JPS596905B2 - Corrosion-resistant materials for chloroprene production plants - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a Ti-Pd alloy consisting of Pd of 0.15% or more and the balance substantially of Ti, which exhibits excellent corrosion resistance when treating a chloroprene production process liquid.

A process liquid treated in the production of chloroprene, for example, 3,4 dichlorobutene (CH2CHCH(1-CH
From 2(1), chloroglene (CH2=C(1-CH
The equipment materials used to produce CH2) are subject to the presence of moisture, exposure to high temperatures of around 100°C, and the presence of hydrochloric acid produced by the decomposition of chlorinated hydrocarbons.
In addition, due to the structure of the device, and because the rubber component easily polymerizes, it is easy to form a film and crevice corrosion is likely to occur, making it highly corrosive. Currently, materials with appropriate corrosion resistance have not yet been obtained for devices.

For example, when looking at materials for monomer strippers that are part of these processes, the generally widely used type 316 or 316 Lm austenitic stainless steel suffers from severe general corrosion and corrosion mainly in the welds and surrounding areas. Due to the frequent stress corrosion cracking that occurs at °C, the lifespan of °C towers is relatively short (・.

In addition, Hastelloy B, a high-grade metal material made by adding Mo and Fe to Ni, is an excellent corrosion-resistant material in a reducing atmosphere, but local corrosion and cracks occur near the weld in this atmosphere, making it difficult to withstand use. It's only about a year at most.

As mentioned above, conventional materials have a short lifespan, which not only increases the cost of replacing equipment, but also causes problems in operations due to the replacement work.

Under these circumstances, the present inventors conducted research on corrosion-resistant metal materials for various chloroprene manufacturing process liquids, and as a result found that a Ti alloy containing a small amount of Pd has excellent corrosion resistance, and completed the present invention. This is what I did.

Although Ti has excellent corrosion resistance in an oxidizing atmosphere, it is severely attacked in a reducing atmosphere, such as a hydrochloric acid or sulfuric acid solution.

However, when Pd is added to this, anodic passivation is imparted, so it is presumed that the corrosion resistance is improved.

Therefore, the more Pd there is, the greater the effect, so it is desirable to add a large amount, but since Pd is very expensive, 0.15%
A value of about 0.20% or more is practical.

If it is less than 0.15%, corrosion resistance will not be sufficient.

Next, the corrosion-resistant material of the present invention was tested in a monomer stripper, which is a part of the highly corrosive process of a chloroprene manufacturing plant.
Or, it will be explained by comparing it with Hastelloy alloy and the like.

The present inventors have developed Ti-Pd alloy as well as SUS31
6, SUS316L, and commercially available alloys were inserted into the bottom and top stages of a monomer stripper, and the corrosion resistance of each material was actually tested.

The test results are shown in Tables 1 and 2, respectively.

Note that the values in parentheses in Table 1 are the results for the second time.

All values are obtained from tests lasting more than one month.

The reason why corrosion is more severe at the bottom is because the temperature is higher than at the top.

As is clear from these tables, SUS 3 1 6 and austenitic stainless steel are highly corroded, and if welds are present, cracks occur frequently, making the device unusable in a short period of time.

This includes C r. Even in high-grade stainless steel with a larger amount of Ni or Mo added, the effect is recognized, but it is slight and the degree of erosion is O. lm/year or more, and is still not suitable as a corrosion-resistant material.

Among the stainless steels, high Cr type duplex stainless steel containing 25% Cr is the most corrosion resistant.

Although Ni-based alloys seem to be suitable materials because of their low corrosion, they cannot be used because, as mentioned above, they cause localized corrosion near welds and cracks easily.

The Ti-Pd alloy of the present invention has 0. 1 mJIl/ye
It is clear that the corrosion rate is less than ar and that the material is fully usable.

In addition, a field test was conducted for 3 months as a seal plate material for a tray, but almost no change occurred.

Thus, it is clear that the corrosion-resistant material of the present invention is far superior to conventional materials in field tests.

This not only results in significant cost savings, but also eliminates the need for time-consuming and operational problems caused by replacing towers due to corrosion, which is a huge benefit.

Claims (1)

[Claims] 1. A titanium-palladium alloy for use in a chloroprene manufacturing process liquid treatment equipment containing 0.15 to 0.2% palladium and the remainder being substantially titanium.