LDPE Autoclave Reactor

As the mixture moves through the reactor, the spread in the distribution narrows, indicating a product of high quality. The solution also indicates that the molecular viscosity increases as the chains of radicals grow, consistent with expectations. 

---

Polyethylene, LDPE, autoclave reactor - Lyondell-Fguistar (LyondellBasell)... 

LDPE, also known as high pressure polyethylene, is produced at pressures ranging from 82—276 MPa (800—2725 atm). Operating at 132—332°C, it may be produced by either a tubular or a stirred autoclave reactor. Reaction is sustained by continuously injecting free-radical initiators, such as peroxides, oxygen, or a combination of both, to the reactor feed. 

The SCB distribution (SCBD) has been extensively studied by fractionation based on compositional difference as well as molecular size. The analysis by cross fractionation, which involves stepwise separation of the molecules on the basis of composition and molecular size, has provided information of inter- and intramolecular SCBD in much detail. The temperature-rising elution fractionation (TREE) method, which separates polymer molecules according to their composition, has been used for HP LDPE it has been found that SCB composition is more or less uniform [24,25]. It can be observed from the appearance of only one melt endotherm peak in the analysis by differential scanning calorimetry (DSC) (Fig. 1) [26]. Wild et al. [27] reported that HP LDPE prepared by tubular reactor exhibits broader SCBD than that prepared by an autoclave reactor. The SCBD can also be varied by changing the polymerization conditions. From the cross fractionation of commercial HP LDPE samples, it has been found that low-MW species generally have more SCBs [13,24]. 

Application To produce low-density polyethylene (LDPE) homopolymers and EVA copolymers using the high-pressure free radical process. Large-scale tubular reactors with a capacity in the range of 130-400 Mtpy, as well as stirred autoclave reactors with capacity around 100 Mtpy can be used. 

Low density PE LDPE high pressure pipe or autoclave reactor 915-930 12.3 10.0... 

High-Pressure LDPE. The original ICI (and, later, Du Pont) process uses steel autoclave reactors, operating at pressures ranging from... 

Application The high-pressure Lupotech A autoclave reactor process is used to produce low-density polyethylene (LDPE) homopolymers, EVA and various acrylic type copolymers. Single-train capacity of up tol 25,000 tpy can be provided. 

Description A variety of LDPE homopolymers and copolymers can be produced on these large reactors for various applications including films, molding and extrusion coating. The melt index, polymer density and molecular weight distribution (MWD) are controlled with temperature profile, pressure, initiator and comonomer concentration. Autoclave reactors can give narrow or broad MWD, depending on the selected reactor conditions, whereas tubular reactors are typically used to produce narrow MWD polymers. 

Continuous stirred-tank reactors (CSTRs) are used for large productions of a reduced number of polymer grades. Coordination catalysts are used in the production of LLDPE by solution polymerization (Dowlex, DSM Compact process [29]), of HDPE in slurry (Mitsui CX-process [30]) and of polypropylene in stirred bed gas phase reactors (BP process [22], Novolen process [31]). LDPE and ethylene-vinyl acetate copolymers (EVA) are produced by free-radical polymerization in bulk in a continuous autoclave reactor [30]. A substantial fraction of the SBR used for tires is produced by coagulating the SBR latex produced by emulsion polymerization in a battery of about 10 CSTRs in series [32]. The CSTRs are characterized by a broad residence time distribution, which affects to product properties. For example, latexes with narrow particle size distribution cannot be produced in CSTRs. 

Computational fluid dynamics (CFD) approaches are emerging as alternative detailed tools for examining polymerization systems with complex mixing and reactor components. Recent examples on LDPE cases include Kolhapure and Fox [118], micromixing effects in tubular reactors Zhou etal. [119], tubular (and autoclave) reactors Wells and Ray [120], analysis of imperfect mixing effects applicable to many reactive flow systems, including LDPE autoclaves and Buchelli etal. [121], fouling effects. 

LDPE is being manufactured using either an autoclave reactor (AR as in ICI process) or a tubular reactor (TR process of IG Farbenindustrie, now BASF). The high-strength tubes are L = 0.5-2 km long with iimer/outer diameters ID/OD = 70/180 mm thus, L/OD = 3,000-11,000. Since the operating conditions in AR and TR are different (T = 180-330 and 140-340 °C and P = 100-250 and 200-350 MPa, respectively), the polymers have different properties. 

Two types of reactors are used for the production of LDPE either a stirred vessel (autoclave) or a tubular reactor. The autoclave reactor operates adiabatically. The tubular reactor is cooled with a jacket. The autoclave reactor has a length to diameter ratio (L/D) between 4 and 16. Tubular reactors have L/D ratios above 10000. The inner diameter of the high pressure tubes used for the tubular reactors range between 25 and 100 mm. The operating pressure ranges between 100 and 250 MPa (1000-2500 bars) for the autoclave reactor and between 200 - 350 MPa (2000 - 3500 bar) for the tubular reactor. A basic flow diagram for LDPE processes is shown in Figure 3.7. 

LDPE is produced either in a tubular reactor (PFTR, LDPE tubular process) or in a high-pressure, continuous stirred tank reactor (CSTR, LDPE autoclave process). In both process designs the very high pressures require very special, thick-walled equipment and fatigue is a major design aspect for the applied pumps and compressors. 

In the LDPE autoclave process, the general process design (e.g., ethylene compression, high and low pressure product separation and ethylene recycling) is very similar to the LDPE tubular process. Instead of the jacketed tube reactor, however, the autoclave process employs a high-pressure stirred tank reactor. The reactor is designed to allow a residence time of 30-60 s (typical reactor volumes are around 1 m for large plants). The autoclave is usually operated in an adiabatic manner the reaction heat is removed by the fresh ethylene... 

Ihe tubular reactor provides LDPE with a broader SCB distribution than the LDPE produced in the autoclave reactor. However, the autoclave reactor has a significantly higher SCB content in the region, with 10-15 methyl branches/1000 carbons. Wild also provided data showing the significant differences in the SCB distribution of various LDPE samples prepared by each type of reactor xmder different polymerization conditions. 

Figure 5.7 Comparison of the short chain branching distribution of LDPE produced from an autoclave reactor (O) and from tubular reactor (A) using TREE method. Reprinted from [17] with permission from John WUey and Sons.

Free-radical polymerization [79, 93] Low-density polyethylene (LDPE) accounts for almost two-fifths of the global polyethylene production capacity, reaching about 45 million tons per year in 1996. LDPE is exclusively produced by free-radical polymerization in a tubular or autoclave reactor, each of which accounts for about 50% of the total capacity. In the tubular reactor, a small amount of initiator is injected into a turbulent monomer flow for initiating the exothermic free-radical chemistry. Under extreme operating conditions (T 140-300°C, p 1000-3500 atm), these... 

E/CO is produced commercially by the high-pressure copolymerization of ethylene and carbon monoxide using techniques similar to those used to make high-pressure, low-density polyethylene homopolymer (LDPE). The monomers undergo random copolymerization under well-controlled temperatures and pressures in either tubular or stirred autoclave reactors ... 

Exxon Mobil Chemical Co. High-pressure free radical process tubular or stirred autoclave reactor. Total installed capacity 1.7 MMT/y. LDPE (density 912-935 kg/m ) and EVA (up to 30 wt% VA). 

The current maximum size of autoclave reactors is about 25001 for a capacity of approximately 200kiloton/year of LDPE. The length to diameter ratio L/D can be as low as 2 for a single zone and up to 20 for multizone reactors. Residence time ranges between 8 and 60 s. 

---