Introduction
Dipropylene glycol (DPG) is a low molecular weight diol, belonging to the propylene glycol family of chemical compounds. It is a clear, viscous, colorless liquid with a slightly bittersweet taste and low vapor pressure. DPG is primarily produced as a co-product during the hydrolysis of propylene oxide to manufacture monopropylene glycol (1,2-propylene glycol or 1,2-propanediol).
1. Properties of Dipropylene Glycol
Dipropylene glycol (DPG) exhibits the following key properties:
- Low Toxicity and Biocompatibility: DPG has low human toxicity, making it suitable for use in food, cosmetic, and pharmaceutical products. It meets the requirements of the U.S. Food and Drug Administration (FDA) and is classified as generally recognized as safe (GRAS).
- Solubility and Miscibility:DPG is completely miscible with water and has good solvent properties, making it useful as a solvent in various applications.
- Physical Properties:
- Boiling Point: Around 230-240°C
- Freezing Point: Around -60°C
- Viscosity: Relatively low viscosity, typically around 50-60 cP at 25°C
- Odor: Mild odor
- Chemical Stability:DPG exhibits good chemical stability and low corrosivity, making it suitable for various industrial applications.
2. Uses & Benefits of Dipropylene Glycol
Industrial Applications
Dipropylene glycol (DPG) is widely used as a raw material in the manufacture of unsaturated polyester resins. It imparts desirable properties like flexibility, chemical resistance, and dimensional stability to the resins. DPG is also employed in:
- Functional fluids like aircraft de-icing fluids, antifreezes, lubricants, inks, and heat transfer fluids.
- Paints and coatings as a solvent and coalescent.
- Plasticizers and cellophane production.
3. Personal Care and Cosmetics
DPG is widely used in personal care products and cosmetics due to its low toxicity, excellent solvent properties, and good emollient characteristics. It acts as a humectant, solvent, and viscosity modifier in:
- Skin and hair care products like moisturizers, shampoos, and conditioners
- Makeup and color cosmetics like lipsticks, mascaras, and foundations
- Sunscreens and sunless tanning products
4. Synthesis of Dipropylene Glycol
1. Synthesis Routes
Propylene Oxide Hydration
- Traditional route: hydration of propylene oxide derived from petrochemical sources
- Catalytic process (150-180°C) with ion exchange resin or acid/alkali catalysts
- Non-catalytic high-temperature process (200-220°C)
1. Biobased Synthesis from Glycerol
- Acid-catalyzed condensation of bioderived propylene glycol
- Hydrogenation of glycerol over transition metal catalysts
- Produces wholly biobased dipropylene glycol without using propylene oxide
4. Reaction Conditions and Catalysts
- Acid catalysts: sulfuric acid, ionic liquids
- Base catalysts: alkali compounds
- Transition metal catalysts: copper, copper oxide, zinc oxide, oxides of groups 2-6 and 8-10 elements
- High pressure and temperature for glycerol hydrogenation
5. Product Purification
- Vacuum distillation for energy-efficient continuous production
- Refining and purification to achieve >99.9% purity and low color (<10)
6. Dipropylene glycol as a solvent for the extraction of aromatic hydrocarbons. Analysis and evaluation of the solvency properties and simulation of the extraction processes
Marilena Nicolae, Florin Oprea, Elena M. Fendu
Abstract
Solvent properties, solvation power and selectivity, are calculated for dipropylene glycol (DPG). Additionally, the performances realized by DPG in extraction columns were evaluated by simulating in PRO/II software the extraction of aromatic hydrocarbon from a fraction of Catalytic Reforming naphtha based on the binary interaction parameters obtained from liquid–liquid and vapor–liquid equilibrium experimental data for the binary mixtures of DPG with representative aromatic and non-aromatic hydrocarbons with six up to eight carbon atoms, as determined in previous works.
The simulation of the extraction columns was achieved for different operating conditions: solvent mass ratios from 1:1 up to 4:1 and different numbers of theoretical trays in simple columns, solvent mass ratios from 1:1 up to 4:1 and different reflux ratios in columns operated with reflux of extract, and in columns operated with reflux of raffinate.
The results show that DPG has a good solvation power, and its utilization in extraction ensures a pure raffinate is obtained.
Introduction
Removal of aromatic hydrocarbons from fuels, particularly from gasoline, is of great interest in the current context of environmental protection legislation. Taking this into account, there are developing research studies aiming to find new processes and/or new solvents that more efficiently extract aromatic hydrocarbons from their mixtures.
Recently, researchers from DDBST (Dortmund Data Bank Software and Separation Technology) developed software (Gmehling and Schedemann, 2014) that allows for prediction of the solvent capacity and selectivity of solvents, starting from equilibrium data, physicochemical and transport properties data existing in DDB (Dortmund Data Bank) and using predictive thermodynamic models, such as UNIFAC (UNIQUAC Functional-group Activity Coefficients) (Fredenslund et al., 1975), modified UNIFAC (Lohmann et al., 2001, Lohmann and Gmehling, 2001, Gmehling et al., 2002) and equations of state based on group contributions, such as PSRK (Predictive Soave–Redlich–Kwong) (Holderbaum and Gmehling, 1991, Gmehling, 1995) and VTPR (Volume Translated Peng–Robinson) (Schmid et al., 2014).
The UNIFAC model was extensively used to predict phase equilibria in different mixtures of hydrocarbons and various solvents (Mukhopadhyay and Dongaonkar, 1983, Mukhopadhyay and Pathak, 1986, Wang et al., 1998, Radwan et al., 1997). The UNIQUAC (Universal-Quasi Chemical) (Abrams and Prausnitz, 1975) and NRTL (Non Random Two Liquids) (Renon and Prausnitz, 1968) models were also utilized in different studies to describe better phase equilibria in binary, ternary, and multicomponent mixtures of aromatic and non-aromatic hydrocarbons and tetraethylene glycol (Darwish et al., 2003), n-methyl-2-pyrrolidone (Al-Jimaz et al., 2007), and sulfolane (Mukhopadhyay and Sahasranaman, 1982).
The study presented in this paper is part of a wide research study developed in our department, which refers to the utilization of propylene glycols (monopropylene glycol (MPG), dipropylene glycol (DPG), tripropylene glycol (TPG) and tetrapropylene glycol (TePG)) as solvents for aromatic hydrocarbon extraction. Some assumptions regarding the solvent properties of MPG are presented by Oprea and Guţu (2008), and research studies were stopped because MPG was found to have weak solvent properties. Instead, the studies performed on dipropylene glycol revealed that it has a great affinity for aromatic hydrocarbons. Liquid–liquid equilibrium data between DPG and non-aromatic and aromatic hydrocarbons with six to eight carbon atoms are presented in a previous work (Nicolae and Oprea, 2012).
During the developed experiments, it was found that DPG is completely miscible with aromatic hydrocarbons (benzene, toluene, ethylbenzene and xylenes). As consequence, vapor–liquid equilibrium data between DPG and the aromatic hydrocarbons mentioned below were determined (Nicolae and Oprea, 2014). For tripropylene glycol, the research is in progress, while for TePG, currently, only the physical and transport properties have been determined (Fendu and Oprea, 2013).
1. Solvent properties estimation
Evaluating the possibility of using a new compound as a solvent for the extraction of aromatic hydrocarbons implies the knowledge of the most important properties of the solvent: the capacity and the selectivity. There are some investigations on the prediction of the selectivity and the capacity of the most well-known and utilized solvents, starting from a small amount of equilibrium data and physical properties of the solvents: the first work (Deal and Derr, 1964) was published in 1954, and…
2. Results and discussion
Analysis of the results proves that under identical operation conditions, in the case of the simple extraction column, the quantity of aromatic hydrocarbons extracted with DPG is considerably greater than the quantity of aromatics extracted with DEG. This result demonstrates that DPG has a high solvation power. In addition, for both solvents, DEG and DPG, the quantity of hydrocarbons solubilized is found to increase with the solvent ratio and the number of trays in the column. This relationship…
3. Conclusions
Solvent properties: the solvation power and selectivity of DPG were determined under different temperatures and solvent ratios. The values obtained by the calculations show that DPG has a high solvation power and exhibits a good selectivity for aromatic hydrocarbons with eight carbon atoms and for benzene. The simulation performed demonstrated that in the presence of water, the selectivity of DPG decreases.
The performances of DPG in the extraction column were evaluated by simulation in PRO/II…
4. Supplementary material
This material contains tables with the variation of the DPG selectivity for each aromatic hydrocarbon in the presence of the aliphatic and naphthenic hydrocarbons with the same number of carbon atoms as a function of temperature and solvent ratio; this material also contains tables that present the mass balance for each type of extraction column: simple column, column with reflux of extract, and column with reflux of raffinate for an operation version. This material is available via the..
7. Safety Information of Dipropylene Glycol
1. Toxicity and Safety Profile
Dipropylene glycol has a relatively low toxicity profile. The U.S. Food and Drug Administration has determined it to be “generally recognized as safe” (GRAS) for use in foods, cosmetics, and medicine. Toxicology studies on rats and mice found no evidence of carcinogenic effects from dipropylene glycol exposure, even at high doses. However, high doses did increase the incidence of kidney disease, liver inflammation, and nasal tissue atrophy in rats.
2. Environmental and Occupational Safety
Dipropylene glycol has low volatility and minimal odor, reducing risks of inhalation exposure. It is non-corrosive and has low skin irritation potential, minimizing risks from dermal contact. Proper handling and storage practices should still be followed to mitigate risks of accidental ingestion or eye contact. Appropriate personal protective equipment may be advisable for occupational settings.
3. Safety in Consumer Products
The low toxicity and mild sensory properties of dipropylene glycol make it suitable for use in consumer products like cosmetics, personal care items, and food additives. However, product formulations should be carefully designed to limit overall exposure levels, especially for vulnerable populations like children. Proper labeling is important to enable informed consumer choices.
4. Biodegradability and Environmental Fate
Dipropylene glycol is expected to be readily biodegradable in the environment based on its chemical structure. Appropriate disposal methods should still be followed to prevent uncontrolled releases that could impact water sources or ecosystems. Overall, dipropylene glycol has a favorable environmental profile compared to many industrial chemicals.
8. DIPROPYLENE GLYCOL (MIXED ISOMERS AND DOMINANT ISOMER) CAS N°:25265-71-8 & 110-98-5)
SIDS Initial Assessment Report for
11th SIAM
(USA, January 23-26, 2001)
CAS No: 25265-71-8 and 110-98-5
Sponsor Country: U.S.A
1. Human Health
Dipropylene glycol (DPG) is not acutely toxic by oral (LD 50 >13 g/kg bw/day from 7 rat studies and 17.6 g/kg bw/day from a guinea pig study), dermal (LD 50 > 5g/kg bw/day in 2 rabbit studies) or inhal ation (no deaths observed in rats and guinea pigs at 6 to 8 g/m3 ) routes of exposure. DPG is slightly irritating to the skin and eyes of rabbits. Based on human data, DPG is not a skin sensitizer. Repeated exposures of rats to DPG did not result in adverse effects at levels up to 5% (estimated NOAEL is about 6.2 g/kg bw/day) in drinking water.
At about 12.5 g/kg bw/day (10%), kidney lesions appeared in about 30% of the rats. Results from an OECD 422 combined repeat dose/reproductive/developmental toxici ty test on the structural analogue, tripropylene glycol (TPG), demonstrated a NOAEL of 200 mg/kg bw and a LOAEL of 1000 mg/kg bw for repeated dose toxicity, with increased relative weight for liver and kidney. Metabolic fate data on TPG demonstrates that TPG is readily converted to DPG, PG, and CO2 in rats.
Thus, data from TPG are relevant to DPG. DPG did not cause fetal toxicity or teratogenicity in rats (NOAEL = 5 g/kg bw/day) or rabbits (NOAEL = 1.2 g/kg bw/day). No reproductive studies have been conducted on DPG. However, the structural analogues, propylene glycol and TPG, have been tested for reproductive effects and shown to have NOAELs of 10.1 g/kg bw in mice and 1 g/kg bw in rats, respectively.
Thus, the lack of reproductive effects from TPG and the high NOAEL for PG reproductive toxicity indicate that no reproductive effects are expected in animals exposed to DPG, in the absence of maternal toxicity. DPG is not a genetic toxicant based on in vitro (bacterial and mammalian cells in culture) and in vivo (micronucleus) studies.
2. Environment
Dipropylene glycol (DPG) is not volatile, but is miscible with water. Air monitoring data are not available, but concentrations of dipropylene glycol in the atmosphere are expected to be extremely low because of its low vapor pressure and high water solubility. Low levels of DPG (0.4 ng/l) in drinking water were reported in one study.
It is biodegraded in water and expected to be biodegraded in soil, as indicated by >70% degradation after 28d in a Zahn-Wellens test. It is not expected to bioaccumulate, with measured BCFs between 0.3 and 4.6 in fish. Measured aquatic toxicity data on fish and amphibians report toxicity at >5,000 and 3,181 mg/L, respectively. Based on QSAR data for Daphnia and algal toxicity, and the measured data for fish and amphibians, DPG is not expected to be toxic to aquatic organisms except at very high concentrations.
Using an assessment factor of 100 and the fish 96-hour LC 50, the PNEC is >50 mg/l; if the amphibian data are used, the PNEC is 32 mg/l.
3. Exposure
4. SIDS Initial Assessment Report
1. Identity
Commercial dipropylene glycol (CAS # 25265-71-8; (CH3-CHOH-CH2O-CH2-CHOHCH3) is composed of 3 isomers (2,2′-dihydroxydiisopropropylether (CAS-No.: 108-61-2); 2,2′-dihydroxydipropylether (CAS-No.: 110-98-5); 2-hydroxypropyl-2′-hydroxyisopropylether (CAS-No.: 106-62-7) and is typically 98% pure. It is a liquid that possesses the following physico-chemical properties and characteristics:
2. Production
Dipropylene glycol is produced as a byproduct of the manufacture of propylene glycol. The United States (US) production capacity of dipropylene glycol (i.e., byproduct production capacities of propylene glycol plants) was 131 million pounds (60 thousand tonnes) in 1998. The US Domestic demand in 1998 was 108 million pounds (49 thousand tonnes). In 1998, dipropylene glycol was produced in the US by The Dow Chemical Company, Eastman Chemical Company, Huntsman Corporation, Lyondell Chemical Company, and Olin Corporation. (ChemExpo Chemical Profile, 1998). Worldwide capacity is estimated at 235 million pounds (107 thousand tonnes).
3. Use
Dipropylene glycol is used primarily as an industrial intermediate, but is also used as a substance in consumer products, and as an ingredient in pesticidal formulations. Uses of dipropylene glycol as a substance capitalize on its superior performance as a plasticizer as well as properties (e.g., high solvency, high viscosity) that permit dipropylene glycol to act as a functional ingredient of fluids.
4. Exposure
As most dipropylene glycol in the US is used in industrial applications, occupational exposures via the dermal or inhalation route present a potential for exposure. In the commercial service and consumer settings use as a functional fluid (e.g. in hydraulic brake fluids, cutting oils) or as an ingredient in pesticides present a potential for inhalation exposure in addition to dermal exposure…
5. DIPROPYLENE GLYCOL EXPOSURE POTENTIAL
Only two of the 18 branded products shown in the above table currently (May, 2001) maintain active registrations in the US, and both contain dipropylene glycol in the 1 to 5 percent range. Exposure of dipropylene glycol from environmental sources is expected to be low. Very low levels of dipropylene glycol have been reported in drinking water (0.2 and 0.4 ng/l) and 5 paper mill waste water treatment plants effluents (11 µg/l ). Because of its low volatility detection of dipropylene glycol in air samples is not expected.
1. Environmental Exposure
Based on the available data, dipropylene glycol is expected to present a low hazard to the environment. If released into the environment, it will preferentially partition into water. Because of its low soil sorption coefficient (Koc), dipropylene glycol is expected to mobilize if spilled on soil and will not adsorb to particles. Volatility is not expected to be a significant fate process for this material due to its low vapor pressure and high water solubility. Photodegradation of the material in air or water is also not expected to be a significant fate process.
Once in the environment, dipropylene glycol is capable of being degraded under aerobic conditions by bacteria present in soil and water. As is typical for ethers and glycols, dipropylene glycol is hydrolytically stable. Results of the octanol/water partition coefficient (expressed as log Kow) and from bioaccumulation studies with carp (MITI, 1992) indicate that dipropylene glycol is not expected to significantly accumulate in aquatic organisms (BCF 0.3 to 4.6).
Effects on the Environment
Based on a combination of test data, quantitative structure activity relationship analysis (QSAR), and data on analogs (propylene glycol, tripropylene glycol), dipropylene glycol presents a low hazard concern for the environment. Representative results for dipropylene glycol include:
Toxicity values for the analogs propylene glycol and tripropylene glycol also support the expected lack of aquatic toxicity, with fish LC50 values of >46,000 mg/l and >1,000 mg/l, invertebrate EC50 values of 10,000 mg/l and > 1,000 mg/l and aquatic plant EC50 values of 19,000 mg/l and >1,000 mg/l for propylene glycol and tripropylene glycol, respectively. Although chronic study data for dipropylene glycol are not available, QSAR predictions suggest that this test substance will not cause chronic toxicity to aquatic organisms.
Published studies are not available on the effects of dipropylene glycol on terrestrial organisms or plants, however, little effect is expected, since dipropylene glycol degrades in soil, has very low bioaccumulation potential, and is of low toxicity to aquatic organisms.
Conclusions
Commercial dipropylene glycol (CAS # 25265-71-8; (CH3-CHOH-CH2O-CH2-CHOHCH3) is composed of 3 isomers and is typically 98% pure. The commercial product is typically composed of up to 48% isomer 110-98-5. Dipropylene glycol is produced as a byproduct of the manufacture of propylene glycol. The US production capacity of dipropylene glycol was 131 million pounds (60 thousand tonnes) in 1998. Dipropylene glycol is used as both a reactive intermediate and as a solvent. Reactive intermediate end uses in the US include: plasticizers, unsaturated polyester resins, polyurethane polyols, and alkyd resins. Solvent end uses in the US include: cosmetics, pesticides and functional fluids: specialty deicers, inks, lubricants.
Question
- What is DPG dipropylene glycol used for?
Industrial uses of DPG include as a raw material to produce polymers such as polyester and alkyd resins or as plasticizer in other polymers, for example PVC.
2. Does DPG dissolve in alcohol?
Dipropylene glycol is miscible in water, alcohols, esters and almost organic solvents and various vegetable oils. It is produced during the manufacture of propylene glycol from propylene oxide along with tripropylene glycol and higher glycols.
3. What is the percentage of DPG in perfume?
In fragrance formulations, DPG can be utilized effectively at concentrations up to 26.7%, allowing perfumers to leverage its exceptional fixative properties while considering the overall composition and desired scent characteristics.
4. What is the role of DPG?
Role & Responsibility of the Directorate of Public Grievances (DPG) IF COMPLAINANTS FAIL TO GET REDRESS TO GRIEVANCES FROM (ORGANISATIONS / INSTITUTION NAME), THEY CAN APPROACH DIRECTORATE OF PUBLIC GRIEVANCE (DPG) AT https://dpg.gov.in FOR REDRESS OF GRIEVANCE.
5. Is DPG safe on skin?
The US Environmental Protection Agency (EPA) has determined that under the current conditions of use based on its low-hazard profile, dipropylene glycol is generally considered safe for skin and hair care products. ⁵ However, dipropylene glycol can cause contact dermatitis in some people.26-Sept-2023.