Guide to Biodiesel Dry Washing with DudaLite DW-R10 Ion-Exchange Resin

Introduction

Dry Ion-exchange resins are designed to remove salts, soap, catalyst, glycerin and water from raw B-100 (100% Biodiesel). The resin consists of tough, spherical beads with an average particle size of 400 microns(dry) and a range from 200 to 800 microns. The density is 6.7 pounds per gallon. The resin will swell and expand to up to 130% its original volume as it is used.

There are a few different types of resins available on the market today. The newest product, DudaLite, also known as DW-R10®, performs the best over other similar brands. Others may know of similar brands such as Purolite® PD206 and other resins which help aid ion-exchange resins such as Amberlite®.

Getting Started

When to use an ion-exchange resin

With glycerin removed, biodiesel is run through a metallic tower containing an ion-exchange resin to remove all of these contaminates. It eliminates the complications of water washing and delivers a consistently pure biodiesel product with only the work of a pump needed for each batch being dried.

Should it be used before or after demethylation?

An ion-exchange resin can be used before or after demethylation.

If glycerin is greater than 1000 PPM (>0.1%) after demethylation, ion-exchange resins will reach its maximum loading of glycerin before it reaches its maximum capacity for salt and soap. In This case, ion-exchange resins should be used before demethylation. A methanol wash should then be considered to remove the glycerin from the ion-exchange resin. This glycerin contaminated methanol can be re-used in your next biodiesel batch to avoid waste. By using the methanol wash procedure, you can restore your ion-exchange resin’s absorption capacity until its salt absorption capacity is exhausted.

If glycerin is less than 1000 PPM (<0.1%) after demethylation, you may not be able to justify the efforts of a methanol wash. In that case, the ion-exchange resin is applied as a final polishing step after demethylation.

What flow rate should be used through ion-exchange resins?

For biodiesel with less than 1000 PPM (<0.1%), the maximum flow rate should be 3 bed volumes per hour. If glycerin is greater than 1000 PPM (>0.1%), the flow rate should be set to 1.75 bed volumes per hour. These flow rates are for the lead column, not the size including room for expansion.

How does temperature affect the purification process?

The ideal biodiesel temperature for purification through DW-R10 is between 120°F to 140°F.

When the temperature of the biodiesel drops below 100°F, glycerin absorption rates begin declining. When the temperature is below 80°F, the rate is really slow.

When very low temperatures are involved, the glycerin is held on the outside of the resin and is not actually absorbed into the resin. Consequently, it will tend to "wash out" of the resin when it reaches saturation. This can result in a slug of glycerin in the fuel coming out of the resin when the column has reached full saturation. Running at a low flow rate will allow you to load more glycerin and soap onto the resin but it would have to be done dilligently and preferably with a lead-lag set-up. When temperatures of the biodiesel drop too low, biodiesel will gel and clog the column, preventing any flow at all.

The maximum working temperature for this resin used with biodiesel is not tested. The resin has been successfully used with steam condensate which is typically about 240°F.

How much B-100 can be purified before the resin is exhausted?

There are several factors which affect B-100 contaminant levels. These include the completion of upstream reactions, effective phase separation and feedstock quality. For a well-run system, with an average of 500 PPM of hygroscopic contaminants, about 1500 to 2000 lb of B-100 can be purified per lb of resin.

Beyond optimizing upstream reactions and separation, there are a few ways to maximize purification with the resin. First, a lead/lag configuration can be used to allow full exhaustion of the media without producing off-spec B-100. This is when a 2nd tower with cleaner resin is used after purifying through an initial tower with dirtier resin. The towers swap rolls once the 1st tower has been exhausted and is refilled with new resin.

The second way to maximize usage is to use a methanol wash on the resin when the resin is applied prior to demethylation.

Setting up the exchange columns

How much resin is needed?

For columns treating B-100 with less than 1000 PPM (<0.1%) glycerin, divide the B-100 flow in gallons per hour by 3 to get the gallons of resin required. Then multiply by 6.7 (density of the resin) to get the pounds of resin required.

For columns treating B-100 with more than 1000 PPM (>0.1%) glycerin divide B-100 flow in gallons per hour by 1.8 to get the gallons of resin required. Multiple gallons of resin by 6.7 to get the pounds of resin required.

How deep should my bed of resin be?

A minimum of 30 inches of dry resin is recommended. Remember that the resin will swell to about 2.25 times its dry depth when it becomes wet with glycerin and water. Be sure to accommodate for this expansion with a taller vessel.

How should the strainer at the bottom of the column be designed?

The laterals should have a screen mesh capable of filtering particles down to 125 microns. Strainers must be able to withstand the pressure generated by the swelling of the media.

What other designs features should be considered for the exchange column?

There should be a top fill port configured to allow easy access for resin replacement, a bottom access door to allow for resin removal or strainer replacement, an air vent at the top to allow air removal from the system and sight glasses in the side of the vessel for larger installations to allow for monitoring of the bed.

How many columns should be used?

It’s recommended to have two columns in series at a minimum. A third standby column is recommended for systems that will run continuously. Having two columns in a series allows the lag column to catch any contaminates that get through when the lead column is exhausted. This allows the lead column to be run to complete exhaustion. The lag column is then moved to the lead position and the standby column is put into the lag position while the exhausted column that was in the lead position is rinsed with methanol to remove excess glycerin, or reloaded with fresh resin.

What precautions should be taken when handling ion-exchange resin?

Safety comes first. Please closely review the MSDS. Ensure that everyone wears proper safety equipment. Remember that the beads act like little ball bearings on hard surfaces, people can easily slip on these! Sweep away any spilled material immediately.

How is the resin loaded into an exchange vessel?

Add clean biodiesel to the vessel until at least four inches covers the bottom strainer. Add the resin slowly at first to avoid damaging the strainer at the bottom of the vessel. After the proper quantity of resin is added, fill the vessel from the bottom slowly with B-100. Be sure to have a top vent open during this step. This approach will displace air from the bed. Do not leave the resin exposed to air any longer than necessary. It will absorb moisture from the air.

What considerations should be taken when designing a large tower?

Beds of resin should not be deeper than 40". Larger diameter towers should be utilized to achieve the higher flow rates required. However, when building a tower for a large scale operation, it is acceptable to make the tower taller in order to eliminate some of the needed diameter. Towers with beds of resin deeper than 40" should never exceed a bed depth of more than 3 times the tower's diameter to allow for adequate expansion without too much compaction and proper flow of the biodiesel. For example, if you have a 30" diameter tower, the absolute maximum dry bed depth should be 30" x 3 = 90".

How to get the most out of the resin

What is the difference between exhausted resin and saturated resin?

Exhausted resin is resin that has all of the active exchange sites loaded with ions exchanged from the process. The resin literally gives up hydrogen, which is replaced with ions (salts) from your B-100.

Saturated resin is resin that has absorbed all of the glycerin and water that it can hold. If the resin is exhausted, it will also lose some of its capacity to absorb water and glycerin.

How do I restore the capacity of the resin for removal of glycerin and water?

If the application is prior to demethylation, it can be washed with methanol to restore absorption capacity.

Can the resin be washed with methanol if it’s only used for final polishing after demethylation?

It’s not a good idea because the residual methanol will get pushed out of the resin and end up in your finished B-100.

What are the recommended steps for washing resin with methanol?

Drain all of the B-100 from the exchange column. Rinse the resin with two bed volumes of clean methanol at a rate of one bed volume per hour. You will notice that the methanol is discolored by the glycerin. Repeat the procedure with one more bed volume of methanol at a rate of one bed volume per hour. Save the dirty methanol for use in the biodiesel process.

How do I tell when the resin is exhausted?

If the product is exhausted this can be detected by a simple test of conductivity of the wash water. Mix one part of biodiesel to three parts distilled water, shake and then let them separate. Then measure the conductivity of the water phase. You will see the conductivity rise quickly when the resin is exhausted. You should monitory the clarify of the B-100. The turbidity will increase when the resin is exhausted.

How do I unload my resin when it is exhausted?

It is a good practice to back flow on bed volume of B-100 to fluff the bed. Next you should drain down the B-100 and remove the resin from the bottom of the column.

What is the shelf life of DudaLite DW-R10?

If kept free of air/moisture and stored in a cool, dry place, the DudaLite DW-R10 will be good for up to about one year. After one year, there will be some degradation of ion exchange capacity. By the end of the second year, the resin will lose about 20% of its capacity.

How much water does DudaLite DW-R10 absorb?

DudaLite DW-R10 loves water. One pound of DW-R10 will absorb 1.2 pounds of water. Once it reaches full capacity for water absorption, it will start giving up the water in preference for methanol and glycerin. Consequently, it is best to "dry" the resin with methanol as soon as it reaches its full capacity for water. It can absorb, then give up the water almost an unlimited amount of times.