LDPE tubular process

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... 

EniChem Polyethylene, LDPE-EVA Ethylene and vinyl acetate monomer Autoclave or tubular process designs with EVA content of VA up to 40% 15 1995... 

Because of the extremely high pressures (15,000 to 45,000 psig), ethylene exists in the liquid phase and polymerization occurs in solution. Owing to high temperatures (typically >200 °C), polyethylene is also dissolved in monomer and the reaction system is homogeneous. LDPE precipitates only after the reaction mass is cooled in post-reactor separation vessels. Relative to other processes, reactor residence times are very short (<30 seconds for the autoclave process and <3 min for the tubular process) (7). 

Table 7.3 Typical operating features of tubular processes for LDPE.

LyondellBasell Polyethylene, LDPE, Tubular Reactor Ethylene High-pressure LupotechT tubular reactor process produces low-density polyethylene (LDPE) homopolymers and EVA copolymers NA 2009... 

The removed heat of reaction can be used to generate low pressure steam for preheating purposes (e.g. tubular processes, high pressure separators or tubular reactors in LDPE processes), other internal usage or for export to an external user. 

Figure 6.20.1 Schematic view of a LDPE tubular reactor process. Three reaction zones are shown to represent the reaction unit. Adapted from Kiparissides (2010).

LDPE is produced in either a stirred autoclave or a tubular reactor total domestic production, divided between the two systems at 45% for tubular and 55% for autoclave, is estimated to be 3.4 million metric tons per year (5). Neither process has gained a clear advantage over the other, although all new or added capacity production in the 1990s has been through the autoclave. 

The first section of this chapter describes the most important high pressure process run under homogeneous conditions to manufacture Low Density PolyEthylene (LDPE). The radical polymerization of ethylene to LDPE is carried out in tubular reactors or in stirred autoclaves. Tubular reactors exhibit higher capacities than stirred autoclaves. The latter are preferred to produce ethylene copolymers having a higher comonomer content. 

LDPE was occasionally found in 1933 by R.O. Gibson and E.W. Fawcett, when they tried to perform reactions with ethylene [1]. Based on their invention. Imperial Chemicals Ltd (ICI), Great Britain, developed a process with a stirred autoclave in which ethylene was radically polymerized under high pressure [2], Later, BASF AG in Germany designed a tubular reactor to produce LDPE under similar high-pressure conditions [3]. 

Application To produce low density polyethylene (LDPE) and ethylene vinyl acetate (EVA) by the high-pressure, autoclave or tubular EniChem process. 

Sumitomo Chemical Co.,Ltd. Polyethylene, LDPE-EVA Ethylene and vinyl acetate Tubular and autoclave processes with EVA up to 41% 8 1994... 

ExxonMobil LDPE, EVA high pressure autoclave and tubular (separate processes) organic peroxides Autoclave operates about 1600 bar, tubular about 2800 bar... 

Application To produce low-density polyethylene (LDPE) homopolymers and ethylene vinyl acetate (EVA) copolymers using the high-pressure free radical process. Large-scale tubular reactors with a capacity in the range of 130,000 tpy-425,000 tpy, as well as stirred autoclave reactors with capacity around 125,000 tpy can be used. 

PBE with both short and long branches are prepared from radical polymerization in the traditional high pressure process. These PE are called low density polyethylene (LDPE). A molecular model of a conformation of a typical LDPE is shown in Eig. 3.3. LDPE with different proportions of short and long branches are formed using autoclave or tubular reactors. There are many short branches with average... 

Chemically, LLDPE can be described as linear polyethylene copolymers with alpha-olefin comonomers in the ethylene chain. They are produced primarily at low pressures and temperatures by the copolymerization of ethylene with various alpha-olefins such as butene, hexane, octane, etc., in the presence of suitable catalysts. Either gas-phase fluidized-bed reactors or liquid-phase solution-process reactors are used. (In contrast, LDPE is produced at very high pressures and temperatures either in autoclaves or tubular reactors.)... 

---