Abstract: Houdry lumps can be reduced by controlling the reactors in a fixed bed dehydrogenation process for producing olefins according to defined rules. A programmable logic controller can apply the rules to the operation of the dehydrogenation unit and control the operation of individual reactors according to the rules. By doing so, the performance of dehydrogenation units can be improved without adding any heat generating inerts, such as CuO-? alumina For example, the dehydrogenation units can be operated according to combinatorics in the programmable logic controller such that the farthest two reactors in the dehydrogenation unit never operate in parallel in the dehydrogenation or air regeneration steps.

Abstract: A system for treating ethylene oxide-containing sterilization exhaust gas comprises a reaction column further comprising a column body, and an inner cavity configured to contain a liquid substrate for catalyzing ethylene oxide in ethylene oxide-containing sterilization exhaust gas; wherein the column body comprises a bottom portion having a gas inlet pipe and a liquid outlet pipe, the gas inlet pipe configured to inject the ethylene oxide-containing sterilization exhaust gas into the inner cavity and the liquid outlet pipe configured to discharge the liquid substrate from the inner cavity; and wherein, the column body comprises a top portion comprising a gas outlet pipe having a gas inlet above a liquid level of the liquid substrate; and at least one gas distributor configured to disperse the ethylene oxide-containing sterilization exhaust gas injected from the gas inlet pipe into the inner cavity.

Abstract: Methods of performing a startup of an oxidative coupling of methane reaction to produce C2+ hydrocarbons are described. The methods can include incrementally varying startup parameters of the oxidative methane reactor and using the feed gas as a coolant such that high C2+ hydrocarbon selectivity is achieved.

Abstract: Metal oxide catalysts comprising various dopants are provided. The catalysts are useful as heterogeneous catalysts in a variety of catalytic reactions, for example, the oxidative coupling of methane to C2 hydrocarbons such as ethane and ethylene. Related methods for use and manufacture of the same are also disclosed.

Abstract: Methods of performing a startup of an oxidative coupling of methane reaction to produce C2+ hydrocarbons are described. The methods can include incrementally varying startup parameters of the oxidative methane reactor and using the feed gas as a coolant such that high C2+ hydrocarbon selectivity is achieved.

Abstract: The present disclosure relates generally to methods and systems for achieving enhanced catalytic performance via the strategic arrangement of multiple catalyst beds in series, where each catalyst bed comprises a compositionally-distinct catalyst, and each catalyst facilitates the conversion of the same structural moieties on the reactant to form the same product. Arranging multiple catalyst beds according to the methods and systems disclosed herein allows a predictable enhancement of conversion of the reactant to product without the need for time-consuming experimentation to test all possible catalysts configurations.

Abstract: In some embodiments provided herein are processes for controlling carbon dioxide output levels coming from an oxidative dehydrogenation (ODH) process. Carbon dioxide output from an ODH process includes that produced in the ODH reaction and carry over when carbon dioxide is used as an inert diluent. Under certain circumstances carbon dioxide can also be consumed in the ODH process by acting as an oxidizing agent. By varying the amount of steam introduced into the ODH process an operator may alter the degree to which carbon dioxide acts as an oxidizing agent. This in turn allows a level of control in the degree to which carbon dioxide is consumed in the process, effecting overall carbon dioxide output. Minimizing the carbon dioxide output provides an opportunity to limit or eliminate the requirement for release of carbon dioxide into the atmosphere.

Abstract: The present invention relates to a process for controlling the antifoam injection based on the pressure differential of the column. More specifically, the present invention relates to a process for controlling the antifoam injection based on the pressure differential of an aromatics extraction unit using an intelligent differential pressure transmitter. The controller communicates with the antifoam injection system so that the antifoam is injected to the unit only when it is required.

Abstract: Metal oxide catalysts comprising various dopants are provided. The catalysts are useful as heterogenous catalysts in a variety of catalytic reactions, for example, the oxidative coupling of methane to C2 hydrocarbons such as ethane and ethylene. Related methods for use and manufacture of the same are also disclosed.

Abstract: Butadiene is made from a butene rich feed, passing a superheated butene rich feed including superheated steam and oxygen at a temperature of at least about 343° C. (650° F.) over a catalyst bed having a depth of over about 69 cm (27 inches) of granules of ferritic oxidative dehydrogenation catalyst. Inlet conditions being controlled such that the oxidative dehydrogenation reactions initially occur in the lower most layers of catalyst. Process control includes monitoring the temperature throughout the bed and increasing the inlet temperature in response to a drop in the temperature in the active layer, when the active layer of oxidative dehydrogenation catalyst begins to become deactivated so that the reaction zone moves upwardly in the oxidative dehydrogenation bed.

Abstract: The startup of a tubular reactor containing fresh or regenerated molecular sieve catalyst and cooled by steam generation on the shell side, as part of an olefin oligomerization process, is improved by, during the startup phase of the reactor, controlling the pressure on the shell side of the reactor at maximum 10 barg. The startup may be further improved by controlling the inlet temperature of the hydrocarbon startup stream to the reactor, by controlling the flow of reactant olefins to the reactor, or by controlling the nature and/or concentration of the olefins in the reactor feed.

Abstract: Process for performing an endothermic reaction in a reactor containing catalyst tubes, the catalyst tubes containing a catalyst promoting the endothermic reaction, the process comprising the steps of, a. contacting the catalyst contained in the catalyst tubes with a feed flow passing through the channels from an entrance end to an exit end, b. contacting an outer surface of the catalyst tubes with a flow of a heating medium having an initial heating temperature and flowing co-currently with the flow of feeds to heat the surface by convection, c. mixing at least part of the heating medium after having been contacted with the catalyst tubes with a flow of fresh heating medium having a start temperature higher than the initial heating temperature to form the co-current heating medium having the initial heating temperature and reactor for carrying out the process.

Abstract: An apparatus and method are provided for processing hydrocarbon feeds. The method may pass a pyrolysis feed to a thermal pyrolysis reactor and expose at least a portion of the pyrolysis feed to high-severity operating conditions in a thermal pyrolysis reactor, wherein the thermal pyrolysis reactor is operated at operating conditions that include pressure?36 psig and provide a reactor product that has a C3+ to C2 unsaturate weight ratio?0.5.

Abstract: The invention relates to a method for extracting hydrocarbon mixtures that have an increased proportion of hydrocarbons of a medium chain length (8 to 16 carbon atoms), or the corresponding pure compounds. Firstly, a starting material is provided that includes at least 50 wt. % unsaturated hydrocarbon compounds having oxygen. The compounds include olefin fragments of the formula —C1CxH2x—CH?CH—CyH2y+1 with at least 14 carbon atoms, carbon atom (C1) being saturated with substituted or unsubstituted heteroatoms and/or hydrogen. In a conversion reactor, this starting material is brought into contact with a porous catalyst based on carbon, in the absence of oxygen, and at a temperature of between 200 and 800° C.; and a product mixture that contains hydrocarbons is produced containing an increased proportion of hydrocarbons with medium chain lengths. Finally, the product mixture including hydrocarbons is collected and fed to a separating device in which a product separation is carried out.

Abstract: A method for control of the air/fuel ratio of the burner(s) (excess air) of a thermal cracker includes three steps. The thermal cracker has three consecutive zones or portions through which combustion gases pass, a firebox portion, a bridge wall portion and a convection portion The first step is to direct a wavelength modulated beam of near infrared light from two different tunable diode lasers located in the bridge wall portion through combustion gas from the burner to a pair of near infrared light detectors, each positioned to receive the wavelength modulated beam of near infrared light from a different one of the two tunable diode lasers to generate a detector signal. The second step is to analyze the detector signals for spectroscopic absorption at wavelengths characteristic of oxygen and carbon monoxide to determine their respective concentrations in the combustion gas.

Abstract: An apparatus and method are provided for processing hydrocarbon feeds. The method enhances the conversion of hydrocarbon feeds into conversion products, such as ethylene and propylene. In particular, the present techniques combine a first hydrocarbon feed with a second hydrocarbon feed and a hydrogen (H2) containing stream to manage the hydrogen content of the feed provided to a pyrolysis reactor. The mixture is then exposed to high-severity operating conditions in a pyrolysis reactor and further processing into desired olefins.

Abstract: Systems and methods conducive to the formation of one or more alkene hydrocarbons using a methane source and an oxidant in an oxidative coupling of methane (OCM) reaction are provided. One or more vessels each containing one or more catalyst beds containing one or more catalysts each having similar or differing chemical composition or physical form may be used. The one or more catalyst beds may be operated under a variety of conditions. At least a portion of the catalyst beds may be operated under substantially adiabatic conditions. At least a portion of the catalyst beds may be operated under substantially isothermal conditions.

Abstract: Olefin feeds with high olefin content and/or containing a substance that generates water when contacting the catalyst, are oligomerised over solid phosphoric acid catalyst in tubular reactors by introducing the olefin feed into the reactor and maintaining the reacting mixture under conditions whereby the peak temperature is controlled to be below 265° C. and preferably a single liquid or dense phase is maintained and the average temperature throughout the reactor is maintained in the range 190° C. to 260° C.

Abstract: A method for improving performance of a catalyzed reaction carried out in a moving bed system having a reaction zone. A process stream is introduced into the reaction zone at a temperature, and the temperature of the catalyst introduced to the reaction zone is different from the process stream introduction temperature to increase conversion.

Abstract: A radiant heat chemical reactor is configured to generate chemical products including synthesis gas products. Two or more tubes in the radiant heat chemical reactor separate an exothermic heat source, such as flames and gas from a regenerative burner, from the endothermic reaction of the reactant gas occurring within the cavity of the refractory vessel. The exothermic heat source heats a space inside the tubes. One or more feed lines supply chemical reactants to the cavity area between an inner wall of the cavity of the refractory vessel of the chemical reactor and the two or more tubes that are internally heated located with the cavity.

Abstract: This invention is directed to a process for producing olefin product from an oxygenate feed that includes dimethyl ether (DME). The process uses an olefin forming catalyst that contains a porous crystalline material, preferably a porous crystalline aluminosilicate molecular sieve material. The process produces high quantities of light olefin (i.e., ethylene, propylene, and mixtures thereof).

Abstract: Systems and methods for operating transport reactors are provided. The method can include fluidizing one or more particulates within a transport reactor. The one or more particulates can include one or more carbonaceous materials. The method can also include maintaining one or more pressure differentials between two or more points within the transport reactor using at least one integrally geared compression system. The at least one integrally geared compression system can include a bull gear, at least one pinion, and two or more compressors.

Abstract: Methods for monitoring ionic liquids using vibrational spectroscopy may involve contacting an infrared (IR) transmissive medium with the ionic liquid, recording an IR spectrum of the ionic liquid, and quantifying at least one chemical characteristic of the ionic liquid based on the IR spectrum. The IR spectrum may be recorded ex situ or in situ. Methods for controlling ionic liquid catalyzed processes are also disclosed, wherein a condition of the ionic liquid may be determined during such processes based on IR spectral analysis of the ionic liquid.

Abstract: A process for the dehydrogenation of alkanes. In several reactors of the adiabatic, allothermal or isothermal type or combinations thereof a gaseous alkane-containing material stream is passed through a catalyst bed in continuous operating mode. The gas stream produced contains an alkene, hydrogen and a non-converted alkane. In order to achieve a constant product composition, at least one of the process parameters of temperature, pressure or steam/hydrocarbon ratio is recorded in the form of measured values at one or several points of at least one of the reactors, where at least one of the process parameters is selectively controlled and influenced such that the composition of the product gas at the outlet of one reactor remains constant throughout the operating period.

Abstract: Disclosed herein is a method of recovery of the activity of a molecular sieve catalyst following use of the catalyst in an OTO conversion process. This is achieved by a regeneration apparatus and a method of regenerating a molecular sieve catalyst, comprising two stages. In a pretreatment stage, the catalyst is pretreated under pretreatment conditions by heating the catalyst to a temperature of between 320° C. to 700° C. in an oxygen depleted medium for a residence time of between 1 minute to two hours; and, in a regeneration stage, the catalyst is regenerated under regeneration conditions by heating the catalyst at a temperature of between 200° C. to 700° C. in an oxidizing medium for a residence time of between 1 to 60 minutes.

Abstract: A process is proposed for continuously operating a plant for preparing acetylene from hydrocarbons by partial oxidation, cleavage in an arc or pyrolysis of hydrocarbons to obtain a reaction gas mixture which is conducted through one or more compressors, the pressure of the reaction gas mixture on the suction side of the compressor being controlled within a predefined range by means of a conventional controller, which comprises additionally using a higher-level model-supported predictive controller which reacts to abrupt changes in the mass flow rate of the reaction gas mixture.

Abstract: In the oligomerization of olefins in a tubular reactor employing a molecular sieve catalyst, the temperature of the reaction is monitored and the space velocity of the olefin feed to the reactor is reduced as the temperature increases. This has been found to increase catalyst life and lead to extended production runs. Further extensions of the production run are achieved by improving reactor operating stability as the end of the production run approaches.

Abstract: A method for improving performance of a catalyzed reaction carried out in a moving bed system having a reaction zone. A process stream is introduced into the reaction zone at a temperature, and the temperature of the catalyst introduced to the reaction zone is different from the process stream introduction temperature to increase conversion.

Abstract: The present invention relates to method for reaction control of an exothermic reaction, comprising the steps: i) carrying out an exothermic reaction in a reactor to produce product, ii) measuring temperature and/or pressure in the reactor, and iii) introducing inert product already produced previously in the exothermic reaction from a storage container into the reactor, if temperature and/or pressure exceed(s) critical value(s). as well as an apparatus for carrying out an exothermic reaction.

Abstract: Processes, methods and apparatus relating to olefin oligomerization include the use of Raman spectrometry to monitor the concentration of reactants, products or other chemical components. One or more oligomerization conditions are adjusted in response to those monitored concentrations. The present processes, methods and apparatus are capable of monitoring olefin oligomerization with the use of low resolution Raman spectrometry equipment, even where there is some degree of overlap between Raman spectral peaks. Apparatus for olefin oligomerization reactions have at least one Raman probe located in the oligomerization equipment, the Raman probe providing an output signal, and Raman spectrometry equipment located outside the oligomerization equipment and operatively connected to at least one Raman probe.

Abstract: A catalytic process development apparatus and method for simulating a commercial scale methanol and/or DME to propylene catalytic conversion system that includes a plurality of series-connected plug-flow reactors. The method involves simulating the operation of the series-connected plug-flow reactors by operating a series of multistage series-connected laboratory scale plug-flow reactors, the stages of which each containing a zeolite catalyst bed, each of the laboratory scale reactors corresponding to a separate one of the commercial scale series-connected reactors. Fresh feed, including methanol and/or DME, is supplied to the first of the laboratory scale reactor stages, and selected ones of steam, methanol and/or DME, contaminants and reaction products are supplied to selected ones of the laboratory scale reactor stages. The simulation is repeated at different sets of operating conditions and catalyst characteristics.

Abstract: A process is proposed for continuously operating a plant for preparing acetylene from hydrocarbons by partial oxidation, cleavage in an arc or pyrolysis of hydrocarbons to obtain a reaction gas mixture which is conducted through one or more compressors, the pressure of the reaction gas mixture on the suction side of the compressor being controlled within a predefined range by means of a conventional controller, which comprises additionally using a higher-level model-supported predictive controller which reacts to abrupt changes in the mass flow rate of the reaction gas mixture.

Abstract: In a tube bundle reactor for carrying out endothermic or exothermic gas phase reactions, comprising a tube bundle of reactor tubes filled with catalyst, having their ends fastened tightly in tube sheets (3, 4), a fluid heat carrier (10) flowing around the tubes during operation, a shell (5) enclosing the tube bundle, a gas inlet head (6) spanning one of the tube sheets, a gas outlet head (7) spanning the other tube sheet, the reactor tubes being in fluid communication with the gas inlet and outlet heads (6, 7), further comprising at least one stage thermometer (9) installed in a thermometer tube (2) disposed in the tube bundle, the at least one stage thermometer (9) is axially movable inside the thermometer tube (2), and the tube bundle reactor (1) comprises a mechanical positioning means (8) to effect the axial movement of the stage thermometer (9). Moreover, a method is proposed for measuring a temperature profile in tube bundle reactors of the kind specified.

Abstract: Processes, methods and apparatus relating to olefin oligomerization include the use of Raman spectrometry to monitor the concentration of reactants, products or other chemical components. One or more oligomerization conditions are adjusted in response to those monitored concentrations. The present processes, methods and apparatus are capable of monitoring olefin oligomerization with the use of low resolution Raman spectrometry equipment, even where there is some degree of overlap between Raman spectral peaks. Apparatus for olefin oligomerization reactions have at least one Raman probe located in the oligomerization equipment, the Raman probe providing an output signal, and Raman spectrometry equipment located outside the oligomerization equipment and operatively connected to at least one Raman probe.

Abstract: Processes, methods and apparatus relating to olefin oligomerization include the use of Raman spectrometry to monitor the concentration of reactants, products or other chemical components. One or more oligomerization conditions are adjusted in response to those monitored concentrations. The present processes, methods and apparatus are capable of monitoring olefin oligomerization with the use of low resolution Raman spectrometry equipment, even where there is some degree of overlap between Raman spectral peaks. Apparatus for olefin oligomerization reactions have at least one Raman probe located in the oligomerization equipment, the Raman probe providing an output signal, and Raman spectrometry equipment located outside the oligomerization equipment and operatively connected to at least one Raman probe.

Abstract: A reactant selected from the group consisting of alkanes, alkenes, alkynes, dienes, and aromatics is reacted with a halide selected from the group including chlorine, bromine, and iodine to form a first reaction product. The first reaction product is reacted with a solid oxidizer to form a product selected from the group including olefins, alcohols, ethers, and aldehydes, and spent oxidizer. The spent oxidizer is oxidized to form the original solid oxidizer and the second reactant which are recycled.

Abstract: Alcohols, ethers, aldehydes, and olefins are manufactured from alkanes by mixing an alkane and a halogen selected from the group including chlorine, bromine, and iodine in a reactor to form alkyl halide and hydrogen halide. The alkyl halide only or the alkyl halide and the hydrogen halide are directed into contact with metal oxide to form an alcohol and/or an ether, or an olefin and metal halide. The metal halide is oxidized to form original metal oxide and halogen, both of which are recycled.

Abstract: A process for controlling an oxygenates to olefin reactor is disclosed which comprises: contacting oxygenate-containing feedstock, e.g., methanol, in a reaction zone in the presence of a molecular sieve oxygenate to olefins conversion catalyst under conditions sufficient to provide an olefins-containing effluent containing alkyl alcohol and dialkyl ether, e.g., methanol and dimethyl ether; analyzing a single gas phase of the effluent determine alkyl alcohol concentration and dialkyl ether concentration; and adjusting reactor conditions, e.g., WHSV, as a function of alkyl alcohol concentration and dialkyl ether concentration, as necessary to provide a substantially consistent effluent composition. A corresponding apparatus for carrying out the process is also provided.

Abstract: The present invention relates to a process for the arylation of olefins by reaction of haloaromatics or arylsulfonates with olefins in the presence of a palladium catalyst, a bulky nitrogen base and a salt.

Abstract: A method for monitoring and improving the performance of a chemical manufacturing process by monitoring transients associated with the operation of process equipment located dowstream of upstream equipment is disclosed. Transients on signals such as the motor current to downstream powder feeding equipment provide early indications of changes in chemical process performance which can then be corrected by altering chemical manufacturing process conditions.

Abstract: The present application relates to a process for the continuous polymerization of isobutene while maintaining at a constant desired value a property P (viscosity or average molecular mass) of the polymer produced. The polymerization is conducted in a reactor comprising a boiling liquid reaction phase which contains the monomer and the polymer being formed, in equilibrium with a gas phase on top of the said liquid phase, by continuous introduction into the reactor of a catalyst and of a C4 hydrocarbon feed mixture comprising the monomer, and by continuous withdrawal from the reactor of the liquid reaction phase, which is subsequently subjected continuously to at least one purification step which is intended to isolate the polyisobutene produced.

Abstract: Isobutene polymerization process wherein a property P (viscosity or average molecular weight) of the polyisobutene product is maintained constant. The polymerization is conducted continuously in a reactor comprising a boiling liquid reaction phase in equilibrium with a gas phase, by continuous introduction into the reactor of a catalyst and of a C4 hydrocarbon feed mixture comprising the monomer, and by continuous withdrawal from the reactor of the liquid reaction phase. The process comprises the determination of a target value V of the partial pressure, PiC4, of the isobutene in the reactor gas phase corresponding to the desired value of the property P, by virtue of an empirical relationship established beforehand between the property P of the polyisobutene product and PiC4.

Abstract: A two-step method and apparatus for controlling cracking severity in the effluent from a cracking furnace such as an ethylene cracker. The method includes two steps. The first step consists of determining the near infrared spectrum of effluent in-line. The second step consists of changing the temperature and/or residence time of the furnace according to the determination of the first step. The apparatus includes a light source mounted on a conduit for the effluent, a light detector mounted on the opposite side of the conduit from the light source to receive light emitted from the light source, means for sheltering the light source from the effluent, means for sheltering the lights detector from the effluent, means for flowing a fluid past the light source at a higher pressure than the pressure of the effluent; and means for flowing a fluid past the light detector at a higher pressure than the pressure of the effluent.

Abstract: A method comprising:

Abstract: A process for selective hydrogenation of unsaturated compounds such as acetylenic compounds or diolefins is carried out in the presence of a catalyst comprising at least one support, at least one metal from group VIII of the periodic table and at least one additional element M selected from the group formed by germanium, tin, lead, rhenium, gallium, indium, gold, silver and thallium. The process is characterized in that the catalyst is prepared using a process in which said metal M is introduced in an aqueous solvent, in the form of at least one organometallic compound comprising at least one carbon-M bond.

Abstract: A thermodynamic model is formed which allows determination of the temperature at which waxes or paraffins appear in petroleum fluids, and notably in crudes, as well as the solid fraction that precipitates when the temperature of the petroleum fluid falls below this critical value. A differentiation is established between n-paraffins, iso-paraffins, naphthenes and aromatics. The model utilizes an analytical representation of the fluids by pseudo-components, the physico-chemical parameters of most of them being determined by combination of the corresponding parameters of a certain number of pure hydrocarbons gathered in a database. The model takes account of the non-ideality of the solid, liquid, and gas phases. Two of the pseudo-constituents including the heaviest fractions are represented by two ficticious molecules, each being defined by a molar distribution among various groups which constitute them, and a group contribution method is used to calculate the thermodynamic properties thereof.

Abstract: An improved method of continuously controlling a multi-zone heater used in a chemical process has been developed. Each zone of the multi-zone heater has an ideal heat flux, FI, and an actual heat flux, FA, and the difference between the heat flux ratios, .DELTA.(FA/FI), of consecutive zones is to be less than a tolerance, T, where T is in the range of about 0.0 to about 0.1. The control is effected by determining the ideal heat flux, FI, of each zone in the heater and determining the actual heat flux, FA, of each zone in the heater. The difference between the heat flux ratios of FA/FI in consecutive zones is then calculated as .DELTA.(FA/FI). A manipulated variable of the chemical process is then adjusted according to an algorithm relating the changes in the manipulated variable to changes in the actual heat flux of each zone to afford a new value of the actual heat flux FAN where .vertline..DELTA.(FAN/FI).vertline..ltoreq..vertline..DELTA.(FA/FI).vertli ne. for consecutive zones.

Abstract: A method for polymerizing or copolymerizing .alpha.-olefin in a vapor phase condition by supplying to a reactor a catalyst composed of a solid catalyst component containing at least titanium and/or vanadium as well as magnesium and an organic aluminum compound wherein the current due to the electric charge transferred from polymer particles electrified to an electrode disposed at a position where sheet-like polymers will be produced in a reactor, as a result of contact of the polymer particles in the reactor with the electrode is determined, and the polymerization or copolymerization is carried out under such condition where the mean value of current is zero or a positive value. As a result, it becomes possible to prevent production of sheet-like polymers and to stably continue the reaction for polymerization.

Abstract: In an endothermic steam active catalytic process employing a fixed catalyst bed in a fuel fired reactor for the dehydrogenation of alkanes to alkenes, wherein a reaction temperature above about 500.degree. C. (932.degree. F.) is maintained for commercially feasible conversions, and wherein catalyst activity declines during a production period, apparatus for control of a process temperature so as to compensate for catalyst activity decline includes a temperature sensor mounted in the reaction effluent stream in combination with a temperature controller which automatically adjusts the quantity of fuel supplied to the fired reactor.

Abstract: An alkane-containing feedstream is passed through one or more tubes, which may contain alkane-dehydrogenation catalyst, immersed in a bed of fluidized particles. The bed is at an elevated temperature which maintains the temperature within the tube(s) at an alkane-dehydrogenation temperature. The particles may be inert, chemically active and/or catalytically active. In one embodiment, cracking catalyst particles are circulated between a reaction zone wherein they contact a cracker feedstock which is converted to cracked hydrocarbon products and a regenerator (22) wherein carbonaceous deposits on the catalyst particles are exothermically removed by contact with an oxygen-containing gas (24). Hot regenerated particles from the regenerator (22) are recirculated (27) to the reaction zone for re-use therein.