Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
1999-05-18
2003-04-08
Nazario-Gonzalez, Porfirio (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C562S535000, C562S549000, C568S477000, C568S478000, C568S479000
Reexamination Certificate
active
06545178
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method for the production of acrolein and acrylic acid. More particularly, in the production of acrolein and acrylic acid by the catalytic gas phase oxidation of propylene with a molecular oxygen-containing gas, the present invention relates to a method for enabling acrolein and acrylic acid to be stably produced with a high yield for a long time while effectively repressing the formation of such by-products as various aldehydes, carboxylic acids, high boiling compounds, and tarry substances without impairing the performance of a catalyst.
2. Description of the Related Art
The practice of producing acrolein and acrylic acid by the catalytic gas phase oxidation of propylene with a molecular oxygen-containing gas is widely prevailing on a commercial scale. Generally, the production of acrylic acid is effected by a two-step reaction which comprises a former step of producing acrolein mainly by the gas phase oxidation of propylene with a molecular oxygen-containing gas and a latter step of further oxidizing the reaction gas containing the acrolein thereby producing acrylic acid.
At the former step for oxidizing propylene with a molecular oxygen-containing gas, however, a side reaction occurs to produce organic acids such as terephthalic acid and maleic acid, high boiling compounds, and tarry compounds besides the main reaction which produces acrolein. As a result, these by-products contaminate the reaction apparatus and, in an extreme case, prevent the reaction apparatus from being normally operated because they form deposits such as carbonized materials, aggravate pressure drop, and plug pipes or degrades the quality of product. If the reaction apparatus is provided with purification means for the removal of these by-products, the provision will entail such problems as increasing the cost of equipment, boosting the cost of production. Further, acrolein and other highly reactive compounds give rise to after reaction.
Heretofore, for the purpose of repressing these side reactions, such measures as suddenly cooling the outlet gas of a reaction vessel of the former step thereby repressing the formation of side reactions or retaining the temperature of the outlet gas of the reactor above a fixed level thereby repressing the contamination of a reaction apparatus due to the deposition of high boiling compounds and tarry compounds have been resorted to (as disclosed in U.S. Pat. No. 3,876,693, for example).
These measures, however, necessitate special devices adapted exclusively for their own purposes and entail consumption of a large amount of energy for cooling or heating and consequently prove economically disadvantageous because of an inevitable addition to the cost of production. Besides, they are deficient in effect. Especially, they are not ratable as fully effective regarding the contamination of the apparatus with organic acids, high boiling compounds, and tarry compounds, the deposition of carbonized materials, and the deterioration of the quality of product.
As concerns the reclamation of a reaction product gas as part of a material gas, a method for limiting the amount of organic compounds such as organic acids has been proposed (as disclosed in U.S. Pat. No. 4,147,885, for example). This patent application, however, has absolutely no mention of the quality of the raw material propylene gas.
It is an object of this invention, therefore, to provide in the production of acrolein and acrylic acid by the catalytic gas phase oxidation of propylene with a molecular oxygen-containing gas, a method which enables acrolein and acrylic acid to be stably produced with a high yield for a long time from propylene by effectively repressing such side reactions as are responsible for the formation of organic acids, high boiling compounds, and tarry compounds, the deposition of carbonized materials, and the deterioration of the quality of products.
This invention, in a process of two-step reaction for the production of acrylic acid by the catalytic gas phase oxidation of propylene with a molecular oxygen-containing gas, is directed at providing a method for stably and continuously for a long time producing acrolein mainly from propylene with a high yield and consequently producing acrylic acid ultimately with a high yield by effectively repressing such side reactions as are responsible for the formation of organic acids, high boiling compounds, and tarry compounds, the deposition of carbonized materials, and the deterioration of the quality of products.
SUMMARY OF THE INVENTION
We have performed a study with a view to solving the problems encountered in the production of acrolein and acrylic acid by the catalytic gas phase oxidation of propylene with a molecular oxygen-containing gas as described above and, as a result, have acquired the following knowledge.
(1) The organic acids, high boiling compounds, and tarry compounds are formed by the side reactions irrespectively of differences in reaction conditions, activity of catalyst, or selectivity of the formation of acrolein.
(2) While these by-products occur only in extremely small amounts as compared with acrolein and acrylic acid which are main products, they form a serious hindrance to a continuous and stable operation.
(3) The amounts of their formation are affected more by the impurities contained in the raw material propylene and their amounts than by the performance of a catalyst.
(4) The presence of unsaturated compounds other than propylene largely affects the performance of a catalyst and the amounts of by-products to be formed.
(5) The effects on the performance of a catalyst and the amounts of by-products to be formed increase in accordance as the degree of unsaturation of impurities in propylene is heightened or the basicity gains in intensity.
Then, we have continued the study and have discovered that the side reactions are effectively repressed and the problems mentioned above are consequently solved by lowering the total content of unsaturated hydrocarbons of 2-5 carbon atoms other than propylene in the raw material propylene below 500 ppm (by weight). The present invention has been perfected based on this knowledge.
Specifically, in the production of acrolein and acrylic acid by the catalytic gas phase oxidation of propylene with a molecular oxygen-containing gas in the presence of an oxidation catalyst, this invention concerns a method for the production of acrolein and acrylic acid which comprises lowering the total content of unsaturated hydrocarbons of 2-5 carbon atoms (excluding propylene) in the raw material propylene below 500 ppm (by weight).
Further in the production of acrylic acid by a two-step reaction comprising a former step for producing acrolein mainly by the catalytic gas phase oxidation of propylene with a molecular oxygen-containing gas in the presence of an oxidation catalyst and a latter step for producing acrylic acid by the gas phase oxidation of the acrolein-containing reaction gas in the presence of an oxidation catalyst, this invention concerns a method for the production of acrylic acid which comprises lowering the total content of unsaturated hydrocarbons of 2-5 carbon atoms (excluding propylene) in the raw material propylene below 500 ppm (by weight).
DESCRIPTION OF THE PREFERRED EMBODIMENT
The characteristic feature of this invention comprises using a raw material propylene of which the total content of unsaturated hydrocarbons of 2-5 carbon atoms except that propylene (hereinafter referred to simply as “unsaturated hydrocarbons of 2-5 carbon atoms”) is below 500 ppm (ppm by weight; applicable similarly hereinafter). The content of the unsaturated hydrocarbons of 2-5 carbon atoms is preferred to be not more than 450 ppm, more preferred to be not more than 300 ppm, and particularly preferred to be not more than 200 ppm.
In this invention, propylene having a content of unsaturated hydrocarbons of 2-5 carbon atoms of not more than 500 ppm, preferably not more than 450 ppm, more preferably not more than 300 ppm, and par
Kawajiri Tatsuya
Nakamura Daisuke
Tanimoto Michio
Fish & Richardson P.C.
Nazario-Gonzalez Porfirio
Nippon Shokubai Co. , Ltd.
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