Method and device for purifying substances by means of crystallization

A process for the purification of acrylic acid comprising:

• crystallizing a molten material comprising acrylic acid and at least one impurity having a tendency to precipitate;
• adding solvent or a solvent mixture to the molten material in a quantity sufficient to retain at least one impurity having a tendency to precipitate in solution, wherein the solvent has a superior dissolving capacity for at least one of the impurities having a tendency to precipitate, compared to acrylic acid and wherein the mixture comprises two or more impurities having a tendency to precipitate selected from the group consisting of maleic acid, an anhydride of maleic acid, and phenothiazine, a quantitatively more significant impurity having a tendency to precipitate is retained in solution and wherein a solvent or a mixture of solvents is added which is suitable for retaining multiple impurities in solution;
• and
• removing the impurity having a tendency to precipitate, which is retained in solution, from the crystal.

A process for the purification of acrylic acid comprising:

• crystallizing a molten material comprising acrylic acid and at least one impurity having a tendency to precipitate;
• adding water to the molten material in a quantity sufficient to retain at least one impurity having a tendency to precipitate in solution, and wherein the mixture comprises two or more impurities having a tendency to precipitate selected from the group consisting of maleic acid, an anhydride of maleic acid, and phenothiazine, a quantitatively more significant impurity having a tendency to precipitate is retained in solution;
• and
• removing the impurity having a tendency to precipitate, which is retained in solution, from the crystal.

A process for the purification of acrylic acid comprising:

• crystallizing a molten material or a mixture comprising acrylic acid and at least one impurity having a tendency to precipitate;
• adding solvent or a solvent mixture to the molten material or the mixture in a quantity sufficient to retain at least one impurity having a tendency to precipitate in solution, wherein the solvent has a superior dissolving capacity for at least one of the impurities having a tendency to precipitate, compared to acrylic acid and wherein the mixture comprises two or more impurities having a tendency to precipitate selected from the group consisting of maleic acid, an anhydride of maleic acid, and phenothiazine, a quantitatively more significant impurity having a tendency to precipitate is retained in solution and wherein a solvent or a mixture of solvents is added which is suitable for retaining multiple impurities in solution;
• and
• removing any residual impurities still precipitating, despite the addition of said solvent or mixture of solvent, from the molten material.

A process for the purification of acrylic acid comprising:

• crystallizing a molten material comprising acrylic acid and at least one impurity having a tendency to precipitate;
• adding solvent or a solvent mixture to the molten material in a quantity sufficient to retain at least one impurity having a tendency to precipitate in solution, wherein the solvent has a superior dissolving capacity for at least one of the impurities having a tendency to precipitate, compared to acrylic acid and wherein the mixture comprises two or more impurities having a tendency to precipitate selected from the group consisting of maleic acid, an anhydride of maleic acid, and phenothiazine, a quantitatively more significant impurity having a tendency to precipitate is retained in solution and wherein a solvent or a mixture of solvents is added which is suitable for retaining multiple impurities in solution;
• and
• removing any residual impurities still precipitating, despite the addition of said solvent or mixture of solvent, from the molten material.

A process for the purification of acrylic acid comprising:

• crystallizing a molten material comprising acrylic acid and at least one impurity having a tendency to precipitate;
• adding water to the molten material in a quantity sufficient to retain at least one impurity having a tendency to precipitate in solution, and wherein the mixture comprises two or more impurities having a tendency to precipitate selected from the group consisting of maleic acid, an anhydride of maleic acid, and phenothiazine, a quantitatively more significant impurity having a tendency to precipitate is retained in solution;
• and
• removing any residual impurities still precipitating, despite the addition of water, from the molten material.