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.

ParameterValue
Chemical formulaC4H10
Molecular (molar) mass, g/mol58,12
Density at 25 °C (77 °F), g/ml2,064
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 temperature135 °C 
Critical pressure, MPa3,66
Critical density, g/ml0,221
Solubility in water at 25 °C (77 °F), mg/kg48,9
Steam pressure at 21 °C (70 °F)310 KPa / 45 psia
Latent heat of vaporization, kJ/kg366,5
Minimum ignition temperature460 °C / 860 °F
Lower flammability limit by volume1,8%
Upper flammability limit by volume8,5%
Lower flammability limit by weight, g/m328
Upper flammability limit by weight, g/m3203
Global Warming Potential (GWP)3
Ozone Depletion Potential0
Hazard Class2.1
ASHRAE Safety ClassA3
Freon R600a, characteristics (properties), table.

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,°Ct,°FP, barAP, barGP, psiaP, psig
-70-940,05-0,970,70-14,00
-68-900,05-0,960,81-13,89
-66-870,06-0,950,92-13,78
-64-830,07-0,941,05-13,65
-62-800,08-0,931,20-13,50
-60-760,09-0,921,36-13,34
-58-720,10-0,911,53-13,17
-56-690,12-0,891,73-12,97
-54-650,13-0,881,95-12,75
-52-620,15-0,862,18-12,52
-50-580,17-0,852,45-12,25
-48-540,19-0,832,73-11,97
-46-510,21-0,803,05-11,65
-44-470,23-0,783,39-11,31
-42-440,26-0,753,77-10,93
-40-400,29-0,734,17-10,53
-38-360,32-0,704,61-10,09
-36-330,35-0,665,09-9,61
-34-290,39-0,635,61-9,09
-32-260,42-0,596,17-8,53
-30-220,47-0,556,77-7,93
-28-180,51-0,507,42-7,28
-26-150,56-0,458,12-6,58
-24-110,61-0,408,86-5,84
-22-80,67-0,359,66-5,04
-20-40,72-0,2910,52-4,18
-1800,79-0,2311,44-3,26
-1630,86-0,1612,41-2,29
-1470,93-0,0913,45-1,25
-12101,00-0,0114,56-0,14
-10141,080,0715,741,04
-8181,170,1616,992,29
-6211,260,2518,313,61
-4251,360,3519,725,02
-2281,460,4521,206,50
0321,570,5622,778,07
2361,680,6724,439,73
4391,800,7926,1811,48
6431,930,9228,0213,32
8462,071,0529,9615,26
10502,211,1932,0017,30
12542,351,3434,1519,45
14572,511,5036,4021,70
16612,671,6638,7624,06
18642,841,8341,2426,54
20683,022,0143,8329,13
22723,212,2046,5531,85
24753,412,3949,3934,69
26793,612,6052,3637,66
28823,822,8155,4640,76
30864,053,0358,7044,00
32904,283,2762,0747,37
34934,523,5165,5950,89
36974,783,7669,2554,55
381005,044,0373,0758,37
401045,314,3077,0462,34
421085,604,5881,1666,46
441115,894,8885,4570,75
461156,205,1989,9075,20
481186,525,5194,5379,83
501226,855,8499,3284,62
521267,196,18104,2989,59
541297,556,53109,4594,75
561337,926,90114,79100,09
581368,307,28120,32105,62
601408,697,68126,04111,34
621449,108,09131,96117,26
641479,528,51138,08123,38
661519,968,95144,41129,71
6815410,419,40150,96136,26
7015810,889,86157,70143,00
R-600a freon pressure table.

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

log(p)-h thermodynamic diagram of R600a (isobutane) in the International System of Units (SI).
Log(p)-h thermodynamic diagram of R600a (isobutane) in the International System of Units (SI).

log(p)-h thermodynamic diagram for R600a (isobutane) in Imperial units.
Log(p)-h thermodynamic diagram of R600a (isobutane) in American units.

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

RefrigerantR600aR290R134aR404AR22R12
Chemical formulaCH-(CH3)3C3H8CF3-CH2F44/52/4CHF2ClCF2Cl2
Critical temperature in °C13596.710172.596.1112
Molecular weight in kg/kmol58.144.110297.686.5120.9
Normal boiling point in °C-11.6-42.1-26.5-45.8-40.8-29.8
Pressure (absolute) at -25 °C in bar0.582.031.072.502.011.24
Liquid density at -25 °C in kg/l0.600.561.371.241.361.47
Steam density at temperatures up to -25/+32 °C in kg/m31.33.64.410.07.06.0
Volumetric capacity at -25/45/32 °C in kJ/m3373116472513341244727
Enthalpy of vaporization at -25 °C in kJ/kg376406216186223163
Pressure (absolute) at +20 °C in bar3.08.45.711.09.15.7
Comparative characteristics of refrigerants R600a, R290, R134a, R404A, R22 and R12.

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

Pt,°Ct,°FVlPlHlSlt,°Ct,°FVvPvHvSvLv
0,004-100-1481,4620,684-6,3950,067-100-14865,2340,015428,192,577434,585
0,006-95-1391,4730,6793,0360,121-95-13941,0780,024433,8612,539430,825
0,01-90-1301,4830,67412,5490,173-90-13026,6480,038439,622,505427,072
0,015-85-1211,4940,66922,1440,225-85-12117,7640,056445,4652,475423,321
0,023-80-1121,5050,66431,8230,276-80-11212,140,082451,3922,448419,569
0,033-75-1031,5160,6641,5870,326-75-1038,4870,118457,3972,424415,81
0,048-70-941,5280,65551,4390,375-70-946,0590,165463,4792,403412,04
0,067-65-851,5390,6561,380,423-65-854,410,227469,6332,385408,253
0,093-60-761,5510,64571,4130,471-60-763,2660,306475,8552,368404,442
0,126-55-671,5640,6481,540,518-55-672,4590,407482,1422,354400,602
0,168-50-581,5760,63491,7640,564-50-581,8790,532488,4892,342396,726
0,221-45-491,5890,629102,0860,61-45-491,4560,687494,8932,331392,807
0,287-40-401,6020,624112,5120,655-40-401,1430,875501,3492,323388,837
0,368-35-311,6160,619123,0420,7-35-310,9071,102507,8532,315384,811
0,466-30-221,630,614133,6820,744-30-220,7281,373514,42,309380,719
0,584-25-131,6440,608144,4330,787-25-130,5911,693520,9872,305376,554
0,725-20-41,6590,603155,30,831-20-40,4832,069527,6072,301372,307
0,891-1551,6740,597166,2860,874-1550,3992,506534,2572,299367,972
1,013-11,7610,8321,6840,594173,4810,901-11,7610,8320,3542,826538,5872,298365,106
1,085-10141,690,592177,3950,916-10140,3323,012540,9332,297363,537
1,31-5231,7060,586188,6320,958-5230,2783,593547,6282,297358,996
1,570321,7220,58120010320,2354,257554,3372,297354,337
1,8675411,740,575211,5041,0425410,25,012561,0562,298349,552
2,20610501,7580,569223,1491,08310500,175,867567,7782,3344,629
2,5915591,7760,563234,941,12415590,1466,831574,4972,302339,558
3,02220681,7960,557246,8811,16520680,1267,913581,2072,305334,326
3,50725771,8160,551258,981,20525770,119,126587,9012,309328,921
4,04730861,8370,544271,2411,24630860,09510,48594,572,312323,329
4,64835951,8590,538283,6721,28635950,08311,988601,2072,317317,535
5,312401041,8830,531296,281,326401040,07313,666607,8022,321311,522
6,044451131,9070,524309,0731,366451130,06415,529614,3442,326305,271
6,849501221,9330,517322,061,406501220,05717,595620,8232,331298,763
7,73551311,960,51335,2511,446551310,0519,886627,2232,336291,972
8,692601401,9890,503348,6571,486601400,04522,426633,5282,341284,872
9,739651492,020,495362,2911,526651490,0425,242639,7182,347277,427
10,875701582,0530,487376,1691,566701580,03528,369645,7662,352269,597
12,107751672,0890,479390,3091,607751670,03131,846651,6432,357261,334
13,438801762,1280,47404,7321,647801760,02835,721657,3132,362252,582
14,874851852,170,461419,4641,687851850,02540,057662,7352,367243,27
16,42901942,2170,451434,541,728901940,02244,927667,8572,371233,318
18,081952032,2690,441450,0011,77952030,0250,43672,6182,374222,618
19,8651002122,3280,43465,9041,8111002120,01856,697676,9372,377211,032
21,7781052212,3950,418482,3291,8541052210,01663,91680,6992,378198,37
23,8261102302,4730,404499,3891,8971102300,01472,331683,7412,379184,352
26,0191152392,5680,389517,2631,9421152390,01282,372685,8082,377168,544
28,3661202482,6880,372536,2591,9891202480,01194,741686,4592,371150,2
30,881252572,8520,351557,0062,041252570,009110,866684,8142,361127,808
33,5781302663,1150,321581,2552,0991302660,007134,723678,4392,3497,184

Table of thermodynamic properties of freon R600a.

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