[How to] Moisture absorbents(Silica Gel) quantity for API packing

Hiii all..... Good day !!!

Back with a typical post this time, its not requested by anyone, but most of the process engineers need to know about this...!! As lack of knowledge on this may lead to several failures and may locate us in a worst situation.

Being a process engineer, many-a-time we have faced stability failures in case of manufactured API's. and the immediate response or action we may take is to review the subject batch manufactured process parameters. But there might be some hidden things which cant be brought into spot light, as we cannot blame those without any technical justification. To those things which are hidden can be brought into focus with appropriate justification. and that's the main motto of this post.


i.e., How to calculate the quantity of moisture absorbents required for a certain packing ?

This is going to be a very short post....!!

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What is the general packing procedure ?

As per me, the API shall be packed in white poly bag with goose neck packing, the white poly bag containing API shall be enclosed or kept tight in a black poly bag and the tight black poly bag shall be packed in a Triple laminated pack. 
Sometimes based on the requirement, the poly bags may be used in double no.

Where the Moisture absorbents shall be added ?

Basically, the  absorbents shouldn't get in contact with the packed API and the main job of them is to absorb the moisture that enters the packing. So, they shall be placed in between the white poly bag and black poly bag, black poly bag and triple laminated bag, triple laminated bag and HDPE container.





How an API may degrade ?


A manufactured API will have an varying shelf time, and during continuous storage it may degrade based on several factors, out of those all i'll mention some. they are due to photolytic degradation, oxidative degradation, thermal degradation etc. 


How can we address the above mentioned degradations ?

And from the mentioned all cases, we find very rare products which undergo photolytic degradation and those fall under it shall be stored with sophisticated packing methods. Those come under thermal degradation shall be stored in FG(Food Grade) under 2-8 C. The API's which under go oxidative degradation shall be stored in FG by taking necessary precautions such as placing moisture absorbents where ever required and wherever the probability of moisture presence is high.


Is the quantity of moisture absorbents to be placed is a calculated quantity or any predicted quantity ? 

As per me everything we perform / want to perform will hold a calculation and sometimes we donno that backup and sometimes we will be well aware of that.

So, by now whoever reading the post got some basic info about packing importance, and i want to add a one liner here, "Packing holds the same importance like manufacturing, Don't neglect it, if you, then be prepared for worse consequences". 





Now lets start the show,

I'll give you a general case study of API packing, 

lets suppose an API of 30 Kgs need to be packed, 
Bulk density of the API material is 0.47 Kg/L,

Packing procedure: 
1. Place API in White LDPE poly bag 813 x 1270, Slightly apply nitrogen, Tag it with a permanent tag tightly.
2. Place the White poly bag containing 30 Kgs API in Black poly bag 813 x 1270.
3. Place X qty of silica gel and tag it tight.
4. Place the Black poly bag in a triple laminated bag 813 x 1270.
5. Place Y qty of silica gel and tie it tight.
6. Place the Triple laminated bag in a 100 L HDPE drum.
 7. Place Z qty of silica gel and close the container with a clamp.

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So, here in the packing procedure, we need silica gel in three locations,

1. Between White poly bag and Black poly bag,
2. Between Black poly bag and Triple laminated bag,
3. Between Triple laminated bag and HDPE container.

Now as an Process Engineer, it our job to determine the required quantities. If the same task is handed over to some non-technical guy, then they might get onto the thumb laws, like for 50 L bag place 50 grams of silica gel or 100 grams of silica get. But as per me thats not correct.

Anyway, i'll show you the way that i'll prefer.

As per the packing procedure we need to place the API in white poly bag primarily.

So the shape of white poly bag will be cylindrical shape (As shown below).

The Bag size i.e., mentioned above is 813 x 1270 ~ 32" x 50 ",

Here, Width, W = 32" = 81.3 cms = 813 mm.

         Height, H = 50" = 127 cms = 1270 mm.

So the bag volume will be 𝛑(R^2).H,  Here as per our understanding, Circumference 2𝛑R = 2W.

So, Volume will be 𝛑(R^2).H = (w^2)H / 𝛑.

Now we need to calculate the volume occupied by our 30 Kgs API = 30 / 0.47 = 63.83 L.

[0.47 is the BD of API].

And now we gotta place this in a white poly bag having dimensions 813 x 1270 mm.

After placing the API and making it squeeze tight, the White poly bag will have shape of API.

Then we gotta place this in Black poly bag, and then between White and Black bags we need to add X qty of silica gel.

Volume of API including White poly bag will be ~64 L,

Volume of Black poly bag with dimensions 813 x 1270 will be 

= ( 81.3 ^2 ) x 127 / (3.141*1000) = 267 L.

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If we have placed the 64 L of White poly bag inside the Black poly bag, then the head space left in the Black poly bag shall be 267 - 64 = 203 L.

As per theory, at 100% RH, maximum possible water content in air shall be 30.4 gm/Cu.m

So we have 203 L of empty space, the moisture content shall be 

203 x 30.4 / 1000 = 6.179 grams

Now we need to calculate the silica gel quantity required,
For that we need to know the adsorption capacity of silica gel, as per the manufacturer's quality, it will be 0.2 grams of moisture per 1 gram of silica gel.




So, now the silica gel required between White poly bag and Black poly bag is 

6.179 / 0.2 = 30.89 grams ~31 grams,

And as a safety factor lets have 30% excess, so it will be 40.3 grams ~41 grams.

So, now we got X as 41 grams.

In the same way, the Silica get required between Black poly bag and Triple laminated bag is as follows,

Head space between Black poly bag and Triple laminated bag is 203 L,

Actual Silica gel required is 31 grams, considering safety factor it shall be 41 grams.

In the same way, the Silica get required between Triple laminated bag and 100 L HDPE container is as follows,
Head space between Triple laminated bag and HDPE container shall be 36 L,




Actual Silica get required is 5.5 grams, considering safety factor of 30%, required Qty is 7.2 ~8 grams.


That's it, you are done........!!!

X = 41 grams, Y = 41 grams, Z = 8 grams.

Hope you got it......!!!

For the readers convenience, i'm share a template to do the work for you,
Download it below.

Download it Here

If you are having any queries, feel free to comment / contact me,

Comments are most appreciated.......!!!

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About The Author

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Hi! I am Ajay Kumar Kalva, Currently serving as the CEO of this site, a tech geek by passion, and a chemical process engineer by profession, i'm interested in writing articles regarding technology, hacking and pharma technology.
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