Anionic Clusters Enhanced Catalytic Performance of Protic Acid Ionic

Subscriber access provided by the University of Exeter

Article

Anionic Clusters Enhanced Catalytic Performance of Protic Acid Ionic Liquids for Isobutane Alkylation Aoyun Wang, Guoying Zhao, Fangfang Liu, Latif Ullah, Suojiang Zhang, and Anmin Zheng Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b00768 • Publication Date (Web): 07 Jul 2016 Downloaded from http://pubs.acs.org on July 12, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Industrial & Engineering Chemistry Research is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 57

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Industrial & Engineering Chemistry Research

Anionic Clusters Enhanced Catalytic Performance of Protic Acid Ionic Liquids for Isobutane Alkylation Aoyun Wang, †,‡ Guoying Zhao, ‡ Fangfang Liu, §,* Latif Ullah, ‡ Suojiang Zhang, ‡,* Anmin Zheng, η †

College of Chemical and Pharmaceutical Engineering, Hebei University of Science and Technology, Shijiazhuang, 050018, People’s Republic of China ‡

Beijing Key Laboratory of Ionic Liquids Clean Process, State Key Laboratory of

Multiphase Complex Systems, Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing, 100190, People’s Republic of China §

College of Textile and Garment, Hebei University of Science and Technology, Shijiazhuang, 050018, People’s Republic of China

η

State Key Laboratory of Magnetic Resonance and Atomic Molecular Physics,

Wuhan Center for Magnetic Resonance Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, People’s Republic of China

1 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Abstract: Isobutane alkylation is a typical carbocation chain growth reaction that requires proper acidity with less acidity change for its enhanced lifetime and activity of the catalyst. In this work, a family of protic ionic liquid/triflic acid as synergistic catalysts have been developed for isobutane alkylation, with special emphasis on its reusability. The slowest acidity change was found with varied concentrations of triflic acid for the protic ionic liquids which is probably buffered by binding and releasing the solubilized acid in the formed anionic cluster [N222H][CF3SO3(CF3SO3H)x] as indicated by FT-IR and 1H NMR spectroscopy. As a promising isobutane alkylation catalyst, the protic ionic liquids has shown a maximum selectivity towards C8 up to 86.23%, research octane number (RON) up to 97.3, and reusability up to 36 runs, outclassing the sulfuric acid or triflic acid catalysts under the same reaction conditions. Apart from the excellent catalytic performance, the new catalytic system showed better impurities compatibility and significantly less corrosion rate to carbon steel and stainless steel than sulfuric acid and pure triflic acid.

1. Introduction. Isobutane alkylation with low molecular weight olefins (C2-C5) is an important unit in refinery to produce cleaner-burning gasoline blending components with high octane number, low RVP (Reid vapour pressure), low sulfur, and zero alkenes and aromatic1. However the overwhelming alkylation technologies in the sulfuric acid (H2SO4) or anhydrous hydrofluoric acid (HF) as catalysts, cause safety and environmental issues2. The growing human needs for both high-quality gasoline and sustainable technologies drives the academia and industry to explore safer, cleaner and more efficient catalyst3. 2 ACS Paragon Plus Environment

Page 2 of 57

Page 3 of 57

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Among many potential alternative catalysts, ionic liquids (ILs) has aroused much attention. Owing to its outstanding acidic properties, chloroaluminate-based ionic liquids have been firstly and mostly investigated to catalyse the isobutane alkylation4. The selectivity of trimethylpentanes and RON of alkylate catalysed by chloroaluminate-based ionic liquids developed for isobutane alkylation by Liu,4 Zhang5 and Angueira

6

were up to 87.5 wt% and 100.5, better than most of the

commercial alkylation catalysts, but the nature of chloroaluminate ionic liquids, such as sensitivity to water, viscosity, makes it difficult to be applied in industry. In addition, a subset of Brønsted acidic ionic liquid solutions also proved to be promising catalyst for isobutane alkylation with enhanced activity and stability7. The binary mixture of imidazolium-based ionic liquids/strong acid (sulfuric or triflic acid) reported by Tang exhibited a better catalytic performance with an optimized C8-alkylates selectivity up to 75.8% over the pure acid themselves8. We have discovered that the addition of protic ammonium-based ionic liquids or Trifluoroethanol into triflic acid (TfOH）dramatically enhanced its catalytic activity. Up to 91.5% C8-alkyalte selectivity were achieved at the optimized condition, which are much better than the sulfuric acid. However the investigated [N222H]HSO4/TfOH or CF3CH2OH/TfOH were only reused no more than 10 runs due to the quick decline of their acidity9, 10. It is challenging to design a catalyst system that have the combine advantages of the both high activity and stability. Controlling the acidity of reaction process is very important for many reactions, as acidity fluctuations can affect the outcome. For isobutane alkylation, there is a most 3 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 57

suitable acidity range for a catalyst, whatever HF, sulfuric acid or solid acid, to selectively yield the C8-alkyalte. It is also worth mentioning that higher or lower acidity can accelerate the production of side products such as light ends (C5-C7) or heavy ends (C9+ and acid soluble oil)11. However, the acidity range and the corresponding catalyst concentration is varied with the composition and structure of a catalyst. For example, the concentration of sulfuric acid in industrial alkylation process is usually controlled in a range of 90 to 96 wt.% the acidity of which correspond to -10.4 to -11.6 in Hammett value (H0) scale to produce good quality alkylate oil. In contrast, the best concentration range of HF for alkylation is usually controlled in a range of 82 wt.% and 88 wt.%, which correspond to about -9.0 to -8.0 in H0 scale. Therefore, an efficient and stable catalytic system should prevent or at least slow down acidity change with its concentration variation due to the addition of a base, accumulation of impurities, or the acid reduction. In many chemical or biochemical application, aqueous buffer solutions are always used to control the hydrogen ion concentration and maintain the system pH value though an equilibrium between the acid HA and it’s conjugate base according to Le Chatelier's principle. Comparably, the proton activity and the solution acidity in an ionic medium can also be held via creating a quasi-ionic liquids buffer solution by adding a conjugate acid (or base) species to the ionic liquid12. Recently Seddon has found that the acidity of several systems of general formula [R-mim][A]–HA could be buffered by binding the solubilized acid in the anionic cluster form like [A(HA)x]−, such as [Cl(HCl)x]−, [Br(HBr)x]−, [F(HF)x]− and [(HSO4)(H2SO4)x]− and other 4 ACS Paragon Plus Environment

Page 5 of 57

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


hydrogen-bonded anions clusters13, 14 etc. Thus it is very interesting to design ionic liquids catalyst sharing the same anion with conjugate acid, and investigate how the anion species affect its catalytic performance. Triflic acid has exhibited excellent catalytic activity for isobutane alkylation when mixed with ammonium based ILs8. Herein, a liabry of protic ionic liquids [N222H]+ with varied acid molar ratio are prepared and applied to catalyse isobutane alkylation. The physicochemical properties of [N222H]CF3SO3/TfOH (viscosity, density, interfacial tension and in particular acidity in Hammett scale) were correlated with the anion species and structure, Based on that, the process variables such as the ratio of catalyst to feed olefins, reaction temperature and time was studied and optimized for isobutane alkylation. We found that the [N222H]CF3SO3/TfOH with χTfOH=0.69 can be reused for at least 36 runs without the obvious loss of activity, due to the buffering action of the anion clusters, [N222H][CF3SO3(CF3SO3H)x] (x=0,1,2). 2. Experimental Section 2.1 Materials and Instruments. Triflic acid (TfOH,> 99.9% in purity) was purchased from the 718th Research Institute of China Ship Building Industry Corporation. N, N-diethylethanamine (≥ 99.0%) was purchased from Xilong Chemical Co. Ltd. China. Trifluoroethanol (>99.9%) was purchased from Chemical Development Institute of Weihai Yunqing. Sulfuric acid (H2SO4, ≥98.0%) was obtained from Beijing Chemical Works, China. Isobutane (>99.7% in purity) was supplied from Linggas, ltd. Butene (C4 cut from industrial alkylation feed) was obtained from Sinopec Beijing Yanshan Company. 5 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 57

The mixture of isobutane and butene with a mole ratio of 8.5:1 was premixed in a storage vessel (Table 1). All reagents were used as received without further purification unless otherwise noted. FT-IR spectra were obtained with a Nicolet 380 spectrometer.1H NMR spectra were obtained with a JEOL ECA-600 (600 MHz) spectrometer.

13

C NMR spectra were

measured with a Bruker Advance III (600 MHz) spectrometer. Mass spectra (MS) in ESI mode were recorded on a Bruker microTOF-Q II spectrometer. The viscosity and density was determined with a Paar AMVn automatic viscosity analyser, using falling ball viscometer (Austria Anton Paar).Interfacial tension was measured with an automatic tension meter (Powereach JK99C1). 2.2 Preparation of ionic liquid Triethylamonium

trifluoromethanesulfonate

([N222H]CF3SO3).

The

triethylamonium trifluoromethanesulfonate was prepared by neutralization of N, N-diethylethanamine and TfOH according to the published methods15. In a typical procedure, 101.0g N, N-diethylethanamine was added into a three necked flask. Then 150.0g TfOH was dripped into the cooled and vigorously-stirred solution under nitrogen atmosphere in an ice bath.

After at least three hours reaction, the ionic

liquids synthesized was dried under high vacuum for 48 h prior to use. A transparent liquid was produced with a yield of 93.46%.The ionic liquid was determined by 1H NMR (JNM-ECA600), ESI/MS (Bruker micro TOF Q II.), 1H NMR (600 MHz, CDCl3, 25 ◦C): δ (ppm) 7.11–7.07(s, 1H), 3.10–3.07 (m, 6H), 1.12 (m, 9H). ESI/MS: m/z (+) 102.1, m/z (−) 148.9. 6 ACS Paragon Plus Environment

Page 7 of 57

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Triethylamonium hydrogensulphate ([N222H]HSO4). The triethylamonium hydrogen sulphate was prepared by neutralization of N, N-diethylethanamine and H2SO4. The yield was 81.60%, white viscous liquid. ◦

1

H NMR (600 MHz, CDCl3, 25

C): δ (ppm) 7.10–7.06 (s, 1H), 3.15–3.12 (m, 6H), 1.13 (m, 9H), 2.13–2.08 (s, 1H).

ESI/MS: m/z (+) 96.9, m/z (−) 102.1. 2.3 Acid Strength Determination. The Hammett acidity of the catalyst system was determined by

13

C NMR with

mesityl oxide as an indicator according to the literature16, 17. In a typical procedure, the mesityl oxide was dissolved into the catalyst and its concentration varied between 0.05 and 0.8 mol/L. Subsequently, the prepared ionic liquid samples were loaded into an NMR tube assembled with a coaxial inner tube filled with tetramethylsilane. The 13

C NMR spectra were acquired at 300 K on a Bruker Avance III 600 MHz

spectrometer.

For each mesityl oxide-ionic liquids system, the chemical shift

differences of Cß and Cαfor the infinite dilution (∆δ0) of mesityl oxide was determined from the chemical shift differences of Cß and Cα (∆δ) measured at three different concentrations by exploration.

The Hammett value (H0) were calculated according

to the reported equations10. The measured Hammett value of 95 to 98% H2SO4 was in well agreement with the reported value by Dan Frcasiu18. 2.4 Corrosion Tests. Corrosion tests were carried out according to the national standards of corrosion resistance GB/T 19291-200319 and GB/T 4334.6-200020. Three different type materials (carbon steel, 304 Stainless steel and 316 Stainless steel) were polished with 7 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 57

400 mesh abrasive paper before use. Subsequently they were immersed in the catalyst for thirty days at room temperature after being weighed and dried. After thirty days the materials were again scrubbed, dried and weighed. The corrosion rate was obtained from the mass difference of the sample before and after the immersion, surface area of the sample, test time and density of the sample: CR = (87600*(Mb-Ma))/(S*t*ρ) In which: CR = corrosion rate, mm/a; Mb= mass of the sample before tested, g; Ma = mass of the sample after tested, g; S = surface area of the sample, cm2; t = test time, h;

ρ= density of the sample, g/cm3. 2.5 Alkylation Procedure. Alkylation were carried out in a 200 mL autoclave equipped with a PTFE-inner lining to avoid contact with the catalyst and surrounded by cooling groove with ethanol as a working fluid to control the reaction temperature as reported in literature9, 16

. A two-stage propellant stirrer provided effective agitation with three paddles on the

shaft. In a typical procedure, a given amount of catalyst was added into the reactor. Subsequently the reactor was purged and pressurized with nitrogen gas. When the temperature was adjusted to the desired temperature, the isobutane/butene mixture (mole ratio 8.5:1) prepared beforehand was introduced into the stirring reactor using dual piston pump at the given feeding rate. Then the reaction system was stirred for another given reaction time. After the reaction, the upper oil was decanted from the acid and washed several times with NaHCO3 solution.


Page 9 of 57

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


For the catalyst recycling experiments, after the isobutane/butene mixtures were reacted, the stirrer in the reactor was stopped for 3 to 5 minutes allowing the product/catalyst well separation and then the product was pressed out and collected using sample flask. Fresh C4 feedings were then pump into the reactor while vigorously stirring to start the next run. The RON of alkylates produced was calculated according to the corresponding method21. The alkylate was quantitatively analysed by a gas chromatograph (SHIMADZU GC 2014) equipped with a capillary column (DB-Petro,100 m × 0.25 mm) and a ﬂame ionization detector. The RON of alkylates produced was calculated according to the reported method25. And the tail gas was analysed by gas chromatography (SP 6890) offline with a capillary column (HPPLOT Al2O3 S, 50 m×0.53 mm) 22. In this study, standard uncertainties u of alkylation variables are u(T) = 0.1 °C, u(p) = 0.01 MPa, u(t) = 0.1 min, respectively. RON, weight fraction of alkylate composition and acid strength are expressed with the average value of multiple measurements (triplicate or more) within the experimental error ±1.0%, and the number in the tables and figures shown are determined by the ultimate errors of the inherent and standard deviation. 3. Results and discussion 3.1. Acid Strength For isobutane alkylation, the acidity of a catalyst (acid strength and nature) is the most important factor affecting the product quality. Higher acidity than the most suitable acidity range of the catalyst would accelerate the side cleavage 9 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 57

reaction and the production of light-end paraffin (C5-C7). Lower acidity would boost

the

side

oligmerization

and

the

production

of

heavy-ends

(C9+).Moreover, as the acidity of the catalyst changes, it affect the whole-lifetime catalytic performance with the concentration, the accumulation of impurities introduced and the side products. Therefore, we first investigated the effect of acid concentration on the acid strength of four catalytic systems in this study (Figure 1). The molar fraction χTfOH is simply calculated by: χTfOH = (mole of TfOH)/ (mole of ionic liquid +mole of TfOH) The acidity of the two catalytic systems including [N222H]HSO4/TfOH and [N222H]CF3SO3/TfOH respectively at varied χTfOH were determined via

13

C

NMR with mesityl oxide as an indicator according to the reported method17. And the acidity values of the H2O/TfOH and CF3CH2OH/TfOH were extracted from the literatures respectively10. As shown in Figure 1, the addition of water into triflic acid sharply decrease the acidity of triflic acid. The Hammett acidities of TfOH/H2O were sharply reduced down to -10.4 from -14.1 with χTfOH decrease from 1 to 0.9, which is probably because the addition of water in TfOH changed the microstructure and composition of the ionic species similar as in sulfuric acid-water system. In contrast, the acidities of [N222H]HSO4/TfOH and CF3CH2OH/TfOH decreased gradually from -14.1 to -13.0 and -10.8, respectively, with the reduction of TfOH mole fraction from 1.0 to 0.9. While for [N222H]CF3SO3/TfOH, the 10 ACS Paragon Plus Environment

Page 11 of 57

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


acidities decreased even more slowly from -14.1 to -13.8. Their acidity reduction from -14.1 to –10.4 need about 0.52 mole fraction of [N222H]CF3SO3 addition. All the above results indicated that the [N222H]CF3SO3/TfOH probably formed a “qusia” buffer solution and inhibit its acidity changes to some extent, which is good for alkylation. To have a further insight into the qusia-buffering action, we investigated the microstructure of [N222H]CF3SO3/TfOH catalyst system using fourier transform infrared (FT-IR) spectrum(Figure 2) and nuclear magnetic resonance (NMR) spectrum (Figure 3). According to the references

23

, the bands concentrated in the range 1420–

1030 cm−1 corresponds to the chemical bonds feature of sulfonic groups of fragmentation of triflic acid. The sulfonic anion SO3− is a highly polarizable group. The position and intensity of its stretching vibrations can give information of this anion and types of interactions in which this anion is implicated based on the high polarity of the sulfonic anion group, SO3−. As shown in Figure 2, characteristic vibrations for CF3SO3- and CF3SO3H were detected, and it is in agreement with the reference

23

. The local symmetry

(stretching vibration in 800-950cm-1, symmetric stretching vibration at 1030 cm−1, asymmetric stretching vibration at 1200 cm−1) is relative to the S-O and S=O in the –SO3− groups. The χTfOH = 0.49 system contains one S-O-H vibrations at 838.24cm-1, symmetric S=O stretching vibration at 1030 cm−1 and various vibration of SO3 belong to a multiple complex anions at 1200 cm−1.For 11 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 57

χTfOH= 0.59, 0.69, 0.79 and 0.90, the structure of multiple complex are similar to and intermediate between χTfOH= 0.49 and pure triflic acid. The S–OH bending vibrations are weaken and upfield-shifted with respect to pure triflic acid because of exist of the hydrocarbon bonding in the anionic clusters. According to the literature13,14, 24, 25, the acidity could be buffered by binding the solubilized acid in the anionic cluster form. Hence we speculated that anionic clusters [CF3SO3(CF3SO3H)x]−(x=0, 1, 2) (Figures 4-6), which could buffer the acidity, may be formed between TfOH and [N222H]CF3SO3. For χTfOH= 0.49, the signal at 9.56 ppm (1H chemical shift of active hydrogen) corresponds to the CF3SO3H (Figure 4). The signal at 6.25 ppm corresponds to protonation of triethylamine. For χTfOH= 0.59, the signal at 10.37 ppm integrates to one protons located on the dinuclear cluster, [CF3SO3(CF3SO3H)]− (Figure 5). They are hardly deshielded relative to the CF3SO3H, because they are partaking in strong hydrogen bonds, each shared between two oxygen atoms: S–O–H⋯O–S. The formation of dinuclear anion result in strong internal hydrogen bonds, weaker external hydrogen-bonding interactions with cation25. Thus, the signal of the N– H proton is shifted upfield by ca. 0.10 ppm. For χTfOH= 0.69, χTfOH=0.79 and χTfOH=0.90, the signal at 11.36 ppm integrates

to

two

protons

corresponding

to

the

trinuclear

complex,

[CF3SO3(CF3SO3H)2]− (Figure 6). These protons are composing strong hydrogen bonds, stronger than those of the dinuclear system26, resulting in the 12 ACS Paragon Plus Environment

Page 13 of 57

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


downfield shift of this signal compared to χTfOH= 0.69.The more upfield-shifted signal corresponding to the N–H proton indicate that the bond to nitrogen is stronger13. In summary, the FT-IR and the 1H NMR spectroscopy shows that the composition in the [N222H]CF3SO3/TfOH system varied with the change of χTfOH.

The

main

composition

is

[N222H]CF3SO3

for

χTfOH

=0.49,

[N222H][CF3SO3(CF3SO3H)] for χTfOH =0.59 and [N222H][CF3SO3(CF3SO3H)2] for χTfOH =0.69 , 0.79 and 0.90. 3.2 Physical properties of [N222H][CF3SO3(CF3SO3H)x](x=0, 1, 2) It is well accepted that the isobutane-butene alkylation is highly exothermic, controlled by reaction kinetics and mainly take place at or near the interface of acid/hydrocarbon dispersion27,

28

. Larger interfacial areas, faster product

separation, and better heat transfer result in higher quality alkylates. Therefore, some other physical properties of the catalysts, which may have important effect on the overall alkylation process, are also studied in this paper. Density, viscosity, and interfacial properties of [N222H][CF3SO3(CF3SO3H)x] at varied mole fraction χTfOH, are summarized in Table 2. The density of [N222H][CF3SO3(CF3SO3H)x] at the investigated χTfOH is a little lower than that of 98% H2SO4 (1.8133 g·cm-3) and similar to that of the reported composite chloroaluminate ionic liquid Et3NHCl-AlCl3 (1.6132 g·cm-3). In contrast, the viscosity and interfacial tension of [N222H][CF3SO3(CF3SO3H)x] is far lower than that of 98% sulfuric acid (25.8×10-3 Pa·s) and chloroaluminate ionic liquid 13 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 57

Et3NHCl-AlCl3 (98.5×10-3 Pa·s). The above results indicated that it is more favourable to the heat transfer, mass transfer in the alkylation process, and easier to product gravitate separation than Et3NHCl-AlCl3 anionic liquid using [N222H][CF3SO3(CF3SO3H)x] as catalyst. 3.3 Effect of process variables on alkylation. Effect of Acidity Strength of Catalyst. Effect of acid strength on isobutane alkylation was studied (Figure 7). As shown in Figure 7, the optimal acidity range of [N222H][CF3SO3(CF3SO3H)x] to produce best alkylate is between -13.77 (χTfOH=0.90) and -10.4 (χTfOH=0.49) in H0 scale, which is different from other catalyst such as sulfuric acid (-11.6 to -10.4)16, HF (-9.0 to -8.0)11, and even [N222H]HSO4/TfOH. The maximum C8 selectivity was up to 86.23%, the highest RON (97.3) and minimum side products (C5-C7, 3.8% and C9+, 9.44%) were achieved at -11.52, while at -10.7 for TfOH/water11,-9.2 for [N222H]HSO4/TfOH9 and -9.6 for CF3CH2OH/TfOH10. Below the optimum acidity, there was increased C9+ fraction in the product stream with the acidity reduction of the catalyst, which leads the product with lower quality. In contrast, there was much more C5-C7 and C9+ in the alkylate product than C8 when the H0 =-13.77 and -14.1. This is because the acidity of them is above the higher limit of the optimal acidity range.

All the above results indicated that

not only the acid strength but also the composition and microstructure of catalyst have important effect on its catalytic performance8, 10, 17.


Page 15 of 57

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Effect of Volume Ratio of Acid to Feed Hydrocarbon. The volume ratio of acid to feed hydrocarbon must be carefully controlled during alkylation process and it affect the interfacial surface area of acid/hydrocarbon emulsion and thus the product quality10. The lowest acid consumption and best octane are achieved when the acid/hydrocarbon ratio is maintained between 45/55 and 65/35 for H2SO4. The effect of acid/hydrocarbon ratio for [N222H][CF3SO3(CF3SO3H)x] were studied at 5 ℃ (Figure 8). The C8 selectivity and RON of product increased with the acid/hydrocarbon ratio change from 7/50 to 30/50 and varied lightly when the acid/hydrocarbon ratio is beyond 30/50. The maximum C8 selectivity

(86.23%)

and

RON

(97.3)

were

achieved

with

30/50(acid/hydrocarbon) in the investigated range, a little lower than that of chloroaluminate-based ionic liquids with 30/50(acid/hydrocarbon) in the investigated range. When the acid/hydrocarbon ratio is lower than the recommended ratio, an emulsion with hydrocarbon as continuous phase is formed, which disappears quickly and we get poor quality alkylates. In contrast, higher ratio of acid in the reactor allows less residence time for the hydrocarbons to fully react, which also results into the poor quality alkylates 29. Effect of the Reaction Temperature. Reaction temperature usually has a profound effect on the alkylate selectivity as alkylation of isobutane with butene is an exothermic reaction. In order to study the effect of temperature on the isobutane alkylation, we firstly calculated the Gibbs free energy of the reaction and equilibrium constants under 0.4 MPa, different temperatures30. 15 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 57

There is however a huge number of competitive side reactions and possible products. Therefore we have chosen the following six main alkylation reaction for Simplifying the thermodynamic calculation and analysis: R1

i-C4o + C4= → 2, 2, 4-TMP

R2

i-C4o + C4= → 2, 2, 3-TMP

R3

i-C4o + C4= → 2, 3, 3-TMP

R4

i-C4o + C4= → 2, 3, 4-TMP

R5

i-C4o + C4= → 2, 4-DMH

R6

i-C4o + C4= → 3-MH

Where TMP is the trimethylpentane, DMH is the Dimethyl hexane and MH is the Methyl heptane. The Gibbs free energy data of all pure components at different temperatures, 0.4 Mpa were collected from the Aspen properties in Aspen Plus program. The Gibbs free energy of every independent alkylation at different temperatures (△G) was calculated according to the Reaction Gibbs function (Figure 9). From Figure 9, it can be known that the calculated △G of every independent alkylation at different temperature are negative, which indicated that the alkylation is spontaneous in the investigate temperature range. With the increase of temperature, the △G shows an increasing tendency and tend to be positive. This shows that increasing the reaction temperature will decrease the spontaneous degree of the alkylation reaction and the formation of the TMP and DMH.

In other words, lower reaction temperature is favorable towards the 16 ACS Paragon Plus Environment

Page 17 of 57

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


production of C8 alkylate in view of thermodynamics. But in practical process, too low temperature will increase the energy consumption and viscosity of the reaction

system.

Highly

viscous

catalyst

can’t

form

well-dispersed

acid/hydrocarbon emulsion and affect the alkylate quality. Therefore we further investigated the effect of reaction temperature on the alkylate composition and RON in the range between 5 ℃ and 30 ℃ (Figure 10 and Figure 11). As the temperature increases, the isooctane fraction decreased from 86.23% to 64.16% and RON from 97.3 to 91.3, accompanying the products) and

increase of light ends (C5-C7

heavy ends (C9+ products)(Figure 10).

In addition, the TMP

fraction also decreased with the reaction temperature increase. But the DMH fraction-the thermodynamic more favorable isomers first decreased with the reaction temperature and reach a minimum value at 15 ℃, which may be determined not only

by thermodynamics but also by reaction kinetics26. Based

on an overall consideration of energy consumption, viscosity, thermodynamic and so on, we took 5 ℃ as the fixed reaction temperature for further optimizing the other reaction variables. Effect of the Reaction Time. The time needed for the alkylation reaction depends on the degree of mixing and other parameters such as of acid and olefins phases. The degree of emulsification of acid and olefins in the reactor affects a great deal on the quality of alkylates. So the contact time should be a bit greater than the time required for complete emulsification of the two phases. If the reaction time is too short, the two 17 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 57

phases viz. acid and olefins will not be completely emulsified, which adversely affects the quantity and quality of yield. On the other hand, if the reaction time is too long, then it will result in an increased side reactions, resulting in the low quality of alkylation product. Extended reaction time, has also another setback to the industry, which is in terms of insufficient acid consumption, increased power and reaction apparatus occupation. Moreover, the biggest drawback of extended contact time is, that apart from alkylation reactions, side reactions may occur which will cause a rapid decline in the quality of alkylates. Practice has proved that, it takes about 5 to 30 minutes to reach a steady state after the addition of acid and an olefins phase stream into the reactor. For the effect of reaction time on alkylation was investigated (Figure 12).As we can see, the maximum RON and C8 was observed at 10 minutes. 3.4 Reusability of Catalyst under Optimized Conditions Based

on

the

optimized

reaction

conditions,

the

reusability

of

[N222H][CF3SO3(CF3SO3H)2] (χTfOH =0.69) were studied to understand their lifetime in the isobutene alkylation. After the isobutane/butene mixtures were reacted, the stirrer in the reactor was stopped for 3-5 minutes allowing the product/catalyst to separate well, then the product was pressed out and collected using sample flask. Fresh C4 feedings were then pump into the reactor while vigorously stirring to start the next run. As shown in Figure 13, the [N222H][CF3SO3(CF3SO3H)2] catalyst show far better catalytic performance during its whole active lifetime than that of the triflic acid alone. The high initial acidity of the pure triflic acid leads to the production of 18 ACS Paragon Plus Environment

Page 19 of 57

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


large amount of heavy ends(C9+,30.86%) , light ends(C5-C7,13.19%) and a certain amount of acid soluble oils(ASO) in the first runs as evidenced from its color transition into brown. The produced ASO moderate the acidity of the triflic acid and improve the isooctane selectivity from 55.95% to 58.06% as a hydride transfer promoter. However after 22th catalytic runs, the activity of triflic acid dropdown sharply as the C8 selectivity decreased down to 54.21% and C9+ increased steeply up to 30.74%.

In contrast, the [N222H][CF3SO3(CF3SO3H)2] can be reused up to 36

cycles without obviously loss activity and show higher and C8 selectivity range from 55.68% to 71.45% during its whole catalytic cycles than that of pure triflic acid. The light ends (C5-C7) were inhibited down to around 10% and heavy ends(C9+) around to 22% using [N222H][CF3SO3(CF3SO3H)2]

as catalyst. These results also indicated

that the addition of [N222H]CF3SO3 not only just moderate the acidity of triflic acid but in-situ formed a new catalytic species or micro-cluster which inhibit the side oligmerization, and therefore the ASO and heavy ends (C9+)production. In other words, the resulted hydrogen bonded cluster enhance its catalytic performance and lifetime. 3.5 Effect of the Impurities. Various contaminants presenting in the hydrocarbon feeds affect the alkylation process to various degrees. The common hydrocarbons used to produce alkylate are the C4 raffinate after MTBE production, in which there are always trace amount of water, methanol. MTBE, N-butyl mercaptan, and so on. Herein, we investigated how these fours presentation contaminants affect the 19 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 57

performance of [N222H][CF3SO3(CF3SO3H)2] catalyst (Figure 14 , Figure 15, Figure 16 and Figure 17). As shown in Figure 14, H2O as an impurity has no profound effect on the catalytic activity of [N222H][CF3SO3(CF3SO3H)2] system provided that its weight fraction is not more than 10 mg/g. Even trace amount of water (< 1 mg/g) improved the catalyst’s activity probably tiny H2O help increasing the protonation ability of catalyst. As the weight fraction of H2O is larger than 10 mg/g, the RON and C8 selectivity decreased sharply and the C9+ fraction increased sharply, indicating the acidity of catalyst dropped out from the suitable acidity range. Obviously water content =10 mg/g is the turning point of the performance of [N222H][CF3SO3(CF3SO3H)2] catalyst and is therefore treated as the accumulation up limit of water in the catalyst. Similarly, the accumulation up limit of methanol (CH3OH), MTBE and N-butyl mercaptan (n-C4H9SH) accumulated in the catalyst are be 5 mg/g, 20 mg/g and 5 mg/g respectively (Table 3). 3.6 The Corrosion of Different Steels in Catalyst The

corrosion

rates

of

three

different

kinds

of

steels

in

[N222H][CF3SO3(CF3SO3H)2] increased in the order of 316 Stainless steel < 304 Stainless steel < carbon steel (Table 4). Similar changing tendency were found in TfOH and H2SO413. It is worth mentioning that the corrosion rates in [N222H][CF3SO3(CF3SO3H)2] are far lower than that in TfOH and H2SO4 (Table 4), indicating that the [N222H]CF3SO3 exhibited good inhibition properties26. For example, the corrosion rate of carbon steel in H2SO4 is 37.04×10-3 mm/a, 20 ACS Paragon Plus Environment

Page 21 of 57

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


nearly 30 times more than that in [N222H][CF3SO3(CF3SO3H)2]. The results of corrosion test supports the advantage of the [N222H][CF3SO3(CF3SO3H)2] catalyst system. 4. Conclusions

In this study, the isobutane alkylation was catalysed by TfOH with a family of protic ionic liquids based on TfOH and base. Variety molar ratio of ionic liquid was mixed in TfOH to tune acidity. [N222H]CF3SO3 showed its sluggish variation in the acidity of TfOH, buffering the acidity change, lengthening the life of TfOH. The anionic clusters, [CF3SO3(CF3SO3H)x]−(x=0, 1, 2) were characterized with 1H NMR for χTfOH=0.90, 0.79, 0.69, 0.59, 0.49. The

optimized

conditions

of

isobutane

alkylation

catalysed

by

[N222H][CF3SO3(CF3SO3H)x] (x=0, 1, 2) as follow: feed rate 500 mL/h, χTfOH 0.69, acid/hydrocarbon 30/50, 5 ℃, and 10 min. Under the optimal conditions, a maximum in selectivity to C8 up to 86.23%, RON up to 97.3, and reusability up to 36 runs was achieved. In addition, the addition of ionic liquid changed density, viscosity, interfacial intension with alkylate, system’s impurity compatibility and the causticity, which affect industrialization. The green, inexpensive, active, selective and stable catalytic system shows its potential in catalysing alkylation to produce clean alkylation oil and industrialization.

AUTHOR INFORMATION 21 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 57

Corresponding Author *Tel.: + 86 0311 81668811. E-mail addresses: [email protected].

*Tel.: + 86 010 82627080. E-mail addresses: [email protected].

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT

This work was financially supported by the National Natural Science Foundation of China (51374193), the Special Program for International Science and Technology Cooperation and Exchange Program of China (2014DFA61670), Beijing Natural Science Foundation (2122052), International Cooperation and Exchange of the National Natural Science Foundation of China (51561145020) and International Partnership Program for Creative Research Teams (20140491518).


Page 23 of 57

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


REFERENCES 1. Ipatieff, V. N.; Schmerling, L., Alkylation of Isoparaffins. Adv. Catal. 1948, 1, 27-64.

2. Corma,

A.;

Martinez,

A.,

Chemistry,

Catalysts,

and

Processes

for

Isoparaffin-Olefin Alkylation - Actual Situation and Future-Trends. Catal. Rev 1993, 35, (4), 483-570.

3. Hommeltoft, S. I., Isobutane alkylation - Recent developments, and future perspectives. Appl. Catal. A-Gen. 2001, 221, (1-2), 421-428.

4. Liu, Y.; Li, R.; Sun, H. J.; Hu, R. S., Effects of catalyst composition on the ionic liquid catalyzed isobutane/2-butene alkylation. J. Mol. Catal. A-chem. 2015, 398, 133-139.

5. Zhang, J.; Huang, C.; Chen, B.; Ren, P.; Pu, M., Isobutane/2-butene alkylation catalyzed by chloroaluminate ionic liquids in the presence of aromatic additives. J. Catal. 2007, 249, (2), 261-268.

6. Angueira, E. J.; White, M. G., Super acidic ionic liquids for arene carbonylation derived from dialkylimidazolium chlorides and MCl3 (M = Al, Ga, or In). J. Mol. Catal. A-chem. 2007, 277, (1-2), 164-170.

7. Yoo, K., Ionic liquid-catalyzed alkylation of isobutane with 2-butene. J. Catal. 2004, 222, (2), 511-519.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 57

8. Tang, S. W.; Scurto, A. M.; Subramaniam, B., Improved 1-butene/isobutane alkylation with acidic ionic liquids and tunable acid/ionic liquid mixtures. J. Catal. 2009, 268, (2), 243-250.

9. Cui, P.; Zhao, G. Y.; Ren, H. L.; Huang, J.; Zhang, S. J., Ionic liquid enhanced alkylation of iso-butane and 1-butene. Catal. Today 2013, 200, 30-35.

10.

Ren, H.; Zhao, G.; Zhang, S.; Cui, P.; Huang, J., Triflic acid catalyzed

isobutane alkylation with trifluoroethanol as a promoter. Catal. Commun. 2012, 18, 85-88.

11.

Olah, G. A.; Batamack, P.; Deffieux, D.; Török, B.; Wang, Q.; Molnár, Á.;

Surya Prakash, G. K., Acidity dependence of the trifluoromethanesulfonic acid catalyzed isobutane-isobutylene alkylation modified with trifluoroacetic acid or water. Appl. Catal. A-Gen. 1996, 146, (1), 107-117.

12.

MacFarlane, D. R.; Vijayaraghavan, R.; Ha, H. N.; Izgorodin, A.; Weaver, K.

D.; Elliott, G. D., Ionic liquid "buffers"-pH control in ionic liquid systems. Chem. Commun. 2010, 46, (41), 7703-7705.

13.

Matuszek, K.; Chrobok, A.; Coleman, F.; Seddon, K. R.; Swadźba-Kwaśny,

M., Tailoring ionic liquid catalysts: structure, acidity and catalytic activity of protonic ionic liquids based on anionic clusters, [(HSO4)(H2SO4)x]− (x = 0, 1, or 2). Green Chem. 2014, 16, (7), 3463-3471.


Page 25 of 57

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


14.

McCune, J. A.; He, P.; Petkovic, M.; Coleman, F.; Estager, J.; Holbrey, J. D.;

Seddon, K. R.; Swadzba-Kwasny, M., Bronsted acids in ionic liquids: how acidity depends on the liquid structure. Phys. Chem. Chem. Phys. 2014, 16, (42), 23233-23243.

15.

Desset, S. L.; Reader, S. W.; Cole-Hamilton, D. J., Aqueous-biphasic

hydroformylation of alkenes promoted by "weak" surfactants. Green Chem. 2009, 11, (5), 630-637.

16.

Huang, Q.; Zhao, G. Y.; Zhang, S. J.; Yang, F. F., Improved Catalytic

Lifetime of H2SO4 for Isobutane Alkylation with Trace Amount of Ionic Liquids Buffer. Ind. Eng. Chem. Res. 2015, 54, (5), 1464-1469.

17.

Bui, T. L. T.; Jess, A., Investigations on Alkylation of Isobutane with

2-Butene Using Highly Acidic Ionic Liquids as Catalysts: Untersuchungen zur Alkylierung von Iso-Butan mit 2-Buten unter Verwendung von hochaciden ionischen Flüssigkeiten als Katalysatoren. Universität Bayreuth, Lehrstuhl für Chemische Verfahrenstechnik: 2007.

18.

Fărcaşiu, D.; Ghenciu, A., Determination of acidity functions and acid

strengths by 13C NMR. Prog. Nucl. Mag. Res. Sp 1996, 29, (3-4), 129-168.

19.

Corrosion of Metals and Alloys-General Principles for Corrosion Testing;

GB/T 19291-2003; Standards Press of China: Beijing ,China, 2004. ISBN: 155066.1-20248.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

20.

Page 26 of 57

Method of copper sulfate-sulfuric acid test for stainless steels; GB/T

4334.6-2000;

Standards

Press

of

China: Beijing,

China,

2001.

ISBN:

155066.1-17464.

21.

Chauvin, Y.; Hirschauer, A.; Olivier, H., Alkylation of Isobutane with

2-Butene

Using

1-Butyl-3-Methylimidazolium

Chloride

Aluminum-Chloride

Molten-Salts as Catalysts. J. Mol. Catal. 1994, 92, (2), 155-165.

22.

Haifang, L. Study on Isobutane Alkylation Utilizing Ionic Liquid/Acid as

Catalyst. Master Hebei University of Science and Technology, 2013.

23.

Roualdes, S.; Topala, I.; Mahdjoub, H.; Rouessac, V.; Sistat, P.; Durand, J.,

Sulfonated polystyrene-type plasma-polymerized membranes for miniature direct methanol fuel cells. J. Power Sources 2006, 158, (2), 1270-1281.

24.

Dong, K.; Zhang, S., Hydrogen bonds: a structural insight into ionic liquids.

Chem.-Eur. J. 2012, 18, (10), 2748-2761.

25.

Kumar, M.; Venkatnathan, A., Mechanism of proton transport in

ionic-liquid-doped perfluorosulfonic acid membranes. J. Phys. Chem. B 2013, 117, (46), 14449-14456.

26.

Hou, G. L.; Lin, W.; Deng, S. H.; Zhang, J.; Zheng, W. J.; Paesani, F.; Wang,

X. B., Negative Ion Photoelectron Spectroscopy Reveals Thermodynamic Advantage of Organic Acids in Facilitating Formation of Bisulfate Ion Clusters: Atmospheric Implications. J. Phys. Chem. Lett. 2013, 4, (5), 779-785. 26 ACS Paragon Plus Environment

Page 27 of 57

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


27.

Lu, D.; Zhao, G.; Ren, B.; Jiang, Z.; Zhang, S., Isobutane alkylation

catalyzed by ether functionalized ionic liquids. J. Chem. Ind. Eng.2015, 66, (7), 2481-2487.

28.

Li, X.; Yang, F.; Zhou, Q.; Zhang, S., Synthesis and Properties of

1-Methyl-3-Alkylimidazolium Tetrahalogenoferrate Magnetic Ionic Liquids. Chin. J. Process. Eng. 2010, 10, (4), 788-794.

29.

Kranz, K. Intro to Alkylation Chemistry. Mechanisms, Operating Variables,

and Olefin Interactions. DuPont STRATCO® Clean Fuel Technology: Leawood, KS, 2008. http://www2.dupont.com/Sustainable_Solutions/en_US/assets/downloads/stratco/Alk ylationChemistry.pdf.

30

Yigong, H. E.; Zheng, M. A. N., Thermodynamic analysis on i-C40/C4=

alkylation. J. Fuel. Chem. Techno. 2006, 34, (5), 591-594.

31.

Berenblyum, A. S.; Katsman, E. A.; Hommeltoft, S. I.; Zavilla, D.; Zhlobich,

E. A., Isooctane degradation in the presence of trifluoromethanesulfonic acid. Kinet. Catal. 1999, 40, (3), 431-431.

32.

Editorial Board Association of sulfuric acid. Sulfuric acid manual; Chemical

Industry Press,Beijing : China, 1982. ISBN: 15063.3271.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 57


Page 29 of 57

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 1. Effect of TfOH mole fraction (χTfOH) on the acid strength at atmospheric pressure, room temperature.

Figure 2. FT-IR spectra of the [N222H][CF3SO3(CF3SO3H)x](x=0, 1, 2) system, for χTfOH =1.00, 0.90, 0.79, 0.69, 0.59 and 0.49.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure

3.

1

H

NMR

spectra

(600

MHz,

25°C,

Page 30 of 57

neat)

of

the

[N222H][CF3SO3(CF3SO3H)x] (x=0, 1, 2) system, for χTfOH =0.90, 0.79, 0.69, 0.59 and 0.49.

Figure 4. Molecular structure of [CF3SO3 (CF3SO3H)x]− (x=0) using ball and stick mode.


Page 31 of 57

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5. Molecular structure of [CF3SO3(CF3SO3H)x]− (x=1) using ball and stick mode.

Figure 6. Molecular structure of [CF3SO3(CF3SO3H)x]− (x=2) using ball and stick mode.

Figure 7. Alkylate composition and RON varied with acid strength of catalyst system. Reaction conditions: reaction time 10 min, catalyst 40 mL, feed rate 500 mL/h, acid/hydrocarbon 30/50, 5 ºC.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 57

Figure 8. Effect of volume ratio of acid to olefins on alkylate composition and RON. Reaction conditions: reaction time 10 min, catalyst 40 mL, feed rate 500 mL/h, χTfOH 0.69, 5 °C.

Figure 9. The Gibbs free energy change trend of alkylation at different temperatures under 0.4 MPa.


Page 33 of 57

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 10. Effect of reaction temperature on alkylate composition and RON. Reaction conditions: reaction time 10 min, catalyst 40 mL, feed rate 500 mL/h, χTfOH 0.69, acid/hydrocarbon 30/50.

Figure 11. Effect of reaction temperature on isooctane distributions. Reaction conditions: reaction time 10 min, catalyst 40 mL, feed rate 500 mL/h, χTfOH 0.69, acid/hydrocarbon 30/50.

Figure 12. Effect of reaction time on alkylate composition and RON. Reaction conditions: catalyst 40 mL, feed rate 500 mL/h, χTfOH 0.69, acid/hydrocarbon 30/50, 5 °C.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 57

Figure 13. The reusability of [N222H]CF3SO3/TfOH catalyst. Reaction conditions: catalyst 40 mL, feed rate 500 mL/h, χTfOH 0.69, acid/hydrocarbon 30/50, 5 °C, 10 min.

Figure 14. Effect of H2O contents in catalyst on the alkylation reaction. Reaction conditions: catalyst 40 mL, feed rate 500 mL/h, χTfOH 0.69, acid/hydrocarbon 30/50, 5 °C, 10 min.


Page 35 of 57

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 15. Effect of Methanol contents in catalyst on the alkylation reaction. Reaction conditions: catalyst 40 mL, feed rate 500 mL/h, χTfOH 0.69, acid/hydrocarbon 30/50, 5 °C, 10 min.

Figure 16. Effect of MTBE contents in catalyst on the alkylation reaction. Reaction conditions: catalyst 40 mL, feed rate 500 mL/h, χTfOH 0.69, acid/hydrocarbon 30/50, 5 °C, 10 min.

Figure 17. Effect of N-butyl mercaptan contents in catalyst on the alkylation reaction. Reaction conditions: catalyst 40 mL, feed rate 500 mL/h, χTfOH 0.69, acid/hydrocarbon 30/50, 5 °C, 10 min.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 36 of 57

Table 1. Composition of isobutane/butene mixture. Composition

Content (wt. %)

Isobutane

83.78

n-Butane

6.09

(E)-2-Butene

2.51

(Z)-2-Butene

0.95

Isobutene

3.01

n-Butene

3.65

Alkanes/Olefins

8.88(regard as 8.5)


Page 37 of 57

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 2. Density, viscosity and interfacial tension varied with χTfOH on at Pressure p=0.1 Mpa and Temperature T=20 °Ca. χTfOH ρ(g·cm-3)

Std.

η(103Pa·s)

Std.

σ(mN·m-1)

Std.

1.00

1.68

0.010

1.61

0.030

6.34

0.115

0.90

1.66

0.009

2.56

0.038

8.73

0.121

0.79

1.61

0.010

4.67

0.020

9.36

0.117

0.69

1.55

0.008

9.36

0.032

9.31

0.114

0.59

1.55

0.014

11.17

0.042

8.94

0.115

0.49

1.45

0.010

11.42

0.025

9.14

0.120

98%H2SO4

0

1.81b

--

25.76c

--

25.25

0.095

Et3NHCl-AlCl3 IL

0

1.61

0.007

98.50

0.024

--

--

[N222H]CF3SO3

a

ρ, η is the density and viscosity of catalyst, respectively; σ is the of interfacial tension of catalyst with alkylate; Std is the standard deviation. Standard uncertainties u are u(T) = 0.1 °C, u(p) = 0.01 MPa , and the combined expanded uncertainty Uc is Uc(ρ) = 0.008 g·cm−3 (0.95 level of confidence).b The density of sulfuric acid reported by ref. 32. c The viscosity of sulfuric acid reported by ref. 32.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 38 of 57

Table 3. The threshold value of impurities in catalyst. Impurities

Quantity(mg/g)

H2 O

Anionic Clusters Enhanced Catalytic Performance of Protic Acid Ionic

Recommend Documents