Tabularx - merge cells

Question

I have a table made using tabularx and I'd like to merge some of the cells which have the same content so that only one entry is required. When I try to use multicolumn as per enter link description here but this skews the table when additional text is added.

Can I have advice on either a) fixing the problem using tabularx or b) a better package to accommodate large amounts of text and numbers?

I have attached an MWE and image of the output.

MWE

\documentclass[11pt,a4paper]{report}
\usepackage{color}
\usepackage[hidelinks]{hyperref}
\usepackage{graphicx, epstopdf}
\usepackage{etoolbox}%This package combined with the \pathcmd rewrites the standard style for 'Chapter' to allow the fancy horizontal and vertical lines. 
\patchcmd{\chapter}{\thispagestyle{plain}}{\thispagestyle{mystyle}}{}{}
\graphicspath{{../Visuals/}}
\usepackage{gensymb}
\usepackage{adjustbox}
\usepackage{tabulary}
\usepackage{tabularx}
\usepackage{booktabs,caption, makecell}
\usepackage{pdflscape,afterpage,caption}
\usepackage[british]{babel}
\usepackage[backend=bibtex, citestyle=ieee, bibstyle=ieee]{biblatex}
\usepackage[section]{placeins}%Allows you to permanently fix figures. 
\usepackage{titleps}%fancy page borders? 
\usepackage[left=2.5cm, right=2.5cm, top=3.5cm, bottom=3.5cm]{geometry}
%\usepackage{caption}
\captionsetup[figure]{font=scriptsize,labelfont=scriptsize}
\usepackage{microtype}
\usepackage{setspace}
\usepackage{amsmath}
\usepackage{datetime}
\usepackage{lipsum}%random text generator. [1-XXXX] to specify the number of paragraphs. 
\newdate{date}{28}{02}{2018}
\date{\displaydate{date}}
\onehalfspacing
\setcounter{secnumdepth}{3}

\newcolumntype{Z}{ >{\centering\arraybackslash}X }

\renewcommand\theadfont{\bfseries}
%\renewcommand\theadalign{cc}
\usepackage[autolanguage, np]{numprint}

\begin{document}

\begin{table}[!h]
\setlength\tabcolsep{4pt}
\caption{Caption}
\begin{tabularx}{\textwidth}{*{6}{Z}}
%\toprule
\multicolumn{4}{c}{} \\
\midrule
\thead{Test}  & \thead{Theoretical \\ Yield (mg)} & \thead{Flow \\ rates \\} & \thead{Residence \\ time, \\ $\tau$ (minutes)} & \thead{Temperature \\ ($\degree$C)} & \thead{Solvent} \\%
\midrule
1 & TEXT & TEXT & TEXT & TEXT & TEXT \\
2 & 70.0 & 64, 65, 71 & 10 & -15 & DCM \\
3 & 70.0 & 64, 65, 71 & 10 & 5 & DCM \\
4 & 70.0 & 64, 65, 71 & 10 & 10 & DCM \\
 \bottomrule
 \label{Label}
\end{tabularx}
\end{table}

\end{document} 

Thanks in advance!

Answer 1

i guess that you looking for something like this:

\documentclass[11pt,a4paper]{report}
\usepackage{booktabs, makecell, multirow}
\renewcommand\theadfont{\small\bfseries}
\renewcommand\theadgape{}
\usepackage[skip=1ex]{caption}
\usepackage{siunitx}

\begin{document}
    \begin{table}[!h]
\caption{Caption}
\label{Label}
\setlength\tabcolsep{0pt}
\begin{tabular*}{\linewidth}{@{\extracolsep{\fill}} *{6}{c} }
    \toprule
\thead{Test}
    & \thead[b]{Theoretical \\ Yield (mg)}
            & \thead[b]{Flow \\ rates}
                    & \thead[b]{Residence \\ time $\tau$\\  (minutes)}
                            & \thead[b]{Temperature \\ (\si{\celsius})}
                                    & \thead[b]{Solvent} \\
    \midrule
1   & TEXT & TEXT & TEXT & TEXT & TEXT \\
2   & \multirow{3}{*}{70.0}
            & \multirow{3}{*}{64, 65, 71}
                    & \multirow{3}{*}{10}
                            & -15   & \multirow{3}{*}{DCM}  \\
3   &       &       &       & 5     &                       \\
4   &       &       &       & 10    &                       \\
    \bottomrule
\end{tabular*}
    \end{table}
\end{document}