Processes for preparing organic compounds having improved color characteristics

This is a divisional application of prior U.S. application Ser. No. 10/635,983 filed on Aug. 7, 2003, the disclosure of which is incorporated herein by reference.

This disclosure relates to processes for preparing carboxylic acids, ketones, and esters having improved color characteristics.

There are numerous known processes for producing carboxylic acids, ketones, and esters. For example, U.S. Pat. Nos. 3,887,595, and 6,211,405 disclose processes for producing carboxylic acids by carbonylating olefinically unsaturated compounds such as alcohols, ethers, and esters. U.S. Pat. No. 5,281,752 discloses a process for producing lower carboxylic acids by reacting alkanes with carbon dioxide. U.S. Pat. No. 5,091,587 discloses a process for the preparation of ketones which comprises reacting a conjugated diolefin and water in the liquid phase in the presence of a catalyst system comprising: a group VIII metal compound and a source of protons. U.S. Pat. No. 4,010,188 discloses a process for the oxidation of saturated hydrocarbons in the presence of a catalyst to produce acids. U.S. Pat. No. 3,293,292 discloses a liquid phase oxidation of butane in the presence of a cobalt containing catalyst system to produce carboxylic acids. U.S. Pat. No. 4,487,720 discloses a process of the production of acids by oxidizing saturated aliphatic aldehydes in the presence of catalyst systems. U.S. Pat. No. 5,026,903 discloses a process for producing of glycol esters such ethylidene diacetate by the reaction of mixtures of dimethyl acetal, methyl acetate and carbon monoxide. The catalyst system charged to the reactor contains rhodium atoms, lithium iodide and optionally an organic ligand. U.S. Pat. No. 4,268,689 also discloses a process for the production of glycol esters.

A problem associated with carboxylic acids, ketones, and esters production and storage is color quality. To use carboxylic acids and other organic compounds for certain applications, the compounds must exhibit a light color. Generally speaking, the darker color values for these organic compounds do not affect the functionality of the compounds for most applications. However, most purchasers of these organic compounds believe that “water white” compounds are of higher quality than compounds possessing higher color properties and demand water white organic compounds. Typically, compounds exhibiting an APHA color (Pt—Co) of 15 or less are considered to be of water white quality. If the compounds are not of a water white quality, expensive purification schemes must be undertaken to purify the product to achieve acceptable color characteristics. For example, expensive and multiple hydrogenation and acid treatment processes may be necessary to achieve a compound having water white characteristics.

This disclosure relates to processes for preparing certain organic compounds such as carboxylic acids, ketones, and esters having low color characteristics. A first embodiment involves combining water with the organic compound at a concentration of 100 ppm to 50,000 ppm water. A second embodiment involves removing a product stream containing the organic compound from a reaction system in which the organic compound is prepared and introducing the product stream into a distillation column having a lower portion and an upper portion wherein the upper and lower portions are maintained at a temperature of from about 23° C. to about 250° C. and at a pressure of about 10.1 kPa to about 202.6 kPa. Subjecting the product stream to distillation under these conditions thermally breaks down, or removes, precursors of color bodies, having boiling points lower than the boiling point of the product being produced.

A third embodiment includes combining the process of the first two embodiments by producing a product that has been subjected to isolation and purification in a system including a distillation column operating at the temperatures and pressures described above and combining water with the organic compounds as described above.

These processes may be implemented to prepare carboxylic acid, ketone, and glycol ester products having stable APHA color values of 15 or less. Having a stable APHA color of 15 or less means that the products will exhibit a color value within this range after being boiled for at least one hour at one atmosphere (101.3 kPa) pressure.

This disclosure relates to processes for preparing certain carboxylic acids, ketones, and esters having low color properties. The organic compounds include C₁ to C₆ carboxylic acids, ketones having boiling points from 54° C. to 170° C., and esters having boiling points from about 168° C. to about 250° C. These various organic compounds may be the reaction product of a variety of processes for producing these compounds. For example, carboxylic acids are often commercially prepared by carbonylation of alcohols, esters, or ethers to produce the corresponding carboxylic acid. A widely used commercial carbonylation process is the production of acetic acid from carbonylation of methanol. Of course, the carbonylation process is applicable to the carbonylation of higher homologues of methanol to form acids that are the higher homologues of acetic acid. The carboxylic acids useful in the preparation process described in this disclosure may be the reaction product of other processes such as oxidizing corresponding aldehydes, alkanes, and alkenes.