Chemistry of hydrocarbon compounds – Production of hydrocarbon mixture from refuse or vegetation – From synthetic resin or rubber
Reexamination Certificate
2001-08-24
2003-03-18
Dang, Thuan D. (Department: 1764)
Chemistry of hydrocarbon compounds
Production of hydrocarbon mixture from refuse or vegetation
From synthetic resin or rubber
Reexamination Certificate
active
06534689
ABSTRACT:
FIELD OF THE INVENTION
The present process relates to a field of waste processing, and it can mainly be used to produce a gasoline, diesel and fuel oils of waste plastics by pyrolysis and catalytic cracking.
BACKGROUND OF THE INVENTION
Pyrolysis is the known process of thermal destruction of hydrocarbons in oxygen-free environment under temperature of 400-900° C. and small excess pressure. This process, for example, is widely used in petroleum refinery for obtaining low molecular monomers from naphtha, and it can used for waste plastics processing with fuels production as an alternative of its incineration or landfilling.
A number of operating condition variables affects the thermal destruction. These are so-called 3 T's: temperature, time (residence time) and turbulence (or mixing). It is possible to understand the turbulence as method of gas/solid (feedstock) contacting and conditions of mixing pyrolysis products together with gas. A degree of reduction in size has an essential effect. High temperature (700-900° C.) and short residence time (1 second and less) are used for obtaining great quantity of low molecular monomers from petroleum feedstock. It is an endothermic process demanding heat supply from outside.
At present it is known a method of waste plastics pyrolysis in a fluidized bed (Patents: JP.52155603A2, U.S. Pat. No. 3,901,951, EP0502618, U.S. Pat. No. 5,364,995, EP0567292 and U.S. Pat. No. 5,481,052; investigations of Prof. W. Kaminsky in Hamburg University). Grainy inert materials, for example, quartz, sand or ceramic crumb, are used for making a fluidized bed. This material can be used as a circulating heat carrier, being heated in a separate apparatus. A fluidizing agent is inert gas or circulating pyrolysis gas. Preliminary shredding a feedstock is necessary for this technology. A reactor is provided with equipment for a feedstock supply and withdrawing a possible solid residue. A gas stream (pyrolysis products and fluidizing gas) and particles of inert material, escaping from the location of a fluidized bed, are separated within a cyclone.
In comparison with other methods of waste plastics processing, for example, those carried out in the rotary kiln reactor and the shaft reactor, pyrolysis in a fluidized bed has the following advantages: design simplicity, compactness, no moving parts (for the kiln reactor), low operating cost and lower capital cost, the increase of products yields, the enhance of products quality. These advantages are associated with well-known properties of a fluidized bed: uniformity of temperature field without temperature gradients, (those gradients are typical for above-mentioned packed bed reactors), effective mass exchange and a possibility to use a circulating solid heat carrier.
However, fluidization technique has also its own disadvantages, when it is used for such chemical processes as pyrolysis requiring very short residence time. Among these disadvantages are:
Mixing feedstock in the whole volume of a fluidized bed,
Impossibility to ensure short contact time,
Back mixing of pyrolysis products.
A possibility of very short residence time is provided by pyrolysis carried out in an upflow tubular reactors (risers), in which circulating fine solid heat carrier is transported in delute phase with inert gas or circulating pyrolysis gas (Patents: U.S. Pat. Nos. 4,147,593, 5,136,117 and 5,792,340). Feedstock, heat carrier particles and transporting gas are delivered to the bottom of the riser. Pyrolysis products, fluidizing gas and circulating inert material particles are separated in a cyclone. This system is also named as a circulating fluidized bed. Risers enable essentially to reduce residence time in comparison with a fluidized bed. For example, transition from catalytic cracking of petroleum feedstock in a fluidized bed to catalytic cracking in a riser enable to reduce catalyst residence time from several minutes to several seconds. Also, conditions of feedstock/solid contacting get essentially better in a system, employing a riser.
However, conversion in a riser has its own disadvantage. A vector of gas velocity and a vector of particle gravity are directed to opposite directions. It creates the known “slip effect”, when particle velocity relative to reactor walls falls behind gas velocity by terminal velocity. This circumstance reduces solid particles residence time in the reactor, and it promotes back mixing of solid particles and, respectively, of gas, which is observed at the reactor walls. Although, this mixing is considerably inferior in comparison with that in a fluidized bed.
This disadvantage is absent in a downflow tubular reactor, known under names: “downer”, “downflow circulating fluidized bed”, “downcomer”). In this reactor the above-mentioned vectors coincide. The main advantages of this type of configuration over riser reactors are a short residence time with a narrow residence time distribution, little or no solids back mixing, and lower pressure drops since gravity acts in the same direction as the flow stream. Feedstock and heat carrier particles are delivered to the top of the reactor from a packed or fluidized bed placed in a special section or a separate apparatus. After going out of the downer, Products and particles of a circulating solid heat carrier are separated in a cyclone. A method and a reactor are patented in connection with the fluid catalytic cracking process (FCC) (Patents: U.S. Pat. Nos. 4,385,985, 5,449,496, 5,843,377, 5,582,712). The expediency of using these reactors for ultrapyrolysis of organic feed is discussed in scientific papers.
However, the use of risers and downers for pyrolysis of mixed feed, components of which have various conversion velocity, or for pyrolysis of shredded feedstock with a large range of particles size, has a restriction since hard-converted or coarse particles can break through a reactor. Or, in this case, it is necessary to select a reaction volume for these components. First of all, it concerns the mixed plastics, composing the larger part of municipal solid waste and containing mainly of polyethylene, polypropylene, polyvinyl chloride and polystyrene. In this respect, a fluidized bed reactor enables to process a feedstock with wider range of conversion velocity distribution.
There are known attempts to solve this problem by step-by-step increasing waste plastics pyrolysis temperature, when lower temperature is established for pyrolysis of light-converted polymers. Then, this temperature is increased for pyrolysis of hard-converted polymers (Patents: U.S. Pat. Nos. 5,386,070, 5,895,827). increasing temperature on a next stage of pyrolysis can be achieved also with a delivery of a hot circulating solid heat carrier, as it is widely used for the FCC process including catalytic cracking in a downer (Patent: U.S. Pat. No. 4,514,285).
Potential presence of polyvinyl chloride is one more peculiarity of mixed plastics pyrolysis. Hydrogen chloride, effecting equipment corrosion, is evolved during such plastics pyrolysis. Two-stage processing is used in this case. At first, feed melting is carried out at temperature of 200-300° C. The evolved hydrogen chloride is delivered to an adsorber with calcium oxide or similar compound. Melted feed is subjected to a following pyrolysis (Patents: U.S. Pat. Nos. 3,901,951, 5, 821,395).
During pyrolysis of mixed plastics waste at respectively low temperature (480-590° C.), it is possible to yield about 85% of liquid hydrocarbons (C
5
-C
40
). These hydrocarbons are a good feed for following catalytic cracking since they do not consist of sulfur, basic nitrogen and such metals poisoning a catalyst as nickel and vanadium.
Methods of pyrolysis, described in the patents U.S. Pat. Nos. 5,481,052 and 5,821,395 of BP Chemicals, Ltd., England and the patent U.S. Pat. No. 5,976,355 of Stone & Webster Engineering Corp., USA are the nearest methods to the presented method. In the patents of BP Chemicals, Ltd., waste plastics pyrolysis is carried out in a fluidized bed. In the patent of Stone & Webster Engineering Corp., thermocatalytic c
Blank Rome LLP
Dang Thuan D.
Pyrocat Ltd.
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