Method for preparing alkylphenol through alkylation of phenol and isopropanol
By using H-Beta molecular sieve catalysts to regulate the reaction conditions of phenol and isopropanol in a fixed-bed reactor, the environmental pollution problem of traditional alkylphenol synthesis processes has been solved, achieving efficient and selective alkylphenol preparation and promoting the high-value transformation of lignin resources.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHENYANG AEROSPACE UNIVERSITY
- Filing Date
- 2026-01-28
- Publication Date
- 2026-05-05
AI Technical Summary
Traditional alkylphenol synthesis processes rely on highly corrosive and polluting homogeneous acid catalysts, which have problems such as difficult catalyst recovery, severe equipment corrosion, and significant environmental pollution, making it difficult to achieve the green and efficient conversion of lignin-derived phenols into high-value-added fuels.
Using H-Beta molecular sieve as a catalyst, the alkylation reaction of phenol and isopropanol was carried out in a fixed-bed continuous process. The reaction temperature, hydrogen pressure and mass hourly space velocity were controlled to prepare alkylphenols.
This method achieves good catalyst stability, mild reaction conditions, and high product selectivity, enabling efficient preparation of high-carbon-number liquid fuel precursors and demonstrating significant industrial application value.
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Figure CN121974784A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of biomass energy chemical technology, and in particular to a method for preparing alkylphenols by alkylation of phenol and isopropanol. Background Technology
[0002] The chemical composition of lignin-derived oils varies significantly due to the influence of raw material sources and preparation processes. Its core components remain primarily phenolic compounds, including polycyclic phenols, alkylphenols with different substitution types, and alkoxyphenols. These phenolic compounds are key precursors for the preparation of aromatic hydrocarbons, cycloalkanes, and alkylcyclohexanols, among other liquid fuels. However, the cycloalkanes produced by direct hydrogenation and deoxygenation of low-carbon-number phenols (such as phenol, methylphenol, and guaiacol) do not have sufficient carbon chain length to meet the molecular structure requirements of high-carbon-number fuels (such as aviation kerosene or higher alcohols). Therefore, introducing alkyl branches onto the benzene ring to increase the carbon number and regulate the product structure is crucial for promoting the conversion of lignin-derived oils into high-value-added fuels.
[0003] CC coupling is a crucial method for achieving benzene ring alkylation, enabling the targeted introduction of specific alkyl chains. As a typical acid-catalyzed process, this method plays an irreplaceable role in the conversion of lignin-derived phenols into aviation fuels. By effectively increasing the carbon number and calorific value of phenolic compounds, it lays the foundation for subsequent complete hydrodeoxygenation to produce high-performance fuels. However, traditional alkylphenol synthesis processes, such as the Friedel-Crafts alkylation of phenol and propylene, while technically mature, typically rely on highly corrosive and polluting homogeneous acid catalysts (such as concentrated sulfuric acid, aluminum trichloride, and hydrofluoric acid), resulting in problems such as difficult catalyst recovery, severe equipment corrosion, and significant environmental pollution. Therefore, developing novel catalytic systems that are green, efficient, highly selective, and operate under mild reaction conditions is not only an urgent need to improve the sustainability of lignin-derived phenol alkylation processes but also an important direction for realizing the high-value conversion of lignin resources and promoting the industrialization of biomass fuels. Summary of the Invention
[0004] In view of this, the present invention provides a method for preparing alkylphenols by alkylation of phenol and isopropanol based on H-Beta molecular sieve catalysis. This method employs a fixed-bed continuous process, which has advantages such as adjustable product selectivity and good catalyst stability.
[0005] To achieve the above objectives, the present invention provides the following solution: This invention provides a method for preparing alkylphenols by alkylation of phenol and isopropanol, comprising the following steps: Step 1: The H-Beta molecular sieve is subjected to calcination pretreatment to obtain the pretreated molecular sieve; Step 2: The pretreated molecular sieve is loaded into a fixed-bed reactor, and after the air is vented, it is preheated to 200℃~350℃; Step 3: Dissolve phenol in isopropanol to obtain a mixed raw material; Step 4: Pump the mixed raw materials into a fixed-bed reactor to contact the pretreated molecular sieve, at a temperature of 200℃~350℃, a hydrogen pressure of 0.1MPa~1.5MPa, and a mass hourly space velocity of 2-5h. -1 Under certain conditions, an alkylation reaction was carried out to obtain alkylphenols.
[0006] In a preferred embodiment of the present invention, the silica-to-alumina ratio of the H-Beta molecular sieve is 10 to 20.
[0007] In a preferred embodiment of the present invention, in step 1, the conditions for the calcination pretreatment are set as follows: the temperature is increased to 400°C at a heating rate of 10°C / min, and calcined for 100 min.
[0008] In a preferred embodiment of the present invention, in step 2, the air in the fixed-bed reactor is vented out by introducing nitrogen gas.
[0009] In a preferred embodiment of the present invention, the flow rate of nitrogen is 100 mL / min.
[0010] In a preferred embodiment of the present invention, in step 3, the molar ratio of phenol to isopropanol is 1:(1~5).
[0011] The present invention also provides a method for preparing alkylphenols that can directionally control the product distribution. The method for preparing alkylphenols by alkylation of phenol and isopropanol described above can achieve the conversion of alkylphenols to polyisopropylphenols or monoisopropylphenols by adjusting the molar ratio of phenol to isopropanol, reaction temperature, hydrogen pressure and mass hourly space velocity.
[0012] In a preferred embodiment of the present invention, when the target product is polyisopropylphenol, the molar ratio of phenol to isopropanol is 1:(3~5), the reaction temperature is 300°C, the hydrogen pressure is 1.0 MPa, and the mass hourly space velocity is 2~3 h⁻¹. -1 ; The polyisopropylphenols include 2-isopropylphenol and 3-isopropylphenol.
[0013] In a preferred embodiment of the present invention, when the target product is mainly monoisopropylphenol, the molar ratio of phenol to isopropanol is 1:1, the reaction temperature is 300°C, the hydrogen pressure is 0.5 MPa, and the mass hourly space velocity (WHSV) is 4 h⁻¹. -1 ; The monoisopropylphenol includes 2-isopropylphenol, 3-isopropylphenol, and 4-isopropylphenol.
[0014] Compared with the prior art, the present invention has the following beneficial effects: This invention utilizes H-Beta molecular sieves as a catalyst and phenol and isopropanol as raw materials (isopropanol also serves as a solvent) in a fixed-bed reactor. By controlling parameters such as reaction temperature, H2 pressure, and mass hourly space velocity, highly selective preparation of mono- or poly-isopropyl-substituted phenols is achieved. The catalyst of this invention exhibits excellent stability, mild reaction conditions, and high product selectivity, enabling efficient preparation of liquid fuel precursors (isopropyl-substituted phenols) such as aromatic hydrocarbons, cycloalkanes, and alkylcyclohexanols, demonstrating significant industrial application value.
[0015] The method of this invention is particularly suitable for upgrading lignin-derived phenolic compounds to prepare liquid fuel precursors such as aromatic hydrocarbons, cycloalkanes, and alkylcyclohexanols. Attached Figure Description
[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0017] Figure 1 The effect of the feed molar ratio of phenol to isopropanol on the alkylation reaction of phenol and isopropanol in Example 1.
[0018] Figure 2 The effect of operating conditions on alkylation conversion and product distribution at a phenol to isopropanol molar ratio of 1:5 in Example 2 is shown.
[0019] Figure 3 The effect of operating conditions on alkylation conversion and product distribution under a phenol to isopropanol molar ratio of 1:1 in Example 2 is shown.
[0020] Figure 4 The changes in alkylation conversion and product distribution over 8 hours in Example 3 are shown; where (a) the molar ratio of phenol to isopropanol is 1:1; and (b) the molar ratio of phenol to isopropanol is 1:5. Detailed Implementation
[0021] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.
[0022] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included within the scope of this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.
[0023] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.
[0024] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.
[0025] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.
[0026] This invention provides a method for preparing alkylphenols by alkylation of phenol and isopropanol, comprising the following steps: Step 1: The H-Beta molecular sieve is subjected to calcination pretreatment to obtain the pretreated molecular sieve; Step 2: The pretreated molecular sieve is loaded into a fixed-bed reactor, and after the air is vented, it is preheated to 200℃~350℃; Step 3: Dissolve phenol in isopropanol to obtain a mixed raw material; Step 4: Pump the mixed raw materials into a fixed-bed reactor to contact the pretreated molecular sieve, at a temperature of 200℃~350℃, a hydrogen pressure of 0.1MPa~1.5MPa, and a mass hourly space velocity of 2-5h. -1 Under certain conditions, an alkylation reaction was carried out to obtain alkylphenols.
[0027] In a preferred embodiment of the present invention, the silica-to-alumina ratio of the H-Beta molecular sieve is 10 to 20.
[0028] In a preferred embodiment of the present invention, in step 1, the conditions for the calcination pretreatment are set as follows: the temperature is increased to 400°C at a heating rate of 10°C / min, and calcined for 100 min.
[0029] In this invention, the purpose of calcination is to remove the moisture and impurities adsorbed on the surface of the molecular sieve, remove the residual template agent from the preparation process, and stabilize the crystal structure of the molecular sieve, so as to improve the catalytic effect of the molecular sieve.
[0030] In a preferred embodiment of the present invention, in step 2, the air in the fixed-bed reactor is vented out by introducing nitrogen gas.
[0031] In a preferred embodiment of the present invention, the flow rate of nitrogen is 100 mL / min.
[0032] In this invention, isopropanol serves as both an alkylating agent and a solvent.
[0033] In a preferred embodiment of the present invention, in step 3, the molar ratio of phenol to isopropanol is 1:(1~5).
[0034] In some specific embodiments, the alkylphenol obtained by alkylation reaction is discarded after the first 30 minutes of reaction product, and the liquid product is collected after the reaction has been running for 150 minutes (i.e., the product of the first 30 minutes is discarded, and the reaction is run for another 120 minutes to collect the product of the first 120 minutes); after collecting the reaction product, a separation and purification step is also included.
[0035] In some specific embodiments, the pretreated molecular sieve is packed into the middle layer of the fixed-bed reactor, with a molecular sieve dosage of 6g and a single experiment duration of 90min.
[0036] The present invention also provides a method for preparing alkylphenols that can directionally control the product distribution. The method for preparing alkylphenols by alkylation of phenol and isopropanol described above can achieve the conversion of alkylphenols to polyisopropylphenols or monoisopropylphenols by adjusting the molar ratio of phenol to isopropanol, reaction temperature, hydrogen pressure and mass hourly space velocity.
[0037] In a preferred embodiment of the present invention, when the target product is polyisopropylphenol, the molar ratio of phenol to isopropanol is 1:(3~5), the reaction temperature is 300°C, the hydrogen pressure is 1.0 MPa, and the mass hourly space velocity is 2~3 h⁻¹. -1 ; The polyisopropylphenols include 2-isopropylphenol and 3-isopropylphenol.
[0038] In a preferred embodiment of the present invention, when the target product is mainly monoisopropylphenol, the molar ratio of phenol to isopropanol is 1:1, the reaction temperature is 300°C, the hydrogen pressure is 0.5 MPa, and the mass hourly space velocity (WHSV) is 4 h⁻¹. -1 ; The monoisopropylphenol includes 2-isopropylphenol, 3-isopropylphenol, and 4-isopropylphenol.
[0039] The alkylphenols prepared by the method of this invention can be used as precursors for the preparation of liquid fuels such as aromatic hydrocarbons, cycloalkanes and alkylcyclohexanols.
[0040] Unless otherwise specified, the technical solutions described in this invention are all conventional solutions in the field, and the reagents or raw materials used are all purchased from commercial channels or are publicly available unless otherwise specified.
[0041] The commercially available H-Beta molecular sieve used in this invention has a specific surface area >550 m². 2 / g, bulk density ≥0.35g / mL, moisture content ≤1.5%, silicon-aluminum ratio 10-20.
[0042] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.
[0043] Preparation Example 1 Step 1: Place the commercial H-Beta molecular sieve (Si / Al=10-20) in a beaker; Step 2: Place the beaker in a muffle furnace and heat it to 400℃ at a rate of 10℃ / min. Calcine for 100min to remove the water and impurities adsorbed on the surface of the molecular sieve and obtain the calcined H-Beta molecular sieve catalyst. Step 3: Fix the calcined H-Beta molecular sieve (6g) to the middle layer of the fixed-bed reactor bed using a porous metal tray; Step 4: Using phenol and isopropanol as reaction raw materials, and isopropanol as solvent, prepare the raw material solution according to the set molar ratio and store it in the raw material tank at room temperature. Step 5: Introduce nitrogen gas into the reaction system (flow rate 100 mL / min) to purge air, and then heat the preheating furnace, heating belt and fixed bed to the target temperature; Step 6: After the system parameters stabilize, start the high-pressure liquid pump, discard the reaction products in the first 30 minutes, and collect the liquid products after the reaction has proceeded for 150 minutes.
[0044] The reaction results under different molar ratios of phenol and isopropanol and under different reaction conditions are shown in Examples 1 to 3.
[0045] Example 1 300℃, 1MPa, 2h -1 The alkylation conversion rate and product distribution of phenol under the operating conditions vary with the molar ratio of phenol to isopropanol as follows: Figure 1As shown, with the molar ratio of phenol to isopropanol increasing from 1:1 to 1:5, the conversion rate of phenol increased from 81.11% to 97.16%. Excess isopropanol resulted in a more complete reaction of phenol. At molar ratios of 1:3 and 1:5, the product was mainly polyisopropyl-substituted phenol. Furthermore, with increasing isopropanol content, the selectivity for 2,4,6-triisopropyl substituents in the product increased, reaching a maximum of 18.21%, while the selectivity for 3,5-diisopropylphenol decreased from 25.21% to 15.95%. At a feed ratio of 1:1, the proportions of 2-isopropylphenol, 2-propylphenol, and 3-isopropylphenol were 85.53%, with 2-isopropylphenol isomerization producing 25.97% 2-propylphenol.
[0046] Example 2 The effects of reaction temperature, pressure, and space velocity on conversion and product distribution when the molar ratio of phenol to isopropanol is 1:5 are as follows: Figure 2 As shown, Figure 2 (a) shows a mass hourly space velocity of 2h. -1 The effect of temperature on phenol conversion and alkylation product distribution under normal pressure was investigated. The highest phenol conversion was observed at 300℃. At 250℃, insufficient energy prevented complete reaction of phenol, resulting in the production of a small amount of propoxybenzene. The product from complete hydrogenation-deoxylation (HDO) of propoxybenzene was identical to that of phenol, rendering alkylation meaningless as it did not add carbon atoms. At 350℃, the overall selectivity for diisopropyl-substituted and triisopropyl-substituted phenols reached 100%. The selectivity for 2,6-diisopropyl-substituted phenols gradually decreased to 8.92%, while the selectivity for 2,4-diisopropylphenol gradually increased to 58.77%. The selectivity for 3,5-diisopropylphenol reached its highest value of 25.21% at a molar ratio of 1:3.
[0047] Figure 2 Figure (b) shows the results at 300°C and a mass hourly space velocity of 2 h⁻¹. -1 The effect of pressure on phenol conversion and alkylation product distribution under operating conditions was investigated. Phenol conversion increased with increasing pressure, reaching a maximum of 95.38% at 1 MPa. Further increases in pressure had no significant effect on conversion. The proportion of 2,4,6-triisopropylphenol gradually increased with increasing pressure, reaching a maximum of 18.72%. Increasing the reaction pressure from 1 MPa to 1.5 MPa had no significant effect on phenol conversion or alkylation product selectivity; therefore, 1 MPa is the optimal reaction pressure at a molar ratio of 1:5.
[0048] Figure 2 Figure (c) shows the effect of different space velocities on phenol conversion and alkylation product distribution under operating conditions of 300℃ and 1MPa. The space velocity was increased from 2 h⁻¹ to 1 h⁻¹. -1 Upgraded to 3h -1There was no significant difference in phenol conversion rate at different times, with a space velocity of 3 h⁻¹. -1 The highest conversion rate was achieved at 74.42% at a space velocity of 5 h⁻¹, but the conversion rate of phenol decreased with further increases in space velocity. -1 The conversion rate decreased to 64.25% over time. Changes in space velocity had no significant effect on product selectivity. (3h) -1 Mass air velocity is the operating condition with the highest productivity.
[0049] The effects of reaction temperature, pressure, and space velocity on conversion and product distribution when the molar ratio of phenol to isopropanol is 1:1 are as follows: Figure 3 As shown; Figure 3 Image (a) shows an airspeed of 3h. -1 The effect of temperature on phenol conversion and alkylation product distribution under normal pressure was investigated. When isopropanol was insufficient, 250℃ was the optimal temperature for phenol conversion, indicating that this temperature fully activated the phenol, achieving a conversion rate of 77.29%, with 2-isopropylphenol and 3-isopropylphenol accounting for 33.50% and 27.06%, respectively. Further increasing the temperature significantly reduced the phenol conversion rate; at 350℃, the conversion rate dropped to 19.39%, and the substituted phenols 3,5-diisopropylphenol, 2,4-diisopropylphenol, and 2,6-diisopropylphenol completely disappeared. High temperatures were unfavorable for the formation of diisopropylphenol and triisopropylphenol; 300℃ was most favorable for the formation of 2-isopropylphenol and 3-isopropylphenol, consistent with the results obtained under a phenol to isopropanol molar ratio of 1:5.
[0050] At 300℃ for 3 hours -1 Investigating the effect of pressure on the alkylation of phenol and isopropanol under operating conditions, such as Figure 3 As shown in (b), increased pressure facilitates the conversion of phenol, and at 1 MPa, 25.97% of 4-isopropylphenol is produced, while the proportion of 3-isopropylphenol decreases significantly. At 1 MPa, the selectivity of 3-isopropylphenol decreases to 30.38%. Compared to a reaction pressure of 0.5 MPa, the improvement in selectivity for 2-isopropylphenol and 3-isopropylphenol at 1 MPa is not significant and not economically viable; therefore, 0.5 MPa is the optimal pressure for the production of 2-isopropylphenol and 3-isopropylphenol.
[0051] The effect of space velocity on the alkylation of phenol and isopropanol, as follows Figure 3 As shown in (c), the conclusions obtained are consistent with the previous research results. It shows that the phenol conversion rate gradually decreases with increasing space velocity, but the proportions of 2-isopropylphenol and 3-isopropylphenol continuously increase, reaching a space velocity of 5 h⁻¹. -1 The selectivity for monoisopropyl-substituted phenols reached 92.33%, but since the phenol conversion was only 70.26%, the space velocity was 4 h⁻¹. -1The yields of 2-isopropylphenol and 3-isopropylphenol were optimal.
[0052] Example 3 At a phenol to isopropanol molar ratio of 1:5, at 300℃, 1MPa, and for 3 hours... -1 The molar ratio of phenol to isopropanol was 1:1, at 300℃, 0.5MPa, and for 4 hours. -1 An 8-hour continuous alkylation experiment was conducted under these conditions to investigate the stability of the calcined H-Beta molecular sieve catalyst in catalyzing the alkylation reaction. The results are as follows: Figure 4 As shown in the figure, the phenol conversion rate remained stable in both groups of experiments, with a significantly higher conversion rate at a molar ratio of 1:5 compared to 1:1. The selectivity of 3,5-diisopropylphenol gradually decreased, reaching 15% at 8 hours. The selectivity of 2,4,6-triisopropylphenol remained constant. The selectivity of monoisopropyl-substituted phenols decreased to 72.8% at 8 hours. The phenol conversion rate remained stable in both groups of experiments, with no significant deactivation observed. At a phenol to isopropanol molar ratio of 1:5, the product selectivity remained essentially constant; at a phenol to isopropanol molar ratio of 1:1, the selectivity of monoisopropyl-substituted phenols decreased slightly at 8 hours (to 72.8%). H-Beta molecular sieves exhibited good stability in this process.
[0053] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.
Claims
1. A method for preparing alkylphenols by alkylation of phenol and isopropanol, characterized in that, Includes the following steps: Step 1: The H-Beta molecular sieve is subjected to calcination pretreatment to obtain the pretreated molecular sieve; Step 2: The pretreated molecular sieve is loaded into a fixed-bed reactor, and after the air is vented, it is preheated to 200℃~350℃; Step 3: Dissolve phenol in isopropanol to obtain a mixed raw material; Step 4: Pump the mixed raw materials into a fixed-bed reactor to contact the pretreated molecular sieve, at a temperature of 200℃~350℃, a hydrogen pressure of 0.1MPa~1.5MPa, and a mass hourly space velocity of 2-5h. -1 Under certain conditions, an alkylation reaction was carried out to obtain alkylphenols.
2. The method for preparing alkylphenols by alkylation of phenol and isopropanol according to claim 1, characterized in that, The H-Beta molecular sieve has a silica-to-alumina ratio of 10 to 20.
3. The method for preparing alkylphenols by alkylation of phenol and isopropanol according to claim 1, characterized in that, In step 1, the conditions for the calcination pretreatment are set as follows: the temperature is increased to 400℃ at a heating rate of 10℃ / min, and calcined for 100min.
4. The method for preparing alkylphenol by alkylation of phenol and isopropanol according to claim 1, characterized in that, In step 2, nitrogen gas is introduced to purge the air from the fixed-bed reactor.
5. The method for preparing alkylphenols by alkylation of phenol and isopropanol according to claim 4, characterized in that, The flow rate of the nitrogen gas is 100 mL / min.
6. The method for preparing alkylphenol by alkylation of phenol and isopropanol according to claim 1, characterized in that, In step 3, the molar ratio of phenol to isopropanol is 1:(1~5).
7. A method for preparing alkylphenols capable of directionally controlling product distribution, characterized in that, The method for preparing alkylphenol by alkylation of phenol and isopropanol according to any one of claims 1 to 6 achieves the conversion of alkylphenol to polyisopropylphenol or monoisopropylphenol by adjusting the molar ratio of phenol to isopropanol, reaction temperature, hydrogen pressure and mass hourly space velocity.
8. The method for preparing alkylphenols according to claim 7, characterized in that, When the target product is polyisopropylphenol, the molar ratio of phenol to isopropanol is 1:(3~5), the reaction temperature is 300℃, the hydrogen pressure is 1.0 MPa, and the mass hourly space velocity is 2~3 h⁻¹. -1 ; The polyisopropylphenols include 2-isopropylphenol and 3-isopropylphenol.
9. The method for preparing alkylphenols according to claim 7, characterized in that, When the target product is mainly monoisopropylphenol, the molar ratio of phenol to isopropanol is 1:1, the reaction temperature is 300℃, the hydrogen pressure is 0.5 MPa, and the mass hourly space velocity (WHSV) is 4 h⁻¹. -1 ; The monoisopropylphenol includes 2-isopropylphenol, 3-isopropylphenol, and 4-isopropylphenol.