1,4-Cyclohexanedimethanol Process via Recycled Alcohol Feedstock
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Solution Overview
Problem
The existing process for producing 1,4-cyclohexanedimethanol from dimethyl terephthalate is inefficient due to high energy consumption, equipment costs, and purification challenges, including the formation of solids that reduce heat exchange efficiency and the need for additional purification steps to remove methanol and catalysts.
Innovation Solution
An integrated process where the by-products from the hydrogenation step are recycled as raw materials for the esterification of terephthalic acid, combining esterification and purification steps to produce 1,4-cyclohexanedimethanol, using (4-methylcyclohexyl)methanol as the alcohol feedstock, and involving multiple hydrogenation and distillation steps to recover the product.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If dimethyl terephthalate is prepared by esterification of terephthalic acid with methanol under high pressures and temperatures, then the esterification reaction proceeds effectively, but expensive specialized process equipment is required and energy consumption increases
Solution Approach 1:
The patent changes the esterification parameters by using (4-methylcyclohexyl)methanol instead of methanol, and conducting the reaction at lower temperatures and pressures. This alternative alcohol feedstock allows the esterification to proceed under milder conditions, reducing energy consumption while maintaining effective conversion of terephthalic acid to the diester
2Productivity
If dimethyl terephthalate is prepared by esterification of terephthalic acid with methanol, then the esterification reaction proceeds effectively, but expensive specialized process equipment is required
Solution Approach 1:
The patent changes the esterification parameters by using (4-methylcyclohexyl)methanol instead of methanol, and conducting the reaction at lower temperatures and pressures. This alternative alcohol feedstock allows the esterification to proceed under milder conditions, reducing energy consumption while maintaining effective conversion of terephthalic acid to the diester
3Productivity
If dimethyl terephthalate is prepared by esterification of terephthalic acid with methanol, then the esterification reaction proceeds effectively, but DMT tends to form solids within the reflux zones that cause plugging and reduce heat exchange efficiency
Solution Approach 1:
The patent changes the esterification parameters by using (4-methylcyclohexyl)methanol instead of methanol, and conducting the reaction at lower temperatures and pressures. This alternative alcohol feedstock allows the esterification to proceed under milder conditions, reducing energy consumption while maintaining effective conversion of terephthalic acid to the diester
4Reliability
If DMT is distilled prior to hydrogenation to remove partial esterification products and catalysts, then catalyst poisoning is prevented, but additional purification steps and processing time are required
Solution Approach 1:
The patent removes the intermediate distillation step entirely by using an alternative esterification process that produces a cleaner diester product. The use of (4-methylcyclohexyl)methanol and modified reaction conditions eliminates the formation of problematic by-products that would require removal, allowing the diester to be directly hydrogenated without intermediate purification
Solution Approach 2:
The modified esterification process is self-purifying in that it naturally produces a cleaner product stream that does not require additional distillation steps. The alternative alcohol feedstock and reaction conditions result in a diester that is ready for hydrogenation without needing to remove catalysts or by-products
5Productivity
If the hydrogenation of DMT releases methanol, then the hydrogenation reaction proceeds effectively, but additional purification and processing steps are required to recover and recycle methanol
Solution Approach 1:
The patent changes the hydrogenation substrate from dimethyl terephthalate to the diester of terephthalic acid with (4-methylcyclohexyl)methanol. This structural change in the ester group means that upon hydrogenation, the by-product is (4-methylcyclohexyl)methanol rather than methanol. The alternative alcohol feedstock allows the esterification to proceed under milder conditions
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This process simplifies the purification of 1,4-cyclohexanedimethanol, reduces energy consumption and equipment costs, and improves the efficiency of the production process by recycling by-products, thereby enhancing the overall production efficiency and reducing operational expenses.
Implementation Method 1
contacting terephthalic acid and (4-methylcyclohexyl)methanol in a mole ratio of alcohol to acid of at least 2:1, in a reaction zone at a temperature of 200°C to 300°C under superatmospheric pressure, while removing water from the reaction zone, to form an esterification product mixture
Implementation Method 2
contacting the esterification product mixture with hydrogen in a first hydrogenation zone in the presence of a catalyst effective for hydrogenation of an aromatic ring to produce a liquid effluent comprising bis(4-methylcyclohexyl)methyl) cyclohexane-1,4-dicarboxylate
Implementation Method 3
contacting the effluent from the first hydrogenation zone with hydrogen in the presence of an ester hydrogenation catalyst in a second hydrogenation zone to produce a hydrogenation product comprising 1,4-cyclohexanedimethanol
Implementation Method 4
distilling the hydrogenation product from step (iii) to recover a distillate comprising a majority of the (4-methylcyclohexyl)methanol in the hydrogenation product and a distillation bottoms comprising a majority of the 1,4-cyclohexanedimethanol
Implementation Method 5
allowing the distillation bottoms to form an lower layer comprising a majority of the 1,4-cyclohexanedimethanol in the distillation bottoms and a upper layer comprising a majority of the 4,4'-oxybis(methylene)bis(methylcyclohexane)
Data Source
AI summary
Disclosed is an integrated process for the preparation of 1,4-cyclohexanedimethanol from terephthalic acid. Terephthalic acid is esterified with (4-methylcyclohexyl)methanol and the terephthalate ester hydro genated to 1,4-cyclohexanedimethanol in a 2-stage process. The (4-methylcyclohexyl)methanol that is formed during the hydrogenation step is recycled to the esterification reaction. Also disclosed is a method for purifying and recovering the 1,4-cyclohexanedimethanol product.