Hydrocarbons - Autoignition Temperatures and Flash Points

The tables and figures below show the autoignition temperature (AIT) and flash point (FP) for different hydrocarbons. In the figures, the AIT and FP are shown as function of number of carbon atoms in the hydrocarbons, which are grouped as n-alkanes, 1-alkenes, 2-methylalkanes, 3-methylalkanes, 2,2,dimethylalkanes, 2-methylalkenes, cycloalkanes, alkylcyclohexanes, cycloalkenes, alkylbenzenes and alkylnaphthalenes.

• Autoignition temperature = kindling point
• is the temperature at which a material spontaneously ignites in a normal atmosphere without an external source of ignition.
• is the temperature required to supply the activation energy for combustion
• is usually applied to combustible fuel mixtures
• Flash point - the lowest temperature at which vapour of a volatile material can be ignited whit an ignition source present

• Values of autoignition temperature are generally higher than flash point, as given for pure hydrocarbons in the tables and figures below .
• With an increase in pressure the autoignition temperature decreases. This is particularly important from a safety point of view when hydrocarbons are compressed.
• Hydrocarbons with high vapor pressures (lighter compounds) have low flash points. Generally, flash point increases with an increase in boiling point.
• Flash point is an important parameter for safety considerations, especially during storage and transportation of volatile petroleum products (i.e., LPG, light naphtha, gasoline) in a high-temperature environment. The surrounding temperature around a storage tank should always be less than the flash point of the fuel to avoid possibility of ignition.
• Flash point should not be mistaken with fire point, which is defined as the minimum temperature at which the hydrocarbon will continue to burn for at least 5 s after being ignited by a flame.
• Temperature classification of equipment in hazardous areas are related to surrounding substances auto-ignition temperature.

See also Flash Point - Fuels

IUPAC name	Common name	Flash point		Autoignition temp
		°C	°F	°C	°F
Benzene	Benzol	-11	12	555	1031
But-1-ene	1-butene, 1-butylene, Ethylethylene	-80	-112	360	680
But-2-ene	Cis-2-butene	-72	-98	325	617
But-2-ene	Trans-2-butene	-73	-99	324	615
1,2-butadiene		<-50	<-58	340	644
1,3-butadiene	Biethylene, divinylbutadiene, pyrrolylene, vinylethylene	-85	-121	415	779
N-butane		-60	-76	365	689
Butylbenzene		58	136	410	770
Butylcyclohexane		41	106
Butylcyclopentane		32	90
1-butyne	Ethylacetylene	<-14	<6.8
2-butyne	Crotonylene	-25	-13
Cyclobutane		<10	<50
Cyclodecane		65	149
Cycloheptane		6	43
1,3-cyclohexadiene		-8	18
Cyclohexane	Hexamethylene, hexanaphthene	-18	0	260	500
Cyclohexene		-17	1	265	509
Cyclohexylbenzene		99	210
Cyclooctane		28	82	250	482
Cyclopentane		-51	-60	320	608
Cyclopentene		-29	-20	309	588
Cyclopropane	Trimethylene			495	923
o-cymene		53	127
N-decane		46	115	200	392
2-decanol		85	185
1-decene		44	111	230	446
2,3-dimethyl-2-butene	Tetramethylethylene	<-20	<-4	400	752
1,2-dimethylbenzen	orto-xylene	30	86	465	869
1,3-dimethylbenzen	meta-xylene	25	77	540	1004
1,4-dimethylbenzen	para-xylene	25	77	540	1004
2,2-dimethylbutane	Neohexane	-48	-54	435	815
2,3-dimethylbutane	Diisopropyl	-29	-20	415	779
2,2-dimethylhexane		-3	27
2,2-dimethylpentane		-21	-6	320	608
3,3-dimethylpentane		-15	5	320	608
2,3-dimethylpentane		-12	10	330	626
2,4-dimethylpentane		<-20	<-4	325	617
2,2-dimethylpropane	Neo-pentane, trimethylethane	-19	-2	450	842
Diphenyl methane		130	266
N-docosane		211	412
Docosanoic acid	Behenic acid	176.3	349
N-dodecane		80	176	200	392
Dodecanoic acid	Lauric acid	134.1	273
1-dodecanol	Lauryl alcohol	119	246
1-dodecene		76	169	225	437
N-eicosane		187	369
Ethane		-135	-211	515	959
Ethene	Ethylene			440	824
Ethylbenzene		15	59
Ethylcyclohexane		22	72
Ethylcyclopentane		-4	25
Ethyne	Acetylene			305	581
N-heptacosane		269	516
N-heptadecane		148	298
N-heptane		-7	19	220	428
2-heptanol		59	138
1-heptene	1-heptylene	-8	18	250	482
Cis-2-heptene		-6	21
Trans-2-heptene		-1	30
Cis-3-heptene		-7	19	260	500
Trans-3-heptene		-6	21
1-heptyne		-2	28	245	473
N-hexadecane		135	275
N-hexane	Hexane	<-20	<-4	230	446
3-hexanol		41.7	107
1-hexene		-26	-15	255	491
Cis-2-hexene		-25	-13	244	471
Trans-2-hexene		-25	-13	244	471
Hexylbenzene		80	176
1-hexyne		-20	-4	263	505
3-hexyne		-14	7
Isobutylbenzene		55	131
Isopropylbenzene	Cumene	31	88	420	788
Methane		-135	-211	595	1103
2-methyl-1,3-butadiene	Isoprene	-54	-65	220	428
2-methyl-1-butene		-37	-35
3-methyl-1-butene		-58	-72	365	689
1-Methyl-1-cyclohexene		-4	25
4-Methyl-1-cyclohexene		-1	30
2-methyl-1-heptene		14	57
2-methyl-1-hexene		-6	21
2-methyl-1-octene		31	88
2-methyl-1-pentene	1-methyl-1-propylethylene	-26	-15	300	572
2-methyl-1-propene	Isobutene, Isobutylene	-80	-112	465	869
2-methyl-2-butene	Trimethylethylene, beta-iso-amylene	-45	-49	290	554
Methylbenzene	Toluene, toluol	6	43	535	995
2-methylbutane	Iso-pentane	-51	-60	420	788
Methylcyclohexane	Heptanaphthene	-4	25	260	500
Methylcyclopentane		<-10	<14	315	599
2-methyldecane		50	122
2-methylheptane		6	43
3-methylheptane		6	43	410	770
4-methylheptane		6	43
2-methylhexane		-10	14	280	536
3-methylhexane		-11	12	280	536
1-methylnaphthalene		94	201	485	905
2-methylnaphthalene		98	208	488	910
2-methylnonane	iso-decane	46	115
2-methyloctane	isononane, dimethylheptane	26	79
2-methylpentane	iso-hexane, i-caproylhydride	<-7	<19.4	300	572
3-methylpentane	Diethylmethylmethane	<-20	<-4	300	572
2-methylpropane	iso-butane	-83	-117	460	860
2-methylundecane		42	108
Naphthalene		80	176	540	1004
N-nonadecane		168	334
N-nonane		31	88	205	401
2-nonanol		82.2	180
3-nonanol		79.5	175
4-nonanol		79.5	175
1-nonene		26	79
N-octadecane		165	329
N-octane		12	54	205	401
1-octanol	Capryl alcohol	81	178	259	497
1-octene	1-caprylene	10	50	240	464
N-pentadecane		114	237
N-pentane		-49	-56	260	500
1-pentene	n-amylene, propylethylene	-51	-60	280	536
Pentylbenzene	Phenylpentane, amylbenzene	66	151
1-pentyne	Propylacetylene	<-20	<-4
Phenanthrene		171	340	>450	>842
Propane		-104	-155	470	878
Propene	Propylene	-108	-162	485	905
Propylbenzene		39	102	450	842
Propylcyclohexane		35	95	248	478
Propylcyclopentane		16	61
Propyne				340	644
Pyrene	Benzo(def)phenanthrene	200	392
Styrene		32	90
N-tetradecane		100	212
N-tridecane		79	174
Tridecanoic acid	Tridecylic acid	139.6	283
1,2,3-trimethylbenzene		51	124
1,3,5-trimethylbenzene	Mesitylene, trimethylbenzol	44	111	550	1022
2,2,4-trimethylpentane	Iso-octane	-9	16	410	770
N-undecane		61	142	195	383
Undecanoic acid		128	262
3-undecanol		94	201
1-undecene		63	145
o-xylene		17	63
m-xylene		25	77
p-xylene		25	77

In oil industry, the following terms for the different hydrocarbons are used:

Paraffins: Alkenes -  lineare, saturated molecules, straight or branched chains

Olefins: Alkenes - lineare, unsaturated molecules, straight or branched chains  (these are normally not present in unprocessed crude oil)

Naphthenes: Cycloalkanes - saturated ring structures, or cycloalkenes - partly saturated ring structures, with or without substituents connected to the ring

Aromatics: Unsaturated 6-ring structures (3 doble bounds in one ring), with or without substituents

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