ION Exchange Resins for Drywashing Biodiesel
By Rick Da Tech
ION exchange resins are high tech man made resins that are capable of trapping soap molecules on the surface of a resin bead. Different ION exchange resins work in different ways and use different techniques to clean the biodiesel. All of them generate a new waste stream, the spent beads.
Available ION Exchange Resins
A partial listing of the available resins:
- ALX Enterprises DW-R10tm
- Amberlite bd10dry is made by Rohm and Hass Chemical Co.
- Dowex DR-G8 made by Dow Chemical
- PD206 is made by Purolite, a subsidiary of 3M
- Lewatit GF 202 is made by Lanxess
- Tulsion T-45 BD made by Thermax
Pros and Cons
Each resin works in a slightly different way so there are some fine differences between them. They are enough alike from a Homebrewer’s perspective that we can lump them all together for this discussion. They all do work and remove the soaps from your biodiesel. They are much more economical when processing with new oil than with used oil.
The manufactures of these resins recommend keeping soap content of the unwashed biodiesel below 500 ppm of soap. That’s how much you usually have after the first or second wash. Commercial biodiesel producers using new oil can meet the 500 ppm level in unwashed biodiesel. With the exception of the Lewatit GF202 the resins re
move the soap by replacing the metal ion in the soap with a hydrogen ion forming FFA that is passed through the resin and left in the biodiesel. If there is too much soap, there will be too much FFA in the finished biodiesel to meet TAN (Total Acid Number ASTM D664). Commercial producers have found that if the biodiesel contains more than 1200 ppm going into the drywash towers, it will not meet ASTM D664.
Homebrewers using or standard single stage base method on WVO will have three to five times that much soap in our unwashed biodiesel. That means we would be using it three to five times faster than a commercial biodiesel producer. To make it economical, you would have to wash using some other "wash" technique first to bring your soap levels down. The manufactures typically recommend an acid eserification stage if you plan to use waste cooking oil.
Some of these can be partially regenerated using either methanol or an acid, but all of them eventually become used up or spent. Once spent, you will have to find a way to dispose of the waste.
Two problems that home brewers run into when using resins are "compaction" and "fouling". Compaction is caused when the beads grow in size over their normal lifespan and do not move up the tube adjusting for the increase in size. Compaction can cause ruptured resin tubes, burst resin beads, and decreasing flow rates and eventually stopping the flow altogether. Compaction requires a resettling of the beads to resolve the problem. This can sometimes be accheived by backflowing biodiesel through the bed at a high rate to upset the beads. Fouling is a coating of the top layer of resin with contaminates, typically glycerin or undissolved soaps, that result in flow stoppages. It is usually prevented by a combination of increased settling times and filtering. Backflushing with biodiesel or methanol are the usual methods for resolving fouling.
Fouling can be prevented by giving the biodiesel enough time to clear up before passing over to the resin bed. In unwashed biodiesel that has had no water introduced, the cloudiness is caused by soap particles not dissolved in the biodiesel. Settling is the cheap way to remove the cloudiness. A major factor in getting settling to work is having a wide temperature variation. As the biodiesel chills at night more soaps become undissolved and fall out to the bottom. When it warms up in the daytime, the soaps dissolve back into the biodiesel and clear up. If you are settling in a location with little or no temperature variation you may never clear up. To get it to clear up you will either have to filter the undissolved soaps out with a 10-20 micron filter or you can heat the biodiesel until it clears, usually 10 degrees F or so.
ALX Enterprises DW-R10TM
DW-R10TM from ALX Enterprises LLC is currently the most commonly available dry wash resin avalable to home brewers. It is a dry ion exchange resin designed to remove salts, soap, catalyst, glycerin and water from raw B-100. It can be used either before or after the methanol has been removed from biodiesel. MSDS
AmberliteTM BD10dryTM made by Rohm and Haas is an ion exchange resin. It will remove both glycerin, and soap. It is designed to be used after glycerin separation and before the methanol is removed. It can be regenerated for use with glycerin removal, but not soap removal. When it becomes saturated with soap, it must be removed and disposed of properly.
Product InformationWeb Site
DOWEXTM DR-G8 is a dried cation resin designed as a processing aid to reduce and remove trace salts, soaps, glycerin and other organics from a crude biodiesel stream. This dried media will also serve as a desiccant media to retain and remove trace water. It is designed to be used after settling out the glycerin and removing the methanol.
Product InformationWeb site
LEWATIT® GF 202
The GF202 resin is a Sodium based macroporous design that will remove glycerin and soap from biodiesel. It operates as an adsorber with the glycerin sticking to the bead and the soaps attaching to the glycerin, so it can be regenerated by flushing with Methanol many times. Being sodium based it does not convert soap into FFA and introduce acid to the finished biodiesel like all the other resins. The manufacture recommends removing the methanol down to 0.1% before passing through the beads. Soap levels are recommended to be less than 500ppm. They are shipped wet and do not swell with use like the other resins, meaning no compaction issues. They can however foul if the biodiesel is below 40C or if it has not sufficiently settled. Recommended flow rates are 1-1/2 to 2 bed volumes per hour. It is shipped in 25 liter bags and 200 liter kegs. Pricing is about $12 per liter. The beads are shipped wet and must be flushed with 5 bed volumes of dry methanol before use.
Product InformationWeb Site
Purolite® PD206 is a dry ion exchange resin that functions as a combined desiccant and ion exchange media it is specially formulated to enable maximum removal of free glycerin as well as catalyst, soaps and salts from crude biodiesel. It is designed for use after settling the glycerin and before or after methanol recovery. Purolite expands roughly 200% during use. Manufactures recommeded maximum flow rate is 0.3 gallons per hour per pound of resin. Maximum recommended soap levels are 750-1000ppm if ASTM Acid numbers are to be met. Manufacture recommend a tower that is three times taller than is wide to prevent compaction and channeling. Purolite is an American company and is aggressively marketing their product in the US. Pricing is about $10 per pound.
Product InformationWeb Site
Thermax Tulsion T-45 BD Marco is a hydrogen based macroporous design, that will remove both glycerin and soap from biodiesel. It removes the soaps by both ION exchange and absorbtion. When the beads have absorbed as much as they can, it can be flushed with methanol, typically 5 bed volumes, to restore most of their adsorption capability. It takes regeneration with sulfuric acid to restore it to new condition. The beads work with or without methanol removal prior to passing through the tower. If the methanol is removed and the soaps given time to settle, the the beads will last longer. Maximum recommended soap levels are 2500ppm. Recommended flow rates are 2-2.5 bed volumes per hour. Optimal operating temperature is 85°F to 95°F. Thermax is an Indian company with distributors in the US including Arbor Biofuels Company. It is shipped dry and costs about $9 per pound. For more information see the Thermax web site.
Ion Exchange Resins for Cleaning Biodiesel: How Do They Work?-- A two-page Tech Note from University of Idaho about ion exchange resins, a waterless method of cleaning biodiesel.