Claims:We Claim:

1. A process for preparing pseudo boehmite crystals comprising:
calcining aluminum trihydrate to form alumina;
milling the alumina to obtain alumina particles having a particle size distribution in the range of 10 to 80µm;
forming a slurry of the alumina particles in an aqueous solution of acetic acid;
heating the slurry under a pressure; and
flashing the slurry by withdrawing the pressure to form pseudo boehmite crystals.

2. The process as claimed in claim 1, wherein the slurry is heated at a pressure in the range of 32 bar to 1.01325 bar.

3. The process as claimed in claim 1, wherein the aqueous solution of acetic acid has a volume/volume ratio of water and acetic acid in the range of 0.5:1 to 1:2.

4. The process as claimed in claim 1, wherein the aluminum trihydrate is calcined to form alumina having a specific surface area in the range of 150 to 300m2/g.

5. The process as claimed in claim 1, wherein the slurry of the alumina particles has a solid content of 15 to 25%.

6. The process as claimed in claim 1, wherein the slurry of the alumina particles is heated at a temperature ranging from 120 to 220°C.
7. The process as claimed in claim 1, further comprising separating the pseudo boehmite crystals from the slurry.

8. The process as claimed in claim 8, further comprising drying the pseudo boehmite crystals at a temperature ranging from 80 to 90°C.

9. The process as claimed in claim 1, wherein the formed pseudo boehmite crystals have a specific surface area in the range of 90 to 260m2/g.

Dated this 19th day of July, 2017

Essenese Obhan
Of Obhan & Associates
Agent for the Applicant
Patent Agent No. 864 , Description:FIELD OF INVENTION
The present disclosure relates to a process for preparing pseudo-boehmite crystals from aluminum trihydrate.

BACKGROUND
The term, boehmite, is used in the chemical industry to describe alumina hydrates which exhibit X-Ray Diffraction (XRD) patterns close to that of the Aluminum oxide-hydroxide [AlO(OH)], naturally occurring boehmite or diaspore. Boehmite, usually broadly describes a wide range of alumina hydrates which contain different amounts of water of hydration, different surface areas, pore volumes, specific densities and also exhibit different thermal characteristics while undergoing thermal treatments. XRD patterns of alumina hydrates, although exhibit the characteristic boehmite [AlO(OH)] peaks, usually vary in their widths and can also shift in their location. The sharpness of the XRD peaks and their location are indicative of degree of crystallinity, crystal size and amount of imperfections in the crystal structures.
Broadly, boehmite aluminas can be categorized into two categories; the first category contains boehmites which have been synthesized and/or aged at temperatures close to 100°C and most of the time under ambient atmospheric pressures. This type of boehmite is poorly crystallised form of boehmite and is generally referred to as quasi-crystalline boehmites or pseudo-boehmites. The second category of boehmite consists of so-called micro-crystalline boehmites. Micro crystalline boehmites are boehmites with high degree of crystallinity, relatively large crystal size and low surface area. XRD pattern of pseudo-boehmite differs from crystalline boehmite in broadening of the reflections and higher ‘d’ spacing values.
Pseudo-boehmite is widely used for making catalyst substrate for various applications, majorly in petroleum and polymer industries. Pseudo-boehmite is having property of self-binding and easily forms into extrudates and pellets. Extruded pseudo-boehmite material can be activated into transition phases having high surface area, pore volume and excellent thermal stability. The unstable transition alumina (pseudo-boehmite) is having property of formation of gel with acids like hydrochloric acid, acetic acid or formic acid. Gelling property of pseudo-boehmite makes it highly desirable for use in the manufacture of Fluid Catalytic Cracking (FCC) catalysts. FCC of petroleum products requires gelling catalysts for efficient cracking of the petroleum products.
Pseudo-boehmite is generally manufactured commercially by processes involving neutralisation of aluminium salts by alkalis, acidification of aluminate salts and hydrolysis of aluminium alkoxide. In the said processes, there is a generation large amounts of hazardous wastes due to large scale precipitation and washing, thereby leading to environmental pollution.
Thus, there is need and scope for a new and improved process for preparing pseudo-boehmite from aluminum trihydrate, which can produce pseudo-boehmite in high yield and purity, which is simple and easy to carry out, economical and reduce wastage, environmental friendly and reduce energy requirements.

SUMMARY
The present disclosure relates to a process for preparing pseudo-boehmite crystals from aluminum trihydrate. The process comprises of calcining aluminum trihydrate to form alumina, milling the alumina to obtain alumina particles having a particle size distribution in the range of 10 to 80µm, forming a slurry of the alumina particles in an aqueous solution of acetic acid, heating the slurry under a pressure, and flashing the slurry by withdrawing the pressure to form pseudo boehmite crystals.

BRIEF DESCRIPTION OF DRAWINGS
Figure 1: illustrates XRD patterns of boehmite crystals obtained in accordance with example 1 of the disclosed method.
Figure 2: illustrates XRD patterns of boehmite crystals obtained in accordance with example 2 of the disclosed method.
Figure 3: illustrates XRD patterns of boehmite crystals obtained in accordance with example 3 of the disclosed method.
Figure 4: illustrates XRD patterns of pseudo-boehmite crystals obtained in accordance with example 4 of the disclosed method.

DETAILED DESCRIPTION
For the purpose of promoting an understanding of the principles of the invention, reference will now be made to embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the disclosed process and system, and such further applications of the principles of the invention therein being contemplated as would normally occur to one skilled in the art to which the invention relates.
It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof.
Reference throughout this specification to “one embodiment” “an embodiment” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrase “in one embodiment”, “in an embodiment” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.
The present disclosure provides a process for preparing pseudo-boehmite crystals from aluminum trihydrate. Specifically, the disclosed process provides pseudo-boehmite crystals with high specific surface area and enhanced functionality.
The process for preparing pseudo-boehmite crystals comprises of calcinating aluminum trihydrate to form alumina. In accordance with an embodiment, the aluminium trihydrate is calcinated at a temperature in the range of 300°C to 500°C. The calcination may be carried out in any known equipment including but not limited to a calciner, an electric furnace, a vertical shaft kiln or a rotary kiln. In a preferred embodiment, the aluminium trihydrate is calcinated in a calciner. In accordance with an embodiment, the alumina formed by calcining the aluminum trihydrate has a specific surface area in the range of 150 to 300m2/g. In a preferred embodiment, the alumina has a specific surface area of 200 to 300m2/g.
The alumina so formed is milled to obtain alumina particles. In accordance with an aspect, the alumina is milled to obtain alumina particles having a particle size distribution in the range of 10 to 80µm. Milled alumina enables efficient conversion to pseudo-boehmite and requires lower energy. The alumina may be milled in any milling equipment including but not limited to ball mill or microfiner. Preferably the calcined alumina is milled in a grinding media such as a ball mill made of alumina. Preferably, the calcined alumina is milled with 18 to 25% of grinding media made of alumina having greater than 90% alumina.
A slurry of the alumina particles is formed in an aqueous solution of acetic acid. In accordance with an aspect, the aqueous solution of acetic acid for forming the slurry of alumina has a volume/volume ratio of water and acetic acid in the range of 0.5:1 to 1:2. Preferably, the volume/volume ratio of water and acetic acid in the aqueous solution of acetic acid is 1:1. In accordance with an aspect, the slurry of the alumina has a solid content in the range of 15 to 25%.
The slurry of the alumina particles in the aqueous solution of acetic acid is formed at a pH in the range of 2 to 4. Maintaining the pH of the slurry of the alumina particles between 2 to 4 suppresses the crystalline phase of the boehmite, during heating of the slurry. As a result, the pseudo boehmite crystal remains semi amorphous boehmite, thus avoiding the formation of gibbsite. Reference may be made to example 4, illustrating that only pseudo-boehmite is obtained when the slurry of alumina particles is formed in water and acetic acid.
The process further comprises of heating the slurry under pressure. The slurry of the alumina particles is heated at a temperature in the range of 120°C to 220°C and preferably between 170°C to 220°C. The slurry of the alumina particles is heated at a pressure in the range of 32 bar to 1.01325 bar and preferably between 32 to 20 bar. In accordance with an embodiment, the slurry of alumina particles is heated under pressure in an autoclave.
Heating the slurry of the alumina particles at such a temperature helps to retain the crystalline phase of boehmite, thus allowing the formation of pseudo boehmite crystals from aluminum trihydrate.
The process further comprises flashing the slurry by withdrawing the pressure to form pseudo boehmite crystals.
The pseudo boehmite crystals thus obtained are separated from the slurry. Any known technique including but not limited to filtration or centrifugation may be used to separate the pseudo boehmite crystals from the slurry.
The separated pseudo boehmite crystals may be dried. The methods for drying include but are not limited to spray drying, tray drying or rotary drying. In accordance with an embodiment, the pseudo boehmite crystals are dried in a tray drier.
The pseudo boehmite crystals obtained by the disclosed process have a specific surface area in the range of 90 to 260m2/g. The pseudo boehmite crystals obtained, having a specific surface area in the said range are ideal for use as refinery catalysts for fluid catalyst cracking of hydrocarbons.
The following comparative example(s) of preparing pseudo-boehmite crystals from aluminum trihydrate are exemplary and should not be understood to be in any way limiting. XRD patterns of the products obtained were determined in comparison with Joint Committee on Powder Diffraction Standards file in terms of 2? and intensity values of the XRD patterns.
EXAMPLES

Example 1
Aluminum trihydrate was calcined in a calciner at 300oC - 500oC in a continuous mode at feed rate of 20 to 22 kg/hour. Calcined alumina particles were transferred into an autoclave and water (2210 g) was added to the calcined alumina to form 15% solid slurry having a pH 9. The slurry was heated to 220° for different periods of time at a pressure of 32 bar to 1.01325 bar atmospheric pressure. The slurry was flashed by withdrawing the pressure abruptly. The product was filtered out and dried overnight in a tray drier at 80°C.
Phase analysis of the product by XRD (X-Ray Diffraction) was carried out. XRD patterns and size of the product were as shown in the following Table 1:
Table 1
d 50 µm Heating time
minutes Specific Surface Area m2/g XRD
patterns
70 120 40.7 Boehmite
70 60 113.1 Boehmite
70 5 182.0 Boehmite

Table 1 shows that the product formed was boehmite crystals. Specific surface area (SSA) of the product decreased with increasing heating time. Fig 1 of the accompanying drawings represents XRD pattern of the product for a heating period of 60 minutes.

Example 2
Aluminum trihydrate was calcined in a calciner at 300 - 500oC in a continuous mode at feed rate of 20 to 22 kg/hour. Calcined alumina (390 g) was milled in a jar bill to an average alumina particle size distribution of 5 – 10 µm. Alumina particles were transferred into an autoclave and water (2210 g) was added to the alumina particles to form a 15% solid slurry having a pH 9. The slurry was heated to varying temperatures for 5 minutes at a pressure of 32 bar to 1.01325 bar atmospheric pressure. The slurry was flashed by withdrawing the pressure abruptly. The product was filtered and dried overnight in a tray drier at 80°C.
Phase analysis of the product by XRD was carried out. Figure 2 illustrates the XRD pattern of the product. XRD patterns and size of the product were as shown in the following Table 2:
Table 2
d 50 µm Heating temperature °C Specific Surface Area
m2/g XRD patterns
10 200 79.9 Boehmite
10 160 212.00 Boehmite

The XRD patterns of the product obtained, indicated that only Boehmite is obtained when the slurry of Alumina particles is formed in water alone. Boehmite alumina heated to 200°C for 5 mins and having SSA of 79.9 is as shown in Fig 2 of the accompanying drawings.

Example 3
Aluminum trihydrate was calcined in a calciner at 200oC in a continuous manner at a feed rate of 20 to 22 kg/hour. Calcined alumina particles were transferred into an autoclave and water (2210 g) and HCl (100ml) in 1:1 v/v ratio were added to the calcined alumina to form a 15% solid slurry having an acid pH between 2 and 4. The slurry was heated to 200°C at different periods of time at a pressure of 32 bar to 1.01325 bar atmospheric pressure. The slurry was flashed by withdrawing the pressure abruptly. The product was filtered and dried overnight in a tray drier at 80°C.
Phase analysis of the product by XRD was carried out. Figure 3 illustrates the XRD pattern of the product. XRD patterns and sizes of the products were as shown in the following Table 3:
Table 3
d 50 µm Heating Time
minutes Specific Surface Area m2/g XRD patterns
10 120 189.5 Boehmite
10 30 255.5 Boehmite

The XRD patterns of the product obtained, indicated that only Boehmite is obtained when the slurry of Alumina particles is formed in HCl.

Example 4
Aluminum trihydrate was calcined in a calciner at 200oC in a continuous mode at a feed rate of 20 to 22 kg/hour. Calcined alumina particles were transferred into an autoclave and water (2210 g) and acetic acid (100ml) in 1:1 v/v ratio were added to the calcined alumina to form a 15% solid slurry having an acid pH between 2 and 4. The slurry was heated at 120°C for 120 mins at a pressure of 32 bar to 1.01325 bar atmospheric pressure. The slurry was flashed by withdrawing the pressure abruptly. The product was filtered and dried overnight in a tray drier at 80°C.
Phase analysis of the product by XRD was carried out. Fig 4 of the accompanying drawings shows XRD pattern of product obtained. XRD patterns and sizes of the product were as shown in the following Table:
Table 4
d 50 µm Heating Time
minutes Specific Surface Area m2/g XRD patterns
10 120 150 Pseudo-boehmite
70 120 260 Pseudo-boehmite

The XRD patterns of the product obtained, indicated that only Pseudo-Boehmite is obtained when the slurry of Alumina particles is formed in water and acetic acid.

INDUSTRIAL APPLICABILITY
The disclosed process enables a process for preparation of pseudo boehmite crystals with high specific surface area, that are ideal and well suited for use as refinery catalysts for fluid catalyst cracking of hydrocarbons. Specifically, the above described process to obtain pseudo boehmite crystals is simple, easy to perform, economical, reduces the process time and energy required, and significantly improves properties of the desired product. High yield, simple to perform process steps and reduced process time makes the process very efficient.