THE  PROPOSED  TECHNOLOGY VARIANTS

• A  second  variant,  in  which  the  esterification  was supposed to be  executed  in    co-­‐

current  technique, without    direct  addition  of  apolar  solvent  in the esterification column, but in the neutralization step. This has been conceived for difficult  to  process  feedstock for the sake of controlling longer residence time, but I found that this function was only useful to demonstrate that the counter current operation is being the optimal conduct of the esterification.  

Process description:

The main operational elements of the technology consist of 6 column type contact devices. Four are reactors and two are columns. The series of operations are: esterification.

neutralization- trans-esterification- product refining- reagent and solvent recovery.

In the first column the main reaction if the conversion of FFA content of the feedtock into FAME, either in co-current operation (case of medium to high FFA content, highly difficult to handle colloid structures, such as of yellow grease) or in counter-current (case of medium to low FFA content, low colloid characteristics, close to real solution feedstocks). Trans-esterification of tri-glycerides has also taking place, alongside with the most important secondary reaction a degumming. Indifferent of the mode of contact gums are collected at the bottom of the column, and therefore even the system of co-current operation functions as a counter-current operation too. In a typical execution the column is filled with structured ceramic packing. The ceramic packing material has been selected to promote adherence of the polar phase onto the surface of the packing. In counter current execution the feedstock is diluted with hexane solvent. In co-current execution, depending on the result of the screening reaction the feedstock can or cannot be diluted with the hexane solvent.

In more advanced mode of operation the column will be emptied and after pulling out the ceramic structured packing ion exchange resins will be packed. In a pilot plant this can be afforded, in an operational system a twin column must be included for the sake of cleaning and activating the catalyst bed.

Operational conditions of the column can be controlled to raise the temperature close to 110 C. To maintain the reagent and the solvent in liquid state the pressure of the column can be as high as 10 bar. Control of temperature is provided by ovens, control of pressure by the metering pumps and pressure controller. As in all of the liquid-liquid contacting devices the interface control is placed in the bottom and withdrawal of the extract phase is done by conductivity signal of the solenoid valves.

Separation of polar and apolar phases is done in either variant in the second column. The neutralizing agent is composed by byproduct streams of trans-esterification and crude biodiesel refining. The glycerol content of the neutralization stream acts as extraction agent and drags residual gum components into the extract stream. Even in the case of operating the first column with the ion exchange resin this function will constitute an important feature of the system. Accordingly the pH=12-14 mixture is added in a quantity to have an effluent acidity of pH= 7-9. The interface is controlled at the bottom section via conductivity signals.

If the polar phase accumulates to the level designated the electric signal is opening the solenoid valve and discards an aliquote of polar phase. The neutralized stream leaves the column by overflow mode.

The third column is the trans-estericiation reactor. It’s operation is identical to the first column.

The fourth column’s function is to extract residual reagents and byproducts into the extract phase. In the upper part of the column deionized water, in the lower part of the column sulphuric acid solution are metered against the stream of the crude biodiesel that

constituted the raffinate of the trans-esterification column. Extract phases of the third and fourth column are collected and the mixture constitutes the neutralization stream for the second column.

Recycle of the solvent and reagent are done in the fifth and sixth column. The solvent recycle column operates in extractive distillation mode, residual water content of the bottom product biodiesel is reduced by this at low heat stress and high throughput device (instead of the generally employed this film vapour evaporators). Products of the sixth column are reagent grade methanol that is recycled and an inferior quality mixture of glycerol, water, salt and polar constituents. It has been beyond the scope of the pilot plant to produce any kind of refined glycerol.

The whole system is being provided means of VOC control and all the electric elements are explosion proof.

FIGURE  3.31   PROCESS  FLOW  SCHEME,  RETROFITTED  BIODIESEL  DEMONSTRATION  PLANT For the sake of illustration: volume of reactors: 2.5 m³.

The prime merit of the retrofitted case consists in rational exploration of physical assets,

“secondary merits” include flexible and ease in control and operate system. As presented in paragraph 3.10, capacity of an existing conventional plant can be retrofitted for increase in capacity and improvement of product quality reliability be reducing the necessary time in processing and by improving selectivities.

The first block of loop reactor system performs the duty of esterification-degumming.

According to the simple batchwise operation mode in the first loop reactor the FFA content of the feedstock is converted into FAME. Along the conversion sequrnce the entire system is pumped through the loop reactor back into the main vessel. Pipes in the loop reactor are filled with packing to provide static mixing. Alternatively pipes can be filled with ion

exchange resin. This block has also been dedicated to treat and recuperate FFA and crude biodiesel components of G-phase of other biodiesel processors. In such a loop-reactor block I created a flexible mode of operation for either small, medium or even large scale processors. The apolar phase of the process is pumped into the second block of loop-reactor, after neutralization and settling as the polar phase has been discarded into the vessel of MeOH recycling feed tank. The interface is being observed in a sight glass. Metering is done by manual addition of streams. The system at present state is not able tzo be operated under high pressure. For conversion into higher pressure operation the loop reactor must be replaced. A special advantageous feature of this schemes consists in very easy switch over from sulphuric acid catalyzed system to ion exchange resin catalyzed system. For the catalyst regeneration and system cleaning the loop reactor must be doubled.

The second block performs the cycles of trans-esterification-crude biodiesel refining. As in the case of the first block phase separations are realized with observing the interface in the sight glass. There is a slight trick in the figure. There are two sigh glasses in this block, because of the very fast settling of the glycerol formed, that cannot be entrained by the stram in the loop. After the G-phase discard via the sight glass the rude biodiesel is washed in two (or more) times by the addition of 10% sulphuric acid and deionized water solvent.

There is an additional decanting option in the third block, in the feed tank for solvent recycle and biodiesel drying. Distillation of both streams is done according to the scheme described earlier.