WO2024033276A1

WO2024033276A1 - Amorphous non-nano silica spheres

Info

Publication number: WO2024033276A1
Application number: PCT/EP2023/071757
Authority: WO
Inventors: Joana R. COSTA; Maria Manuela Estevez Pintado; Morrison Clark DALE; Alexander Clark DALE; Rhys Thomas DALE; Yong Huang; Ana Raquel Mendes Ferreira Monteiro Madureira
Original assignee: Amyris Bio Products Portugal Unipessoal Lda; Universidade Católica Portuguesa
Priority date: 2022-08-08
Filing date: 2023-08-07
Publication date: 2024-02-15

Abstract

Disclosed herein are non-nano amorphous silica spheres and methods for manufacturing silica using renewable resources. Embodiments of the disclosed non-nano amorphous silica spheres have an average particle size ranging between 1 µm and 10 µm. Also disclosed are compositions containing same and methods for the preparation and use thereof.

Description

AMORPHOUS NON-NANO SILICA SPHERES

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application No. 63/370,684, filed on August 8, 2022, which is herein incorporated by reference in its entirety.

BACKGROUND

Silicon dioxide (also known as silica) is one of the most common minerals in the earth's crust. Conventionally, silica is sourced from non-renewable resources (such as sand, gravel, clay, granite, diatomaceous earth, and many other forms of rock) using environmentally harmful methods. For example, sourcing silica from sand by dredging requires significant energy consumption and emits large amounts of CO2.

Silica is used widely in personal care products, including cosmetics, due to its multifunctioning nature, primarily as an absorbent powder and thickening agent in cosmetics. Silica employed in personal care products, however, are currently sized as nano material; /.<?., having particle sizes in the range of 2 -50nm. Consumers and researchers are becoming increasing aware and concerned about interactions of biological systems (such as the skin) and nanomaterials.

What is needed is a renewable, environmentally responsible form of silica in a non-nano size to address the unmet needs of the industry.

SUMMARY

Disclosed herein are methods of deriving silica from biological materials, compositions of such matter, articles of manufacture and amorphous silica spheres. Evidence demonstrates what is disclosed herein to be superior to the silica obtained from sand and other non-renewable sources of silica in personal care products, particularly cosmetics. The following disclosure also offers an alternative to microplastics which are currently being phased out of many cosmetic products.

For example, the silica, methods, compositions of matter and articles thereof disclosed herein improve the properties of personal care products, particularly cosmetics, such as smoothness for spreadability, abrasiveness for cleansing and exfoliating, soft focus, soft scrub, matte finish, light deflection and oil absorption. Furthermore, the amorphous silica spheres disclosed herein also improve the even distribution of pigments in cosmetics, prevent setting thereof in applying makeup, and enhance the absorption by the skin of other ingredients. For example, the disclosed amorphous silica spheres have unique sphericity, high oil absorption, particle size distribution and oil/water absorption ratio. These characteristics supply benefits such as sebum control, mattification, and anti-aging effects without drying the skin.

As described in further detail below, the claimed invention relates to unique amorphous silica spheres consisting of amorphous spheres having particles with an average size between 1 to about 10 pm and methods for their manufacture. Additional embodiments of the invention relate to compositions of matter containing the amorphous silica spheres of the invention and a suitable carrier therefore adapted for admixture with personal care products; compositions of matter comprising a personal care product and product improving amounts of the above described amorphous silica spheres; compositions of matter comprising a personal care product and product improving amounts of the above described compositions containing the amorphous silica spheres and a carrier, and articles of manufacture, each comprising packaging material containing any of the above described products or compositions, wherein each packaging material contains instructions for the use thereof.

DESCRIPTION OF DRAWINGS

Fig. l is a block diagram of an embodiment of the invention comprising a method of preparing the above-described amorphous silica spheres.

Fig. 2 is a more detailed block diagram of Fig. 1.

Fig. 3 is a block diagram of a metals mitigation method which may be incorporated into the methods depicted in Figs 1 and 2.

DETAILED DESCRIPTION

The amorphous silica spheres disclosed herein differ from those currently manufactured in various respects, including size, composition, and methods of manufacture. For example, the amorphous silica spheres of the claimed invention are between 1 to 10 pm in size - significantly larger that the nano-particles employed in traditional articles of manufacture. Moreover, the claimed invention derives from the unexpected discovery that amorphous silica spheres of the above particle size range perform unexpectedly superior to traditional silica, particularly in personal care products, such as cosmetics, for example.

The amorphous silica spheres of the present invention are prepared by reacting a biogenic ash; e.g. sugarcane bagasse ash (SCBA) with a base to form a silicate, although it will be understood by those skilled in the art that any suitable biogenic ash may be employed in the practice of the invention. Although the invention is exemplified herein employing sodium hydroxide (NaOH) in pellet form or in aqueous solution to produce sodium silicate, it will be understood by those skilled in the art that any suitable base may be employed including, but not limited to lithium hydroxide (LiOH), potassium hydroxide (KOH) and the like.

The silicate is solubilized and then acidified to yield precipitated amorphous silica. Although the invention is exemplified herein employing sulfuric acid (H2SO4) to form the amorphous silica, it will be understood by those skilled in the art that any suitable acid may be employed.

The amorphous silica is then homogenized to form particles of essentially uniform size and spray dried to produce the desired non-nano amorphous spheres. Although milling is described in the examples, it will be understood by those skilled in the art that any suitable homogenization method may be employed.

Surprisingly, it has been found, as set forth in the following examples, that the sphericity and size of the ultimate non-nano amorphous silica spheres is dependent on the size of the SiCh particles fed to the spray dryer. Thus, a SiCh feed to the spray drier having a particle size of 0.1 - 1 micron ultimately yielded non-nano amorphous silica spheres having a particle size of from about 1 to about 10 microns. Moreover, as demonstrated in the Examples below, acid concentration, % silica, and temperature during the neutralization/precipitation step determine the oil absorption/density of the final product.

The foregoing description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the claimed invention, since the scope of the claimed invention is best defined by the appended claims.

Several methods of preparing amorphous silica sphere according to the claimed invention are described in the following examples. These examples are not to be taken in a limiting sense. Rather, these examples are provided merely for the purpose of illustrating the general principles of the claimed invention, since the scope of the claimed invention is best defined by the appended claims.

EXAMPLES

EXAMPLE 1

Referring to FIG. 1, the ash was separated from impurities such as sand, for example in the Siever 1 and conveyed to Heating Mix Reactor 2 where it was mixed with a 50% NaOH solution and allowed to react at 350°C for 20 minutes to produce sodium silicate [Na2SiOs], which was then conveyed to Filter Press 3 where the silicate solution was separated from solid waste.

The silicate solution was conveyed to Mixer 4 to which was added H2SO4 [10% (v/v) or 17.26% (w/w)] to promote silica gel formation by precipitation. Liquid waste was drained from the mixer and the silicate solution sent to Filter Press 5 where water was added and, after filtration to remove liquid waste, a silica gel in the form of a wet cake remained.

The wet cake was slurried in water in Mixer 6 where it was homogenized as described further below.

The homogenized solution was then fed to Spray dryer 7 to produce the final non-nano amorphous silica spheres product having an average particle size ranging between 1 to 10 microns.

EXAMPLE 2

Fig. 2 illustrates in greater detail the method carried out in the system depicted in Fig. 1. Examples of raw materials used in Fig. 2 are shown below in Table 1.

Table 1

As described in further detail below, the final product of the method illustrated in Fig. 2 are amorphous silica spheres, with a particle size between 2-8 microns. Furthermore, the feed composition using the method illustrated in Fig. 2 include: Ashes/NaOH 1 kg sifted ash: 1.5 kg NaOH (dw). Exemplary storage and temperature conditions are shown below in Table 2.

Table 2

Referring now to Fig. 2, the steps illustrated are summarized in Table 3 and described in further detail below.

Table 3

As shown in Fig. 2, raw sugar cane fly ash was sieved through a 100 mesh screen (Siever) as in Example 1 to produce a dry biogenic ash essentially free of large particles and non- biogenic silica such as quartz and field sand, for example. While not shown in Fig. 2, dry biogenic ash can be sifted through 100 - 120 mesh screens. The expected yield is 50 - 60% through the 100 mesh screen shown in Fig. 2.

Optionally, the ash may be pretreated with acid (2a) as described below to remove metal impurities that may be present.

The ash was conveyed to the mix reactor to which a 50% solution of sodium hydroxide was added. Reaction was allowed to proceed at the depicted temperature and time:

2NaOH + SiO₂ Na₂SiO₃ + H₂O.

The reactions produce amorphous sodium silicate (Na₂SiO₃). Optimally, the reaction takes place at 185 - 350 °C (just above NaOH pellets 318 °C, melting point). According to certain embodiments disclosed herein, the mass ratio of 1.5 : 1 (NaOH: ash) is the optimized ratio. Further options include:

• Option 2.1 : Higher Temp (350 C), NaOH pellets, Shorter Time (2 hours)

• Option 2.2: Lower Temp (185 C), 50% NaOH, Longer Time (7 hours)

According to the foregoing, if reactor option 2.1 is chosen (Higher Temp / Shorter Time), the ash material may form large solids that require milling to allow for the material to be solubilized after the reaction. The material needs to be put into solution prior to filtration.

Since the theoretical solubility of sodium silicate is 22 g/100 ml water, the methods disclosed herein may further optimize water quantity by using higher values. Further alternatives include speeding up the sludge removal at the filtration unit. Moreover, during scaleup the water content can be adjusted depending on the mixer conditions (open or closed) and filtration system.

The sodium silicate solution was next filtered in the filter press 1 to remove all insoluble material and produce a clear/clean sodium silicate filtrate. For example, a filter press rated at 0.3-3 cfm or pore size 0.5 - 5 pm is preferably used for this separation. Furthermore, filter aids may be employed (e.g., AC) and/or filtration with a tighter membrane may be used to remove fine suspensions. It will be understood by those skilled in the art that any suitable means may be employed to separate unwanted materials.

Although a filtration system comprising a filter press or modular filter is preferred, It will be understood by those skilled in the art that any suitable means may be employed to separate unwanted materials including, but not limited to vacuum filtration and the like. Vacuum filtration tends to produce high tension and sludge may break through the filter paper. Often, pore size is a limiting factor and not the membrane material (e.g., a material that must be resistant to the pressure and high pH). Furthermore, with respect to the vacuum filtration, independent of the water added and the final solution, the remaining sludge has a viscosity of 50 cP and a density of 1.32 (room temperature). The resulting product of these vacuum filtration methods is a transparent yellow to brown solution with a pH of 11 to 12. Wastes produced include a black sludge rich in sodium hydroxide, minerals (mainly sodium, potassium, iron and calcium) and residual sodium silicate (pH 11 - 12).

Returning to Fig. 2, acid is next added to the clear sodium silicate filtrate stream to promote silica gel formation by precipitation. Preferably, sulfuric acid [ 10-30% solution] is added to the sodium silicate solution in a mixed reactor until a pH of 6-7 is reached. To generate final product silica with controlled density and oil absorption, the precipitation temperature should preferably be lower than 30 °C (see Table 4). A pH potentiometer may be employed to monitor the addition of acid and the decrease in pH. The reaction produces a precipitated amorphous silica gel and sodium sulphate as residue, according to the equation: Na₂SiO₃ + H2SO4 SiO₂ + Na₂SO₄ + H₂O

Table 4, shown below, illustrates the impact of precipitation temperature on final product density and oil absorption.

Table 4

The product is filtered to remove amorphous silica gel [typically a 20 - 30% solid wet cake]. The wet cake may be contaminated with metal impurities such as Al, Fe, and Cr, which are removed by be re-slurrying the wet cake in water and acid washing with an either an inorganic acid at a pH of less than 0.95 or an organic acid with chelating functionalities at pH 2-3 (see Example 3). As disclosed herein, the acid washed silica solution is next filtered, preferably through a filter press using filter press media rated at 3 cfm or pore size 0.5 - 5 pm. It will be understood by those skilled in the art that any suitable type of filter may be employed to isolate the wet cake which is used for the next step in the process.

For example, according to Fig. 2, the sodium silicate produced by the filter press was conveyed to the neutralization mixer to which H2SO4 [10% (v/v) or 17.26% (w/w)] was next added to achieve a pH of 7 to promote silica gel formation by precipitation. It will be understood by those skilled in the art that any suitable inorganic or organic acid may be employed.

The precipitated silica gel was removed and optionally acid washed at pH of 0.9 before being sent to the filter press rated at 3 cfm or pore size .5 - 5 , wherein liquid waste and soluble materials were removed to produce a silica gel in the form of a wet cake. It will be understood by those skilled in the art that any suitable separation means may be employed in this step.

The wet cake was slurried in water (e.g., RO water) in the mixer to form a 5-7% solution at a pH of 5.5 - 8.5. The slurried wet cake was transported to the homogenizer/mill where it was resuspended in water and homogenized/milled at high pressure e.g., 3,000, 5,000 psi, 6,000 psi, etc.) for 1 - 2 passes to reduce the particle size thereof to below 1 micron.

The homogenized solution was then fed to the spray dryer to produce the final non-nano amorphous silica spheres having a moisture of less than 5% (LOD) and an average particle size ranging between 1 to 10 microns. EXAMPLE 3

The silica gel can be subjected to an acid wash to remove metals. The main metal impurities in silica are Al, Fe and Cr, which can be mitigated by using inorganic acids at pH lower than 0.95 or using organic acids with chelating functionalities at pH 2-3. The metals (Al, Fe and Cr) removal efficiency of acids from high to low are listed as below: HC1 > H2SO4 = Citric Acid > HNO3 > Acetic Acid. For example, the method illustrated in Fig. 2 was modified as follows:

Step 5a. Use of sulfuric acid for acid wash on silica gel:

• Concentration and pH: used 1 M H2SO4 with the pH of the silica solution lower than 0.95

• Reaction time: 5-14 hr

• Temp: 25 °C or higher

• Mixing: 200-300 rpm to make sure solution is well mixed

• Silica gel concentration: 5-7 wt%

• After acid wash, the silica cake was rinsed with ~3 B V DI water followed by weak NaOH (0.2 g/L) and DI water to bring the pH of rinse water back to 6.5

• TDS < XX or Conductivity < 100 Micro Siemens

Step 5b. Use of citric acid for acid wash on silica gel:

• Citric acid concentration 7 wt% (range 5-10 %) with the pH of the silica solution between 2-3

• Reaction time: 14 hr

• Temp: 25 °C or higher

• Mixing: 200-300 rpm to ensure the solution is well mixed

• Silica gel concentration: 5-7 wt%

• After acid wash, the silica cake was rinsed with ~3 B V DI water followed by weak NaOH (0.2 g/L) and DI water to bring the pH of the rinse water back to 6.5

• TDS < XX or Conductivity < 100 Micro Siemens Table 5, shown below, illustrates the estimated metal levels of final product after acid wash on dry basis silica (indicated by an asterisk (*)) or on wet basis silica (indicated by underlined text).

Table 5

As shown in Table 5, the following metal removal efficiencies are provided according to the methods disclosed herein: • Cr3 removal: HC1 (82%) > H2SO4 = Citric (40-50%) > HNO3 (29%) >Acetic acid (18%)

• Al/Fe removal: HC1 (88/76%) > H2SO4 >= Citric acid > HNO3 >Acetic acid

• Cr6 removal: Ascorbic acid can reduce Cr6 to Cr3 at low pH.

The results demonstrate that a citric acid/sulfuric acid washing of the silica gel or the sugarcane bagasse ash (SCBA) provides the most efficient metals mitigation.

In addition, as mentioned previously, the acid (e.g., citric acid) may be used as an acid wash on the sifted ash (SCBA). For example, the methods illustrated in Fig. 2 were modified as follows:

Optional step 2a. Use of Citric acid for acid wash on sifted ash (SCBA): • Citric acid concentration 7 wt% and pH of the silica solution between 2-3

• Reaction time: 14 hr

• Temperature: 25 °C or higher • Ash concentration: 10 wt%

• After acid wash, the silica cake was rinsed with ~3 BV DI water followed by weak NaOH (0.2 g/L) and DI water to bring the pH of the rinse water back to 6.5

Exemplary results of optional step 2a described above and illustrated in Fig. 2 are shown below in Table 6.

Table 6

Acid choice may vary based on the disclosed methods and equipment employed; however, H2SO4 or citric acid is preferred since HC1 is not compatible with stainless reactors. An acid wash (e.g., citric acid) may be performed on the sifted ash and thereby reduce >50% Cr, Fe and Al.

OTHER EMBODIMENTS

It is to be understood that while the invention has been described in conjunction with the detailed description thereof, the foregoing description is intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the following claims.

Claims

WHAT IS CLAIMED IS:

1. Amorphous silica spheres having an average particle size between 1 pm and 10 pm.

2. A method of preparing the amorphous silica spheres of claim 1, comprising: reacting a biogenic ash with a base to produce a silicate; acidifying the silicate to produce a silica gel cake; suspending the silica gel cake in water; homogenizing the suspended silica gel cake in water; and spray drying the homogenized silica gel cake to produce the amorphous silica spheres.

3. The method of claim 2, wherein said biogenic ash is sugar cane bagasse ash.

4. The method of claim 2, wherein said base is sodium hydroxide and said silicate is sodium silicate.

5. The method of claim 2, wherein said silicate is acidified with H2SO4.

6. A composition of matter adapted for admixture with a personal care product comprising the amorphous silica spheres of claim 1, and a compatible carrier therefore.

7. The composition of claim 6, wherein said personal care product is a cosmetic.

8. A composition of matter comprising a personal care product and the amorphous silica spheres of claim 1.

9. The composition of claim 8, wherein said personal care product is a cosmetic.

10. A composition of matter comprising a personal care product and the composition of claim 6.

11. The composition of claim 10, wherein said personal care product is a cosmetic.

12. A method of enhancing the properties of a personal care product comprising admixing therewith the amorphous silica spheres of claim 1.

13. The method of claim 12, wherein said personal care product is a cosmetic.

14. A method of enhancing the properties of a personal care product comprising admixing therewith a composition of claim 6.

15. The method of claim 14, wherein said personal care product is a cosmetic.

16. An article of manufacture comprising packaging material containing the amorphous silica spheres of claim 1, said packaging material containing instructions for the use thereof.

17. An article of manufacture comprising packaging material containing the composition of claim 6, said packaging material containing instructions for the use thereof.

18. An article of manufacture comprising packaging material containing the composition of claim 7, said packaging material containing instructions for the use thereof.

19. An article of manufacture comprising packaging material containing the composition of claim 9, said packaging material containing instructions for the use thereof.

20. The method of claim 2, including the step of removing metal impurities by washing either the biogenic ash or the silica gel with an acid.

21. The method of claim 2, further comprising a step of removing non-biogenic impurities from the ash prior to reaction with the base.

22. The method of claim 21, wherein said removal is effected with a si ever.

23. The method of claim 22, wherein said siever comprises a 100 to 120 mesh screen.

24. The method of claim 2, wherein the base: ash mass ratio is optimally 1.5 : 1.

25. The method of claim 4, wherein the reaction of biogenic ash with NaOH pellets is conducted at 350°C for about two hours.

26. The method of claim 4, wherein the reaction of biogenic ash with NaOH solution is conducted at 350°C for about two hours.

27. The method of claim 2, wherein the silica gel cake is precipitated at about 30 °C.

28. The method of claim 2, wherein the biogenic ash is reacted with an aqueous base to produce a silicate solution.

29. The method of claim 28, further comprising a step of separating the silicate from solid waste.

30. The method of claim 29, wherein the step of separating the silicate from solid waste is effected in a filter press.

31. The method of claim 30, wherein the filter press comprises a 0.3-3 cfm filter cloth.

32. The method of claim 29, wherein the step of separating the silicate from solid waste is effected by vacuum filtration.

33. The method of claim 2, further comprising a step of separating the precipitated silica gel from solid waste.

34. The method of claim 33, wherein the step of separating the silica gel from solid waste is effected in a filter press.

35. The method of claim 34, wherein the filter press comprises a 0.3-3 cfm filter cloth.

36. The method of claim 33, wherein the step of separating the silica gel from solid waste is effected by vacuum filtration.

37. The method of claim 2, wherein said silica gel is precipitated from said silicate by admixture with an acid.

38. The method of claim 37, wherein said acid is H2SO4.

39. The method of claim 38, wherein the concentration of TbSC is 10% (v/v) or 17.26% (w/w).