In this work, comparative testing of the activity of low-percentage palladium and palladium-nickel catalysts supported on activated diatomite with a commercial nickel catalyst from BASF was carried out in the process of hydrogenation of polyalphaolefins (PAO-4). It has been found that palladium catalysts carry out the process under milder conditions, demonstrate higher activity compared to nickel catalysts, significantly reduce the process time, and provide a higher degree of hydrogenation. The activity of bimetallic catalysts is lower than that of monometallic palladium catalysts. The physicochemical characteristics of catalysts and polyalphaolefin oils also have been determined.
Research Article
Palladium-nickel supported and palladated activated diatomite as an efficient catalyst for poly-α-olefins hydrogenation
https://doi.org/10.21203/rs.3.rs-2343781/v1
This work is licensed under a CC BY 4.0 License
Journal Publication
published 26 Jun, 2023
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Hydrogenation
Catalyst
Diatomite
Poly alpha-olefin
Synthetic oils derived from α-olefins are mainly used to produce the universal automotive, multigrade engine and transmission oils, hydraulic fluids, as well as industrial oils for refrigerators, compressors, and other units operating under heavy loads at elevated temperatures. They are also used as an engine oil for powerful medium-speed diesel engines and diesel locomotives [1,2].
Poly-α-olefins (PAOs) are obtained by oligomerization of higher α-olefins (for example, decene-1) on various homogeneous and heterogeneous acid catalysts, controlling the molecular weight of oligomers and their molecular weight distribution during the synthesis [3–6].
The products of α-olefin oligomerization contain unsaturated double bonds, so they must be subjected to hydrogenation to saturate the bonds and achieve oxidation stability [7,8]. There are few open data on PAOs hydrogenation. Currently, the hydrogenation of PAOs is carried out under industrial conditions on high-percentage dispersed nickel catalysts, which have fairly high activity. As practice shows, during the hydrogenation of oligomers on these catalysts at temperatures up to 260°C and pressures up to 3 MPa, their isomerization occurs, which significantly affects the properties of the obtained hydrogenates. In particular, the crystallization temperature rises significantly, and further use of the synthetic oils obtained becomes limited [9, 10].
Researchers have used different metals, prevalently noble metals, in catalysis as to increase a rate of the synthetic oils hydrogenation; was also confirmed that palladated catalysts favors a mild conditions in the PAOs hydrogenation [11–13].
Considering the cost of noble metals, the catalytic study and techniques are using small and ultra-small nanoparticles of relevant noble metal dispersed over various support matrices [14,15]. Diatomite is advised as an alternative substrate material to support catalytic particles due to its extended porous structure, broad pore sized distribution range and strong adsorption capacity. Unique morphology of diatomite can provide a dispersed growth template for ordered arrangements and reaction of three-dimensional nanoparticles. Catalytic nanoparticles can be loaded and dispersed over the diatomite surface to enhance their catalytic activity [16].
Catalysts obtained under current investigation were tested along with related heterogeneous commercial Ni catalyst. In this paper we investigated PAO-4 hydrogenation over synthesized monometallic palladium (0.5 and 1.0%) and bimetallic (1.0%Pd-0.3% Ni and 1.0%Pd-0.8%Ni) catalysts supported on activated diatomite and commercial Ni5249P catalyst. The physicochemical characteristics of the catalysts and poly-α-olefin oils, the activity of the catalysts, and the degree of hydrogenation were discussed.
2.1 Materials
Natural initial diatomite was obtained from Mugalzhar deposit of Kazakstan, sieved and fraction below 100 µm was collected. Palladium (II) chloride (PdCl2, (≥ 99.9%) and nickel (II) chloride hexahydrate (NiCl2·6H2O, 99%), hydrochloric acid were purchased from Sigma Aldrich Corporation (USA). All reagents are analytical grade and were used without further purification. Distilled water was the solvent used in this investigation.
Commercial nickel catalyst (Ni5249P, BASF, 65%Ni/SiO2/MgO) and a PAO-4 (Group IV base oils, oligomers of decene-1, CAS:68037-01-4) were supplied from JSC “TANECO” (Nizhnekamsk, Tatarstan). Hydrogen gas (≥ 99.99%) was purchased from “Kaztechgaz” Ltd., (Kazakhstan).
2.2 Methods
2.2.1 Characterization
The microstructure of the samples was studied by scanning electron microscopy (SEM) with a microscope Quanta 200i 3D. The images were taken in the modes of registration of secondary and reflected electrons at an accelerating voltage of 15 kV.
The phase composition of the catalysts was studied by X-ray phase analysis. The diffraction patterns of the catalysts were obtained on diffractometer D8 Advance A25 (Bruker) with СuKα radiation (λ = 0.1540 nm) and Ni-filter in the angle range of 4–80° (2θ) with a scan step of 0.02° sec-1. JCPDS (Joint Committee Power Diffraction Standard) files were used for phase identification.
Nitrogen adsorption-desorption isotherms were recorded using the automatic volumetric vacuum system ASAP 2020 Micrometrics at 77 K. Prior to analysis samples were degassed in a vacuum at 300 K until the gas emission ceased completely. The total specific surface area and pore size distribution were calculated with BET (Brunauer–Emmett–Teller) [17] and BJH (Barrett-Joyner-Halenda) [18] methods using the Micrometrics ASAP 2020 software.
Metals content was quantified using an inductively coupled plasma optical emission spectrometer (ICP-OES, Optima 3300DV Perkin-Elmer).
Samples morphology was studied using transmission electron microscopy (TEM) with JEM-2010 (JEOL, Japan) at a grating resolution of 0.14 nm, and accelerating voltage of 200 kV. Specimens were previously dispersed in ethanol under sonication and then applied dropwise onto a carbon-coated copper mesh grid. The average diameter of metal particles and their size distribution was determined with the Image J (all NPs captured with TEM under investigation were measured, n ≥ 600).
IR spectra of initial PAO-4 and hydrogenated PAO-4 (PAO-4) samples were registered with FTIR spectrometer Perkin Elmer Spectrum 65 in the range of 400–4000 cm–1 with a scanning step of 4 cm–1.
The bromine number characterizing the quantitative content of double С=С bonds in PAO and hydrogenated PAO was calculated according to ISO 3839:1996/AMD 1:2020 method [19].
Viscosities of PAO-4 and hydrogenated PAO were evaluated by measuring the kinematic viscosity with a Cannon–Fenske Viscometer (Glass Capillary Viscosimeter, ASTM D 446) following the standard method ASTM D 445 [20] and a viscosity index by ASTM D 2270 [21]. Pour Point (PP) as a lowest temperature at which oil tends to flow (below which oil solidifies) was determined with the NewLab 300 automatic analyzer (Linetronic Technologies, Switzerland) according to ASTM D 97 [22]. All the analysis were performed in duplicate, and results are expressed as the average of those two values.
2.2.2 Hydrogenation reactor configuration
The commercial Parr 4848 Series (Fig. 1) comprised of a 100 mL vessel (60 mL working volume) manufactured in T316 stainless steel fitted with magnetic T316SS stirrer drive unit. The vessel head was equipped with a gauge adapter (pressure gauge 0–14 bar), avent needle valve, a check valve safety rupture disc, a gas inlet valve, a liquid needle valve and s stirrer drive shaft with straight four blade impeller. The H2 gas was supplied via gas sparger tube and quantifies by a gas flowmeter (Bronkhorst), an internal dip tube with 5 µm sintered Mott filter was used for sampling, which along with thermocouple (J-type) acted effectively as baffles. A variable speed motor provides the stirring speed (200–1600 rpm). An aluminum block heater was employed, and the temperature was controlled by the Series 4848 Controller.
FIGURE 1
2.3 Experimental
2.3.1 Catalysts preparation
2.3.1.1 Diatomite surface activation
Crude diatomite (D) surface is blocked by impurities which interfere with catalytical particles deposition and furthermore final catalytic performance of the material. In order to resolve this issue, the surface of natural diatomite was activated under acidic (HCl) and thermal (500oC) conditions. Firstly, deionized water and HCl were added into the flask to obtain 10% HCl solution. Then, the appropriate amount of diatomite was incorporated into it for another 2h stirring at the temperature of 80°C. Diatomite and HCI solution mass ratio of 1:3. Then, the mixture was filtered and annealed in an oven at 500°C for 3h. Finally, the material was milled in a ball mill machine. X-ray fluorescence analysis revealed that the main components of activated diatomite (hereafter referred to as activated diatomite as AD) are SiO2 (87.9%) and Al2O3 (9.8%).
2.3.1.2 Preparation of mono- and bi-metallic/diatomite catalysts
The X-MeAD (X-Me/activated diatomite composites, X indicates the mass ratio of metal in the catalyst (wt.%) and Me states for the metal) were synthetized by adsorption precipitation method. Typically, 1.0 g of activated diatomite was immersed in 50 mL of ultra-pure water and dispersed via sonication. Then appropriate amount of PdCl2 solution (10 mmol/L) was added under continuous stirring. After 50 min the completeness of reaction was confirmed by clarification of solution over the black solid. In order to prepare bi-metallic diatomite composite similar procedure was employed to perform co-precipitation of PdCl2 and NiCl2·6H2O on activated diatomite from pre calculated volumes of their 10 mmol/L solutions. Afterwards samples were vacuum-filtered, washed extensively with DI, dried in a bench oven for 2h at 120°C and denoted as 0.5%Pd/AD and 1.0%Pd/AD (for monometallic) and 1.0%Pd-0.3%Ni/AD and 1.0%Pd-0.8%Ni/AD (for bimetallic) composites.
2.3.2 Hydrogenation of PAO
The preliminarily powdered catalyst was loaded into the reactor in the amount of 0.6 g and 60 ml of PAO-4. The reactor was sealed and purged with nitrogen to remove air. The temperature was set in the range of 110–150°C. After the selected temperature was reached, the reactor was purged with hydrogen, the required pressure was set (1.0 MPa), and mechanical stirring was switched on at a rate of 800 rpm. During the catalytic experiment, samples of the catalyzate were taken from the reactor at a specified time. The reaction rate was measured by the volumetric method [23].
In a given time period, hydrogenation reaction rate (W) was determined using formula (1):
where Vi and Vf are the initial and final hydrogen uptake amounts (mol), respectively, Δt is the time interval during which the rate is calculated (sec) and a is the pressure-dependent coefficient in the system.
3.1 Characterization
The Fig. 2. presents the X-ray phase analysis of the prepared catalysts. The XRD patterns of Pd/AD and Pd-Ni/AD catalysts show a similar trend to activated diatomite. Against the background of a single diffuse broad peak corresponding to the amorphous structure of the material, several peaks (2θ = 20.8о, 26.5о) stand out, all of which are identified as belonging to α-quartz [24]. Pd and Ni species had no diffraction patterns, possibly due to their low content and low crystallinity.
Therefore, ICP-OES (Table.1) was used to analyze the different loadings of Pd and Ni particles, and the results show that the actual palladium loading levels in 0.5% Pd/AD and 1.0% Pd/AD catalysts are 0.49 and 0.98%, respectively. Furthermore, the actual loading concentration in 1.0%Pd–0.3%Ni/AD and 1.0%Pd–0.8%Ni/AD catalysts are 0.97(Pd), 0.28 (Ni) and 0.96(Pd) and 0.75 (Ni)%, respectively. One can notice after these measurements that the mass loadings of the catalysts are very close to the desired ones.
FIGURE 2
Nitrogen adsorption and desorption isotherms and pore size distribution of catalyst samples are shown in Figs. 3.
FIGURE 3
The all sorption isotherms represented in Fig. 3a are type IV isotherms, and the shape of the hysteresis loops is that of H2 type, which refers to objects with tubular pores with narrow open ends, indicating capillary condensation of gases in mesopores [25]. The porous characteristics and dispersion of the catalysts are presented in Table 1.
| Sample | SBET, m2/g | Average pore diameter, nm | Pore volume (cm3 g− 1) | Actual Pd concentration (%)* | Actual Ni concentration (%)* |
|---|---|---|---|---|---|
| AD | 60.0 | 19.0 | 0.08 | ||
| 0.5%Pd/AD | 54.0 | 19.0 | 0.08 | 0.49 | 0.48 |
| 1.0%Pd/AD | 50.0 | 19.0 | 0.07 | 0.98 | 0.97 |
| 1.0%Pd–0.3%Ni/AD | 45.0 | 18.0 | 0.07 | 0.97 | 0.28 |
| 1.0%Pd–0.8%Ni/AD | 40.0 | 17.0 | 0.05 | 0.96 | 0.75 |
| * determined using ICP-OES. | |||||
Table 1
Increasing the concentration of Pd (from 0.5 to 1.0%) and Ni (from 0.3 to 0.8%) leads to a slight decrease in the surface area, pore diameter, and total pore volume of the catalysts. A slight decrease in the specific surface area and pore volume with an increase in the concentration of Pd and Ni indicates the localization of a part of Pd and Ni inside the support pores. The pore diameter distribution curves of the obtained catalysts (Fig. 3b) have one maximum (15–23 nm). The average pore diameter of the 0.5% and 1.0%Pd/AD catalysts calculated by the BJH method is 19.0 nm, while the 1.0%Pd–0.3%Ni/AD and 1.0%Pd–0.8%Ni/AD catalysts are 18.0 and 17.0 nm, respectively.
On the other hand, the catalyst samples were characterized by SEM microscope in order to check their morphologies and their textures. The obtained data are illustrated in the Figs. 4).
FIGURE 4
The SEM images of all catalyst samples show that there is no significant difference in surface textures, macropores of numerous fragments of diatom bodies are completely open, the skeleton and structure of the crystal lattice are preserved. In fact, this observation confirms the theory of filling up the pores by BET measurements and the metallic particles were incorporated totally inside pores.
The Fig. 5 shows TEM images and particle size distribution histograms for mono and bimetallic catalysts. Figure 5a and 5b show that the palladium particles are uniformly distributed on the support surface due to the strong interactions of noble metallic particles. The loading of 0.5 and 0.1%Pd/AD catalysts have particles 1–8 nm in size on their surfaces, however, their predominant particle size is 2–5 nm. The 1.0%Pd–0.3%Ni/AD and 1.0%Pd–0.3%Ni/AD catalysts (Fig. 5c and 5d) are characterized by a wide range of crystallite size distributions. On the surface of the 1.0%Pd–0.8%Ni/AD catalyst, particles 1–10 nm in size predominate.
FIGURE 5
3.2. Hydrogenation of poly-α-olefin oils (PAO-4)
The prepared catalysts were tested in the process of hydrogenation of poly-α-olefin oil (PAO-4) at a temperature of 110°C and a hydrogen pressure of 1.0 MPa. The constant stirring speed was 800 rpm. Figure 6a shows reaction rate curves as a function of the amount of hydrogen uptake and Fig. 6b shows kinetic profiles of PAO-4 hydrogenation.
FIGURE 6
Figure 6a clearly shows that during the PAO-4 hydrogenation, the reaction rate on monometallic catalysts is higher than on bimetallic ones. At the same time, at lower temperatures (110°C), the hydrogenation rate increases significantly with increasing palladium content in the catalyst (monometallic). Figure 6b shows that hydrogen uptake on a 0.5% Pd/AD catalyst in 1400 ml completes the hydrogenation reaction in 190 minutes and on a 1.0% Pd/AD catalyst in 130 minutes. On the contrary, with an increase in the Ni concentration in the bimetallic catalyst (1.0%Pd–0.8%Ni/AD), the reaction rate is much lower, and the reaction time according to the kinetic curve (Fig. 6b) increases to 400 minutes.
The catalytic hydrogenation of poly-α-olefins in the production is carried out with nickel catalysts. As reported in the literature [10,26], in addition to nickel catalysts having low activity, the hydrogenation process proceeds at very high temperatures and pressures, and these severe conditions can lead to thermal degradation of the hydrogenation product.
The Fig. 7 shows the results of activity studies of the BASF nickel catalyst (65% Ni/SiO2/MgO) in the process of hydrogenation PAO-4 under similar conditions to those for palladium catalysts (1 MPa, 110 and 150°C). At a temperature of 110°C, the activity of a nickel catalyst is 6 times lower than that of a 1.0% palladium catalyst (Fig. 6), and at the same time, it practically coincides with the activity of a bimetallic catalyst with a content of 0.8% Ni. Increasing the temperature up to 150°C in the process leads to a sharp increase in the activity of the nickel catalyst, comparable to the activity of a palladium catalyst containing 0.5% Pd at 110°C.
FIGURE 7
The Fig. 8 shows the IR spectra of samples of the initial and hydrogenated PAO-4 on 0.5% Pd/AD, 1.0% Pd/AD, 1.0% Pd–0.3% Ni/AD, and 1.0% Pd–0.8% Ni/AD catalysts.
FIGURE 8
It can be seen from Fig. 8a that the IR spectra of the initial PAO-4 in the IR spectra of the initial PAO-4 in the range from 2800 to 1103 cm− 1 and from 1300 to 1500 cm− 1, along with intense absorption bands characterizing the vibrations of the С-Н bond in the functional groups -CH3- and -CH2-, weak absorption bands at 969 cm− 1 in the functional groups = CH2. It has been noted that the IR spectrum data are in good agreement with the results of the work [27].
Figure 8b, 8c, and 8d show that in the IR spectrum after hydrogenation of the initial PAO-4 (Fig. 8a), the peaks characterizing the absorption bands of C-H stretching vibrations in the functional groups = CH2 (969 cm− 1) disappear. The Fig. 8e shows that the double bond is not completely eliminated in the IR spectrum obtained after PAO-4 hydrogenation with a 1.0% Pd – 0.8% Ni/AD catalyst. The physicochemical parameters of the initial and hydrogenated PAO-4 are presented in Table 2.
| Parameters | Before hydrogenation | After hydrogenation | |||||
|---|---|---|---|---|---|---|---|
| 0.5% Pd/AD | 1.0% Pd/AD | 1.0%Pd–0.3%Ni/AD | 1.0%Pd–0.8%Ni/AD | Ni catalyst | |||
| 110оС | 150 оС | ||||||
| Bromine number, gBr2/100 g | 26 | 0.2 | 0.2 | 0.3 | 1.97 | 1.96 | |
| Kinematic viscosity, mm2/s, | 100 оС | 3.9 | 4.0 | 4.1 | 3.9 | 3.9 | 3.9 |
| 40 оС | 18.7 | 19.0 | 20.0 | 19.0 | 18.6 | 18.9 | |
| Viscosity index | 113 | 117 | 118 | 117 | 114 | 115 | |
| Pour point, оС | -76 | -70 | -70 | -69 | -70 | -69 | |
Table 2
The bromine numbers of PAO-4 hydrogenated on nickel catalysts are close to those for bimetallic 1.0%Pd–0.3%Ni catalysts and are 1.96.
The obtained results indicate the advantage of low-percentage palladium catalysts supported on activated diatomite compared to commercial nickel catalysts. The use of palladium catalysts allows the process to be carried out under milder conditions, with greater activity and provides a higher degree of hydrogenation. Partial replacement of palladium by nickel in the bimetallic catalyst leads to a decrease in the activity of the catalyst.
Acknowledgements
The authors would like to thank the Ministry of Science and Higher Education of the Republic of Kazakhstan (Grant No. AP14871087) for providing financial support.
Conflict of interest
The authors declare no conflicts of interest.
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Authors' contributions
Yermek Aubakirov: Experimental data
Kainaubek Toshtay: Experimental data and writing paper
Ali Auyezov: Experimental analysis
Rachid Amrousse: Writing paper
Seitkhan Azat: Experimental analysis
Yerbolat Sailaukhanuly: Experimental tool
Ulantay Nakan: Experimental tool
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No competing interests reported.