SUSTAINABLE SOURCES FOR BASIC ORGANIC RAW MATERIALS-1

Most important basic organic raw materials include ethylene, propylene, butadiene and benzene, toluene, and xylene. They are feedstocks for polymers, fuel blending components, solvents, pharmaceutical, fine and specialty chemicals. Light olefines are usually produced from thermal cracking of naphtha (light oil), which is fraction of crude oil (with about 10%~20% content of naphtha fraction). BTX light aromatics are also from naphtha via a "Pt-reforming" process. It is well known that the resources of crude oil, especially naphtha, is limited and the prices of these basic raw materials are soaring.

Propane as an alternative raw material for Propylene

Propylene is produced mainly as a by-product in steam cracking of naphtha for ethylene formation and a by-product in FCC petroleum manufacturing. Current global output of propylene is ~ 70 million tons/year. Propylene is mainly used to produce polypropylene, and epioxide/glycol, acrolein/acrylic acid/acronitrile, etc. Nowadays the output of propylene from normal production is insufficient. It is not easy to effectively increase the output of propylene from the current pathways because of limitation of current light oil resources. Sometimes people even use ethylene and butene to produce propylene via metathesis reactions.

It is therefore important to seek alternative raw materials for propylene. Among some candidates propane, which is cheaper and more abundant, is arousing extensive attention. As early as in late 1970s, UOP published a process converting propane to propene (Oleflex Process) via direct dehydrogenation. However, the thermodynamics is not favored unless the reaction is done at high temperatures. If oxygen is added to make it into oxydehydrogenation, the formation of water and partially carbon dioxide will offset the energy requirement for dehydrogenation. Propane has been explored to produce acrolein/acrylic acid via selective oxidation. The conversion of propane into light aromatics was developed by BP-UOP (Cyclar process) and has been commercialized by Chevron-SABIC.

Propane can convert to acrolein/acrylic acid via selective oxidation (Scheme 1). It can also convert to produce BTX via dehydrodimericyclization (Scheme 2), and to produce propene via dehydrogenation or oxydehydrogenation.



For the selective oxidation of propane to acrolein (Scheme 1), it is important for catalyst development and process design to increase k1 and k2 (i.e, rate constants for oxydehydrogenation of propane to propene and of propene to acrolein) and at the same time decrease k3, k4, and k5, i.e., to inhibit the total oxidation of the reactant, intermediates, and product to CO2. It is important to design high activity catalysts and modify the surface acidity of the catalysts to achieve these goals.


The aromatization of propane employs a modified ZSM-5 type catalyst. Propane undergoes cracking and dehydrogenation on Metal-ZSM-5 (Metal = Ga or Zn). It is believed that the superacid sites on ZSM-5 account for the cracking (k1), which is an undesired side reaction and that the dehydrogenation of propane (k2)occurs mainly on the metal sites, which are promoted by the acid function of the zeolite. Acid sites are responsible for activation, cracking, oligomerization of propene, and hydrogen transfer of lower alkenes. Metal sites are responsible of activation via dehydrogenation and dehydrocyclization. The adjustment of k1, k2, as well as H-transfer and dehyderocyclization, i.e., the balance of acid and metal sites and the density of acid sites are important for the activation of propane and the selectivity of aromatics. However, the coking and regeneration of the acidic zeolite catalyst is very important for process design.

RENEWABLE AND SUSTAINABLE SOURCES FOR BASIC ORGANIC RAW MATERIALS-2

Converion of Coal, Natural Gas, Biomass into Basic Raw Materials via Syngas (CO + H2)

Syngas can be readily converted to synthetical oil via Fischer-Tropse synthesis. Synthetical oil (mainly C1 ~ C40 alkanes), like crude oil, can be processed to fuel and basic raw materials like petrochemical procedures. In addition to ordinary F-T synthesis, a so-called MFT process, or two-stage FT synthesis with the first stage ordinary FT and second stage containing a HZSM-5 catalyst, can convert syngas to gasoline products and gaseous hydrocarbons, from which ethylene and propylene can be separated. Some special FT synthesis using modified catalysts such as Cu-Mn spinel structure materials can directly convert syngas to lower olefines. Another approach is to convert syngas to methanol, the latter can easily be converted to gasoline (the famous Mobil MTG process), olefines (MTO), or aromatics (MTA). Modified ZSM-5 type catalysts can be used for these processes.

Coal can be converted to syngas via gasification. So can be biomass. Natural gas can be converted to syngas via steam reforming. Therefore, liquid fuels (gasoline and diesel) and basic raw materials can be produced from coal, natural gas, and biomass. These processes are shown in Scheme 3.


BioEthanol as Starting Raw Material for Chemcials

Bioethanol has now become a big industry and this industry seems to become much bigger in the near future. People regard bioethanol as renewable and sustainable new energy source, although some contraversies such as the rivalry of bioethanol for human food widely exist. Actually, bioethanol can also be a good source of basic raw materials. In early days, ethylene, the most important organic chemical raw material, was produced from dehydration of ethanol. Later, things reversed as petrochemical industry well developed after World War II, when industrial ethanol was mostly produced mainly via hydration of ethylene. Now that bioethanol has already become an important fuel blender, we should well expect that bioethanol should also be new resources for basic organic raw materials, as well as other more valuable fine and specialty chemicals, instead of merely a fuel blender. Nowadays, countless new bioethanol companies are setting up every day. It should lead to more research on bioethanol also as a starting raw chemical material.