Diesel additive package

Joined
Dec 6, 2014
Messages
22
Location
New Zealand
Greetings good people of the forum. I have an unusual issue I'm requesting guidance from the knowledgable and experienced. I recycle waste plastic and oil to diesel by thermal cracking methods refineries have used for 100+years. To explain briefly, the waste hydrocarbon mixture is heated to its' boiling point and evaporated. By means of reflux and series condensers I'm able to fractionate a nice diesel product from the vapor. One issue is the formation of gum which I discovered in various parts of the plant and vehicle fuel systems. Research points to oxidation as the cause. It is partially dissolvable in xylene, gasoline and diesel but easily dissolves with methanol. Because my diesel is refined from hydrocarbon it has no additives and this aspect forms the basis of my question. Please advise a suitable additive package to deal with the various issues, in particular: Antioxidant to stabilize and inhibit gum formation. Solvents to clean the system of gum and other deposits. Other additives as may seem beneficial. I operate on a hobby status and make fuel for my own use only. Indeed far more time has been devoted to the building and running than anyone could imagine. Please advise. Thankyou.
 
Joined
Sep 19, 2008
Messages
2,594
Location
Pennsylvania
As a chemist, I can tell you that gums and other solid-like materials are caused by the presence of double bonds and tertiary carbons bearing a hydrogen atom which can come off and form a radical (like the double bond can form a radical) and this leads to polymerization, the formation of higher molecular weight species. When the weight gets high enough anfd the cross linking density high enough, you get "insoluble" solids. Refineries deal with this by hydrogenating under pressure to remove double bonds, for example, or by using a refing process that keeps their formation to a minimum. Keep in mind that plastic and waste oil contain metals (oil more so then plastic) which can cause all kinds of wierd things to occur when you heat up such a mixture to high temperatures. A typical antiocidant used in fuels is a hindered phenolic product that acts as a sacrificial molecule, reacting preferentially with oxygen to form a quinone. This is a lot of what is in gasoline storage products so you might want to add Stabil to your product and see if that makes a difference. Adding alcohols to diesel is, in my opinion, a no-no. Also, the effects of solvents other than hydrocarbons that you might add would have to be checked for effects on rubber hoses, seals, pumps, etc.
 
Joined
Sep 19, 2008
Messages
2,594
Location
Pennsylvania
Excalibur, here is a Wikipedia article on metathesis. This is just a little bit of information but gives you an idea of what can happen when organics are heated and metals, for example, are present. http://en.wikipedia.org/wiki/Olefin_metathesis I give you a lot of credit for trying this type of re-use of waste oils and plastics. Perhaps using your fuel in some ratio with purchased diesel fuel and some fuel stabilizer added, you may be able to burn this stuff without gumming up pumps,etc. By the way, try to see if the gums are soluble in diesel fuel additives designed to keep injectors clean. If so, dose your fuel with the recommended amount and see if it more forgiving in the fuel system. Keep us updated on your work in this area, please!!
 
Last edited:

Excalibur

Thread starter
Joined
Dec 6, 2014
Messages
22
Location
New Zealand
Thanks for great replies. aa1986, thanks, welcome Nyogtha please join the thread. Boomer, yes the insoluable aspect of the gum is amazing. Today I tested an injector cleaner on the gum without success. Thinners containing some MEK and isobutanol was noticeably better but no where near as effective as methanol. Yes, agreed methanol isn't worth the risk as an additive. Hindered Phenolic? I looked at my notes. 2,6-ditertiary-butyl-4-methyl-phenol is one I jotted down when studying antioxidant testing on fuels. Elsewhere I find it listed as fuel additive AO-32, for jet fuels and gasolines. Good thought, I hadn't considered the presence of metals would cause strange reactions. Waste oil would have plenty of superfine metal. Adding pump-diesel does help my vehicle performance. I do wonder whether it has the additives my raw diesel lacks. I use Caltex diesel which I believe has Polyetheramine PEA.
 
Joined
Oct 13, 2014
Messages
2,744
Location
San Antonio, TX
Originally Posted By: Boomer
Refineries deal with this by hydrogenating under pressure to remove double bonds, for example, or by using a refing process that keeps their formation to a minimum.
Nope, for gasoline range and lighter molecules olefins typically have significantly higher octane values than their normal alkane counterparts, so refineries try to not hydrogenate such molecules. Post-treatment of gasolines containing olefins for sulfur removal using hydrogenation uses very selective hydrogenation and performance guarantees are based in part on how little the octane loss is between feed & product. Examples would be PrimeG+ and Exxon SCANFiner technologies, among others. If you own a gasoline powered vehicle, you may want to bone up on this. Now to Excalibur, gasoline antioxidants are typically either hindered phenols or phenylaminediamine chemistry. For distillate based fuels (jet fuels based on kerosene cuts and diesel fuels), metal deactivators can commonly be used along with antioxidants to inhibit metal catalyzed polymerization reactions. I've used AO-22 in both commercial and military grade jet fuels for antioxidant with great success (which is phenylaminediamine based). It is something to be very careful with handling & use. Wikipedia Link for reference As far as metal deactivators are concerned, you need to see if you're exposing the fuel to any yellow metals as copper is the real culprit. Replacement of yellow metal components in heat exchangers with carbon steel components simplifies both cooling water treatment chemistry requirements as well as finished fuels additive requirements in an industrial setting. If your material isn't being exposed to yellow metals in production or use you don't really need a metal deactivator. Where antioxidants and metal deactivators hinder polymerization, detergent & dispersant additives help make surfaces less "sticky" for such gums to form on and adhere to. After an engine is shut down, "soakback" of heat tends to let gums form on surfaces where fuel evaporates, whether that's carburetors or fuel injectors. Techron is a good handy detergent / dispersant additive at the retail level, but what it's dissolved in may have too low a flash point for your application. Chevron Oronite would be an example designed for diesel fuels. https://www.oronite.com/products/diesel-additives.asp Olefins on their own aren't a bad thing in fuels and attempting to build and safely operate a backyard hydrotreater isn't something I'd advise. The real bad actors are the diolefins, being much more unstable than olefins with a single double bond. Pyrolysis gasoline from steam crackers must be sufficiently hydrotreated to remove diolefins before blending into motor gasoline for example, and diolefins produced by Thermofor or fluid catalytic cracking or coking significantly increase acid consumption and polymer production in alkylation units, so some alkylation units have selective hydrogenation units for the alkylation unit feed stream to treat the diolefins without wrecking the olefins to be alkylated. None of this is practical for a backyard application, and I'm confident there's a boatload of diolefins in your cracked materials. With additives, you may reach some crossover point where additional additive not only isn't incrementally beneficial, it can actually aggravate the problem. Hope this helps.
 
Joined
Oct 13, 2014
Messages
2,744
Location
San Antonio, TX
AO-37 would be a good example of a hindered phenol antioxidant for distillate fuels. FWIW I don't think there's going to be an easy solution to keeping gums from forming in your equipment, but additives to the cooled finished product should be beneficial. Old thermal crackers were manually decoked, modern fired heaters use steam-air decoking to spall as much buildup as possible and burn the really tenacious stuff off the heater tubes, or pig the heater tubes.
 
Last edited:

Excalibur

Thread starter
Joined
Dec 6, 2014
Messages
22
Location
New Zealand
Originally Posted By: Nyogtha
As far as metal deactivators are concerned, you need to see if you're exposing the fuel to any yellow metals as copper is the real culprit. Replacement of yellow metal components in heat exchangers with carbon steel components simplifies both cooling water treatment chemistry requirements as well as finished fuels additive requirements in an industrial setting. If your material isn't being exposed to yellow metals in production or use you don't really need a metal deactivator. Where antioxidants and metal deactivators hinder polymerization, detergent & dispersant additives help make surfaces less "sticky" for such gums to form on and adhere to. After an engine is shut down, "soakback" of heat tends to let gums form on surfaces where fuel evaporates, whether that's carburetors or fuel injectors. Techron is a good handy detergent / dispersant additive at the retail level, but what it's dissolved in may have too low a flash point for your application. Chevron Oronite would be an example designed for diesel fuels.
Nygotha, thankyou for the great reply! I have taken the time to study and digest the information. Most helpful. Re yellow metals. Yes, there is some! Copper and brass. Even some gaskets are made from copper. Would stainless or aluminum present any reactive problem? My main condenser is 316 stainless. Is the superfine yellow metal contamination that can often be seen in waste oils as "glitter" an issue as far as reactiveness goes? One thought is to settle or centrifuge waste oil feedstock beforehand. Pics of the gum in my vehicle filter: Pic shows gum in filter. Note I scratched the gum with my fingernail to determine how soft/sticky it was. Here I cut the filter open to inspect. The disk to the right is the flipside of what you see in pic one, after I cut and separated it. Note the trickle runs on the inside of the tin outer housing (left) Nyogtha, that's a great description of the soakback effect. I did notice the gum is very selective where is chooses to settle. Some of the gum could be from boil-over problems the plant exhibits from time to time. It is very frustrating as it occurs without a real fixed pattern. Few things I've identified that are likely to aggravate it: WMO feedstock sometimes has visible green glycol which wants to hold a water content. The retort is tall and narrow which is thought to be more likely to get boil over events. There's been no chance to test boiling chips. I have thermocouples monitoring retort temperatures, one in the liquid feedstock, another above liquid level and a third measuring the amount of heat being applied. I am able to add preheated feedstock to make the process continuous but it does add another dimension of variables because the add feedstock could be made from a range of fractions. This itself could lead to boil over. Any thoughts on how to calm down the retort but still run a reasonable pace? Currently the retort vessel is dismantled while I upgrade the refractory so I want to do all my modifications before next run. Comments, discussion invited and appreciated. Thankyou.
 
Joined
Dec 12, 2002
Messages
43,672
Location
'Stralia
Excalibur, just as you were posting, I saw this one of your pics on another place. I think it's telling, as one of my ideas to combat varnish in engines has been to cool the oil filter to below the varnish settling point...and that's seriously what I've seen AS varnish. Paper isn't cooled, and doesn't catch it. The can IS... I think that can be worked with
 
Joined
Oct 13, 2014
Messages
2,744
Location
San Antonio, TX
Excalibur, I'll PM my e-mail address to you as this discussion has become far more complex than your initial post regarding additive suggestions.
 

Excalibur

Thread starter
Joined
Dec 6, 2014
Messages
22
Location
New Zealand
Originally Posted By: Shannow
I think it's telling, as one of my ideas to combat varnish in engines has been to cool the oil filter to below the varnish settling point...and that's seriously what I've seen AS varnish. Paper isn't cooled, and doesn't catch it. The can IS... I think that can be worked with
Shannow, a very interesting prospect. I'd like to know more. Have you done any trials? Another suggestion was made some weeks ago to chill the fuel and extract gum/varnish with a centrifuge. I believe the thought was that gum/varnish is heavier by specific gravity so should fall to g-force. Polyetheramine has got me going. I've started studying. What's known about PEA?
 

Excalibur

Thread starter
Joined
Dec 6, 2014
Messages
22
Location
New Zealand
I had another thought... If gum was settling out from being chilled then it should be doing that in the tank which is exposed to passing breeze. I suppose a diesel fuel tank is subject to cooling to deal with the heat from hot diesel bleeding back in the return line. In this way, the injector pump can run at reduced temperature and offer cool diesel to the injectors. Some years ago, I ran vegetable oil as diesel. Twice I discovered the tank badly gummed up. No thinners I had would budge the stuff but caustic made short work of it. Interestingly, I moved to a plastic tank which I had inside the van which showed no sign of the oxidation/gum forming. I reasoned that the earlier gum forming was due to the steel tank reactiveness or the sudden drop in temperature the hot returning fuel was subject to. With the current gum in my hydrocarbon based diesel, I think that if a solvent to dissolve it could be found then it would remain in solution till it was injected and burned. The difficulty with this idea is identifying a solvent concentration that would be aggressive enough to dissolve the evil stuff yet not harsh enough to deteriorate seals.
 
Joined
Dec 12, 2002
Messages
43,672
Location
'Stralia
Couple of items that are in my thought process... Varnish doesn't collect where it is formed, it settles out somewhere cooler...keep the temperature up and it stays soluble. It's the turbine governor and valve gear hydraulics that I've had issues with, not the bearings)...Thus my cooled filter idea. Industrially, it can be removed via cellulose depth media or electrostatics. I sponsored an engineering thesis on varnish and membrane patch colorimetry (a blotter test, but quite advanced)...see ASTM D7843. We proved that meaningful results can be gained using a flat bed scanner, and a calibration test card from Kodak. http://www.cleanoil.com/products/varnish-potential-testing-mpc.html shows a process. Solvents can't touch it...the petroleum ether washes the oil out from around the varnish on the filter paper, leaving the varnish to stain the paper... You've found alcohols (polar) do the work, which is sensible, as varnish is polar, sticks to metal, then sticks to itself. Have you seen that green "fuel doctor" at Supercheap auto ? It's less solvent, and more detergent http://www.scienceinthebox.com/alcohol-ethoxylates-non-ionic-surfactants
 
Joined
Nov 11, 2010
Messages
9,783
Location
Saskatoon canada
Originally Posted By: another Todd
My hat is off to all you posters in this thread...some brilliant minds at work for sure! Interesting stuff.
+1 Wow. I've gotta read it again.
 

Excalibur

Thread starter
Joined
Dec 6, 2014
Messages
22
Location
New Zealand
Shannow, thanks for the thoughts. I spent a good few hours with Mr.Google researching and reading. I learnt quite a bit. I tested my gum for melting point and the nearest I can pin it to is 80°C/176°F. The Fueldoctor, an alcohol ethoxylate based additive was an interesting read. They claim it cost 1c per liter to treat ones' diesel so the price is OK. Alcohol based additives wouldn't have been my first choice but prudently I'd best keep open minded. A study of alcohol ethoxylate showed it is used in detergents, washing powders and shampoos etc. Also as a wetting agent for sprays. Part of me says I only need what ordinary pump diesel has for additives, then I need to work out how to procure them. To illustrate this point, my van goes noticeably better even if I put a few percent bought diesel in with a tankful of my homemade. My thought is that it has enough cleaning additives to make a difference even at that ratio.
 
Top