US2274629A - Nitro-type ignition promotor for diesel fuels - Google Patents

Description

C. ELLIS Feb. 24, 1942.

NITRO-TYPE IGNITION PROMOTOR FOR DIESEL FUELS 2 Sheets-Sheet l Filed April 4, 1939 C. ELLIS Feb. 24, 1942.

NITRO-TYPE IGNITION PROMOTOR FOR DIESEL FUELS 2 shets-sheet 2 Filed April 4, 1939 Mn mb-M FIG 4 B3 C@ @W Patented Feb. 24, 1942 NITRO-TYPE IGNITION PROMOTOR FOR DIESEL FUELS Carleton Ellis, Montclair, N.

J., assigner to Standard Oil Development Company, a corporation oi' Delaware mi Application April 4, 1939, swarm. 265,910

Claims.

This invention 'relates to fuels for Diesel engines and is concerned particularly with petroleum fuels adapted to ignite at relatively lower temperatures under compression.

The widespread use of engines of the Diesel type has been retarded to some extent by the high compression required to secure adequate ignition speed. 'I'his requirement, reflected in the inordinate strength of materials demanded in engine construction, has resulted in a very cumbersome engine design which has limited the eld of application of the Diesel engine.

Owing to the very low fire hazard involved in Diesel engine operation due to the fuel employed, great effort has been made to utilize this type of engine in the aviation field. To gain strength without greatly adding to the weight per h orse power over the present forms of gasoline-burning aviation engines, resort has been had to costly alloy steels and the like, thereby raising the cost of engine construction per horse power to many times that of the gasoline engine.

To assist in the reduction in Diesel engine weight proposals have been made to add to the fuel a dope of the nitric ester type which would accelerate ignition, For example, the addition of several per cent of ethyl nitrite or nitrate has been recommended, Effective dopes of this nitro type are costly and although initial expense of engine plant may be reduced the expense of operation is increased in considerable measure. Furthermore. such dopes generally possess a flash point considerably lower than that exhibited by normal Diesel fuels, and when added in appreciable proportions usually effect a substantial reduction in` the ash point of the Diesel fuel, thereby increasing the fire hazard associated with the handling and use of such fuels. Other dopes of the nitro type which have been suggested are, for example, nitrobenzene, nitrotoluene, or picric acid (trinitrophenol) In general, the nitrohydrocarbons including both nitroparans and nitroaromatics are ineffectual for increasing the cetane number of a Diesel fuel; the cetane number increase for these substancesbeing usually no greater than one point on the addition of 1% of the nitrohydrocarbon. All such dopes are obtained from extraneous sources, that is, from hydrocarbons not inherently present in this class of fuels obtained from petroleum.

The present invention involves the treatment of petroleum and related fuels cheaply to confer thereon the quality of lower ignition temperatures without the necessity of adding ignition temperature depressants, or dopes, made extraneously. It is applicable particularly to relatively non-volatile petroleum fuels of the Diesel type, that is, fuels which unlike ordinary gasoline do not spontaneously evaporate when exposed to the atmosphere and which present a very low fire hazard because of their much higher re and flash points. Furthermore, this lowering of ignition temperature is accompanied by an increase in the octane value of the fuelthat is, when employed in a Diesel engine the fuel exhibits a higher, or increased, antiknock value.

One procedure whereby I confer on the fuell the quality of lower ignition temperature is by treating such fuel with nitric acid. Nitration may be carried out at room temperature or at higher or lower temperatures. Other nitrating agents which I may employ are mixtures of concentrated sulphuric and nitric acids, sulphuric acid and sodium nitrate, or the oxides of nitrogen. The latter (i. e., oxides of nitrogen) may be preparedV by the action of sulphuric acid on sodium or potassium nitrite, by the action of nitric acid on copper, by the passage of air (i. e., a gas containing both oxygen and nitrogen) through an electric arc, by the catalytic oxidation of ammonia, or by any other convenient method. Preferably a small proportion of air, or other oxygen-containing gas, is mixed with the oxides of nitrogen before passing into the oil. With some types of Diesel fuel liquid oxides of nitrogen, instead of the gaseous oxides, may be employed as the nitrating agents.

Although concentrated nitric acid or mixtures of concentrated nitric and sulphuric acids or of concentrated sulphuric acid and sodium nitrate may be employed, preferably I dilute such nitrating agents with water until the concentration of the reactive agent, or agents, is that represented approximately by the sludge-minimum point, i. e.. the concentration of the nitrating agent at which substantially no sludge or only the minimum quantity is formed during the nitration step and simultaneously nitration of the oil proceeds to a degree suiiicient to yield a fuel of lower ignition temperature (as determined by the hot plate method). It is also desirable that the concentration of the nitrating agent be suchthat substantially no oxidation of the hydrocarbon constituent of the fuel to acidic bodies occurs.

Instead of using commercial sulphurie acid I may employ the acid recovered from the sludge produced in the sulphuric acid rening of petroleum, or other related hydrocarbon distillates. Recovery of acid from such sludge can be accomplished by diluting the latter, for example, with one or two volumes of water and removing the insoluble portion which separates ondilution. In some instances, e. g., when the proportion of water-insoluble material is small or when such material exerts no deleterious effect on the fuel being treated, dilution of the sludge with water prior to use can be omitted.

It is desirable in the nitrating operation that vigorous oxidation, or other objectionable reaction, resulting in the formation of sludge be avoidcd in so far as possible. As previously mentioned, the concentration of the nitratlng mixture preferably should be at the sludge-mini-v mum point. For this reason, the proportion of nitrating agent and the temperature of nltration will vary with different fuels, although generally the more dilute the acid employed the higher the temperature at which nitration is effected. The exact strength of the nitrating agent and the temperature required for any individual fuel will, therefore, vary with the degree of unsaturation and other chemical characteristics of the oil. With some oils intended for Diesel fuel it may be necessary to treat first with a small proportion of concentrated sulphuric acid, and afterwards subject the treated oil to the action of the nitrating mixture. In the preferred method, however, I omit this preliminary treatment with sulphurc-acid. Furthermore, since nitro compounds, as a rule, exhibit a specific gravity greater than the corresponding hydrocarbons and in the preferred' method of operation little or no sludge is formed, the increase in specific gravity of the treated fuel may be taken as a qualitative indication of the degree of nitration attained.

Mild nitration of Diesel fuel often results in very little change occurring in the specific gravity or flash and iire points of the oil, but with increasingl nitration both the fire and flash .points as well as the specific gravity of the fuel become higher. .At the 'same time the temperature at which ignitionof the fuel takes place is greatly decreased. yThis lowering of ignition temperature accompaniedvby adecrease in fire hazard (i. e., increase in -flash and fire points) brought about by'nitration of the fuel is a surprising and unusual combination of properties which -I regard as being particularly advantageous in the use of heavy non-volatile fuels of the Diesel type. Another` advantage of nitration is the marked improvement-in` odor of many fuels, more especially those fuels containing mercaptans and other compounds possessing disagreeable odors.

The accompanying drawings or graphs indicate an increase of specific gravity with increase in degree of nitration; also certain changes in flash and fire pointsA and ignition temperatures as nitration progresses and the effect of addition of extraneous nitro compounds on flash and re points. In the drawings, Fig. 1 serves to illustrate the increase inV flash and fire points of a Diesel fuel with increasing degree of nitration as indicated by the specific gravity of the product. Fig. 2 shows the decrease in flash and fire points of untreated Diesel fuel due to the addition of nitroethane; Bind-the decrease in these same properties of a n'itrated fuel on the addition ,ofv nitro.-

ethane or 2 methyl 2 nitropropane -"1,3 dinitrate. Fig'. 3 represents the increase infdegree of nitrationga's indicated by the specific gravity of the oil, when various concentrations of nitric acid are employed'inthe nitration of Diesel fuel. Fig. 4 indicates the' decrease inv ignition temperature of the fuel (as determined by the hotl plate method) with increase -in specific gravity due to nitration. Reference to these drawings will be made in various places throughout the specification.

In some instances, it may be advantageous to employ catalysts in the nitrating step. One example of such a catalyst is aluminum nitrate. In other'instancesit is found that a mixture of nitrating agents effects desirable reaction much more rapidly than a single agent. As an illusan aqueous solution of sulphuric acid and sodium nitrate'usually ywill furnish the same degree of nitration of some oils in considerably less time than an aqueous solution of nitric acid, the concentration of the latter being equal to that formed by the expected interaction of sulphuric acid and sodium nitrate in the first case.

One procedure for treating Diesel fuels consists in mixing the oil and nitric acid (or nitrating mixture the temperature being maintained, for example, by -heating or cooling coils. as the case may be, and agitating the mixture until the desired degree of nitration is attained. The mixture then is allowed to settle and the acid and oil layers separated. The oil is washed with water or other'washing and/or neutralizing,r mcdium to remove free acid and, if necessary, is filtered through an inert material, e. g., fine sand, to eliminate small dispersed particles of sludge. Modifications of this procedure are the addition y of the nitrating agent inl two or more portions to the oilor of theoil in two or-more portions to the nitrating agent. Other modifications can be secured by varying the temperature. Thus, a portion of theA nitrating agent can be added and the temperature of. treating kept at, say, 0f" C. After the more reactive constituents of the oil have become nitrated, more of the agent is added and the temperature increased to, say, C. 0r, partial nitration maybe effected by employing'dilute nitric acid;- e. ga. sp. gr. 1.05, followed by treatment with Vmoreconcentrated acid e. g..`

. tion of me' fuel'results only asinall increase vsuclfi deposits in thfuelf`jets11quicklyzresults in their becoming more or less-"closed, thus resultingin reduction of the fuel supply tothe engine.

tration, under the same conditions of treating,

In cases when the fuel is.used at not too great an interval after being' prepared', incoiporation of an oxidation inhibitor, of which a-naphthol is an example, may retard sludge-formation sufficiently to permit the fuelbeing employed without any ill effects on the'engine.- In still other cases it may be necessary to age the fuel, i. e., keep it stored, until Vde'positionis substantially complete. This aging may be done at atmospheric temperature, or at somewhat elevated temperatures, e. g., C. Either the nitrated fuel may beaged, the resulting sludge removed by filtration or other means, and the aged fuel blended with a non-nitrated fuel, or the blended fuel may be aged and any precipitated material separated from the main body of the oil.

rease in the. pour-j Some nitrated Diesel fuels may contain a small proportion of bodies which exert a corrosive action on some metal surfaces, as for example, the fuel tank, jets, or other parts of the Diesel engine. One procedure whereby such action may be inhibited is the addition of a small proportion of an anti-acid, e. g., high boiling tertiary alkylamines (tributylamine), triethanolamine, or gaseousammonia. 'Another method of reducing corrosion consists in subjecting the nitrated fuel to a mild reduction by hydrogen or other reducing agents. Furthermore, corrosion of metals by nitrated Diesel fuel can be minimized by avoiding exposure of the fuel to moisture or to sunlight.

It has been noted that some petroleum distillates, intended for use asA Diesel fuels, contain a small proportion of bodies presumably of the phenolic type. Phenolic compounds, as a rule,

Such treatment prior to nitration not only yields a nitrated Diesel fuel of greatly reduced corro sive action, but also decreases the proportion of sludge formed during the nitrating operation.

As stated in Serial No. 670,753, nitrated fuels maybe used alone, or, if desired, may be blended with non-nitrated fuels such as normal Diesel oils or hydrogenated oils including those which have been made by hydroforming (hydrogenolysis) and milder treatments of the hydroning type. For example, blends in somecases may be constituted of equal volumes of a nitrated and a non-nitrated oil. In other cases'one-fourth part or less of the nitrated or non-nitrated oil may be present, and the remaining three-fourths part or more being composed of the other constituent, or other proportions used.

I may also lower the temperature of ignition of normal Diesel fuel by incorporating substantially at the time of use a desired proportion of nitrated fuel or of substances capable of causing such lowering. One way of accomplishing this regulation and adjustment is the use of two fuel tanks, one of which holds the nitrated fuel (activating liquid) or other ignition temperature depressant and the other holds the Diesel oil normally required. Streams of liquids from both tanks pass through a mixing chamber before introduction into the engine. By regulating the ow of the activating liquid a greater or lesser lowering of ignition temperature may be secured. Such an initiation of activated combustion in desired degree is of advantage, for example, in startinga cold engine at which time a greater proportion of the activating liquid can be used.

or higher than Diesel fuels. -Examples of such oils are the white oils obtained by the drastic treatment of gas oil, or higher-boiling distillates, with sulphuric acid. In other cases I may employ, as the material to be nitrated, such semisolid or solid petroleum fractions as petrolatum, vaseline, sweater-oil or paraffin wax. These liquid. semi-solid, or solid petroleum fractions can be nitrated by any of the previously-mentioned procedures and the resulting product, consisting for the most part of nitrated and nonnitrated petroleum hydrocarbuns. added to the Diesel fuel in ignition-temperature-lowering proportions. j

Addition of nitrated semi-solid or solid petroleum fractions, because of the presence of nonnitrated hydrocarbons, may result insome instances in an undersirable 'increase in the pour point of the Diesel fuel. Thus Diesel fuel containing dissolved nitrated paraffin wax, for example when subjected to a lowering of temperature, e. g. when exposed to cold weather, may become sufficiently viscous and cease to flow readily or, if the temperature lowering is sufficiently great, may even become solid and nonowable. Such physical changes in the oil would result in a partial or complete plugging of the fuel lines from the feed tank to engine or to the fuel jets, therebyresulting in faulty performance or stalling of the engine. l To overcome this difculty I may, e. g., extract the nitrated semi-solid or solid petroleum fractions with a selective solvent, thereby effectingfa separation of nitrated and non-nitrated petroleum hydrocarbons.

Examples of selective solvents which I employ for this purpose are acetone, methyl and ethyl alcohols, and ethylene dichloride. Extraction may be carried out at atmospheric temperature or at lower temperatures, the latter being particularly advantageous as the solubility of the non-nitrated petroleum hydrocarbons is greatly reduced thereby. After extraction is complete, undissolved non-nitrated petroleum hydrocarbons are separated fromthe solution of nitrated petroleum hydrocarbons. The solution may then be subjected to evaporation, distillation, or any other convenient operation whereby the solvent is removed from the nitrated hydrocarbons. In this manner I obtain a concentrate of nitrated petroleum hydrocarbon ignition temperature depressants which may be added to Diesel fuels in proportions sufficient to secure the desired ignition temperature lowering. The non-nitrated portion can again be subjected to m'tration and solvent vextraction whereby an additional concentrate of nitrated petroleum hydrocarbons is obtained.

In some instances it may be desirable to extract nitrated Diesel fuel with a selective solvent thereby obtaining a concentrate of ignitiontemperature depressants. An example of a selective solvent which I have found suitable for this purpose is aniline as it is soluble only to a limited degree in the fuel at atmospheric, or a lower, temperature. After extraction of the nitrated oil, the aniline solution of ignition temperature depressants is treated, e. g. with an aqueous solution of a mineral acid whereby the aniline is dissolved leaving an insoluble concentrate of ignition temperature depressants. The extracted fuel may be washed with dilute acid, to remove any dissolved aniline, and again nitrated and extracted to yield an additional concentrate of ignition temperature depressants.

Extraneous nitrated ignition temperature de- -able for Diesel engine operation.

` faction of the mixture followed by fractional distillation, or by any other convenient method. Polymerization of isobutylene to the dimeric, trimeric, or higher polymers is accomplished with the aid of catalysts such as boron trifiuoride. dilute sulphuric acid (e. g. 65-70 per cent acid) or aluminum chloride. Unchanged isobutylene and diisobutylene can be separated from the polymerization product by distillation leaving a residue of triisobutylene and higher polymers. Treatment of these residual polymers with nitric acid. sodium nitrate and sulphuric acid sludge,

oxides 'of nitrogen, or other nitrating agents furnishes nitrated hydrocarbons which may be added to nitrated or non-nitrated Diesel fuels as ignition temperature depressants. Alternatively, the isobutylene polymers can, be blended with untreated Diesel fuel and the blended fuel subjected to the action of nitrating agents.

Although I prefer to exclude addition of costly dopes, such as ethyl nitrate or ni'tropropane. I do not wish to imply that additionvof nitrated compounds, obtained by the treatment of extraneous hydrocarbons, may not `be made. Preferably I'employ those nitratedcompounds, the addition of which do not increase the lire hazard of the fuel by unduly lowering its flash point. An example of such a compound is 2-methyl-2- nitropropane-1,3-dinitrate. 'Ihis compound is obtained by nitrating 2methyl2nitro1,3-propanediol which in turn is made by the action of formaldehyde on nitroethane. The formation of the dinitrate may be represented in the following manner:

einen CnsCHrN-Or EUCH() CH3- N02 Y mon Caron como Cm- -No 2x1-Non Clh- -Nol V+ 211,0

y mon cmxm Analogous nitrodihydroxy alcohols, which in turn may be converted to the corresponding dinitrates, are obtained bythe substitution of acctaldehyde for formaldehyde. Although I may add such nitrated ignition temperature depressants, e. g., 2-methyl-2-nitropropane 1,3 dinitrate, made from extraneousV sources to normal Diesel fuels, preferably such ignition temperature depressants, or primers, are incorporated as auxiliary primers with nitrated Diesel fuels or with blended fuels one constituent of which is nitrated Diesel fuel. An example of the latter is a blended fuel, comprising one-fourth part by volume of nitrated Diesel fuel and three-fourths part by volume of suitable hydrogenated cil, to which is added 1 per cent by volume of 2-methyl- 2-nitropropane-1,3-dinitrate.

The ,low member of the dinitrates of nitrodihydroxy alcohols, namely 2-methyl-2-nitropropane-1,3-dinitrate, in pure form is a white solid which melts at about 39 C., consequently, 1

ycondensation of nitroparafilns with acetaldehyde or a mixture of acetaldehyde and formaldehyde. Reactions involved in forming these liquid dinitrates are represented in the following manner;

Clin-CHOU C l'l's-(ll--NOQ ClhOlI in the presence of a-base" (e. g, Na, K, carbonate or hydroxide).

y u frhcnrNo, matteo nono These Fresulting nitric,A esters of nitrodihydroxy alcohols are liquids under normal conditions, dissolve readily intov hydrocarbon oils, and remain in solution at concentrations greater than 1% by volume even at lower temperatures.

Carrying this invention still further, since the mixed-aliphatic aldehydes, including-those higher than formaldehyde, are much better than formaldehyde alone for preparing ignitiontemperature depressants effective in hydrocarbon Diesel fuel oils, the use of aldehydric mixture simply prepared by partial oxidation of hydrocarbons without necessitating expensive steps of isolating any particular aldehyde, such as formaldehyde, renders the process of preparing the ignition temperature depressants much more useful from an industrial viewpoint.

A convenient method of producing the reactants to be used in obtaining the desired liquid nitric esters of nitrodihydroxy alcohols is afforded by aprocess of simultaneously nitrating and partially oxidizing' hydrocarbons when the partial oxidation is controlled to avoid formation of acids. In nitrating'liquid"hydrocarbons, this operation is controlled after the fashion described in nitrating Diesel fuels vand the high boiling isolen polymers. A fuel Anitrated with limited oxidation is suitable for treatment with an alkaline catalytic agent for causing.`condensation of aldehydic products with nitropara'ilns formed in the nitration, with additional aliphatic; aldehydes, including formaldehyde, used in any amount found desirable for promoting the reaction. The resulting condensation productl may then be esterifled with a nitratingy agent.`

To produce a concentrated ignition temperature depressant for hydrocarbon fuels which are to be employed without nitration, I prefer to form the aldehydes and nitroparaiilns by vapor phase nitration and-partial oxidation of low boiling hydrocarbons. tcularly suitable forobtaining high yields of primary nitroparaillns and mixtures of formaldehyde with higher aliphatic aldehydes. It

This procedure is parrecoverable from separated gaseous products -for recycling, while nitroparaflins and aldehydes form a liquid layer, which can be decanted from a heavier` liquid layer of spent nitric cd. The withdrawn nitroparains mixed with al bhydes are then catalytically condensed to prdduce the nitroalcohols which are in turn nitrated.

For assuring the production of suflicient aldehydes, the nitration of the hydrocarbons may be regulated to favor the partial oxidation reaction by increasing the proportion of nitric acid to hydrocarbons, by using a more concentrated nitric acid, by increasing temperatures, lowering the reaction zone pressure, or by the assistance of catalysts which selectively promote oxidation to aldehydes. Generally more than 1 mole of nitric acid (about 50 to 80%. acid) is used with 2 moles of the hydrocarbons. The pressure employed may be of the order of 200 to 1000 pounds per square inch, and the temperature in the range of about 300 C. to 600 C. For increased efficiency, at least some of the aliphatic aldehydes may be prepared more readily apart from the nitroparaflins by an oxidation step applicable to gaseous ,hydrocarbons of the same type used in producing the nitroparafns. The substances which I particularly propose to treat for obtaining the aldehydes and nitroparaffins employed in making the desired mixture of nitroalcohols with the least.demand on the processing and procurement of expensive pure chemicals are, in general, petroleum or natural occurring products including gaseous hydrocarbon mixtures from various sources, e. g., cracking still hydrocarbon gases, other refinery gases, and natural gas. These hydrocarbons should have preferably saturated compositions, Whether straight chain, branched, or cyclic in structure. Higher yields of the desired products are favored by using paraffinc hydrocarbons higher than methane.

A partial oxidation step directed toward proi ducing high yields of formaldehyde and' acetaldehyde consists in controlling the concentration of the oxidizing agent which, for practical purposes, is preferably air, and by maintaining optimal temperatures and pressures. Selective mild oxidation catalysts, such as, copper oxide, lower nitrogen oxides, or glass surfaces, permit the use of lower temperatures subject to some variations for particular hydrocarbons treated, concentration of reactant and activity of the oxidizing agent and catalyst, appropriate conditions for high yields of the aldehydes are temperatures from about 200? C. to 600 C.; pressures of from 100 to 200 atmospheres; oxygen to carbon ratios of 5 to 15 mole per centi and a short time ofcontact preferably amounting to less than 1 minute.

In condensing the nitroparaflins with the aldehydes, it is important to use a limited amount of a base as a catalyst, less than 1% being sufficient. Large proportions of an alkaline agent will favor the formation of. salts rather than the desired nitrodihydroxy alcohols. After adding about 2 moles of the aldehydic mixture" composed, for example, mainly of formaldehyde and acetaldehyde in about equi-molecular proportion, to a mole of the nitroparaiiins composed, for example, mainly of nitroethane and analogous nitroparaffins, the reaction mixture is maintained .at about 40 C. to 60 C. for about 1 hour or longer; `then evaporated to dryness or neutralized and distilled under vacuum. The crude nitroalcohols recovered as a residue or distillate may be further purified or be directly nitrated simply by reaction at low temperatures with a nitrating mixture such as strong nitric acid. mixed with concentrated sulfuric acid. 'I'he resulting nitration product is a heavy yellow oil which may be washed and dried before being added to a hydrocarbon fuel having a suitable boiling range and viscosity for use in Diesel engines.

The following examples will illustrate my invention.

Example 1.-One hundred parts of Diesel fuel are agitated with 1 volume of concentrated sulphuric acid. The mixture is allowed to settle and the acid layer withdrawn. One hundred voltating for minutes with 2.5 volumes of a nitrating mixture consisting of equal volumes of Run No.

Vol.

Sp. gr. of oi fuel acid product Hot-pla te Temp behavior Sludge Percent Did not ignite. Do. Ignites. Do. Do.

The above data. indicate that nitration of the fuel Approx. f minimum 6o Product Sp. gr. ignition temperature o Untreated fuel. 0. 927 550 un l 0. 932 550 0, 938 500 0. 942 500 0. 950 430 Referring to Fig. 4, in which is plotted ignition temperature against specific gravity, it is noted urnes of the acid-treated fuel are nitrated by agithat as the specic gravity increases, due to nitration of the fuel, the ignition temperature of the oil is substantially decreased.

Example 4.The results tabulatedbelow were Only the product, obtainedin run 8, which had a specific gravity of 0.880 ignited readily when dropped onto a hot plate.

Example 5.-The approximate ignition points and the flash and fire points of the products obtained in Example 4 are given below.

. FI h F I Ap xrox. v as irc mln mum I mm 5p' gr' point point ignition temperatura I". F. C'. Untreatod fuel 0.847 i 180 500 Fuel heated lor 8 hr t 70 C 0. 850 109 i90 500 R 5 0.803 208 221 500 0. 854 i90 212 50() 0. 855 170 102 500 0.880 212 234 400 The above data indicate that both the flash point and iire point increase with the degree of nitration. 'The increase in flash and fire points with increase in specific gravity of the fuel are represented graphically in Fig. 1.

Example 6.Diesel fuel from a Pennsylvania crude petroleum was treated with nitric acid at atmospheric Atemperature for 8 hours. In each instance 250 volumes of oil and 50 volumes of nitrating agent were employed. The specific gravity of the nitrating agent varied, in the different runs, .from 1.09 1to 1.42. The results ob-` tained are given in the following table.

` 1' Sp. gr. Sp'gr Color of oi Ilot i -p ale nu agita product sludge behavior Percent Untrcatcd colorless... 0.825 Dld not ignite fuel. 1 at 550 C.

. do 0.825 Do. Lightyellow 0.825 Do. ..-d0.----.. 0.826 D0. Yollo 0.827 1 Do. Oilangc ycl 0.835 l Ignltcs at 400 C.

^ ow. 0rnnge.. 0.830 4 lgnltes ni3l`-0 C.

The relation between the. specific gravity of the nitrated fuel and thespeciflc gravity of the acid gravity of the fuel increased from 0.847 to 0.864. Based on the increase in specific gravity the degree of nitration was about the same as that secured by treating the fuelfor 8 hours at 70 C. with nitric acid of specific gravity 1.09.

Example 8.--Acid sludge obtained 'in the eul= phuric acid refining of-water white was diluted with an lequal volume of water. The aqueous layerl sp. gr. 1.24. was employed in the following manner in the nitration ofColombian Diesel fuel. Sodium nitrate was added to the aqueous layer in the proportion of 2.594 moles per liter. Fifty volumes of the resulting solution were agitated with 250 volumes of Colombian Diesel fuel at C. for 8.hours. The oil product, after washing, drying and nltering'through sand, had a spe'- ciflc gravity 0.864 as compared with 0.847 for the untreated fuel.

Example 9.-Colombian Diesel fuel was heated to 70 C. and, while kept at this temperature. a stream of dry oxides of nitrogen, diluted with air, was passed through the liquid for 5 hours.

Very little sludge was formed and the specific gravity of the oil increased from 0.847 to 0.862. In this instance the oxides of nitrogen were obtained by the action of nitric acid (1 volume of concentrated acid and "1 -volume oi water) on copper.. -lv

v Example 10.-Nitration is effected by conducting a stream of oxides of-nitrogen, mixed with air, into Diesel fuel kept at latmospheric temperature. In this case, the oxides of nitrogen were generated for the purpose by the action of sulphuric acid on sodium nitrite.

Example 11.-As shown in Example 5, the flash and fire points of an untreated Diesel fuel are 161 F. and 180 F., respectively. When 5 per cent by volume of nitroethane (boiling at 238239 F.) is added to this fuel Athe flash and fire peints of theblended fuel were found to be 97 F. and 111 F. respectively.

Example 12.-Nitrated` Colombian Diesel fuels containing an auxiliary primer were prepared by adding 5 per cent by volume of nitroethane or of 2 methyl- 2 nitropropane1,3dinitrate (as made according to Example 20) to the fuel made according to run '1 in Example 4. The flash and fire points of these fuels were li'ound to be as follows:

Flash Fire Fu point point F. F. Ru117.. v 176 lil2 Run 7+5% nitroethane 133 140 Run 7+5% nitrodlnltrau` 172 180 l Flush Fire E m I point point l". I lf. li-nn. Dil-.sol 274 200 li-nn. Diesel-P592 ethyl nitrate 200 Example 14.-The pour points ofv some of the fuels described in Example 2 were found to be as follows:

. l Pour Product Sp. gr point C. Untreated lucl 0. 027 -10 Run 2 0. 938 -5 Run 3 0. 950 -3 Example 15.-The pour points of the fuels described in Example 4 are tabulated below:

Example 16.-One hundred parts of hard white paraiiin wax were treated at 100 C. for 25 hours with concentrated nitric acid and aluminum nitrate. Forty-three partsof acid were initially added, two equal portions (of 43 parts each) of acid were added during the course of nitration, one at the end of 7 hours and one at the end of 14.5 hours, and a third portion of 21.5 parts of acid was added at the end of 22.5 hours. One hundred and twenty-two parts of aluminum nitrate, Al(NO3)39H2O, were employed as the catalyst. The product, after removal of the acid layer and washing with water, was a yellow-colored, soft, low-melting solid. This product may be added to Diesel fuel, for example, in proportions of 2%, v3% or 5% by weight, to decrease the ignition temperature of the fuel.

Example 17.-A portion of the product from Example 16 was extracted at room temperature with acetone, using 41 parts of nitrated paraffin wax and 40 parts of acetone. In this instance extraction yielded 29 parts of light yellow-colored acetone-soluble material, and about 12 parts of almost white acetone-insoluble material. Addition of by weight of the acetone-soluble portion to Diesel fuel effected a substantial lowering of the ignition temperature of the fuel as 'I'he mixture was chilled to 0 C..-

Example 20.--Formaldehyde (2 moles) with a trace oi' dissolved potassium hydroxide was added to nitroethane (1 mole). The resulting clear solution was heated at 50 C. to 60 C. until the reaction between the formaldehyde and nitroethane was completed. The product was then neutralized and distilled .under a vacuum. The nitrodiol recovered (Z-methyl-2-nitro-1,3-propanediol) further purified by recrystallizatlon from ether was a white crystalline solid having a melting point of 150 C. This material nif trated at 0 C. to 5 C. with a nitrating mixture yellow colored viscous oil which ignited more' readily on a hot plate than the residue from the extraction step.

Example 19.--Two volumes of nitrated Diesel fuel (run 8, Example 4) were agitated with 1 volume of aniline. After allowing the mixture to separate, the oil and aniline layers were separated. The aniline layer was washed with dik'lute hydrochloric acid and then with water (to The extracted Diesel fuel was washed consisting of 1 part of '10% nitric acid to 2 parts of concentrated sulphuric acid by weight formed the corresponding nitric ester Ywhich is a solid having a melting Point of 39 C. This solid nitric ester was substantially insoluble in a hydrocarbon Diesel fuel, less than .5% by volume forming a saturated solution at normal temperatures. This solid, however, was much more soluble in a nitrated Diesel fuel orin a hydrocarbon Diesel fuel when added in a 4,mixture containing liquid nitric esters.

Example 21..--A liquid nitric ester product was prepared in accordance with the procedure in Example 20 bysubstituting formalin (containing the equivalent of a. mole of formaldehyde and methyl alcohol) and a mole of acetaldehyde for the 2 moles of formaldehyde. After the condensation reaction was completed, the product was evaporated to dryness leaving a heavy yellow oil which was washed with water to remove any free acid and dried. This oil although it ignited spontaneously when dropped on a hot plate, did not explode when struck or when fired in a rifle cap. When added in a ratio of 1 part by volume to 100 parts by volume of fuel, this liquid product increased the cetane number of the Diesel fuel by more than 8 points, i. e., improved a 40 'cetane number Diesel oil to 49.

Example 22.-The oily nitrated product as prepared in Example 2l may be employed as an auxiliary ignition temperature depressant when added toA nitrated Diesel fuel in the proportion of 1 part by volume to 16 parts by volume of the fuel.

Example 23.-A portion of the nitrated fuel, as prepared in Example 9, was stored in a closed container for 12 days. At the end of this period a small quantity of black deposit had formed. This was removed by filtration and the fuel stored for 5 hours at 80-85" C. and then 'l hours 'at C. ThisA aging of the fuel yielded only a very small proportion of dark colored scum. Removal of this filtration and further aging of the oil for 24 hours. at l-50 C. failed to produce any additional dark colored deposit.

Example 24.--Four volumes of polymerized isobutylene (consisting principally of the trimeric and higher polymers) were treated, at '70 C., for 8 hours with 1 volume of nitric acid (specic gravity 1.20). No sludge was formed during nitration. This treatment increased the specific gravity of the fuel from 0.761 to 0.864 and lowered its ignition temperature from 660 F. to 395 F. Addition of l per cent by volume of the nitrated product to Colombian and Pennsylvania Diesel fuels lowered their ignition temperatures by 8 F. and 12 F. respectively.

Example 25.--Pennsylvania Diesel fuel was agitated for 8 hours at room temperature with 20 per cent its volume of nitric acid (specific gravity 1.42). About 2 per cent of sludge was formed. After separation of the nitrated oil layer it was washed with water, and then treated with solid magnesium carbonate to remove acidic bodies. The nitrated product possessed a cetane number of 84 (determined by engine test) as compared with 62 cetane number for the untreated fuel.

Example 26.--To volumes of Colombian Diesel oil was added 1 volume of -nitric acid (specific gravity 1.09) and the mixture was Istirred for 11 hours at 70 C. A small amount of sludge (1%) was formed during nitration andthe specic gravity of the oil changed from 0.850 to 0.870. The nitrated product possessed a certain number (determined by engine tests) of 67 as compared to 44 for the untreated oil.

Example 27.--Twenty volumes of Colombian' Diesel oil (specific gravity 0.850) were treated y at 70 C. with 1 volume of nitrating-mixture consisting of acid-sludge and sodium nitrate (see Example 8) for 8 hours. The specific gravity of the product was 0.860. The nitrated oil possessed a cetane number of 54 as compared to 44 for the untreated fuel. y

Example 28.-Nitrogen determinations were made on the nitrated Colombian fuels prepared in Examples 26 and 27. The increases in specific gravity, percentage of nitrogen, and cetane numbers are tabulated below:

i Specific Octane l` n( i gravity number yNiiropl` n Pcrcrnl intrcuilri fllci 0. 850 44 0.008 Example 27.... 0. 860 54 0.006 Example 20. (i. 870. l (i7 0. 42

Increased Octane percent nu|nnitrogen hcr Cotone i w' 1 iN troni .n increase llivs'sl oli Perce nl It is to be noted thatthe nitroaromatic dope gives negative results, the nitrooctane only increases the cetane number by 7 points when the nitrogen content or the doped Vfuel is increased by nearly l/2% while the fuel nitrated in accordance with Example y26 is improved. to the extent of 23 points with the nitrogen content of the fue] being increased by less than 1/2%. These facts evidence that the nitration of the fuel accomplishes more than merely an addition of nitrohydrocarbons in situ on the basis of the marked cetane number increase in proportion to the nitrogen content increase. The nitration of the fuel may well be considered to incorporate into l the hydrocarbon compounds not merely the simple nitro (-'N0z) group but also more highly active-nitrogenoxygen groupings which depress ignition temperature of the fuel to the same degree as do nitric esters of nitrohydroxy alcohols which have been described.

Example 29.-One volume of the product from Example 26, possessing a cetane number of 67, was blended with 1 volume of untreated Colombian oil (cetane number of 44) to give a fuel havinga cetane number of 61. ilse 1 volume of the product from Example 26 was blended with 3 volumes of untreated Colombian oil to yield a fuel possessing a cetane number of 48.5.

Example 30.-Twenty volumes of Pennsylvania Diesel fuel and 1 lvolume of nitric acid (specific gravity 1.35) were stirred at atmospheric temperature for 12 hours. No sludge was formed and the final product was orange colored. In this instance the specific gravity of the untreated fuel was 0.825 and that of the nitrated fuel was 0.827. The flash and flre'points of the untreated oil were found to be 274 F. and 299 F., respectively. For the nitrated oil the fire and ash points were 277 F. and 299 respectively. The cetanev number of the fuel was increased from 63 to 80 by the treatment with nitric acid. The nitrogen content of the nitrated fuel was 0.32 per cent.

Example 31 .-Ten volumes of Pennsylvania Diesel fuel were agitated, at room temperature, for 12 hours with 1 volume of nitric acid (specific gravity 1.42). The nitrated fuel, orange in color and possessing a specific gravity of 0.842. was blended with varying amounts of untreated Pennsylvania Diesel fuel to give 'three blended fuels: (A) containing approximately 2 volumes of nitrated fuel and 1 volume of untreated fuel. (Bo) consisting of approximately 1 volume of nitrated 'fuel and 1 volume of untreated fuel, and (C) Imade by adding 1 volume of blend (B) to 1 volume of untreated fuel. Thecetane numbers of the various blends were found to be as follows: (A) 86;` (B) 82.5: (C) 72. The cetane number of the untreated Pennsylvania oil was 63.

Example 32.-Several mixed fuels were prepared by blending blend A from Example 31 with an untreated Colombian Diesel oil. The cetane numbers are given below:

.Blond A Example 33.-The increase in cetane number with increase in nitrogen content for the blended fuels described in Example 31 is given below:

according to run 7, Example 4, except that the A heating time was extended to 5 hours. The quantity of sludge obtained was about 0.25 per cent, as compared with 1 per cent for run 7, Ex, ample-4.

From the foregoing it will be seen that my invention contemplates the process of treating Ppetroleum oil, of the usual specific gravity and of recognized boiling range of fuels employed in Diesel engines, with nitrating agents including nitric acidpnitric-sulphuric acid mixtures, oxides of nitrogen, and the like. In the preferred method, treatment of the fuel is accompanied by a simultaneous lowering of temperature of ignition and increase of flash and fire points of the fuel. My invention involves the use of nitrating agents diluted withwater to the approximate sludge minimum-point, i. e., nitrating agents yielding the minimum quantity of sludge when employed in the treatment of Diesel fuels thereby producing fuels of lower ignition temperatures. It also involves the treatment of petroleum fractions heavier than Diesel fuels with such nitrating agents, separation of the nitro products formed thereby from the non-nitrated petroleum hydrocarbons, and adding these nitro products to Diesel fuels in proportions suiiicient to effect ignition temperature lowering.

In this specication the term ignition temperature is employed to denote the temperature of a hot plate, electrically heated, which will effect spontaneous ignition or inammation (not merely evaporation) of the Diesel fuel when the latter is dropped on it.

It will be noted that the methods of nitration herein described are applicable to Diesel fuels obtained from several sources. Such methods may be applied also to many other types of Diesel fuels including hydrogenated fuels and the like. The optimum conditions of nitration, e. g., the concentration of the nitrating agent or agents, the proportions used, temperatures employed, or duration of treatment, will depend upon the chemical and physical characteristics of the fuel at hand.

It is important to recognize that the fuel oi' the present invention should not be confused with gasoline fuels as customarily used in automobile engines of the regulation spark ignition four cycle type. The new fuel is largely or wholly heavier than gasoline andis not readily ignited like gasoline by approach of flame. Diesel fuels are relatively non-volatile hydrocarbon oils generally boiling within the range of about 300 F. to 700 F. and usually exhibiting a specic gravity of about 0.80 to 0.90 or higher. On the other hand, ordinary gasoline boils from about 90 F. to 400 F., with a specific gravity of approximately 0.70 to 0.74. Again, the flash point of Diesel fuel ordinarily should not be lower than 150 F. or thereabout. On the other hand the flash point of commercial gasoline is quite low,

r 9 being around 15 \F. and even lower. Furthermore it is not an object so to lower the ignition properties as to thrust upon'the new fuel the yilre hazard commonly associated with gasoline, but rather to lower in moderate degree the temperature of ignition under Diesel compression conditions and simultaneously increase the security from re hazard (by increasing the flash and re points) characteristic. of the Diesel engine and for which its use in airplane propulsion is advocated. r

My invention also provides a step in the operation of Diesel engines exposed to rapid variation in atmospheric pressure which consists in altering, in accordance with the pressure fluctuation, the proportion of catalyst (ignition temperature depressant) of, temperature ignition admitted to the combustion chamber. It shouldbe noted that for aviation purposes this proportion roughly speaking may be regarded as in inverse ratio, that is, the lower the atmospheric density the greater the proportion of catalyst or temperature ignition depressant admitted.

i Substances included in the term nitro compounds are not only those in which a nitro, or NO2, group is inflxed or implanted in the hydrocarbon molecule, and which are often produced by the action of nitric acid or a mixture of nitric and sulphuric acids on parafiinic or cyclic hydrocarbons, but also such nitrogen containing compounds as nitrosites and nitrosates. The former type (nitrosites) are the compounds formed by the interaction of nitrogen trioxide and olens, while the latter (nitrosates) are the results of the reaction between olens and nitrogen tetroxide. The olens may be either acyclic or cyclic. In some instances nitric acid reacts directly with certain types of unsaturated hydrocarbons forming addition products of the nitro type. This occurs particularly in the controlled nitration of the isoolefin polymers because these unsaturated polymers are sufdciently reactive to become combineddirectly and simultaneously with two or more of the various Oxy-nitrogen groups, nitroso, nitro, nitrite, and nitrate groups.

Mixed nitro type nitric esters obtainedin the low temperature nitration of the mixed nitrodihydroxy alcohols and of unsaturated hydrocarbons which form the nitro type addition products are particularly effective for the purpose of this invention. All such compounds, containing these various nitrogen-oxygen groupings, when present in the fuel may serve to depress its ignition temperature suiiiciently to allow its being employed in Diesel engines.

The present application is a continuation-inpart of my United States application Serial No. 62,759, filed February 7, 1936, now Patent No. 2,240,558, issued May 6, 1941.

I claim:

1. A Diesel fuel comprising a hydrocarbon Diesel fuel oil and a minor proportion of a liquid dinitrate ester of a nitrodihydroxy alcohol in which at least one of the carbon atoms joined to a nitrate group is a secondary carbon atom joined to an alkyl group, said dinitrate ester being present in an amount sufficient to improve the ignition qualities of the fuel.

2. A Diesel fuel comprising a hydrocarbon Diesel fuel oil and a minor proportion of a compound of the formula: l

CHs-CHNO:

CH:- -NOr HzNOs 10V y 3.'A Diesel fuel comprising a hydrocarbon Diesel fuel blended with a minor proportion of a liquid dinitrate-ester of nitrodihydroxy alcohol containing atleast 5 carbon atoms per molecule in which a secondary carbon atom joined to a nitrate group is also joined to an alkyl group,

' said ester being a dinitrate of a nitroparalnaldehyde addition product and being blended with the hydrocarbon Diesel fuel in an amount suilicient to substantially improve the ignition qualities of the fuel.

4. A Diesel fuel comprising a hydrocarbon Diesel fuel blended with a minor proportionof 'liquid dinitrate ester of nitrodihydroxy alcohol containing at least 5 carbon atoms per molecule in which'a secondary carbon atom joined to a nitrate group is also joined toan alkyl group. said ester being a dinitrate of an addition product of a nitroparamn with -both acetaldehyde and formaldehyde and being blended with said hydrocarbon fuel in an amount suiilcient to improve the ignition qualities of the fuel.

5. A Diesel fuel comprising a hydrocarbon Diesel fuel blended with a minor proportion of a liquid dinitrate ester of a nitrodihydroxy alcohol containing Vat least 5 carbon atoms per molecule inwhich a secondary carbon atom Joined to a nitrate group is also joined to an alkyl group, said ester being a dinitrate of a nitroparailfin-acetal-l dehyde'addition product and bein'g blended with the hydrocarbon Diesel fuel in an amount sumcient to substantially improve the ignition qualities of the fuel.

CARLETON ELLIS.

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