A combination of two first-order reactions that had different rate constants was found to describe the rate of color development in the 288-343 °C diesel fraction from hydrocracked Llyodminster atmospheric bottoms. These two reactions were the conversion of color precursors which were either (a) unsaturated compounds or (b) heteroatom compounds. The color precursors were correlated with the composition of the diesel fraction. The heteroatom color precursors were correlated with the combination of sulfur and nitrogen content of the diesel fraction. The unsaturated color precursors were correlated with its density, since density can be related to the aromatic content. The rate constants were related to catalyst composition. The fact that all of the parameters in the correlation were related to physical phenomena supported the hypothesis that color development is related to these two types of color precursors. The hydrocracking conditions were 17.3 MPa, 415 °C, 0.59 LHSV, and 570 L (H 2 at STP)/L of feed [2400 scf/bbl]. Eleven different hydrocracking catalysts were examined, most of which contained two components, a conventional CoMo:γAl 2 O 3 component and a zeolite component (sodalite containing nickel, SOD-Ni). The same two rate expressions were found to describe the results obtained from all of the catalysts. The conversion of the heteroatom compounds that were color precursors was associated with the CoMo:γAl 2 O 3 component of the catalyst component. The conversion of the unsaturated compounds that were color precursors was associated with the SOD-Ni catalyst component.

This article presents a methodology which draws heavily on the philosophy of the Input-Output models and having been made completely operational has already been used on three occasions in two countries for the purposes of regional development of construction materials industries.This methodology, or more precisely the strictly formalized part of it is an extension of that of rectangular Input-Output models with modifiable coefficients. Thus, not surprisingly, it resembles fairly closely the approach by simulation, although the proposed model contains some simple optimizing sub-models. While obviously normative, these sub-models play a descriptive rôle in the model as a whole.It is to be noted that the approach presented here can be applied to only one sector of the economy at a time. What is more, although capable of various extensions it will never be more than an auxiliary instrument destined to be used jointly with other analysis and planning instruments.It is vital for any valid regional analysis not to restrict its investigations exclusively to what goes on in the region directly concerned. Even if the objective of the analysis is limited to a single region, one must take into account the interrelations between regions within the national economy and with foreign economies: important feedbacks affecting the region concerned may on occasion travel far beyond its limits before returning. The type of a model presented here, thanks to a great number of interrelations of which it can systematically keep track may turn out to be particularly useful here