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  • Thursday 9 August 2018

    [How to] Evaluate filtration feasibility in ANFD

    Hiii all......!!!

    Its been a gap, since i been posting regularly, 

    Recently i've received a query about one of my previous post i.e., about filtration, i've posted about selection of filters, and one guy from a reputed pharma has approached me through mail, as he need in depth about ANFD filtration, and i thought that it can make a separate post as many of us were not upto the mark in this topic, as many a time we cant distinguish which sort of reaction mass can be filtered in ANFD.

    For distinguishing the same, we should be possessing enough knowledge about filtration terminology and the commonly used parameters for explaining the filtration.

    So, lets startup with some technical terms,

    What is Permeation ?

    Permeation is type of passage through a resistive medium.

    What is Permeative flux ?

    Usually flux is defined as amount / quantity of material passing through an area in specified time. Coming to Permeative flux, it can be defined as amout / quantity that is permeated through a material medium of unti area in specified time. 
    Usually given units as Liters/min.Sq.m.

    What is Specific Cake resistance ?

    During filtering slurries, cake will be formed on the filtration barrier, and as on filtration going the cake thickness will increase depending upon the retained volume. The retained cake will add some excess resistance to the slurry which is being filtered along with the filter. The excess added resistance is Specific cake resistance. will hold units as m / Kg.

    What is cake Concentration ?

    Cake concentration in terms of filtration denotes the solids concentration in slurry. 
    will have units like density i.e., Kg/Cu.m.

    The above mentioned are the most used terms to describe / distinguish the nature of filtration.

    Now lets jump into the topic and based on the preliminary evaluation we can conclude whether the reaction mass can be filtered or not, out of those i can mention some here, 

    If reaction mass is Sticky / slimy / free flowing ANFD is not preferred,
    If the material nature is Crystalline, ANFD is preferred,
    If the reaction mass is acidic in nature, ANFD can be preferred, if its basic then the mass would be sticky, so ANFD is not preferred,
    If the nucleation is better i.e., coarser, ANFD is preferred, if its finer ANFD is not preferred.

    That's it..!!! This is preliminary evaluation, if i've missed out something just go ahead and comment, i'll add those in the above listing.

    Sometimes we cant decide whether we need to select an ANFD or not, and at that time we need to consider a experiment with a buckner filter and performing an experiment is an easy task, but evaluating that and generating a systematic data is vital.

    You may also like:
    [How to] Reduce drying time in ANFD effectively ? 
    [How To] Calculate assay of liquid product without concentration ?  

    So, now lemme tell you what sort of input need to be recorded from the performed experiment,

    1. Pore Size of the filter cloth,
    2. Filter Dia,
    3. Reaction mass volume,
    4. Applied vacuum,
    5. Filtrate volume,
    6. Filtration time,
    7. Weight of wet cake,
    8. Cake height.

    So, in a total the above 8 parameters need to recorded perfectly, so in case of any miss recording / wrong recording, it may lead to faltu results.

    So now, Lets start the calculation,

    Permeation flux = Filtrate volume / ( Filter area x Filtration duration ),

    Filter Area = 0.785 x ( Filter Dia ^ 2 ),

    Cake Concentration = ( Wet cake wt.  x 0.2 / Reaction mass volume ) x 1000,

                                                     ( 2 x (Filter Area^2) x 133.32 x Filtration time x applied vacuum) 
    Specific Cake Resistance = ____________________________________________
                                                     ( Cake Concentration x Rxn. mass viscosity x (Rxn. mass vol.^2))

    Its all done now .....!!!

    Now lets know about the limits of the above discussed to distinguish the filtration,

    If the permeation flux is greater than 45 Lts / mins. Sq.m, then it would be good filtration and you can go ahead with ANFD,
    If it is between 15 and 45, it would be moderate filtration and while scaling up we cant assure that the filtration will be good enough and even we cant assure consistent filtration rate, so we have to prefer an trial in pilot plant,
    If the rate below 15, its better to move with centrifuge or filter press.

    Like Permeation flux we are also having Specific cake resistance, below is the classification to distinguish the filtration nature,

    If cake resistance is ,

    10 ^ 7 to 10^8           -        Good filtration,
    10^8  to  10^10         -        Moderate filtration,
    above 10^10              -        Slow filtration

    That's it.......!! This post is done here itself,

    Lets suppose, now here i'll give one case study / sample calculation with some input data,

    Filter cloth size      :  5 µ,

    Buckner filter dia  :  5 cms,

    Slurry volume        :  1000 ml,

    Viscosity                 :  0.3 cP,

    Applied Vacuum  : 500 mmHg,

    Filtrate volume    :  650 ml,

    Filtration time     :   20 minutes,

    Wet cake weight :  230 grams,

    Cake thickness   :   150 mm,

    Also Read:
    [How to] Evaluate RC1e study ? 
    [How To] Select a batch size for a manufacturing process ?  

    Now the result is,

    Permeation flux - 16.56 Lt/Sq.m. min,

    Cake concentration - 46.00 Kg/Cu.m,

    Specific cake resistance  -  4.46 x 10^10 m/Kg.

    So as per the above discussion, the filtration is poor, not good enough in ANFD.

    I've prepared an automated sheet for you guys and this sheet will do the work for you,

    Below is the screenshot of the automated sheet:

    Credits: Pharma Engineering

    Any queries feel free to comment / reach me through mail ....!!!

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

    Related Posts:
    [How to] Design a Scrubber ? 
    Guidelines for Process Development & Optimization  
    [How to] Select a filter for a specific operation ?  
    [How to] Calculate NPSH (Net Positive Suction Head) ?

    About The Author

    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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    1. Which dryer was most appropriate for water medium drying. As a process engineer i am suffering from drying time cycle for water medium slurries in ANFD.


      1. Hiii Ramana,

        Glad to hear from you again, it depends upon the material nature which we need to dry, if its pluffy we can go with RCVD, it it is crystalline then we need to move with ANFD(Hot water circulation shall be provided for agitator shaft, bottom dish and to jacket also),

        If the material is crystalline and non-hygroscopic, then we can go with FBD with intermittent material milling.

        AJAY K

      2. Hi Ajay & Varma...
        We need to check the material nature first(Pluffy, crystalline, agglomeration etc.)
        LOD of the wet cake..
        If the water medium materials need to be taken care for ANF filtration and RCVD drying ..
        As ANF is not much suitable for water medium mostly and rCVD... Chances for agglomeration and lumps formation ..
        Need to be follow step wise heating procedure under vacuum to avoid sudden cusion of material...
        One more important point is XRD of the particle for choosing drying equipment..

      3. Hi Nazeer,

        Wahts you said is correct, but the agglomeration will usually depends on the crystallization pattern, as if the dilution is high, the agglomerate size will be low and the solvent entrapment will be low, as if the entrapment is low automatically the material will get free during press dry.
        If lumps are formed in ANFD then they can be addressed by changing the washing mode, i.e., by giving a run wash / polish wash.
        And if XRD is present its better to move with calculated risk.


    2. Based on above specific cake resistance how can we decide fitration equipment like centrifuge ,filter press ,PNF

      1. Hii Sir,

        If the cake on the filter medium increases, the rate of filtration will decrease, as the height will act as a excess barrier and sometimes it may lead to pore blocking, so if the cake resistance is low, filtration will be good, if it is high then the filtration will be poor.

        AJAY K

    3. Dear sir,
      Is there any exceptional cases that bases can also be used or blindly we dont choose bases in ANFD. Or if it passes in other cases like permeate flux and cake resistance, then what shall we do?
      Thanks and regards

      1. Dear Rakesh,

        If needed a machine trial need to be taken to evaluate the filtration efficiency, apart from that i cant suggest anything.

        Best Regards,
        AJAY K

      2. Dear sir,
        Thanks for your response.
        Then What are the steps carried out for selecting a filter? and how to check filtration efficiency?
        Thanks and regards
        rakesh kumar

      3. Hiii Rakesh,

        Pl follow the below link for selection of filters,

        Filtration efficiency shall be evaluated through R&D experiment,
        and the filtration feasibility in a particular equipment shall be evaluated through a machine trial in pilot plant with small batch quantity. or else we can request the vendor to check the filtration feasibility in vendor's manufacturing site itself, if it is feasible then we have to quote.

        Best Regards,
        AJAY K

    4. Dear sir,
      Is there any exceptional case that we can use ANFD for bases also?
      Thanks and regards,

      1. Dear Rakesh,

        As per me nothing is exceptional, we can use ANFD for bases also but the filtration wont gain any momentum and it can be perfectly used in cases where the impurities have higher affinity towards mother liquors. But it'll be a bottle neck w.r.t. time.

        Best Regards,
        AJAY K

    5. Sir in the equation of cake concentration you write ,Cake Concentration = ( Wet cake wt. x 0.2 / Reaction mass volume ) x 1000,In the equation aforementioned equation why you multiply 0.2 with weight of the wet cake???How it is coming so?

      1. Dear Pratim,

        sorry i haven't mentioned there, that's bulk density of material,

        ** I'll update it now

        Best Regards,
        AJAY K

    6. And during calculation of sp.cake resistance you are neglecting resistance of the filter medium but sir it is also necessary for calculaing sp.cake resistance??

      1. Hii Pratim,

        Good to see you back here, Specific cake resistance is amount of resistance added by the settled or retained cake on the filter barrier which excludes the filter medium. It shouldn't be shownup in the Specific cake resistance.

        Best Regards,
        AJAY K

    7. Hi Ajay, thanks for your work to make the filtration excel calculation. Here I want to know the data for ease of separation through cake resistance. I couldn't change it as the sheet is password protected. Can send me through unprotected version. To my email

    8. Dear Ajay
      How to calculate the Nitrogen pressure requirement to reduce the filtration time in ANFD (That means relation between time and pressure)

    9. IS filtration in ANFD a constant pressure filtration process?


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    Hi! I am Ajay Kumar Kalva, owner 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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