Resid conversion processes

Resid conversion is now in a significant transition period as the demand for transportation fuels increases. To satisfy the changing pattern of product demand, significant investments in resid conversion processes... 

OS 72] [R 6] [P S3] For five reactions with non-quantitative conversions, processing was repeated at a doubled residence time (420 instead of 210 s). A control experiment with a reaction of quantitative conversion was also successfully made at the best residence times. Much higher conversions were obtained in this way for all five reactions, being about 20% in each case. 

Reported residue conversion is significantly high for the five types of included reactors and largest for the slurry type of reactor. Besides, the slurry reactor together with the ebullated bed reactor can handle heaviest feedstocks and highest metal contents. Resid conversion requires higher temperatures, and pressure drop is essentially zero in these two reactors. However, product quality is better for the fixed and moving bed processes. 

Naber et al (9) have demonstrated that FCC still has a considerable potential to remain the (resid) conversion "workhorse" of the oil industry. At present about 45% of the world s crude can be envisioned to be within the frontiers of Resid FCC (figure 1). Apart from the importance of FCC feed pretreatment and FCC unit design, also the impact of FCC catalyst performance is crucial to allow the processing of heavier feeds. 

Important biomass fuel properties for thermochemical conversion processes are reported as proximate and ultimate analyses. The proximate and ultimate analyses for selected biomass feedstocks are presented in Table 33.5. For comparison, the analyses from two selected coal samples are also presented. Biomass generally has a lower energy density than coal, oils, and natural gas it also has higher oxygen content. The higher volatiles and oxygen content of biomass translate into a higher reactivity compared to traditional fossil fuels. In terms of thermochemical conversions, this means that less severe process conditions (lower temperature and shorter residence time) are required for bio-... 

Knowledge of the effects of various independent parameters such as biomass feedstock type and composition, reaction temperature and pressure, residence time, and catalysts on reaction rates, product selectivities, and product yields has led to development of advanced biomass pyrolysis processes. The accumulation of considerable experimental data on these parameters has resulted in advanced pyrolysis methods for the direct thermal conversion of biomass to liquid fuels and various chemicals in higher yields than those obtained by the traditional long-residence-time pyrolysis methods. Thermal conversion processes have also been developed for producing high yields of charcoals from biomass. 

A residuum (pi. residua, also shortened to resid, pi. resids) is the residue obtained from petroleum after nondestructive distillation has removed all the volatile materials. The temperature of the distillation is usually maintained below 350°C (660° F) because the rate of thermal decomposition of petroleum constituents is minimal below this temperature but the rate of thermal decomposition of petroleum constituents is substantial above 350°C (660°F). If the temperature of the distillation imit rises above 350°C (660°F), as happens in certain units where temperatures up to 395°C (740°F) are known to occur, cracking can be controlled by adjustment of the residence time. This entry introduces some of the basic chemistry behind the synthesis and conversion processes. 

Therefore, in a mixture as complex as petroleum, the reaction processes can only be generalized because of the difficulties in analyzing not only the products but also the feedstock as well as the intricate and complex nature of the molecules that make up the feedstock. The formation of coke from the higher molecular weight and polar constituents of a given feedstock is detrimental to process efficiency and to catalyst performance. One method by which the process chemistry can be rationalized is to separate the resid and its conversion products into fractions using solubility/ insolubility in volatile liquids as well as adsorption/ desorption on solids. In this way a number of resids and resid conversion products were separated into coke (toluene insoluble), asphaltenes (toluene soluble/ n-heptane insoluble), resins (n-heptane soluble, adsorbs on alumina), aromatics (n-heptane soluble, does not adsorb on alumina), and saturates (n-heptane soluble, does not adsorb on alumina). 

Electron-transfer (ET) reactions play a central role in all biological systems ranging from energy conversion processes (e.g., photosynthesis and respiration) to the wide diversity of chemical transformations catalyzed by different enzymes (1). In the former, cascades of electron transport take place in the cells where multicentered macromolecules are found, often residing in membranes. The active centers of these proteins often contain transition metal ions [e.g., iron, molybdenum, manganese, and copper ions] or cofactors as nicotinamide adenine dinucleotide (NAD) and flavins. The question of evolutionary selection of specific structural elements in proteins performing ET processes is still a topic of considerable interest and discussion. Moreover, one key question is whether such stmctural elements are simply of physical nature (e.g., separation distance between redox partners) or of chemical nature (i.e., providing ET pathways that may enhance or reduce reaction rates). 

During the last six years a fluidized bed fast pyrolysis process for biomass has been developed at the University of Waterloo (The Waterloo Fast Pyrolysis Process). This process gives yields of up to 70% of organic liquids from hardwoods or softwoods, which are the highest yet reported for a non-catalytic pyrolytic conversion process. A fluidized sand bed is used as a reactor and optimum liquid yields are normally obtained in the range of 450 to 550 C at about 0.5 seconds gas residence time with particles of about 1.5 mm diameter or smaller. Two units are in use, one with a throughput of 20 to 100 gms/hr, and another with a throughput of 1 to 4 kg/hr. 

Studies of reaction intermediates and transition states, that are carried out at low pressures using model systems, should be correlated with studies of reaction intermediates during catalytic reactions. Interesting areas for investigations are the catalytic conversion of chiral molecules and high temperature, short residence time processes involving free radicals that include pyrolysis and catalytic combustion. 

The coefficients of the Arrhenius equation determined in this manner, are the basic data for the calculation of the kinetics of pyrolysis (crack) reactions and therefore also the basis for the choice of process conditions, such as pre-setting of reactor temperatures, residence times etc. in thermal conversion processes. 

The marine aerosol lacks the cmstal component except in regions affected by the advection of desert dust plumes. The electrolyte fraction is a mixture derived from sea salt, largely sodiiun chloride, and from gas-to-particle conversion processes, largely sirlfates and nitrate. Sea-salt components reside in the coarse particle mode products from gas-phase reactions occm primarily in the accumulation mode. Sea salt contains a certain amoimt of sirhate. Additional (excess) sulfate arises from the oxidation of SO2... 

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