Abstract In the production field of petrochemical fine chemicals, the distillation separation of non-oil materials (such as organic solvents, specialty chemicals, fine intermediates, etc.) is a key process link. Combining the characteristics of equip...
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Abstract
In the production field of petrochemical fine chemicals, the distillation separation of non-oil materials (such as organic solvents, specialty chemicals, fine intermediates, etc.) is a key process link. Combining the characteristics of equipment such as tray columns, packed columns, and thin-film evaporators, this paper systematically analyzes the application scenarios, equipment selection principles, and engineering practices of different distillation technologies in the treatment of non-oil materials, providing technical references for petrochemical enterprises.
Non-oil petrochemical materials usually have the following characteristics:
- Thermosensitivity: Fine chemicals such as epoxides and organosilicon monomers are prone to decomposition, polymerization, or discoloration at high temperatures, requiring low distillation temperatures and short residence times.
- Wide viscosity range: Viscosity can vary by hundreds of times, from low-viscosity solvents (such as methanol and ethyl acetate) to high-viscosity polymer intermediates (such as polyether polyols).
- Close boiling points: Isomer separation (e.g., p-xylene/o-xylene) and azeotrope separation require high-efficiency mass transfer equipment with high requirements for theoretical plates.
- Significant corrosiveness: Organic acids, halogenated hydrocarbons, and other materials have strict requirements on equipment materials, requiring the selection of corrosion-resistant materials or special coatings.
- High product purity: Electronic-grade chemicals and pharmaceutical intermediates usually require a purity of≥99.5%, or even above 99.9%.
- Yield sensitivity: High-value-added products are extremely sensitive to material loss, and each 1% increase in yield can bring significant economic benefits.
- Energy consumption control: Distillation is a high-energy-consuming unit operation, and energy consumption can account for 30-50% of the total production cost. Energy saving and consumption reduction are core demands.
- Environmental compliance: Requirements for VOCs emission control and waste liquid reduction are increasingly strict.
2.1.1 Core Advantages
- Large operating flexibility: Tray columns are limited by flooding and weeping, but well-designed columns have a load adjustment range of 30%-110%, adapting to production fluctuations.
- Strong adaptability to low liquid-gas ratios: When the liquid-gas ratio < 0.5, packed columns experience a sharp drop in efficiency due to poor wetting, while tray columns can still maintain stable mass transfer effects.
- Convenient maintenance: Trays can be disassembled for inspection and repair, resulting in low maintenance costs for systems requiring regular cleaning of scaling and polymers.
- Economy for large diameters: When the column diameter > 800mm, the cost of tray columns is usually 15-25% lower than that of packed columns.
2.1.2 Typical Applications
- Aromatics separation: Benzene-toluene-xylene rectification using float valve trays or sieve trays, with a column diameter of 1.5-3.5 meters and 40-80 theoretical plates.
- Recovery of chlorinated hydrocarbons from chlor-alkali by-products: Treatment of organic systems containing HCl using Hastelloy or PTFE-lined trays, operating pressure of 0.2-0.5MPa.
- Solvent dehydration: Dehydration and rectification of isopropanol and ethanol using azeotropic distillation process, column diameter of 0.8-2.0 meters.
2.1.3 Design Key Points
- Tray selection:
- Sieve trays: Simple structure, low cost, suitable for clean systems.
- Float valve trays: Maximum operating flexibility and good anti-clogging performance.
- Bubble cap trays: Small throughput but high efficiency, suitable for low liquid-gas ratios.
- Tray spacing: Conventional 450-600mm; reduced to 350mm for high-load columns and increased to 600-800mm for vacuum columns.
- Weir and downcomer system: Adopting弓形downcomers, with the downcomer area accounting for 12-15% of the column cross-sectional area, ensuring a liquid residence time of 3-7 seconds.
2.2.1 Core Advantages
- Extremely low pressure drop: The pressure drop per theoretical plate is only 0.01-0.3kPa, which is 1/5 of that of tray columns, making it particularly suitable for vacuum distillation and thermosensitive materials.
- High separation efficiency: Structured packings (such as corrugated packings and grid packings) have an HETP of 0.15-0.5 meters, which is much better than the 0.5-1.0 meters of tray columns.
- Large throughput: The porosity of the packing layer is > 90%, and the gas velocity can reach 1.5-2 times that of tray columns, increasing the processing capacity per unit cross-sectional area by 30-50%.
- Strong corrosion resistance: Non-metallic packings such as ceramics, graphite, and PTFE can be selected, suitable for highly corrosive systems.
2.2.2 Typical Applications
- Vacuum distillation:
- Thermosensitive organic compounds (e.g., vitamin intermediates) with a vacuum degree of 1-10kPa, using metal structured packings.
- High-boiling compounds (e.g., plasticizer DOP) with a vacuum degree < 1kPa, selecting wire mesh corrugated packings.
- Corrosive systems:
- Purification of organochlorosilanes: Using ceramic Raschig rings or ceramic saddle packings.
- Mercaptan-containing materials: Selecting graphite packings or PTFE-coated metal packings.
- Fine separation:
- Isomer separation (p/o/m-xylene): Metal orifice corrugated packings with an HETP of 0.2-0.3 meters.
- High-purity solvent preparation (electronic-grade IPA): Structured packed columns with more than 100 theoretical plates.
2.2.3 Design Key Points
Packing selection matrix:
|
Packing Type |
HETP (m) |
Pressure Drop (Pa/m) |
Capacity Factor |
Application Scenarios |
|
Metalrandom packing (Pall ring) |
0.4-0.6 |
150-250 |
Medium |
Conventional rectification |
|
Ceramic Raschig ring |
0.5-0.8 |
200-300 |
Low |
Highly corrosive systems |
|
Metal structured packing (250Y) |
0.25-0.35 |
80-150 |
High |
Vacuum/high-efficiency separation |
|
Wire mesh corrugated packing |
0.15-0.25 |
50-100 |
Highest |
Ultra-vacuum/thermosensitive materials |
Liquid distributors:
- Spray type: Suitable for low-viscosity (<5mPa·s) materials, with a distribution point density > 100 points/m².
- Trough type: Medium viscosity (5-50mPa·s), with a distribution uniformity of±5%.
- Pipe type: High viscosity (>50mPa·s) or solid-containing materials.
Redistributor spacing:
- Random packing: Install one layer every 5-8 meters.
- Structured packing: Install every 10-15 meters or every 3-4 layers of packing.
2.3.1 Core Advantages
- Ultra-low residence time: Materials stay on the heating surface for only 2-10 seconds, avoiding decomposition of thermosensitive materials.
- Ultra-vacuum operation: Can operate at an absolute pressure of 0.1-100Pa, reducing the evaporation temperature by 50-100℃.
- High viscosity adaptability: Can handle materials with a viscosity of up to 10⁴mPa·s.
- High single-stage separation efficiency: Single-stage evaporation is equivalent to 2-5 theoretical plates.
2.3.2 Typical Application Scenarios
- Purification of epoxy resin monomers:
- Material: Bisphenol A epoxy resin (E-51)
- Operating conditions: 0.1-1.0Pa, 160-180℃
- Effect: The standard deviation of epoxy value decreased from 15% to 5%, and the color APHA decreased from 150 to 50.
- Separation of organosilicon monomers:
- Material: Recovery of dimethylsiloxane (M₂) from high-boiling residues
- Operating conditions: 1-10Pa, 120-150℃
- Yield improvement: The total yield of M₂increased by 2-3%, bringing an annual additional benefit of 9 million yuan (for a 50,000-ton/year plant).
- Plasticizer purification:
- Material: Dioctyl phthalate (DOP), dioctyl terephthalate (DOTP)
- Operating conditions: 0.5-5Pa, 260-280℃
- Purity improvement: From 99.0% to 99.6%+, meeting food-grade requirements.
- Thermosensitive pharmaceutical intermediates:
- Material: An antibiotic side-chain intermediate
- Operating conditions: 0.5Pa, 80-100℃(atmospheric boiling point 220℃)
- Decomposition rate: From 8% to <1%.
2.3.3 Equipment Selection
Comparison of thin-film evaporator types:
|
Type |
Throughput (kg/h) |
Viscosity Range (mPa·s) |
Vacuum Degree (Pa) |
Suitable Materials |
|
Falling film |
50-500 |
<50 |
10-1000 |
Low-viscosity solvents |
|
Wiped film |
20-200 |
10-10⁴ |
0.1-100 |
High-viscosity/scaling materials |
|
Short-path distillation |
5-100 |
5-10³ |
0.1-10 |
Ultra-thermosensitive/high-value-added materials |
Typical specification parameters (taking wiped film evaporator as an example):
- Evaporation area: 0.5-5.0 m²
- Heating jacket temperature: Up to 350℃(thermal oil), 400℃(molten salt)
- Wiper speed: 50-300 rpm (adjustable)
- Material: 316L (standard), Hastelloy C-276 (high corrosion), titanium (chlorine-containing systems)
Pre-separation column + rectification column combination:
Case: Recovery of light components from by-products of phenol-acetone co-production plant
- Pre-separation column: Packed column, D=1.2m, H=8m, separating C3-C5 light hydrocarbons.
- Rectification column: Tray column, D=1.8m, 45 theoretical plates, separating benzene/toluene/heavy components.
- Effect: Total energy consumption reduced by 18%, and product purity all >99.5%.
Thin-film evaporator + packed column combination:
Case: Polyether polyol production
- Stage 1: Thin-film evaporator (wiped film type, 2.5m²) to remove oligomers and solvents.
- Operating conditions: 50-200Pa, 130-150℃
- Removal rate: Oligomers >95%, residual solvent <0.03%
- Stage 2: Packed rectification column (metal structured packing) to recover solvents for recycling.
- Operating conditions: Atmospheric pressure, reflux ratio 3:1
- Solvent purity: >99.8%, recovery rate >98%
- Economic benefit: Solvent loss reduced from 5% to 0.8%, saving 4.2 million yuan annually.
3.3.1 Heat Pump Distillation
Applicable scenarios: Systems with a relative volatility of 1.2-2.0 and a top-bottom temperature difference of 20-50℃.
Case: Ethanol-water rectification
- Adopting mechanical vapor recompression (MVR) heat pump.
- Top vapor (78℃, 50kPa) compressed to 110℃and 120kPa, then sent to the reboiler.
- Energy saving effect: Steam consumption reduced by 65%, saving 1.8 million yuan annually (for a 10,000-ton/year plant).
3.3.2 Heat-Integrated Distillation
Dividing Wall Column (DWC) technology:
Case: Separation of benzene-toluene-xylene ternary components
- Traditional scheme: Two rectification columns in series.
- Dividing wall column scheme: A partition is set in one column to achieve pre-separation and main separation.
- Effect: Equipment investment reduced by 30%, energy consumption reduced by 25%, and floor space reduced by 40%.
Project background:
- Material source: Aqueous DMF waste liquid from pharmaceutical and synthetic leather enterprises (DMF content 15-30%)
- Treatment scale: 8,000 tons/year of waste liquid, recovering 2,000 tons/year of DMF
- Product requirements: Industrial-grade DMF (purity≥99.9%, moisture <0.05%)
Process route:
1. Pre-concentration: Packed column (ceramic saddle packing)
- Column diameter: DN600, packing layer height 6 meters
- Operating conditions: Atmospheric pressure, top temperature 65℃, bottom temperature 105℃
- Outlet concentration: DMF 70-80%
2. Rectification purification: Tray column (sieve tray)
- Column diameter: DN800, 30 theoretical plates
- Operating conditions: Micro-negative pressure (-5kPa), top temperature 48℃
- Product purity: DMF 99.92%, moisture 0.03%
3. Deep dehydration: Thin-film evaporator
- Specification: Wiped film type, evaporation area 1.5m²
- Operating conditions: 10-50Pa, temperature 80-100℃
- Final product: DMF 99.95%, moisture <0.01%
Technical innovation points:
- Adopting a three-stage separation of "packed column pre-concentration + tray column rectification + thin-film evaporator deep dehydration".
- The pre-concentration column uses ceramic saddle packing, which is resistant to DMF corrosion and has good anti-scaling performance.
- The thin-film evaporator has a short residence time (3-5 seconds), avoiding high-temperature decomposition of DMF.
Economic and technical indicators:
- Total investment: 6.8 million yuan
- DMF recovery rate: 92%
- Operating cost: 2,800 yuan/ton of DMF (including steam, electricity, and labor)
- Market price: 6,500 yuan/ton
- Payback period: 2.1 years
- IRR: 38%
Project background:
- Material: Crude bisphenol A epoxy resin (epoxy value 0.50-0.53, color APHA 150-200)
- Product requirements: Electronic-grade epoxy resin (epoxy value 0.51±0.01, color <30, metal ions <5ppm)
- Treatment scale: 3,000 tons/year
Technical difficulties:
- Epoxy resin is highly thermosensitive and prone to polymerization and discoloration at >180℃.
- High viscosity (about 500mPa·s at 150℃)
- Contains impurities such as oligomers and unreacted bisphenol A.
Process scheme: Short-path molecular distillation
Equipment parameters:
- Type: Wiped film short-path distiller
- Evaporation area: 0.8m²
- Heating temperature: 160-180℃
- Vacuum degree: 0.1-1.0Pa (oil diffusion pump system)
- Wiper speed: 150-200rpm
- Condenser temperature: -10℃(ethylene glycol refrigerant)
- Material: 316L stainless steel, polished Ra≤0.4μm
Process flow:
1. Preheating: Heat the crude product to 120℃to reduce viscosity.
2. Feeding: Continuous feeding with a metering pump, flow rate 8-12kg/h.
3. Evaporation: Light components (water, oligomers) evaporate into the condenser.
4. Collection: Heavy components (products) are discharged from the bottom of the column, and light components are collected as waste.
Product quality comparison:
|
Indicator |
Raw Material |
Product |
Improvement Range |
|
Epoxy value |
0.50-0.53 |
0.51±0.005 |
CV reduced from 6% to 1% |
|
Color APHA |
150-200 |
<30 |
Reduced by 83% |
|
Viscosity CV |
15% |
5% |
Reduced by 67% |
|
Metal ions |
15-25ppm |
<5ppm |
Reduced by 75% |
|
Bisphenol A residue |
500-800ppm |
<50ppm |
Reduced by 93% |
Economic benefits:
- Equipment investment: 1.8 million yuan
- Product unit price increase: From 18,000 yuan/ton to 32,000 yuan/ton
- Annual additional sales revenue: 42 million yuan
- Annual operating cost: 1.8 million yuan (electricity, refrigerant, labor)
- Annual additional net profit: 36 million yuan
- Payback period: 0.5 years
Project background:
- Original equipment: Tray column, diameter DN2000, 40 sieve trays, throughput 50 tons/hour
- Existing problems:
- High pressure drop (0.8kPa per tray, total pressure drop 32kPa), high energy consumption.
- Low separation efficiency, solvent recovery purity only 98.5%, loss rate 3%.
- Trays are prone to clogging, requiring cleaning 2-3 times a year.
Renovation scheme: Replacement with a metal structured packed column
Technical scheme:
- Packing type: Metal orifice corrugated structured packing (250Y type)
- Packing layer height: 12 meters (divided into 4 layers, 3 meters per layer)
- Liquid distributor: Porous pipe distributor, distribution point density 120 points/m²
- Redistributor: Installed at the top of each packing layer, adopting trough-tray type.
Renovation effect comparison:
|
Indicator |
Before Renovation (Sieve Tray Column) |
After Renovation (Packed Column) |
Improvement |
|
Total pressure drop (kPa) |
32 |
6.5 |
Reduced by 80% |
|
HETP (m) |
0.8 |
0.3 |
Reduced by 62% |
|
Solvent purity (%) |
98.5 |
99.7 |
Increased by 1.2% |
|
Solvent loss rate (%) |
3.0 |
0.8 |
Reduced by 73% |
|
Steam consumption (tons/hour) |
6.5 |
4.2 |
Reduced by 35% |
|
Annual maintenance times |
2-3 |
<1 |
Reduced by 67% |
Economic analysis:
- Renovation investment: 4.2 million yuan
- Annual steam saving: 20,000 tons (steam price 200 yuan/ton)
- Annual reduction in solvent loss: 960 tons (solvent price 6,000 yuan/ton)
- Annual maintenance cost saving: 800,000 yuan
- Annual economic benefit: 9.8 million yuan
- Payback period: 5.1 months
Based on the above analysis, the following selection decision process is proposed:
- Thermosensitivity: Decomposition temperature <150℃ →Priority consideration of thin-film evaporators or vacuum packed columns.
- Viscosity: >100mPa·s→Thin-film evaporators or tray columns, avoiding conventional packed columns.
- Corrosiveness: High corrosion→Packed columns (non-metallic packings) or tray columns with special materials.
- Theoretical plates <20→Tray columns or random packed columns.
- Theoretical plates 20-50→Tray columns or structured packed columns.
- Theoretical plates >50→Structured packed columns.
- Vacuum degree <10kPa→Packed columns (significant pressure drop advantage).
- Atmospheric pressure or pressurization→Both tray columns and packed columns are applicable.
- Liquid-gas ratio <0.5→Tray columns.
- Liquid-gas ratio >2→Packed columns.
- Column diameter <800mm→Packed columns have lower cost.
- Column diameter >800mm→Tray columns have lower cost.
- High maintenance frequency→Tray columns (easy to disassemble).
- Energy consumption sensitivity→Packed columns or thin-film evaporators.
Step 5: Priority Selection for Special Scenarios
- Polymerizable systems→Avoid packed columns, select tray columns or thin-film evaporators.
- Foaming systems→Packed columns (good foam-breaking effect).
- Solid-containing suspensions→Tray columns or wiped film evaporators.
- Ultra-high-purity products→Thin-film evaporators or high-efficiency structured packed columns.
On-line monitoring technology:
- Real-time monitoring of temperature distribution in trays/packing layers (optical fiber temperature measurement).
- On-line pressure drop analysis to warn of flooding and weeping.
- On-line component analysis (on-line chromatography, NIR spectroscopy).
Intelligent control system:
- Operation parameter optimization based on machine learning.
- Fault diagnosis expert system.
- Digital twin technology for process simulation and optimization.
High-capacity packings:
- Fourth-generation structured packings (HETP 0.1-0.2 meters, capacity increased by 50%).
- 3D-printed customized packings (complex flow channel design).
New types of trays:
- Directed sieve trays (extended gas-liquid contact time, efficiency increased by 15%).
- Composite float valves (operating flexibility expanded to 20-120%).
- Popularization of MVR heat pump technology: Popularized in rectification systems with low temperature differences (<30℃), expected to save energy by 50-70%.
- Solar-assisted heating: Using solar collectors to provide partial heat for distillation, suitable for northwest and north China.
- Waste heat cascade utilization: Optimization of multi-pressure level steam networks to maximize heat recovery.
Zero-emission technology:
- VOCs condensation recovery + adsorption concentration to achieve up-to-standard emission of waste gas.
- Evaporation and crystallization of high-salt wastewater to achieve zero discharge of wastewater.
Skid-mounted modularization:
- Miniaturized and modularized distillation devices (throughput <10 tons/day).
- Rapid deployment (delivery cycle <3 months), suitable for multi-variety and small-batch production in fine chemicals.
1. Tray columns are suitable for scenarios with large liquid-gas ratios, high operating flexibility, and frequent maintenance, and have obvious economic advantages when the column diameter >800mm.
2. Packed columns perform excellently in vacuum distillation, thermosensitive materials, and high-efficiency separation fields, with significantly better separation efficiency and energy consumption control than tray columns.
3. Thin-film evaporators are the best choice for handling high-viscosity, thermosensitive, and high-value-added materials. Although the investment is high, the product quality is significantly improved.
4. Combined processes (such as evaporation + rectification, pre-separation + rectification) can balance separation effect and economy, and are the mainstream direction of engineering practice.
Design stage:
- Fully conduct material property tests (viscosity, thermal stability, phase equilibrium data).
- Use professional process simulation software (Aspen Plus, HYSYS) for process optimization.
- Reserve 10-15% design margin to cope with material fluctuations.
Equipment procurement:
- Prefer mature suppliers and investigate their performance and after-sales service capabilities.
- Select imported or domestic first-line brands for key components (such as distributors and packings).
- Sign performance guarantee clauses to clarify indicators such as separation efficiency and energy consumption.
Construction and installation:
- Control the levelness of the liquid distributor of the packed column within±2mm/m.
- Inspect the levelness and spacing of each tray after installation of the tray column.
- Conduct strict leak detection for the vacuum system, with a vacuum degree deviation <10%.
Commissioning and operation:
- Formulate a detailed start-up plan and proceed step by step (system inspection→purging and replacement→water test run→feeding).
- Establish an operating parameter database and record the optimal operating window.
- Conduct regular equipment inspections and establish a maintenance system.
Enterprise level:
- Cooperate with universities and research institutes to develop new types of packings and trays.
- Introduce CFD simulation technology to optimize the flow field distribution in the column.
- Establish a pilot platform to verify new processes and technologies.
Industry level:
- Formulate technical standards and specifications for distillation of non-oil materials.
- Build a technical exchange platform to promote experience sharing.
- Promote the in-depth application of intelligent manufacturing and green manufacturing in the distillation field.
Through scientific selection, refined design, strict construction, and optimized operation, the distillation separation system for non-oil petrochemical materials can achieve efficient, energy-saving, environmentally friendly, and economical production goals, creating significant economic and social benefits for enterprises.
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