FAQ

What are some of the common problems experienced with low-grade magnesium silicates?
How do ion exchange resins work?
What impacts the performance of Resins?
What design parameters for the columns need to be considered?
How long does the resin last?
How do you know if the resins are exhausted?
Will these resins work for me?
Do I require any filtration with these resin systems?

 

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What are some of the common problems experienced with low-grade magnesium silicates?
Most magnesium silicates have their origins in edible oil purification. Producers should be aware and cautious of the following disadvantages of low-grade silicates. Common problems experienced with low-grade magnesium silicates include:

• Poor "wetting out" capability:
  Low grade silicates experience difficulty during the mixing process and experience ' clotting" which renders a large portion of the silicate as useless.
• High moisture content:
  Low-grade silicates contain a high moisture content. This will hinder the achievement of international quality standards and will 'cloud' the physical appearance of the fluid and clarity is usually difficult to achieve. Some products contain bleaching agents which may make the fuel appear lighter in color, but still contains high levels of production residues.
• Inconsistent particle size distribution:
  Inconsistent particle size distribution will result in poor removal capability and inevitable pump seizures.
• Poor absorbency capability:
  Low-grade silicates will reduce the ability for effective removal of production residues and soaps.
• High dosage ratio:
  Typically, 3-5% by weight ratio may be required to compensate for the poor removal of production residues and soaps, thereby increasing production and removal costs.
• Poor pH neutralization capability:
  As production residues and soaps are not effectively removed when using lower- grade silicates, this negatively impacts on the alkaline reduction of the fuel which may cause engine damage and seal failure over time.
• Inconclusive performance data:
  Published performance data on low-grade silicates is seldom published.

 

How do ion exchange resins work? Two or three purification vessels or "columns" are usually required. These can best be described as "lead", "lag" and "standby" columns. The lead column does the bulk of the polishing and the second (lag) column does the trace polishing. The standby column is used in case of emergency or when the lead column exhausts. Raw biodiesel flows through the lead and lag column. When the effluent of the second column contains increased glycerine levels, this column then becomes the lead column. If available, the standby column then goes into the lag position and the original column goes into standby.

Single tower operation is not advisable.

 

What impacts the performance of Resins? Higher levels of glycerine, methanol and water will rapidly exhaust the adsorption capacity of the resin. Resins have a finite capacity for the removal of impurities from biodiesel. Careful upstream monitoring of crude biodiesel is required to prevent premature exhaustion of resin. This may require diagnostic evaluation equipment.

Therefore, if using this method, it is important to ensure that only residual levels of hydrophilic compounds are present in the crude biodiesel. To facilitate this, separation equipment i.e.,. methanol recovery systems, glycerine centrifuges etc, are a fundamental pre-requisite of the production plant and process. The completion and overall efficiency of the reaction is also important to monitor.

 

What design parameters for the columns need to be considered? Size and configuration of the columns is dependant on the individual plants operating conditions. The columns are designed to have a man-way at the top and bottom to facilitate the loading and unloading of the resin. Providing a man-way located above the support screen is recommended to allow for inspection of the columns and in order to repair internal piping/flow-distributors, nozzles etc.

A consultancy session is advised to ensure that the column parameters and internal distribution system is adequate to suit the plant in question. Flow rate, fluid distribution and residence time need to be properly controlled.

Extra space within the column is recommended to allow for a 150% increase in resin volumes due to the swelling, and in order to minimize the impact on the upper distribution arrangement of the resin.

As the crude or "unwashed" biodiesel flow path enters the column, the distribution of 'used and unused" resin is difficult to control. Internal flow dynamics are important at this point. "Unused" resins, which do not enjoy maximum contact time with the fuel, do not contribute much to the purification process. This may result in higher wastage as the whole column is usually replenished at one time.

To reactivate a column, it first needs to be cleaned out (using a liquid solvent) to remove the spent resin, as well as to remove production residues i.e.,. soap, catalyst and methanol. Failure to clean the column properly will result in a build-up of production residues over time, thereby minimizing the effect of any new added resin. This is usually a troublesome process due to the swelling of the resin making it difficult to remove. Smaller columns which, are not cleaned out properly due to limited access and no inspection points, would usually display a significant build-up and internal "caking" over time, thereby discounting the effectiveness of future washes.

Some producers employ methanol to clean out the columns. This results in a highly hazardous effluent waste containing soaps, production chemicals and residues. This would then need to be disposed of using a certified hazardous waste contractor at the producer's expense.

 

How long does the resin last? The actual life of the resins will depend on the plant's process designs and operating characteristics, as well as the methyl ester feed quality.

Typical claims are that 1kg of resin can treat 900-1600 kg of biodiesel. These replenishing rates are usually more frequent in reality, especially if WVO is used in the process.

The frequency of "rebedding" (replacing the spent resin) does depends very much on the initial impurity level of the biodiesel, the amount of biodiesel treated, and the size of the column.

Smaller columns would require more frequent replenishing than large columns and are generally not as effective. Larger columns would perform better due to increased contact time and greater surface area. Smaller columns, with lower resin holding capacity, used with poor grade biodiesel i.e.,. made from WVO , may prove troublesome and expensive.

 

How do you know if the resins are exhausted? Resins adsorb methanol and water first, so biodiesel does need to be relatively clean prior to use. Soap particles will "blind" the ion bed which apparently can be "regenerated" with a methanol wash, but information of the exact workings of this practice is proving difficult to secure.

To control a column to determine when the resin is spent i.e.,. no longer functional, the producer will need to monitor the soap, production chemical residues and glycerol levels by taking regular samples from the column exit and apply the necessary analysis. This is a time consuming process that requires expensive and sophisticated diagnostic equipment.

In addition, published performance data on the performance of resins is difficult to secure.

 

Will these resins work for me? Resins are primarily aimed largely at mass producers with top-quality processes. More sophisticated biodiesel production facilities, using virgin oils, may find this to be a satisfactory purification method.

Small / medium scale producers, using batch-style reactors, would not usually consider this method due to the poorer quality of the initial biodiesel that would exhaust the resin too rapidly and require constant replenishing, resulting in high wastage and inflated running costs.

 

Do I require any filtration with these resin systems? High levels of contamination are very common in the final product with resin systems. These would include solid contaminants and high moisture content. If the producer has not effectively cleaned out the column and not calculated the replenishing time of the resin accurately due to poor monitoring, this will further increase overall contamination levels and compound the problem. As production residues build up within the columns, so do contamination levels that could cause significant engine damage if not effectively removed. Resin fragmentation is common due to the compression experienced is the bed as well as when the resin is allowed to dry. Final polishing is essential at this point.