CA1104822A

CA1104822A - Polymers to improve combustion efficiency of hydrocarbons

Info

Publication number: CA1104822A
Application number: CA289,856A
Authority: CA
Inventors: Ronald J. Kopko; Robert L. Stambaugh
Original assignee: Rohm and Haas Co
Current assignee: Rohm and Haas Co
Priority date: 1976-11-19
Filing date: 1977-10-31
Publication date: 1981-07-14
Also published as: FI773382A; DE2750876A1; SE7711950L; GB1569344A; BE860964A; IT1091481B; JPS5364206A; NO773920L; FR2371639A1; ZA776771B; NL7712521A; FR2371639B1

Abstract

It has been conceived and demonstrated that addition of small amounts of very high molecular weight polymer to liquid hydrocarbon fuels can enhance combustion efficiency (improve heat recovery) when that fuel is employed in spray combustion processes.

Description

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Liquid hydrocarbon fuels as such are not combustible. Rather, they musk first be vaporized and mixed with air, or oxygen, ko burn. As middle distillate or heavier petroleum ~uel fractions have low ~, 5 vapor pressures~ ef~icient atomization is a critical aspeck o~ spray combustion o~ such fuels. Atomizakion produces fine liquid ~uel parkicles, the ~argesur~ace area o~ which leads to ~ast evaporation and thus rapid and ef~icient combuskion. Considerable work has been done in thls area and a great deal o~ art has developed over the years.
; Even with efficient atomization stoichiometric combustion cannot be achieved. Limitation in this regard ls imposed by the ability to reach a condition o~ perfect mixing in the time and size scale o~ the combuskion pro-cess and equipment. In order to gek complete combustion, j therefore, it is necessary to supply excess air to the process. Excess air~ to the extent it provides complete combustion~ serves to increase combustion e~lciency.
However, too much air can lead to decreases in heat ~ ~ 20 recovery. All o~ khe oxygen nok involved in the combustion ;~ process as well as all o~ the nitrogen in the air is heated and thus carries heat out the stack. Further, the greater the excess air the greater the mass rlOw through ~-~ the s~stem and the shorter khe kime scale for hea~ trans-fer. Hence, achieving erficient combustion and heat recovery requires a delicate balance of atomization and sxGess alr coupled with optimized combustion chamber and h~eat recovery system designs.

-2-2;2 Because of the restrictions imposed by the overall equipment design~ t;here has also been consid-erable interest over the years in ^hemical modification of combustion. There are at least two ways to approach the problem chemic:ally -- the first through modi-fication of the atomization process and the second through catalytic effects on thecombustion process itself. Indeed both appear to have been employed.
Fluid properties which influence mist particle ' size in an atomization process include density, surface tension, and viscosity. Of these, density and viscosity do not seem to be promising approaches. Density could not be altered significantly by an additive. Viscosity, on the other hand, is easily increased by low levels of polymers but increased viscosity would lead to larger mist par~icles, apparently the wrong direction for improved ~ combustion. Surface tension is readily influenced by low : levels of additives and this would seem to be the most rewarding route. A variety of claims to combustion efficiency improvement have been made which apparently involve this concept, although it is not necessarily apparent that all workers understood this. For example, ` ~ polar materials such as alcohols, esters or ketones, amines, o:rganic phosphates and nitrates, and alkali or alkaline earth metal or (alkyl) ammonium sulfonates or carboxyIates have been described. Such approaches are not j .
particularly effective and are not generally practiced commerFially.

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Combustion eff:lciency lmprovements via cata-lytic e~ects are also widely claimed. Most wldely - described are the transition metal salts of carboxylic ~ acids, in particular, naphthenates or sulfonates, chelates -3 5 of the transition metals, carbonyl, cyclopentadienyl or other coordination compounds of` the transition elements and even tetraethyl lead. While these are generally accepted to be effective to at least some degree, they are all ash-containing and thus leave deposits in the combustion ¦ 10 system. The balance of improved combustion against increased . maintenance caused by the deposits is generally unfavorable and has prevented widespread use of these additives.
Hence, progress in the chemical modifica~ion Or combustion has been modest at best and significant ~ 15 advances would still be of great valueO
¦ ~ Our recent work raises new interest in the ; possibility of using "viscoslty" to influence m~* particle size and/or size distribution.~- As pointed out`earlier, addition of polymers to ~uels would appear to be in the~
wrong directlon to favorably influence combustion. How-j ~ ever, this Iooks on use of polymers merely as a means to ln-: , crease viscosity, and fails to recognize that polymers impart ¦
.~ non-Newtonian characteristics-to fluids which sometimes result in strange and unexpected properties. At least ~j 25 three such applications have received attentlon in recent years.
A variety of polymers have been described which decrease th~e amount of stray mist generated in mist lubri-cation sysbems. Included are~ poly(meth)acrylates, ~ - 4 ~ ~ :
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polyisobutylene and polystyrenes and olefin copolymers, in particular the ethylene-propylene type. In fact the nature of this limited art suggests that the general phenomenon involved may well be a common characteristic of oil-soluble polymers, recognizing of course that details of polymer structure are important to optimiza-tion. While the mechanism of action has not been defined, it is apparently not viscosity phenomenon but rather in-; volves viscoelastic properties of the fluids. Further, it ¦ 10 is believed that ~hese polymers function because they influence aerosol particle siæe and size distribution About this same time it was discovered thatpolymers can exert very dramatic effects on fuel particu-late dissemination when that fluid is subjected to a severe shock. Such a phenomenon is of interest in trying to control the generation of the combustible mist cloud which is generated upon impact during an airplane crash.
Polymers claimed to have activity in this area include polyisobutylene, ethylene-propylene copolymers~ polymers and copolymers of alkylstyrene, olefin-sulfur dioxide ¦ polymers, poly (~-olefins) of C6_20 and hydrogenated s~yrene-isoprene copolymers and polar polymers in general which are capable of forming associative intermolecular bonds. Again, activity appears to be common to all high ~ 25 molecular weight polymers. Also7 the phenomenon involves -` more than just viscosity and is apparently tied to the viscoelastic properties of the fuels.

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~i More recently a third related area has been disclosed. High molecular ~eight polybutenes have ~een claimed to reduce stray mist generated in industrial metal cutting operations. In this case several other types of polymers are claimed not to work. ~owever, these others are lower molecular weight than the effective polybutenes and thus would not necessarily be expected to impart the same high degree of viscoelasticitJ as the claimed polymers.
Any of these three phenomena and particularly the three taken as a whole indicate that a polymer dissolved in a fluid can effect its misting characteris-tics. Polymers can exert an influence on mist particle size and possibly even size distribution. It is recognized that in spray combustion both aerosol size and size distri-bution influence flame speed. Use of polymers to control fuel mist particle size thus opens new possibilities in improving combustion efficiency. It is the purpose of this invention to demonstrate that fuels containing high molecular weight polymers do indeed permit higher heat recovery than is possible with conventional fuels. While ~'~ it is believed that ~his results from the viscoelastic pro-perties of such fuels, it is not intended that this :.
invention be restricted to any such mechanism.
To summarizejthis invPntion relates to I~quid fuels containing high molecular weight polymers and the process of burning said fuels~by means of spray combustion.
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These polymer-modified fuels provide improved combustion efficiency and heat recovery over that obtainable with ' - : - . . ..

conventional, unmodified fuels. A variety of polymers described herein can effect comb-us-tion efficiency and heat recovery improvements.
While the use of polymers in fuels is not new, per se, their use to effect combustion efficiency lmprovements is novel. Further, the inclusion of the preferred polymers of this invention at the optimum concentration to effect combustion efficiency improvements are not described in connection with fuels or the burning of said fuels.
Illustrative of the present invention a polymer, preferably a hydrocarbon polymer, in particular, polyiso-butylene or an ethylene-propylene copolymer, of weight average molecular weight of lO,000 to 10,000,000, preferably 50,000 to 1,000,000, is dissolved in a hydrocarbon fuel, most commonly a No. 2 distillate or No. 6 residual fuel, at 10 to 5000 ppm, preferably 100 to 1000 ppm. Said fuel is burned in a conven-tional spray combustion apparatus and heat recovery improvements over that of the polymer-free base fuel of l to 6~, or more commonly 3 to 5~, are observed.
~; 20 mhe present invention resides in a method of improv-ing the combustion efficiency of a liquid hydrocarbon fuel and heat recovery therefrom, which comprises spraying a 1i~1 hydro-carbon fuel in a heating unit to provide atomization thereof, and burning said fuel in-said atomized state, said liquid hydrocarbon fuel containing from about lO ppm to about 5000 ppm of a polymer soluble therein and capable of providing smoke reduction equivalent to at least about 1.5 Smoke Spot Number :
units as measured by ASTM Standard Test Method D2156-65, said polymer being selected from the group consisting of polyiso-butylene, poly(l-butene), poly (~-olefins), ethylene-propylene copolymers or ethylene-propylene-diene terpolymers, styrene-butadiene or s-tyrene-isoprene copolymers~ polybutadiene, poly~
isoprene, alkylated polystyrenes or copolymers thereof, atactic polypropylene, low density polyethylene, poly (meth)-acrylates and copolymers thereof~ and fumarate polymers or copolymers, said polymer having a weight average molecular weight in the range o~ from about: 10,000 to about 10,000,000.
Virtually any hydrocarbon soluble polymer will provide the combustion efficiency improvements of the present invention, provided their solubility characteristics are satisfactory, their molecular weight is su~ficiently high and the proper concentration is employed. Suitable polymers include polyisobutylene, poly(l-butene), poly (~-olefins), ethylene-propylene copolymers or ethylene-propylene-diene terpolymers, styrene-butadiene or styrene-isoprene copolymers or their hydrogenated analogs, poly-.

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- 7a -butadlene, polyisoprene, alkylated polystyrenes such as t-butylstyrene or copolyme:rs thereof, atactic polypro-pylene, low density polyethylene, poly(meth)acrylates and copolymers thereof, and fumarate polymers or copolymers.
Other hydrocarbon fuel soluble polymers which can be prepared in surficiently high molecular weight may be readily apparent to those skilled in the art.
`~ High molecular weight polyisobutylene, low density polyethylene, atactic polypropylene and other poly (~-olefins~ are readily available in sufficiently high molecular weight from acid or Ziegler catalysis. Prepara-tion of such polymers is well known to those skilled in the art. Polymers with weight average molecular weights of 203000 to 10,000~000 are easily obtainable.
Ethylene-propylene copolymers are also readily available and may cover a wide range of ethylene-propylene ratios. Most generally useful are copolymers which are high in ethylene content, specifically about 50 to 80 mole ~j 20 percent. However, copolymers outside of this range may also be useful. For example, lower ethylene contents may provide economic advan~ages without serious deterioration of properties while higher ethylene contents, up to ;~ about 95~mole percent, may be use~ul provided details of ~olymer microstructure are care~ully controlled so as to maintain fuel solubility. Weight average molecular .: : . :
weights may vary from 10,000 to 10,000,000.
The ethylene-propylene polymers may also contain ~ , .
~,~ low leve]s, generally less than about 10~, of a noh-:, conjugated diene such as 1,4-hexadiene, dicyclopentadiene, ,, ~ :

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or ethylidenenorbornene. Comments about the et~ylene and propylene contents are as above.
The styrene-butadiene and styrene-isoprene copolymers may be either random or block copolymers. In the case of the random copolymers, the products may contain from about 30 to about 50 weight percent diene. Weight average molecular weight should be high and may range ~rom about 30,000 to about 10,000,000. If ~he copolymers are blocks, they may contain two or more blocks. In ~ 10 general the styrene blocks may range ~'rom about 5000 to g about 50,000 in molecular weight while the diene may range ~ rom about 10,000 to about 1,000,000. Any of the - styrene-diene copolymers may be partially or completely hydrogenated.
Polymers o~ conJugated dienes, such as buta~
¦ diene or isoprene, covering a wide range of structures are also generally useful. Polymers may be either of the 1,4 or 1,2 type and ~he 1,4 may be in either the cis-or trans-conflguration. However~ polymers high in cis-1,4 are preferred. These polymers may also be partially or ; completely hydrogenated.
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fumarates covering a range o~ structures are also e~ective.
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Any combination of ester groups in the Cl-2~ range may be included and these alkyl~groups may be either linear or branched. The average carbon~ohain length where a mixture is used must be at leaat 6 carbon atoms and is ¦ preferably about 8 to 10 carbon atoms. Weight average ~:
molecular wei6hts may~be about 50,000 to about 15,000,000.
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The quantity of polymer additive added to the liquid fuel ma~ vary over a wide rangeO Usually, however, the polymer additive will vary between abou~
10 ppm and about 5000 ppm, on a weight basis.
The fuels useful in this invention encompass virtually a~y liquid hydrocarbon fuel which can be employed in spray combustion. Included are gasoline, methanol, kerosene, diesel fuel, fuel oils of the No. 1, No. 2, No. 4, No. 5~ or No. 6 types, and turbine fuels.
It has become fre~uent practice to blend used lubricating oil into fuels and fuels of this type are included in the scope of this invention.
The fuels of this invention may also include any of the other additives commonly used. Examples include pour point depressants, anti-oxidants, rust inhibitors, stabilizers, metal deactivators, in~ector detergents~
induction system deposit contr~ addltives, carburetor detergents, corrosion inhibitors, sludge dispersants~
demulsifiers, and slag modifiers as well as other types of combustio__modi~iers._ In addition to molecular weight and solubility in liquid heating fuels, useful polymers can be selected on the basis of a decrease in Smoke Spot No. as determined by the Smoke Reduction Test described in ASTM Test Procedure D-2156-65 (1975 Annual Boo~ of ASTM Standards, Part 24, Petroleum Products and Lubricants (II), published by American Society fo~ Testing and Materials, Philadelphia, Pa.
The test procedure is summarized below. It has been found that a decrease in'~ac~axac~ Smoke Spot Mos. pro~iding a diffexence of at least about 1.5 units correlates with improved combustion efficiency and heat recovery, as demonstrated in some of the Examples hereina~ter (a Smoke Spot measurem~nt was not made in Example 3). The Smoke Spot Nos. are scaled from 0 to 10 (no smoke to complete opacity) and readings can often be made visually on smoke emissions, using khe Bacharach Smoke Spot N~ber indicator, in increments of about 0.5 unitsO The practical upper limit on difference in Smoke Spot Nos. is about 4 units since higher differences indicate a base smoke condition of drastically high density.
Description of Combustion ~ffici~,ncy Test Procedure Two tests were employed in this work~ The first and simpler is the Smoke Reduction Test while the second, more comprehensive test, is the Heat Recovery Test. In every case evaluated the ability of an additive to reduce smoke was invariably accompanied by an improvement in heat recovery and a reduction in excess oxygen. Hence the first test was generally,used for screening purposes while the latter was used to quantify results (to measure heat recovery).

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, A. Smoke Reduction Test The effect ofadditives in reducing smoke produced from burning Mo. 2 fuel oil in a conventional home heating unit was determined using a modification of the procedure described in ASTM D-2156-65 (1975 Annual Book of QSTM
Standards, Part 24, Petroleum Producks and Lubricants (II), Published by American Society for Testing and Materials, Philadelphia, Pa.). The furnace employed in this work was a New Yorker Unipac oil fired boi:Ler with flame ¦ 10 retention, Model S-165-AP. Boiler temperature was main-tained by circulating the water through a shell and tube heat exchanger.
Prior to making any smoke measurements, the boiler was broughtup to at least 140~. burning unmodified fuel. Draft over the fire was adjusted to 0.01 to 0.02 inches of water. A smoke sample was taken using a smoke tester of the type described in ASTM D-2156-65. Air was adjusted so as to give a Smoke Spot Number of 2-3. The burner was then turned off and switched to test fuel. The ~ :
20~ boiler was re-fired and the circulator started in order to dump excess heat. Smoke readings were taken at 10, : ~
20 and 30 mlnutes in order to assure that equilibrium con-ditions were reached. Base fuel was run periodically for rererence purposes~
~ B. Heat~ Recovery Test ~ -~ Eq~uipmen~t~rorthis test is~the same as that g~ described~ln the Smoke~Reduction~Tests. ~Prior to flring the ~ burner approximately~six gallons~ ~ test fuel was weighed.
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The burner and fuel timer were started sirnultaneously.
During this cold start the boiler water circulating pump was inoperative. Draft over the f:ire was maintained at 0.01 to 0.02 inches of water. Af'ter five minutes of' firing, a smoke reading was taken as above. The circu-lating pump was activated and allowed to run continuously - once the bulk boiler water temperature reached 200F.
During the two-hour test, data were taken - accordlng to the schedule in Table I. At the end ~
the test the fuel timer was stopped and the burner was . turned off. The remaining f'uel was weighed and the average fuel flow rate was calculated. The average heat recovery eff'iclency was then calculated using the data for the heat recovered in the heat exchanger cooling water and the gross ~iring rate of the boller. A base fuel referenc~ was run e:ther before o~ after every test fuel.

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In the Examples, the disclosure and the claims all parts and percentages are by weight unless other~lise ; stated.
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Trlplicate tests were run in the Heat Recovery Test using No. 2 :~uel oil treated with 1000 ppm Or an - e'thylene-propylene copolymer of composition 62/38 by weight and a weight average molecular weight of about 80,000. Results shown below show an average heat recovery relative to base fuel o~ about 1.6~.

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Example 2 An ethylene-propylene terpolymer with a weight ratio of ethylene/propylene of about 55/45 but also containing about 4 weight percent 1,4-hexadiene and weight average molecular weight of about 850Jooo was evaluated in No. 2 fuel oil at a concentration of 200 ppm. Heat recovery improvement was 3.3~. Smoke was reduced from 3.5 in the control to 1.5 for the polymer-treated fuel and excess oxygen decreased from 4.4~ to 4.0 ' , Example 3 .: 10 A polyisobutylene of weight average molecular weight . ~
o~ 1,750,000 was evaluated in duplicate heat recovery tests at 150 ppm. Heat recovery galns of 5.7 to 6.1~ were JI ob~ained.

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Example 4 ; The polymer in Example 1 was re-evaluated using : a flame diffuser end cone the opening of which was larger than standard by 3/16". The relative improvement over base fuel was 4 . 8~o. Reduction of excess air to match ~- the base case smoke level resulted in further improvement to a net heat recovery improvement of 6. l~o.
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Example 5 ¦ A polyisobutylene of weight average molecular weight of 5,500,000 used at 25 ppm gave relati;e heat recovery improvements of 2.5?~o using the standard diffuser cone and 4. l~o using the modified cone of Example 4.

` ~ Example 6 The ethylene-propylene copolymer of Example 1 was evaluated at 125 ppm in the Heat Recovery Test. Relative heat recovery gains over the base case of 2 . 5~o and 2 . 9~o were made in duplicate tests.

Exampl~e 7 A~n et~hylene propylene c~opolymer with an ethylene content of 59 weighb~percent and~a welght average molecular weight of 150,000 was evaluated in No. 2 fuel oil in the Smoke Reduc~tlon Test~at~300 ppm. Base fuel gave a~Smoke Spot No. of 2.5 while the polymer-modified fuel gave a t'ng o~<l ln the 5m ke Reducti~n Test. ;;

:~ . , . . -; EXAMPLE 8 A polymethacrylate with mixed alkyl groups - including C4~ 12~ 14~ 16~ 18 in such proportions to give an average of Cg, said polymer ha-ving a viscosity average J 5 molecular weight of 1,650,000, was evaluated at 2000 ppm _~! . in the Smoke Reduction Test. Base fuel gave a Smoke Spot No. of 3 while the polymer-treated fuel gave 1 to 1.5.

A polymethacrylate containing mixed alkyl groups of Cl, 12~ 13~ 15 in such proportions as to give an average of C10, said polymer having a weight average molecular weight of about 60,000, provided smoke reduction of 1.5 numbers under base fuel when used at about 4000 ppm.

~- 15 ~ A~polyisobutylene of' viscosity average molecular . 3 we~ght of 10,000 used at 1800 ppm gave a Smoke Spok No. of'. . ~ .
~ 1.5 as compared to a~basic fuel rating of 4.

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: : A polybutadiene.with a cis-1,4 structure was evaluated at:300 ppm in the Smoke Reduction Test.

- Base fuel gave~a Smoke Spot ~o. of 4 to 5 while the ~ .
~:j polymer-treated fuel gave a 1 to 2 Smoke Spot No.

A styrenefumarate copolymer used at 3300 ppm . 25 gave a Smoke Spot No. of l to 2 compared to a base fuel value of a 4 Smoke Spot No.

~: : EXAMPLE 13 : An:ethylene~propylene copolymer having a : weight ratio~of ethylene/propylene of about 10/90 and ,:

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viscosity average molecular weight of' about 225~000 ~las evaluated in the Smoke Reduction Test at a concentration - of 500 ppm. A Smoke Spot No. of 3 to 3.5 f'or the control was reduced to 0.5 to 1 when combusting the polymer modi~ied ruel.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of improving the combustion efficiency of a liquid hydrocarbon fuel and heat recovery therefrom, which comprises spraying a liquid hydrocarbon fuel in a heating unit to provide atomization thereof, and burning said fuel in said atomized state, said liquid hydrocarbon fuel containing from about 10 ppm to about 5000 ppm of a polymer soluble therein and capable of providing smoke reduction equivalent to at least about 1.5 Smoke Spot Number units as measured by ASTM Standard Test Method D2156-65, said polymer being selected from the group consisting of polyisobutylene, poly(l-butene), poly (? -olefins), ethylene propylene copolymers or ethylene-propylene-diene ter-polymers, styrene-butadiene or styrene-isoprene copolymers, polybutadiene, polyisoprene, alkylated polystyrenes or copolymers thereof, atactic polypropylene, low density polyethylene, poly (meth)acrylates and copolymers thereof, and fumarate polymers or copolymers, said polymer having a weight average molecular weight in the range of from about 10,000 to about 10,000,000.

2. The method of Claim 1 wherein the reduction in Smoke Spot Number is from about 1.5 to about 4 units.

3. The method of Claim 1 wherein said polymer is an ethylene-propylene copolymer.

4. The method of Claim 1 wherein said polymer is a polymethacrylate.

5. The method of Claim 1 wherein said polymer is polyisobutylene.

6. The method of Claim 1 wherein the fuel is No. 2 distillate or a No. 6 residual fuel.

7. The method of Claim 1 wherein the polymer has a weight average molecular weight of from about 50,000 to about 1,000,000 and is present in the fuel in an amount of about 100 to 1000 ppm., and the reduction in Smoke Spot Number is from about 1.5 to about 4 units.

8. The method of Claim 7 wherein the polymer is polyisobutylene.