, 26 - 29% w / w of the bicarbonate is converted into carbonate.

[0085] 15. The method according to item 11, wherein by maintaining the temperature of the heat treatment zone at 300 °C, 35 - 39% w / w of the bicarbonate is converted into carbonate.

[0086] Examples

[0087] Example 1: Preparation of Chemically Modified Sodium Bicarbonate Particles

[0088] The sodium bicarbonate particles are fed into the feed zone of a co - rotating twin - screw extruder through a positive displacement top - feeder.

[0089] The extruder used: Omega 20P of STEER Engineering Private Limited

[0090] Length of the feed zone = 200 mm

[0091] Length of the heat treatment zone = 1 m

[0092] The extruder has a forward - conveying screw configuration to avoid the backward movement of the bicarbonate particles towards the feeder. The screw configuration of the extruder is provided in Table 1A below.

[0093] Table 1A - Screw Configuration

[0094]

[0095] * Components used:

[0096] - RSE: 3 - blade right - hand screw element (3RSE)

[0097] - NRF: Standard (Normal) to RSE transition element

[0098] - RFV: Conventional flight shovel element

[0099] - RFN: RFV to standard screw element

[0100] - CHS: Champer and step

[0101] The feed zone is maintained at approximately 30 °C. The heat treatment zone is maintained at 200 °C. For different tests A to H, the screw speed and feed rate are different. The chemically modified particles leaving the extruder are collected in trays, cooled, and packaged. The effects of changing the feed rate and screw speed on the properties of the chemically modified sodium bicarbonate particles are studied, and the results are provided in Table 1B below:

[0102] Table IB: Influence of Changing Feed Rate and Screw Speed

[0103]

[0104]

[0105] The pH was measured by a Thermo Scientific pH meter. The pH of sodium bicarbonate before feeding into the extruder was 8.24

[0106] Example 2: Preparation of Chemically Modified Sodium Bicarbonate Particles

[0107] The sodium bicarbonate particles were fed into the feed zone of a co-rotating twin-screw extruder through a positive displacement top feeder.

[0108] Extruder used: Omega 20P from STEER Engineering Private Limited

[0109] Length of the feed zone = 200 mm

[0110] Length of the heat treatment zone = 1 m

[0111] The extruder has a forward conveying screw configuration to avoid any backflow of bicarbonate towards the feeder. The screw configuration of the extruder is provided in Table 2A below.

[0112] Table 2A - Screw Configuration

[0113]

[0114] The feed zone was maintained at approximately 30 °C. The heat treatment zone was maintained at 200 °C. The screw speed was set at 500 rpm, and the feed rate was maintained at approximately 620 g / min. The chemically modified particles exiting the extruder were collected in trays, cooled, and packaged.

[0115] The chemically modified particles were studied to determine their consistency during a one-hour run. Samples of the chemically modified particles were collected at the exit of the extruder at 5-minute intervals. Solutions of 5 g of each sample in 200 ml of deionized water were prepared at room temperature and the pH values were determined. The results are provided in Table 2B below.

[0116] Table 2B: pH of Chemically Modified Particles

[0117] Time interval (minutes) pH 5 8.91 10 8.87 15 8.9 20 8.91 25 8.85 30 8.93 35 8.98 40 8.92 45 9.02 50 8.98 55 8.96 60 8.97 Average pH 8.93 Standard deviation (SD) 0.05 Relative standard deviation (RSD) 0.56

[0118] The pH was measured by a Thermo Scientific pH meter

[0119] Observation: Throughout the process, the pH of the sample remained constant with a relative standard deviation (RSD) of 0.56%, indicating the consistency of the chemically modified particles obtained by this method.

[0120] The scanning electron micrograph (SEM) of the product (( Figure 1A ) was compared with the SEM of commercially available chemically modified sodium bicarbonate particles ( Figure 1B ). The SEM showed that the surface modification of the chemically modified particles obtained by the disclosed method was significantly continuous. Example 3: Preparation of Chemically Modified Sodium Bicarbonate Particles

[0121] The sodium bicarbonate particles were fed into the feed zone of a co-rotating twin-screw extruder through a volumetric top feeder.

[0122] The extruder used: Omega 20P from STEER Engineering Private Limited

[0123] Length of the feed zone = 200 mm

[0124] Length of the heat treatment zone = 1 m

[0125] The extruder has a forward conveying screw configuration to avoid any backflow of bicarbonate towards the feeder. The screw configuration of the extruder is provided in Table 1A below.

[0126] Table 3A: Screw Configuration

[0127]

[0128] *SSV-3RSE: Special Shovel Element Transition Element (SSV-3RSE)

[0129] *SSV: Special Shovel-Type Element

[0130] The feed zone was maintained at approximately 30°C. The heat treatment zone was maintained at 220°C. During this process, approximately 250 kg of sodium bicarbonate particles were fed into the extruder. The screw speed was set at 500 rpm, and the feed rate was maintained at 620 g / min. The chemically modified particles exiting the extruder were collected in trays, cooled, and packaged.

[0131] The pH of the untreated sodium bicarbonate particles and the chemically modified particles was measured. The initial pH of a 1% (w / v) solution of the untreated sodium bicarbonate particles was 8.40. The average pH of 1% solutions of 30 samples of the chemically modified particles collected every 10 minutes from the exit of the extruder is provided in Table 3B below.

[0132] Table 3B - Average pH of 1% solutions of 30 samples of chemically modified particles

[0133] Parameter pH of 1% solution Average (n = 30) 9.42 Standard deviation 0.07 Relative standard deviation (%) 0.70

[0134] The water activities of the untreated sodium bicarbonate particles and the chemically modified particles obtained from the disclosed process were calculated and the values are provided in Table 3C below.

[0135] Table 3C - Water activity

[0136]

[0137] Observation: Throughout the method, the pH remained constant with a relative standard deviation of 0.70%, indicating the consistency of the chemically modified particles obtained by this method during long-term test runs.

[0138] Example 4: Preparation of Chemically Modified Sodium Bicarbonate Particles

[0139] The sodium bicarbonate particles were fed into the feed zone of a co-rotating twin-screw extruder through a positive displacement top feeder.

[0140] Extruder used: Omega 20P from STEER Engineering Private Limited

[0141] Length of the feed zone = 200 mm

[0142] Length of the heat treatment zone = 1 m

[0143] The extruder has a forward conveying screw configuration to avoid any backflow of bicarbonate towards the feeder. The screw configuration of the extruder is provided in Table 4A below.

[0144] Table 4 - Screw configuration

[0145]

[0146] The feed zone was maintained at approximately 30 °C. The heat treatment zone was maintained at 220 °C. During the process, approximately 250 kg of sodium bicarbonate particles were fed into the extruder. During the process, the screw speed was set at 500 rpm and the feed rate was maintained at 620 g / min. The chemically modified particles leaving the extruder were collected in trays, cooled and packaged.

[0147] The pH of the untreated sodium bicarbonate particles and the chemically modified particles was measured. The initial pH of a 1% solution of the untreated sodium bicarbonate particles was 8.38. The average pH of 1% solutions of 10 samples of the chemical particles collected at 15-minute intervals from the exit of the extruder was 9.26 and the relative standard deviation was 0.39%.

[0148] Observation: Throughout the process, the pH remained constant with a relative standard deviation of 0.39%, indicating the consistency of the chemically modified particles obtained by this method during long-term test runs.

[0149] Example 5: Preparation of Chemically Modified Sodium Bicarbonate Particles

[0150] The sodium bicarbonate particles were fed into the feeding zone of a co-rotating twin-screw extruder through a positive displacement top feeder via a side feeder with a position perpendicular to the extruder barrel.

[0151] The extruder used: Omega 20P from STEER Engineering Private Limited

[0152] Length of the feeding zone = 200 mm

[0153] Length of the heat treatment zone = 1 m

[0154] The extruder has a forward conveying screw configuration to avoid any backflow of bicarbonate towards the feeder. The screw configuration of the extruder is provided in Table 5A below.

[0155] Table 5 - Screw Configuration

[0156]

[0157] The feeding zone was maintained at approximately 30°C. The heat treatment zone was maintained at 220°C. During this process, approximately 100 kg of sodium bicarbonate particles were fed into the extruder. During this process, the screw speed was set at 500 rpm, and the feeding rate was maintained at 36 kg / hr. The chemically modified particles exiting the extruder were collected in trays, cooled, and packaged.

[0158] The pH of the untreated sodium bicarbonate particles and the chemically modified particles was measured. The pH of a 5% solution of the untreated sodium bicarbonate particles was 8.03. The average pH of 17 samples of 5% solutions of the chemically modified particles collected at 10 - minute intervals from the exit of the extruder was 8.68, and the relative standard deviation was 0.6%.

[0159] Observation: Throughout the process, the pH remained constant with a relative standard deviation of 0.6%, indicating the consistency of the chemically modified particles obtained by this method during long-term test runs.

[0160] The carbon dioxide content of the chemically modified sodium bicarbonate particles was also measured. The difference in weight between a flask with 50 ml of 2N sulfuric acid solution and the weight after adding the sample (5 g of input sodium bicarbonate / 5 g of treated sodium bicarbonate) gave the weight of the retained carbon dioxide in the sodium bicarbonate after the passivation process.

[0161] Observation: The relative carbon dioxide retention of the chemically modified particulate sodium bicarbonate is 96.88% compared to the untreated particulate sodium bicarbonate.

[0162] Example 6: Preparation of Chemically Modified Potassium Bicarbonate Particles

[0163] The potassium bicarbonate particles were fed into the feed zone of a co-rotating twin-screw extruder at a rate of 37.2 kg / hr through a positive displacement top feeder via a side feeder perpendicular to the extruder barrel. The product leaving the extruder was passed over a downstream screw conveyor and finally into a receiver.

[0164] Extruder used: Omega 20P from STEER Engineering Private Limited

[0165] Length of the feed zone = 200 mm

[0166] Length of the heat treatment zone = 1 m

[0167] The extruder has a forward conveying screw configuration to avoid any backflow of bicarbonate towards the feeder. The screw configuration of the extruder is provided in Table 6 below.

[0168] Table 6 - Screw Configuration

[0169]

[0170] The feed zone was maintained at approximately 30°C. The heat treatment zone was maintained at 350°C.

[0171] The pH and water activity of the untreated potassium bicarbonate particles and the chemically modified particles were measured.

[0172] The pH of a 5% w / v solution of the untreated sodium bicarbonate particles was 8.34. The average pH of a 5% solution of three samples of the chemically modified particles collected from the outlet of the extruder was 9.40.

[0173] The initial water activity of the untreated potassium bicarbonate particles was: 0.462 a w . The water activity of the chemically modified potassium bicarbonate particles was: 0.057 a w .

[0174] Observation: The pH remained constant throughout the treatment, indicating the consistency of the chemically modified particles obtained by this method during long-term test runs.

[0175] Example 7: Effect of Variation in Temperature of the Heat Treatment Zone on the Carbonate Content of Chemically Modified Sodium Bicarbonate Particles

[0176] Sodium bicarbonate granules are fed into the feeding zone of a co-rotating twin-screw extruder at a rate of 36 kg / hr.

[0177] The extruder used: Omega 20P from STEER Engineering Private Limited

[0178] Length of the feeding zone = 200 mm

[0179] Length of the heat treatment zone = 1 m

[0180] The extruder has a forward conveying screw configuration to avoid any backflow of bicarbonate towards the feeder. The screw configuration of the extruder is provided in Table 7A below.

[0181] Table 7A - Screw Configuration

[0182]

[0183] The feeding zone is maintained at approximately 30°C. As provided in Table 7B, the heat treatment zone is maintained at different temperatures during different trials. Each trial runs for approximately 30 minutes. Samples of the chemically modified granules are collected at regular time intervals (0 min, 10 min, and 30 min). The sodium carbonate content and pH of the samples are determined.

[0184] Estimation of Sodium Carbonate in Sodium Bicarbonate Granules

[0185] Preparation of sample solution S1: Transfer 2000 mg of sodium bicarbonate to a 100 ml volumetric flask. Add 70 ml of diluent to the (volumetric) flask and sonicate to dissolve the sodium bicarbonate and mix well.

[0186] Estimation of sodium carbonate: Pipette 25 ml (V3) of S1 into a 100 ml conical flask. Add a few drops of phenolphthalein indicator and immediately titrate with 0.1 M HCL until the solution becomes colorless. Take the average of the readings for 3 samples. The sodium carbonate content in mg is calculated using the following formula:

[0187]

[0188] Amount of sodium carbonate in the sample solution (mg) = M3 x molar mass of sodium carbonate in g / mol X 100 (dilution of the sample)

[0189] % Sodium carbonate = amount of sodium carbonate in mg X 100 weight of the sample in mg

[0190] M2: Molar concentration of 0.1 M HCl in mol / dm 3 Calculated.

[0191] M3: In mol / dm3 The molar concentration of sodium carbonate in the sample solution calculated

[0192] VB: The volume of 0.1 M HCl consumed for half-neutralization of sodium carbonate in mL.

[0193] V3: The volume of the sample (S1) taken in ml.

[0194] Table 7B - Influence of the temperature in the heat treatment zone

[0195]

[0196]

[0197] Observation: The amount of conversion of sodium bicarbonate to sodium carbonate can be controlled by changing the temperature in the heat treatment zone.

[0198] Industrial applicability

[0199] The present disclosure provides chemically modified bicarbonate particles and methods for preparing them. The particles are mostly modified on the surface.

[0200] The disclosed methods effectively provide a consistent degree of chemical modification of the particles. The methods are economical and do not require special controls to maintain room temperature and / or humidity. The disclosed methods allow for the continuous manufacture of chemically modified bicarbonate particles.

[0201] The chemically modified particles obtained from the method are dry, passivated, and free-flowing. The amount of the corresponding carbonate formed is consistent throughout the run. The pH of the solution of the particles exhibits a standard deviation of less than 1%, indicating that the obtained particles have been uniformly modified. In addition, the obtained particles exhibit enhanced stability and shelf life.

Claims

1. Chemically modified bicarbonate particles, which comprise: bicarbonate and carbonate, wherein a 5% aqueous solution of the chemically modified bicarbonate particles has a pH in the range of 9.25 to 9.6 and a water activity in the range of 0.05 - 0.3, and wherein the particles contain 3% to 40% w / w of carbonate.

2. The chemically modified bicarbonate particles of claim 1, wherein the pH of a 5% aqueous solution of the particles has a standard deviation of no more than 0.1, wherein the standard deviation is calculated by measuring the pH of at least 10 aliquots of the chemically modified bicarbonate particles.

3. The chemically modified bicarbonate particles of claim 1, wherein the bicarbonate is selected from sodium bicarbonate, potassium bicarbonate, and calcium bicarbonate.

4. The chemically modified bicarbonate particles of claim 1, wherein the particles contain 11% to 14% w / w of carbonate.

5. The chemically modified bicarbonate particles of claim 1, wherein the particles contain 15% to 19% w / w of carbonate.

6. The chemically modified bicarbonate particles of claim 1, wherein the particles contain 26% to 29% w / w of carbonate.

7. The chemically modified bicarbonate particles of claim 1, wherein the particles contain 35% to 39% w / w of carbonate.

8. The chemically modified bicarbonate particles of claim 1, wherein the chemically modified bicarbonate particles are obtained by treating particles of bicarbonate in a co-rotating twin-screw extruder by a method comprising: feeding the particles of bicarbonate into the feed zone of the extruder; treating the fed particles in the heat treatment zone of the extruder at a temperature in the range of 200°C to 350°C for a residence time in the range of 3 to 20 seconds to convert 3% to 40% w / w of the bicarbonate present in the fed particles to carbonate, thereby obtaining the chemically modified bicarbonate particles; and collecting the chemically modified bicarbonate particles from the extruder.

9. The chemically modified bicarbonate particles of claim 8, wherein 10% to 40% w / w of the bicarbonate is converted to carbonate.

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