A granulation process for guanidino acetic acid

Abstract

The present application relates to the technical field of granulation process, and proposes a guanido acetic acid granulation process, comprising the following steps: S1, after pretreatment of the water-containing guanido acetic acid, pretreated guanido acetic acid is obtained; S2, after preliminary dispersion of the pretreated guanido acetic acid, an adsorbent is added, and after mixing and standing, a mixture is obtained; S3, after microwave crystallization treatment and post-treatment of the mixture, guanido acetic acid crystalline particles are obtained; the adsorbent is polyacrylic acid sodium, and the weight average molecular weight of the polyacrylic acid sodium is 8-12 million. Through the above technical scheme, the problems of large energy consumption, low forming efficiency and easy caking of powder in the guanido acetic acid granulation process in the related art are solved.

Description

Technical Field

[0001] This invention relates to the field of granulation technology, and more specifically, to a granulation process for guanidinoacetic acid. Background Technology

[0002] Existing guanidinoacetic acid granulation technologies are mainly divided into two categories: extrusion granulation and wet granulation, both of which have significant technical drawbacks. Extrusion granulation requires high-power equipment for strong extrusion, resulting in high equipment energy consumption, rapid component wear, and the need for an additional drying process, leading to high overall energy consumption and production costs. It also demands stringent control of equipment parameters, has a complex operating procedure, and is prone to malfunctions such as material blockage. Furthermore, it is susceptible to problems such as uneven particle size, high breakage rate, and the forming rate is significantly affected by equipment precision. Wet granulation also faces issues of energy waste and low forming efficiency. It requires strict control of parameters such as solvent ratio and drying temperature, has a narrow process window, and is difficult to operate. It is prone to uneven particle adhesion and cracking / pulverization after drying. It consumes large amounts of solvent, and the drying process is time-consuming and energy-intensive, further increasing costs. The products obtained by both processes are simple guanidinoacetic acid granules with strong intermolecular forces, making them highly susceptible to moisture absorption and clumping during storage and transportation, resulting in poor stability and severely limiting production efficiency.

[0003] Therefore, it is necessary to propose a granulation process that consumes less energy, has high molding efficiency, and is not prone to agglomeration. Summary of the Invention

[0004] This invention proposes a granulation process for guanidinoacetic acid, which solves the problems of high energy consumption, low molding efficiency, and easy agglomeration of powder in the granulation process of guanidinoacetic acid in related technologies.

[0005] The technical solution of this invention is as follows: This invention proposes a granulation process for guanidinoacetic acid, comprising the following steps: S1. After pretreatment of aqueous guanidinoacetic acid, pretreated guanidinoacetic acid is obtained; S2. After the pretreated guanidinoacetic acid is initially dispersed, an adsorbent is added, and the mixture is allowed to stand to obtain a mixture. S3. After microwave crystallization and post-treatment, the mixture is used to obtain guanidinoacetic acid crystal particles. The adsorbent is sodium polyacrylate, and the weight-average molecular weight of the sodium polyacrylate is 8 million to 12 million.

[0006] As a further technical solution, in step S1, the pretreatment includes the following steps: centrifuging and sieving the aqueous guanidinoacetic acid to obtain pretreated guanidinoacetic acid, wherein the water content of the pretreated guanidinoacetic acid is 10wt%~20wt%, preferably 15wt%, and the particle size of the pretreated guanidinoacetic acid is 100~200 mesh, preferably 100 mesh.

[0007] In the granulation process of guanidinoacetic acid of the present invention, the water content of the pretreated guanidinoacetic acid is controlled to be 10wt%~20wt% to ensure the stability of subsequent adsorption and crystallization effects, and the particle size is 100~200 mesh to ensure that the guanidinoacetic acid meets the requirements of subsequent mixing processes.

[0008] As a further technical solution, in step S1, the centrifuge used for centrifugal separation has a separation factor ≥3000, preferably 3000.

[0009] As a further technical solution, in step S2, the adsorbent is a pretreated adsorbent, and the preparation method of the pretreated adsorbent includes the following steps: the adsorbent is vacuum dried at 80~85℃ for 2~3h to obtain the pretreated adsorbent, the preferred temperature is 80℃ and the preferred time is 2h.

[0010] As a further technical solution, in step S2, the mass ratio of the pretreated guanidinoacetic acid to the adsorbent is 20:1~2.

[0011] As a further technical solution, in step S2, the rotation speed of the initial dispersion is 50~60 r / min, preferably 50 r / min, and the initial dispersion time is 5~8 min, preferably 5 min.

[0012] As a further technical solution, in step S2, the mixing speed is 100~200 r / min, preferably 150 r / min, and the mixing time is 10~20 min, preferably 15 min.

[0013] As a further technical solution, in step S2, the mixing equipment is a double helix conical mixer, model SHI-500.

[0014] As a further technical solution, in step S2, during the mixing process, the filling rate of the mixer is 60%~70%, preferably 65%.

[0015] In the granulation process of guanidinoacetic acid of this invention, the equipment is cleaned before mixing to remove residual impurities. Then, the equipment is started and run unloaded for 5 minutes to check whether the stirring paddle operates smoothly without abnormal noise and whether the inner wall of the mixer is smooth and free of adhesion. The filling rate of the mixer is set to 60%~70% (i.e., the total mass of the guanidinoacetic acid mixture and sodium polyacrylate does not exceed 70% of the effective volume of the equipment) to avoid overfilling and uneven mixing.

[0016] As a further technical solution, in step S2, the settling time is 3 to 5 minutes, preferably 3 minutes.

[0017] In the granulation process of guanidinoacetic acid of the present invention, after standing, the material settles and the discharge port is opened to collect the mixture into a hopper with a heat insulation layer. The outer layer of the hopper is wrapped with a moisture-proof film to prevent moisture absorption.

[0018] As a further technical solution, in step S3, the microwave crystallization process includes the following steps: feeding the mixture into the drying chamber of the microwave drying equipment through a screw feeder, and then performing microwave crystallization after spreading the material.

[0019] As a further technical solution, the microwave frequency of the microwave crystallization is 2450~2500MHz, preferably 2450MHz, the power of the microwave crystallization is 8~10KW, preferably 9KW, and the time of the microwave crystallization is 15~30min, preferably 20min.

[0020] As a further technical solution, the microwave crystallization device is a tunnel microwave device.

[0021] In the granulation process of guanidinoacetic acid of the present invention, the equipment needs to be preheated and adjusted before microwave crystallization. The temperature inside the drying chamber is calibrated by the temperature sensor of the equipment, and the temperature is 35~45℃. The stirring device (paddle type stirring, made of 304 stainless steel) is started and the stirring speed is adjusted to 50~100r / min, preferably 80r / min, to ensure that there is no friction between the stirring paddle and the inner wall of the equipment and that the operation is stable.

[0022] As a further technical solution, the feeding speed of the mixture is 50~100kg / h, preferably 80kg / h, and the thickness of the spreading material is 2~5cm, preferably 3cm.

[0023] As a further technical solution, in step S3, the post-processing includes cooling and sieving in sequence.

[0024] As a further technical solution, step S3 includes finished product testing and packaging storage after screening.

[0025] As a further technical solution, the cooling device is a cooler, model SL-10, the cooling method is air cooling, the cooling temperature is 25~30℃, preferably 25℃, and the cooling time is 10~15min, preferably 12min.

[0026] In the granulation process of guanidinoacetic acid of the present invention, the material is cooled to prevent the high-temperature material from absorbing moisture during the subsequent screening process.

[0027] As a further technical solution, the screening equipment is a vibrating screen, the vibrating screen is made of stainless steel, the aperture of the vibrating screen is 10 mesh, the vibration frequency of the vibrating screen is 1500~2000r / min, preferably 1800r / min, and the screening time is 10~15min, preferably 12min.

[0028] In the granulation process of guanidinoacetic acid of the present invention, during the sieving process, qualified powder (particle size 10-60 mesh) is collected through the collection hopper below the screen. The residual material above the screen (mainly incompletely dispersed sodium polyacrylate agglomerates) is collected and returned to the swing granulator for re-crushing. After crushing, it can be added back to the mixing process for recycling, thereby improving the utilization rate of raw materials.

[0029] In the granulation process of guanidinoacetic acid of this invention, after sieving, the guanidinoacetic acid crystal particles are sampled and tested. The moisture content is measured using a Karl Fischer moisture analyzer and is required to be ≤10%. The particle size distribution is measured using a laser particle size analyzer to ensure that the proportion of 10-60 mesh particles is ≥98%. The crystal morphology is analyzed using an X-ray diffractometer, requiring sharp crystal peaks and no impurity peaks, indicating a stable crystal structure. At the same time, the purity (≥80%) and active ingredient content (≥80%) of the product are tested. Only after all indicators meet the requirements is the product considered a qualified finished product.

[0030] In the granulation process of guanidinoacetic acid of this invention, qualified finished products are packaged in double layers: the inner layer is a polyethylene film bag (thickness ≥ 0.08 mm), and the outer layer is a paper-plastic composite bag (moisture-proof rating ≥ IPX5). Each bag weighs 25 kg. During the packaging process, dry nitrogen gas (purity ≥ 99.9%) is introduced into the bag, and the product information is labeled after sealing. The packaged finished products are stored in a cool and dry warehouse with the warehouse temperature controlled at 15~30℃ and the relative humidity ≤ 60%. Direct sunlight and high temperature and high humidity environments are avoided, and the shelf life can reach more than 12 months.

[0031] The working principle and beneficial effects of this invention are as follows: 1. In the granulation process of guanidinoacetic acid of the present invention, a guanidinoacetic acid-sodium polyacrylate composite system is adopted in combination with crystallization technology. Through the interaction between sodium polyacrylate and guanidinoacetic acid molecules, combined with directional crystallization control, the crystal structure and particle morphology of guanidinoacetic acid are changed, which fundamentally improves the stability and molding efficiency of the particles, and realizes the synergistic effect of chemical treatment and physical molding. It effectively avoids the problems of guanidinoacetic acid itself being prone to agglomeration and poor molding stability, which are the core of existing extrusion granulation and wet granulation, which rely on simple physical molding and external force extrusion or liquid phase bonding to achieve particle molding, without improving the problem of guanidinoacetic acid itself being prone to agglomeration and poor molding stability at the molecular level. 2. In the granulation process of guanidinoacetic acid of the present invention, sodium polyacrylate is added as an adsorbent, and the weight average molecular weight of sodium polyacrylate is limited to 8 million to 12 million. Sodium polyacrylate with a weight average molecular weight of 8 million to 12 million has a suitable molecular chain length. In the mixed system with guanidinoacetic acid, the appropriate molecular chains can fully extend and entangle with each other to form a dense three-dimensional network structure. This network structure can firmly anchor the guanidinoacetic acid crystals, greatly improve the compressive strength of the particles, and solve the problem of easy breakage of traditional granulation particles. It can also form a uniform protective film on the particle surface, effectively blocking the contact between moisture in the air and guanidinoacetic acid molecules, and reducing the agglomeration rate. 3. The granulation process of guanidinoacetic acid in this invention does not rely on high extrusion pressure or additional solvents for molding, and has a high tolerance for process parameters. Even if the mixing ratio fluctuates by ±5% and the crystallization temperature fluctuates by ±3℃, the product qualification rate can still be maintained above 95%. The granulation process does not require precise control of complex external force or solvent parameters, the process steps are simplified, the operation difficulty is significantly reduced, and it is more suitable for large-scale continuous production. High-strength extrusion equipment is not required, and the power requirements of the equipment in the granulation process are significantly reduced. At the same time, the crystallization control technology can shorten the molding cycle, reduce the energy consumption of auxiliary processes such as drying, and greatly reduce the energy consumption and equipment operation and maintenance costs in the production process. 4. In the granulation process of guanidinoacetic acid of this invention, in terms of product quality, the granulation rate of sodium polyacrylate with a weight average molecular weight of 8-12 million can reach 95%-98%, with almost no raw material loss; moreover, the granulated particles have uniform particle size and regular morphology, and are not easily broken or agglomerated during storage and transportation, significantly reducing subsequent storage and transportation costs. In contrast, low molecular weight sodium polyacrylate has insufficient binding force, low granulation rate, and poor particle stability, which not only increases raw material waste but also affects downstream application effects due to product quality fluctuations. Detailed Implementation

[0032] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0033] Example 1 A granulation process for guanidinoacetic acid includes the following steps: S1. After centrifugation, the aqueous guanidinoacetic acid was passed through a 100-mesh sieve to obtain pretreated guanidinoacetic acid. The centrifuge used during centrifugation had a separation factor of 3000, and the water content of the obtained pretreated guanidinoacetic acid was 15 wt%. S2. Slowly add pretreated guanidinoacetic acid to the mixer, close and seal the feed inlet, start the mixer and premix at 50 r / min for 5 min. After initial dispersion, add the adsorbent through the feed port at the top of the equipment, adjust the speed to 150 r / min and mix for 15 min. After mixing, let stand for 3 min. After the material settles, open the discharge port and collect the mixture into a hopper with a heat insulation layer. Wrap the outer layer of the hopper with a moisture-proof film to prevent moisture absorption. The adsorbent is sodium polyacrylate with a weight average molecular weight of 8 million to 12 million. Before use, it is vacuum dried at 80℃ for 2 h to obtain the pretreated adsorbent. The mass ratio of pretreated guanidinoacetic acid to pretreated adsorbent is 20:1. S3. The tunnel microwave equipment is preheated to 40℃. After debugging, the mixed material is evenly fed into the drying chamber of the microwave drying equipment through a screw feeder at a feeding speed of 80kg / h. The material thickness in the drying chamber is 3cm. The microwave power is set to 9KW and the microwave frequency to 2450MHz. Microwave crystallization is performed for 20min. After completion, the material is discharged from the outlet of the microwave drying equipment and immediately sent to the cooler. It is cooled at 25℃ for 12min. A vibrating screen is selected, and the cooled material is fed into the vibrating screen. The equipment is started and vibrated at a frequency of 1800r / min for 12min. After screening, guanidinoacetic acid crystal particles are obtained.

[0034] Example 2 A granulation process for guanidinoacetic acid includes the following steps: S1. After centrifugation, the aqueous guanidinoacetic acid was passed through a 100-mesh sieve to obtain pretreated guanidinoacetic acid. The centrifuge used during centrifugation had a separation factor of 3000, and the water content of the obtained pretreated guanidinoacetic acid was 15 wt%. S2. Slowly add pretreated guanidinoacetic acid to the mixer, close and seal the feed inlet, start the mixer and premix at 50 r / min for 5 min. After initial dispersion, add the adsorbent through the feed port at the top of the equipment, adjust the speed to 150 r / min and mix for 15 min. After mixing, let stand for 3 min. After the material settles, open the discharge port and collect the mixture into a hopper with a heat insulation layer. Wrap the outer layer of the hopper with a moisture-proof film to prevent moisture absorption. The adsorbent is sodium polyacrylate with a weight average molecular weight of 800-1200 million. Before use, it is vacuum dried at 80℃ for 2 h to obtain the pretreated adsorbent. The mass ratio of pretreated guanidinoacetic acid to pretreated adsorbent is 20:1.5. S3. The tunnel microwave equipment is preheated to 40℃. After debugging, the mixed material is evenly fed into the drying chamber of the microwave drying equipment through a screw feeder at a feeding speed of 80kg / h. The material thickness in the drying chamber is 3cm. The microwave power is set to 9KW and the microwave frequency to 2450MHz. Microwave crystallization is performed for 20min. After completion, the material is discharged from the outlet of the microwave drying equipment and immediately sent to the cooler. It is cooled at 25℃ for 12min. A vibrating screen is selected, and the cooled material is fed into the vibrating screen. The equipment is started and vibrated at a frequency of 1800r / min for 12min. After screening, guanidinoacetic acid crystal particles are obtained.

[0035] Example 3 A granulation process for guanidinoacetic acid includes the following steps: S1. After centrifugation, the aqueous guanidinoacetic acid was passed through a 100-mesh sieve to obtain pretreated guanidinoacetic acid. The centrifuge used during centrifugation had a separation factor of 3000, and the water content of the obtained pretreated guanidinoacetic acid was 15 wt%. S2. Slowly add pretreated guanidinoacetic acid to the mixer, close and seal the feed inlet, start the mixer and premix at 50 r / min for 5 min. After initial dispersion, add the adsorbent through the feed port at the top of the equipment, adjust the speed to 150 r / min and mix for 15 min. After mixing, let stand for 3 min. After the material settles, open the discharge port and collect the mixture into a hopper with a heat insulation layer. Wrap the outer layer of the hopper with a moisture-proof film to prevent moisture absorption. The adsorbent is sodium polyacrylate with a weight average molecular weight of 800-1200 million. Before use, it is vacuum dried at 80℃ for 2 h to obtain the pretreated adsorbent. The mass ratio of pretreated guanidinoacetic acid to pretreated adsorbent is 10:1. S3. The tunnel microwave equipment is preheated to 40℃. After debugging, the mixed material is evenly fed into the drying chamber of the microwave drying equipment through a screw feeder at a feeding speed of 80kg / h. The material thickness in the drying chamber is 3cm. The microwave power is set to 9KW and the microwave frequency to 2450MHz. Microwave crystallization is performed for 20min. After completion, the material is discharged from the outlet of the microwave drying equipment and immediately sent to the cooler. It is cooled at 25℃ for 12min. A vibrating screen is selected, and the cooled material is fed into the vibrating screen. The equipment is started and vibrated at a frequency of 1800r / min for 12min. After screening, guanidinoacetic acid crystal particles are obtained.

[0036] Comparative Example 1 The difference between Comparative Example 1 and Example 2 is that the weight-average molecular weight of sodium polyacrylate is 1 million to 3 million.

[0037] Comparative Example 2 The difference between Comparative Example 2 and Example 2 is that the weight-average molecular weight of sodium polyacrylate is 3 to 5 million.

[0038] Comparative Example 3 The difference between Comparative Example 3 and Example 2 is that the weight-average molecular weight of sodium polyacrylate is 5 million to 8 million.

[0039] Comparative Example 4 The difference between Comparative Example 4 and Example 2 is that the weight-average molecular weight of sodium polyacrylate is 12-15 million.

[0040] Comparative Example 5 Compared with Example 2, Comparative Example 5 differs in that step S3 includes the following: the mixture is fed into a cooler and cooled at 25°C for 12 minutes. A vibrating screen is selected, and the cooled material is fed into the vibrating screen. The equipment is started and vibrated at a frequency of 1800 r / min for 12 minutes. After the screening is completed, guanidinoacetic acid crystal particles are obtained.

[0041] Comparative Example 6 This comparative example uses a conventional extrusion granulation method to obtain guanidinoacetic acid particles.

[0042] Comparative Example 7 This comparative example uses a conventional wet granulation method to obtain guanidinoacetic acid particles.

[0043] Experimental Example 1 The properties of the guanidinoacetic acid crystalline particles obtained in Examples 1-3 and Comparative Examples 1-5 were tested according to the following test methods: 1. Granulation particle size: Pass through a 20-mesh sieve and calculate the proportion of guanidinoacetic acid crystal particles after sieving; 2. Granule anti-caking property: Take 100g of guanidinoacetic acid crystal granules, store the guanidinoacetic acid crystal granules in an environment with a humidity of 75% and a temperature of 25℃ for 7 days, pass them through a 20-mesh sieve, calculate the proportion of agglomerated material on the sieve, and obtain the agglomeration rate. The test results are shown in Table 1: Table 1 Performance test results of Examples 1-3 and Comparative Examples 1-5

[0044] As shown in Table 1, when the guanidinoacetic acid-sodium polyacrylate composite system is used in the granulation process in combination with crystallization technology, and the weight-average molecular weight of sodium polyacrylate is 8 million to 12 million, the granule shape can be improved and the agglomeration performance can be reduced.

[0045] Experiment Example 2 The properties of the guanidinoacetic acid particles prepared in Example 2 and Comparative Examples 6-7 were tested according to the following test methods: 1. Agglomeration rate: Take 100g of guanidinoacetic acid crystal particles, store the guanidinoacetic acid crystal particles in an environment with a humidity of 75% and a temperature of 25°C for 7 days, pass them through a 20-mesh sieve, calculate the proportion of agglomerated material on the sieve, and obtain the agglomeration rate. 2. Morphological regularity: The particle morphology was observed using a scanning electron microscope (SEM), and the proportion of regular crystals in 100 particles was counted. 3. Production qualification rate: Using the production methods of Example 2 and Comparative Examples 6-7 respectively, 10 batches were produced continuously, each batch weighing 100kg. The percentage of qualified products was calculated and the average value was taken.

[0046] The test results are shown in Table 2: Table 2 Performance test results of Example 2 and Comparative Examples 6-7

[0047] As shown in Table 2, existing technologies only achieve physical molding through external extrusion (extrusion granulation) or liquid-phase bonding (wet granulation), which does not change the inherent defects of guanidinoacetic acid molecules being prone to aggregation and having irregular crystal structures, resulting in products that are prone to agglomeration and have low molding rates. The granulation process in this invention can effectively improve the morphological regularity of the particles and reduce the agglomeration rate.

[0048] Experimental Example 3 The preparation processes of Example 2 and Comparative Examples 6-7 were measured and scored as follows: 1. Comprehensive energy consumption per ton: Refer to the method in GB / T 2589-2020 "General Rules for Calculation of Comprehensive Energy Consumption" to measure the electricity and water consumption of the entire granulation process (raw material mixing - molding - screening) and calculate the energy consumption per ton of product; 2. Cost per ton of granulation: Calculate the total cost of granulation per ton of product by including energy consumption cost, equipment depreciation cost, and raw material loss cost; 3. Operational difficulty rating: A 10-point scale is used, with 5 senior process engineers scoring based on parameter control complexity and failure rate, and the average value is taken.

[0049] The test results are shown in Table 3: Table 3 Performance test results of Example 2 and Comparative Examples 6-7

[0050] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A granulation process for guanidinoacetic acid, characterized in that, Includes the following steps: S1. After pretreatment of aqueous guanidinoacetic acid, pretreated guanidinoacetic acid is obtained; S2. After the pretreated guanidinoacetic acid is initially dispersed, an adsorbent is added, and the mixture is allowed to stand to obtain a mixture. S3. After microwave crystallization and post-treatment, the mixture is used to obtain guanidinoacetic acid crystal particles. The adsorbent is sodium polyacrylate, and the weight-average molecular weight of the sodium polyacrylate is 8 million to 12 million.

2. The granulation process for guanidinoacetic acid according to claim 1, characterized in that, In step S1, the pretreatment includes the following steps: centrifuging and sieving the aqueous guanidinoacetic acid to obtain pretreated guanidinoacetic acid, wherein the water content of the pretreated guanidinoacetic acid is 10wt%~20wt% and the particle size of the pretreated guanidinoacetic acid is 100~200 mesh.

3. The granulation process for guanidinoacetic acid according to claim 1, characterized in that, In step S2, the adsorbent is a pretreated adsorbent, and the preparation method of the pretreated adsorbent includes the following steps: the adsorbent is vacuum dried at 80~85℃ for 2~3h to obtain the pretreated adsorbent.

4. The granulation process for guanidinoacetic acid according to claim 1, characterized in that, In step S2, the mass ratio of the pretreated guanidinoacetic acid to the adsorbent is 20:1~2.

5. The granulation process for guanidinoacetic acid according to claim 1, characterized in that, In step S2, the initial dispersion rotation speed is 50~60 r / min, and the initial dispersion time is 5~8 min.

6. The granulation process for guanidinoacetic acid according to claim 1, characterized in that, In step S2, the mixing speed is 100~200 r / min, and the mixing time is 10~20 min.

7. The granulation process for guanidinoacetic acid according to claim 1, characterized in that, In step S2, the settling time is 3 to 5 minutes.

8. The granulation process for guanidinoacetic acid according to claim 1, characterized in that, In step S3, the microwave crystallization process includes the following steps: feeding the mixture into the drying chamber of the microwave drying equipment through a screw feeder, and then performing microwave crystallization after spreading the material.

9. The granulation process for guanidinoacetic acid according to claim 8, characterized in that, The microwave frequency of the microwave crystallization is 2450~2500MHz, the power of the microwave crystallization is 8~10KW, and the time of the microwave crystallization is 15~30min.

10. The granulation process for guanidinoacetic acid according to claim 1, characterized in that, In step S3, the post-processing includes cooling, sieving, finished product testing, and packaging and storage in sequence.

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