Nov-2024

Integration of biomass feedstocks directly into refineries

Integrating biomass feedstocks directly into refineries requires evaluation of feedstock availability/composition, infrastructure, and commercial viability.

Vahide N Mutlu and Başak Tuncer
SOCAR Türkiye Research & Development and Innovation Inc.

Article Summary

In modern society, petroleum refineries and the petrochemical sector remain vital for economic progress, yet their traditional practices have significant ecological impacts. The growing demand for environmental sustainability has driven a re-evaluation of these industries’ reliance on fossil fuels. Renewable alternatives, such as agricultural residues, forestry byproducts, energy crops, and municipal solid waste (MSW), allow a diversification of feedstocks. However, such diverse feedstocks bring new challenges due to the different forms of biomass and, within each form, regional and seasonal variations in composition and availability. Evaluating these biomass feedstocks and how to integrate them into the production of fuels and chemicals is crucial for sustainable development. This requires deploying various newer conversion technologies such as pyrolysis, gasification, and fermentation alongside traditional refining processes such as hydrotreating, catalytic cracking, and isomerisation.

Decarbonisation efforts must target emission reductions throughout the life-cycle of petrochemical products, from production to disposal. Additionally, the issue of plastic pollution demands improved life-cycle management to reduce landfill and environmental contamination. Biomass integration, alongside conventional plastic recycling, can promote a circular economy, while biopolymers offer the potential for biodegradable alternatives (see Figure 1).

Diversity of biomass types and feedstocks
Lignocellulosic biomass, sourced from agriculture and forestry waste streams, provides a sustainable form of biomass when it does not compete with food production or cause deforestation. Despite the annual global production of 146 billion tons, only a fraction is currently used for biofuels and biochemicals. Forest residues, which totalled 274 million tons in 2011, are expected to become the dominant feedstock for biorefineries, reaching 6 billion tons annually by 2050 (Guragain & Vadlani, 2021).

Algae, known as ‘green gold’, offer another promising biomass source due to their unique lipid and carbohydrate compositions. The potential of algae in the petrochemical industry depends on efficient cultivation, lipid extraction, and scalability for both fuel and non-fuel products (Chandra, Iqbal, Vishal, Lee, & Nagra, 2019).

MSW provides an unconventional, yet valuable biomass source. Global MSW production was 1.3 billion tons in 2011, and is projected to reach 2.6 billion tons by 2025 (Kurian, Nair, Hussain, & Raghavan, 2013). The primary challenge is not the availability of biomass feedstock but the innovation required to convert these diverse streams into usable feedstocks. Strategic biomass selection must consider the final product requirements, regional availability, and environmental impact to optimise integration into petrochemical processes.

Technological advancements in biomass integration
Integrating biomass conversion processes into existing petroleum refinery configurations can result in significant capital savings by eliminating the need for constructing separate biofuel production facilities, thereby enhancing the competitiveness of biofuels (Prasetyo, et al., 2020). Over the last 15 years, several petroleum refineries have been converted into biorefineries to hydrotreat used cooking oils in the production of hydrogenated vegetable oil (HVO) for use as renewable diesel and, more recently, sustainable aviation fuel (SAF). Biomass feedstocks such as lignocellulosic biomass, the organic fraction of MSW, and the chemical recycling of plastic all require a conversion process to break down complex hydrocarbons into simpler molecules. These conversion technologies include:

υ Pyrolysis: Pyrolysis, a thermal decomposition process, uses high temperatures in the absence of oxygen to break down organic materials like lignocellulosic biomass into valuable byproducts. This process produces a bio-oil or py-oil, which needs further treatment, usually by co-processing with petroleum feeds within the current refinery infrastructure to yield biofuels. From an economic perspective, the cost of retrofitting a petroleum refinery for py-oil co-processing is deemed financially feasible. Pyrolysis of biomethane has also been developed as a low-carbon intensity route to renewable hydrogen.

ϖ Gasification: Gasification converts biomass into synthesis gas (syngas), a mixture of carbon monoxide and hydrogen. The syngas can then be used to produce various fuels and chemicals and generate electricity. The exploration of gasification within the petrochemical context delves into its adaptability, environmental impact, and the intricacies associated with seamlessly integrating gasification technologies into existing infrastructures.

ω Fermentation: Fermentation is a traditional process used to produce alcohol in the food and drink industry. More recently, it has been deployed as a more eco-friendly route to producing fuels and chemicals. Microorganisms convert organic materials into ethanol, which is blended with gasoline or used in the Alcohol-to-Jet route to SAF.

Effective integration of biomass into a petroleum refinery
When integrating biomass into a petroleum refinery (see Figure 2), it can be introduced and processed using relatively minor modifications of existing processes. The choice of insertion point depends on factors such as the type of biomass, existing refinery infrastructure, and desired end products.

Feedstock pre-processing is vital and includes size reduction, drying, and impurity removal. Depending on the feedstock, additional treatments, like chemical or enzymatic processing, may be applied. These steps optimise the compatibility of the biomass with refinery technologies, improving the efficiency of gasification or liquefaction and ensuring smooth integration into refinery operations.

Integration with hydrotreatment units
Hydrotreatment units are ubiquitous in modern refineries. The process involves preheating and mixing the feedstock with hydrogen in a high-pressure reactor with a catalyst composed of nickel, cobalt, and molybdenum metals supported on alumina. This setup removes impurities such as sulphur, nitrogen, and metals while saturating olefins and aromatics to improve the stability and combustion properties of the final products.

Vegetable oils and animal fats are particularly well-suited for hydrotreating, producing renewable diesel and jet fuel by hydrogenating triglycerides and free fatty acids, removing oxygen, and creating hydrocarbons similar to those from fossil fuels. This process reduces emissions to produce fuels compatible with existing infrastructure, and enhance fuel stability and performance.