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Propylenglycol

Teknisk information

Nyttig viden om Propylenglycol

Mono Propylenglycol, benævnes ofte Propylenglycol men også  Propan- 1,2-diol, MPG, PG og Fødevare Grade.

Propylenglycol har i mange år været den gængse glycol til anvendelse i procesanlæg indenfor fødevare- og bryggerivirksomheder, samt hvor der er krav om ikke-giftige produkter. F.eks. hvor rådgivere eller slutbrugeren ønsker at fjerne enhver risiko for forgifting ved uheld, hvilket kan forekomme med blandinger af vand og Ethylenglycol.

Propylenglycol klassificeres nogle gange som lægemiddel eller velegnet til brug i lægemiddelprodukter. F.eks. USP, EP and JP.  En anden generisk klassifikation, der bruges i USA er GRAS (Generally Considered As Safe), hvilket ofte er i betydningen "fødevareegnet".  Men ingen europæiske lande har godkendt Propylenglycol som fødevareadditiv, og derfor bør mærkningen med "fødevareegnet" anses for ikke at være korrekt. 

Ren Propylenglycol består en LD50 test på >20,000mg/kg BW, hvilket placerer produktet som "Relativt harmløs" i henhold til Hodge & Sterner Skalaen.
Til sammenligning skulle et mindre barn med en vægt på 30 kg konsumere ca. 600 ml ren propylenglycol, før der vil opstå alvorlig sygdom. Dvs. at giftighed er et relativt begreb.

Propylenglycol har en meget lavere kapacitet for effektiv varmeoverførsel sammenlignet med blandinger baseret på Ethylenglycol. Propylenglycol er også mere viskøs ved lave temperaturer og er derfor vanskeligere at pumpe. En vegetabilsk baseret Propylenglycol er fornylig lanceret på markedet, dog er den ikke altid økonomisk bæredygtig. Propan-1,3-diol har overførsels- og pumpekarakteriska meget lig Propan-1,2-diol, men med en bedre miljømæssig profil.

Minimum anbefalet volumen af Propylenglycol

for at minimere biologisk forurening.

Der stilles hyppigt spørgsmål om den anbefalede minimumkoncentration af Propylenglycol, der skal anvendes i en opløsning af vand. Hydratech anbefaler minimum 25-30% v/v, som yder frostbeskyttelse til under -10°C, men brugeren har ofte kun brug for en frostsikring til f.eks. -2°C. Det kræver en væsentlig mindre mængde Propylenglycol.

Der er dog adskillige årsager til den anbefalede minimumkoncentration. 

1)     Korrosions-, scaling og biologisk kontrol. Hydratech´s Propyleneglycol baserede varmeoverførselsvæsker er formulerede til at operere i både køle- og varmesystemer i mange forskellige koncentrationer. For at yde beskyttelse over lang tid. skal den første blanding også have den rigtige balance mellem korrosions-, scaling- og biologiske hæmmere for at opretholde korrekt korrosionskontrol ved forskellige koncentrationer. Hæmmerne i CoolFlow NTP er formuleret til at give den bedst mulige ydelse og levetid for væsken ved Propylenglycolkoncentrationer på mellem 25 og 60% v/v. Ved at reducere Propylenglycol koncentrationen til under 25% reduceres koncentrationen af hæmmerne til et niveau, som vil kunne give systemet utilstrækkelig korrosions-, scaling og biologisk beskyttelse.

2)    Forhøjet pH bufferevne mod syrenedbrydning. Både Ethylen- og Propylenglycol nedbrydes, når de udsættes for høje temperaturer. Med en højere koncentration af væske, vil der også altid være en højere koncentration af hæmmere i blandingen. Den højere koncentration af hæmmere giver forhøjet pH bufferydelse til at bekæmpe syreholdige biprodukter, som kan dannes i forbindelse med nedbrydningen af Propylenglycolen. 

3)    Biologisk integritet af væsken. Den tredje årsag til at anvende mindst 25% Propylenglycol i systemet skyldes muligheden for baktiervækst.
Med koncentrationer på 20% eller mere, hæmmer både Ethylen- og Propylenglycol væksten og spredningen af de fleste mikrober og svampe.
Den reducerede overfladespænding i glycolopløsningen ødelægger bakteriernes cellevægge, hvilket giver et miljø, der ikke understøtter bakterievækst. Ved meget lave glycolkoncentrationer, f.eks. under 1%, vil både Ethylen- og Propylenglycol fungere som næring til bakterier. Ved niveauer over 1 og under 20%, kan nogle bakterier overleve med begrænset vækst, specielt ved moderate temperaturer. 

Tabellen nedenfor viser typiske resultater for mikrobiel aktivitet som Propylenglycol koncentrationer reducerer..

Tilstedeværelsen af bakterier inbefatter ikke altid bakterievækst. Glycolblandinger med 25% eller mere er biostatiske, ikke biocidale. Hvis en bakteriekilde derfor skulle blive tilført Propylenglycolblandinger, kan væsken vise tilstedeværelsen af bakterier. Derfor anbefaler Hydratech en rensning af nye installationer inden ibrugtagning samt periodiske tests af systemets væske for at kontrollere for enhver biologisk aktivitet - Se venligst mere under SureFlow vedligeholdelsesprogrammet. For yderligere at minimere kontamination fra eksterne kilder, indeholder alle Hydratechs formuleringer både kort- og langtids biocider.

 

Helbreds- Sikkerheds- & Miljøinformationer om Propylenglycol

1)  OECD Screening Information Data Set (SIDS) Assessment for Propylene Glycol

Chemical Name  Propylene glycol (1,2-dihydroxypropane)   CAS No. 57-55-6
Structural Formula  CH3-CHOH-CH2OH
Recommendations  The chemical is currently of low priority for further work.

Summary Conclusions

Human Health
Propylene Glycol is not acutely toxic. The lowest oral LD50 values range between 18 and 23.9 grams (5 different species) and the reported dermal LD50 is 20.8 grams. Propylene Glycol is essentially non-irritating to the skin and mildly irritating to the eyes. Numerous studies support that Propylene Glycol is not a skin sensitizer. Repeated exposures of rats to propylene glycol in drinking water or feed did not result in adverse effects at levels up to 10% in water (estimated at about 10 g/kg bw/day) or 5% in feed (dosage reported as 2.5 g/kg bw/day) for periods up to 2 years. In cats, two studies of at least 90 days duration show that a species-specific effect of increased Heinz bodies was observed (NOAEL = 80 mg/kg bw/day; LOAEL = 443 mg/kg bw/day), with other haematological effects (decrease in number of erythrocytes and erythrocyte survival) reported at higher doses (6-12% in diet, or3.7-10.1 g/cat/day). Propylene glycol did not cause fetal or developmental toxicity in rats, mice, rabbits, or hamsters (NOAELs range from 1.2 to 1.6 g/kg bw/day in four species). No reproductive effects were found when propylene glycol was administered at up to 5% in the drinking water (reported as 10.1 g/kg bw/day) of mice. Propylene glycol was not a genetic toxicant as demonstrated by a battery of in vivo(micronucleus, dominant lethal, chromosome aberration) and in vitro (bacterial and mammalian cells and cultures) studies. No increase in tumors was found in all tissues examined when propylene glycol was administered in the diet of rats (2.5 g/kg bw/day for 2 years), or applied to the skin of female rats (100% Propylene Glycol; total dose not reported; 14 months) or mice (mouse dose estimated at about 2 g/kg bw/week; life-time). These data support a lack of carcinogenicity for Propylene Glycol.

Environment [Also refer to Environmental Fate information in section 2) below]
Propylene Glycol is not volatile, but is miscible with water. Air monitoring data is not available, but concentrations of Propylene Glycol in the atmosphere are expected to be extremely low because of its low vapour pressure and high water solubility. It is readily biodegraded in water or soil. Four studies reported >60% biodegradation in water in 10 days. Propylene Glycol is not expected to bioaccumulate, with a calculated BCF <1. Measured freshwater aquatic toxicity data for fish, daphnia and algae report LC/EC50 values of >18,000 mg/l. Therefore, Propylene Glycol is not acutely toxic to aquatic organisms except at very high concentrations. Using an assessment factor of 100 and the Ceriodaphnia data (48- hour EC 50 = 18,340 mg/l), the PNEC is 183 mg/l.

Exposure
Propylene glycol production capacity in the USA was 1312 million pounds (596 kilotonnes) in 1998. Domestic demand was 1050 million pounds (477 kilo-tonnes). Propylene glycol is used as an ingredient in cosmetics at concentrations of <0.1% to >50%.  Approximately 4000 cosmetic products contained propylene glycol in 1994. Uses of propylene glycol, with percent of demand, are: Unsaturated polyester resins 26%;  Antifreeze and de-icing fluids 22%;  Food, drug and cosmetics uses 18%;  Liquid detergents 11%;  Functional fluids (inks, specialty anti-freeze, de-icing lubricants) 4%;   Pet foods, 3%;  Paints and coatings 5%;  Tobacco 3%;  Miscellaneous including plasticiser use 8%.

Please Login for access to complete pdf of OECD SID for Propylene Glycol.

2)  Environmental Fate of Propylene Glycol

2.1  In Soil
Soil factors affecting the fate and behaviour of Propylene Glycol in the terrestrial environment are pH, organic matter, clay content, cation exchange capacity, aeration and texture.  The major processes that determine the mobility and distribution of Propylene Glycol in the terrestrial environment are partitioning into surface and ground water given the high aqueous solubility, as well as rapid biodegradation and photolysis. Volatilization and sorption to soils are fate processes with only minor importance.

Propylene Glycol is approximated to have a half-life in soil due to biodegradation equal to or less than that in water (from 1 to 5 days). However, degradation rates will vary with soil properties, temperature and other environmental conditions. ATSDR (1997) estimated the half-life of Propylene Glycol in water to be l to 4 days under aerobic and 3 to 5 days under anaerobic conditions, assuming first order kinetics. The half-life in soil is expected to be equal to or slightly less than that for water.Soil temperature potentially has a large influence on Propylene Glycol biodegradation rates. Klecka et al. (1993) evaluated the effects in microcosms of substrate concentration and temperature on the microbially-mediated loss rates of five different ADFs, which included Ethylene Glycol, Propylene Glycol, and Di-Ethylene Glycol. The soil was a sandy loam with 2.8% organic carbon content.  High levels of glycols were not inhibitory to biodegradation, and all three glycols degraded rapidly in soils with starting concentrations ranging from 390 to 5,300 mg/kg (the soils were collected from an area adjacent to a international airport runway).

Complete biodegradation for soils with lower initial concentrations (>400 ppm Propylene Glycol) occurred after about 11 days; however, a soil with a starting concentration of approximately 3,300 ppm (w:w) Propylene Glycol showed a loss at 8°C of about 76% over a 111 d period (leaving a remaining concentration of approximately 800 ppm). The initial degradation appeared to follow zero-order kinetics;  i.e. the rate of loss was independent of the initial starting concentration at levels above 100 ppm w:w.  Average degradation rates were in the range of 66 to 93 mg/kg soil/day at 25&C; 20 to 27 mg/kg soil/day at 8°C.; and only 2.3 to 4.5 mg/kg soil/day at -2°C.  Environmental temperature is a major factor influencing biodegradation rates, therefore.  No information was found on concentrations of Propylene Glycol in soil within a field setting.

2.2 In Water
Propylene Glycol is highly soluble in water, and readily metabolized by microbes and higher organisms once released into the environment. The biodegradation process requires oxygen; therefore, dissolved oxygen (DO) concentrations in receiving waters may be negatively impacted following a large Propylene Glycol release.  Corrosion inhibitor additives may also cause adverse effects to the biodegrading microorganisms, thereby slowing the degradation process. Research results of a Propylene Glycol based heat transfer fluid containing tolytriazole in water had a degradation rate approximately three times lower (slower) than for pure Propylene Glycol. Bielefeldt et al. (2002) examined secondary effects of Propylene Glycol introduction to soils on groundwater flow using 15 cm saturated sand columns. Rapid Propylene Glycol biodegradation was found to be accompanied by a decrease in the saturated hydraulic conductivity by one to three orders of magnitude, likely as a result of bacterial biomass build-up around soil particles.

2.3  In Air
Propylene Glycol is not expected to readily volatilize into air from water, due to its high solubility and low vapour pressure. If released into the atmosphere during high temperatures, Propylene Glycol should exist almost entirely in the vapour phase and undergo rapid photochemical oxidation. The half-life for this reaction has been estimated to be 20-32 hours.