Recycling of the water-phase from hydrothermal conversion of biomass: Comparative study of water composition using lignin and microalgae as feedstocks

Recycling of the water-phase from hydrothermal

conversion of biomass

Comparative study of water composition using lignin and

microalgae as feedstocks

Carlos Fellipe de Abreu Thomaka

Master thesis, 60 hp

Master Program in Chemistry – 120 ECTS 2018-2019

I

Abstract

The transformation processes turn biomass into valuable products. They are

advantageous techniques that are necessary to reduce the use of fossil fuels and increase

the use of renewable resources. The hydrothermal carbonization (HTC) is a process that

requires great amount of water, biomass and energy to produce a material called

hydrochar. The hydrothermal carbonization also produces a liquid product, called

water-phase, that is usually neglected in most of the studies. In this project, the water-

phase from an HTC process using lignin and microalgae as feedstock were

characterized. Several analyses were performed to identify the composition, inorganics

concentration levels and properties such as pH. In addition to these analyses, the

recycling of the water-phase was performed to evaluate the impacts on hydrochar yield,

composition and inorganic concentration levels. The HTC process was conducted in

triplicates at 240 °C for 6 h in a 1 l reactor and recycled for four times. While the HTC

operation using microalgae was performed in triplicates at 240 °C for 6 h in 20 ml

reactors and recycled once due to lack of samples. In the first cycle the hydrochar yield

was 44.79 % and increased over four cycles to 50.98 %. The increase of the hydrochar

yield on the lignin process showed that the water-phase recycling is possible and

advantageous on the hydrochar yield perspective. The hydrochar yield of the

microalgae process also increased over the cycles (26.80 ± 6.22 %). The composition

identified mainly aromatic compounds such as guaiacol, vanillin and ethanone, 1-(3-

hydroxy-4-methoxyphenyl)- as the species with higher abundance in the analyzed

water-phases. The concentration of sodium and sulfur increased over the recycling from

8.75 to 22.91 g/l for sodium and from 2.14 to 5.06 g/l for sulfur. The increased

concentrations of these inorganics could represent a drawback on the recycling due to

their effects on the environment. The results are promising and numerous. They provide

new information about the compounds that can be found in the water-phase and the

possibility of reusing the water-phase to reduce costs in the process and consequently,

turning the HTC into a more profitable technique.

II

III

List of abbreviations

ALK Alkaline

DA Dealkaline

EPA Environmental Protection Agency

GC Gas Chromatography

HHV Higher heating value

HPLC High-Performance Liquid Chromatography HTC Hydrothermal Carbonization.

LC Liquid Chromatography

MS Mass spectrometry

SCW Super Critical Water STDev Standard Deviation

PAH Polyaromatic hydrocarbons TOC Total Organic Carbon.

XPS X-Ray Photoelectron Spectroscopy

IV

Author contribution

The author conducted the laboratory experiments that included the hydrothermal carbonization operation, gas chromatography analysis, solids analysis, ash content, non-volatile residue, liquid-liquid extraction and pH measurements. The samples generated by the author were also handled and pre-treated by him. The first 4 lignin samples were provided by Alexandra Charlson, the data relative to these samples was provided by Kenneth Latham. Microalgae sample were provided by Francesco (SLU).

The ICP-MS operation was conducted by Erik Björn at Umeå University. The student

had orientation on the ICP-OES by Erik Björn, and then the student conducted all the

analysis on this instrument. Andriy Rebryk assisted on the GC-MS analysis.

V

Table of contents

Abstract ... I List of abbreviations ... III Author contribution ... IV Table of contents ... V

1. Introduction ... 1

Aim of the diploma work ... 1

1.1-Biomass ... 1

1.1-Lignin... 1

1.2-Microalgae ... 2

1.2-Thermochemical processing ... 3

1.3-Hydrothemal processing ... 4

1.4-A brief state of the literature: HTC of lignin and microalgae ... 5

1.5-Motivation and objectives ... 7

2. Popular scientific summary including social and ethical aspects ... 8

2.1 Popular scientific summary... 8

2.2 Social and ethical aspects ... 9

3. Experimental ... 10

3.1 Chemicals and samples ... 10

3.2 Analysis of provided samples ... 11

3.2.1 pH, solid particles, ash content and non-volatile residues ... 11

3.2.2 GC-MS ... 12

3.2.3 ICP-MS/OES... 13

3.3 HTC operation and water-phase generation ... 13

3.4 Analysis of generated samples ... 14

3.5 Quality assurance and quality control for the GC-MS ... 15

4. Results ... 15

4.1 Analysis of provided lignin samples - pH measurements, solid particles, ash content and non-volatile content ... 15

4.1.1 pH measurements, solids, ash content and non-volatile residue ... 15

4.1.2 GC-MS ... 16

4.1.3 ICP-MS / ICP-OES ... 17

4.2 HTC operation –Hydrochar yield ... 17

4.3 Analysis of generated samples ... 18

4.3.1 pH measurement ... 18

4.3.2 GC-MS ... 19

4.3.3 ICP-MS/ICP-OES ... 20

4.4 Microalgae recycling ... 21

5. Discussion ... 21

5.1 Recycling results discussion – Hydrochar yield and composition change over recycling ... 22

5.2 Differences between the provided samples and generated samples ... 22

5.3 Microalgae hydrochar yield discussion ... 23

5.4 Sodium and sulfur concentration ... 24

6. Conclusions and Outlook ... 24

Acknowledgement ... 25

References ... 25

Appendix ... 31

VI

Appendix 1 – Instrumental Parameters and procedures ... 31

Appendix 2 – False positive identified ... 32

Appendix 3 – Mismatches list... 36

Appendix 4 - GC-MS SPECTRA ... 37

Appendix 5 – HTC operation full data sheet ... 85

Appendix 6 – Guaiacol Quantification Data set ... 86

VII

1

1. Introduction

The use of fast and natural growing materials as feedstock to provide energy and valuable products is the main target of the green industry, which is necessary to help develop a more sustainable world. Using fewer resources, such as water and biomass, and generating fewer residues than the usual processes is an interesting option to the evolution of industrial processes. Presently, the use of natural resources results in a massive generation of waste. Due to a lack of knowledge about reusing resources in industrial processes, water and biomass are currently not optimized. Hence, introducing waste as feedstocks requires a remodeled process. Additionally, reducing the use of water is a key factor to improving the sustainability of the green industry.

Aim of the diploma work

The studies aim is to obtain information about the composition of a hydrothermal carbonization process that used lignin as feedstock; the impact of recycling the water- phase in the hydrochar yield of a process using lignin as feedstock and a process using microalgae as feedstock. The studies try to evaluate changes in the composition and properties of the water-phase over the recycling cycles.

1.1-Biomass

Biomass can be defined as the amount of mass of a living organism

and “all the living material in a given area: often refers to vegetation. Also called biota”

. The biomass has become important as an alternative source of energy and chemicals. The most advantageous form of biomass is the lignocellulose

. This material has an estimated global growth of 146 billion tons per year and it is considered essential to the sustainability of the planet

. The attractiveness of this material grew constantly due to its potential uses such as source of valuable products, food production, recycle pollutants and remediate contaminated material

. The lignocellulosic material’s fast growth combined with its diverse applicability resulted in a vast generation of waste, which was an important resource for the green industry that turned lignocellulose residues into products. Among the many different sources of biomass, lignin and microalgae were the focus of this thesis and they will be discussed below.

1.1-Lignin

The lignocellulosic material is mainly formed by three biopolymers: cellulose, hemicellulose and lignin. Lignin is less used by the industry than the other two due to the lack of knowledge on its use. However, it has been appearing more often in the literature because of its potential, which will be discussed later

. Lignin is the second most abundant biopolymer and responsible for strengthening the lignocellulose structure

. This biopolymer requires more energy to break its structure than the other two biopolymers

. Moreover, the combustion of lignin generates more energy than the other two biopolymers, it has a calorific value of around 23.3-26.6 MJ/kg, which is 3-4 MJ/kg higher than cellulose and hemicellulose

. While lignin is composed of three different monomers, cellulose and hemicellulose are composed of glucose monomers.

Figure 1a shows the three different phenolic monomers with methoxy groups

.

They are combined randomly into an amorphous and highly branched structure

to

form lignin. Their combination is still being studied, because the polymerization and

bonding depend on the material analyzed

. Their aromatic nature also means that lignin

could be a source of aromatic compounds that have been mostly obtained by the

2 processing of fossil fuels

. In addition Figure 1b shows flavor ester used in the industry that can be obtained from the depolymerization of the lignin

. This complexity of the structure has been challenging in the endeavor to find a more profitable use for the lignin rich waste generated in the pulp/paper mill industry.

Figure 1 - a) Lignin monomers; b) Guaiacol and vanillin are important to obtain flavor esters. Adapted from ¹⁰.

The pulp and paper industry is one of the major industries in the world, with an estimated world production of 390 million tons

. It has an important role in many countries, including Sweden, representing a large part of the economy. During the processing of the pulp/paper industry, the lignocellulosic material undergoes physical and chemical treatment to dismantle the structure and separate the biopolymers

. One of the most commonly adopted chemical treatments has been Kraft pulping, which uses powerful chemicals, such as sodium sulfide (NaS) and sodium hydroxide (NaOH)

. Kraft pulping results in an environmentally toxic waste, called black liquor, that contains mainly lignin and hemicellulose

. Black liquor was often used in recovery boilers to optimize the energy usage, e.g., a Swedish kraft pulp mill generates an energy excess of around 7 GJ/m³ton for pulp produced

. As mentioned above, the combustion of lignin generates around 24 MJ/kg. Therefore, the removal of lignin from the black liquor reduces the excess of energy generated in the recovery boilers

. It was estimated that only 2 % of the lignin obtained from the pulp/paper waste was given any application besides energy generation in recovery boilers

. Lignin extraction from black liquor can be made by acidification, with sulfuric acid, lignin precipitation and filtration

. Kraft lignin contains sulfur and sodium, around 18.1 % of sodium concentration in total dissolved solids

.The need of studying the transformation of lignin is essential to recover valuable materials and reduce waste emissions. As mentioned above, biomass can be from different sources. The microalgae are a source of biomass that can be cultivated in wastewater. It has a waste emission mitigation capacity that will be discussed further.

1.2-Microalgae

The microalgae have been appearing in the literature as another advantageous

form of biomass. It uses waste water and additionally carbon dioxide that is bubbled in

the water as source for carbon and nutrients for growing

.The microalgae is an

unicellular organism that reproduces with a faster rate than terrestrial plants and it is

composed by a mix of lipids, carbohydrates and proteins

. In the literature, it is

3 possible to find different applications for this type of biomass such as: production of acetic acid, biofuel and nutritional supplements

. The microalgae ability to fixate CO

combined with its fast-growing cycle turns it into an attractive material for environmental science and sustainability

.

Currently, high quantities of CO

(around 7 % of the global emissions) are generated by the cement industry. The intensive need of energy to maintain the furnaces working and burning emissions are responsible for the high generation of carbon dioxide

. Which turns this industry into a potential candidate to use microalgae to reduce the amount of released CO

.

The algal biomass cultivation dispenses the need of arable land and clean water

. Natural microalgae production is low and costly

. The exploitation of flue gas in combination with wastewater has the potential to make the microalgae production more attractive

.

Hence, after determining the source of the biomass, it is necessary to choose a transformation process. The transformation of biomass into useful products such a soil amendment, fuel or adsorbent material. Most of the transformation processes requires low moisture in the feedstock. Since the microalgae is cultivated in an aquatic environment, the high-water content of the microalgae leads to a need of pretreatment in most of the transformation processes

, which represents disadvantages of this type of biomass. Nonetheless, the green process should be stimulated, and hindrances needs to be studied and bypassed. Thermochemical processing is an alternative to treat biomass and it is widely used for its transformation into useful and valuable products

. It transforms biomass into products from biofuels (gas, liquid and solid) to adsorbent material for remediating processes

. Some thermochemical processes will be covered in the next section.

1.2-Thermochemical processing

The thermochemical processing is the oldest way handling biomass since a simple bonfire is an example of it

. It is based on applying heat to the biomass to obtain products or energy

. Many different types of thermochemical processes exist, and their conditions will be further explained in the following sections. The thermochemical biomass conversation processes are flexible in terms of conditions such as the parameters of temperature and pressure; environment such as inert or oxidative; final products such as gas, liquid or solid; and pre-treatment requirement or not

. Figure 2 illustrates a simplified diagram including the most common thermochemical processes available in the literature. The drying step is the major source of cost and time of the pre-treatments

. Therefore, a separation can be made into processes that require drying and processes that can be conducted without this pre-treatment of the biomass such as hydrothermal processing. Pyrolysis, combustion and gasification are shortly explained below.

Figure 2 - Thermochemical processing types, biomass conversion with and without pretreatment. Adapted from ¹³.

4 Pyrolysis is an important biomass conversion technology that is usually used to maximize the amount of liquid fuel produced, called bio-oil, is attractive in terms of logistics

. However, it is possible to alter the temperature and reaction time to obtain gas and solid products

.This technique uses a different range of temperatures in an inert environment, absence of oxygen

. The reaction time may vary from seconds to days, while the used temperatures can vary from 290-1000 °C, requiring variable heating rates

. Moreover, the requirement of pre-treatment such as fragmentation and drying of the biomass can generate additional costs

.

Combustion is the total oxidation of the biomass

. This thermochemical process is a technique that basically converts all biomass into energy

. It uses high temperatures, up to 1000 °C, and usually requires fragmentation and drying of the biomass

. Nonetheless, the process has low energy conversion efficiency

. While the combustion can generate, depending on the conditions and feedstock, large amounts of pollutants such as CO

, inorganic volatiles (potassium, sulfur and nitrogen) and even polyaromatic hydrocarbons (PAH). The PAH are well-known toxic compounds that are constantly monitored

, and they are issues associated with this technique.

The gasification is an efficient biomass conversion technology that uses high temperature and partial oxidizing environment

. Although the process is considered efficient for transforming biomass into energy, it requires different pre-treatments and catalyst

. The pre-treatments of the feedstock used in the gasification are size fragmentation, densification, and drying

. Therefore, the gasification is not simple and demands a complex set-up.

Evans et al. 2010 conducted a sustainability assessment that evaluated the use of pyrolysis, combustion and gasification for biomass conversion to generate electricity.

After analyzing factors such as greenhouse gas emissions, electricity price and efficiency, the authors concluded that processing biomass with these thermochemical processes were favorable when comparing to other energy generation options such as use of fossil fuels. Furthermore, the authors included the negative impacts of using agricultural crops that could be used as food and the excess of water used in the processes

.

Drying is one of the most common pre-treatments required for conventional thermochemical processes, as illustrated in Figure 2, in contrast to hydrothermal treatment techniques which can use wet biomass as feedstock. The hydrothermal treatment is a technique that has existed for a long time, but its importance has been rising within the last few years due to its applicability and flexibility. The hydrothermal treatment does not require drying the biomass; it can use mild temperatures (lower than 300°C); and it can produce liquid, gas or solid products

. The hydrothermal treatments will be explained in the next section.

1.3-Hydrothemal processing

Hydrothermal processing is roughly 100 years old

. The processes use water as a reaction media, which represents a way to transform biomass into products and deal with usual hindrances such as pre-treatment of feedstock

.

The water can be used in its supercritical or subcritical conditions, which are

state related to the critical point. The critical point is the highest temperature and

pressure, represented on a phase diagram, where liquid and gas phase can coincide

.

The water has a critical point of around 374 °C and 22.1 MPa

. Therefore, supercritical

conditions are characterized by the temperature and pressure above the critical point,

while subcritical conditions are any temperatures lower than the critical point

.

Supercritical and subcritical conditions are commonly used in the industry to alter the

properties of solvents and each state has its own effects on the solvent properties such

as: dielectric constant, viscosity and solubility. While the water is a well-known polar

5 solvent, it is possible obtaining non-polar characteristics when using different conditions

.

There are three types of hydrothermal processing: hydrothermal carbonization (HTC), hydrothermal liquefaction (HTL) and hydrothermal gasification. The HTC uses subcritical water as a reaction media while the other two techniques make use of supercritical water for the process.

The hydrothermal liquefaction produces mainly liquid products, with solids and gases as byproducts. It uses temperatures from 250-373 °C

. It is a process with lower temperatures than pyrolysis and no need for pre-treatment of biomass

. The hydrothermal gasification uses temperatures around 600°C and pressures around 30 MPa, much lower than the normal gasification 800-1000 °C

. Hydrothermal liquefaction and gasification are not the focus of this project and will not be discussed in detail.

Hydrothermal carbonization, also known as wet torrefaction, is a process that maximizes the solid fraction in the products. Therefore, the process still generates a liquid phase and small amounts of gases, between 1-3 % of the raw material

. The solid product obtained in the HTC is called hydrochar. The hydrochar is generated under wet conditions, which results in a mixture of solid and liquid product, i.e. a slurry. A separation process, usually filtration, must be used to separate the hydrochar from the liquid. The liquid product obtained from the separation is referred to as process water or water-phase.

The HTC process uses a huge amount of water. The biomass/water ratio can vary from three to ten times

. Once the process gets scaled up, the water usage will be a financial and environmental issue. The process water from the reactor contains species which need treatment prior to the release in the environment. Since the focus of the HTC process research is with the solid product, the liquid has been neglected in most of the recent literature

. However, few studies have shown that the recycling of the water-phase can increases in the hydrochar yield

. One of the gaps of the literature is the lack of a study containing information about the recycling of the water-phase generated in a process with microalgae and studied with the composition of the water- phase during the recycling with lignin as feedstock. Another gap is the lack of knowledge of the water-phase composition of an HTC using lignin as feedstock. This study seeks to obtain data which will help to address the research gaps. Therefore, a short review on the literature will be presented in the next section.

1.4-A brief state of the literature: HTC of lignin and microalgae

The literature research provided information of the current state of the hydrothermal carbonization. Table 1 represents the literature summarized on HTC of lignin and microalgae, including recycling of the water-phase. The literature that contained lignin and microalgae used as feedstock was briefly described below.

In Kang et al. 2012, dealkali lignin was used in an HTC process at 225 °C, 245 °C and 265 °C for 20 hours. The study presented hydrochar yield, energy recovery, carbon recovery and higher heating value (HHV) of the hydrochar produced. The authors determined that higher process temperatures accelerate the process generating lower yield and higher carbon content.

In Atta-Obeng et al. 2017, lignin from a biorefinery was used to produce

hydrochar in an HTC process. This study used different process temperatures to analyze

the effect on the hydrochar yield morphological and physicochemical properties of the

hydrochar obtained. The authors identified the highest yield on the lowest process

temperature (200°C) and major morphological changes occurred in processes higher

than 300°C.

6 In Wikberg et al. 2016, kraft lignin acidified and alkalinized were used in an HTC process at 220 °C for 4 hours. Their study analyzed kraft lignin and the hydrochar composition using pyrolysis/gas chromatography. The authors identified that the kraft lignin was able to produce higher yield of hydrochar and higher carbon recovery than glucose and galactoglucomannan. The acidic and alkaline hydrochar presented similar compositions with a visible higher presence of guaiacol and p-cresol.

Table 1 - Gathering of the literature on HTC, recycling and HTC of microalgae

Study Feedstock Reference

HTC Recycling

Poplar wood chips ⁶⁴Stemann 2013

Grape pomace, orange pomace, poultry litter ⁶⁶Catalkopru 2017

unbleached tissue paper ⁶⁵Weiner 2014

loblolly pine ⁵⁷Uddin 2014

HTC of Lignin / No

Recycling

Kraft Pulp, Kraft lignin acidic, kraft lignin alkaline ⁶¹Wikberg 2016

lignin commercial ⁶²Atta-obeng 2017

Lignin (DA) ⁵⁸Kang 2012

cellulose, xylan, lignin ⁶⁷Kim 2016

HTC microalgae

Chlamydomonas reinhardtii, lignocellulosic prairie grass (20%) lignin, D.

salina

37Steven M. Heilmann 2010

Dunaliella salina, Chlamydomonas reinhardtii ³⁸Steven M. Heilmann 2011

Spirulina, loblolly pine, sugarcane bagasse, Lipid extracted algae spirulina ³²Broch

Nannochloropsis sp ³³Lu 2015

A. platensis ⁶⁸Yao 2016

Hippeastrum. reticulatum, Chlorella vulgaris ³⁴Park 2018

In Kim et al. 2016, lignin was used in an HTC process in different temperatures (180-280 °C) for 30 min in a 1 L reactor. The authors determined that the decomposition of the lignin initiated at 250 °C and that the process temperature of 200 °C was optimal.

However, the carbon fixation did not increase until the reaction at 250 °C.

The information gathered about HTC processes using lignin was that lower temperatures presented higher hydrochar yield. Also, no study showed the composition analysis of the water-phase generated.

In Heilmann et al. 2010 and Heilmann et al. 2011, microalgae were used in an HTC process to generate hydrochar. The authors presented a series of analysis of different algal materials and the hydrochar formed along with comparation between the lignocellulosic materials and hydrochar. The authors also identified the future importance of evaluating the liquid product of the process due to the high nitrogen content.

In Lu et al. 2015, microalgae were used in an HTC process to facilitate the extraction of lipids for biofuels and dietary supplementary purposes. The authors identified that the HTC process produced a hydrochar that retained around 85 % of the total fatty acids.

In Broch et al. 2014, microalgae were used in an HTC process at 175-215 °C for 30 minutes in a 2 L reactor. The authors determined high-value chemicals in a low amount (less than 1 % of the dry algae). However, the authors determined that the microalgae were able to produce an energy-dense hydrochar.

In Yao et al. 2016, microalgae were used in an HTC process to be used along

with algal production. The authors recovered the water-phase generated and used for

another algal production. The authors also determined that the method could save up to

60 % of the conventional nitrogen usage.

7 In Park et al. 2018, microalgae were used in an HTC process at 180-270 °C for 60 minutes. The authors evaluated carbon recovery, carbon content and energy recovery of the hydrochar obtained. They determined that the microalgae were an efficient source to generate a potential biofuel.

The gathering of the studies gives information about the process temperature and time. The HTC can use microalgae as a feedstock to obtain a hydrochar with an efficient carbon fixation and that can be used as a biofuel. Also, the gathering presented no studies about the recycling of the water-phase on the HTC.

1.5-Motivation and objectives

As mentioned above, the HTC process can transform residues that contain biomass into valuable products using mild temperatures and water as solvent. One of the disadvantages of the process was the amount of water required, that can vary from seven to ten times the amount necessary. This led to a need to reduce the water consume from the environmental and social aspects. The water-phase is usually ignored during the studies with lignin. The lack of knowledge of the water-phase composition of an HTC process using lignin is evident. Therefore, it was necessary to investigate the composition of the water-phase and the possibility of reusing the water-phase without reducing the hydrochar yield. Also, it is important to understand that the recycling may increase the yield of the hydrochar or concentrate toxic compounds in the water-phase.

The inorganics are commonly present in the water-phase such as sodium and sulfur.

The inorganics present in the biomass are also of importance due to impacts in the environment. The sodium is considered as hazardous in groundwater and often undetermined according to the environmental protection agency (EPA)

. The salinity of irrigation water can be harmful for the crops and may be considered toxic to sensitive crop, i.e. fruit trees

. While elemental sulfur and sulfur species have harmful effect on terrestrial animals, humans, aquatic environmental

. Also, sulfur is common to be the cause of corrosion problem

.

It is known that the HTC can “clean” the biomass, while the water-phase generated contains most of the inorganics present

. Moreover, the lignin obtained from the black liquor contain contaminants such as sulfur and sodium ( around 18.1 %

).

The water-phase containing those inorganic cannot be discharged in the water sources without treatment

. Hence, the analysis techniques and methods about the water-phase generated should be enough to give information about the concentration levels of inorganics, composition and acidity.

The water-phase generated in HTC processes is typically studied by analysis of pH, total organic carbon and a composition analysis such as gas chromatography with mass spectrometry (GC-MS), liquid chromatography with mass spectrometry (LC-MS) or inductively coupled plasma with mass spectrometry (ICP-MS)

. The glucose reactions in the HTC and water-phase composition are well-known and abundant in the literature

. Nevertheless, the literature that utilized these techniques did not used the lignin as feedstock. The information about lignin composition were searched for different processes and studies

.

The species present and how the composition changes over the recycling can be

identified with a non-target analysis of this water-phase. The literature gathering, gave

enough information to understand the composition of lignin and what to expect on its

water-phase. Since lignin is based on three different phenolic monomers, a mix of

phenolics and methoxylated molecules were expected and, some of them, constitutes a

good variety of antioxidants

. Therefore, the gas-chromatography with mass

spectrometry was selected for the non-target analysis. This method uses a library tool

that facilitates the determination of unknown species.

8 Vanillin, catechol and syringol are usually found in the water-phase of a hydrothermal decomposition of lignin

. The vanillin can be used to produce vanillic acid. This can be used as a flavoring agent, while the catechol is widely used as a precursor in the industry to synthetize chemicals such as pesticides and pharmaceuticals. The syringol can be used to produce syringic acid, which presents useful biomedical properties and great importance in the industry

. Hence, the presence of those compounds can attract more attention to the water-phase generated.

Although, lignin and microalgae have distinct composition the microalgae were another important focus of this project due to its benefits discussed earlier.

The microalgae were provided by the Francesco of the Swedish university of agricultural studies sciences (SLU). According to the literature, it is possible to obtain cellulose and starch in the microalgae composition

. Starch and cellulose are sugar based biopolymers which are decomposed into glucose during the thermal treatment and it generates a series of different organic molecules such as organic acids and aldehydes

.

Also, it is commonly found HTC processes that used microalgae as feedstock

. It was not possible to find literature that studied the recycling and the water-phase composition of the water-phase on an HTC process using lignin.

Therefore, analyzing the water-phase and obtaining more information of its composition and evaluating the effects on the hydrochar yield is of great importance.

2. Popular scientific summary including social and ethical aspects

2.1 Popular scientific summary

Biomass is a renewable abundant natural resource that can be used in many industrial activities. The used biomass is usually a plant-based material composed of different molecules. The most known molecules are cellulose, hemicellulose and lignin, where lignin is the most complex molecule of them. Its structure changes for every source of biomass. Another source of biomass that is being studied more by the research community is the microalgae. This organism grows faster than the terrestrial plants and it is produces in an aquatic environment.

The processes that changes the biomass into useful products are transformation processes. These processes make use of biological activities or temperature, where temperature is a key factor in thermochemical processes. The presence of water in the biomass is counterproductive due to the need of more energy to break the material’s structure. The hydrothermal processing uses temperature and water to transform biomass into products. The use of water is beneficial in this process and a wet biomass can be used without previously drying. Currently, there are three different types of hydrothermal processing: hydrothermal carbonization (HTC), hydrothermal liquefaction (HTL) and hydrothermal gasification. The hydrothermal carbonization demands lower temperatures of the hydrothermal processes. Also, it produces mainly solids and liquid products.

The project sought information about the liquid product composition of a lignin HTC, the recycling of the liquid products into the process, and the liquid product composition of a microalgae HTC. Furthermore, the composition was studied during the recycling cycles and the impacts on the solid product yield.

As a result, compounds in the liquid product were identified which could be

alternatively used by the industry. Those compounds are usually obtained from different

non-renewable sources. The recycling of the liquid products did not show an increase or

decrease in the solid product yield. However, this information was valuable to allow the

water recycling and to avoid excessive use of water.

9 2.2 Social and ethical aspects

The global risk report from the world economic forum 2018 classifies water crises as being number five on the top ten risks in terms of impact

, while failure of climate-change mitigation and adaption is number five on the top ten risks in terms of likelihood

. However, climate change has an impact on the water supply

.

Industrial processes have a major impact on the environment. The pulp/paper mill is the third largest industry to use freshwater in its processes and, consequently, produces as much wastewater as it uses water for their activities

.

This work was aimed to provide information of a green process used to transform waste into useful products, to reduce the use of resources and to obtain information about the products that can be generated.

The demand of clean water resources increases together with the population.

Most of the industrial activities demand a considerable amount of water volume for cooling or a transformation process. The reuse of the water in a transformation process can be essential to make it feasible. In addition, reducing the amount of water for industrial processes could reduce the environmental impact on the planet.

Another environmental impact in industrial activities is the generation of great amounts of waste. Great water demand and generation of waste are characteristics of the pulp/paper industry. The pulp/paper mill waste contains a substance called lignin, which is present in the composition of the plants. The lignin is a high-energetic molecule that can be burned to produce energy. This complex molecule can be used in transformation processes to obtain a versatile material, called hydrochar. The hydrochar can then be used as a fuel, adsorbent material or soil amendment.

Hence, to reduce the impacts of the industrial activities using natural resources wisely is a key factor. Another important resource that has been highlighted in the research community is the microalgae. However, microalgae cultivation is costly due to the need of nutrients in the media. The use of wastewater generated in industry could reduce these costs, since the wastewater already contains some of the needed nutrients.

In addition, microalgae are also able to mitigate global warming. The use of microalgae is associated with the remediation of wastewater ponds, due to CO

fixation and absorption of contaminants such as ammonia

.Furthermore, the reuse of lignin to obtain fuels or valuable materials is associated with the reduction of CO

(greenhouse gas) emission due to reducing the use of fossil fuels, which generate greater amount of greenhouse gases

.The most worrying impacts of industrial activities are the generation of waste and the use of large quantities of water. The pulp/paper industry plays an important role in the impacts mentioned. The pulping is the first stage of the paper production industrial process

. The bleaching of pulp generates compounds that can be found in the decomposition of lignin such as guaiacols, syringols and catechols

. The kraft pulping is the chemical process that is widely used. This technique uses sodium hydroxide and sodium sulphite and generates around 50 m

of effluent per ton of paper

93

. The effluent contains around 11-25 g/l of lignin

.

Another listed industry that plays a major role in environmental impacts, is the cement industry. The cement industry is responsible for around 5 % of the global CO

release

. This discharge is associated with the demand of the energy to keep the furnaces working and to obtain the products of the calcination of the raw materials

. The cultivation of microalgae on wastewater contaminated with flue gas from the cement industry is feasible and synergetic with needs to further reduce the CO

emission

. The HTC process can turn this cultivated biomass into biofuel that can then be used in the same industry, closing a loop and reducing the need of fossil fuels to generate electricity.

The foment of the green processes is advantageous for the environment and

synergetic for some of the pulp/paper mills and the cement industry. It is undeniable that

the world is at the risk due to pollution, greenhouse effect and water scarcity. Improving

10 the HTC process, reducing its water consumption and improving its yield will be essential to increase its use among the industry.

3. Experimental

The experimental part was divided into three segments: (i) analysis of the provided lignin and microalgae samples, (ii) HTC operation and water-phase generation and (iii) analysis of generated samples.

3.1 Chemicals and samples

The chemicals used were phenanthrene D10 (Sigma Aldrich), guaiacol (Sigma Aldrich), p-cresol (Sigma Aldrich), dichloromethane (Fisher Scientific), nitric acid 65 % (Suprapur), acetone (GPR Rectapur), sodium sulfate (Merck), dealkaline lignin (TCI Chemicals), sulfur standard for ICP-MS (Spectrascan). Water-phase samples from HTC lignin processes were provided to the author for an initial study. Table 2 compiles information about the origin of the samples. The provided samples were DA-280-12, DA-300-12, ALK-300-12 and ALK 280-4, while the generated samples were 1L0-4L4 and microalgae.

Table 2 - HTC Sample information: feedstock used, temperature of the process and process time

Sample Name Feedstock Temperature (°C) Time (h)

DA-280-12 Dealkaline lignin 280 12

DA-300-12 Dealkaline lignin 300 12

ALK-300-12 Dealkaline lignin (with alkaline treatment) 300 12 ALK-280-4 Dealkaline lignin (with alkaline treatment) 280 4

1L0-1L4 Dealkaline lignin 240 6

2L0-2L3 Dealkaline lignin 240 6

3L0-3L4 Dealkaline lignin 240 6

4L0-4L4 Dealkaline lignin 240 6

Microalgae Microalgae 240 6

The lignin hydrochar samples (n=4) were obtained during carbonization of 100 g of lignin and 700 ml of deionized water in a 1000 ml HTC reactor. X-ray photoelectron spectrometry (XPS) data was provided with carbon content in biomass and in the hydrochar.

The XPS data analysis from the DA-280-12 was used to obtain an estimative of the carbon content that can be found in the water-phase. The XPS data provided information about the atomic carbon percentage content on the surface of the feedstock and the hydrochar generated. Therefore, a balance calculation was carried out to estimate the amount of carbon on the water-phase.

The samples were generated in an HTC reactor of 1000 ml in 240 °C during 6 h.

The samples were named in a way of identifying the week produced and the number of the cycle. The weeks were 1-4 and the cycle were from 0-4. The cycle zero is the first run with pure deionized water and the run number four is the last recycle. Therefore, the experiment is characterized by four recycles for each week. However, the sample 2L4, which corresponds to the second week fourth run could not be collected due to an error in the procedure. The reactor dried out completely, there was some leakage during the process and no liquid could be collected.

The analysis conducted on each sample were slightly different. The water-phase

samples DA-280-12, DA-300-12, ALK-300-12 and ALK-280-4 were to evaluate the

analysis and their importance. It was necessary to gain knowledge to understand the

11 samples and the relevance of the analysis. Table 3 provides information about the analysis conducted on each of the samples. The pH analysis was conducted on all samples except the microalgae, since there was not enough water-phase (pH meter;

Mettler Toledo seven easy). The non-volatile residue analysis (NVR) was used only on the samples DA-280/300-12 and ALK-280/300-4/12. The GC-MS was utilized to identify the organic compounds on the sample DA-280-12, microalgae and generated samples (1L0-4L4). While the ICP-MS and inductively coupled plasma with optical emission spectroscopy (ICP-OES) were used to quantify the amount of sulfur (S) and sodium (Na), respectively.

Table 3 - Overview of the analysis conducted on the samples.

Analysis

Name

pH Solids particles

Ash content

Non-volatile Residues

GC- MS

ICP-MS and ICP- OES

Samples produced by the author in

the HTC

DA-280-12 X X X X X X -

DA-300-12 X X X X - X -

ALK-300-

12 X

X X X - - -

ALK-280-4 X X X X - - -

Microalgae -

- - - X - X

1L0-4L4 X - - - X X X

All experiments were conducted in triplicates and a quality blank was produced to determined quality of the results. Means and standard deviations (STDev) were calculated for the samples 1L0-4L4. The samples 1L0, 2L0, 3L0 and 4L0 were used to obtain the mean run 0. The sample procedure was then adopted for the run 1, run 2, and run 3.

3.2 Analysis of provided samples

3.2.1 pH, solid particles, ash content and non-volatile residues

The samples were removed altogether from the freezer and placed in the fume hood during the analysis period. The pH measurements were conducted on the next day, after defrosting, and it was intended to be repeated every week for four weeks to verify the stability. However, only the sample DA-280-12 could be measured in two different weeks due to equipment issues that followed this analysis. Therefore, the samples DA- 300-12, ALK-300-12 and ALK-280-4 could only be measured in the first week. The solid analysis was conducted using paper filters with different pores sizes 10 μm (Munktell Ahlstrom Grade 3 125 mm) and 0.45 μm (Supelco nylon 66 membranes 47 mm). Figure 3 illustrates the partitioning of the water-phase and facilitates an overview of the different particle sizes distributed in the samples.

First, 5 ml of the water-phase using a glass pipette was transferred directly to the

first pre-dried paper filter (10 μm), dried in an oven 110 °C overnight. Then 5 ml of

distillated water was used to wash the filter afterwards to make sure that the smaller

particles would be collected in the end. The volume was collected in a small beaker,

5 ml of distillated water was used to clean the Buchner flask. The paper filter was then

changed to the 0.45 μm and the solution was filtered again, with 5 ml of distillated water.

12 The paper filters were cautiously collected and set to dry in an oven at 110 °C overnight.

The ash content was measured after placing the filter paper inside crucibles and burning in a furnace that was set to ramp the temperature 600 °C in 4 h and hold the 600 °C for 2 h to assure that all the material is burned.

Figure 3 - solid partitioning

The non-volatile residue analysis was conducted by measuring 10 ml and 5 ml of each sample. Therefore, the sample was put into a crucible and dried in the oven (50 °C) for two days to ensure that all liquid evaporated. The remaining content was called non-volatile residue. The results were presented in percentage, which was calculated using Equation 1.

Eq 1

3.2.2 GC-MS

The gas chromatography with mass spectrometry (GC-MS) is a technique that separates and identify many compounds in a mixture. The sample is injected through a column with determined affinity to polar or non-polar compounds

. Whereas the sample is vaporized, a carrier gas (helium) is used to transfer the species through the column

. The compounds travel throughout the column at different retention times due to their molecular size and polarity of the molecule. At the end of the column, the compounds reach the mass spectrometer where they are bombarded by electrons

. The fragmentation of the compounds is measured and compared to a library to identify the compounds

.

The GC-MS was selected due to its ability to identify compounds with facility with the use of a library software (Agilent technologies, MassHunter Workstation quantitative analysis version B.08.00/Build 8.0.598.0). The technique required samples without any solids and water content. The preparation of the samples included dilution 1:10, a liquid-liquid extraction followed by a filtration in syringes. The procedure is more detailed in the Appendix 1.

Peak identification was accomplished by comparing mass spectra to the mass spectral library of National Institute of Standards and Technology (NIST) 2017. In order to make the results comparable, a surrogate standard (phenanthrene D10) was used to estimate the efficiency of the step prior to the chromatography (filtering and liquid- liquid extraction). The calculation of the surrogate standard recovery was based on

. It was a simple ratio between the component peak area obtained in the samples that were filtered and extracted and the component peak area a sample with known quantity of surrogate standard in DCM. The surrogate standard was not chemically similar to the targeted samples. Moreover, matrices effects could not be assessed. The use of an internal standard was necessary but could not be completed due to the lack of resources.

The base peak area and component area were the parameters used for analysis. The base peak area is the area of the highest intensity peak identified for a certain species. While the component area takes all the peaks related to the species identified.

𝑁𝑉𝑅 % = 𝑁𝑉𝑅(𝑔)

𝐿𝑖𝑞𝑢𝑖𝑑(𝑔) ∗ 100

13

This technique dissociates the species into atoms prior to analysis. Therefore, only elemental analysis is possible. The sample as liquid droplet was injected, sprayed and mixed to an ionized gas, called plasma

. The mixture is called aerosol and the plasma is a state of the matter with distinct properties for the solid, liquid and gas phases

. It possesses great energy and it dissociates the atoms of the molecular species and ionizes them, further

. The element ion formed on the ICP is then transferred to the mass spectrometry to be measured and identified

. This analysis is considered to have a low detection limit for the elements that range from less than 0.10 ppt to 10.00 ppb

. Sodium is abundant in greater quantities and it cannot be quantified without great dilution. The subsequent technique, ICP-OES, was able to quantify the sodium amount without further dilution. The ion formation follows the same procedure.

The difference lies in the detection method. The elemental ions formed are excited into a “higher” state

. When the electrons drop from this state, they emit a photon. This photon is then redirected by mirrors and measured and later identified and quantified

.

The induced coupled plasma analysis was selected due to facilitate determination of inorganic concentrations of water samples. Initially, the ICP-MS (Perkin Elmer SCIEX / Elan DRC-e Axial field technology) and ICP-OES (Perkin Elmer Optima 2000DV) analysis were conducted for the samples DA-280-12 and DA-300-12.

The XPS data obtained from the previous samples allowed the estimation of sulfur and sodium quantities. The samples were filtrated in 0.45µm syringe filters and diluted with a factor of 1000 to set the values closer to the detection limit values of the equipment.

The sulfur was detected in ICP-MS equipment using oxygen as a reaction gas, to reduce interferences. The sulfur species are highly reactive with the oxygen reaction gas and forming another species (SO). Consequently, the SO species were measured instead of the S. The sodium was detected in the ICP-OES equipment due to the detection limits of the equipment. A set of standard solutions were prepared in the range of 1-20 mg/l and acidified with 2 %v/v of 65 % HNO

(Suprapur). The sulfur solution (Spectrascan) 1001 ± 3 µg/ml was used to prepare the standards, while a sodium sulfate solution (Merck) of 1 mg/ml was prepared in the lab and used to prepare the standards.

3.3 HTC operation and water-phase generation

The HTC equipment was set to run at 240 °C and to hold this temperature for 6 h

and then cooled down to a temperature around 30 °C. No heating curves were obtained,

but after 1 h the target temperature was reached. The water-phase produced on the first

run was identified as 1L0, while the first recycle was 1L1 and then successively. The

water-phase was recycled for four-times for each replicate. Figure 4 illustrates the

process, where the make-up water was the volume necessary to set the volume back to

700 ml. The cleaning operation was conducted as fast as possible to reduce the time that

the water-phase rested outside, and the volume of the sample analysis was 50 ml. The

stirring part of the reactor was not used, and the cooling coil was located around the

stirring part of the reactor.

14

Figure 4 - Schematics of HTC process and recycling

The calculation of the hydrochar yield was based on the loaded biomass amount, lignin and microalgae, respectively. The yields were calculated using Equation 2.

Eq 2

A triplicate experiment with one recycling cycle of a microalgae HTC experiment was conducted. The microalgae experiment was conducted in an HTC process in 240 °C and 6 h in 20 ml reactors due to scarcity of the precursor. The microalgae mass was weighted 10 g and 8 ml of deionized water was used for each reactor. The microalgae sample had around 15 % of dry mass. The small reactors leaked during the experiments, turning into an inconvenience to the repetition of the experiments. Since, not much volume was recovered, the pH analysis was not conducted. The GC-MS experiments were conducted similarly to the lignin samples. A method developed by the student was used to estimate the amount of non-reacted lignin and to calculate the yield of hydrochar. The method was consisted in weighting around 1.0 g of the mass obtained from the HTC and washing with acetone until a clear coloration was obtained.

3.4 Analysis of generated samples

The analysis of GC-MS and ICP-MS/OES for the generated samples were conducted the same way as the provided samples. While the pH analysis was performed rapidly after defrosting of the samples in a room temperature water bath to avoid any possible decomposition that may occur. There was no analysis of solids, ash content and non-volatile residues for the generated samples. The generated samples were used to attempt the quantification of phenol, 2-methoxy-(guaiacol).

To quantify a certain species a calibration curve covering the estimated concentration range is necessary. However, no information about the concentration levels of guaiacol in the generated samples were available. Therefore, a calibration curve covering a wide range (1-500 μg/ml) was used to attempt the quantification. Afterwards, a set of known concentration solutions of guaiacol were used to obtain a calibration curve. The concentration obtained on the quantitative analysis were further adjusted using the recovery and dilution as seen in Equation 3.

𝑦𝑖𝑒𝑙𝑑 𝑤𝑡% = 𝑚𝑎𝑠𝑠 ℎ𝑦𝑑𝑟𝑜𝑐ℎ𝑎𝑟

𝑚𝑎𝑠𝑠 𝐿𝑖𝑔𝑛𝑖𝑛 × 100

15

Equation 3- Normalization of the concentration calculated

Eq 3

3.5 Quality assurance and quality control for the GC-MS

The used GC-MS method showed a small amount of carry over to the subsequent samples on the run sequence. This error was only possible to determine for the screening of the calibration curve when a solution of 500 µg/ml. An error of the procedure was carried when the blank solution was put after the 500 µg/ml solution. Therefore, the blank base peak areas of guaiacol and p-cresol were the higher values of the chromatogram. The carry-over was avoided adding a blank solution in-between the sequence.

Moreover, a short procedure was held preparing a blank with 40 ng/ml of the phenanthrene D10 to observe the carry over during the calibration curve preparation. It was observed that in the first solution was phenanthrene D10 present and, therefore, the carry-over was confirmed.

The used recovery calculation method for guaiacol was a rough estimative due to the lack of chemical similarity between the surrogate standard and the guaiacol. In addition, matrices effects were not estimated while using the pure surrogate standard.

Another important aspect to discuss was the possibility of having non-ideal results due to the decomposition of the samples. Samples 2L2, 3L0-3L4, 4L3 and 4L4 had apparent problems on the first chromatography injections. This repetition could contain errors due to the stability of the samples which were not assessible.

The assessment of the blank samples used during this project were considered an important aspect on the quality assurance and quality control. Despite the carry over problem presented, the blanks were considered acceptable to assure that no contamination happened. Mismatches and false positive were discussed on the Appendix 2 and Appendix 3.

4. Results

4.1 Analysis of provided lignin samples - pH measurements, solid particles, ash content and non-volatile content

4.1.1 pH measurements, solids, ash content and non-volatile residue

The pH measurement values of the provided samples are presented in Table 4.

The measurements for the samples could not be repeated for four weeks due to equipment’s issues. However, the sample DA-280-12 was the only sample that were analyzed twice, and the pH values varied from 7.69 to 7.79. Therefore, the first measurement is presented in Table 4. However, a pH measurement of the sample DA- 280-12 was made as a practice for handling the following samples. This measurement was conducted in a sub-sample that was defrosted in a water bath and provided a pH of 4.68.

Table 5 provides the results for the solids particles, ash content and non-volatile residues. The DA-280-12 ash analysis for the paper filter of 0.45 μm were performed twice and no ash was measured. The results presented in Table 5 were not enough to determine an effect of the temperature or type of lignin used. The solid particle results of the alkaline lignin for both paper filters 10 μm and 0.45 μm showed a much higher standard deviation than the dealkaline results. The ash results for the paper filter of

𝐶𝑜𝑛𝑐

= 𝐶𝑜𝑛𝑐

𝑟𝑒𝑐𝑜𝑣𝑒𝑟𝑦 ∗ 𝐷𝑖𝑙𝑙𝑢𝑡𝑖𝑜𝑛 𝐹𝑎𝑐𝑡𝑜𝑟

16 10 μm showed similar results for both DA-280-12 (1.6 mg) and DA-300-12 (1.5 mg).

While the ash results for the paper filter of 10 μm showed similar results for the ALK- 300-12 (2.7 mg) and ALK-280-4 (3.0 mg). Apparently the ALK-280-4 had the higher standard deviation values for the assays presented in Table 5. The non-volatile residues percentage is equivalent of (g NVR/100 g of water-phase).

Table 4 - pH values for the first measurement. The measurement was performed over once every week for four weeks. However, the standard deviation calculated was very low and basically insignificant.

Therefore, just the first values were presented.

pH

DA-280-12 7.69

DA-300-12 7.92

ALK-300-12 9.38

ALK-280-4 9.23

Table 5 - Solid particles analysis and ash content for the different paper filter used 10μm and 0.45μm;

Non-volatile residues analysis for the provided samples. Means values and standard deviation used.

Samples 10μm Solids particles (mg)

0.45μm Solids particles (mg)

10μm Ash (mg)

0.45μm Ash (mg)

Non- volatiles residues (%) DA-

280-12

3.3±0.41 3.8±0.21 1.6±0.062 0.00 0.58%±0

.0033 DA-

300-12

2.1±0.15 1.6±0.49 1.5±0.19 1.2±1.6 2.4%±0.

056 Alk-

300-12

2.3±0.78 3.5±2.1 2.7±0.34 1.8±0.33 0.83%±0

.0020 Alk-

280-4

5.1±1.3 5.4±3.1 2.9±0.95 4.3±2.3 3.8%±0.

18

4.1.2 GC-MS

The GC-MS of the provided samples were necessary as a way of validating the GC-MS method used for the generated samples. Therefore, one sample was chosen to obtain the needed information. Sample DA-280-12 was tested undiluted, diluted 10 times and diluted 20 times to observe the saturation of the peaks. This analysis identified the need of diluting the sample in 10 times.

Table 6 - GCMS Non-target analysis of DA-280-12. The retention time representing an important parameter for identifying samples and the match factor of the library software while identifying each species

Retention Time

Match factor (%)

Compound name Base peak area (% of

total) 13.3251 61 Phenol, 2-methoxy- (guaiacol) 8.42

16.5816 85.8 Catechol 6.98

13.0272 95.1 p-Cresol 6.39

9.9938 70.9 Cyclopropylacetylene 4.76

13.3532 57.8 Catechol 4.75

7.9345 83.9 Cyclopentane, 1,2,3,4,5-pentamethyl- 4.28

16.4758 96 2-Methoxy-5-methylphenol 4.05

8.8589 67.3 4-Octene, 2,6-dimethyl-, [S-(E)]- 3.93

12.3277 95.9 O-Cresol 2.98

17 Therefore, prior to the non-target analysis GC-MS, the sample DA-280-12 was diluted 10 times, filtered and a liquid extraction with DCM was conducted. The analysis was able to identify 543 species and the full data set can be found in Appendix 4.

Hydroxybenzenes species were more frequently found in this sample. The results were organized according to the base peak area percentage related to the total base peak areas.

There were nine compounds with base peak area percentages higher than 2 % and they were listed in Table 6. The three compounds that had higher base peak area percentages were guaiacol (8.42 %), catechol (6.98 % and 4.75 %), p-cresol (6.39 %). The species had a total area percentage of 26.54 %. Those compounds were possible candidates to be quantified during the analysis of the samples generated.

4.1.3 ICP-MS / ICP-OES

The inorganic analysis of the provided samples was performed to obtain information on the possible effect of the temperature, and it was only conducted on the samples that were used in the same feedstock as the generated samples, dealkaline lignin.

As mentioned in the introduction section, sodium and sulfur were likely to be in the dealkaline lignin samples. Sodium and sulfur discharged in the environment may represent problems due to toxicity and sulfur may represent problems with corrosion.

The provided samples DA-280-12 and DA-300-12 results were compiled in Table 7.

The concentrations of sulfur and sodium were higher in the 300 °C sample compared to the 280 °C. Also, the concentration of sodium in both samples were much higher than sulfur. It was not possible to compare the concentrations with other studies in the literature, since no study performed such water-phase analysis. However, a study performed by Catalkopru et al. 2017 where three different biomass sources were analyzed identified a maximum of 2.264 g/l of sodium in the water-phase

. Compared to this study, the identified sodium concentrations in the provided samples were around 24-35 times higher. The reason for this could be that the higher temperature processes presented a higher concentration of elements which could relate to the increase in solubility of the elements while the temperature of the solvent increases.

Table 7 - Sulfur and sodium concentration in the provided samples.

Samples S Na

DA-280- 12

10.86 56.20 g/l

DA-300- 12

14.37 79.73 g/l

4.2 HTC operation –Hydrochar yield

The hydrochar produced by the DA-280-12 is rich in carbon (around 80 %), the carbon percentage in relation to the total carbon input from the lignin was only 38 %.

Which means that around 62 % of total carbon loaded is in the water and gas content.

This was an interesting information that showed the amount of carbon contained in the water-phase. Therefore, a great part of carbon of the feedstock have not been utilized.

The first impact of the recycling that could be observed was that the cleaning process became easier through the cycles. The char tends to get stuck in the reactor and the cooling coil when the process is done. However, after the first recycle it was possible to remove the hydrochar from these spots easier than after the first run.

The HTC operation generated samples every day for four weeks and the full data

sheet can be found in the Appendix 5. Each week corresponds to a replicate of the

experiment. Table 8 presents the mean hydrochar yield for each run. The run 0

corresponds to the first run on every week (1L0, 2L0, 3L0 and 4L0). The hydrochar