Carbon blacks may be utilized as pigments, fillers, reinforcing agents and for a variety of other applications. Carbon blacks are widely utilized as fillers and reinforcing pigments in the compounding and preparation of rubber compositions and plastic compositions. Carbon blacks are generally characterized on the basis of their properties including, but not limited to, their, surface areas, surface chemistry, aggregate sizes and particle sizes. The properties of carbon blacks are analytically determined by tests known to the art, including iodine adsorption surface area (I.sub.2 No.), nitrogen adsorption surface area (N.sub.2 SA), dibutyl phthalate adsorption (DBP), dibutyl phthalate adsorption of the crushed carbon black (CDBP), cetyl-trimethyl ammonium bromide absorption value (CTAB), Tint value (TINT), Dmode and .DELTA.D50. It is advantageous in the compounding and preparation of rubber and plastic compositions to utilize a carbon black that is easily dispersed in the media.
Carbon blacks are also widely utilized as pigments in the formulation of ink compositions, paints and the like, wherein it is generally desirable to use a carbon black pigment which can be easily dispersed. For example, newsink compositions are made in two stages. First the carbon black pigment and a dispersing vehicle, comprising resin, additives, and oil or solvent, are mixed to form a "premix" and then the premix is ground, for example, in a shot mill, to complete the dispersion of the carbon black in the ink composition. Dispersion of the carbon black pigment in the ink composition occurs during the formation of the premix and during the grinding of the premix. A carbon black pigment which is easy to disperse will allow an ink maker to produce an ink in a reduced period of time, which results in improved economy. For the above reasons, and others, it would be advantageous to produce an easily dispersible carbon black pigment.
Carbon blacks are generally produced in a furnace-type reactor by pyrolyzing a hydrocarbon feedstock with hot combustion gases to produce combustion products containing particulate carbon black. A variety of methods for producing carbon blacks are generally known.
In one type of a furnace carbon black reactor, such as shown in U.S. Pat. No. 3,401,020 to Kester et al., or U.S. Pat. No. 2,785,964 to Pollock, hereinafter "Kester" and "Pollock" respectively, a fuel, preferably hydrocarbonaceous, and an oxidant, preferably air, are injected into a first zone and react to form hot combustion gases. A hydrocarbon feedstock in either gaseous, vapor or liquid form is also injected into the first zone whereupon pyrolysis of the hydrocarbon feedstock commences. In this instance, pyrolysis refers to the thermal decomposition of a hydrocarbon. The resulting combustion gas mixture, in which pyrolysis is occurring, then passes into a reaction zone where completion of the carbon black forming reaction occurs.
In another type of a furnace carbon black reactor a liquid or gaseous fuel is reacted with an oxidant, preferably air, in the first zone to form hot combustion gases. These hot combustion gases pass from the first zone, downstream through the reactor, into a reaction zone and beyond. To produce carbon blacks, a hydrocarbonaceous feedstock is injected at one or more points into the path of the hot combustion gas stream. The hydrocarbonaceous feedstock may be liquid, gas or vapor, and may be the same or different than the fuel utilized to form the combustion gas stream. Generally the hydrocarbonaceous feedstock is a hydrocarbon oil or natural gas, however other hydrocarbonaceous feedstocks such as acetylene are known in the art. The first (or combustion) zone and the reaction zone may be divided by a choke or zone of restricted diameter which is smaller in cross section than the combustion zone or the reaction zone. The feedstock may be injected into the path of the hot combustion gases upstream of, downstream of, and/or in the restricted diameter zone. Furnace carbon black reactors of this type are generally described in U.S. Pat. Reissue No. 28,974 and U.S. Pat. No. 3,922,335 the disclosure of each being incorporated herein by reference.
In generally known reactors and processes, the hot combustion gases are at a temperature sufficient to effect pyrolysis of the hydrocarbonaceous feedstock injected into the combustion gas stream. In one type of reactor, such as disclosed in Kester, feedstock is injected, at one or more points, into the same zone where combustion gases are being formed. In other type reactors or processes the injection of the feedstock occurs, at one or more points, after the combustion gas stream has been formed. The mixture of feedstock and combustion gases in which pyrolysis is occurring is hereinafter referred to, throughout the application, as "the effluent". The residence time of the effluent in the reaction zone of the reactor is sufficient, and under conditions suitable, to allow the formation of carbon blacks. In either type of reactor, since the hot combustion gas stream is continuously flowing downstream through the reactor, pyrolysis continuously occurs as the mixture of feedstock and combustion gases passes through the reaction zone. After carbon blacks having the desired properties are formed, the temperature of the effluent is lowered to a temperature such that pyrolysis is stopped, thereby halting the further production of carbon blacks.
In generally known processes the lowering of the temperature of the effluent to stop pyrolysis is accomplished by injecting a quenching fluid, through a quench, into the effluent. As generally known to those of ordinary skill in the art, pyrolysis is stopped when the desired carbon black products have been produced in the reactor. One way of determining when pyrolysis should be stopped is by sampling the effluent and measuring its toluene extract level. Toluene extract level is measured by ASTM D1618-83 "Carbon Black Extractables--Toluene Discoloration". The quench is generally located at the point where the toluene extract level of the effluent reaches an acceptable level for the desired carbon black product being produced in the reactor. After pyrolysis is stopped, the resulting mixture of combustion gases and carbon black generally passes through a heat exchanger to further cool the mixture. This heat exchanger is often advantageously utilized to preheat the combustion air to be utilized in the process while at the same time cooling the quenched mixture from the reactor. Thus, this heat exchanger is often referred to as the combustion air heat exchanger.
After passing through the combustion air heat exchanger the quenched mixture passes through a secondary cooler to further cool the mixture. A secondary quench is typically utilized for the secondary cooler. The purpose of the secondary cooler is to further lower the temperature of the quenched mixture to a temperature such that the bag filter system utilized to separate the carbon blacks will not be damaged.
After further cooling of the mixture by the secondary cooler the cooled mixture passes downstream into separating means whereby the carbon blacks are recovered. The separation of the carbon black from the gas stream is readily accomplished by conventional means such as a precipitator, cyclone separator or bag filter. This separation may be followed by pelletizing using, for example, a wet pelletizer.
The temperature of the effluent in the reactor is generally above about 1750.degree. F., often reaching over 3300.degree. F. In conventional processes, the quench that stops pyrolysis cools the effluent to below about 1650.degree. F., often to about 1400.degree. F. The resulting quenched mixture enters the heat exchanger (combustion air heat exchanger) at this temperature and is further cooled by the heat exchanger to about 1000.degree. F. The secondary cooler further cools the mixture to about 500.degree. F., a temperature that will generally not damage the separation means such as the bag filter system.
As set forth above, in heretofore generally utilized carbon black production processes, pyrolysis of the carbon black yielding feedstock in the hot combustion gas stream is stopped by a quench injecting a quenching fluid, typically water. The use of a water quench may disadvantageously result in tiny drops of water being carried with the quenched mixture into the combustion air heat exchanger contacting the heat transfer surfaces thus causing a hard fouling layer of carbon black to build up on the internal heat transfer surfaces of the heat exchanger. This hard fouling layer of carbon black is difficult to remove, and decreases heat transfer through the surface, and thus is disadvantageous.
Also, occasionally in heretofore generally utilized carbon black production processes bits of the hard fouling layer are broken loose and entrained into the product stream due to large changes in the operating conditions of the reactor. These bits of hard fouling layer pass through the reactor and end up mixed in with the collected carbon black product. The material mixed in the carbon black product makes the product difficult to disperse.
Additionally the water droplet evaporation process, of the quench water, causes the formation of micropellets of carbon blacks in the gas stream. These micropellets are more difficult to disperse in the final application media.