Selective hydrogenation of phenylacetylene in the

Selective hydrogenation technology of phenylacetylene in the presence of styrene

1 preface

styrene (st) is an important monomer for the production of polystyrene, ABS resin and styrene butadiene rubber. At present, the styrene market gap in China is still large. In order to meet the market needs, in addition to building new styrene units to obtain new styrene production capacity, it is also an effective way to recover styrene from the by-products of other existing units, such as recovering styrene from the pyrolysis gasoline produced by the steam cracking ethylene unit. The cost of recovering styrene from cracked gasoline per ton is only equivalent to 60% - 70% of styrene produced by benzene alkylation and dehydrogenation

for the method of recovering styrene from pyrolysis gasoline, it is generally believed that the feasible method is extraction distillation. However, the chemical structure of phenylacetylene (PA) and styrene is similar, and the interaction between them and extractive distillation solvent is also similar. Therefore, the effective separation of styrene and PA cannot be achieved by extractive distillation. Crude phenylethylene obtained from ethylbenzene dehydrogenation also contains a small amount of PA. The presence of PA will not only increase the consumption of catalyst in anionic polymerization of styrene, but also be harmful to chain length and polymerization speed. Unreacted styrene in polystyrene (PS) will lead to deterioration of properties, such as discoloration, degradation, taste change and odor release. There are many foreign patents and literatures on how to remove PA from styrene, that is, using appropriate catalysts to selectively hydrogenation PA to styrene, but there is no domestic research report in this field

2 phenylacetylene hydrogenation catalyst

many foreign companies have applied for patents for their pa selective hydrogenation catalyst, such as shell company and Dow Chemical Company in the United States, Mitsubishi Petrochemical Co., Ltd. in Japan, Asahi chemical, Japanese chemical, Showa electric, Mitsui East Asia, electrification company and DSM company in the Netherlands. The following mainly introduces the important catalysts of Mitsubishi petrochemical, Dow Chemical and DSM

according to the active components, the main catalysts reported in the patent can be divided into palladium based catalysts, nickel based catalysts, copper based catalysts and multi-component catalysts

2.1 Mitsubishi Oil and Chemical Co., Ltd. reported a series of PA hydrogenation catalysts with palladium as the main active component. The catalyst carrier used by the company is Φ 3x3mm cylindrical γ- Alumina, the catalyst supports that can be used include gel supports synthesized from aluminum, silicon, etc., or diatomite, porous clay, etc. The optimal content of palladium is 0.05% - 0.5% (mass). The catalyst is prepared by impregnation. The general preparation steps are: impregnate with 0.2% - 0.6% (mass) PdCl2 solution according to the needs of the final load of the catalyst Φ 3x3mm cylindrical γ- After alumina, it was dried at 110 ℃ for one day and night, and reduced with hydrogen flow at 400 ℃ for 16 hours to obtain the final hydrogenation catalyst

the patented catalyst of Mitsubishi Petrochemical is generally used under atmospheric pressure ~ 0.98mpa, and the selectivity of the catalyst is low under high pressure. The operating temperature should not be too high, otherwise the proportion of hydrogenation of styrene will increase significantly, usually at ℃. Too low a reaction temperature is detrimental to the stability of catalyst activity. The optimal range of liquid space velocity (LHSV) is 10 ~ 300h-1, and the linear velocity of logistics in the reactor is preferably between 0.05 ~ 4cm · s-1. This is because: if the linear velocity of logistics is 0.05cm · s-1, the polymer will attach too much to the catalyst surface, the catalyst activity will be unstable, and the hydrogenation catalyst efficiency will be low. When the linear velocity of flow is 5cm · s-1, the pressure drop of catalyst bed increases, and stable catalyst activity cannot be obtained. The optimal amount of hydrogen is times that of unsaturated impurities in the raw material. Mitsubishi oiling catalyst is said to be able to handle acetylene content of 1 ~ 1. Diene content 5 Crude phenylethylene. However, the highest conversion rate of PA hydrogenation reported by them was only 88%, which was the result of reaction at reactor linear velocity of 2.00cm · S-1 and 1.06cm · S-1 for 8 hours at 80 ℃, and the conversion rate after 40 days was 84%. The earlier catalyst can only obtain about 40% pa conversion. The study of angel et al. Also showed that the selectivity of Pd/Al2O3 catalyst for selective hydrogenation of PA was ≤ 78%. In addition, they also found that if the hydrogenation catalyst contains iron oxide, the catalyst deactivates faster. Among them, the source of iron oxide may be the iron oxide flying out of the dehydrogenation reactor, and the carbon dioxide generated in the dehydrogenation reactor may cause carbonic acid corrosion in some heat recovery devices. The market of plastic machinery enterprises in China will be more open to the role of iron oxide generated. To this end, they proposed a solution: that is, a pretreatment reactor is set before the hydrogenation reactor to remove iron oxide, and the filler in the pretreatment reactor is iron oxide adsorption or filtration material. The carrier of hydrogenation catalyst, porous inorganic oxide and graphite particles can be used as fillers, which are also good fillers. Because the generated oxide can be completely adsorbed by the magnet, the magnet is also a good filler. If the raw material to be hydrogenated contains water, the catalyst will be poisoned and completely deactivated. Because:

(1) the affinity between water and the catalyst surface is strong, and water covers the catalyst surface

(2) the catalyst is oxidized by water, etc

Mitsubishi Petrochemical also disclosed a kind of two-component catalyst in the early stage -- a catalyst mainly composed of palladium and added with a second element. The preparation method is the same as that of single metal catalyst, and the carrier is still used γ- Alumina, the ratio of two metals is 10:1. The better second elements are sulfur, antimony, lead, etc. At 20 ℃, it is 9 for containing PA, When 60% styrene and 40% ethylbenzene were hydrogenated, most of PA was removed after two hours of reaction. However, the researchers of Mitsubishi petrochemicals believe that the hydrogenation effect of palladium catalyst without adding other elements is good, which may also be one of the reasons why they less develop multi-component catalysts. However, the hydrogenation loss of styrene on one component palladium catalyst is up to 5% (mass)

2.2 catalyst of Dow Chemical Company

the hydrogenation catalyst used by Dow Chemical Company in the early stage was ordinary Pd/C catalyst. When they hydrogenated the C8 fraction of pyrolysis gasoline with 46.96% xylene, 50.33% st, 0.74% pa and the rest non reactive C8, they added 900ml C8 fraction into 3L reactor, added 30g Pd/C catalyst, stirred it, and the reaction temperature was 25 ℃, after 50 minutes, PA could not be detected, but the loss of styrene was not explained. The catalysts available in this process also include Rexroth nickel, Pt, PD, Ru, Rh, Cu, etc. In a patent published by Dao in 1989, four kinds of γ- The hydrogenation of PA with 235 curtain wall supporting device Cu and various other element catalysts prepared by alumina commodity carrier. One catalyst containing 8.39% copper (by mass) and adding a small amount of nickel (Ni), cobalt (CO), molybdenum (MO), silver (Ag) and chromium (CR) can reduce PA in crude phenylethylene from 1.1x to 2 within 72 hours. The use conditions of this catalyst are: atmospheric pressure, 5 ~ 35 ℃, lhsv:h-1, h2:pa ≈ 100 (molar ratio), 2 ~ 3 times of excess H2 dissolved in the monomer, and the polymer content is not greater than 3. In addition, Dow Chemical Company also studied the preparation of supports for hydrogenation catalysts such as platinum (PT), palladium (PD) and copper (Cu), and the required supports γ- Al2O3, containing ≤ 50% (mass) α- Al2O3, 0.15% Si in the form of SiO2 or Na in the form of Na2O, 0.01% (mass) Fe in the form of Fe2O3, requires the specific surface area of the carrier to reach 68 ~ 350m2 · g-1, the requirements for pore distribution are 40 ~ 98% pore diameter 4 ~ 12NM, and 2 ~ 25% pore diameter is carbon fiber filament nm wound on the reel of the mechanical arm. The catalyst prepared by the support reacts at 22 ~ 30%, and the PA content can be reduced below 1x

2.3 DSM catalyst

the disadvantage of palladium catalyst is that when it is used in styrene medium containing a small amount of impurities, the catalyst will be deactivated rapidly when the X axis is the load coordinate, so its service life is very short. DSM company has conducted in-depth research on nickel catalyst and given an industrial scale implementation example (the company has a set of pyrolysis gasoline recovery styrene unit with a production capacity of 27000 tons · year-1)

generally, nickel catalyst will not be selected to replace palladium catalyst, because when acetylene is converted to olefins, the activity and selectivity of nickel catalyst are lower than palladium catalyst. The researchers of DSM company selected the supported catalyst with nickel content of 10% - 25% (mass) for selective hydrogenation of PA and achieved good results. The advantage of this catalyst is that it is cheaper than palladium catalyst, and the commercially available nickel catalyst has greater catalytic activity and specific surface area. The nickel catalyst used is a nickel catalyst on a support, and the applicable support materials include: silicon oxide, α-、θ-、γ- Al2O3, zeolite, carbon and oxidation carriers such as magnesium oxide, titanium oxide and zirconia are preferably used θ- and γ- Al2O3 is used as the carrier

although DSM does not disclose the specific synthesis conditions of the catalyst, the catalyst is prepared by impregnating the carrier with a nickel salt solution to load nickel on the carrier, and water is often used as a solvent. The impregnated carrier is dried, calcined at high temperature, and finally treated with hydrogen at high temperature to activate the nickel oxide supported on the carrier. The high dispersion of nickel on the support makes the support have a large catalytic active surface area. The larger the catalytic active surface area in the catalyst, the better the hydrogenation of PA. The preferred nickel content in the catalyst is 11% to 25% by mass, preferably greater than 11% by mass and less than or equal to 20% by mass. From a technical and economic point of view, the content of nickel catalyst should be kept as low as possible. If the nickel content is large, the catalyst price is high, and when the nickel content becomes large, the dispersion of nickel in the catalyst becomes worse

in addition to nickel, the catalyst can also contain a small amount of other compounds that enhance catalytic activity and selectivity. Examples of these compounds are chromium, gold, rhodium and ruthenium. The catalyst can also be modified by sulfur compounds

2.4 other catalysts

Asahi Kasei discloses a high-temperature high-speed PA hydrogenation catalyst composed of more than one element of tungsten and zinc. It is found that trace acetylene compounds contained in aromatic vinyl compounds can be removed through the catalyst bed containing more than one element of tungsten and zinc under the condition of water vapor and high temperature. This catalyst contains more than one element of tungsten and zinc. It is best to use its oxide state, and alumina, silicon dioxide, etc. can be used as the carrier. The recommended reaction temperature is ℃. If the reaction temperature is too high, vinyl compounds will undergo hydrogenation reaction; However, if the temperature is too low, the target reaction will be slow. Unlike the palladium catalyst of Mitsubishi oiling, this catalyst has no special limit on the amount of water required in the reactant. It is recommended that the molar ratio of water to benzene ring be 1 ~ 30 and the space velocity be H-1

one of its examples is the preparation of tungsten oxide into φ 3mm spherical catalyst, styrene and steam containing 1.1xpa are introduced into the 25.4mm reactor equipped with 100ml catalyst, the molar ratio of the two is 1:10, and the space velocity is 10000h-1. The temperature of catalyst bed is controlled at 300% by heating furnace. After passing through the catalyst bed, the PA content decreased from 1.1x to 2x. The catalyst can be used repeatedly

carturan et al. Showed that single component Pd catalyst was more suitable for hydrogenation reaction, while Pt catalyst was not suitable for hydrogenation reaction because of its low selectivity. For PD Pt alloy catalyst, with the increase of Pt content