High hydrocarbon space velocity process for preparing...

Details High hydrocarbon space velocity process for preparing... High hydrocarbon space velocity process for preparing...

2000-11-08

2003-09-16

Richter, Johann (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Carboxylic acids and salts thereof

C562S512200

Reexamination Certificate

active

06620968

ABSTRACT:

This invention relates to an improved process for preparing unsaturated aldehydes and acids utilizing high load reaction conditions. In particular, the invention relates to a process for preparing (meth)acrolein and/or (meth)acrylic acid from a reactive hydrocarbon utilizing a high reactive hydrocarbon space velocity thereby providing a process having increased capacity and throughput.
Unsaturated aldehydes and carboxylic acids are important commercial chemicals. Of particular importance are (meth)acrylic acid and (meth)acrolein. The highly reactive double bond and acid/aldehyde function of (meth)acrylic acid and (meth)acrolein make them especially suitable as a monomer or as a manufacturing feedstock which may be polymerized alone or with other monomers to produce commercially important polymers. These unsaturated acids/aldehydes are also useful as a starting material for esterification to produce commercially important (meth)acrylate esters or for producing other material using other reaction mechanisms. Such materials derived from (meth)acrylic acid or (meth)acrolein are useful as plastic sheets, parts, paints and other coatings, adhesives, caulks, sealants, and detergents as well as other applications.
The chemical reactions for the preparation of (meth)acrylic acid and/or (meth)acrolein are fairly well known. For instance, the preparation of acrylic acid from propylene generally proceeds in a vapor phase two step catalytic oxidation reaction. In the first step propylene is oxidized in the presence of oxygen, diluent inert gasses, water vapor, and appropriate catalysts to produce acrolein according to equation (I):
C
3
H
6
+O
2
→C
2
H
3
CHO+H
2
O+heat  (I).
The acrolein is then oxidized, in a second step, in the presence of oxygen, diluent inert gasses, water vapor, and appropriate catalysts to form acrylic acid according to equation (II):
C
2
H
3
CHO+½O
2
→C
2
H
3
COOH+heat  (II).
The two stage vapor phase catalytic oxidation of propylene to acrylic acid is generally performed using-either tandem reactors wherein a separate reactor is utilized for each step or stage (e.g., see the description in U.S. Pat. No. 4,873,368) or by utilizing one reactor to perform both steps (e.g., see the description in U.S. Pat. No. 4,256,783). Furthermore, the acrolein may be prepared according to Equation (I) and then utilized as a feedstock for the preparation of various other materials.
The preparation of methacrolein and methacrylic acid from isobutylene proceeds in a similar manner.
It is known in the art that the productivity of such (meth)acrolein and/or (meth)acrylic acid manufacturing processes may be increased by feeding a higher concentration of the starting hydrocarbon to the reactor or by increasing the space velocity of the total reactant feed. For instance, see U.S. Pat. No. 5,929,275 which discloses a propylene space velocity of 128 hr
−1
in a process for making acrolein from propylene.
The reactive hydrocarbon space velocity, defined below, is a measure of the volume of reactive hydrocarbon which contacts a particular volume of catalyst per unit time. Consequently, when the concentration of the reactive hydrocarbon or the total space velocity is changed the reactive hydrocarbon. space velocity will change. For instance, when the reactive hydrocarbon concentration or the total space velocity is raised the reactive hydrocarbon space velocity will rise giving rise to higher load conditions.
However, attendant with such reaction conditions are several problems. For instance, in the preparation of acrolein and/or acrylic acid when propylene in the reactant composition is fed at high propylene concentrations or fed at higher space velocity, because each step of the two step oxidation of propylene to acrylic acid is highly exothermic, as the propylene concentration and/or space velocity get higher there is a danger that the reaction may proceed too quickly and become difficult to control. In extreme cases, catastrophic events may occur such as a runaway reaction.
Increased heat production from these reaction conditions also may lead to an increase in so-called hot spot formation and in an increase in the temperature maximum at a particular hot spot. Hot spots are maximums through which the reaction temperature of a particular reaction passes through as the reactants flow through the contact tube. Such hot spots can result in shortened catalyst life and impaired selectivity for the desired product.
Consequently, the oxidation of propylene to acrylic acid is generally practiced in the art utilizing a propylene concentration in the reactant gas feed composition of between 4 and 7 volume percent of the total reactant feed composition with a suitable space velocity. Typically, in the prior art, the reactive hydrocarbon space velocity is in a range of from 75 to 100 hr
−1
. Generally, it is acknowledged in the art that such operating parameters will allow suitable safety with acceptable productivity and that operation outside these ranges is risky.
However, in the present day production of, for instance acrylic acid, it is a constant goal of manufacturers to gain the most productivity from manufacturing processes. It is thus a constant goal to be able to operate under high load conditions, i.e., greater than 100 hr
−1
reactive hydrocarbon space velocity to achieve such increased productivity.
U.S. Pat. No. 4,203,906 describes a single reactor system for preparing acrylic acid from propylene utilizing (see Example 5) a reactive hydrocarbon space velocity of 94.5 hr
−1
.
U.S. Pat. Nos. 4,365,087 and 4,873,368 have dealt with the problem of increasing process productivity/capacity by raising the propylene concentration. However, the reactions were run with a higher contact time (lower space velocity) for the starting reactants. As a result the reaction was run at typical reactive hydrocarbon space velocities of about 85 to 90 hr
−1
(see for instance Example 1 of '087 and Examples 1-3 of '368).
U.S. Pat. No. 5,929,275 describes processes for the preparation of acrolein using reactive hydrocarbon space velocities from 100 to 128 hr
−1
(see the Examples). However, the control of hot spot formation under high load conditions is effected by controlling the amount of the catalytically active component to be loaded on an inactive carrier, the particle size of the catalyst, the particle size of the carrier and the calcining temperature of the catalyst-loaded carrier.
The present inventors have now discovered that high load conditions including increased reactant concentration and/or increased space velocity, heretofore thought unavailable, may be utilized in (meth)acrylic acid/(meth)acrolein manufacturing processes. Accordingly, a novel process for preparing (meth)acrylic acid and/or (meth)acrolein is described herein wherein the following advantages are provided:
(1) increased throughput/capacity is provided without additional capital expenditure;
(2) increased throughput/capacity is provided without unacceptable additional catalyst life reduction; and
(3) product yield loss is more than compensated for by higher throughput.
In one aspect of the present invention, there is provided a catalytic vapor phase oxidation process comprising (A) providing an oxidation reactor comprising a plurality of contact tubes disposed in a reactor shell, the inside of the reactor shell being divided into at least first and second heat transfer zones through each of which a heat transfer medium passes; each of said contact tubes containing at least two oxidation catalysts, said at least two oxidation catalysts being jointly capable of effecting the oxidation of a reactive hydrocarbon to a product gas comprising (meth)acrylic acid; said contact tubes containing at least two oxidation catalysts being packed with said at least two oxidation catalysts in such a manner so as to provide a peak-to-salt temperature sensitivity of not more than 9° C.; and (B) feeding a reactant composition comprising (i) at least o

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