TRUEFuel: Colourimetric Formulations for Fuel Dyes
This system is engineered to enable the visual detection of ethanol in fuel blends through a reversible and stable colour change.
BACKGROUND
This proposal outlines a commercial collaboration opportunity focused on the development of advanced marking systems for fuels, centered around innovative chromogenic formulations. The use of dyes in fuels is a well-established practice and, in many countries, a legal requirement. The primary goal is to differentiate untaxed fuels (known as “dyed”) from taxed fuels (“clear” or “white”), thereby preventing misuse that can lead to tax losses and safety risks.
Aviation fuel is a clear example, as aviation gasoline is always dyed, both for safety reasons and for tax regulation compliance. The dyes used must be highly soluble in hydrocarbon-based, non-polar solvents typical of fuels. Commonly used are azo-type dyes (e.g., Solvent Red) for red tones and anthraquinone-based dyes (e.g., Solvent Green, Solvent Blue) for green and blue tones.
Modern fuel dyes incorporate longer, branched alkyl side chains (such as 2-ethylhexyl or tridecyl), which significantly improve solubility and overall performance. Major innovations in this field came from Morton International and BASF, who developed high-solubility versions of traditional dyes. Despite the availability of these advanced liquid dyes, some refineries still use powdered forms, which pose significant handling, sustainability, and safety challenges.
In this context, Crystal Violet Lactone (CVL) stands out as a well-known organic dye based on a triarylmethane structure, with remarkable chromogenic properties. CVL is responsive to various external stimuli such as temperature, light, pH, and solvent type, allowing for intense and precise colour change. In its pure state, CVL is a white crystalline powder, highly soluble in non-polar or slightly polar organic solvents. Under acidic conditions, it undergoes a ring-opening reaction, forming a highly conjugated chromophore that absorbs strongly in the visible spectrum and gives rise to a vivid blue colour.
This multiresponsive capability enables CVL to function as a smart marker in piezochromic, thermochromic, halochromic, and solvatochromic systems, with applications in intelligent materials, sensor technologies, and colour-changing inks. Additionally, CVL has been used as an additive in fuel dye formulations and was protected under a BASF patent (DE4422336A1, 1994). However, earlier technologies presented limitations such as reduced colour efficiency at room temperature and issues with reproducibility.
TECHNOLOGY OVERVIEW
The proposed technology introduces an innovative colourimetric formulation for fuel marking based on crystal violet lactone (CVL), a widely studied and commercially relevant chromogenic compound. This system is engineered to enable the visual detection of ethanol in fuel blends through a reversible and stable colour change, thus offering a smart, responsive solution for applications in fuel authentication, quality control, and anti-adulteration efforts.
The approach leverages the unique chemical behavior of CVL in the presence of ethanol and hydrophobic ionic liquids, forming a novel sensor formulation capable of producing a distinct blue colouration upon interaction with ethanol-contaminated fuels.
Technical Components and Formulation Process
The formulation process consists of several key steps, integrating solvent systems, dye solubilization, and functional additives:
- Solvent System Preparation
A binary solvent mixture is used to replicate typical fuel conditions and simulate adulteration scenarios:
Heptane as a non-polar solvent chosen as a model for hydrocarbon-based fuels such as gasoline or diesel. It provides a realistic, inert environment for testing fuel solubility and dye behavior.
Ethanol acting as both a test analyte (simulating ethanol-adulterated fuel) and a polarity modifier, slightly increasing the solvent’s polarity to initiate the dye’s chromogenic response.
- Dye Dissolution
CVL, a leuco dye, is typically a white crystalline powder in its closed-ring (non-coloured) form. When added to the heptane/ethanol mixture, the dye dissolves completely, forming a homogeneous solution. The solvent environment plays a crucial role in the equilibrium between the leuco (colourless) and open (coloured) forms of the dye.
- Addition of Hydrophobic Ionic Liquid
To enhance the dye’s sensitivity and stability, a hydrophobic ionic liquid is introduced into the formulation at varying weight percentages (2 wt%, 5 wt%, 10 wt%, and 20 wt%).
These ionic liquids are carefully selected for:
-High compatibility with non-polar solvents
-Ability to solubilize polar molecules in apolar media
-Interaction with the chromophore structure of CVL, enabling stabilization of the open-ring, blue-coloured form
Inventive Step and Mechanism of Action
The key inventive feature of this formulation is the unexpected stabilization of the open-ring form of CVL—normally a highly reactive and transient species—in a predominantly apolar medium. Under standard conditions, CVL reverts quickly to its leuco form in hydrocarbon fuels, minimizing visual detectability.
However, when the ionic liquid is present, the blue, open form of CVL remains stabilized even in a heptane-rich, low-polarity medium. This phenomenon is surprising, as ionic liquids are not typically effective in preserving such polar chromophoric states in non-polar solvents.
The ionic liquid likely interacts with the electron-deficient central carbon in CVL’s open form, either via electrostatic stabilization or π–cation interactions, helping maintain the extended conjugated system responsible for the visible colour.
APPLICATIONS AND BENEFITS
The proposed colourimetric fuel dye technology presents a versatile and impactful solution with broad applicability across several industries. Its primary strength lies in its ability to visually indicate the presence of ethanol in hydrocarbon-based fuels through a stable and reversible colour change, offering an immediate and accessible method for fuel authentication and quality control. This innovation is especially valuable in sectors such as fuel distribution, regulatory enforcement, automotive and aviation maintenance, industrial fuel monitoring, and refinery operations.
In fuel distribution networks, the technology can be used to monitor the authenticity and integrity of fuels as they move through transport, storage, and retail stages. The ability to detect adulteration or mixing of taxed and untaxed fuels helps prevent fraud, protects tax revenue, and ensures consumer confidence. Regulatory bodies and customs agencies can use this technology for rapid, on-the-spot inspections without the need for laboratory analysis or expensive instrumentation, allowing for more frequent and effective monitoring.
In the automotive and aviation sectors, the colourimetric response can help confirm that the correct type of fuel is being used, reducing the risk of engine damage due to ethanol contamination. This is particularly important for aircraft and machinery not designed to handle ethanol-blended fuels. Similarly, in industrial and agricultural settings, where engines often rely on specific fuel compositions, the ability to verify purity quickly can prevent costly damage and operational downtime.
Refineries and blending facilities also benefit from this technology, as it allows for real-time quality control during production without interrupting processes. The liquid formulation is easy to integrate into existing fuel streams and does not require additional infrastructure or complex analytical tools.
What sets this technology apart from traditional solutions is its responsiveness, sensitivity, and practicality. Unlike conventional powdered dyes, which can be difficult to handle and often lack stability in fuel, this formulation—based on crystal violet lactone and stabilized by hydrophobic ionic liquids—offers excellent solubility in hydrocarbon media and high visual clarity. The response is immediate and does not require instruments, making it accessible for both technical personnel and non-specialists.
Conventional methods of detecting ethanol or verifying fuel authenticity often involve time-consuming laboratory testing, specialized spectroscopy, or the use of dyes that are not optimized for stability in non-polar solvents. In contrast, this new formulation is cost-effective, highly adaptable, and can be tuned in sensitivity by varying the concentration of the ionic liquid additive. It also eliminates some of the health and environmental concerns associated with powdered dyes, as it is provided in liquid form, reducing the risk of spills or inhalation.
If widely adopted, this technology could address several persistent problems in the fuel industry. It would help combat fuel fraud and tax evasion by making it significantly harder to mislabel or adulterate fuels undetected. It would improve safety in sectors where the use of incorrect fuel types can have severe consequences. It would also fill a gap in the market for quick, accurate, and affordable field-testing tools for fuel analysis.
By combining the unique chromogenic behaviour of crystal violet lactone with the stabilizing power of carefully selected ionic liquids, this technology offers a novel, non-obvious advancement in fuel marking science. It delivers a practical and innovative response to the needs of regulators, suppliers, and consumers, making it a promising solution for a more transparent, safer, and better-regulated fuel industry.
INTELLECTUAL PROPERTY
- National Patent: [PT] Formulação Colorimétrica para Deteção de Álcoois em Combustíveis [EN] Colorimetric Formulation for the Detection of Alcohols in Fuels – Inventors: Andreia F. M. Santos and Luis C. Branco – Ref.: PT 119864
OPPORTUNITY
NOVA Inventors
Luís Branco
Andreia Santos
