KR950008198B1 - A method for controlled catalyst sulfidation - Google Patents

Abstract

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Description

How to Control Catalytic Sulfation Reactions

Hydrogenation of carbon monoxide (Fisher-Tropsch-methanation and related processes) and hydrogenation of polyunsaturated organic compounds are long-standing examples of industrial large-scale hydrogenation processes in which selectivity of the catalyst is most important in terms of economics. In order to maximize the yield of the desired product in the reactor, waste of raw materials resulting from the production of useless byproducts should be avoided. In addition (and more importantly), the energy and material costs of the separator should be minimized. In light of today's trends in the energy market, energy-consuming unit operations such as varieties are expected to increase the total cost of future manufacturing industries. This trend is also reflected in intensive research activities in catalyst development and reactor design over the last 15 years.

The requirement for high catalytic activity (high production capacity per unit mass of catalyst) is often at odds with the requirement for high selectivity (high preference for any desired reaction and low activity for other undesired reactions). Some representative examples of commercially important hydrogenation processes that conflict with catalytic activity and selectivity include the following:

Partial hydrogenation of polyunsaturated natural triglycerides to produce fatty acids. In this case, saturated triglyceride (stearin) is not preferable.

Partial hydrogenation of acetylene to ethene, ethene is probably the most important of all petrochemical compounds and is used as a starting material in the manufacture of plastics such as polyethene and PVC. The saturated product (ethane) of this hydrogenation reaction can only be used as fuel.

Partial hydrogenation of 2-ethyl-hexanal to 2-ethyl-hexanal to produce octanoic acid. Fully-hydrogenated products (2-ethyl-hexanol) have completely different properties and are used as PVC-softeners.

The development of selective catalysts has been carried out mainly as listed below:

* Substitution of active metal components. Palladium, in contrast to nickel, has been shown to be very selective, for example in the hydrogenation of acetylene and unsaturated aldehydes. Changes in the active ingredient are often associated with an increase in each of the catalysts (as in this case).

Alloys of active metals with other less active metals, Ni / Cu alloys, in some cases, exhibited significantly higher selectivity than conventional nickel catalysts. However, a problem is that one of the components exhibits surface integration at high temperatures.

Poisoning of the catalyst by sulfur compounds. Sulfur, which generally causes serious problems due to unwanted catalyst deactivation, forms new types of catalyst sites with substantially higher selectivity than the original ones interacting with metal catalysts. However, such techniques must be applied under tightly controlled methodological conditions, or there is a risk of total inactivation.

Nickel / sulfur-catalysts (NiS, Ni ₂ S and Ni ₃ S ₂ ) have long been known to provide much higher selectivity for the hydrogenation of cooking oils than nickel catalysts.

In the past, elemental sulfur was added to the hydrogenation reactor for the purpose of modifying the nickel catalyst, but the results were generally difficult to predict. Ni / S-catalysts are commercially available today, resulting in more reproducible results—higher selectivity and lower activity compared to conventional nickel catalysts.

The problem in the manufacturing industry is that one must select one of the limited number of catalysts available on the market at a significantly increased cost as the requirements for catalyst specificity increase.

The present invention is directed to a new and flexible method of applying to a particular optimum level of catalytic poisoning that a buyer can use directly in his plant. In this way it is possible to prepare catalysts which are most suitable for temporary raw material storage and the desired products, using conventional nickel-catalyst as starting material.

Technology

The process of the present invention is optionally based on compound adsorption, which in this case means the addition of a small amount of H ₂ S at a low rate for a certain time or through a certain number of pulses of the reactor in which the main reaction proceeds. . H ₂ S, which is irreversibly adsorbed at the appropriate temperature, is not adsorbed anywhere on the catalyst surface, because much of the surface is covered by adsorption with reaction materials. In addition, the method of the present invention utilizes a mass transfer effect: in reaction conditions with very high hydrogenation rate constants as well as H ₂ S adsorption, the rate observed is entirely controlled by the external mass transfer rate of H ₂ and H ₂ S respectively. do. The concentration of these molecules at the catalyst surface (which causes poisoning) is then much lower than the corresponding saturation concentrations, which is effectively used to control the poisoning process dynamically and thermodynamically.

Experiment method

In a glass reactor equipped with a turbine impeller, 400 ml of sunflower oil and 20 g of Ni-catalyst (82% Ni supported on alumina-silica-carrier) are charged. The mixture is heated to 180 ° C. at a stirrer speed of 1200 r · pm under a nitrogen atmosphere before the hydrogenation is initiated. During the poisoning phase, the hydrogen stream is 25 ml / s (1 atm, 25 ° C). Known volumes (5.43 ml) of gas dosing loops are used to inject different amounts of H ₂ S into the mixing flask, from which the main stream of hydrogen carries H ₂ S into the hydrogenation reactor. Continuously check the results obtained from different poisoning experiments using detectors of on-line flamephotomultiplicator, which can quickly and easily measure the H ₂ S-absorption of the catalyst. . The hydrogenation time was 70 minutes in all cases, regardless of the amount of H ₂ S added.

Using the method described above, eight different catalyst samples were prepared by adding 4, 8, 10, 15, 20, 25, 34 and 60 loops of H ₂ S. 0.12 g of catalyst is taken from each of these samples to perform activity and selectivity tests in a slurry reactor operating under kinetic conditions (without removing mass transfer restrictions). The conditions in the slurry reactor were as follows: P _H2 = 5.0 atm, temperature = 180 ° C, hydrogen flow rate = 5 ml / s (1 atm, 25 ° C), catalyst load = 0.12 g and stirring rate = 180 r.pm without poison A commercial Ni / S catalyst having the same Ni content as the nickel catalyst was used as a control.

The results summarized in Table 1 show that the highest concentration of mono-unsaturated fatty acids is almost independent of the degree of poisoning, whereas the trans / cis-ratio of mono-unsaturated fatty acids is directly related to the degree of poisoning. have. In addition, it can be seen from this table that the activities of the Ni / S catalyst according to the present invention are significantly higher in all cases than the activities of commercial Ni / S-catalysts having the same Ni-content.

In summary, the present invention clearly demonstrates that the selectivity of conventional nickel catalysts provides a facile method of modifying their selectivity while the activity is still higher than that of commercial Ni / S catalysts. It can also be seen that the method of the present invention provides a method that allows for a flexible response to changing operating conditions in the platter by allowing only a limited portion of the catalyst surface to be poisonous.

TABLE 1

Note 1. The composition is mol%.

Note 2. All hydrogenation was carried out at 5 bar, 180 ° C.

Activity comparison of the samples in initial reaction rate

Claims (1)

A method for controlling a catalytic sulfidation reaction, characterized in that during the hydrogenation of natural oils, H ₂ S is added to a reverse phase hydrogenation reactor to sulfide the nickel-containing catalyst so that the catalytic sulfidation proceeds simultaneously with the hydrogenation reaction.