Recycling of organic solvents

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Concept (need and benefits)

Organic solvents are volatile organic compounds that are used alone, or in combination with other agents, to dissolve raw materials, products or waste material, as a cleaning agent, viscosity modifier, surfactant, preservative or as a carrier of other substances which remain fixed after the solvent evaporates.

Throughout industry, there is a wide range of applications for solvents. The most important are the following: car manufacturing, synthetic fibers, paints, varnishes, paper, inks, glass, polyurethane, metal laminates, lubricants and additives, resins and pigments; as well as in the transport and solvent distribution sector, pharmaceutical industry, laboratories, printing processes and graphic arts and chemical industries in general, among many others.

The most commonly used organic solvents are aliphatic hydrocarbons (e.g. pentane, hexane, and heptane), alicyclic hydrocarbons (e.g. cyclohexane and methylcyclohexane), aromatic hydrocarbons (e.g. benzene, toluene, xylene, ethylbenzene and styrene), halogenated hydrocarbons (e.g. methylene chloride, chloroform, trichlorethylene, carbon tetrachloride, 1,2-dichloroethane, freons and 1,1,1-trichloroethane), alcohols (e.g. methanol, ethanol, i-propanol and butanol), glycols (e.g. ethylene glycol and diethylene glycol), ethers (e.g. 2-methoxyethanol and butoxyethanol), esters (e.g. methyl acetate, ethyl acetate, i-propyl acetate and methyl methacrylate), ketones (e.g. acetone , butanone-2, hexanone-2 and cyclohexanone) and others, such as nitroparaffins and carbon disulfide.

The emission of organic solvents into the atmosphere is widely regulated due to their severe and detrimental effects on people’s health and the environment, and so must be treated. Used solvents are often contaminated and can sometimes be sold as fuel in heat and electricity cogeneration plants; alternatively, they can be recovered which saves purchasing fresh solvent and is the most sustainable option.

Technology and the Condorchem Envitech Offer

To ensure that the organic solvent has something of value to the customer, Condorchem Envitech performs initial laboratory testing to assess the solvent’s recoverability. If satisfactory, Condorchem Envitech can carry out on-site testing in collaboration with the customer to exploit the full recovery potential of the organic solvent.

The most competitive process for the recovery of organic solvents depends on their composition and the possible dissolved pollutants they contain. In general, the processes used most to recover organic solvents are the following:

  • Separation by membrane technology

    Organic solvent nanofiltration membranes chemically resist a wide range of organic products, such as alkanes, aromatic compounds, alcohols, ethers, ketones and esters, and separate contaminated mixtures and organic solvents at low temperatures via fractionation operations. Membrane separation can be used as a single process or in addition to basic separation operations (e.g. distillation, extraction and absorption).

    This very selective process has special relevance when it is desired to recover compounds that are sensitive to high temperatures or of high economic value.

  • Multi-stage adsorption

    Using an adsorption tower with activated carbon as filler and a desorption tower, certain organic solvents can be recovered and concentrated. The recovery efficiency can reach 95%, but depends on the concentration of the solvent, the kind of pollutants it carries and the effluent temperature. Nitrogen gas is used for desorption and final recovery of organic solvents.

    Instead of activated carbon, polymeric adsorbents can be used, depending on the solvent to be recovered.

  • Distillation

    The most sustainable and economical solution for organic solvent recovery is distillation. The raw material is subjected to a vacuum to reduce its boiling temperature and the heat required in the distillation equipment. Depending on the level of contaminants in the initial raw material, the temperature and vacuum pressure can be adjusted to achieve recovery of the solvent. One reason for this process being widely used is that it is practically viable regardless of the initial solvent mixture composition; this is a significant advantage over other processes.

    The non-distilled (concentrated) material may be able to be recovered energetically. Once again, and based on our extensive experience, Condorchem Envitech will assess the treatment possibilities with the customer.