ESTERIFICATION/TRANS-­ESTERIFICATION   Batch and  continuous  modes  of  operation have been done

2.2.4   ESTERIFICATION/TRANS-­ESTERIFICATION  

Kinetic studies: kinetics   of  (trans)-esterification   have   been   analyzed   by   using   glass   reactors  with  attached  thermometer  and  

reflux   condenser,   placed     on   a   magnetic   stirrer   with   heater   (IKA   RT   5   power).  

This technique was developed because of the special case of fast separation of the raffinate and extract phases. Those conventional techniques as in figure 2.4 can be used only for those biodiesel systems in which the separation rate of the phases is slow, especially under intensive mixing. 50   ml   vessels  have been designed to make   possible  performing the  analysis  in  series   without   high   loss   of   solvents   and   auxiliaries (figure 2.5).    

Mode of operation: Flasks have been

filled with the feedstock-solvent mixture. The system was brought to test conditions.

Reagent-­‐catalyst   mixtures   were   administered   on   reaching   the   specified   temperature   into  the  stirred  solvent-­‐feedstock  mixture through the condenser directly into the bulk of the mixture by the use of a glass tube attachment. Any other steps (freezing, product refining, etc.) have been similar to the routine described in the previous section.

Loop reactor system: Fast settling of the byproduct made possible to shift the equilibrium toward the desired direction. For this a loop reactor structure had to be constructed. There have been a series of loop reactors used in the study. The very first apparatus was made of all-glass construction with a capacity of 1 l. The second was manufactured of stainless steel with a flask capacity of 5 l. This was modified further to operate the system under moderate pressure (10 bar). Figure 2.6 gives an indicative description of the stainless steel system.

Mode of operation: Feedstock and solvent are metered through the condenser into the jacketed main vessel of the apparatus. The condenser is cooled with cold water. The entire content of the main holding vessel is circulated and the jackets of the loop reactor and the main vessel are heated with a circulator set to a temperature close to the boiling point of the solvent at the given pressure. Catalyst and reagent is fed into the main vessel through the condenser. The overhead valve is closed and through a check valve the system is being pressurized with nitrogen. Reaction time starts when the system is at reaction conditions (temperature, pressure). Upon completion the reaction time, while maintaining the circulation by the pump, heating is closed off, the system is slowly depressurized, by care taking not to splash out the content through the condenser. When the system is at atmospheric pressure known amount of cold water is added to freeze any progress in the reactions. Along the progress of the reaction the sight glass gives an indication on accumulation of byproducts. In cases of heterogeneous catalysis reaction experiments the loop reactor has been filled with catalyst.

Separation of byproducts and product refining have also been performed in the loop reactor system. Separation of the bottom layer was assisted by the existence of the sight glasses. Addition of materials have been practiced through the condenser. Any other product separation and treating routines have been the same as described earlier.

This   apparatus provided the knowledge basis   for   affordable   revamp   scenarios   of   existing  units  to  retrofit to multiple  capacities  and  improve  efficiency  without  excessive   costs.

FIGURE    2.5   50  ML  APPARATUS

Parr  (NAKI⁷)/type  reactor:     Moderately high   pressure experiments (10-20 bar) have been performed in  stainless  steel  bomb  reactor. A special provision was added to the known system: A box, manufactured of perforated material was hanged onto the cover body of the apparatus. In this box 3A molecular sieve was added to study the efficiency of water removal in esterification under different than atmospheric pressure experiments.

 Mode of operation: The reactor was  filled  with  substrate,  reagent,  solvent,  magnetic   stirring  bar  and  catalyst,  closed    and  pressurized  with  nitrogen.    Heating  and  stirring   was  done  with  heater  with  magnetic  stirrer.  

Upon  reaching  the  prescribed  reaction  time   the   reactor   was   chilled   in   ice   water   bath   and   depressurized.   Downstream   product   refining  protocol  was  similar  to  operations   in  glass  reactor  vessels.

ATMOSPHERIC CONTINUOUS   COUNTER   CURRENT  TESTS  have  been  performed in glass column systems as in figure 2.3.   The   complete reaction system   for   technology   trials  has  been  composed  by  the  use  of  3(4)   columns   coupled   in   series (figure 2.7.)   Ceramic   rashig   rings   of   5x5x1 (mm)   were   packed   in   sections   into   these   columns.    

Functions of the columns:

Column 1: similar to the apparatus in figure 2.3 for esterification (degumming) of high FFA feedstocks. (height 2.5m, diameter:

35 mm).

Column 2: similar to column 1, operated in series. The addition of this column was necessary to extend to reaction time without scarifying the capacity of the system. (height 2.5m, diameter: 35 mm)

Column 3: neutralization column (height 2m, diameter: 35 mm)

Column 4: similar to column 1, dedicated to trans-esterification. (height 2.5m, diameter:

35 mm)

Atmospheric continuous   co-current   esterification, counter current trans-esterifica-tion tests.Special  regime  was  structured  for   co-current   esterification,   followed   by   counter   current   neutralization   and   phase   separation  and  trans-­‐esterification  with  the  

same  pieces  of  unit  operations as described in the previous section.

7   It   is   to   report   that   the   reactor   known   as   Parr-­type   was   known   as   NAKI   reaktor,   designed   in   the   Institute   of   High   Pressure   Chemical   Processes,   a   spin   off     research   institute   of   the   Department   of   Chemical   Technology   of   Budapest   Technical  University.

FIGURE    2.6     LOOP  REACTOR  APPARATUS  

Moderate pressure continuous  counter current tests.The  scheme  of  the  stainless  steel   reactor  device,  that  is  basically  similar  to  the  single  glass  column  system  is  illustrated   in  figure  2.3.  Along  with  writing  this  thesis  a  pilot  plant  of  stainless  steel  columns  and   elements  is  in  course  of  production.  A  few  distinctive  elements  request  the  illustration   in  a  distinct  figure.    Comparison  of  the  glass  and  stainless  steel  columns  is  presented  in   table  2.5  

TABLE  2.5     COMPARISON  OF  THE  GLASS  AND  STAINLESS  STEEL  SYSTEMS  

SPECIFICS   GLASS STEEL  

Figure 2.3 2.7

Pressure  range,  bar   Atmospheric,  1 moderate  pressure,  2-­‐10  

Pressure  control   None Pressure  regulator  valve  

Heat  management   Jacketed   column   with   circulated   heat   transfer   fluid  

Thermo-­‐isolated  

columns   with   in-­‐line   electric  heaters      

Temperature  range,  °C   Room-­‐55   Room-­‐150  

Temperature  control   By  the  circulator   By   automatic   software   temperature   in   the   column   controlled   by     heat  applied  to  the  oven    

Column   internal  

diameter,  mm  

30 75

Packing  height,  mm   1500   2000  

Packing   Ceramic   Rashig   ring,  

5*5x1 (mm) Ceramic   Rashig   ring,  

5*5x1 (mm)   interface  control   Conductivity   probe   and  

visual  check   conductivity   probe   +   sight  glass

Products  withdrawal   Raffinate:   overflow,  

extract:  solenoid  valve   Raffinate:   Pressure   regulator,   extract:  

solenoid  valve  

Boiling  control   Reflux  head  condenser   Heat   exchanger   coil   in   the   upper,   double   wide   part  of  the  column  

Sampling   along   the  

column   Considered     Considered  

Pumps   Diaphragm   Diaphragm  

FIGURE  2.7.     CONTINUOUS  COUNTER  CURRENT  SYSTEM  MADE  OF  GLASS

FIGURE  2.8.     STAINLESS  STEEL  CONTINUOUS  COUNTER  CURRENT  REACTOR  

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