R600a freon (isobutane): characteristics (properties), tables, diagrams

The use of isobutane as R600a refrigerant began in the early 20th century. Later it was replaced by freon R12 (difluorodichloromethane). Following the adoption of the Montreal Protocol and its annexes, R600a returned to the refrigeration industry in the 1990s.

It was then introduced as a replacement for CFC (chlorofluorocarbon) and HCFC (hydrochlorofluorocarbon) refrigerants, which were harmful to the environment. This freon has gained popularity in the refrigeration industry due to its environmental friendliness.

The main advantage of R600a is its low environmental impact. It has a very low global warming potential (GWP) and does not deplete the ozone layer (ODP=0). Its global warming potential (GWP) is only three, which is significantly lower than other commonly used refrigerants such as R134a and R404a. It is also energy efficient at medium temperatures. This makes it more cost-effective in the long run.

The main disadvantage of R600a is flammability. Its use requires additional safety measures both during the development of equipment and during its operation. In addition, R600a has lower thermal conductivity than other refrigerants. Therefore, it may not be suitable for use in high temperature refrigeration systems.

Properties and characteristics of R600a freon

The table below shows the physicochemical properties and characteristics of R600a freon.

Parameter	Value
Chemical formula	C4H10
Molecular (molar) mass, g/mol	58,12
Density at 25 °C (77 °F), g/ml	2,064
Vapor density (air=1)	2,06
Melting point at 100 kPa	-159 °C / -255 °F
Boiling point at 100 kPa	-12°C / 10°F
Flash point	-83 °C / -117 °F
Critical temperature	135 °C
Critical pressure, MPa	3,66
Critical density, g/ml	0,221
Solubility in water at 25 °C (77 °F), mg/kg	48,9
Steam pressure at 21 °C (70 °F)	310 KPa / 45 psia
Latent heat of vaporization, kJ/kg	366,5
Minimum ignition temperature	460 °C / 860 °F
Lower flammability limit by volume	1,8%
Upper flammability limit by volume	8,5%
Lower flammability limit by weight, g/m3	28
Upper flammability limit by weight, g/m3	203
Global Warming Potential (GWP)	3
Ozone Depletion Potential	0
Hazard Class	2.1
ASHRAE Safety Class	A3

Pros and cons of the R600a

Like any freon, isobutane has its pros and cons. Let’s look at them.

Advantages of freon R600a

1. Does not destroy the Earth’s ozone layer. Has low global warming potential. It is only three times more than carbon dioxide and almost 500 times less than R134a.
2. Equipment using R600a operates at a pressure lower than other refrigerants. Therefore, it is cheaper, more durable and produces less noise.
3. Isobutane is one of the cheapest refrigerants.
4. To refill equipment you need much less R600a compared to similar refrigerants.
5. If isobutane leaks from the system, it can be topped up rather than replaced completely.

Cons of freon R600a

1. Due to the high flammability of the refrigerant, special safety precautions must be observed when storing the refrigerant.
2. R600a is not suitable for equipment with large refrigerant charges and air conditioning systems.
3. Isobutane production involves high risks of fire and explosion.

Compressor oil compatibility

• Mineral (M): Compatible with R600a refrigerant.
• Alkylbenzene (AB): Compatible with Freon R600a.
• Semi-synthetic (M+AB): Compatible with R600a.
• Polyester (POE): Limited compatibility. These oils have high solubility in hydrocarbons. It may be necessary to use higher viscosity POE.
• Polyalkylene glycol (PAG): Not compatible.
• Polyalphaolefins (PAO): Not compatible.

Pressure-temperature table for freon R600a

Below is a table of the relationship between temperature and pressure at the boiling point. The following abbreviations are used:

• t,°C – temperature in degrees Celsius.
• t,°F – temperature in degrees Fahrenheit.
• P, barA – absolute pressure in bar.
• P, barG – excess pressure in bar.
• P, psia – absolute pressure in pounds per square inch.
• P, psig – excess pressure in pounds per square inch.

Pressure and temperature table for R600a refrigerant (isobutane)

t,°C	t,°F	P, barA	P, barG	P, psia	P, psig
-70	-94	0,05	-0,97	0,70	-14,00
-68	-90	0,05	-0,96	0,81	-13,89
-66	-87	0,06	-0,95	0,92	-13,78
-64	-83	0,07	-0,94	1,05	-13,65
-62	-80	0,08	-0,93	1,20	-13,50
-60	-76	0,09	-0,92	1,36	-13,34
-58	-72	0,10	-0,91	1,53	-13,17
-56	-69	0,12	-0,89	1,73	-12,97
-54	-65	0,13	-0,88	1,95	-12,75
-52	-62	0,15	-0,86	2,18	-12,52
-50	-58	0,17	-0,85	2,45	-12,25
-48	-54	0,19	-0,83	2,73	-11,97
-46	-51	0,21	-0,80	3,05	-11,65
-44	-47	0,23	-0,78	3,39	-11,31
-42	-44	0,26	-0,75	3,77	-10,93
-40	-40	0,29	-0,73	4,17	-10,53
-38	-36	0,32	-0,70	4,61	-10,09
-36	-33	0,35	-0,66	5,09	-9,61
-34	-29	0,39	-0,63	5,61	-9,09
-32	-26	0,42	-0,59	6,17	-8,53
-30	-22	0,47	-0,55	6,77	-7,93
-28	-18	0,51	-0,50	7,42	-7,28
-26	-15	0,56	-0,45	8,12	-6,58
-24	-11	0,61	-0,40	8,86	-5,84
-22	-8	0,67	-0,35	9,66	-5,04
-20	-4	0,72	-0,29	10,52	-4,18
-18	0	0,79	-0,23	11,44	-3,26
-16	3	0,86	-0,16	12,41	-2,29
-14	7	0,93	-0,09	13,45	-1,25
-12	10	1,00	-0,01	14,56	-0,14
-10	14	1,08	0,07	15,74	1,04
-8	18	1,17	0,16	16,99	2,29
-6	21	1,26	0,25	18,31	3,61
-4	25	1,36	0,35	19,72	5,02
-2	28	1,46	0,45	21,20	6,50
0	32	1,57	0,56	22,77	8,07
2	36	1,68	0,67	24,43	9,73
4	39	1,80	0,79	26,18	11,48
6	43	1,93	0,92	28,02	13,32
8	46	2,07	1,05	29,96	15,26
10	50	2,21	1,19	32,00	17,30
12	54	2,35	1,34	34,15	19,45
14	57	2,51	1,50	36,40	21,70
16	61	2,67	1,66	38,76	24,06
18	64	2,84	1,83	41,24	26,54
20	68	3,02	2,01	43,83	29,13
22	72	3,21	2,20	46,55	31,85
24	75	3,41	2,39	49,39	34,69
26	79	3,61	2,60	52,36	37,66
28	82	3,82	2,81	55,46	40,76
30	86	4,05	3,03	58,70	44,00
32	90	4,28	3,27	62,07	47,37
34	93	4,52	3,51	65,59	50,89
36	97	4,78	3,76	69,25	54,55
38	100	5,04	4,03	73,07	58,37
40	104	5,31	4,30	77,04	62,34
42	108	5,60	4,58	81,16	66,46
44	111	5,89	4,88	85,45	70,75
46	115	6,20	5,19	89,90	75,20
48	118	6,52	5,51	94,53	79,83
50	122	6,85	5,84	99,32	84,62
52	126	7,19	6,18	104,29	89,59
54	129	7,55	6,53	109,45	94,75
56	133	7,92	6,90	114,79	100,09
58	136	8,30	7,28	120,32	105,62
60	140	8,69	7,68	126,04	111,34
62	144	9,10	8,09	131,96	117,26
64	147	9,52	8,51	138,08	123,38
66	151	9,96	8,95	144,41	129,71
68	154	10,41	9,40	150,96	136,26
70	158	10,88	9,86	157,70	143,00

Isobutane and the Montreal Protocol

Since freon R600a has a very low global warming potential and an ozone depletion potential of 0, it is not subject to the Montreal Protocol, Kyoto Protocol, etc. Rules for using R600a vary by country.

In Europe and Asia, R600a freon is a widely used refrigerant for low-power refrigeration equipment. However, it is important to note that isobutane is highly flammable, so safety regulations exist to ensure proper handling and storage.

In the United States, R600a is not as widely used due to safety concerns. The Environmental Protection Agency (EPA) classifies it as a restricted substance. It is mainly used for the production of mixed refrigerants.

Mixed refrigerant applications

R600a is commonly used in small refrigeration systems such as domestic refrigerators, freezers, beverage coolers, freestanding display cases and vending machines. The characteristics of R600a do not allow it to be used in air conditioning systems. However, it can be used in small portable air conditioners and dehumidifiers.

In recent years, isobutane has begun to be used as part of mixed refrigerants. It is added to improve the performance of new gases. Below is a list of EPA-approved freons that include R600a.

• GHG (R406A) — 4%.
• GHG-X4 (R414A) — 4%.
• Hot Shot (R414B) — 1.5%.
• ISCEON 79 (R422A) — 3.4%.
• ICOR XAC1 (R422B) — 3%.
• ICOR XLT1 (R422C) — 3%.
• ISCEON MO29 (R422D) — 3.4%.
• RS-44, new composition (R424A) – 0.9%.
• RS-24, new composition (R426A) – 0.6%.
• RS-52 (R428A) — 1.9%.
• RS-45 (R434A) — 2.8%.
• HCR-188C (R441A) — 6%.
• GHG-HP — 4%.
• GHG-X5 — 4%.
• ICOR AT22 — 1.5%.

Thermodynamic log(p)-h diagrams for freon R600a

Safety precautions when working with R600a

Food conditions

Store away from sources of ignition in a well-ventilated place at temperatures not exceeding 45°C / 115°F. Avoid incompatible materials and conditions. Do not allow containers with isobutane to be located near open fire sources, heated surfaces, or electrical appliances.

Precautions for handling R600a

When working with R600a, proper precautions must be taken to ensure safety. It is important to wear protective equipment, including gloves and safety glasses, and work in a well-ventilated area. It is also extremely important to avoid open flames and ignition sources as R600a is highly flammable.

Emergency procedures for R600a

In the event of a leak or other emergency involving R600a, it is imperative that you leave the area immediately and contact emergency services. Avoid using electrical equipment or creating sparks in the affected area. Those who have trouble breathing should seek medical attention if necessary.

Comparison of R600a, R290, R134a, R404A, R22 and R12

Refrigerant	R600a	R290	R134a	R404A	R22	R12
Chemical formula	CH-(CH3)3	C3H8	CF3-CH2F	44/52/4	CHF2Cl	CF2Cl2
Critical temperature in °C	135	96.7	101	72.5	96.1	112
Molecular weight in kg/kmol	58.1	44.1	102	97.6	86.5	120.9
Normal boiling point in °C	-11.6	-42.1	-26.5	-45.8	-40.8	-29.8
Pressure (absolute) at -25 °C in bar	0.58	2.03	1.07	2.50	2.01	1.24
Liquid density at -25 °C in kg/l	0.60	0.56	1.37	1.24	1.36	1.47
Steam density at temperatures up to -25/+32 °C in kg/m3	1.3	3.6	4.4	10.0	7.0	6.0
Volumetric capacity at -25/45/32 °C in kJ/m3	373	1164	725	1334	1244	727
Enthalpy of vaporization at -25 °C in kJ/kg	376	406	216	186	223	163
Pressure (absolute) at +20 °C in bar	3.0	8.4	5.7	11.0	9.1	5.7

Thermodynamic properties of R600a (isobutane), table

Below is a table of the thermodynamic properties of freon R600a on the saturation line. For convenience, the following abbreviations are used:

• P – pressure, bar.
• t,°C – temperature in degrees Celsius.
• t,°F – temperature in degrees Fahrenheit.
• Vl – specific volume of liquid, dm3/kg or l/kg.
• Pl – liquid density, kg/dm3 or kg/l.
• Hl – liquid enthalpy kJ/kg.
• Sl – entropy of liquid kJ/kg*K.
• Vv – specific volume of steam, m3/kg.
• Pv – vapor density, kg/m3.
• Hv – steam enthalpy kJ/kg.
• Sv – steam entropy kJ/kg*K.
• Lv – latent heat.

Table of thermodynamic properties of freon R600a on the saturation line

P	t,°C	t,°F	Vl	Pl	Hl	Sl	t,°C	t,°F	Vv	Pv	Hv	Sv	Lv
0,004	-100	-148	1,462	0,684	-6,395	0,067	-100	-148	65,234	0,015	428,19	2,577	434,585
0,006	-95	-139	1,473	0,679	3,036	0,121	-95	-139	41,078	0,024	433,861	2,539	430,825
0,01	-90	-130	1,483	0,674	12,549	0,173	-90	-130	26,648	0,038	439,62	2,505	427,072
0,015	-85	-121	1,494	0,669	22,144	0,225	-85	-121	17,764	0,056	445,465	2,475	423,321
0,023	-80	-112	1,505	0,664	31,823	0,276	-80	-112	12,14	0,082	451,392	2,448	419,569
0,033	-75	-103	1,516	0,66	41,587	0,326	-75	-103	8,487	0,118	457,397	2,424	415,81
0,048	-70	-94	1,528	0,655	51,439	0,375	-70	-94	6,059	0,165	463,479	2,403	412,04
0,067	-65	-85	1,539	0,65	61,38	0,423	-65	-85	4,41	0,227	469,633	2,385	408,253
0,093	-60	-76	1,551	0,645	71,413	0,471	-60	-76	3,266	0,306	475,855	2,368	404,442
0,126	-55	-67	1,564	0,64	81,54	0,518	-55	-67	2,459	0,407	482,142	2,354	400,602
0,168	-50	-58	1,576	0,634	91,764	0,564	-50	-58	1,879	0,532	488,489	2,342	396,726
0,221	-45	-49	1,589	0,629	102,086	0,61	-45	-49	1,456	0,687	494,893	2,331	392,807
0,287	-40	-40	1,602	0,624	112,512	0,655	-40	-40	1,143	0,875	501,349	2,323	388,837
0,368	-35	-31	1,616	0,619	123,042	0,7	-35	-31	0,907	1,102	507,853	2,315	384,811
0,466	-30	-22	1,63	0,614	133,682	0,744	-30	-22	0,728	1,373	514,4	2,309	380,719
0,584	-25	-13	1,644	0,608	144,433	0,787	-25	-13	0,591	1,693	520,987	2,305	376,554
0,725	-20	-4	1,659	0,603	155,3	0,831	-20	-4	0,483	2,069	527,607	2,301	372,307
0,891	-15	5	1,674	0,597	166,286	0,874	-15	5	0,399	2,506	534,257	2,299	367,972
1,013	-11,76	10,832	1,684	0,594	173,481	0,901	-11,76	10,832	0,354	2,826	538,587	2,298	365,106
1,085	-10	14	1,69	0,592	177,395	0,916	-10	14	0,332	3,012	540,933	2,297	363,537
1,31	-5	23	1,706	0,586	188,632	0,958	-5	23	0,278	3,593	547,628	2,297	358,996
1,57	0	32	1,722	0,581	200	1	0	32	0,235	4,257	554,337	2,297	354,337
1,867	5	41	1,74	0,575	211,504	1,042	5	41	0,2	5,012	561,056	2,298	349,552
2,206	10	50	1,758	0,569	223,149	1,083	10	50	0,17	5,867	567,778	2,3	344,629
2,59	15	59	1,776	0,563	234,94	1,124	15	59	0,146	6,831	574,497	2,302	339,558
3,022	20	68	1,796	0,557	246,881	1,165	20	68	0,126	7,913	581,207	2,305	334,326
3,507	25	77	1,816	0,551	258,98	1,205	25	77	0,11	9,126	587,901	2,309	328,921
4,047	30	86	1,837	0,544	271,241	1,246	30	86	0,095	10,48	594,57	2,312	323,329
4,648	35	95	1,859	0,538	283,672	1,286	35	95	0,083	11,988	601,207	2,317	317,535
5,312	40	104	1,883	0,531	296,28	1,326	40	104	0,073	13,666	607,802	2,321	311,522
6,044	45	113	1,907	0,524	309,073	1,366	45	113	0,064	15,529	614,344	2,326	305,271
6,849	50	122	1,933	0,517	322,06	1,406	50	122	0,057	17,595	620,823	2,331	298,763
7,73	55	131	1,96	0,51	335,251	1,446	55	131	0,05	19,886	627,223	2,336	291,972
8,692	60	140	1,989	0,503	348,657	1,486	60	140	0,045	22,426	633,528	2,341	284,872
9,739	65	149	2,02	0,495	362,291	1,526	65	149	0,04	25,242	639,718	2,347	277,427
10,875	70	158	2,053	0,487	376,169	1,566	70	158	0,035	28,369	645,766	2,352	269,597
12,107	75	167	2,089	0,479	390,309	1,607	75	167	0,031	31,846	651,643	2,357	261,334
13,438	80	176	2,128	0,47	404,732	1,647	80	176	0,028	35,721	657,313	2,362	252,582
14,874	85	185	2,17	0,461	419,464	1,687	85	185	0,025	40,057	662,735	2,367	243,27
16,42	90	194	2,217	0,451	434,54	1,728	90	194	0,022	44,927	667,857	2,371	233,318
18,081	95	203	2,269	0,441	450,001	1,77	95	203	0,02	50,43	672,618	2,374	222,618
19,865	100	212	2,328	0,43	465,904	1,811	100	212	0,018	56,697	676,937	2,377	211,032
21,778	105	221	2,395	0,418	482,329	1,854	105	221	0,016	63,91	680,699	2,378	198,37
23,826	110	230	2,473	0,404	499,389	1,897	110	230	0,014	72,331	683,741	2,379	184,352
26,019	115	239	2,568	0,389	517,263	1,942	115	239	0,012	82,372	685,808	2,377	168,544
28,366	120	248	2,688	0,372	536,259	1,989	120	248	0,011	94,741	686,459	2,371	150,2
30,88	125	257	2,852	0,351	557,006	2,04	125	257	0,009	110,866	684,814	2,361	127,808
33,578	130	266	3,115	0,321	581,255	2,099	130	266	0,007	134,723	678,439	2,34	97,184

Table of thermodynamic properties of freon R600a.

Find more information about refrigerants on the website Freons.Info.